Environmental behavior of the chiral herbicide haloxyfop. 1. Rapid and preferential interconversion of the enantiomers in soil.
Haloxyfop-methyl is a chiral herbicide that was first introduced as racemate and later replaced by "haloxyfop-P-methyl", mainly consisting of the R-enantiomer, which carries the herbicidal activity. We studied the ester cleavage of haloxyfop-methyl and further degradation and chiral inversion of the acid enantiomers in three different soils using enantioselective gas chromatography-mass spectrometry. Our results confirm the rapid ester hydrolysis of haloxyfop-methyl with half-lives of a few hours and indicate that hydrolysis is weakly enantioselective. Further degradation of haloxyfop was slower with half-lives of several days. In all three soils, S-haloxyfop was rapidly converted to R-haloxyfop. In sterile soil, no degradation and no inversion were observed, indicating that both processes are biologically mediated. In soil where 50% of the water had been replaced by deuterium oxide, significant H-D exchange in haloxyfop was observed, pointing to a reaction mechanism involving abstraction of the proton at the chiral center of the molecule.
Agroscope, Institute for Plant Production Sciences, Schloss 1, CH-8820 Wädenswil, Switzerland.
Thomas
T
Poiger
Agroscope, Institute for Plant Production Sciences, Schloss 1, CH-8820 Wädenswil, Switzerland.
Markus D
MD
Müller
Agroscope, Institute for Plant Production Sciences, Schloss 1, CH-8820 Wädenswil, Switzerland.
Hans-Rudolf
HR
Buser
Agroscope, Institute for Plant Production Sciences, Schloss 1, CH-8820 Wädenswil, Switzerland.
Ignaz J
IJ
Buerge
D004777:Environment; D008401:Gas Chromatography-Mass Spectrometry; D006207:Half-Life; D006540:Herbicides / Q000737:chemistry*; D011725:Pyridines / Q000737:chemistry*; D012989:Soil Pollutants / Q000737:chemistry*; D013237:Stereoisomerism
D006540:Herbicides; D011725:Pyridines; D012989:Soil Pollutants; C054176:haloxyfop
chiral inversion; enantioselective GC-MS; enantioselective degradation; haloxyfop; soil