Trace metal pollution in the environment: A comparison of the bio-indicator concept in three bivalves

Three bivalves from the coast of Ghana: Crassostrea tulipa (n = 275), Anadara (Senilia) senilis (n = 310), from two ‘open’ lagoons (Benya and Ningo) and a ‘closed’ lagoon (Sakumo), and Perna perna (n = 155), from rocky shores adjacent to Benya and Sakumo, were analyzed for their total Cu, Zn, Fe, Mn, Cd and Hg concentrations and total body burden/load. The analyses were based on three-size class from two seasons. Average concentrations for oysters (C. tulipa) were: 40, 1197, 477, 16, 0.57 and 0.15 μg/g dw respectively. Cd and Hg levels in dry season samples were higher than those in wet season. While Zn and Fe dry season levels were lower than wet season with no variation in Cu and Mn, average total body burden were: 16, 451, 178, 6.6, 0.25 and 0.11 μg respectively. Geographical variations observed were mostly due to size distribution rather than the ecological differences between stations. Factors observed to influence metal concentrations and accumulation in these organisms include; size, metal bioavailability, season of sampling, hydrodynamics of the environment and reproductive cycle. Element concentrations in bivalves at the same location differ between different species and individuals due to species-specific ability/capacity to regulate or accumulate trace metals. Log-transformed regression analyses between body burden and size were used to compare the species and stations. In addition, the results were compared within class and among classes.