Potential uses of sea urchin embryos for identifying toxic chemicals: description of a bioassay incorporating cytologic, cytogenetic and embryologic endpoints.

Abstract

A method for evaluating pollutant genotoxicity, embryotoxicity and teratogenicity using sea urchin embryos has been developed and was tested using benzo(a)pyrene (BP). Initial results suggested that the bioassay may be a sensitive indicator of pollutant toxicity and mutagenicity since several endpoints can be simultaneously assessed. The bioassay is rapid, inexpensive and appears applicable to a variety of toxicants and delivery methods. The test is based upon the standard 48 h sea urchin development assay and incorporates cytologic-cytogenetic analysis of embryos. Following toxic exposure of gametes, fertilization success is assessed. Embryos then develop for 48 h at which time survival and teratogenesis are evaluated. A subsample of embryos is stained and dissociated into monolayers and mitotic configurations are examined using light microscopy. Embryo mitotic rates are used as an indicator of overall embryonic health. Cytotoxic effects are concomitantly evaluated. Genotoxicity is measured using two methods: (1) anaphase aberration analysis, a technique which assesses abnormalities in the chromosome configurations (such as bridges and fragments) as the groups of chromosomes move to opposite poles and (2) micronucleus formation, a procedure examining the incidence of smaller, secondary nuclei composed of whole chromosomes or chromatid fragments. These two measurements preclude the need to examine individual chromosomes for deletions and exchanges, a laborious process in most aquatic organisms which possess numerous relatively small chromosomes. This genotoxicity-teratogenicity test appears promising for laboratory evaluations of individual substances or of complex chemical mixtures as well as for environmental monitoring of nearshore areas. The standard development assay has been used to screen pharmaceuticals and environmental contaminants and some recent investigations have included mitotic aberration analysis. Experiments in our laboratory suggest that the genotoxicity-teratogenicity test may be a feasible approach to field monitoring. Mutagen loads of spawning adult urchins could be assessed by conducting cytologic-cytogenetic analysis of resulting embryos although initial studies suggest that this method is less sensitive than direct embryo exposures.