Pesticides in the aquatic environment.

A comprehensive literature review is presented concerning pesticides; in particular the organochlorine insecticides, DDT and dieldrin, and their role in the pollution of water resources. The results of a laboratory study on the removal of DDT and dieldrin (HEOD) by adsorption onto a clay of the montmorillonite type (bentonite) are presented. For an initial DDT concentration of 100 μgm/l, the addition of bentonite at concentrations of 1.0 gm/l and 10.0 gm/l results in the removal of about 60 and 72 per cent, respectively, of the insecticide. For an initial HEOD concentration of 100 μgm/1, the addition of bentonite at concentrations of 1.0 gm/l and 10.0 gm/l brings about the removal of about 15 and 30 per cent, respectively, of this insecticide. The results of a laboratory study on the desorption of DDT and HEOD from the bentonite are presented. Both insecticides are desorbed from the clay, the HEOD being desorbed to the greater extent and the DDT desorption being quite minimal. The results of a further laboratory study conducted to ascertain the ability of bentonite clay to remove, by adsorption, insecticides from solution while settling through a quiescent water body are presented. Bentonite at concentrations of 1.0, 5.0, and 10.0 gm/l removes about 44, 48, and 54 per cent, respectively, of DDT from the quiescent water body initially containing 100 μgm/1 DDT. Bentonite at concentrations of 1.0, 5.0 and 10.0 gm/l removes about 14, 23, and 30 per cent, respectively, of the HEOD from the quiescent water body initially containing 100 μgm/1 HEOD. The results of an inorganic blanketing study indicates that the addition of a layer of sand over DDT and HEOD contaminated benthic deposits will block, somewhat, the desorption of these insecticides into the overlying waters.