Impacts of zerovalent iron application on the adsorption behavior of alachlor and metalaxyl in water and soil systems

Alachlor and metalaxyl contaminations of environmental and agricultural water and soil systems cause potential threats to human health. However, information on the pesticide adsorption quantity–intensity (Q/I) relationships in water and soil systems is limited. Therefore, adsorption behavior and the fate of alachlor and metalaxyl in the systems as influenced by the application of zerovalent iron (ZVI, Fe⁰) were investigated using the pesticide adsorption Q/I relationships. After treating ZVI in the systems, the concentration of alachlor rapidly decreased within a few days and then it disappeared at approximately 5–7 experiment days; whereas metalaxyl concentration was reduced by approximately 40–45% during the 28 day experimental period. In particular, ZVI adsorbed more metalaxyl in the aqueous system than in the soil-solution system. The alachlor concentration in the water and soil solution drastically decreased with increasing ZVI treatment, while metalaxyl concentration was relatively slow in its decrease. Adsorption mechanism of the pesticides in the soil-solution system was shown as multiple-site adsorption Q/I fitting. Buffering capacity (BC) of the pesticides increased with ZVI treatment in all sorption sites. The BC values in sandy soil were escalated with increasing ZVI application rates, so that the values were rather higher in sandy soil than in clayey soil. In addition, changes in alachlor concentration with applying ZVI were due to both dechlorination and adsorption; whereas metalaxyl concentration was dependent upon adsorption reaction. Thus, the pesticide adsorption Q/I relationships in different soil-solution systems were critically affected by the ZVI treatment.