Avaliação do risco toxicológico à saúde humana associado ao incremento do fluxo de cromo antrópico em segmentos fluviais afetados por curtumes

Abstract

In this study a dynamic approach based on a mass balance model was used to evaluate chromium influxes and outfluxes in selected segments of the Cadeia and Feitoria rivers (RS, Brazil), with a view to identifying inputs from the activity of tanneries in the region. Using a geochemical tracer from natural sources (iron), in association with the risk analysis method of the Environmental Protection Agency of the United States, the strategy allowed screening the potential increment in toxicological risk to the human health in each segment evaluated, concerning the ingestion of water contaminated with chromium from anthropic sources. In order to apply the numerical model, secondary flow and chromium concentration data were used, obtained at ten sampling points on July/1999, October/ 1999, January/2000 and April/2000. Although the results indicated contents below the detectionlimit for the most toxic form of chromium (hexavalent), a critical scenario was assumed in estimating risk: ingestion of raw water and possibility of converting all of the Cr3+ present into Cr6+. Once the fluxes entering and leaving each segment were calculated, a chromium export was found from the Feitoria river to the Cadeia, and from this to the Caí river, which contributes to the Guaíba lake. All of the risk quotients obtained are below the unity, suggesting the absence of possible adverse toxicological effects caused by the ingestion of chromium-contaminated water. On the other hand, applying the model made it possible to identify river segments and periods of the year with higher risk increments, potentially resulting from tannery contribution. The period of highest risk was January/2000, under conditions of less water availability, which highlight the point contribution of tanneries. The increments in the flux of anthropic chromium, and the corresponding risk increments were higher in the lower reach of the Feitoria river, where tanneries are concentrated.