The influence of seasonality (dry and rainy) on the bioavailability and bioconcentration of metals in an estuarine zone

•We studied bioavailability and bioconcentration of metals in São Paulo river estuary.•Metal concentration in the estuarine zone is important for environmental monitoring.•The seasonality interfered directly in the physicochemical parameters.•The rainfall interfered on heavy metals bioavailability in environment.•Metal concentration values found in São Paulo river estuary are high.

Knowledge on the concentration of metallic elements is important to certify the quality of ecosystems. Such behaviors in estuarine environments are dependent of factors such as rainfall and temperature of the water, interfering directly on the metal concentrations in biotic and abiotic components. This study observed the role that seasonality (dry and rainy) had on the bioavailability of metals (Fe, Zn, Mn, Cu, Ni, and Al) in surface water and sediment, and bioconcentration in oysters (Cassostrea rhizophorae) in the mangrove area of the São Paulo river estuary, Todos os Santos Bay. The metals concentration in three matrices analyzed varied between the periods studied. The values of physicochemical parameters also had significant variations. High levels of Zn and Cu were found in mollusks. The highest concentrations of metals analyzed were Al in waters, Fe in sediments and Zn in mollusks. These results showed that seasonality interferes directly in the physicochemical parameters analyzed (pH, dissolved oxygen, temperature, salinity and Eh), as well as on the bioavailability of metals in both water and sediment, influencing directly on the concentrations found in mollusks.