Laurence Volatier

Unicellular algae used as biosensors for chemical detection in Mediterranean lagoon and coastal waters.

Lagoons and coastal waters are contaminated by a large number of chemicals discharged directly or carried by rivers and runoff water that drain catchment areas in which agricultural activities take place. The inflow of these exogenous compounds constitutes a genuine risk for the health of ecosystems. It is therefore important to detect their presence in the natural environment before they cause irreversible damage. Here we present a study aimed at developing a tool for rapid detection of pesticides and other chemicals in environments liable to be contaminated, in order to propose an early warning system for decision-makers. The study carried out focuses on two herbicides commonly encountered in the environment, i.e. diuron and glyphosate, as well as several of their photodegradation products (DCPU, DCPMU, AMPA). The results presented contribute toward developing a biosensor based on measuring the metabolic activities of immobilized unicellular marine algae. The sensors operation is based on measuring the esterase localized on the external membrane of the algae cells and chlorophyll fluorescence. The tests carried out show that the signal emitted by the sensor is disturbed by the presence of the two herbicides studied. The system proposed appears useful as a tool for controlling environments requiring monitoring.

Urban pollution of sediments: Impact on the physiology and burrowing activity of tubificid worms and consequences on biogeochemical processes.

In urban areas, infiltration basins are designed to manage stormwater runoff from impervious surfaces and allow the settling of associated pollutants. The sedimentary layer deposited at the surface of these structures is highly organic and multicontaminated (mainly heavy metals and hydrocarbons). Only few aquatic species are able to maintain permanent populations in such an extreme environment, including the oligochaete Limnodrilus hoffmeisteri. Nevertheless, the impact of urban pollutants on these organisms and the resulting influence on infiltration basin functioning remain poorly studied. Thus, the aim of this study was to determine how polluted sediments could impact the survival, the physiology and the bioturbation activity of L. hoffmeisteri and thereby modify biogeochemical processes occurring at the water-sediment interface. To this end, we conducted laboratory incubations of worms, in polluted sediments from infiltration basins or slightly polluted sediments from a stream. Analyses were performed to evaluate physiological state and burrowing activity (X-ray micro-tomography) of worms and their influences on biogeochemical processes (nutrient fluxes, CO2 and CH4 degassing rates) during 30-day long experiments. Our results showed that worms exhibited physiological responses to cope with high pollution levels, including a strong ability to withstand the oxidative stress linked to contamination with heavy metals. We also showed that the presence of urban pollutants significantly increased the burrowing activity of L. hoffmeisteri, demonstrating the sensitivity and the relevance of such a behavioural response as biomarker of sediment toxicity. In addition, we showed that X-ray micro-tomography was an adequate technique for accurate and non-invasive three-dimensional investigations of biogenic structures formed by bioturbators. The presence of worms induced stimulations of nutrient fluxes and organic matter recycling (between +100% and 200% of CO2 degassing rate). Nevertheless, these stimulations were comparable within the three sediments, suggesting a low influence of urban contaminants on bioturbation-driven biogeochemical processes under our experimental conditions.

Ecological Engineering Approaches to Improve Hydraulic Properties of Infiltration Basins Designed for Groundwater Recharge

Infiltration systems are increasingly used in urban areas for groundwater recharge. The reduction of sediment permeability by physical and/or biological processes is a major problem in management of infiltration systems often requiring expensive engineering operations for hydraulic performance maintenance. To reduce these costs and for the sake of sustainable development, we proposed to evaluate the ability of ecological engineering approaches to reduce the biological clogging of infiltration basins. A 36-day field-scale experiment using enclosures was performed to test the influences of abiotic (light reduction by shading) and biotic (introduction of the macrophyte Vallisneria spiralis (L.) or the gastropod Viviparus viviparus (Linnaeus, 1758)) treatments to limit benthic biofilm biomass and to maintain or even increase hydraulic performances. We coupled biological characterization of sediment (algal biomass, bacterial abundance, total organic carbon, total nitrogen, microbial enzymatic activity, photosynthetic activity, and photosystem II efficiency) with hydraulic conductivity measurements to assess the effects of treatments on sediment permeability. The grazer Viviparus viviparus significantly reduced benthic biofilm biomass and enhanced hydraulic conductivity. The other treatments did not produce significant changes in hydraulic conductivity although Vallisneria spiralis affected photosynthetic activity of biofilm. Finally, our results obtained with Viviparus viviparus are promising for the development of ecological engineering solutions to prevent biological fouling in infiltration systems.

Benefits and limits of sediment toxicity tests as an aid to decision-making.

With respect to the management of dredged sediments, a crucial issue is whether the removed materials (watered and/or processed) are disposed of or reused in an environmentally sound manner. In this context, the number of studies dealing with hazard or risk assessment has exponentially increased. This emphasis has resulted in the promotion and application of a very large variety of ecotoxicological tests. As a consequence, there is a clear need to highlight the scope and limitations of these tests for their appropriate selection and interpretation. In this paper we discuss the choice, implementation and interpretation of laboratory tests carried out on aquatic organisms at various levels of biological organization. We examine some experimental tools and methods in order to determine how suitable they are in regard to the objectives for which they are employed. To make this discussion more consistent our paper is based on results from research programmes conducted for governmental organizations and industrial partners. The Laboratoire des Sciences de l’Environnement (LSE) was involved with Cemagref de Lyon in a first methodological programme on risk assessment of scenarios of dredged sediment deposition. Another programme for a chemical company was implemented to assess the benefits of a physico‐chemical treatment applied to contaminated dredged sediments in a scenario of reuse or deposit in gravel pits. Currently, the LSE is working on a programme of risk assessment for road sediments in valorization scenarios. From these programmes, we expose how single‐species tests, as well as more complex bioassays and microcosm tests, can be used in an iterative step of risk assessment. Concerning microcosm tests, we also introduce a more realistic system that has been designed to simulate natural hydraulic conditions of gravel pits to assess the effects of toxicants on gravel pit aquatic biota during the sediment immersion phase and the sediment post‐deposition phase (paper in preparation). The benefits of these ecotoxicological approaches are underlined, but limits are discussed with regard to several criteria: ecological relevance, realism, use for decision‐making, cost and complexity of methods involved.

Assessment of ecological risks linked to the discharge of saline industrial effluent into a river

Discharges of saline effluents into rivers can lead to risks for local aquatic ecosystems. A specific ecological risk assessment methodology has been developed to propose a management tool to organisations responsible for managing rivers and industrial companies producing saline effluents. This methodology involves the detailed description of the spatiotemporal system concerned, the choice of ecological targets to be preserved, and the performance of bioassays adapted to each of the compartments of the river. Following development, it was applied to an industrial effluent in eastern France. For the scenario studied, results obtained suggest a high risk for the organisms of the water column and a low risk for the organisms of the periphyton. This difference can be explained by the structure of the latter which integrate extracellular polymers secreted by the organisms of the biofilm, forming a gel with a porous structure that acts as a barrier to diffusion. The methodology formulated permitted identifying the critical points of the spatiotemporal system studied and then using them as the basis for making well-grounded proposals for management. Lastly, proposals to improve the methodology itself are made, especially concerning the integration of the sediment compartment in the version formulated initially.