Rate of transformation of atrazine and bentazone in water-saturated sandy subsoils

Abstract

: When pesticides leach through the soil to the upper groundwater zone, it is important to know whether further transformation occurs before the pumping wells for drinking water are reached. Atrazine and bentazone were incubated (at 10¡C) in Ðve water-saturated sandy subsoils (collected at depths between 1É5 and 3É5 m), simulating the conditions in the Ðeld. In three subsoils with comparatively low pH and intermediate to high redox potential, atrazine was transformed gradually, to leave 1É9%, 6É2% and 17É5% of the dose after about Ðve years. In one of these subsoils, hydroxy-atrazine was detected ; the amount corresponded to half of the dose of atrazine. In one anaerobic subsoil with high pH, the transformation of atrazine was comparatively fast (half-life about 0É15 year). Another anaerobic subsoil, with similar pH and a somewhat higher redox potential, however, showed hardly any transformation. Sterilization of the Ðrst anaerobic subsoil had no e †ect on the rate of transformation. In the course of about Ðve years, bentazone in the Ðrst three subsoils was transformed gradually to leave \0É25%, 11% and 25% of the dose. Bentazone transformation in the two subsoils with high pH and low redox potential was very slow, but the presence of oxygen in one of these subsoils speeded up the transformation. ( 1998 SCI Pestic. Sci., 53, 223È232 (1998

Degradation of herbicides in shallow Danish aquifers: an integrated laboratory and field study

“…Under certain conditions these compounds have been reported to be degradable. In other studies, however, investigations of isoproturon degradation showed an initial transformation under aerobic incubations in chalk aquifer material,52 and bentazone was slowly degraded in aerobic but not in anaerobic aquifer samples during a 3.9‐year study 53…”

“…Several other contributions consider atrazine to be persistent in aquifer conditions 44. 46, 49, 55–59 Conversely, a few investigations have observed aerobic degradation of atrazine60–62 as well as removal of atrazine under anaerobic conditions 53. 63 Although differences in experimental approaches exist between these contributions, they stress the importance of not only investigating aerobic conditions but of also including anaerobic conditions.…”

An appraisal of methods for measurement of pesticide transformation in the groundwater zone

“…When atrazine was incubated in groundwater‐zone materials with intermediate to high redox potentials (at 10 °C), its rate of transformation was found to be quite low 16. 17 Results from the latter study are summarized in Table 2. Only in subsoil with very low redox potential was atrazine transformed at a reasonable rate, possibly by reductive dechlorination 17.…”

“…17 Results from the latter study are summarized in Table 2. Only in subsoil with very low redox potential was atrazine transformed at a reasonable rate, possibly by reductive dechlorination 17. Gamma‐sterilization had no effect on the rapid transformation of atrazine in this subsoil, so the contribution of biotic processes seemed to be small.…”

“…Extrapolation of data from such short experiments is not justified in view of the usual variability of measured data. For example, atrazine had to be incubated in some subsoil materials for a few years in order to establish its rate of transformation 17. Protracted incubation of pesticides in water‐saturated subsoil materials seems to be possible in the case of abiotic transformation, but the microbial activity in the subsoils may decrease over time.…”