title: Elimination of racemic and enantioenriched metalaxyl based fungicides under tropical conditions in the field.
abstract: The elimination has been studied of racemic and enantioenriched metalaxyl applied as an emulsifiable concentrate and wettable powder combined with copper in a Cameroonian field site. The kinetics of the degradation/dissipation of metalaxyl and its acid metabolite were investigated using reversed phase HPLC-MS/MS, while the enantiomeric ratios were measured by HPLC-MS/MS using a Chiralcel OD-H HPLC column. Some soil enzymes activities were determined concurrently for 120d. The elimination of racemic metalaxyl was shown to be enantioselective, with the R-enantiomer being degraded more slowly than the S-enantiomer. Dissipation followed approximate square root first-order kinetics (R>0.98) without lag phases. The enantiomers of metalaxyl have different elimination rates, with half-lives ranging from only 0.8 to 1.5 days. After application to soil, the elimination of metalaxyl in the copper containing formulation was slower. The activities of acid phosphatase, alkaline phosphatase, and alkaline glucosidase were monitored throughout the experiments. No significant influence of metalaxyl and copper could be observed on these parameters. The significantly shorter half-life values of all forms of metalaxyl under field conditions, compared to the previously reported laboratory derived ones, may have implications for the plant disease control with these fungicides in tropical rainforest areas.
authors.affiliation: Institute of Environmental Research (INFU), University of Dortmund, Otto-Hahn-Strasse 6, D-44227 Dortmund, Germany.
authors.forename: Adolphe
authors.initials: A
authors.lastname: Monkiedje
authors.forename: Sebastian
authors.initials: S
authors.lastname: Zuehlke
authors.forename: Saurelle Jacqueline Ngouopiho
authors.initials: SJ
authors.lastname: Maniepi
authors.forename: Michael
authors.initials: M
authors.lastname: Spiteller
mesh_terms: D000135:Acid Phosphatase / Q000378:metabolism; D000409:Alanine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D000469:Alkaline Phosphatase / Q000378:metabolism; D001673:Biodegradation, Environmental; D002163:Cameroon; D003300:Copper / Q000737:chemistry; D005659:Fungicides, Industrial / Q000737:chemistry / Q000378:metabolism*; D012988:Soil Microbiology; D012989:Soil Pollutants / Q000737:chemistry / Q000378:metabolism*; D013237:Stereoisomerism; D014329:Tropical Climate; D001617:beta-Glucosidase / Q000378:metabolism
chemical_list: D005659:Fungicides, Industrial; D012989:Soil Pollutants; C028175:metalaxyl; D003300:Copper; D000469:Alkaline Phosphatase; D000135:Acid Phosphatase; D001617:beta-Glucosidase; D000409:Alanine