Immunological and cytotoxicological responses of the Asian clam, Corbicula fluminea (M.), experimentally exposed to cadmium.

Bivalve molluscs, as filter-feeding organisms, are known to accumulate metals that can produce deleterious effects on organisms. The phagocytic activity of haemocytes and lysosomal alterations in the digestive gland cells were measured in the freshwater Asian clam exposed to cadmium, in order to assess the possible use of immunocompetence and lysosomal responses as biomarkers of freshwater quality. Clams were exposed in the laboratory to nominal concentrations of 3, 10, 21.4, 46.5 and 100 microg 1(-1) of cadmium and sampled after 7, 15 and 30 days of exposure. The results show a decrease of phagocytic activity after only 7 days of exposure to 10 microg 1(-1) of cadmium. This response was also observed as the exposure time was increased. Lysosomes in the digestive cells increased in size and number after 7 days of exposure as cadmium concentration increased. After 30 days of exposure, a decrease in size and number indicated a change in the response to the metal from concentrations of 46.5 microg 1(-1) of cadmium. A dose and time response both in phagocytic activity of haemocytes and lysosomal structure demonstrated a possible use of these biomarkers in freshwater biomonitoring.

Artificial streams in the assessment of environmental hazard of chemicals.

Artificial streams are dynamic mesocosms, simulating aquatic systems and rivers. They are useful to study ecotoxicity of chemicals and their effects on flora and fauna colonizing the streams or introduced into the channels. These artificial rivers can also be used to study the influence of ecological and hydrodynamic parameters, such as the kind of substrate of river and flow rate. Responses of the bivalve Unio tumidus to substrate type (silt, sand, and pebbles) and water flow rate (high and low) were investigated after 15 and 35 days in the channels, in order to optimize the experimental conditions for ecotoxicity study with methyl methacrylate (MMA). The toxicological effects of different concentrations of MMA on bivalves and on communities of invertebrates and diatoms were determined after several weeks of exposure at a high flow rate. Biomarkers responses measured in the digestive gland and the gills of U. tumidus were the activities of detoxification systems as early indicators of toxicity and lipid peroxidation as a marker of cytotoxicity. Effects of MMA resulted in a decrease in antioxidant activities. Disturbances in bivalves appeared at lower concentrations than in communities. This indicates sensitivity of the biomarkers studied, which are predictive indicators of ecotoxicity.

Validation of biomarkers for impact evaluation of aqueous industrial waste in mesocosms.

The use of exposure biomarkers in measuring the impact of aqueous waste holds promise because such tools have short response times, are flexible in use and may give an indication about the type of pollution. However, their ecological significance has not yet been demonstrated. It is necessary to validate these responses under controlled conditions before using such biomarkers for biomonitoring. The TotalFinaElf company has developed a pilot scheme incorporating such controlled conditions. This pilot is a dynamic open mesocosm (16 channels 40 m in length supplied with river water). The research programme currently carried out in the "Pilot Rivers" aims at validating biochemical parameters (components of phases I and II (de)toxication metabolism and propionylcholinesterase activity), measured in a fresh water bivalve Corbicula fluminea as a biomarker of water quality. The comparison between biomarker responses and community ones (reference) gives information about the precocity and sensitivity of these biomarker responses. Pure substances (trichloroethylene (TCE), cadmium (CD) and anthracenic oil (AO)) have been injected during one month. Biomarker responses are as sensitive as the most sensitive community response in the presence of CD and AO. With TCE, community responses are more sensitive. Precocity of biomarker response is observed only in the presence of CD.

Characterisation of the impact of aqueous industrial waste in mesocosms: biological indicators and pilot streams.

The use of exposure biomarkers in measuring the impact of aqueous waste holds out promise because such tools have short response times, are of flexible use and give an indication of the type of pollution. However, their ecological significance has not yet been demonstrated. During field studies focusing on aqueous industrial waste, the correlations obtained between several biocoenotic indicators and biomarkers measured in a fresh-water bivalve (Corbicula fluminea), demonstrate the need for work to be carried out under controlled conditions. Working in partnership with the Adour Garonne Water Board, the ELF company has developed a pilot scheme incorporating such controlled conditions. This pilot is made up of 16 canals 40 m in length supplied by river water. The pilot scheme, which is currently at the validation stage, makes it possible to reconstitute an aquatic ecosystem which, once established, will be exposed to perfectly controlled pollution conditions. The responses provided by all the indicators--biocoenotic and microbiological indicators, biomarkers--will then be correlated in order to attribute an ecological significance to the biomarkers.

Interest of a multibiomarker approach in the assessment of freshwater ecosystem quality: laboratory and field studies.

The aims of this study were to validate several biochemical parameters as biomarkers of pollution in the freshwater bivalve Corbicula fluminea and to underline the interest of a multibiomarker approach in environmental biomonitoring. The study was divided into a laboratory exposure to 4 doses of trichloroethylene, toluene, cadmium chloride or a coal tar fraction for 5 days and a field exposure for one week in 5 sites surrounding an industrial effluent outlet. Whatever the product was, parameters that exhibited significant responses were mainly parameters related to oxidative stress and components of phase I metabolism. As a result of discriminant analysis, doses were clearly discriminated from the control and from each other. Likewise, products were discriminated from each other, based on results of the whole parameter responses obtained for the first dose. Concerning the field experiment, all biochemical parameters assayed exhibited significant responses for sites located downstream of the effluent outlet, compared to the upstream reference site. Through a discriminant analysis, sites could be distinguished from each other in terms of pollution intensity. In order to characterise pollution at a qualitative level, further laboratory and field studies are needed to obtain typical profiles for the main pollutants present in freshwater ecosystems.

Potential biomarkers of trichloroethylene and toluene exposure in Corbicula fluminea.

Freshwater clams Corbicula fluminea were exposed in aquariums to four doses of trichloroethylene-TCE-(1.56 up to 100 mg/1) or toluene-TOL-(7.5 up to 60 mg/1) for 5 days. At the end of exposure, components of (de)toxification metabolism of phases I and II, parameters related to oxidative stress and propionylcholinesterase activity were assayed. Determination of TCE and TOL concentrations in water revealed an important evaporative loss during the experiment, characteristic of acute and occasional contaminations by such products occurring in the environment. Appropriate statistical methods such as ANOVA, Tukey test and discriminant analysis underlined the relevance of cytochromes P450 and P418, NADH-cytochrome c reductase, catalase, peroxided and peroxidizable lipids and net peroxidation as biomarkers of exposure to these solvents in C. fluminea. This experiment emphasised the importance of a multi-biomarker approach in environmental surveys and will be completed further by mesocosm studies.