Effect of formulation and repeated applications on the enantioselectivity of metalaxyl dissipation and leaching in soil | Enantioselective behavior of metalaxyl in soil under repeated applications

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BACKGROUND: Soil incubation and column leaching experiments were conducted to address the question of whether the type of formulation (unsupported versus clay supported) and repeated applications of the chiral fungicide (RS)-metalaxyl affected the enantioselectivity of its dissipation and leaching in a slightly alkaline, loamy sand agricultural soil. RESULTS: Regardless of the type of formulation and the number of fungicide applications, the R-enantiomer of metalaxyl was degraded faster than the S-enantiomer, but the individual degradation rates of R- and S-metalaxyl were highly affected by the different application regimes assayed (t1/2 = 2-104 days). Repeated applications accelerated the degradation of the biologically active R-metalaxyl enantiomer, whereas they led to slower degradation of the non-active S-metalaxyl enantiomer. The type of formulation had less influence on the dissipation rates of the enantiomers. For all formulations tested, soil column leachates became increasingly enriched in S-enantiomer as the number of fungicide applications was increased, and application of metalaxyl to soil columns as clay-based formulations reduced the leaching of both enantiomers. CONCLUSION: Pesticide application conditions can greatly influence the enantioselective dissipation of chiral pesticides in soil, and hence are expected to exert a great impact on both the biological efficacy and the environmental chiral signatures of pesticides applied as mixtures of enantiomers or racemates to agricultural soils. © 2015 Society of Chemical Industry.

This work has been financed by the Spanish Ministry of Economy and Competitiveness (MINECO Project AGL2011-23779) and Junta de Andalucía (Research Group AGR-264), cofinanced by European FEDER-FSE funds (Operative Programme 2007-2013). Beatriz Gámiz thanks the Junta de Andalucía for a post-doctoral contract linked to the project P07-AGR-03077. María Adelino thanks MINECO for a predoctoral FPI fellowship. The authors also thank MJ Calderón (IRNAS, CSIC),MI Cardo (IRNAS, CSIC) and P Franco (Chiral Technologies Europe) for technical assistance, and Dr. S Redondo and Dr. E Mateos (University of Seville) for their help with the statistical treatment of the data.

Peer reviewed