DNA strand breaks (comet assay) and embryo development effects in grass shrimp (Palaemonetes pugio) embryos after exposure to genotoxicants.

Grass shrimp embryos develop in egg sacs (stages 1-10) attached to the female for 14-20 days after which they 'hatch' from the egg sacs into a swimming zoea stage (stage 11). Until they emerge from the egg sacs, embryos depend on lipids and lipovitellin stored within the egg. The percent of embryos which hatch after exposure to toxicants relative to controls was the basis of an embryo development assay. Exposure of embryos to chromium(III) chloride, sodium chromate, mercuric chloride, and 2-methyl-1,2-naphthoquinone (MNQ) resulted in a reduced hatching rate. In addition to effects on embryo development, DNA strand damage tests were carried out on contaminant-exposed embryos, using the single-cell electrophoresis method often referred to as comet assay. Development of stage 4 embryos was more affected by MNQ exposure than stage 7 embryos. The hatching rates of stages 4 and 7 embryos exposed to MNQ (172 micrograms/l) were 0 and 90%, respectively. DNA strand damage, measured as DNA tail moments, were 3.4 and 4.4, respectively. Thus, exposure of an early embryo stage to MNQ prevented full embryo development while development of later embryo stages was not affected. It may be that the DNA repair systems are more efficient in later embryo stages than in early stages and thus DNA damaged in the early stages affects development.

DNA damage as a bivalve biomarker.

Bivalves have been used in numerous environmental assessment studies, chiefly because they are sessile deposit or suspension feeding organisms found in or near sites of environmental concern, and they can be easily collected, sorted and deployed at sites of interest. Monitoring studies utilizing bivalves currently rely on the comparison of growth, survival, and contaminant bioaccumulation. Data gathered from 'reference' sites are compared with those of populations at assessment sites. These studies require extended periods of exposure, lasting weeks to months, and the use of a well defined population of test organisms of similar size, age, and condition. In many cases time and resources require researchers to restrict their sampling to the organisms on-hand at a particular site without the benefit of any reference data. Therefore more versatile and sensitive assessment methods are needed. Because effects at higher levels of organization such as growth, development, and survival are initiated at the molecular and cellular levels attempts have been made to identify useful biomarkers at these levels. The proposed advantages of molecular/cellular biomarkers are that they will respond to stress predictably and more rapidly, and will be indicative of the mechanisms of toxicity thereby yielding a rudimentary characterization of the contaminant(s) influencing them. In the following communication we will report on past and current developments in the monitoring of DNAdamage as an environmental biomarker.

DNA damage in mussels at sites in San Diego Bay.

Identification and assessment of introduced and other toxicants is crucial to any comprehensive study of contaminants within the marine environment. The relationship between DNA single-strand breaks and the exposure of marine organisms to environmental contaminants was examined at sites in San Diego Bay, CA. A comprehensive assessment of the extent and consequences of marine environmental contamination in the area of Naval Station San Diego was conducted in the summer of 1995. The study addressed contamination sources, distributions, concentrations, transport, sediment-water exchange, biological effects, and degradation. The biological effects portion of the study (this paper) included contaminant bioaccumulation, organismal growth, and the determination of DNA single-strand breaks using the Comet assay. DNA damage was determined in hemocytes collected from deployed and resident mussels, Mytilus edulis, at six stations in and around the Naval Station San Diego. Deployed mussels were exposed on station for approximately 30 days in plastic mesh bags, placed 1 m above the bottom. Hemocyte samples were collected on days 0, 12, and 32. It was found that stations exhibiting the extremes of contaminant exposure, both highest and lowest concentrations, were easily identified using growth and DNA damage measurements. Sediment chemistry and bioaccumulation data indicated, Hg, Cu, and Zn, to be the most notable contaminants. The Comet assay, and in particular germ cell DNA damage determinations, were found to respond rapidly to station contaminants. Results from this study and an earlier 1993 study suggest that the non-sediment associated effects observed at one station may have been the result of the photoactivation of accumulated PAHs.