Transformation pathways of 14c-chlorothalonil in tropical soils.
Chlorothalonil (CTN) is a chlorinated wide-spectrum fungicide, heavily and widely applied throughout the world. This study was undertaken to directly evaluate the rates and forms of 14C-labeled CTN dissipation in three acid Brazilian soils (Typic Humaquept [GH], Typic Quartzipsamment [AQ], and Typic Hapludox [LE]). Mineralization was not the major metabolic pathway of CTN-degrading microorganisms. However, CTN dissipation was fast in all soils and was mainly due to biodegradation (responsible for 50%, 54%, and 73% of 14C-CTN dissipation in the GH, LE, and AQ soils, respectively), as well as to formation of soil-bound 14C residues (responsible for 46%, 34%, and 18% of 14C-CTN dissipation in the GH, LE, and AQ soils, respectively). Most soil-bound 14C residues were formed in the first day, but aging also contributed to the formation of less reversible forms of CTN-soil complexes. In these acid soils, the most abundant metabolite formed from CTN degradation was 3-carbamyl-2,4,5-trichlorobenzoic acid. A significant fraction of the CTN that had been assumed to be rapidly degradable in soils in previous reports has turned out to be soil-bound residues. Although bioavailability of any compound is reduced when soil complexes are formed, further research is needed to evaluate accumulation and availability of CTN soil-bound residues over long-term applications, and the consequent detrimental effects on the environment and on soil quality and fertility.
Regitano
J B
JB
Departamento de Ecotoxicologia, Centro de Energia Nuclear na Agricultura, Universidade de São Paulo, Caixa Postal 96, CEP: 13400-970, Piracicaba, São Paulo, Brazil. regitano@cena.usp.br
Tornisielo
V L
VL
Lavorenti
A
A
Pacovsky
R S
RS
D001682:Biological Availability; D002250:Carbon Radioisotopes; D004784:Environmental Monitoring; D005659:Fungicides, Industrial / Q000378:metabolism*; D009570:Nitriles / Q000378:metabolism*; D012988:Soil Microbiology; D012989:Soil Pollutants / Q000378:metabolism*
D002250:Carbon Radioisotopes; D005659:Fungicides, Industrial; D009570:Nitriles; D012989:Soil Pollutants; C005806:tetrachloroisophthalonitrile