Organophosphorus and Carbamate Insecticides - Organic Pollutants: An Ecotoxicological Perspective - page 218

granules were found to lose their effectiveness in some “problem” soils where the
insecticide was regularly used. The soils showed enhanced capacity to degrade car-
bofuran, an effect attributed to either or both of the following: (1) the increase in
numbers of preexisting species or strains capable of metabolizing the carbamate
and, presumably, using it as a nutrient and energy source; and (2) the induction of
enzyme systems capable of metabolizing the carbamate (adaptive enzymes). Such
effects have also been found with herbicides, such as MCPA and 2,4-D, where the
enhancement of metabolic capacity of the soil is lost after a period of time if there is
no further exposure to the insecticide.
10.4 Summary
The organophosphorus and carbamate insecticides are anticholinesterases, are read-
ily biodegradable, and do not tend to bioaccumulate in food chains. They are gener-
ally seen as being more environment friendly than the persistent OC insecticides that
they came to replace for many purposes during the 1960s, and have been widely used
in agriculture and for certain other purposes worldwide. However, some of them are
highly toxic to vertebrates and beneficial invertebrates, and have caused mortality
of animals and birds in the field, albeit in limited areas and over limited time spans.
There can be adverse effects on immobile invertebrates when these and other nonper-
sistent insecticides are repeatedly used during the course of intensive agriculture. A
further cause of concern is that they are neurotoxic, and can have behavioral effects
in the field, effects that are difficult to quantify but may be ecologically important.
Recently, there has been growing concern about effects on sites other than AChE in
the nervous system (e.g., on NTE), effects that may have longer-term consequences
for affected individuals than sublethal ChE inhibition.
A few OP compounds are “chemical warfare agents.”
furtHer readIng
Ballantyne, B. and Marrs, T.C. (1992). Clinical and Experimental Toxicology of
Organophosphates and Carbamates , Butterworth/Heinemann, Oxford—Gives an in-
depth account of the toxicology of both groups of compounds including some informa-
tion about the so-called nerve gases.
Eto, M. (1974). Organophosphorus Insecticides: Organic and Biological Chemistry , CRC
Press, Cleveland, OH.
Fest, C. and Schmidt, K.-J. (1982). Chemistry of the Organophosphorus Pesticides , Springer,
Berlin—This and the Eto topic are valuable texts on the basic properties of the OP
insecticides.
Kuhr, R.J. and Dorough, H.W. (1976). Carbamate Insecticides , CRC Press, Boca Raton,
FL—Is a good text of similar ilk on carbamate insecticides.