Determination of heavy metals in choapa river sediments using BCR sequential extraction procedure

Abstract

In recent years Chile has experienced a significant increase in mining activities, which has resulted in an increase in waste generation. The dispersion of these residues in the air, water and soil has led to negative changes in the environment.

This main objective of this study is to identify the influence of the copper mine Los Pelambres (station E2) located in the Choapa River Basin (IV Region Coquimbo). To achieve this goal we performed an analysis of the physical and chemical composition of sediment samples in the summer season taken from the rithron to potamon areas of the watershed. River sediments can provide information and influence the degree of pollution in a given area due to mining discharges. The analysis was based on two types of determinations: total metal content, which provides an assessment of the level of contamination, and studies of different chemicals in which the metal is associated with the sediment.

The results of this study showed that station E2 (Cuncumen River) has a particular behavior in the basin, showing higher content of metallic trace elements; for example, the concentration of Cu (total fraction) was 4814.1 μgg-1. In the rest of the stations the metal content was less than in E2 (total Cu from 42.4 μgg-1 in E1 to 136.2 μgg-1 in E5), therefore it is concluded that there is no direct influence of the mining activity of Los Pelambres station (E2) in the rest of the basin.

BCR sequential extraction of sediments, developed under the auspices of the Community Bureau of Reference, indicated metal mobility. Metal mobility is closely associated with the chemical conditions of the system. In general, metals that could have greatest mobility in the basin are: Cu, Cd, Zn and Mn, found in the soluble acid fraction, together with oxidant (organic matter) and reducing (Fe and Mn oxides) conditions.

The cluster analysis of the total fraction of metal content in sediments indicates that the mine discharge site (E2), has a unique behavior in the basin. Station E2 showed a similarity below 50%, while the rest of the basin showed a similarity above 70%.

Overall the results indicate that the Los Pelambres Mine is not a direct source of heavy metals in the Choapa River Basin, which does not imply that station E2 (Cuncumen River) has no influence on the metal content of sediments. To determine the area of this season, the study area should be narrowed to Cuncumen River (E2) section of the Choapa River Basin, since the physical conditions of the system, hydrographic conditions and climatic do not allow a high rate of discharge and mobility of heavy metals from the mining area with high discharge to the last station (Huentelauquen).