Abstract

Several laboratory conditions for preparing and testing of elutriates from sediments of industrial and urban contaminated areas of the Lagoon of Venice (Italy) were assessed in experiments using embryos of the sea urchin Paracentrotus lividus.

Elutriates were obtained by mixing of aerated offshore sea water and fresh aliquots of sediments (5, 20, 200 g l-1) for four hours. Sediments were then allowed to settle for 12 hours, the supernatant was filtered (at 1 µm) and subsequently tested, undiluted and diluted, at ratios of 1:4 and 1:10. Each diluted sample was again tested after further filtering at 0.45 µm.

Bioassays were carried out on embryos from post-fertilisation to the pluteus stage. The following parameters were observed: survival, frequency of developmental stages, and embryonic growth. The latter was most sensitive to varying experimental conditions, as the length of the skeletal somatic rods of plutei decreased significantly with increasing sediment concentration. Percent survival was slightly reduced in non-diluted and non-filtered treatments only. The frequency of developmental stages was always significantly different in 200 g l -1 elutriates 24 hours after fertilisation.

In bioassays, no direct relationship was observed between sediment concentrations in elutriates and toxic effects, fitting the contamination levels revealed by chemical analysis of elutriates.

When short mixing times were used, the most convenient sediment:water ratio was 1:4 (without further dilution or filtering) which more clearly showed the different degrees of toxicity among sediments.

The elutriate bioassay with lividus embryos is proposed as a rapid and highly sensitive approach for monitoring sediment toxicity in water-column organisms.

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