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Composition of soil organic matter drives total loss of dieldrin and dichlorodiphenyltrichloroethane in high-value pastures over thirty years

journal contribution
posted on 07.01.2021, 03:33 by Christian Krohn, Jian Jin, J Ryan, P Fabijański, Ashley Franks, Caixian Tang
© 2019 Elsevier

The residues of dieldrin and dichlorodiphenyltrichloroethane (DDT), internationally-banned agricultural insecticides, continue to exceed government guidelines in some surface soils 30 years after use. Little is known regarding the soil factors and microbial community dynamics associated with the in-situ biodegradation of these organochlorine chemicals. We hypothesised that soil organic matter, a key factor affecting microbial biomass and diversity, affects the biodegradation and total loss of the pollutants 30 years after use. We sampled 12 contaminated paddocks with residue concentrations monitoring data since 1988 that represent two different agricultural surface-soils. The total loss and current concentrations of the residues was correlated with soil physicochemical properties, microbial biomass carbon, microbial community diversity indices and microbial community abundance. Current dieldrin and DDT residue concentrations were positively correlated with soil organic matter and clay contents. However, key indicators for loss of residues after 23–30 years were low carbon-to‑nitrogen ratios, high microbial-C-to-total-C ratios and high fungal community evenness. The results support the composition of soil organic matter as an important factor affecting degradation of organochlorines and that co-metabolism of dieldrin and DDT could be enhanced by manipulating the composition of soil organic matter to cater for a broad diversity of microbial function.

Funding

Historical data of dieldrin and DDT concentrations were kindly provided by The National Organochlorine Residue Management Program (NORM). Furthermore, thanks to Dr. Grant Rawlin for his help and discussions. Thanks to Dr. Clayton Butterly for helpwith soil chemical analysis, Dr. Gary Clark for help with soil texture analysis, Dr. Corinne Celestina and Dr. Jennifer Wood for their advice on microbial analysis. ProfessorMichael Stear and Dr. Xia Lee (Statistics Consultancy Platform La Trobe University, Melbourne, Victoria) provided guidance with statistical methods. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. CK received an Australian Government Research Training Program Scholarship.

History

Publication Date

15/11/2019

Journal

Science of the Total Environment

Volume

691

Pagination

11p. (p. 135-145)

Publisher

Elsevier

ISSN

0048-9697

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