## 1 Introduction  
Pesticides are mostly used for preventing, fighting and eliminating a variety of pests, such as weeds, insects, rodents, and fungi [1]. However, their extensive use in agriculture worldwide has led to widespread contamination of natural waters and presence of pesticides across the environment [1; 2]. A large number of pesticides with different chemical compositions are currently used all over the world for agricultural purposes. Their widespread use has meant that pesticide residues have been detected in various environmental matrices, such as soil, water and air by several researchers [3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18]. Pesticides are divided into many classes, the most important being organochlorine pesticides (OCPs) and organophosphorus pesticides (OPPs) [19]. OCPs are very stable substances that resist biodegradation in the environment [20; 21]. Therefore, they bioaccumulate, getting recycled through the food web to produce a significant magnification of the original concentration at the end of the chain. OCPs are one of the most persistent organic micro pollutants present in water. As a result of their toxicity and ability to bioaccumulate, they are a possible risk both to human health and the environment [21]. The contamination of water due to extensive use of pesticides for agricultural purposes a serious threat to the environment and human health. Contamination from OCPs is particularly significant, due to their persistence in the environment for a long time, and the high toxicity to aquatic life and human health. Contamination of water by pesticides may occur due to direct run off, careless disposal of empty containers, leaching, misuse, equipment washing, etc. [22]. Along with the dangers for environmental and human health posed by their bioaccumulation and biomagnifying effects in the food chain, OCPs also produce reproductive and carcinogenic impacts in animals and human beings [23]. Agriculture is the largest sector of Pakistan's economy. It presently accounts for 21% of the GDP. Agriculture provides good employment opportunities for 45% of the labor force, and 60% of the country's rural population depends upon the sector for their livelihood. Agriculture has a vital role in ensuring food security, reducing poverty, developing overall economic growth and the transformation towards industrialization. The total import of insecticides was estimated (by weight) during 2009-2010 (38,227 Tons), 2010-2011 (36,183 Tons) and 2011-2012 (22,510 Tons), and had a market value of Rs. 13,473 million (109.13 million Euro), Rs. 13,178 million (106.74 million Euro) and Rs. 8531 million (69.10 million Euro), respectively [24]. The growth rates for insecticides, herbicides and fungicides in Pakistan over the last 10 years were 3%, 5% and 2%, respectively. On average, 63% of the pesticides were used for crops while the rest were used for fruits and vegetables. On average, 75% of pesticide consumption took place in Punjab, followed by 22% in Sinth. However, pesticide use in both Punjab and Sinth is gradually declining, due to a decrease in pesticide application to cotton crops [25]. Of the pesticides used in Pakistan, 74% were insecticides, 14% were herbicides, 9% were fungicides, 2% were acaricides and 1% were fumigants [26]. It has been estimated that almost 80-90% of pesticides were consumed on cotton crops, while the remaining 10-20% were used on sugarcane, paddy, fruits, and vegetables [27]. Early estimates by the World Health Organization (WHO) suggested that one million pesticide poisonings (unintentional acute cases) occurred annually worldwide [28]. This figure only included more serious cases and those registered in hospitals. The WHO has since stated that the cases of poisonings have been underestimated, and there may be a significant increase in the extent of poisonings [29]. Globally, an estimated 20,000 people were killed in 1990 from unintentional pesticide poisonings [28].