CLEARANCE OF ATRAZINE IN SOIL DESCRIBING XENOBIOTIC BEHAVIOR

The primary aim of this study was to evaluate the ''clearance concept' ' as a tool for describing the behavior of xenobiotic movement into an d through soils. As an example, degradation of 2-chlro-4-ethylamino-6- isopropylamino-s-triazine (atrazine) with the formation of metabolites 2-chloro-6-isopropylamino-s-triazine (desethylatrazine) and 2-chloro- 4-ethyiamino-s-triazine (desisopropylatrazine) was investigated. Atraz ine was sprayed post-emergently in doses of 0.125 or 0.5 g active ingr edient/m(2) each on four test plots. Soil type was a sandy-loam, on wh ich corn (Zea mars L.) was cultivated. Soil samples were taken as core s of 0.2 m depth 0, 1, 2, 4, 8, 12, 16 and 20 weeks after application of atrazine, and analyzed by HPLC. Soil concentrations of atrazine wer e highly correlated (r= 0.993, p< 0.001) between the two applications of 0.125 g/m(2) and 0.5 g/m(2). Up to 50 % of the atrazine was measure d as metabolites during the whole vegetation period. Clearance of atra zine from soil was calculated as the total load of atrazine divided by the area under the soil atrazine concentration rime curve. Soil atraz ine clearance was calculated as 5.13 +/- SD 1.10 and 5.17 +/- SD 1.02 liter of soil per day for doses of 0.125 g/m(2) and 0.5 g/m(2), respec tively (from a ''soil unit'' of 1 x 1 x 0.2 meter). The clearance conc ept might be a tool for risk assessment of xenobiotics.