Abbau und Persistenz von Herbiziden in Boeden.
1986
Pawlizki K. H. | Koeniger M.
DEUTSCH: Approximately 18,000 tons of active herbicidal ingredients are used at present annually in the Federal Republic of Germany. The largest amount of these compounds reaches the soil directly or indirectly and there is subject to various conversion processes. Depending upon the nature of the herbicide molecule and the environmental conditions a variable portion of the applied substances is either completely degraded or inactivated by binding tightly to soil colloids. Since not all pesticides loosing their activity are degraded, however, data on both, the persistence of biological activity (= period of herbicidal activity) and the persistence of total residues (= time required for complete mineralisation) are of great importance in evaluating the long-term behaviour of herbicides in soil. Whereas both values are usually in direct proportion to the chemical stability and application rate of the herbicide and in contrary proportion to soil moisture and soil temperature they differ significantly with regard to sorption capacity of the soil. With reference to this parameter increasing humus and clay contents prolong the residence time of herbicides and their metabolites in the soil environment while the period, during which these pesticides remain biologically active, is shortened. Although there has been no indication of any damage of soil functions so far 'bound' residues may constitute a potential environmental risk for their high persistence. In order to be able to detect potential hazards of 'bound' residues in time, as for instance, contamination of untreated crops and ground water or injury of natural cycles and subsequent crops, it is important that the advisory service observes the reactions of suspicious pesticides and their residues over several vegetation periods. On the other hand intensive investigations are necessary to elucidate the structure, the release, the biovailability, the toxicity and the accumulation of 'bound' residues in soil for all herbicides.
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