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Pesticides: how low will they go?

Pesticides are designed to stay in the top several feet of soil, where they can destroy the weeds and crop pests for which they were formulated. Also residing here are microorganisms that are counted upon to ultimately degrade these toxic chemicals into benigh compounds. But new field research by William Jury of the University of California at Riverside shows that the conventional laboratory-scale tests greatly underestimate how much pesticide will flow through the upper oil unchanged. This could explain much pesticide contamination of groundwater.

Working with the herbicide napropamide, and later with four other commonly used pesticides, Jury followed manufacturers' instructions for pesticide use on his 1-acre sandy field in a commercial grape-growing area. He irrigated the soil as usual. Two weeks later he took 20 core samples. Though the pesticide should not have penetrated more than 8 inches, all cores showed that 20 percent of it had traveled--unchanged--to depths of at least 6 feet.

In upcoming tests he hopes to uncover why these pesticides behave so differently in field and laboratory conditions. He suspects that although the pesticides normally show a magnetlike attraction for soil, some compound or mineral in the soil water may hold an even stronger attraction for them. If so, as the water seeped down it would carry along that fraction of the pesticide it had been able to bind up.
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Title Annotation:research on depth of soil penetration
Publication:Science News
Date:Apr 27, 1985
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