in this study, we analyzed the bioconcentration of cd, cr, cu, pb, ni, and Zn in the soft tissue of transplanted oysters in two sites in the potengi estuary for six months. native oysters collected before and after the transplantation experiment provided the background for statistical analyses. cd, cr, and ni showed a strong inverse correlation with oyster weight in both sites. transplantation upstream of the estuary presented increasing concentrations of Zn, cu, and pb and condition index (ci) and decreasing trends for Cd and Ni, whereas Cr oscillated significantly. In the downstream transplantation, cu, pb, and Zn and the ci tended to decrease, whereas for ni, cd, and cr, the concentrations increased. Spatiotemporal principal component analysis correlated these results mainly with proximity to the polluting source, seasonality, and previous exposure to heavy metals. these results helped interpret the responses provided by these biomonitors to environmental changes, whether they are natural or anthropogenic.Industrialization and urbanization are primary sources of heavy-metal contamination in estuaries and coastal ecosystems of tropical and subtropical countries (e.g., Brazil) 1,2 . Deforestation of estuarine margins also impairs the ability of the environment to withstand heavy-metal pollution, as mangrove forests are an important agent in the process of cycling organic matter and nutrients, acting as a "filter" by retaining and detoxifying harmful elements and substances 3-5 . It is a fact that metal pollution in aquatic systems will significantly increase in the future owing to the popularity of new technologies, such as nanotechnology, and the improper disposal of the so-called e-waste 6 .Metals widely available in estuarine environments tend to be trapped in sediments and incorporated into the local food chain. Thus, the presence of heavy metals in sediments can induce toxic effects in living organisms when they exceed certain concentration limits 5 . These limits, according to Farrington et al. 2 , are dependent on the half-life of the metal itself (or the metallic compound) and its nature (whether essential or nonessential) and on the tolerance of the organism to the environment it is exposed to. Once discarded in an estuarine system, heavy metals can undergo various processes, such as dissolution, precipitation, adsorption, and complexation (with organic and inorganic dissolved ligands and particulate matter), and become deposited in bottom sediments 7 . These processes can create a potential source of pollution and adversely affect the environmental quality 8,9 . Certain marine organisms, such as barnacles and bivalve mollusks, can metabolically accumulate large amounts of these metals in their tissues, having efficient strategies to tolerate toxicity and reduce damage in such a way that they can be employed in multipurpose environmental monitoring and several levels of environmental degradation, thus signifying the extent of pollution present in the adjacent water column 10,11 .Bioaccumulation of he...