Polychlorinated biphenyls: Occurrence and biological effects.- DDT residues in marine phytoplankton.- The regulation of pesticides in Argentina.- The possible importance of transfer factors in the bacterial degradation of herbicides in natural ecosystems.- Guidelines for environmental study of pesticides: Determination of bioconcentration potential.- Evaluation of human health hazards on use of dichlorvos (DDVP), especially in resin strips.- Comment on the distinction between hazard and safety in evaluation of human health hazards on use of dichlorvos, especially in resin strips.