Metal levels in seven species of mollusc and in seaweeds from the Shannon Estuary.

Metal levels (iron, zinc, manganese, cobalt, chromium, copper and nickel) were determined in Cerastoderma edule, Mytilus edulis, Monodonta lineata, Patella vulgata, Nucella lapillus, Littorina obtusata and L. littorea at two sites close to the mouth of the Shannon Estuary (Ireland) in November 1993 and May 1994, using standard atomic absorption spectrophotometer techniques. Samples of seaweeds were included at one shore for comparative purposes only. The best all-round indicators for all the metals studied were C. edule, M. edulis and N. lapillus. Metal levels in the seaweeds were much lower than in the molluscs. No species was a universal indicator of the metals studied when site and season were taken into consideration. High levels of metals accumulated from water and:or sediment were observed in a number of cases. Levels of Zn in N. lapillus were significantly different to those in all other species and C. edule had high levels of Ni. These levels were dependent on site and season. A detrended correspondence ordination showed that the two species of bivalve mollusc and P. vulgata formed one cluster and that the remaining gastropod species formed a second cluster. This study shows that species-specific bioaccumulation occurs and is seasonally specific in certain species. This needs to be taken into account when choosing a bioaccumulator model and when comparing data from different studies