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Mangroves are productive ecosystems that are highly threatened by anthropogenic activities. We investigated the environmental quality of the Serinhaém river estuary located in a legally protected area. Through chemical analysis of sediments and tissues of Cardisoma guanhumi , in addition to bioassays with elutriate involving Nitokra sp. and Thalassiosira pseudonana , we determined the contamination status and risk factors related to trace metals in the estuary. For the sediment, the concentrations of Cr and Ni were above the limit established by CONAMA n° 454/2012 in the "City" site, and Cr above the TEL in all sampling sites. Ecotoxicological tests showed high toxicity in samples from "City" and "Tributary". The elements Cr, Mn, Ni and Zn were also higher in crabs from these sites. Cr levels exceeded the Brazilian limit for food consumption. The bioaccumulation factor was not significant. However, the overall analysis proved that this estuary is increasingly impacted by anthropogenic pressure. • The estuary is located in a protected area that was hit by the biggest oil spill accident in the history of Brazil. • The Cr contents were above the TEL for all sample points, indicating a moderate contamination in the sediment. • The bioassay with elutriate showed high toxicity with growth inhibition of Thalassiosira pseudonana. • There was less Nitokra sp spawning after exposure to elutriate from the point close to the urban area. • The Cr content in tissues of Cardisoma guanhumi is above that established for human consumption by Brazilian legislation. [ABSTRACT FROM AUTHOR]