Do pesticides poison our soil?
As biologists learn more about the chemical virtuosity of microbes, a new environmental concern has arisen. Are we storing pesticides in the soil in ways and in forms that will come back to haunt us?
Jean-Marc Bollag, a microbiologist at Pennsylvania State University, and his colleagues have found what he calls ''a previously unknown catalyst (in soil) that can induce polymerization.'' That six syllable word means building up long-chain molecules out of smaller units, such as the products into which pesticides may break down.
Bollag says, ''...we think such occurrences are widespread in nature. If so, the implications are profound.'' he explains that microorganisms or the enzymes they produce ''may be making pesticide breakdown products polymerize or combine with other molecules in soil, producing new kinds of chemical complexes whose impact on the environment is unknown.''
Enzymes are proteins that facilitate chemical processes that otherwise would proceed slowly if they occurred at all. Studying the commonly used pesticide Sevin, Bollag suspects that microbial enzymes in soil may be combining the breakdown products with other similar chemicals in the soil in a form that temporarily locks up the pesticide residues safely. Could they later be released in a dangerous form by other enzymes? Is the soil becoming a reservoir of latent poison that could someday prove as unsuspectedly damaging as have the chemical waste dumps?
Bollag says, ''We don't know the answer. This is one of the issues we are addressing.''
Here is yet another, albeit unclear, warning that the continuing heavy use of pesticides - both insecticides and weed killers - on the land may hold unsuspected hazards. This usage has already undermined the much publicized ''victory over malaria'' of the World Health Organization. A few years ago WHO thought it had won that crusade as mosquitoes associated with the disease were brought under control. However, Georganne Chapin and Robert Wasserstrom of Columbia University, in a major paper in the Sept. 17 issue of Nature, have shown that the mosquitoes are making a comeback, especially in Central America and India.
The mosquitoes have developed resistance to a broad range of pesticides, not because these were used in control programs, but because of excessive use of poisons in farming. Often this involves export crops, such as cotton, rather than food grown for local use.
In spite of such experiences and in spite of the rising cost of the poisons, pesticide use seems to be growing, especially in third-world countries. Now Bollag has added to environmental concern by warning that we may be building up a time-release poison capsule in our soils.