This study investigated two estuaries on the northern coast of Brazil submitted to different anthropic activities. The main objective was to assess the use of oysters (Crassostrea gasar and Paxyodon ponderosus) and phytoplankton as bioindicators of environmental contamination. Water, sediments, phytoplankton and oysters were chemically analyzed by ICP-OES and ICP-MS. The source for metal bioaccumulation in oysters and phytoplankton was assessed using BSAF (Biota Sediment Accumulation Factor) and the isotropic relations of stable carbon (${\delta }^{13}$C and ${\delta }^{15}$N). The oyster-sediment BSAF showed bioaccumulation of Mn, Cu, Zn, Se, Sr, As, Cd and Ba, which was supported by the correlations of Fe, Mn, Cu, Zn, Se, Sr, Al, Ba and Pb with the isotopes (${\delta }^{15}$N and ${\delta }^{13}$C), which confirmed bioaccumulation as well as biodilution and biomagnification in oysters and phytoplankton. That reflects the efficiency of organisms in bioconcentrating metals and their capacity as bioindicators of contamination.

这项研究调查了巴西北部沿海地区两个从事不同人类活动的河口。主要目的是评估使用牡蛎（Crassostrea gasar和Paxyodon tankerosus）和浮游植物作为环境污染的生物指标。通过ICP-OES和ICP-MS对水，沉积物，浮游植物和牡蛎进行化学分析。牡蛎和浮游植物中金属生物富集的来源使用BSAF（生物质沉积物富集因子）和稳定碳的各向同性关系进行了评估（${\delta }^{13}$C和 ${\delta }^{15}$N）。牡蛎沉积物BSAF表现出Mn，Cu，Zn，Se，Sr，As，Cd和Ba的生物富集，这受Fe，Mn，Cu，Zn，Se，Sr，Al，Ba和Pb与铁的相关性的支持。同位素（${\delta }^{15}$N和 ${\delta }^{13}$C），证实了牡蛎和浮游生物的生物富集以及生物稀释和生物放大作用。这反映了生物体在生物富集金属中的效率及其作为污染生物指示剂的能力。