Validation of the asteroid Asterias rubens (Echinodermata) as a bioindicator of spatial and temporal trends of Pb, Cd, and Zn contamination in the field

Abstract

The aim of the present study was to assess the value of Asterias rubens as a bioindicator of metal contamination in the field. Spatial gradients of Pb, Cd, and Zn contamination were identified along Sørfjord, and metal concentrations were consistently higher (1.7–8.3 times) in the body compartments of large asteroids sampled close to the smelters than in those sampled further away. Cd and Pb concentrations in the pyloric caeca varied along the fjord according to a decreasing sigmoidal relationship, while Cd and Pb concentrations in the body wall and the skeleton varied according to a decreasing exponential relationship. This suggests that the bioavailability of these metals has decreased over the last few years at the head of the fjord, which agrees generally with water chemistry data available from the State Pollution Monitoring Programme (Norway). The decrease in metal bioavailability could be a direct consequence of the 1992 remedial action taken in the fjord to reduce heavy metal release from the contaminated sediments. Lead concentrations in the skeletons of large asteroids (12–14cm; 154 ± 63 μg Pb g −1 dry wt) were eight times higher than those in the skeletons of juvenile individuals (0.5–4 cm; 19 ± 8 μg Pb g −1 dry wt) in the population located at the head of the fjord. Asteroids of 12–14 cm length were likely to be 4–7 y old (i.e. born before the remedial action) while small asteroids were born after the remedial action. According to comparisons with allometric relationships in an uncontaminated population and experimental exposures, results indicate that the half-life of Pb in the skeleton is long (i.e. several years) while the half-life of Cd and Zn is much shorter (i.e. several weeks for Cd, and short but not precisely known for Zn). A smaller size and unusual reduction of the skeleton of adult individuals at the head of the fjord were observed and may result from the effects of heavy metal pollution. A comparison between possible sources of contamination in the fjord (metals in water, food, and sediments) indicates that sediment-associated metals are likely to be an important source of contamination in this environment due to the microphagic activity of asteroids.