Evaluation of the bioaccessibility of arsenic in plants used for soil recovery purposes in mining areas

The use of phytostabilizing plants in remediation projects of areas affected by mining activities is one of the valid strategies for recovering the ecosystem.  It is often used to obtain biodiversity with the aim of restoring the environment, but the possible risk represented by the ingestion of the plants by the fauna and the consequent passage of As to the trophic chain is forgotten.

The aim of this study is to evaluate the environmental risk posed by arsenic when revegetation occurs in an area with high levels of this element. To this end, the transfer of arsenic in different plant species that grow spontaneously in an abandoned mining area (Sierra Minera de Cartagena) is analysed, as well as the contribution of these plants to the intake of mammals in the area. In order to make a comparison with the risk analysis applied to human intake, the wild boar is selected since this mammal has a digestive physiology very similar to that of humans. For this purpose, a gastric solution is prepared according to the standard operating procedure (SOP) developed by the Solubility/ Bioavailability Research Consortium (SBRC). Two phases, namely, stomach (AsA) and intestinal (AsN), are considered.

In this way, it is possible to discriminate between plant species with high, non-bioaccessible contents in the aerial part and plant species with the opposite.

For this study, 21 plant species that grow naturally in the soils of the Sierra Minera and their corresponding rhizospheres were collected.

The physical-chemical properties were obtained using the usual procedures. To determine the arsenic content, the soil samples and plant materials were digested in a microwave system and the arsenic concentration was determined using atomic fluorescence spectrometry with an automated continuous flow hydride generation system. Soils are classified into three groups: Low (group 1) (7-35 mg/kg), medium (group 2) (35-327 mg/kg) and high (group 3) (> 327 mg/kg), according to their As content. The descriptive statistical analysis of the population of plants studied shows that the range of As in the roots were from 0.31 to 150 mg/kg, while the concentrations in the leaves were lower (0.21 to 83.4 mg/kg). The possible risk of As entering the food chain through plant species is evaluated. The route of exposure considered is the oral ingestion, calculating the contribution of the plant to the daily dose based on the concentration of arsenic (total and bioaccessible) in the leaves of the analyzed plants

In general, the bioaccessible fraction by intake is low, although it is higher in the areas most influenced by primary and secondary pollution sources. The availability of bioaccessible As in the leaves of the plants is highly influenced by the mineralogical composition of the soils on which it grows.