Water pollution in Pakistan and its impact on public health — A review

Azizullah Azizullah a, Muhammad Nasir Khan Khattak b, Peter Richter a,⁎, Donat-Peter Häder a

Abstract

Water pollution is one of the major threats to public health in Pakistan. Drinking water quality is poorly managed and monitored. Pakistan ranks at number 80 among 122 nations regarding drinking water quality. Drinking water sources, both surface and groundwater are contaminated with coliforms, toxic metals and pesticides throughout the country. Various drinking water quality parameters set by WHO are frequently violated. Human activities like improper disposal of municipal and industrial effluents and indiscriminate applications of agrochemicals in agriculture are the main factors contributing to the deterioration of water quality. Microbial and chemical pollutants are the main factors responsible exclusively or in combination for various public health problems. This review discusses a detailed layout of drinking water quality in Pakistan with special emphasis on major pollutants, sources of pollution and the consequent health problems. The data presented in this review are extracted from various studies published in national and international journals. Also reports released by the government and non-governmental organizations are included.

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 479

2. Major pollutants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .480

2.1. Bacteriological contamination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 480

2.2. Toxic metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482

2.3. Major cations and anions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 485

2.3.1. Cations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 485

2.3.2. Anions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488

2.4. Pesticides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488

3. Sources of water pollution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .491

4. Water pollution and human health . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 493

5. Environmental legislations in Pakistan and their effectiveness . . . . . . . . . . . . . . . . . . . . .493

6. Conclusion and recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .494

1. Introduction

The importance of availability of high quality drinking water can be realized by the press release of UNO Secretary General on world water day 2002. “An estimated 1.1 billion people lack access to safe drinking water, 2.5 billion people have no access to proper sanitation, and more than 5 million people die each year from water-related diseases — 10 times the number killed in wars, on average, each year. All too often, water is treated as an infinite free good. Yet even where supplies are sufficient or plentiful, they are increasingly at risk from pollution and rising demand. By 2025, two thirds of the world's population is likely to live in countries with moderate or severe water shortages”.

Water is an essential element for life. Freshwater comprises 3%of the total water on earth. Only a small percentage (0.01%) of this freshwater

is available for human use (Hinrichsen and Tacio, 2002). Unfortunately even this small proportion of freshwater is under immense stress due to rapid population growth, urbanization and unsustainable consumption of water in industry and agriculture. According to a UNO report, the world population is increasing exponentially while the availability of freshwater is declining. Many countries in Africa, Middle East and South Asia will have serious threats of water shortage in the next two decades. In developing countries the problem is further aggravated due to the lack of proper management, unavailability of professionals and

financial constraint (PCRWR, 2005).

Like other developing countries of the world, Pakistan is also facing critical water shortage and pollution. The country has essentially exhausted its available water resources (PCRWR, 2005); it is considered as water stressed and is likely to have a water scarcity in the near future (Hashmi et al., 2009a;WWF, 2007). The water precipitation rate is lower than the evaporation rate in the country. This causes a continuous decrease in water quantity in its rivers, lakes and diminishing the groundwater as well. The problem is further aggravated by factors like long droughts and lack of construction of new water reservoirs (PCRWR, 2005; Ullah et al., 2009). This decrease in water quantity coupled with increasing demand resulted in severe water shortage in almost all sectors of the country. The per capita water availability in the country dropped from 5000 in 1951 to 1100 m3 per annum (WB-SCEA, 2006). Exponential increase in population of the country and no development of new water resources may cause per capita water availability of less than 1000 m3 from the year 2010 onwards. The situation might get worse in areas situated outside the Indus basin where the average per capita water availability per annum is already below 1000 m3 (PAK-EPA, 2005b). In certain regions, like the drought-affected areas of Sindh Province, people already have no fresh water for drinking and are compelled to drink brackish water (Ullah et al., 2009). In Baluchistan Province, the underground aquifers are dropping at a rate of 3.5 m annually and will be exhausted in the next 15 years (Sajjad et al., 1998). This combination of decreasing quantity and increasing usage in multiple sectors has adversely affected the quality of water and resulted in a serious problem of water pollution. Water quality in most of the rivers, lakes and ground aquifers of the country is considered not to be safe for human consumption.

Various reports present conflicting data about the availability and quality of drinking water to the public in the country. According to national statistics 56% of the total population has access to safe drinking water (Farooq et al., 2008). However, considering international standards for safe and drinkable water, only 25.61% (rural 23.5% and 30% urban) of the population in Pakistan have access to this basic need (Rosemann,

2005). Drinking water supplied by municipalities to the public is mostly contaminated with infectious microorganisms or hazardous chemicals (WWF, 2007). Drinking water in densely populated cities like Karachi, Lahore, Rawalpindi, Peshawar, Faisalabad, Qasur, Sialkot and Gujrat is polluted due to various anthropogenic activities and cannot be recommended for human consumption (Bhutta et al., 2002). The situation is even worse in the capital Islamabad. Analysis of water samples from Islamabad and its twin city Rawalpindi revealed that 94% and 34% of water samples were contaminated with total coli forms and fecal coli forms, respectively (Jehangir, 2002). Pakistan Council of Research in Water Resources (PCRWR) conducted a detailed study on water quality in 23 major cities in all the four provinces of the country from 2002 to 2006. The conclusion of this study (Table 1) reveals that an average of 84-89% of water sources throughout the country have a water quality below the recommended standards for human consumption (PCRWR, 2008a). The poor quality of drinking water available to the public forced people to obtain an expensive alternative in the form of commercially available mineral water packed in plastic bottles. However, this commercially available water is also not completely safe due to the lack of proper monitoring of processing plants (Rosemann, 2005). Weak purchasing power of the public is also a big hindrance in using such an alternative. As a result the majority of the population in Pakistan is exposed to contaminated and polluted water which may cause a multitude of water related health problems.

The increasing pollution of drinking water sources in Pakistan and the consequent effects on human health and the environment is an issue of great concern. This review aims at highlighting the problem of water pollution in Pakistan with special emphasis on major pollutants and their possible impacts on human health. A great majority (≈70%) of the population in Pakistan obtains water from ground aquifers however, surface water is another main source of water for drinking and other domestic purposes (Aziz, 2005). Therefore we concentrate both on ground and surface water sources and summarize the major pollutants and their concentrations in surface and groundwater separately. Furthermore we summarize the various water-linked health problems reported in the country.

2. Major pollutants

Many substances are regarded as active water pollutants and are classified into different groups. The most common among them are pathogens (bacteria, viruses and protozoas), inorganic pollutants (acids, salts and toxic metals), anions and cations (nitrates, phosphate, sulphates, Ca+2, Mg+2 and F−) and water-soluble radioactive substances. In addition, organic compounds like oil and pesticides are also considered potential threats to water quality. All these substances, if they exceed a threshold value, are deleterious and cause severe health problems in humans and other organisms in the ecosystem. Bacteriological contamination, toxic metals like arsenic, iron, cadmium, nickel, pesticides and in some are sanitaria sand fluorides are posing major threats to water quality in Pakistan.

2.1. Bacteriological contamination

Microbial analysis of water is usually carried out to detect total and or fecal coli forms. Coli forms commonly occur in the environment and are generally not harmful to humans but their presence is used as an indicator for water contamination with diseases causing germs and pathogens. The presence of fecal coli orms and E. coli is also an indicator for water contamination with human or animal wastes (Farooq et al., 2008). According to the WHO standard for public drinking water total and fecal coli forms must not be present in 100 mL of water samples i.e. 0 counts/100 mL of water sample (WHO, 1993).

In Pakistan bacteriological contamination has been regarded as the most potential problem of drinking water (PCRWR, 2005). Many studies reveal heavy bacteriological contamination of drinking water in the country as summarized in Table 2 and many of the reported species of bacteria can cause severe health problems (Table 2a). Water sources including rivers, lakes and ground aquifers in most of the regions in the country are highly polluted with bacteriological contamination (Aziz, 2005). In Rawalpindi samples from the water distribution networks and even at treatment plants were found contaminated with total coli form and in some sites with fecal coli form (Farooq et al., 2008; Hashmi et al., 2009b). In Khairpur in the Sindh province, out of 768 drinking water samples 567 (73.83%) and 351 (45.70%) were contaminated with total coli form and fecal coli form, respectively (Shar et al., 2008b). Another study conducted in the same city revealed the presence of total coli forms

and fecal coli forms in all 90 (100%)water samples collected from the main reservoir, distribution lines and consumer taps (Shar et al., 2008a). The situation is not much different in other major cities of the country like Peshawar, Lahore and Karachi. In all these cities drinking water was found contaminated with bacteria (Anwar et al., 1999, 2004;Hussain et al., 2007; Mumtaz et al., 2010; Sarwar et al., 2004; Zahoorullah et al., 2003). Another study conducted in major cities of the country reported 65% and 35% of groundwater samples contaminated with total coli forms and E. coli, respectively, while 100% samples of the surface water had bacterial contamination of both total coli forms and E. coli (PCRWR, 2005). A very recent study reported that water samples from Rawal Lake, Islamabad, (a lake providing drinking water to more than 1.5 million people of Rawalpindi) and its feeding streams were potentially contaminated with bacteria (Mashiatullah et al., 2010).

Surface and groundwater contamination with bacteria is usually attributed to surface runoff through urban areas and pastures, leakage of sewage disposal systems and septic tanks, overloaded sewage treatment plants, disposal systems and raw sewage deep well injection (PCRWR, 2005). Other factors like cross-connection, broken or leaking pipes, back siphon age (backflow of polluted or contaminated water, from a plumbing fixture or cross-connection into a water supply line, due to a lowering of the pressure in the line) and intermittent water supply result in contamination of the distribution system (PCRWR, 2005; Shar et al., 2008b). In rural areas open dug wells and low water table make it further vulnerable to bacterial contamination. It is generally considered that the water is free from bacteriological contamination at the sources and becomes contaminated in pipes due to unauthorized connection or leakage. But in reality the situation is different in the country as water was found to contain bacterial contamination even at the source or treatment plants (Hashmi et al., 2009a; PAK-EPA, 2005a). In the capital, Islamabad (PAK-EPA, 2005a) and Rawalpindi (Farooq et al., 2008; PAK-EPA, 2005a), the filtration and treatment plants do not properly purify water from bacterial contamination before distribution. The situation could be worse

in other cities and especially in rural areas where there is no monitoring of drinking water quality and no treatment plants exist. Bacterial contamination in rural areas is usually expected to be higher than in urban areas. This hypothesis is supported by studies in the rural area of Punjab, where 91.30% and 95.83% of samples from tap and domestic pumps, respectively, were found contaminated with bacteria as compared to 42.85% of tap

water samples from Lahore (Anwar et al., 1999).

Microbial contamination of drinking water is a major contributor to water-borne diseases like diarrhea, nausea, gastroenteritis, typhoid, dysentery and other health-related problems (PCRWR, 2005; Shar et al., 2008a), especially in children and persons with weak immune systems (PCRWR, 2005).Microbial contamination of water in the country is one of the potential threats to public health and needs special attention to take remedial measures to stop its further aggravation.

2.2. Toxic metals

Natural water contains impurities of trace elements heavy metals as it dissolves these substances while moving downward as a hydrological cycle (Ilyas and Sarwar, 2003). In addition, these metals are introduced to both surface and groundwater through several human activities like large scale use of chemicals in agriculture and improper disposal of industrial and municipal wastes. Many of these metals are considered essential for human health (Midrar-Ul-Haq et al., 2005) but upon overloading they cause water pollution and result in severe health problems in living organisms including humans. In Pakistan toxic metals in both ground and surface waters, often exceed the maximum admissible concentrations recommended by WHO for drinking water. The results of various studies conducted on contamination of water with toxic metals in Pakistan are summa rized in Table 3.

Zinc (Zn) and copper (Cu) are essential elements for human health (Solomons and Ruz, 1998) but overexposure can lead to adverse health consequences (Fosmire, 1990; Singh et al., 2006). For drinking water WHO set maximum acceptable concentrations of 3 mg/L and 2 mg/L for Zn and Cu, respectively. Both these metals are usually found well below the WHO standard limits both in ground and surface water in Pakistan (Table 3). Only one study reported conflicting data showing a higher Zn concentration of 4.02mg/L in Karachi (Rahman et al., 1997).

Manganese (Mn) is a naturally occurring mineral in surface and groundwater, but human activities also contribute much to its introduction in water (USEPA, 2004). In Pakistan drinking water contamination with Mn poses a small problem in some parts where it exceeds the WHO standard limits (0.5 mg/L). The highest concentration of Mn (2.56 mg/L) in groundwater was reported from Khyber Pakhtoonkhwa (Midrar-Ul-Haq et al., 2005) followed by 1.06mg/L in water samples from Faisalabad (Mahmood and Maqbool, 2006). However, the majority of the studies reveal Mn concentrations in ground water with in safe limits. As compared to groundwater, in surface water, concentrations of Mn exceed the standard limits of WHO in many cases (Table 3).Manganese is an essential trace nutrient for all forms of life (Emsley, 2003) as it binds to and/or regulates many enzymes in the body (Crossgrove and Zheng, 2004). However, exposure to excessive doses of Mn causes severe disorders in the nervous system with the brain as the main target site (Crossgrove and Zheng, 2004). In its worst form, it may lead to a permanent neurological disorder with symptoms similar to those of Parkinson's disease (Barbeau, 1984; Inoue and Makita, 1996). However, exposure to Mn from drinking water is normally substantially lower than intake from food (USEPA, 2004). Iron (Fe) is one of the most abundant metals on earth and is an essential element for the normal physiology of living organisms. Both its deficiency and overload can be harmful both for animals and plants (Anonymous, 2008). In drinking water the desirable concentration set by WHO is 0.3 mg/L for iron. In Pakistan iron is one of the major pollutants of both ground and surface water. A country-wide study conducted by PCRWR reported an overload of iron in 28% of ground- and 40% of surface water samples (PCRWR, 2005). Various studies reported iron concentrations ranging from 0 to 3.7 mg/L (means) in groundwater and 0.01 to 9.0mg/L in surface water in different areas of Pakistan (Table 3). The summaries of various studies reveal that in comparison to the Punjab and Sindh provinces, the concentration of iron in groundwater of Khyber Pakhtoonkhwa is lower but still higher than the 0.3 mg/L standard in many cases. These elevated concentrations in natural water resources can be a possible risk for human health and environment. Although in comparison to its deficiency, iron overload or overexposure is a less common condition but it can lead to several serious health problems like cancer (Beckman et al., 1999; Parkkila et al., 2001), diabetes (Ellervik et al., 2001; Parkkila et al., 2001; Perez de Nanclares et al., 2000), liver and heart diseases (Milman et al., 2001; Rasmussen et al., 2001; Yang et al., 1998) as well as neurodegenerative disorders (Berg et al., 2001; Sayre et al., 2000).

Cadmium(Cd) is an element of great concern from a toxicity point of view. The safe standard for Cd concentrations in drinking water set by WHO is 0.003 mg/L. In Pakistan Cd concentrations in both ground and surface water, with some exception, are above the WHO safe limits (Table 3). The data of various studies reveal that the groundwater of Khyber Pakhtoonkhwa and Sindh provinces has relatively high contamination of Cd as compared to Punjab. Cadmium is a toxic metal causing both acute and chronic toxicity in humans. Intake of cadmium may cause acute gastrointestinal problems, such as vomiting and diarrhea (Nordberg, 2004) while chronic exposure to cadmium for a long time may cause kidney damage (Barbier et al., 2005), reproductive problems (Frery et al., 1993; Johnson et al., 2003; Piasek and Laskey, 1999), bone damage (Kazantzis, 1979) and cancer (Waalkes et al., 1988).

Chromium is one of the most common elements in the earth crust and water. For drinking water WHO described its maximum allowable concentration at 0.05mg/L. In water sources of Pakistan it has been documented in a wide concentration range by different studies. A study conducted by PCRWR in 23 major cities of the country showed that only 1% of groundwater samples exceed the safe limits for chromium (PCRWR, 2005). In contrast, individual studies reported chromium concentrations ranging above the safe limits of WHO (0.05 mg/L) in most of the cases (Table 3). Analysis of drinking water samples from the residential area of Kasur showed chromium concentrations reaching 9.80 mg/L (mean 2.12 mg/L). In general, chromium had 21-42 times higher concentrations than the recommended quality value (Tariq et al., 2008). Similarly, 75% samples from various sources in Khyber Pukhtoonkhwa and 25% samples from Karachi (Sindh) exceeded the maximum acceptable value for chromium in drinking water (Midrar-Ul-Haq et al., 2005). In most cases chromium concentrations are lower in surface than in groundwater; however, in some cases they exceeded the recommended safe WHO limits (Table 3). Frequently higher concentrations of chromium in drinking water in cities like Lahore, Gujrat and Sialkot have been traced to the leather industry and tanneries (Ullah et al., 2009). Chromium it self is not toxic and plays an important role in the carbohydrate metabolism in the body (Cefalu and Hu, 2004). But some of its compounds especially in its hexavalent status cause skin diseases, cancers, irritants and diseases related to the digestive, excretory, respiratory and reproductive system (Anonymous, 2008).

Nickel, dubbed as “Allergen of the Year 2008”, is a widely distributed element in the environment, and can be found in air, water and soil (Duda-Chodak and BIaszczyk, 2008). The maximum admissible concentration set by WHO for nickel in drinking water is 0.02 mg/L. In Pakistan its concentration varies from 0 to 3.66mg/L in groundwater whereas in surface water from0 to 1.52 mg/L as documented in various studies (Table 3). Among the groundwater samples, the highest range of nickel is reported in water samples from Khyber Pakhtoonkhwa (0.002- 3.66 mg/L) and Karachi (0.01-2.19 mg/L) (Midrar-Ul-Haq et al., 2005). Table 3 shows that in most cases groundwater is contaminated with nickel beyond the standard of WHO. Surface water also shows similar contamination with nickel. Midrar-Ul-Haq et al. (2005) reported that 75% of the surface water samples from the largest city of the country (Karachi) exceed the USEPA criteria for nickel in drinking water. The local population of such areas can be at risk of exposure to high doses of nickel with food and water being the two main sources (Duda-Chodak and BIaszczyk, 2008). Nickel compounds can cause a variety of adverse effects, such as nickel allergy in the form of contact dermatitis, lung fibrosis, cardiovascular diseases, kidney problems and cancer of the respiratory tract (McGregor et al., 2000; Oller et al., 1997; Seilkop and OLLER, 2003).

Lead (Pb) is a normal constituent of the earth's crust and trace amounts naturally occur in soil and water (Raviraja et al., 2008). Drinking water picks up lead contamination from various sources like household paint, vehicle exhausts and industrial wastes (Nadeem-ul-Haq et al., 2009). The safe standard set by WHO for lead in drinking water is 0.01 mg/L. Its concentration is reported from0.001 to 2.0 mg/L in groundwater and 0 to 0.38 mg/L in surface water from various parts of the country (Table 3). A large study conducted by PCWR in major cities revealed that 15% and 1% of surface and groundwater samples, respectively, had lead

above the safe limits (PCRWR, 2005). However, in contrast, individual studies revealed that a higher proportion of water sources in the country had lead above the safe limits, both in surface and groundwater. In Khyber Pakhtoonkhwa (Charsadda and Risalpur) and Karachi 88 and 100% of water samples, respectively, exceeded the critical level for lead (Midrar-

Ul-Haq et al., 2005). Similarly in Sialkot 100% of the samples analyzed exceeded the critical level of 0.01 mg/L for lead in drinking water (Ullah et al., 2009). Physiological functions of lead useful in the human body are not well known(Raviraja et al., 2008), however, exposure to overdoses for longer times affects adversely the major organs and systems of the body such as the nervous, digestive, haematopoietic, cardiovascular, reproductive and immunological system as well as the skeleton and the kidneys (Gidlow, 2004; Riess and Halm, 2007; Venkatesh, 2004). Even at low concentrations lead is a special threat during pregnancy. It may cause developmental delay, low birth weight and miscarriage of the fetus

(Bellinger, 2005; McMichael et al., 1986).

Mercury (Hg) is a naturally occurring element and a “persistent bioaccumulative toxin” (Weiss andWright, 2001). It is introduced to the environment through various natural processes as well as different human activities (Weiss and Wright, 2001). According to the WHO standards, its concentration in drinking water should not exceed 0.001 mg/L. In Pakistan data regarding Hg contamination of water are limited as very few studies exist on the issue. PCRWR reported Hg concentrations beyond the safe limits in 5% of surface water samples but none in groundwater samples (PCRWR, 2005). Rahman et al. (1997) reported Hg concentrations of 0.01 mg/L in groundwater samples from Karachi which is 10 times higher than the WHO standard. A study conducted on three main water reservoirs of the country, namely Tarbela (0.014 mg/L), Chashma (0.017 mg/L) and Lloyd (0.14 mg/L), showed Hg

concentrations beyond the safe limits (Ashraf et al., 1991). However, the available data are very limited and further studies are necessary regarding Hg concentrations in drinking water throughout the country. Hg is a potentially harmful metal to human health and the environment. It is the only metal, which indisputably magnifies through the food chain. Furthermore, in the aquatic environment, it is efficiently transformed into methyl mercury which is its most toxic form (Fatoki and Awofolu, 2003). Being a potential cellular toxin, it adversely affects various important processes within nerve cells. It disrupts the neurotransmitter production and also decreases the production of important hormones including thyroid hormones and testosterone in the body (Fatoki and Awofolu, 2003).

Arsenic (As) is recognized as a big threat to public health in many countries like Bangladesh, India, China, Vietnam, Nepal and Myanmar (Islam-Ul-Haque et al., 2007). The situation is the same in Pakistan, and in many of its regions' concentrations of arsenic in drinking water exceeds the WHO standard of 10 ppb (μg/L). In the early 1990s Ashraf et al. (1991) reported elevated concentrations of arsenic in the large water reservoirs of Pakistan, i.e. Tarbela, (620 μg/L), Chashma (750 μg/L) and Lloyd (620 μg/L). Similarly an average arsenic concentration of 80 μg/L in groundwater samples from Karachi was reported in the nineties (Rahman et al., 1997). However, the issue of arsenic as a threat to drinking water remained unnoticed until a joint study conducted by the Pakistan Council of Research in Water Resources (PCRWR) and the United Nations Children Fund (UNICEF) in 2000. In this study groundwater contamination with arsenic was identified in the Attok and Rawalpindi districts. Subsequent studies have been conducted by PCRWR in various parts of the country which revealed a wide range of arsenic concentrations in water samples. Results obtained by PCRWR for arsenic in various parts of Punjab and Sindh (Table 4) show that a sizable

number of samples exceed the WHO standard of 10 μg/L. In some areas the situation is very alarming as for example in Multan (Punjab), Dadu and Ganbat (Sindh) where more than 50% of the water samples exceed the standard limits of 10 μg/L. The situation is further aggravated as some areas have a contamination of above 50 μg/L and in Sindh even exceeds 200 μg/L (PCRWR, 2008b). Recent studies show elevated arsenic contamination in groundwater of east Punjab reaching 1900 μg/L and 2400 μg/L with 91% of samples exceeding the WHO standard limits of 10 μg/L (Farooqi et al., 2007a,b). In a recent study arsenic reaching 96 μg/L in groundwater and 157 μg/L in surface water (Manchar Lake, Sindh) has been documented (Arain et al., 2009). In conclusion, arsenic contamination is a serious threat to drinking water in Pakistan. Many people in the country are exposed to high doses and are at risk of health problems. Overexposure to arsenic may cause a decrease in white and red blood cells production, gastrointestinal irritation, disrupt the heart rhythm, damage blood vessels and cause “pins and needles” sensation in hands and feet (Abernathy et al., 2003). Long time exposure to arsenic can cause melanosis, leuko-melanosis, hyperkeratosis, cardiovascular disease, black foot disease, neuropathy and cancer (Caussy, 2005).

The overall situation of toxic metals in surface and groundwater shows a large variation in their contamination level and frequency. All toxic metals except copper and zinc have their concentrations beyond the critical limits in many cases. Most of the authors linked the elevated concentration of heavy metals in water to human activities like disposal of industrial, municipal and domestic wastes.

2.3. Major cations and anions

Cations including sodium (Na+), potassium (K+), calcium (Ca+2), magnesium (Mg+2) and anions like nitrates (NO3 −), nitrites (NO2−), carbonates (CO3−2), bicarbonates (HCO3−), sulfates (SO4−2), phosphates (PO4−3), chlorides (Cl−) and fluorides (F−) naturally occur in water and are usually determined in water quality evaluation tests. Data for major cations and anions reported from different parts of Pakistan by various studies are summarized in Table 5 for both surface and ground water.

2.3.1. Cations

Cations such as Na+, K+, Ca+2 and Mg+2 are essential for various processes in the body and their presence in water is necessary in an adequate amount. However, at higher concentrations these cations may make the water unfit for living organisms.

Sodium shows a large variation in various water resources throughout the country as revealed by different studies. However, in general, its concentration is very low in running water i.e. in canals and rivers but extremely high in lakes and groundwater. Its concentration in the Kallar Kahar and Manchar Lakes were much higher than the WHO standard of 200 mg/L (Arain et al., 2008; Mastoi et al., 2008; Raza et al., 2007)making it the major pollutant in both lakes. Na+ concentrations in groundwater samples from Hyderabad reached 1795 mg/L, and 6 out of 7 sites had a concentration above the standard limits (Laghari et al., 2004). Similarly, elevated concentrations of Na+ were recorded in groundwater samples such as 306 mg/L (maximum value 1688 mg/L) in Lahore, 360 mg/L (maximum value 878 mg/L) in Kalalanwala and 989 mg/L (maximum value 5500 mg/L) in Nagar Parkar (Table 5). In Kalu Khuhar, Sindh almost all 21 groundwater samples had Na+ beyond the maximum acceptable concentration(Siddiqui et al., 2005). The study conducted by PCRWRin 23 major cities of Pakistan revealed that 5% of surface and 9% of groundwater had a sodium concentration beyond the standard limits. In Faisalabad, Kasur and Sheikhupura the situation was worse where 43, 30 and 27% of the water samples, respectively, exceeded standard limits (PCRWR, 2005). The high concentrations of Na+ in the seareas maybe due to the saline and brackish nature of water (Raza et al., 2007) and in some cases cation exchange reactions with Ca+2 and carbonates precipitation due to the alkaline nature of the water may contribute to a high Na+ content (Farooqi et al., 2007a). The high sodium concentrations, if present in the form of chlorides and sulphates, make the water salty and unfit for human consumption and irrigation purposes. It may exert osmotic stress on the biota in the water (Raza et al., 2007) and may cause high blood pressure and hypertension in humans (Kawasaki et al., 1978). Like sodium, potassium(K+) is also usually reported above the quality standards. WHO did not define any standard limits for K+. The European Union recommended standards of 12 mg/L (Tariq et al., 2008). Analyzing data of different studies, K+ is documented in a range of 3.5 to 94 mg/L but its mean concentration in most of the studies reached 30 mg/Lwell above the standard of 12 mg/L. According to PCRWR, it exceeds the standard limits in 36-46% of samples from Faisalabad and 20% of samples from Kasur (PCRWR, 2005).

Calcium(Ca+2) is an important element for the human body because it is a structural component of bones, teeth and soft tissues and is essential in many metabolic processes of the body (Bacher et al., 2010). According to the WHO quality standard for public drinking water the Ca+2 concentration should not exceed 100 mg/L. Various studies revealed its concentration above the quality standard (100 mg/L) in groundwater in cities like Hyderabad, Lahore and Kasur in the Punjab province and the Kalu Khuhar and Nagar Parkar areas of the Sindh province (Table 5). In Islamabad, 73% of the drinking water samples exceeded the maximum admissible limits for Ca+2 (PCRWR, 2005). The high concentration of Ca+2 is attributed to the calcareous nature of underground mineral rocks. Studies reveal low concentrations of Ca+2 in surface water as compared to groundwater of the country. Manchar Lake in Sindh province is the only surface water reservoir which showed a Ca+2 concentration above the standard limits (Table 5). The same can be concluded from a country-wide study by PCRWR that reported 28% of groundwater samples having Ca+2 exceeding the limits in comparison to only 5% of surface water samples (PCRWR, 2005). Short-time in take of large amounts of Ca+2 does not generally have any adverse effect because the gastrointestinal tract normally limits the amount of calcium absorbed. However, ingestion of excess calcium for a long time may lead to elevated blood calcium levels (hypocalcaemia) and may cause side effects like hypercalciuria, urinary tract calculi, calcification in soft tissues like kidneys and in arterial walls and suppression of bone remodeling (Heaney et al., 1982). Among other cations few studies reported Mg+2 in groundwater from Hyderabad (Laghari et al., 2004) and surface water of Kallar Kahar andManchar lakes (Arain et al., 2008; Raza et al., 2007) exceeding the maximum admissible limits set by WHO (150mg/L). But in general its concentration falls within the safe limits as evident from Table 5.

2.3.2. Anions

Among the anion nitrogenous compounds nitrites and nitrates are important from the health point of view. These are usually measured during monitoring water pollution throughout the world. Exposure to nitrates from various environmental sources is possible; however drinking water is considered the main source. Normally ground and surface water contain low concentrations of nitrates but can reach high values due to run off or leaching from agricultural lands (PAKEPA, 2005b). Although reports regarding nitrate contamination are conflicting, in some parts of the country it is a threat to public health. Nitrates have been regarded as the fourth most potential contaminant by the National Water Quality Monitoring Program (PCRWR, 2005).

A detailed study on nitrate contamination based on analysis of 747 samples from all over the country reveals that 19% of the samples had nitrate concentrations beyond the safe limits (Tahir and Rasheed, 2008). Furthermore, drinking water contamination with nitrates is reported from large cities of the country like Islamabad, Rawalapindi (Kazmi and Khan, 2005), Lahore (Naeem et al., 2007), Kasur (Farooqi et al., 2007a), Quetta and Faisalabad (PCRWR, 2005). In a well (ground) water sample from Haripur, the nitrate concentration was as high as 1125 mg/L (Kazmi and Khan, 2005). In general, the Punjab and Sindh provinces have higher levels of nitrate contamination than other regions of the country (Tahir and Rasheed, 2008). Nitrate levels in water fluctuate widely from area to area and season to season depending on factors like precipitation and soil type and sometimes can reach levels much beyond WHO standard values for health, particularly during the growing season when fertilizers are heavily applied. In addition to fertilizer application, livestock, manure and atmospheric sources also contribute to nitrate contamination of underground water supplies (Tahir and Rasheed, 2008).

The most common health impact of nitrate ingestion is a blood disorder called “methemoglobinemia” commonly known as blue baby syndrome. High levels of nitrates can also be the cause of increased risk for respiratory tract infections and goiter development in children (Gupta et al., 2000; Weyer et al., 2001). Nitrates in water are also linked with high probability for bladder and ovarian cancer, insulin dependent diabetes mellitus and genotoxic effects at the chromosomal level (Ward et al., 1996).

The other important anion in drinking water is fluoride. It is an essential element for human health and both its deficiency and overexposure lead to adverse effects in teeth and bones. In relation to its effect on human health the optimum range of fluoride concentration concentration in drinking water is very narrow. In a range of 0.7-1.2 mg/L, it is necessary for the prevention of dental caries but above 1.5 mg/L it causes dental and skeletal fluorosis (Center for Disease Control and Prevention (CDCP), 1999). According to the WHO guideline the maximum limits of fluoride in drinking water must not exceed 1.5 mg/L (WHO, 1994) and the same limit is recommended by Pakistan Environmental Protection Agency (PAK-EPA, 2008).

Various studies revealed lower concentrations of fluorides in drinking water of Pakistan, and elevated concentrations do not seem to be a common problem. For example, Ayyaz et al. (2002) and Khan (2000) reported that 84% of water samples collected from various parts throughout the country had fluoride concentrations even below the minimum recommended concentration of 0.7 mg/L for human health. Similarly in water samples from Faisalabad (Kausar et al., 2003) and Karachi (Siddique et al., 2006), it was well below the standard limits with few exceptions from an industrial area of Karachi. Furthermore, a few studies suggest water fluorination to avoid the adverse effects of fluoride deficiency in drinking water (Ayyaz et al., 2002; Khan, 2000). However, the situations are not the same throughout the country. Elevated concentrations of fluoride have been reported from some parts in the North West and South East of the country. In Naranji (Khyber Pakhtoonkhwa), fluoride concentration in spring water was reported reaching 13.52 mg/L (Shah and Danishwar, 2003). Similarly in Nagar Parkar Town (near the Thar deserts of Pakistan) mean fluoride concentrations of 3.33 mg/L (maximum 7.85 mg/L) were found, with 78% of samples exceeding the WHO standard limits (Naseem et al., 2010). The highest fluoride concentrations have been reported from Khalanwala, East Punjab, where it reached as high as 21.1 mg/L (Farooqi et al., 2007a) and 22.8 mg/L, and 75% of samples were above the WHO normal standards (Farooqi et al., 2007b). In large cities of the country 6% of ground and 25% of surface water samples were documented having fluoride levels higher than the standard quality criteria. In cities like Kasur, Quetta and Loralai N20% of water samples had fluoride above the standard limits (PCRWR, 2005). In conclusion, large variation in fluoride concentration is documented in drinking water of the country. For this variation, different geological characteristics of different areas seem to be responsible. Fluoride levels can even differ significantly in water samples from different wells within the same area (Ahmed et al., 2004). The high concentrations of fluoride are attributed mainly to leaching from fluoride-bearing minerals (Naseem et al., 2010; Shah and Danishwar, 2003), industrial wastes (Siddique et al., 2006), agricultural fertilizers and combustion of coal which release fluoride into the air which later reaches the soil with rain (Farooqi et al., 2007b). The overall picture of fluoride in drinking water is complex and needs proper management and monitoring in individual areas. Water should be fluorinated in areas where fluoride concentration is very low while defluorination measures should be taken in areas with elevated fluoride concentrations.

Among other anions, high chlorides occur in areas where the water is saline and show a good correlation with Na+. Phosphates occur well below the safe limits and no study reported them above the standard quality limit. Sulphates exceed standard limits in a few areas (Table 5).

2.4. Pesticides

In the last four decades, the use of pesticides has increased substantially throughout the world. It aims at protection of crops from insect infestation to achieve higher crop yields with better quality (Zia et al., 2008). An estimated quantity of 2.5 million tons of pesticides is used in the world annually with continuous increases (Pimentel, 1995). In Pakistan pesticides were introduced for the first time in 1954 with 254 metric tons of formulation (Jabbar et al., 1993; Tariq et al., 2007). After this in the late 1960s and early 1970s, thousands of tons of pesticides were imported from Europe and USA while some pesticides like dichlorodiphenyltrichloroethane (DDT) and benzene hex chloride (BHC) were produced locally (Ahad et al., 2009). At present an estimated quantity of 70 thousand tons of pesticides are applied every year in Pakistan with an increasing annual rate of about 6% (WWF, 2007). Of the total pesticides used, about 75% are applied to cotton crops and the remaining to others crops such as maize, tobacco, paddy rice, sugarcane, fruits and vegetable (Jabbar et al., 1993).

An estimated amount of only 0.1% of pesticides applied reach the target organisms and the remaining 99.9% disperse through air, soil and water, thus resulting in the pollution of natural ecosystems and affecting human health and other biota (Pimentel, 1995). In addition to field applications, pesticides are introduced to the environment during manufacturing, handling and transportation. In developing countries like Pakistan, the problem is further aggravated by improper storage, careless disposal of pesticides containers and usage of outdated pesticides (Zia et al., 2008). This happens mainly because the farming communities lack awareness of the harmful effects of pesticides. As a result pesticide residues contribute to pollution of soil (Agarwal et al., 1994), ground and surface water (Ahad et al., 2001; Jabbar et al., 1993; Tanabe et al., 2001), drinking water (Fung and Mak, 2001), and even commercially available mineral water and soft drinks (Johnson et al., 2006).

A limited number of data is available on pesticide contamination of drinking water in Pakistan. Major hindrance in the availability of data is the lack of laboratory facilities in the country. Only one or two laboratories in the country have the analytical facilities that can determine specific pesticides in parts per billion (Tariq et al., 2007). In spite of all these limitations pesticides have been detected in water, soil, food and air as reviewed by Tariq et al. (2007). The results of various studies reporting pesticide residues in ground and surface

waters of Pakistan are summarized in Table 6.

In Pakistan pesticides residues were reported for the first time in cattle drinking water in Karachi (Parveen and Masud, 1988). The results reported the contamination of 10 samples out of 79 with chlorinated pesticides or their metabolites at concentrations ranging from traces to 16.7 μg/L. Since most of the pesticides in the country are applied on cotton crops, extensively cotton-growing areas in the plains of Punjab and Sindh are likely to have contamination of pesticides in the water. Analysis of shallow groundwater samples from the Summandri area Faisalabad (a cotton growing area) revealed the presence of pesticides like monocrotophos (40 to 60 μg/L), cyhalothrin (traces to 0.2 μg/L), and endrine (0. 1 to 0.2 μg/L) (Jabbar et al., 1993). In Multan (another cotton growing area), all 12 groundwater samples taken from 6 different sites were found contaminated with pesticides with 33% samples exceeding maximum residual limits (MRLs) (Ahad et al., 2001). Tariq et al. (2004) carried out a shallow groundwater analysis for pesticides residues in four cotton-growing districts of Punjab Province, namely Bahawalnagar, Muzafargarh, Dera Ghazi Khan and Rajan Pur. Out of 8 pesticides analysed for, 6 were detected in water samples of the area at various concentrations but the MCLs established by the USEPA for drinking water were not exceeded.

In Khyber Pukhtoonkhwa province substantial amounts of pesticides are applied on tobacco, sugarcane and maize crops (Ahad et al., 2000). Use of high doses of pesticides on tobacco fields in Khyber Pakhtoonkhwa is a common practice. Farmers in the area may sometime apply more than 10 sprays per crop of tobacco (personal observation, one of the authors is from the area). A study conducted on groundwater from 12 different sites in Mardan division (an extensively tobacco, sugarcane and maize growing area), revealed a contamination with pesticides in 100% of the samples (Ahad et al., 2000). In this study three sites, namely Amber, Swabi (0.82 μg/l), Lahor Shakh, Swabi (0.50 μg/l) and Madras Kalay, Mardan (0.64 μg/l) exceeded the maximum acceptance concentration (MAC) set by European Community (EC).

In Pakistan organochlorin pesticides like DDT have been used extensively in the past on field crops and in the malaria eradication program. Although the use of most of the organochlorin pesticides and their metabolites has been banned in the country, their presence can be detected in the environment even now due to their long persistency. For example Asi et al. (2008) reported various metabolites of DDT like o,p′-DDD, o,p′-DDE, o,p′-DDT, p,p′-DDE and p,p′-DDT in samples of ground and surface water from different districts of Punjab. These metabolites were present at variable concentrations (0.017-1.06 ng/mL) in different samples but in some cases, especially in the cotton growing areas, exceeded the maximum admissible limits set by the European Community. In Mianchannu, District Khanewal, the highest concentration of p,p′-DDT (1.06 ng/mL) was documented, which is 10 times more than the maximum admissible limits (Asi et al., 2008).

DDT had been produced locally in Pakistan. After the ban of the use of such environment non-friendly and toxic pesticides, its factories have been abandoned. The long half life of DDT makes it dangerous till now in many parts of the country, particularly in the vicinity of the demolished factories for its production. A study conducted by Jan et al. (2009) in and around a former DDT-producing factory in Aman Gharh, Nowshera, revealed p,p′-DDT contamination in different water sources ranging from 0.07±0.10 to 0.40±0.14 μg/mL (=70- 400 μg/L). However, their results are conflicting and do not agree with other studies. In a study by Ahad et al. (2009) the water samples from the same area had concentrations of various pesticides ranging from 0 μg/L to 15.17 μg/L. DDT was reported in the range of ±0.05 μg/ L. Furthermore the sample with the maximum level was from a rain water pond instead of a well or some surface water source. Similarly Asi et al. (2008) reported residues of various DDT isomers of up to a maximum of 0.947 μg/L in groundwater and 1.06 μg/L in surface water. Compared with the results of Asi et al. (2008) and Ahad et al. (2009) the concentration of 400 μg/L by Jan et al. (2009) looks extremely high.

As stated earlier the improper storage and handling of pesticides increases the risk of exposure and contamination. In Pakistan no proper planning for handling pesticides is present at the private or at government level. In the 1980s pesticide import and distribution was transferred from the public to the private sector, subsidy on pesticides was abolished and the policy of aerial spraying was withdrawn (Khan et al., 2002). At that time large stocks of pesticides, mostly consisting of banned pesticides, were in government custody but no proper strategy was adopted for handling these stocks. Due to improper storage and careless handling, most of the sacks are rotten, containers are damaged, metal drums are corroded, and pesticides leaked out and may still leak (Ahad et al., 2009). The obsolete stock of outdated pesticides is estimated in Punjab (3805 tons), Sindh (2016 tons), Khyber Pukhtoonkhwa (NWFP) (179 tons), Balochistan (128 tons) and Federal Department of Plant Protection (178 tons) (Ahad et al., 2009). Water samples from nearby areas of such obsolete pesticides stores in three provinces Punjab, Sindh and Khyber Pukhtoonkhwa (NWFP) of the country had residues of organochlorine pesticides like γ-BHC, β-HCH, Heptachlor exoepoxide, Heptachlor endoepoxide, Heptachlor, Endrin, Dieldrin, 4,4-DDT, 4,4-DDE, 2,4-DDT and 2,4- DDD (Ahad et al., 2009). The residual concentrations in water samples from Khyber Pakhtoonkhwa (NWFP), Punjab, and Sindh, were 0- 15.17 (median 0.29) μg/L, 0.25-0.78 (median 0.36) μg/L, and 0.11- 0.83 (median 0.21) μg/L respectively. Although the means were not high, several individual pesticide residues exceeded their individual maximum admissible limits.

The first reported study of pesticide residues in water by Parveen and Masud (1988) was on surface water but afterwards there is no reported study on pesticides contamination in surface water sources until that of Rawal Lake by Ahad et al. (2006). Rawal Lake is a beautiful picnic point in the capital city Islamabad and supplies drinking water to more than 1.5 million people of Rawalpindi. It is noteworthy to mention that this Lake caught attention of print and electronic media in June, 2004 when many dead fish were found in the lake. When the water samples from the lake were analyzed for pesticides, 30.4 μg/L total pesticides were detected (Ahad et al., 2006). While the first sampling and analysis was performed in the dry month of June, the follow-up sampling was done in the rainy season (first week of August) when the lake's total volume increased from 1.85×103 m3 in June to 2.47×107 m3; therefore the total pesticides reduced by 64% (from 30.4 μg/L to 11.2 μg/L) due to dilution and degradation. However, the concentration was still approximately 22 times higher than EEC standards. These concentrations, after receiving treatment in the Water and Sanitation agency (WASA) filtration plant were further reduced by 81%. The water supplied to the general public still had pesticide residues approximately 4 fold higher than EEC standards (Ahad et al., 2006). Another study on Rawal Lake and Simly Lake revealed the presence of residues of various pesticides belonging to the group of organophosphates, organochlorines and pyrethroids, and many of them exceeded the standard of European Union for drinking water (Iram et al., 2009).

Water contamination levels with pesticides residues are quite variable throughout the country but in many cases exceed the standard limits. The situation is further endangered by the high frequency of pesticides occurrence in water. Exposure to multiple pesticides for a prolonged time can cause cytotoxic changes and adversely affect the normal functioning of organs like liver and kidney and possibly produce characteristic clinical effects such as dyspnea and burning sensation in urinary tract (Azmi et al., 2006; Khan et al., 2008). According to the International Agency for research in cancer, pesticides are classified as carcinogens in humans and furthermore the endocrine disrupting pesticides adversely affect the human endocrine systems which can lead to various hormonal dysfunctions (Ejaz et al., 2004). Use of pesticides in present day agriculture cannot be avoided as it is essential for controlling pests to obtain better quality and higher quantity of crops; but on the other hand it is also well known that no pesticide is safe and all have detrimental effects on humans and other biota of aquatic and terrestrial ecosystems. The only way to avoid their adverse effects is their safe use through proper management. Farmers and workers need to be aware of the deleterious effects of pesticides and associated problems. They need to be educated well about the safe handling and use of pesticides to ensure sustainable development with emphasis on high degree of environment and human protection.

3. Sources of water pollution

Water pollution is most often due to human activities (Hammer, 1986). The major ones are indiscriminate disposal of industrial, municipal and domestic wastes in water channels, rivers, streams and lakes, etc. (Kahlown and Majeed, 2003). An estimated 2 million tons of sewage and other effluents are discharged into the world's waters every day. In developing countries the situation is worse where over 90% of raw sewage and 70% of untreated industrial wastes are dumped into surface water sources (Anonymous, 2010). According to Sial et al. (2006), in Pakistan out of 6634 registered industries 1228 are considered to be highly polluting. Due to the high load of organic and toxic materials in their waste effluents, industries became a major source of water pollution in Pakistan (Nasrullah et al., 2006). The major industries contributing to water pollution are textile, pharmaceuticals, ceramics, petrochemicals, food industries, steel, oil mills, sugar industries, fertilizer factories, and leather tanning (Sial et al., 2006; WWF, 2007). These industries produce several hundred thousands of wastewater containing huge quantities of pollutants like nitrates, nitrites, cations and anions such as Ag+, Na+, K+, Mg2+, Ca2+ Cl−, CO3 2−, HCO3 − and toxic metals like arsenic, iron, lead, mercury, chromium, cadmium, copper, nickel, zinc, cobalt and magnesium (Ali et al., 1996; Sial et al., 2006; Ullah et al., 2009). Most of the industries in Pakistan are located in or around major cities. They dispose their waste effluent directly into the nearby drains, rivers, streams, ponds, ditches and open or agricultural land (Ullah et al., 2009) (Fig. 1). For example, River Kabul in Khyber Pakhtoonkhwa, receives an estimated amount of 80,000 m3 (8×107 L) of industrial effluents each day (MOE-PAK, 2005a). Even in the capital city of Islamabad there is no proper management of effluents in its two industrial estates, and wastes are directly drained into the Sawan River (Mian et al., 1998). It has been estimated that only 1% of wastewater of industries in Pakistan is treated before being discharged (MOE-PAK, 2005a). As a result, wastewaters with potentially toxic substances are poured into water bodies without taking into account the environmental hazards caused by these wastes. An estimated amount of 40×109 L of waste effluent is discharged daily into water bodies in Pakistan by different industries (Saleemi, 1993). These waste pollutants do not remain confined to surface water but their percolation to the soil results in contamination of Grodnu water aquifers.

In addition to the industrial wastes, domestic and municipal wastes also pose a serious threat to water. Like industrial wastes, domestic wastes containing household effluent and human wastes are discharged directly to a natural drain or water body and open or agricultural land. In some cases there are sewerage collecting systems, normally discharging to the nearest water body but collecting systems cover less than 50% in many urban cities and only about 10% of the collecting sewages are treated effectively (WWF, 2007). The large cities of the country like Karachi, Lahore, Peshawar, Faisalabad, Rawalpindi, Sialkot and Hyderabad

contribute a major share to wastewater. In some of these cities treatment plants exist; however, many of these are built without the completion of associated sewerage networks. Consequently, the plants are often either under loaded (much of the municipal effluents do not reach the plant due to incomplete sewerage network) or abandoned and hardly a few percent of wastewater are effectively treated (WB-SCEA, 2006). It is estimated that only≈8% of the urban wastewater is treated in municipal treatment plants and the rest is drained into natural water sources without any treatment (WB-CWRAS, 2005). Usually nullahs (Nullah/Nallah is a local terminology used for a ravine, gully or ditch) and storm water drains collect untreated sewage and waste from the cities flowing into streams, rivers and irrigation canals. An estimated quantity of 2000 million gallons (7.5708×109 L) of sewage is being discharged to surface water bodies every day in Pakistan (WB-SCEA, 2006).

Another strong source of water pollution is the extensive use of agrochemicals in agriculture. Water contamination with agricultural chemicals has been reported in developed countries like China (Li and Zhang, 1999) and USA (Hamilton and Helsel, 1995). Conditions in Pakistan are not different. Agriculture chemicals like fertilizers and pesticides applied to the crop lands mix with the irrigation water which leach through the soil and ultimately reach natural water resources. The problem is further aggravated by heavy agriculture runoff and flooding during monsoon seasons. As discussed above, many pesticides have been detected in both surface and groundwater, especially in the areas of extensive agriculture practices. The various fertilizers applied are not totally utilized by crops. Large quantities leach into water resources resulting in increased concentrations of nitrates, nitrites, ammonia, sulphates and phosphates in the water. These nutrients accelerate the growth of algae in surface water and cause eutrophication that poses direct and indirect threats to the environment. Some species of these algae produce toxins in water resources which are harmful to animals and humans (e.g. the cyanobacterium Microcystis, which produces the hepatotoxic microcystin). In addition, some fertilizers contain heavy metals as by product, and the extensive use of such fertilizers results in the accumulation of these toxic metals in soil and water (Li and Wu, 2008). Agricultural drainage contributes to the overall contamination of the water resources, however less than the industrial and domestic wastes (MOE-PAK, 2005a).

All these sources of water pollution, i.e. industrial and domestic wastes and agricultural practices, not only contribute toxic chemicals to water but they also cause widespread bacteriological contamination which results in frequent occurrence of water-borne diseases. In addition, they also result in an increase in parameters like biological oxygen demand (BOD), chemical oxygen demand (COD), total dissolved solids (TDS), total suspended solids (TSS), and salinity and thus deteriorate the water quality and make it unfit for drinking and other purposes.

4. Water pollution and human health

Water contamination is one of the main causes of health problems in human beings. About 2.3 billion peoples are suffering from water related diseases worldwide (UNESCO, 2003). In developing countries more than 2.2 million people die every year due to drinking of unclean water and inadequate sanitation (WHO and UNISEF, 2000). Water related infectious and parasitic diseases account for ≈60% of infant mortality in the world (Ullah et al., 2009).

In Pakistan contamination of drinking water with industrial wastes and municipal sewage coupled with lack of water disinfection practices and quality monitoring at treatment plants is the main cause of the prevalence of waterborne diseases (Hashmi et al., 2009a). It is very hard to quantify exactly the waterborne diseases in Pakistan because of lack of maintenance of records at hospitals (Aziz, 2005). According to a UNICEF report 20-40% of patients in hospitals of Pakistan are suffering from water-linked diseases. These diseases include hepatitis, cholera, dysentery, cryptosporidiosis, giardiasis, and typhoid which account for one third of all deaths in the country (WB-SCEA, 2006). Each year with the onset of monsoon (July and August) rains in summer the situation gets worse with water-borne diseases like hepatitis, typhoid fever, gastroenteritis, dysentery, cholera, E. coli diarrhea, rotavirus diarrhea, malaria, giardiasis and intestinal worms. Lack of effective prevention and control measures contribute in worsening the situation (Qasim, 2008). Diarrhea, which is a water-linked disease, accounts for 14% of illnesses in children below five years old and for 7% of all diseases in people of all ages in Pakistan (Rosemann, 2005). An estimated number of 0.2-0.25 million children in Pakistan die every year due to diarrhea and other water related diseases (Rosemann, 2005; WWF, 2007). In Karachi unclean water has been the cause of renal infection which leads to death of 10,000 people annually (HRDS, 2009).

Many epidemics in the country have been traced to contaminated water. In September 1988 an outbreak of Hepatitis E was noticed in the Pakistan army unit in Abbott bad. It was traced back to fecal contamination of a water system. A total of 107 persons were infected out of 800 people in the unit (Bryan et al., 2002). In late 1993 and early 1994 water-borne epidemics of Hepatitis E (HEV) affected 3827 people in two sectors of Islamabad. Four adults and four new born babies died in the epidemics (Rab et al., 1997). During the summer 2003 the outbreak of acute gastroenteritis in Gadap, Karachi was linked to consumption of fecally contaminated well water. It was most probably due to a rotavirus in drinking water as concluded by Zahra and Jamil (2001). In October, 2004 an outbreak of typhoid fever hit the remote area of Nek Muhammad village near Karachi which claimed three human lives and left more than 300 people infected within one week (Farooqui et al., 2009). The outbreak has been linked to the contaminated water of a reservoir well, the only source of drinking water in the village. Interviews revealed that 98% of the patients suffered weakness, 91% fever, 65% diarrhea, and 42% had vomiting and other symptoms (Farooqui et al., 2009). Although in the developer countries typhoid fever has been almost eliminated, in developing countries like Pakistan it is still a common disease and a major cause of morbidity and mortality due to lack of sewage and water treatment facilities (Ahmed et al., 2006). In the Khairpur district of Sindh Province unclean drinking water has been the cause of very common occurrences of water-related diseases like diarrhea, dysentery and typhoid fever. The Quarterly Report of Infectious Diseases of Civil Hospital, Khairpur reported 25 cases of typhoid fever, 18 cases of diarrhea, and 7 cases of dysentery in the area during 2006-2007 (Shar et al., 2008b). Similarly, in May 2008 consumption of contaminated water led to an episode of gastrointestinal illness in rural Sindh affecting hundreds of people as reported in national press reports (Hannan et al., 2008).

In certain areas of Punjab, problems of bone softening and deformation have been reported as a result of high fluoride concentrations in drinking water (Ahmed et al., 2004). In Manga Mandi, an area near Lahore about 124 children were found suffering from skeletal fluorosis due to high fluoride contents in their drinking water (Ahmad

et al., 2003). In Kalalanwala, near Lahore more than 400 people were reported having bone diseases with a great majority of children (72% patients were under 15 years of age). In addition to the common complaints of joint and back pain, bone deformation and spinal defects were observed in the people of the area. The problem has been traced to a high concentration of fluoride in drinking water of the area (Farooqi et al., 2007a). Arsenic has been reported as a serious problem in many parts of the country but very few studies are available regarding its health effect on the local population. A study conducted by Arain et al.

(2009) revealed that 30-40% people of the Bobak village (near Manchar Lake in Sindh) were suffering from rough skin with black dots and arsenical skin lesions, especially on face, arms and feet due to exposure to high arsenic concentrations. However, the authors concluded that

arsenic was not the only cause of the skin problems. Other factor including malnutrition, improper medical facilities and presence of other toxicants in surface and groundwater may also contribute synergistically with arsenic overload in the area. Another study revealed that 61 to 73% of the population of villages on the bank of Manchar Lake suffer from chronic arsenic toxicity like melanosis and keratosis (Kazi et al., 2009). The authors found a strong correlation between arsenic concentrations in drinking water and hair and blood samples of exposed skin in diseased patients. In addition, the exposed people had clinical features like respiratory problems, anemia, gastrointestinal problems, muscles cramps and weakness. All the health effects were traced to high arsenic content in drinking water. Among people consuming low arsenic water (municipal water with low arsenic) no such problems were observed (Kazi et al., 2009).

Another potential threat to public health is the occurrence of pesticides in drinking water of Pakistan. Few studies have been conducted in the country concerning pesticides exposure and human health. Studies revealed the presence of high quantity of pesticides in blood and their adverse effects on various enzyme levels in the body

and biochemical parameters of blood in Pakistani population exposed to pesticides (Azmi et al., 2006; Ejaz et al., 2004; Khan et al., 2008, 2010). Clinical characteristics like headache, vomiting, dizziness, muscle weakness, shortness of breath, skin rash and burning sensation in the urinary tract due to pesticide exposure have been reported in the country (Azmi et al., 2006; Khan et al., 2010). Although the majority of studies regarding pesticide effects on public health have been conducted in populations exposed to pesticides either as workers or as farmers, the adverse effects can be expected in people exposed to pesticides through drinking water.

5. Environmental legislations in Pakistan and their effectiveness

Pakistan Environmental Protection Ordinance 1983 (PEPO 1983) was the first ever legislation in the country regarding environmental protection (GoP, 1983). This ordinance further resulted in the establishment of two organizations, namely, the Pakistan Environmental Protection Council (PEPC) and the Pakistan Environmental Protection Agency (Pak-EPA). Furthermore, the concept of Environmental Impact Assessment was introduced in the country due to this ordinance. However, slackness in its implementation is evident from the fact that the first meeting of PEPC was held in 1993 after 10 years of its establishment. It was encouraging that in its first meeting the PEPC approved National Environmental Quality Standard (NEQS) and soon formulated the maximum acceptable limits for various pollutants in municipal and industrial discharges and emission. In 1997 a regulatory framework known as Pakistan Environmental Protection Act 1997 (PEPA 1997) was approved to regulate and monitor issues regarding environmental protection in the country (GoP, 1997). In November 2002 national standards for drinking water quality were introduced. Similarly other policies including National Environment Policy 2005, National Sanitation Policy 2006 and National Drinking Water Policy 2009 have been approved (MOE-PAK, 2005b, 2006, 2009). These policies were aimed at preventing water pollution and providing safe drinking water to the general public at affordable costs. Although such ordinances, acts and policies have been approved from time to time, no clear strategy has been devised so far for their implementation. As a result, after appropriate and necessary administrative capacity on paper, its effectiveness is seriously curtailed in practice. For example, the NEQS for industry and municipal discharges were formulated in 1993, but could not be implemented in its spirit until now. The industries do not follow the national standards for pollutants in their waste effluents. Government has introduced different programs like Pollution Charge System, Self Monitoring and Reporting, Cleaner Production in Industry and Common Effluent Treatment Plants to control the pollution due to industrial wastes. But unfortunately no one is implemented appropriately due to weak law enforcement and the problems remained the same (WWF, 2007). Similarly the Environmental Impact Assessment (EIA) system is mandatory but is seldom followed in the public sector. To monitor environmental quality, laboratories have been established in all provinces but are not fully functional due to the absence of skeletal staff and inadequate budgets. Similarly, environmental tribunals have been shaped but are not efficient in all provinces. It seems that laws and a setup for monitoring the environmental issues exist in the country but lack implementation. The main hindrances in implementation are insufficient budgetary allocations and lack of effective coordination and communication among the responsible authorities like federal, provincial and local entities. Political interference cannot be excluded from the factors hindering implementation of environmental laws.

6. Conclusion and recommendations

Both surface and groundwater sources in Pakistan are highly polluted and not safe for human consumption as most of the pollutans exceed the qualitiy standards for drinking water (Table 7). Bacteriological contamination of water is the most potential threat to consumers. Among the heavy metals, with the exception of Cu and Zn, all exceed their standard limits set by WHO in many cases. The frequent and high level occurrence of iron, nickel, chromium, cadmium and arsenic is alarming. Among the cations K+ and Na+ were found above the standard limits in a large number of reports. Nitrates and fluoride are a threat in some parts. Fluoride poses a dual problem, i.e. in some areas it is very lowand needs to be supplemented but in other areas it is too high and needs removal measures. Pesticides occur frequently in water samples from different areas and in many cases exceed the safe limits. Various human activities, particularly disposal of untreated industrial and municipal wastes are the main sources of water pollution in Pakistan. There is a lack of proper monitoring of water quality particularly in rural areas.Water disinfection practices like chlorination are either nonexistent or unsatisfactory and treatment plants, if they exist, are not providing quality water to the public. Bacteriological and chemical pollution of public drinking water have been the cause of waterborne diseases in many parts of the country. However, comparatively comparatively little data are available regarding water-related diseases due to the lack of diagnostic facilities and maintenance of records. Regular surveys need to be conducted in various parts of the country to obtain a clear picture of water-linked diseases. The following recommendations are made which may help to control or diminish the problems of deteriorating water quality in Pakistan.

• There should be continuous monitoring of drinking water throughout the country both in rural and urban locations.

• Local authorities should be provided with facilities for monitoring and purification of drinking water.

• There is a need to shift from an intermittent to a continuous water supply system to avoid the wide spread contamination caused by intermittent water supply.

• There should be a renovation of old and rusty pipelines of the water distribution network.

• There should be sufficient distances between sewage and drinking water supply lines to avoid cross contamination.

• Industrial wastewater disposal should be strictly monitored and all industries should be forced to adapt wastewater treatment measures. Also active and operating sewage collecting and treatment plants in large cities for municipal wastewater treatment must be installed.

• There is a need of the existence and implementation of strict laws with no compromise on quality of public drinking water.

• Public awareness campaigns should be launched to educate the population about the importance of safe drinking water.

• The public should receive guidance to adapt safety measures for stored water inside the houses.

• The farmer community needs to be educated well about the safe handling and use of pesticides and proper application of fertilizers to minimize the contribution of agricultural practices to water pollution.

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