LEACHING AND DEGRADATION OF PESTICIDES IN GROUNDWATER LAYERS

摘要

To date, most of the published data on pesticides and soil describe the fate of environmental contaminants in the upper soil layers, where low transportation, high adsorption and high microbial degradation occur. In contrast, few data are available for groundwater layers (to a depth of 5 m) with filtration media such as sand or stony layers. Laboratory testing systems were developed that allow examinations to be carried out under conditions that are close to natural. These include original sands and stones from the relevant groundwater filtration areas, original water from the same areas, and measurement of the velocity of water migrations. The temperature and pH were determined and exact analyses of the sand quality and particle size were made prior to the experiments. To produce accurate data on leaching and adsorption, and to identify the degradation products more easily, ~(14)C labelled pesticides were applied. To determine the column characteristics, tritium labelled water was used. The following 12 pesticides were investigated: the carbamate insecticide, carbofuran; chlorinated hydrocarbons, lindane, DDT and DDE; phosphoric acid esters, chlorpyrifos, diazinon, malathion and parathion; phenylurea herbicides, diuron and monolinuron; the triazine herbicide, terbutylazine; and the novel chloronicotinyl insecticide, imidacloprid. Although the recovery data of the individual pesticides were similar in the eluates of the two different sand types, in most cases the elution curves differed significantly. The different degradation rates and procedures for the same pesticide were clearly shown by the significantly different concentration values. Concerning elution and degradation, the behaviour of the chemicals differed, even if they belonged to the same class of bioactive compound. Furthermore, the behaviour of the same chemical differed in different types of sand. Because of the low transportation velocity, and the subsequent long retention times of the pesticides in the sand media, microbial degradation (metabolisms) can also take place.