Aplicação do modelo do ligante biótico-BLM-para a predição da biodisponibilidade de zinco nas águas do Rio São Francisco

Abstract

The São Francisco River, in Brazil, has been impacted by many activities located along its watershed, such as: electricity generation, industry, sewer discharge, agriculture. A zinc metallurgical plant that belongs to Votorantim Metais Zinco S.A., located aside São Francisco bank, in the city of Três Marias (Minas Gerais State) has been studying the influence of its zinc production activities upon the aquatic system.Among the many studies developed by Votorantim there is an Environmental RiskAssessment ERA for the quantification of the environmental impacts related to its activities. For a better environmental impact assessment, it was proposed to study the bioavailability of zinc in the waters of São Francisco River and affluents under the influence of the company, and also zinc toxicity to aquatic organisms, which depend on the water quality parameters such as: pH, Eh, alkalinity, hardness and concentration ofdissolved organic matter.To enhance this assessment, the Biotic Ligand Model BLM was used, to predict the speciation of zinc in water and most of the bioavailable zinc was most found near the effluent discharge to the São Francisco River (PSF6-MD) and also near the ConsciênciaCreek confluence with São Francisco River (PSF7-MD). The zinc toxicity to aquatic livings (Daphnia magna e Ceriodaphnia dubia) was also predicted to the studied sites,in which PSF7-MD was found to be toxic to C.dubia.In general, the values predicted by the BLM were consistent with the bioassays (Effluent discharge (PSF6-MD): LC50predicted=LC50measured=0,161mgZn/L; ConsciênciaCreek (PCS1-MD): LC50measured=0,094mgZn/L; LC50predicted=0,171mgZn/L). In the other hand, the zinc toxicity predicted by the BLM to Lavagem Creek (PLV2-Centro)was much lower than the toxicity measured by the bioessay(LC50predicted=0,557mgZn/L; LC50measured=0,101mgZn/L).