Investigation of various physicochemical and environmental parameter influence on pesticide sorption to ditch bed substratum by means of experimental design

Diffuse pollution by pesticide applied in rural catchments may contribute to alter water quality. Besides actions relative to the way the substances are introduced into the environment, it is also possible to limit the contamination by interfering on their transfer pathways from fields to the main river network. Especially, interface areas such as buffer strips or small ditches may play a major part in pesticide diffuse pollution decrease. In ditches a great variety of materials may act as sorbents for organic contaminants: grass, leaves, wood debris or sediments. In this study, laboratory experiments were designed to determine sorption characteristics for three herbicides with different physicochemical properties on sediment and leaves in decay commonly found in agricultural ditches. Sorption capacities were assessed for the herbicides isoproturon, diuron and diflufenican.

Experimental design was carried out to investigate the effects of five parameters on herbicide sorption on sediment and dead leaves. These parameters have been chosen according to parallel field experiment needs. Thus, the influence of initial sorbent moisture, herbicide form, i.e. active substance or commercial formulation, water quality (tap or natural ditch water), bromide ions (used as conservative tracers) and solid/liquid ratio have been tested. Within the parameters investigated, pesticide formulation and solid/liquid ratio were the most important parameters affecting pesticide sorption on both ditch materials.     

Variations of periphytic diatom sensitivity to the herbicide diuron and relation to species distribution in a contamination gradient: implications for biomonitoring

Diatoms are commonly used as bioindicators of trophic and saprobic pollution in rivers. However, more knowledge is needed concerning their sensitivity to toxicants such as agricultural herbicides. In this study, seven species of periphytic diatoms were isolated from the Morcille River (Beaujolais area, France) which presents a streamward contamination gradient by pesticides and particularly diuron. The sensitivity of these species to diuron was assessed through ecotoxicological tests based on short-term growth inhibition of monospecific cultures. After application of an appropriate toxicological model, EC50 were determined and the species were ranked according to their tolerance. EC50 values ranged from 4.5 to 19 μg L(-1). Finally, the results were related to field periphyton samples from an upstream and a downstream site in order to check if variations in specific relative abundance between sites are consistent with differences in tolerance to diuron. Species distribution between sites was only partially in accordance with toxicological results suggesting that other factors (toxic or trophic) have an important influence on diatom communities in the river. Nevertheless, diatoms showed their potential to indicate water contamination by pesticides and toxic indices could be developed in complement to existing trophic indices.     

The combination of chemical,structural, and functional indicators to evaluate the anthropogenic impacts on agricultural stream ecosystems

Environmental Science and Pollution Research - Freshwater contamination by pesticides in agricultural landscapes is of increasing concern worldwide, with strong pesticide impacts on biodiversity,...     

Assessing pesticide concentrations and fluxes in the stream of a small vineyard catchment - Effect of sampling frequency

This study reports on the occurrence and behaviour of six pesticides and one metabolite in a small stream draining a vineyard catchment. Base flow and flood events were monitored in order to assess the variability of pesticide concentrations according to the season and to evaluate the role of sampling frequency on the evaluation of fluxes estimates. Results showed that dissolved pesticide concentrations displayed a strong temporal and spatial variability. A large mobilisation of pesticides was observed during floods, with total dissolved pesticide fluxes per event ranging from 5.7 × 10⁻³ g/Ha to 0.34 g/Ha. These results highlight the major role of floods in the transport of pesticides in this small stream which contributed to more than 89% of the total load of diuron during August 2007. The evaluation of pesticide loads using different sampling strategies and method calculation, showed that grab sampling largely underestimated pesticide concentrations and fluxes transiting through the stream.     

Dynamics and mitigation of six pesticides in a “Wet” forest buffer zone

Pesticide pollution is one of the main current threats on water quality. This paper presents the potential and functioning principles of a “Wet” forest buffer zone for reducing concentrations and loads of glyphosate, isoproturon, metazachlor, azoxystrobin, epoxiconazole, and cyproconazole. A tracer injection experiment was conducted in the field in a forest buffer zone at Bray (France). A fine time-scale sampling enabled to illustrate that interactions between pesticides and forest buffer substrates (soil and organic-rich litter layer), had a retarding effect on molecule transfer. Low concentrations were observed for all pesticides at the forest buffer outlet thus demonstrating the efficiency of “Wet” forest buffer zone for pesticide dissipation. Pesticide masses injected in the forest buffer inlet directly determined concentration peaks observed at the outlet. Rapid and partially reversible adsorption was likely the major process affecting pesticide transfer for short retention times (a few hours to a few days). Remobilization of metazachlor, isoproturon, desmethylisoproturon, and AMPA was observed when non-contaminated water flows passed through the forest buffer. Our data suggest that pesticide sorption properties alone could not explain the complex reaction mechanisms that affected pesticide transfer in the forest buffer. Nevertheless, the thick layer of organic matter litter on the top of the forest soil was a key parameter, which enhanced partially reversible sorption of pesticide, thus retarded their transfer, decreased concentration peaks, and likely increased degradation of the pesticides. Consequently, to limit pesticide pollution transported by surface water, the use of already existing forest areas as buffer zones should be equally considered as the most commonly implemented grass buffer strips.     

Cholinesterase activities as potential biomarkers: characterization in two freshwater snails, Potamopyrgus antipodarum (Mollusca, Hydrobiidae, Smith 1889) and Valvata piscinalis (Mollusca, Valvatidae, Müller 1774)

Anti-cholinesterase insecticides constitute a major portion of modern synthetic pesticides and the assessment of cholinesterase (ChE) inhibition is widely used as a specific biomarker for evaluating the exposure of non-target organisms to these pollutants. However, most studies on this biomarker were developed on vertebrates and among invertebrates, gastropod mollusks are rarely used. Gastropods are important members of aquatic habitats and therefore present a high ecological relevance for freshwater ecosystems. In this context, ChE activities were characterized in two freshwater gastropod mollusks, Potamopyrgus antipodarum and Valvata piscinalis, in order to ascertain their value as sentinel species. Firstly, characterization of ChE activities was performed using different substrates (acetylcholine iodide, butyrylcholine iodide and propionylcholine iodide) and specific inhibitors (eserine, iso-OMPA and BW284c51). Secondly, in vivo effect of a widely used organophosphate insecticide, chlorpyrifos, was tested on ChE activity in both species. Results suggested that P. antipodarum possesses two isoforms of cholinesterases, one isoform which properties are intermediate between an acetyl and a propionyl ChE, and one minor isoform which correspond to a butyryl ChE, while V. piscinalis seems to possess only one isoform which displays typical properties of an acetyl ChE. Chlorpyrifos induced no effect on V. piscinalis ChE. In contrast, P. antipodarum activity was significantly decreased by environmental realistic chlorpyrifos concentrations (2.86 and 14.2 nM) after seven days of contact. The present study suggests that P. antipodarum may be employed as a biological indicator for assessing pesticide contamination.