Assessment of bioaccessible As in a wetland with mining influence (Mar Menor, SE Spain).

Mining areas are so complex that it is sometimes difficult to differentiate between anthropogenic contamination and geogenic anomalies. This is the case in the so-called Sierra de Cartagena-La Unión, which constitutes a mining district of Ag, Pb, Zn, Fe in stratabound sulphide deposits that have been exploited for more than three thousand years. Since the closure programme was implemented in 1991, the area has remained abandoned. This results in runoff from extreme rainfall events, as well as wind action, allowing the transport of dissolved or suspended particles and pollutants from mining areas to the plain of Campo de Cartagena, the Mar Menor and the Mediterranean Sea. In this area, arsenic pollution is one of the main environmental and public health problems. In general, arsenic levels in uncontaminated soils rarely exceed 10 mg/kg, the proposed Generic Reference Level (GRL) being 7.84 mg/kg for the Region of Murcia. In exclusion zones, As concentrations exceed 300 mg/kg, reaching in some cases 5000 mg/kg (coinciding with accumulations of mining waste, ponds, dumps, etc.).

The main objective of this work was to evaluate the potential risk to humans, through the main route of entry, ingestion, represented by the soils of the Rambla del Beal basin (SE Spain) and its mouth in the Lopoyo Wetland (Mar Menor, SE Spain), taking into account:

- Total As content in four different soil fractions (˂2mm; ˂250µm; ˂100µm; ˂63µm).

- Bioaccessible arsenic content in four different soil fractions (˂2mm; ˂250µm; ˂100µm; ˂63µm).

- Two possible adult land uses (agricultural and residential) and one possible child land use (residential).

For the determination of As bioaccessible, in vitro extraction methods were used. Among the various in vitro methods to assess the relative bioavailability of existing metals, the Solubility Bioaccessibility Research Consortium (SBRC) method was selected, as it provides an adequate relationship between bioavailability and bioaccessibility of arsenic, with a high correlation with the results obtained in vivo experiments, distinguishing two phases, stomach and intestinal.

In the area studied, the Lopoyo Wetland is the area that presents the greatest risk to the health of people (both children and adults). It is an area that requires priority intervention for its recovery. The arsenic contamination present and its mobility in this reduction-oxidation zone represents an unacceptable risk for both public health and the ecosystem.

The results highlight the importance of carrying out risk analysis studies on human health at sites potentially contaminated by carcinogenic trace metals such as arsenic, taking into account the concentration of bioaccessible As.  According to the results obtained when the study is carried out with the total concentration of arsenic, i.e. without bioaccessibility, the results of unacceptability of the carcinogenic risk and of the systemic hazard are much higher than those obtained with bioaccessibility, independently of the granulometric fraction on which the determination is carried out. Moreover, these results are reproducible for all possible uses (scenarios) of the site.