Introduction heavy metal pollution

PESTICIDE POLLUTION
Pesticides have long history since the emergence of agriculture. Human beings are facing the development of pests (including weeds, insects and pathogenic agents) causing considerable agricultural losses. If these pests are not controlled, they diminish the quality and quantity of crop production (Richardson, 1998). In the beginning, either some inorganic chemicals or compounds extracted from plants were used as pesticides. The pyrethrine was extracted from Chrysanthemum flowers and used to control the pest development during winter storage of crop. This was reported by the Greek civilization and authorization of this compound is still going on. However, agricultural revolution in the 19^th century has lead to the intensive and diversified use of the pesticides corresponding to compounds derived from minerals and plants. As an example, the development of Bouillie Bordelaise (Bordeaux mixture) in 1880, consisting of copper sulphate and lime allowed better control of cryptogamic diseases in Bordeaux and French vineyard. It is still in use for vineyard and fruit tree protection. Development and application of pesticides for the control of various insectivorous and herbivorous pests is considered as fundamental contributor to this “Green Revolution”. The use of synthetic organic pesticides began during the early decades of 20^th century and increased tremendously after the World War II, with the introduction of synthetic organic molecules such as DDT, aldrin (two insecticides) and the herbicide 2,4-D in the agricultural market. Due to their advantages of being effective and cheap, use of synthetic pesticides is continously increasing in the whole world.

Although pesticide application ensures better yield in agricultural production, however, when they contaminate the soil and water resources, became harmful for the environment and living beings through the food chain (Briceno et al. 2007). Due to their intensive and repeated application, and their relative recalcitrance to biodegradation, pesticide residues are persistent in the environment where they have often been detected beyond the permissible limits in different compartments of the environment as well as in food chain. In many parts of the world, particularly in developing countries, clean drinking water is a limited resource and, in this context, intensive agricultural production is a major environmental and health problem because pesticide residues accumulate in surface and under ground water (Rasmussen et al. 2005). Contamination with pesticides is restricted not only to developing countries but also in Europeon countries, where pesticide residues have often been detected in surface and ground water resources (Gooddy et al. 2002). As a result, the use of pesticides in conventional agriculture has attracted much attention in recent years due to rising public and governmental concerns about their impact not only on environmental contamination but also on human and animal health.

Pesticide exposure to environment is dependent on various factors like production, formulation processing and application doses. A pesticide enter in to the environment via (1) direct intentional application to soil to control pre emergent weeds, plant pathogens, soil insects /pests, and/or (2) indirect unintentional entry followed by foliar application for post emergent weeds and insects/pests (Mathews, 2006; Brieceno et al. 2007). In addition to this a certain portion of pesticides may undergo spillage from formulation plants during processing and waste disposal process as well. Adverse impact of pesticides on soil biology and ecosystem have been described by many researchers (Sacki and Toyota, 2004).

These recalcitrant compounds build up regularly in the environment, as they are not at all biodegradable, and even if degraded, very slowly. Owing to low water solubility, pesticides have strong affinity for particulate matter and consequently enter in to water sediments (Giri et al. 2014). For instance Lindane, the most commonly used isomer of HCH is known to accumulate in food chains, causing toxicity in wild/domestic animals and human beings. Apart from food contamination, human beings are exposed to lindane by inhalation, polluted water and dermal contact (Giri et al. 2014).

Repeated applications of haloginated insecticide endosulfan causes its accumulation in the soil and water environment. Consequent upon accumulation, it is extremely toxic to aquatic fauna, while provoking chronic symptoms like testicular and prostate cance, breast cancer, sexual abnormality, genotoxicity and neurotoxicity in various mammalian species (Giri and Rai, 2012).