CRITICAL EVALUATION OF PESTICIDES IN THE AQUATIC ENVIRONMENT AND THEIR REMOVAL FROM DRINKING WATER
The presence of pesticides in the aquatic environment represents a potential threat to water quality and human health. Relatively soluble herbicides, such as the chlorphenoxy acids and triazines, applied in agriculture can reach drinking water sources. These herbicides show marked seasonal variations in concentration and have a longer residence time in groundwater and surface water than was previously believed. Atrazine and its metabolite, desethylatrazine, are a particular concern in many countries. Conventional treatment technologies, such as flocculation/sedimentation, sand filtration and chlorination are ineffective in the control of pesticides. Potential control has focused on technologies that promote biodegradation (slow sand filtration), destruction (ozonation) or adsorption (granular activated carbon). Granular activated carbon has proved the most effective and reliable barrier to the sporadic, seasonal variations of pesticides with different chemical properties. It has now been established that, during the use of activated carbon, natural organic matter hinders pesticide adsorption through a phenomenon usually termed preloading. Research is therefore now focusing on the identification of the competitive organic fraction, with a view to minimising the concentration of this fraction or preventing preloading.