New lakes of ion surface runoff have also appeared, the largest of which are the Arsanai lake in the Syr Darya basin and the Sarykamysh lake in the Amu Darya basin. 10-20 a. Data on ionic runoff are not precise, since continuous transformation of ionic runoff is still proceeding. Salt flow to land has also increased, owing to water filtration, the withdrawal of groundwater for irrigation, and the discharge of drainage waters to oasis margins. Thus, irrigation developments have led to the mobilization of enormous salt masses accumulated earlier in the land and their redistribution over a vast territory of arid areas. Thus, in the Tashkent area in the Fergana valley, and in some other nearby regions, air pollution exceeds maximum USSR permissible concentrations by 1.5-6 times.
Pollution connected with agricultural production is, however, the most dangerous problem.
Under conditions of cotton monoculture, extensive amounts of fertilizers, defoliants, and herbicides were used on irrigated land. Fertilizer use on irrigated land in Central Asia, for example, exceeds the level in Russia by several times. The use of airplanes in the application of pesticides has also caused air pollution and has led to direct human exposures. Pesticides have also entered the food chain through fodder and drinking water. Up to 13 per cent of water samples from open reservoirs and 37 per cent of food products have contained pesticides.