Effect of carbaryl (carbamate insecticide) on acetylcholinesterase activity of two strains of Daphnia magna (Crustacea, Cladocera).

The present study was designed to investigate the effect of carbaryl (carbamate insecticide) on the acetylcholinesterase activity in two strains (same clone A) of the crustacean cladoceran Daphnia magna. Four carbaryl concentrations (0.4, 0.9, 1.8 and 3.7 µg L(-1)) were compared against control AChE activity. Our results showed that after 48 h of carbaryl exposure, all treatments induced a significant decrease of AChE activities whatever the two considered strains. However, different responses were registered in terms of lowest observed effect concentrations (LOEC: 0.4 µg L(-1) for strain 1 and 0.9 µg L(-1) for strains 2) revealing differences in sensitivity among the two tested strains of D. magna. These results suggest that after carbaryl exposure, the AChE activity responses can be also used as a biomarker of susceptibility. Moreover, our results show that strain1 is less sensitive than strain 2 in terms of IC50-48 h of AChE activity. Comparing the EC50-48 h of standard ecotoxicity test and IC50-48 h of AChE inhibition, there is the same order of sensitivity with both strains.

The sediment-contact test using the ostracod Heterocypris incongruens: Effect of fine sediments and determination of toxicity thresholds.

The toxicity test using freshwater ostracods of the species Heterocypris incongruens is a sub-chronic static test that exposes individuals to whole sediments over a period of 6 d, the endpoints being mortality and growth. We tested the hypothesis that endpoints of the sediment bioassay using Heterocypris incongruens are affected by the presence of fine sediment particles by testing control sediment supplied with the commercial test kit with increasing proportions of kaolin clay as a proxy for fines. While mortality was not affected, the results showed that increasing the presence of clay reduced ostracod growth. Based on the variability in growth, a sublethal toxicity threshold of 35% is proposed to distinguish effects due to sediment properties from those due to toxicity. The relevance of this threshold was verified using data from toxicity tests of ambient sediment samples with low levels of contamination.

Acute and chronic ecotoxicity of carbaryl with a battery of aquatic bioassays.

The ecotoxic effects of carbaryl (carbamate insecticide) were investigated with a battery of four aquatic bioassays. The nominal effective concentrations immobilizing 50% of Daphnia magna (EC50) after 24 and 48 h were 12.76 and 7.47 µg L(-1), respectively. After 21 days of exposure of D. magna, LOECs (lowest observed effect concentrations) for cumulative molts and the number of neonates per surviving adult were observed at carbaryl concentration of 0.4 µg L(-1). An increase of embryo deformities (curved or unextended shell spines) was observed at 1.8 and 3.7 µg L(-1), revealing that carbaryl could act as an endocrine disruptor in D. magna. Other bioassays of the tested battery were less sensitive: the IC50-72h and IC10-72h of the algae Pseudokirchneriella subcapitata were 5.96 and 2.87 mg L(-1), respectively. The LC50-6d of the ostracod Heterocypris incongruens was 4.84 mg L(-1). A growth inhibition of H. incongruens was registered after carbaryl exposure and the IC20-6d was 1.29 mg L(-1). Our results suggest that the daphnid test sensitivity was better than other used tests. Moreover, carbaryl has harmful and toxic effects on tested species because it acts at low concentrations on diverse life history traits of species and induce embryo deformities in crustaceans.

Sensitivity of different aquatic bioassays in the assessment of a new natural formicide.

Agrochemicals have the potential to cause deleterious effects on living organisms and therefore they must be subjected to various (eco)toxicological studies and monitoring programs in order to protect human health and the environment. The aim of this study was to assess the ecotoxicity of a new natural formicide with a battery of three classical and three ecotox-kit tests. The former tests were performed with Aliivibrio fischeri bacteria (Lumistox test), the cladoceran Daphnia magna and Pseudokirchneriella subcapitata algae, and the latter with Thamnotoxkit F(TM) (Thamnocephalus platyurus), Ostracodtoxkit F® (Heterocypris incongruens) and LuminoTox (photosynthetic enzyme complexes). In the range of formicide concentrations tested (from 0.06 to 2.0 g L(-1)), the measurement endpoint values varied from 0.79 g L(-1) for the algal test to > 2 g L(-1) for the LuminoTox and Ostracodtoxkit F® tests. Hierarchical sensitivity ranking based on the no-observed effect concentration (NOEC) values established to assess the formicide ecotoxicity was as follows: algal growth inhibition test ≈ daphnid immobilization test ≈ bacterial luminescence inhibition test > Thamnotoxkit F™ > LuminoTox > Ostracodtoxkit F®. Overall, results from the battery of bioassays showed that this formicide preparation presents low ecotoxicity as compared to the aquatic ecotoxicity of presently commercialized formicides. In conclusion, classical aquatic bioassays are more sensitive than ecotox-kit tests in the assessment and monitoring of the new natural formicide.

Assessment of the LuminoTox leachate phase assay as a complement to the LuminoTox solid phase assay: effect of fine particles in natural sediments.

The LuminoTox solid phase assay (Lum-SPA), developed to assess the potential ecotoxicity of natural polluted sediments, employs stabilized thylakoids isolated from spinach plant extracts. When thylakoids are exposed to polluted samples, the action of pollutants can interfere with transmission of chlorophyll fluorescence linked to Photosystems I and II, causing a decrease in fluorescence emission. To differentiate between bulk and leachate effects, we developed a complementary assay of the Lum-SPA named the LuminoTox leachate phase assay (Lum-LPA). Twelve natural sediments were selected on the basis of their potential ecotoxicity and different quantities of fines. Results showed that in the Lum-LPA, the IC50s were always lower than those observed in the Lum-SPA. Significant inverse correlations were found between the IC50s obtained with the Lum-SPA and the percentage of fines (silt+clay fraction). In order to identify the cause of the higher ecotoxicity found in the Lum-LPA, we tested the supernatant of the liquid phase recovered after centrifugation (3000 g), and it appeared far less toxic than the Lum-LPA filtrates. To confirm the hypothesis that sensitivity in the Lum-LPA could be due to the presence of very fine particles, Photosynthetic Enzyme Complexes (PECs) were exposed to two kinds of clay materials with and without copper (0.6 mg L(-1)). Similar results were obtained in the Lum-LPA for both cases, revealing the sensitivity of this test to very fine particles.

New methodological improvements in the Microtox® solid phase assay.

The classic Microtox® solid phase assay (MSPA) based on the inhibition of light production of the marine bacteria recently renamed Aliivibrio fischeri suffers from various bias and interferences, mainly due to physico-chemical characteristics of the tested solid phase. To precisely assess ecotoxicity of sediments, we have developed an alternative method, named Microtox® leachate phase assay (MLPA), in order to measure the action of dissolved pollutants in the aqueous phase. Two hypotheses were formulated to explain the observed difference between MSPA and MLPA results: a real ecotoxicity of the solid phase or the fixation of bacteria to fine particles and/or organic matter. To estimate the latter, flow cytometry analyses were performed with two fluorochromes (known for their ability to stain bacterial DNA), allowing correction of MSPA measurements and generation of new (corrected) IC50. Comparison of results of MLPA with the new IC50 MSPA allows differentiating real ecotoxic and fixation effect in classic MSPA especially for samples with high amount of fines and/or organic matter.