The use of sea urchin bioassays in the assessment of environmental quality

Abstract

The objectives of the present work were two-fold: to assess the suitability of spermiotoxic and embryotoxic responses in sea urchins as a biomonitoring tool in the assessment of the quality of superficial marine sediment and to assess the effects of tributyltin on sea urchin sperm and embryo development. In spermiotoxic experiments, sperm was exposed to the test mixtures (solid-state sediment or tributyltin). Untreated eggs were fertilized using the supernatant sperm suspension. After 1 h, fertilization success, expressed as first cleavage in A. lixula and elevation of the fertilization membrane in P. lividus and S. granularis/ was read. When the pluteus stage was reached, offspring quality was examined. In embryotoxic tests, embryos were exposed to the test mixtures (solid-state sediment or tributyltin). After 48 h, the quality of the embryos was read. In the assessment of the potential use of spermiotoxic responses in A. lixula as a biomonitoring tool of sediment quality, 7 sites were chosen within Marsamxett Harbour, in order to represent a gradient from relatively highly contaminated to minimally contaminated conditions. The lowest value for both percentage first cleavage and the proportion of normal plutei was recorded in the innermost site of the harbour, which showed a 71% reduction in first cleavage with respect to the sea-water control and a 75% reduction with respect to the outermost site. The amount of normal plutei in this site was 51% less than that in the control and 53% lower than that recorded from the mouth of the harbour. No particular contaminant showed correlation to all the different responses. However, TBT, organic carbon content, lead, zinc, copper and petroleum hydrocarbons were separately correlated to at least one response. No endpoints showed any correlation to MBT, cadmium and sediment grain size. The toxicity of sediments from nine different areas around Malta was assessed using spermiotoxic responses in A. lixula and P. lividus and embryotoxic responses in P. lividus. Responses in A. lixula showed that areas where there is high industrial activity, mainly shipping industries, were the most toxic, whilst more exposed areas with low boating activities were the least toxic. Responses in P. lividus failed to distinguish any differences between the sites under study. Spermiotoxicity in A. lixula was found to be a more sensitive bioassay than spermiotoxicity and embryotoxicity in P. lividus. The discriminatory power, an index intended to identify endpoints which have the widest range in response and the lowest analytical variability independent of the control (Long and Buchman, 1990) was highest for normal development following spermiotoxic tests in A. lixula and lowest for fertilization rate in P. lividus. Tributyltin concentrations ranging from 10 to 400 ng TBT r1 caused a spermiotoxic effect in A. lixula but not in S. granularis. Ethanol was embryotoxic to A. lixula/ S. granularis and P. Hvidus. TBT, working synergistically with ethnnol, caused an embryotoxic effect in A. lixula and S. granularis. The suitability of spermiotoxic and embryotoxic experiments as biomonitoring tools in sediment quality and the ecological significance of the reported effects of TBT are discussed.