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SOIL CHEMISTRY

Influence of Soil Characteristics and Formulation on Alachlor Dissipation in Soil

Institute of Natural Resources and Agrobiology (CSIC), Reina Mercedes, 10, Apdo. 1052, 41080-Seville, Spain

^* Corresponding author (fsopenav{at}irnase.csic.es).

Alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] is one of the most commonly found herbicides in surface and groundwaters of the United States and Europe, and it contaminates these environments even when it is used according to the manufacturer's instructions for conventional formulations. To determine how its persistence in soil is affected by herbicide formulation and soil type, alachlor was applied to several soils in different formulations: technical grade (AT), a commercial formulation (CF), and different ethylcellulose microencapsulated formulations (MEFs). The results show that MEFs provided a prolonged release of the herbicide into the soil solution and protected against its dissipation in soil more than AT or the CF. The half-life in soil (t_1/2) for the AT, CF, and MEFs was up to 2.7, 6.4, and 32.54 d, respectively. The lowest herbicide loss was observed in MEFs prepared using a lower stirring speed or a higher ethylcellulose viscosity during the microencapsulation process. As with AT and the CF, the microencapsulated alachlor persisted longer in the soils with low pH and high clay content. In the soil where alachlor showed the least persistence, MEFs reduced the herbicide loss by 54% compared with the CF. The use of MEFs extended the alachlor concentration in the soil, thereby avoiding the need for using high herbicide application rates and decreasing the risk of environmental contamination.

Abbreviations: AT, alachlor technical grade • CF, commercial formulation • CRF, controlled release formulation • DA, dehydrogenase activity • EC, ethylcellulose • HPLC, high-performance liquid chromatography • MEFs, ethylcellulose microencapsulated formulation • PEG, polyethylene glycol • PVA, polyvinyl alcohol • TPF, 1,3,5-triphenyltetrazolium formazane • TRIS, tris(hydroxymethyl) aminomethane • TTC, 2,3,5-triphenyl-2H-tetrazolium chloride