Edouard His

The Assessment of Marine Pollution - Bioassays with Bivalve Embryos and Larvae

Tens of thousands of synthetic substances are in existence today and hundreds of new compounds are being introduced every year. Because of the complexity of the physico-chemical interactions between pollutants and the marine environment, the potential toxicity of contaminants can be assessed adequately only by means of bioassays with living organisms. From a practical point of view, a bioassay needs to be sensitive and scientifically valid, yield rapid results at moderate cost, and the organism in question must be readily available. Ecotoxicological bioassays with bivalve embryos and larvae fulfil these criteria better than most other tests. They have increasingly come into use during the past three decades and are now commonly employed to ascertain the biological effects of pure chemicals, as well as to determine the quality of effluents, coastal waters and sediments sampled in the field. There do not appear to be very great differences between bivalve species with regard to larval sensitivity to toxicants. The principal species for bioassays are oysters (Crassostrea gigas and C. virginica), and mussels (Mytilus edulis and M. galloprovincialis). Bioassays are conducted with gametes and larvae of ail ages: sperm and unfertilized eggs, embryos, young D-larvae, intermediate umboned larvae, and pediveligers towards the end ofthe pelagic period. Embryos are usually the most sensitive stage. Recent advances now also permit bioassays on metamorphosing pediveligers, a method particularly suited to investigate the effects of adsorbate-contaminated surfaces. There are various criteria for the assessment oftoxic effects, including embryogenesis success (abnormalities), larval growth, mortality, physiology (e.g. feeding or swimming activity), and metamorphosis success. Chronic toxicity studies may be carried out over periods ofseveral weeks, but larval rearing in the laboratory requires considerable effort (e.g. cultivation of algal food). The method of choice for investigations of acute toxicity and for routine monitoring studies is the embryo bioassay because it is very sensitive, relatively simple, and produces results within 24 or 48 hours. The data obtained by different investigators are often difficult to compare, however, because of differences in methodology. There is no firmly established procedure, and further simplification and standardization of techniques is required. In bioassays with a single pollutant, the effective toxic concentration may span several orders of magnitude, depending on bioassay procedures, larval stage and choice of response. Tributyl-tin (TBT) is the most toxic compound ever bioassayed with bivalve larvae, with effective concentrations (EC50) as low as a few nanograms per litre (i.e. 10−3 ppb). Heavy metals (particularly mercury, silver and copper) are next in order of toxicity, with EC50 values between a few micrograms per litre (ppb) and several hundred ppb. Chlorine and some organochlorine pesticides may also have EC50 values of less than 100 ppb, while detergents and petroleum products are generally less toxic

A simplification the bivalve embryogenesis and larval development bioassay method for water quality assessment

A simplification of the standard bivalve embryo-larval bioassay method for seawater quality assessment is described. Methodological features aimed to increase reliability, sensitivity and accuracy, and to reduce time and costs, include: induced natural spawning to guarantee gamete quality, earlier exposure to the test solutions and direct observation without subsampling. In the first example of application, embryos of oysters (Crassostrea gigas) and mussels (Mytilus galloprovincialis) were used to compare the adequacy of artificial and natural seawater for the incubation of bivalve larvae. An average of 91–93% of the embryos developed normally in all cases, and there were no significant differences between species or between the two waters tested, concluding that both species and both types of water are equally suitable for ecotoxicological monitoring purposes. In the second example the C. gigas embryo-larval bioassay was used for the assessment of the water quality in 15 tributaries of an oyster farming area: the Bay of Arcachon. Methods can be applied to freshwater ecotoxicological studies.

A comparison between oyster (Crassostrea gigas) and sea urchin (Paracentrotus lividus) larval bioassays for toxicological studies

Abstract The respective sensitivity of oyster ( Crassostrea gigas ) and sea urchin ( Paracentrotus lividus ) embryos and larvae to salinity, and to various micropollutants (four heavy metals, three pesticides) and to two polluted sediments were compared with a simplified bioassay method. C. gigas embryos and larvae were more sensitive to copper; the sensitivity of both species to tributyltin (TBT) was practically the same; P. lividus was more sensitive to lead and mercury. The only pesticide found to be toxic was a herbicide, Dinoterbe, to which oyster larvae were more sensitive than sea urchin plutei. Of the two sediments tested, the first one had effects on P . lividus embryogenesis only; C. gigas embryos and larvae were more affected by the second sediment which was originated from a harbour and was polluted by heavy-metals. The choice of species for biomonitoring may be based on biological considerations, such as the availability of mature adults for obtaining gametes, or on the salinity of the studied area; the oyster bioassay seems to be more suitable for coastal and estuarine brackish waters, because of the broader salinity tolerance of estuarine bivalve larvae as compared to sea urchin larvae.

Effects of dissolved mercury on embryogenesis, survival, growth and metamorphosis of Crassostrea gigas oyster larvae

The effects of mercury (Hg) concentrations ranging from 0 (control) to 1024 µg 1-1 upon embryogenesis, survival, growth and metamorphosis of Crassostrea gigas (Thunberg) oyster larvae were investigated. Embryogenesis was abnormal in 50 % of the individuals at 11 µg 1-1 . The 48 h LD50 for D·shaped, umbonate and pediveliger larvae were 33, 115 and 200 µg 1-1 respectively. The increase in LD50 was partially explained by the larval weight increase, although weight-specific tolerance to Hg was higher in smaller larvae. Growth, the most sensitive physiological process studied, was significantly retarded at 4 µg 1-1. The metamorphosis rate was significantly reduced when competent pediveligers were exposed to 64 µg 1-1 for 48 h prior to the addition of the metamorphosis inducer epinephrine. The implications of the present results for monitoring pollution by utilising different bivalve larval stages are discussed.

Assessment of the bioavailability and toxicity of sediment-associated polycyclic aromatic hydrocarbons and heavy metals applied to Crassostrea gigas embryos and larvae

Sediments represent a vast sink for contaminants in aquatic systems, and may pose a threat to pelagic and benthic organisms. The objective of this research was to determine the bioavailability and toxicity of sediment-associated PAHs and heavy metals, using embryos and larvae of the oyster Crassostrea gigas, exposed to two sediment fractions: the whole sediment and the elutriate. The percentages of abnormal larvae, the contaminant accumulation and, (in the case of metal contamination), the induction of metallothionein in the larvae, were investigated. Sediment-associated PAHs and heavy metals were available for exposure, as indicated by their accumulation in C. gigas larvae and by the abnormalities induced during larval development. The critical body burden of PAHs (Fluo, Pyr, BaA, Triph, Chrys, BbF, BkF, BjK, BeP, BaP, Per, IP, BPer and the DahA) in the larvae was 0.3 micro g g(-1), above which abnormalities were observed. This value corresponds to concentrations observed for most vertebrate and invertebrate species. The bioavailability of PAHs is determined by their solubility; only the soluble fraction of PAHs is accumulated by the embryos. The bioavailability of metals for the larvae is substantiated by MT induction, correlated with cytosolic metal concentrations. MT induction provided a better early-warning response than the embryotoxicity test currently used for evaluating environmental contamination by metals. This study recommends choosing oyster embryos as a particularly sensitive tool for evaluating sediment quality.

The Effects of Elutriates from PAH and Heavy Metal Polluted Sediments on Crassostrea gigas (Thunberg) Embryogenesis, Larval Growth and Bio-accumulation by the Larvae of Pollutants from Sedimentary Origin

The release, bio-availability and toxicity of contaminants, when sediments are resuspended have been examined, studying concurrently their effects on the embryogenesis and on the larval growth of the Crassostrea gigas larvae and their bio-accumulation in those organisms. Three characteristic sediments have been selected (one contaminated by PAHs, a second by heavy metals and the last by the both pollutants). The organisms were directly exposed to elutriates obtained from each sediment or fed on algae (Isochrysis galbana) contaminated with the same elutriates. The elutriates used in this study show contamination levels similar to those observed in some polluted coastal and estuary environments. The larval growth test has appeared to be more sensitive that the embryotoxicity test. The biological effects and the contaminant bio-accumulation were more pronounced when larvae were directly exposed to different elutriates. In the case of PAHs, the contamination of algae was sufficient to lead to effect on the larval growth of the Crassostrea gigas. In all cases, a fraction of contaminants adsorbed on suspended particles was bio-available and accumulated by the larvae. This study has shown that resuspending polluted sediments constitutes a threat to pelagic organisms and than the C. gigas larval growth may be proposed as a test to protect the most sensitive areas.

Shell growth and gross biochemical composition of oyster larvae (Crassostrea gigas) in the field

Abstract In summer 1985, Crassostrea gigas (Thunberg) larvae were isolated from the plankton of the Bay of Arcachon. Larvae of the same cohort were collected at densities varying from 3×10 6 m −3 (D larvae) to 2×10 3 m −3 (pediveligers). Shell growth rate, total dry weight and gross biochemical composition of larvae from the field were studied. Shell growth rate showed a slow decrease towards the end of the pelagic life, and conversely total dry weight increased more rapidly. Carbohydrate levels were low (0.7–1.7% of total organic matter) and remained practically unchanged throughout the pelagic life. Protein levels increased during the larval stages (61.6–81% of total organic matter) and seemed to be the most important reserves for metamorphosis. Both larval growth and biochemical composition of larvae indicated good environmental conditions for larval development in the Bay of Arcachon during July 1985. It is suggested that studies on growth and biochemical composition of Crassostrea gigas larvae from the field could be used to detect any degradation of the environment.

Mytilus galloprovincialis as bioindicator in embryotoxicity testing to evaluate sediment quality in the lagoon of Venice (Italy)

The possibility of using Mytilus galloprovincialis from natural populations of the lagoon of Venice in toxicity bioassays based on embryo development, according to international standard methods, was investigated. In order to valuate this method for the lagoon, iterative steps including evaluation of reproducibility, sensitivity and discriminatory capacity towards some pure substances and environmental samples were performed. Evaluation of sensitivity towards a reference toxicant (copper) evidenced good replicability and repeatability. Results showed that natural population is better than hatchery population for performing bioassays. Evaluation of applicability to elutriates revealed that the method is able to discriminate among sediments of the lagoon of Venice at different typologies and levels of contamination, showing an important effect for almost all study sites.

Sublethal and lethal toxicity of aluminum industry effluents to early developmental stages of the Crassostrea gigas oyster

The toxicity of the effluent from an aluminum plant on Crassostrea gigas oyster embryogenesis (lethal effects) and larval growth (sublethal effects) was tested. Liquid and solid phases of the effluent were separately tested, and effects of mixing during exposure were also evaluated. The effluent was highly toxic, causing abnormal embryogenesis at 0.03 to 1 g 1−1 and reduced growth at 0.01 to 0.3 g/l. The solid fraction was markedly more toxic than the liquid fraction. Mixing during exposure consistently increased both lethal and sublethal toxicity. Considering the trace metal content of the effluent, Hg is suspected to be primarily responsible for the toxicity, although synergistic effects of Al, Fe, and Cr cannot be discarded. Experimental evidence shows that bioavailable metal species were present not only in the liquid phase as soluble ions, but most importantly, bound to sediment particles. Based on the present data, uncontrolled disposal of aluminum plant effluent may be a major hazard to the environment, involving early life stages and recruitment in marine biota.

The non-toxic effects of a novel antifouling material on oyster culture

The production traits (size, weight, mortality and condition) of Crassostrea gigas oysters were examined when cultured in cages coated with a novel antifouling material consisting of a polymer film based on a hydrogel which had been loaded with the active material (benzalkonium chloride—BCl), a mixture of alkyldimethylbenzylammonium chlorides. Production traits of adult oysters and growth rate of larvae obtained from BCl-exposed adults were equal to the controls. Toxicity of BCl, as assessed by the oyster embryo bioassay, was two orders of magnitude lower than TBT and one order of magnitude lower than copper, the active compounds presently used in antifouling paints.