The sea urchin test system has been determined in our laboratory to be an extremely informative bioassay for pollutants, occurring as individual or as mixtures of xenobiotics. Harmful agents may be identified and characterized biologically to give an integrated set of data dealing with several key events, such as fertilization, mitotic activity, and embryogenesis. Therefore this bioassay may contribute to the assessment of the environmental impact of pollutants, by focusing on several important toxicological aspects.
This study was carried out on some inorganic pollutants [Cd(II), Cu(II), Zn(II), and Se(IV)] and their mixtures. Sublethal pH changes were taken into account as an additional stressor, capable of influencing the toxicities of tested agents. The experiments were performed on Paracentrotus lividus sperm and embryos, and on Echinus esculentus sperm. The results showed distinct patterns of embryotoxicity for the agents tested, which resulted in developmental defects as relatively high levels (>10−5 kmol/m3) for Cd(II) and Se(IV), whereas the embryotoxic effects of Cu(II) and Zn(II) were exerted at lower concentrations (5 × 10−7 kmol/m3) close to their natural seawater levels. Cytogenetic analysis of exposed embryos failed to reveal any morphological or quantitative changes in mitotic activity, at embryotoxic levels of all tested contaminants. The fertilization success of exposed sperm showed peculiar dose-response changes, as a result of the specific contaminant levels and of the simultaneous presence of other contaminants. Specifically, slight increases in Cd(II) or Cu(II) levels enhanced fertilization success, up to critical levels (10−7 to 10−6 kmol/m3); however, further increases in these metal ion concentrations led to a drop in fertilization success. The simultaneous presence of Zn(II) or Se(IV) dramatically changed the dose-response patterns, depending on the different mixtures and the test species.
The results may represent an example of the need to account for the simultaneous presence of several pollutants, whose combined impacts may be substantially different from those of the individual toxins. Moreover, the results attest to the high sensitivity of the sea urchin bioassay, which responds to very slight increases in microelements or contaminant levels above their natural concentrations.
The gametes and embryos of three sea urchin species were exposed to cadmium chloride at concentrations ranging from 10(-8) M to 10(-3) M. When zygotes were reared in the presence of Cd2+, skeletal differentiation displayed some severe abnormalities or was suppressed, as a function of Cd2+ level. The embryotoxic action of Cd2+ was inversely related to salinity and to Ca2+ concentration. Cadmium-exposed larvae displayed similar abnormalities if Cd2+ was present throughout development or only after hatching, while pre-hatching exposure produced no developmental defects. No aberrations in mitotic figures were observed in cleaving eggs following acute exposure to Cd2+. The pretreatment of sperm or eggs did not affect the ensuing development of embryos, both for acutely toxic Cd2+ levels (up to 10(-2) M), and for prolonged exposures in relatively low Cd2+ levels. The fertilization rate was differently affected depending on whether sperm or eggs were pretreated; i.e., the exposure of eggs to Cd2+ promoted fertilization at relatively high Cd2+ levels. If sperm was exposed to Cd2+, a depression of fertilizing capacity was observed at high Cd2+ levels, while lower Cd2+ levels, displayed an opposite action, resulting in an increase in fertilization rate after prolonged sperm exposure.
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