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The knowledge on the contaminants agents' bioaccumulation dynamic in bivalve tissues is important because shell fish consumption may represent a toxic risk to humans. By looking at the selective pressure to which the bivalve mollusks were submitted along their evolutionary process, a better understanding on bivalves as a biologic model for environmental contamination assessments can be achieved. The capacity to control toxic elements by bivalves is especially important to environment toxicology. Bivalves that are able to accumulate high contaminant levels with no apparent toxic effect exhibit special potential as "sentinel species". Different strategies of metal distribution through the organs result in different bioaccumulations patterns in each organ/tissue. Along the last fifty years the bivalves have been widely used as environmental matrix, and their potentiality and limitations for environment toxicology are still under debate. In this review we intend to discuss the principles of bivalve's applicability as a tool for environmental biomonitoring and the present paradigms and future perspectives of bivalves as a model in environment toxicology.

Perna perna (Linnaeus, 1758) is the main marine bivalve mussel yielded commercially in Brazil. In spite of this, scientific data is very scarce regarding its productivity in tropical shallow waters. The Condition Index (CI) is used worldwide in mariculture to assess animal health, harvest time, and yield. In this study, the authors used CI results from nine different methods to assess the season effect on the mussel CI and also to evaluate the potential yield of three southern Brazilian bays. The results from nine CI methods were used for the comparison of the seasonality and yield of mussels reared in three marine bays. Sampling was carried out monthly within two 4-month periods, from December 2008 to August 2009. The results show a trend for seasonal effects on the CI results. The winter months showed the highest and the lowest values. Between bays, higher CI values were detected in animals reared at Sepetiba Bay, followed by Guanabara Bay and Ilha Grande Bay. We suggest that the CI (that considers the ratio between bivalve soft tissue wet weight and total length) should be used by fishermen, since this formula was able to detect differences between sites and is more easily applied.

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