Geostatistical mapping of the concentration of Zn in the Bay of Sepetiba in Rio de Janeiro, Brazil

Abstract

In general, the growth of the economical activities in a country is directly conelated to the increase of pressure on natural systems, leading several authorities and specialists to the discussion of the impacts generated and the main actions to minimize them. Over the last years, such discussions have established new paradigms in the means of production in terms of sustainable growth and preservation of natural resources for future generations. In particular, the concern with the water systems has been great, since those are the ones that are most affected by industrial and domestic activities. Within this confext, this study will approach the contamination with Zn of the Bay of Sepetiba, located in the state of Rio de Janeiro, in the southwest region of Brazil. As a result of the industrial and urban expansion over the last three decades, the region has been rather impacted, particularly with the contamination with Zn, as it has been recorded by several authors. With the purpose of assessing precisely the human action concerning the Zn in the region, the concentrations of this metal were determined by instrumental neutron activation analysis (INAA) in 60 samples geographically referred in a regular network. The distribution and evaluation of the risks due to the contamination with Zn in Sepetiba were investigated through classic statistical techniques and geostatistics. In order to limit the effects of discrepant values and later geostatistical analysis, the data were normalized through a Box-Cox transformation. The parameters of the spatial disfribution of the concentrations of Zn were estimated through the adjustment from the theoretical to the experimental variogram via method of the minimum pondered squares. The mapping of the concentrations of the metal studied in this work was carried out through ordinary kriging. In order to evaluate the quality of the geostatistical analysis, the prection variances maps was designed and the cross-validation was carried out. Aiming at identifying the most critical areas with regards to the confamination with Zn, it was constructed the map of probability of concentration that exceed the contents found in the regions that did not undergo human influence. The results obtained in this study provide precise information to evaluate the risks posed by high concentrations of Znin the Bay of Sepetiba, with the purpose of aiding the authorities in their decisions to effectively control the problem.