Freshwater sediment pesticide biodegradation potential as an ecological indicator of microbial recovery following a decrease in chronic pesticide exposure: A case study with the herbicide diuron

Abstract

The aim of this study was to evaluate the use of freshwater sediment biodegradation potential as an ecological indicator for monitoring microbial recovery following a decrease in chronic pesticide exposure. For this purpose, a four-year case study (2008)(2009)(2010)(2011) was conducted in a small stream (Morcille river) long exposed to high diuron concentrations, increasing from upstream to downstream. Our results show that the ban on diuron in December 2008 resulted in a progressive decrease in its concentrations in the Morcille river over the survey period. However, diuron remained present in the water three years after the ban. The spatio-temporal variations in the sediment biodegradation potential were assessed by radiorespirometry using [ring-U-14C] diuron to estimate diuron mineralization potentials. Between autumn 2008 and autumn 2011, mean diuron mineralization percentage after 15 weeks of incubation decreased by 65% downstream and by 82% in the intermediate sector, and mean 10% diuron dissipation time values increased between 143% (downstream) and 210% (intermediate). Thus the decrease in the level of chronic diuron exposure in the river also caused a fall in sediment diuron-mineralizing capacities, revealing a corresponding recovery of microbial communities. Our results show that the use of freshwater sediment biodegradation potential may be useful for assessing microbial recovery after a decrease in chronic exposure to pollutants, opening prospects for developing a new class of ecological indicator to monitor the recovery of biological quality of water resources. In this way, the use of molecular approaches based on direct extraction of nucleic acids from environmental matrices and their subsequent analysis by PCR-based approaches to quantify the abundance of pesticide-degrading communities could represent a promising alternative. Highlights► We performed a 4-year survey in a river long exposed to diuron. ► The ban on diuron resulted in a gradual fall in its concentrations in the river. ► Sediment diuron biodegradation potential decreased throughout the survey. ► Degradation capacities can be an ecological indicator to gauge microbial recovery.

Pollution‐induced community tolerance (PICT): towards an ecologically relevant risk assessment of chemicals in aquatic systems

“…Based on the relationship between community tolerance and the intensity of exposure, applying PICT towards one specific compound can determine whether this compound still modulates the measured tolerance. A recent case field survey, based on the study of pesticide biodegradation potential in river sediments, showed that adaptation capacities of microbial communities can be used as an ecological indicator of microbial recovery following a decrease in chronic pesticide exposure (Pesce et al, 2013).…”

Assessing Glyphosate and Fluridone Concentrations in Water Column and Sediment Leachate

“…A study showed that 12 out of 15 urban creeks in California were toxic, and sediment pyrethroid pesticide (a replacement for organophosphates for many urban applications) concentrations were sufficient to cause toxicity in amphipod, Hyalella azteca (Amweg et al, 2006). Understanding the pesticide presence and its degradation in sediment environment can provide improved information with regards to the ecological health of a waterbody (Pesce et al, 2013).…”

Effects of mixtures of dissolved and particulate contaminants on phototrophic biofilms: new insights from a PICT approach combining toxicity tests with passive samplers and model substances

“…Nevertheless, a recent study has shown that the ban on diuron in December 2008 has resulted in a progressive decrease in its concentrations in the Morcille River. Thus annual median concentrations recorded at the contaminated station (based on biweekly samples) fell more than fivefold between 2008 (about 110 ng/L) and 2011 (about 20 ng/L), while more than 92 % of water samples collected at the reference station exhibited concentrations below the quantification level of 10 ng/L (Pesce et al 2013). In the present study, the mean diuron concentrations recorded in reference (about 4 ng/L) and contaminated channels (about 28 ng/L) were consistent with concentrations previously observed in the river.…”

“…This small shallow river, which has been extensively studied over the last decade , is characterized by a contamination gradient running upstream (reference site) to downstream (contaminated site). In addition, we used an original PICT approach designed to assess changes in the tolerance of phototrophic communities to metals and pesticides, by combining the use of individual toxicants (diuron and copper, which are among the main herbicides and metals detected in the Morcille river, despite diuron being banned in France since December 2008; Pesce et al 2013), and the use of mixtures of organic pesticides and metals directly extracted from the river using passive samplers (i.e., POCIS and diffusive gradient in thin films (DGT)). Based on PICT assessments, our objective was to compare differences in acquired tolerance to metals and organic pesticides between phototrophic biofilm communities previously exposed to raw or filtered contaminated water.…”