Utilization of biomass as sorbent material to prevent organophosphate pesticides contaminate to soil

Abstract

Four biomass which are agricultural by-products namely, coconut husk (CH), rice husk (RH), peanut shell (PS) and peat moss (PM) were evaluated for their ability to minimize the amount of organophosphate pesticides (OPs) in leachate after spraying onto plants. The biomass have high organic carbon content (35.4-45.4%) and contain various nutrients to support microbial growth; consequently they are expected to sorp OPs and simultaneously promote OPs biodegradation. In this study, the biomass were investigated in comparison to a sandy soil sample taken from tangerine orchard in northern Thailand. The OPs tested were malathion, methyl parathion, chlorpyrifos and profenofos. Sorption studies were carried out by the batch (equilibrium) method. Sorption strength of OPs were in the order that profenofos>chlorpyrifos>methyl parathion> malathion and for a given OP with different types of biomass PM>CH>RH>PS. Soil sorption obviously exhibits the lowest values for all OPs. OP behavior in the biomass-water systems is governed by the compound properties (structural features and hydrophobicity) together with biomass properties (organic carbon contents, size, and surface areas). The study also determined the degradation of OPs after sorption by measuring their half-life (t1/2). The results showed that the half-life of each OPs was depended on the type of sorbed materials. For example, the half-life of chlorpyrifos in coconut husk was 21.6 days, which was the fastest among the tested biomass, whereas; its half-life was 63.6 days in soil. Similarly, malathion, methyl parathion and profenofos were degraded more rapidly in biomasss than in soil. Chlorpyrifos and coconut husks were later selected as a model for soil column study. Leaching experiments were carried out by packing 4 cm coconut husk on top of soil columns (250 mm x 38.5 id mm), and sprayed with 0.25 kg ha-1 chlorpyrifos to the column surface. Leaching tests were performed at a water flow rate of 20 ml hr-1. Results indicated chlorpyrifos mass were retained in the coconut husk layer. The amounts of sorbed chlorpyrifos were retained less than 6.25% after 28 days. At the same time, the number of chlorpyrifos-degrading bacteria was increased, which suggested that the sorbed chlorpyrifos was biodegraded. Moreover, the half-life estimation for other OPs was 9.8, 6.0 and 10.4 days and amount of OPs were retained less than 12.5, 6.25 and 12.5% methyl parathion, malathion and profenofos, respectively. Therefore, covering of soil surface with coconut husk could be a feasible method to reduce contamination of OPs leachate from the sprayed plants through soil.