Biodegradation of pesticides and soil health: It is all about the concentration [25.09.20]
Pesticide treatments are still the method of choice for the control of crop pathogens although their ecotoxicological effect is still not sufficiently elucidated. After application, a considerable part of the pesticides gets into the topsoil, which has important filter and cleaning functions and thus provides essential ecosystem services, e.g. groundwater and water protection. Pesticides can lead to the accumulation of pesticide residues and metabolites in the upper soil layers and impair soil functions and health. Silva et al. (2019) found that only 17% of the 317 agricultural topsoils tested in the European Union (EU) contained no pesticides, while 25% of the soils contained specific pesticide residues, and 58% displayed even mixtures of several pesticides. There is increasing evidence that numerous organic pollutants remain in the soil, although they are completely biodegradable under laboratory conditions. The microbial degradation of higher concentrations of pesticides already is well characterized. A recent study by Hohenheim scientists and their colleagues from the University of Tübingen, instead focuses on the degradation mechanisms at low pesticide concentrations. Their following hypotheses have been tested: (1) Biodegradation of pesticides is limited once their concentration falls below the threshold that triggers the expression of relevant genes (i.e. enzymes involved in signalling and degradation). (2) There are two different concentration thresholds: one for triggering the activity and growth of pesticide-degrading microorganisms, the other for initiating the gene expression of catabolic enzymes. (3) The change in growth and activity of pesticide-degrading microorganisms correlates directly with altered metabolic turnover of pesticides.
Picture Source & Credit: Pixabay
Original Article
Affiliation:
- Department of Soil Biology, Institute of Soil Science and Land Evaluation, University of Hohenheim, Stuttgart, Germany
- Department of Soil Physics, Institute of Soil Science and Land Evaluation, University of Hohenheim, Stuttgart, Germany
- Department of Environmental Analytical Chemistry, Institute of Applied Geoscience, University of Tübingen, Tübingen, Germany
Abstract
The objective of our study was to test whether limited microbial degradation at low pesticide concentrations could explain the discrepancy between overall degradability demonstrated in laboratory tests and their actual persistence in the environment. Studies on pesticide degradation are often performed using unrealistically high application rates seldom found in natural environments. Nevertheless, biodegradation rates determined for higher pesticide doses cannot necessarily be extrapolated to lower concentrations. In this context, we wanted to (i) compare the kinetics of pesticide degradation at different concentrations in arable land and (ii) clarify whether there is a concentration threshold below which the expression of the functional genes involved in the degradation pathway is inhibited without further pesticide degradation taking place.
More informationen on the Hohenheim Departments involved:
 | Prof. Dr. Ellen Kandeler |
 | Prof. Dr. Thilo Streck |
 | Dr. sc. agr. Holger Pagel |
