Spatial Analysis about Structural Patterns of Fate of Chromium (VI) in Relation to pH at Natural Sea Water Bodies

Abstract

One of the most important factors in the redox state of chromium in solution is pH, which, according to its value, can lead to oxidation of Chromium (III) to Chromium (VI). The presence of Chromium (VI) in natural waters is related to discharges from anthropogenic activities, such as leather industry, electroplating, paints, among others. The Chromium (VI) the most important toxicologically, the present state chromates, dichromates and chromic acid . The International Agency for Research on Cancer (IARC) has classified Chromium (VI) in group 1 (carcinogenic to humans) and metallic Chromium and Chromium (III) in Group 3 (not classifiable as to its human carcinogenicity. In Colombia, the permissible exposure values reported by the District Department of Health of Bogota for the general population are up to 10 µgL-1and population exposed up to 20 µgL-1 and the Colombian Technical Standard (NTC 813) indicates as maximum in drinking water, a concentration of 50 µgL-1. In order to study the behavior of Chromium (VI) and pH in solution in marine ecosystems it was carried out systematic type sampling in a square mesh for data variables involved in the Ciénaga de las Quintas magrove swamp, which belongs to the internal waters system of Cartagena de Indias’ Bay, Colombia. 35 field samples were taken in amber glass bottles, adjusting the pH with nitric acid, for further analysis by the Cr method 3500 B. For the pH parameter values were taken in field with a portable pH meter. The exploratory analysis showed that the concentration data for Chromium (VI) did not conform to normal, so underwent a transformation to work with the LOG base 10, for adjustment to normal (S.W., p>0.05), with an average value of 3.23 µgL-1. In contrast, the pH has a homogenous distribution behavior (C.V. = 1.52%) with a mean value of 8.16 µgL-1; making it representative for the system. The pH values are adjusted to normal without needing any adjustment needed (S.W.; p>0.05). To make the structural analysis, with the aim of demonstrating spatial autocorrelation of variables, the Index of Moran (Moran, 1950) was used, which varies between 1 and -1. The pH showed slight spatial relationship or a structure related to a concentration gradient. On the other hand, the concentration of Chromium (VI) showed spatial autocorrelation, the most likely structure is the gradient type.