Effect of bentazon on growth and physiological responses of marine diatom: Chaetoceros gracilis.

The herbicide bentazon (CASRN 25057-89-0) is extensively used in agriculture in Brittany (France) to replace atrazine. Bentazon is not readily adsorbed by soil and therefore it enters adjacent freshwater ecosystems, making its way to estuarine and marine waters areas. Information regarding its effects on marine ecosystems is scarce. Phytotoxicity assessments were conducted in the laboratory on the common diatom Chaetoceros gracilis using both the active ingredient and its formulated product (Basamaïs). The 3 day EC(50) using cell counts were, respectively, 150 mg/L and 60 microg/L for bentazon active ingredient and for bentazon-formulated while cellular volume was increased. Although bentazon is known as a photosystem II inhibitor, it produced an increase of pigment (chlorophylls a, c, and carotenoids) content, ATP synthesis, rates of photosynthesis and respiration, and TBARS formation. Therefore, pigments cannot be used as biomarkers of toxicity. Algal cell recovery from bentazon effects occurred after 6-9 days, suggesting a tolerance mechanism.

In-situ microcosms, a tool for assessment of pesticide impacts on oyster spat (Crassostrea gigas).

Effects of the herbicide Basamaïs (bentazon) and the fungicide Opus (epoxiconazole) on oyster spat (Crassostrea gigas) were assessed using in-situ microcosms in a field experiment lasting 13 days. Six-week-old hatchery spat (mean size 1.1 mm), previously collected on PVC plates, was immersed in glass bottles filled with 200 mum filtered seawater. Bottles were maintained underwater at 6 m depth and their water content changed every other day. Growth, measured as shell area index increase, was 126 +/- 4% in the control bottles. While no growth differences were observed between control and individual pesticide treatments at 10 microg l(-1), oysters treated with a mix of 10 microg l(-1) Opus and 10 microg l(-1) Basamaïs showed a 50% growth reduction compared with the control (P < 0.0001), suggesting a synergistic effect of these contaminants. Laboratory controls in microcosms maintained in a water bath with filtered natural light, were not significantly different from in-situ microcosm controls in the field, for organic weight content or growth. This in-situ experiment in microcosms allowed us to conclude that: (1) oyster spat can achieve significant growth in bottles immersed in situ without supplementary food; (2) this microcosm system is reliable and easy to use for environmental toxicity tests with C. gigas spat; (3) such microcosm systems can also be run in a laboratory water bath instead of more technically difficult immersed field experiments; (4) the synergistic effect observed here, at a concentration simulating a peak agricultural runoff event, suggests that the impacts of pesticides could be a real threat for oysters in estuarine areas.

Toxicity assessment of peptaibols and contaminated sediments on Crassostrea gigas embryos.

Peptaibols are known membrane-modifying peptides that were recently detected in marine sediments and mussels collected from a shellfish farming area (Fier d'Ars, Atlantic coast, France). In this investigation, embryotoxicity bioassays with oysters (Crassostrea gigas) were performed to assess acute toxicity of alamethicin and different groups of peptaibols produced by a Trichoderma longibrachiatum strain isolated from marine environment. C. gigas embryos appeared very sensitive to all the metabolites examined with higher toxic effects for long-sequence peptides (EC50 ranging from 10 to 64 nM). D-shaped larvae with mantle abnormality were particularly noticed when peptaibol concentrations increased. Disturbances of embryogenesis were also observed following exposure to organic and aqueous extract of sediments from Fier d'Ars (EC50=42.4 and 6.6 g L(-1) dry weight, respectively). Although peptaibol concentrations measured in these sediments could explain only a part of the toxic effects observed, this study suggests that these mycotoxins can induce larval abnormalities in a population of exposed animals at environmentally realistic concentrations. Their detection in coastal areas devoted to bivalve culture should be taken into account.

Determination of peptaibol trace amounts in marine sediments by liquid chromatography/electrospray ionization-ion trap-mass spectrometry.

Extraction followed by reverse phase liquid chromatography (LC)/electrospray ionization-ion trap-mass spectrometry (ESI-IT-MS) analysis has been successfully developed for the determination of peptaibols, fungal toxic metabolites, in marine sediments. Spiking experiments showed that the mean recovery of target compounds exceeded 85% at a spiking level of 10 ng/g of sediment (wet weight). Detection and quantification limits were 250 and 830 pg/g of sediment, respectively. The method developed constituted the first sensitive assay for quantification of peptaibol trace amounts in a natural environment. A concentration of 5 ng/g in sediment samples collected from Fier d'Ars was found.

Metal bioaccumulation and metallothionein concentrations in larvae of Crassostrea gigas.

Larval stages of bivalve molluscs are highly sensitive to pollutants. Oysters from a hatchery from Normandy (English Channel) were induced to spawn, and fertilized eggs were exposed to copper or cadmium for 24 h. Metal accumulation (from 0.125 to 5 microg Cu L(-1) and from 25 to 200 microg Cd L(-1)) and MT concentrations were measured in larvae. Compared to controls, larvae accumulated copper and cadmium with an increase in MT concentrations particularly with cadmium (i.e. 130.96 ng Cu (mg protein)(-1) and 12.69 microg MT (mg protein)(-1) at 1 microg Cu L(-1) versus 23.19 ng Cu (mg protein)(-1) and 8.92 microg MT (mg protein)(-1) in control larvae; 334.3 ng Cd (mg protein)(-1) and 11.70 microg MT (mg protein)(-1) at 200 microg Cd L(-1) versus 0.87 ng Cd (mg protein)(-1) and 4.60 microg MT (mg protein)(-1) in control larvae). Larvae were also obtained from oysters of a clean area (Arcachon Bay) and a polluted zone (Bidassoa estuary) and exposed to copper in the laboratory, their MT concentration was measured as well as biomarkers of oxidative stress. Biomarker responses and sensitivity to copper for the larvae from Arcachon oysters were higher than for those from Bidassoa.

In vitro test-based comparison of pesticide-induced sensitivity in marine and freshwater phytoplankton.

This study aims to assess the effects of two pesticides, namely the insecticide carbofuran and the herbicide isoproturon, on monospecifically cultivated marine and freshwater phytoplankton according to standard methods. In the presence of pesticide, growth rates were lower in marine species Chaetoceros gracilis and Phaeodactylum tricornutum than in freshwater species Chlorella vulgaris and Selenastrum capricornutum after 72 hours. The EC50 values were obtained with the REGTOX Macro software, and the NEC values by applying the DEBtox model.

Ecotoxicity of ethylene glycol monomethyl ether and its acetate.

Ethylene glycol monomethyl ether (EGME) and ethylene glycol monomethyl ether acetate (EGMEA) have been tested for their acute and chronic toxicity to various organisms occupying different trophic levels in the aquatic ecosystems. The results obtained in this study and those collected from the literature clearly reveal that EGME does not present short- or long-term ecotoxic effects in the ranges of concentrations likely to be found in aquatic environments. Indeed, in general, concentrations of 1000 to 10,000 mg/L of EGME are necessary before significant adverse effects can be observed in aquatic species. Conversely, acute toxicity occurs in fish at about 50 mg/L of EGMEA, and reproduction of Ceriodaphnia dubia is affected by 0.06 mg/L of this chemical. A teratogenic effect-with a specific malformation of the eyes-occurs in Xenopus laevis in the presence of 75 mg/L of EGMEA. This study was partially supported by the French Ministry of the Environment as part of the PNETOX program (1998).

Ecotoxicity of ethylene glycol monobutyl ether and its acetate.

Ethylene glycol monobutyl ether (EGBE) and ethylene glycol monobutyl ether acetate (EGBEA) were tested for their acute and chronic toxicity to various organisms occupying different trophic levels in the aquatic ecosystems. The obtained results and those collected from the literature clearly show that EGBE affects the survival, growth, and reproduction of aquatic organisms only at concentrations of approximately 100 mg/L or more. EGBEA appears to be slightly more ecotoxic to aquatic species. At 1000 and 10,000 mg/L, both chemicals strongly affect the early stages of development of the Japanese oyster, but such concentrations are too high to be found in aquatic environments. Micronucleus tests on Xenopus laevis show that EGBE and EGBEA are not genotoxic in the range of concentrations tested. Consequently, neither chemical presents a risk to the aquatic environment. EGBE does affect the gonadosomatic index of adult male zebra fish (Danio rerio); however, these are preliminary results and must be confirmed by additional experiments. This study was partially supported by the French Ministry of the Environment as part of the PNETOX program (1998).