Geochemical proxies and bioavailability trace elements in sediments from cachoeira river estuary, ilhéus-ba, brazil

Abstract

The Cachoeira River estuary (CRE) is the largest one in southern Bahia and receives domestic, agricultural and industrial effluents from thirteen municipalities among which they are potential sources of organic matter (OM) and trace elements. The environmental characterization studies carried out in CRE do not include the evaluation and characterization of bio-available trace elements in the sediment and its relationship with environmental and hydrodynamic parameters. This study aimed to make the first assessment of the distribution of the bioavailable trace elements in the CRE bottom sediment to recognize the environmental and sedimentological compartments associated with the pollution degree and/or environmental degradation. The sampling was carried out in November 2016 over 30 pre-established stations with measurement in the field of physical-chemical parameters in the water column and sampling for granulometric and geochemical analysis. The CRE showed great spatial heterogeneity of environmental variables, which is a result of both natural and anthropic order. The marine influence was evidenced by high salinity and pH values that extend up to 11 km from the mouth. The anthropic influence was high notable for the increase in OM percentage in the stations near the sewage treatment plant and the vicinity of the Itacanoeira and Santana rivers. High concentrations of bioavailable trace elements were found in the sediment, with emphasis for As, Cu, Hg, Ni, Pb and Zn, which were in concentrations above the limits established by an environmental protection agency. The high concentration of trace elements in the bioavailable phase in the CRE is a result of the high local hydrodynamics that is the characteristic of well-mixed meso-tide estuaries.