US EPA

2210084 

Technical Report 

Biotechnology Report. Nonbiodegradable and other recalcitrant molecules 

Alexander, M 

1973 

HAPAB/73/2813 

Bioeng 

4 

HAPAB. Pesticides are an important group of synthetic chemicals which may or may not be degraded when released into the environment. Organophosphates are replacing the persistent organochlorines although some of these substitutes have persisted for 15 years. Some of the persistent pesticides like DDT and aldrin are modified either by microorganisms or through nonbiological means, but the product is not rapidly degraded. The polychlorinated biphenyls which have the highest chlorine content tend to accumulate and be magnified in the food chain like the persistent pesticides. Although generalizations are not evident concerning the effects of individual molecular substituents on resistance, the number and position of such substituents govern degradability in a number of dissimilar chemicals. Factors contributing to the recalcitrance of environmental chemicals include: nonexistence of an active organism; lack of similarity of the chemical to substrates of enzymes which catalyze breakdown; lack of sufficient energy or nutrients for growth of organism; toxicity of chemical to organism; failure of chemical to penetrate the cell; and low concentration or inaccessibility of substrate.