Assessment of arsenic and fluorine in surface soil to determine environmental and health risk factors in the Comarca Lagunera, Mexico

Total, bioaccessible and mobile concentrations of arsenic and fluorine are determined in polluted surface soil within the Comarca Lagunera region using standardized protocols to obtain a full description of the environmental behavior for these elements. The composition of mineral phases associated with them is evaluated with microscopic and spectroscopic techniques. Mineralogical characterizations indicate that ultra-fine particles (<1–5 μm) including mimetite-vanadite (Pb₅(AsO₄)₃Cl, Pb₅(AsO₄, VO₄)₃Cl)-like, lead arseniate (Pb₃(AsO₄)₂)-like and complex arsenic-bearing compounds are main arsenic-bearing phases, while fluorite (CaF₂) is the only fluorine-bearing phase. Total fluorine and arsenic concentrations in surface soil range from 89.75 to 926.63 and 2.7–78.6 mg kg⁻¹, respectively, exceeding in many points a typical baseline value for fluorine (321 mg kg⁻¹), and trigger level criterion for arsenic soil remediation (20 mg kg⁻¹); whereas fluoride and arsenic concentrations in groundwater vary from 0.24 to 1.8 mg L⁻¹ and 0.12–0.650 mg L⁻¹, respectively. The main bioaccessible percentages of soil in the gastric phase (SBRC-G) are estimated for arsenic from 1 to 63%, and this parameter in the intestinal phase (SBRC-I) fluorine from 2 to 46%, suggesting human health risks for this region. While a negligible/low mobility is found in soil for arsenic (0.1–11%), an important mobility is determined for fluorine (2–39%), indicating environmental risk related to potential fluorine release. The environmental and health risks connected to arsenic and fluorine are discussed based on experimental data.