Screening of wild plants for use in the phytoremediation of mining-influenced soils containing arsenic in semiarid environments

PURPOSE: When dealing with remediation projects in zones affected by mining activities, the risk posed by the ingestion of the plants by fauna is often forgotten. The purpose of this study is the assessment of arsenic assimilation by the natural vegetation in these areas. To study the transfer to the trophic chain two mammals, the sheep and the vole are selected. The risk analysis is founded on the contribution of these natural plants to the ingestion. MATERIAL AND METHODS: Soil samples and the same number of plants (165) growing in the soils were collected in an old mining area in the southeast of Spain. Physico-chemical properties were calculated by means of the usual procedures. To determine the arsenic content, the soil samples and plant materials were digested by means of a microwave system and the arsenic concentration was determined using atomic fluorescence spectrometry with automated continuous flow hydride generation (HG-AFS). A semiquantitative estimation of the mineralogical composition of the samples was made by X-ray diffraction analysis. RESULTS AND DISCUSSION: The mineralogy and As content of the soils studied depends on the materials related with the mining activity. The descriptive statistical analysis of the population of plants studied points to an As range of 0.31–150 mg/kg in roots, although the concentration in shoots was lower (0.21–83.4 mg/kg). Bioconcentration (BCF) and transfer factors (TF) were studied for each plant species and soil type on which it grew. The results show that As transfer depends on the plant species and the characteristics of the soil. The potential risk of As entering the food chain through the plant species was evaluated. The exposure pathway considered was oral ingestion, calculating the contribution of the plant to the daily dose based on the arsenic concentration in the shoots of the plants analysed. CONCLUSIONS: In the samples studied, the levels of As in roots were higher than in shoots, and increased with the As concentration in the soil. The BCFs were generally very low, and the TFs while slightly higher, seldom exceeded unity. When undertaking with the phytoremediation of contaminated sites, the contribution of the As level in plants to the daily diet of animals should be used as an indicator for the screening of the vegetal species to be used.