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Aging reduces the bioavailability of even a weakly sorbed pesticide (carbaryl) in soil
Author(s) -
Ahmad Riaz,
Kookana Rai S.,
Megharaj Mallavarapu,
Alston Angus M.
Publication year - 2004
Publication title -
environmental toxicology and chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.1
H-Index - 171
eISSN - 1552-8618
pISSN - 0730-7268
DOI - 10.1897/03-569
Subject(s) - carbaryl , bioavailability , environmental chemistry , pesticide , chemistry , pesticide residue , biodegradation , soil contamination , pesticide degradation , bioremediation , soil water , contamination , agronomy , environmental science , biology , soil science , ecology , organic chemistry , bioinformatics
We investigated bioavailability and biodegradation of carbaryl (1‐naphthyl methylcarbamate) in a soil with a long history of pesticide contamination from a storage facility located at Mamoon Kanjan, Pakistan. Carbaryl is weakly sorbed and generally considered to be easily degradable in soil. Extraction studies revealed that 49% of the total carbaryl in soil (88.0 mg kg −1 ) was not water‐extractable and also not bioavailable, as demonstrated by inoculation of the contaminated soil with a carbaryl‐degrading, mixed bacterial culture. Inoculation of the contaminated soil with the carbaryl‐degrading culture showed that the bacteria were capable of degrading only the available (i.e., water‐extractable) fraction of the pesticide. When the soil was pulverized in a ball mill to enhance the release of residue, an additional 19% of the carbaryl became bioavailable. A significant proportion of residue (≈33%) remained unavailable. The long (>12 years) contact time between the pesticide and soil (i.e., aging), allowing possible sequestration into soil nanopores and the organic matter matrices, is suggested to have rendered the pesticide unavailable for microbial degradation. High concentration (88.0 mg kg −1 ) in soil facilitated its persistence and sequestration. Results from the present study demonstrate that even a weakly sorbed and easily degradable pesticide, carbaryl, is effectively sequestrated in soil with time, rendering it partly inaccessible to microorganisms and affecting the bioavailability of the compound.