Seasonal and spatial variation of trace elements in sediments of three chilean basins

Abstract

Total concentrations of trace elements can provide fundamental information on the sediment contamination levels of the pollution indexes and the quality guidelines for sediment risk assessment. However, this information alone is insufficient to understand the mobility, bioavailability and toxicity of these elements in the sediment, since the environmental behavior of trace elements depends largely on their chemical form and binding states. Thus it is important to determine the soluble or labile fraction, since the elements of this fraction will be the most mobile and bioavailable.

In this study we analyze the seasonal and spatial variation of labile fraction trace elements concentration in three Chilean river basins. We also study the impact of mining nearby in one of the sites studied in the three basins.

Samples were taken in spring (November); summer (January), autumn (May) and winter (June). Sediment samples from three selected basins: Aconcagua, Cachapoal and Choapa basins were collected at different points in the river. Six sampling points were chosen in three areas: one station without human intervention (ritron: E1), two in the area of middle ritron (E2-E3) and a third in the sector potamon where increased sedimentation (E4-E5-E6). In the three basins site E2 could be influenced by mining activities, site E2 in the Cachapoal basin is influenced by the El Teniente mine; site E2 in the Aconcagua basin influenced by the Cerro Blanco mine and site E2 in the Choapa basin is influenced by the Los Pelambres mine.

Physical chemical characteristic of sediment were done by described methods. The labile or soluble fraction of Al, As, Cd, Cu, Cr, Fe, Mn, Mo, Ni, Pb and Zn, was extracted from the sediment with acetic acid. Metals were analyzed by ICP-OES.

The eleven trace elements analyzed in the labile fraction were detected in the three basins in most of the stations. The high concentration of Al, Cu, Fe, Mn, Zn in the labile fraction found in the E2 site in the three basins demonstrates the influence of mining activities near this site. The mobility of trace elements to the other sites is depending on the characteristics of the basins. Variation between seasons and sites was observed.