Exogenous organic matter as strategy to reduce pesticide leaching through the soil

Abstract

ABSTRACT This research was to assess the effect of exogenous organic matter (composted sheep manure, CSM) on the sorption, disappearance and leaching of four pesticides (boscalid, flonicamide, myclobutanil and penconazole) using an agricultural soil from a semiarid area (SE Spain) to determine their potential for groundwater pollution. Results of batch equilibrium experiments show that the sorption capacity of amended soil was significantly increased in all cases. In both, unamended and amended soils, a rapid degradation of flonicamide was observed, while boscalid, myclobutanil and penconazole had high persistence (t½ >110 d) although half-lives were higher in amended soil due to the increased adsorption. Leaching experiment indicated that the addition of CSM significantly limited the downward movement of the pesticides through the soil columns especially for boscalid and penconazole, considerably decreasing the amounts recovered of both in leachates. A new leaching index referred as Experimental Leaching Index (ELI) is compared with others such as GUS, RLPI and LIX, based on degradation (DT50) and sorption (K OC) parameters. According to ELI, all pesticides were very mobile (1.5 > ELI ≤ 2) in unamended soil, decreasing their mobility in the amended soil, especially boscalid and penconazole (0.6 > ELI ≤ 1.5).