Combining human and snail indicators for an integrative risk assessment of metal(loid)-contaminated soils

With the new soil uses such as land restoration and to protect wilderness, the human health risk assessment (HHRA) and environmental risk assessment (ERA) should be combined. Based on the relationships demonstrated between an indicator of soil quality, the land snail, and human exposure, the aim of this study is to examine the snail and human risk indicators for twenty-nine soils contaminated by metal(loid)s. HHRA was evaluated by both hazard quotient and carcinogenic risk. When the human health indicators were ranked as uncertain, they were weighted by bioaccessibility to refine the risk assessment. The ERA was performed with risk coefficient after ex situ snail exposure. The results showed strong and novel relationships between human health and environmental risk indicators that had never been found before. For 62% of the soils, both indicators revealed either a confirmed risk or an uncertain level of risk. Overall pollutants present greater risk for human than for environment, with 55 vs 28% of the studied soils classified in the proven risk, respectively. An original integrative risk assessment of polluted soils has been proposed, that shall help setting up relevant strategies to manage contaminated soils considering not only human but also environmental indicators of risk.

Bioaccessibility of metal(loid)s in soils to humans and their bioavailability to snails: A way to associate human health and ecotoxicological risk assessment?

Human health risk assessment (HHRA) and ecotoxicological risk assessment (ERA) of contaminated soils are frequently performed separately and based on total soil concentrations without considering the concepts of mobility, bioaccessibility and bioavailability. However, some chemical and biological assays rarely used in combination can be applied to more accurately assess the exposure of organisms to metal(loid)s and thus to better estimate the links between soil contamination and effects. For humans, the unified bioaccessibility method (UBM) assesses oral bioaccessibility, while for soil fauna such as land snails, the bioaccumulation test reflects the bioavailability of contaminants. The aim of this study is to explore the relationship between oral bioaccessibility and the bioavailability of arsenic, cadmium and lead in twenty-nine contaminated soils. The results show a modulation of bioaccumulation and bioaccessibility of metal(loid)s by soil physicochemical parameters (organic matter especially). For the three metal(loid)s studied, strong relationships were modelled between the UBM and snail tests (0.77 < r²_adj.<0.95), depending on the parameters of the linear regressions (contaminant and phases of the UBM test). The original models proposed demonstrate the feasibility of linking bioaccessibility to humans and bioavailability to snails and the relevance of their association for an integrative risk assessment of contaminated soils.

Cd, Pb and Zn oral bioaccessibility of urban soils contaminated in the past by atmospheric emissions from two lead and zinc smelters

Ingestion of dust or soil particles could pose a potential health risk due to long-term metal trace element (MTE) exposure. Twenty-seven urban topsoil samples (kitchen garden and lawn) were collected and analyzed for Cd, Pb and Zn using the unified Bioaccessibility Research Group of Europe (BARGE) method (UBM) test to estimate the human bioaccessibility of these elements. The quantities of Cd, Pb and Zn extracted from soils indicated, on average, 68, 62 and 47% bioaccessibility, respectively, in the gastric phase and 31, 32 and 23% bioaccessibility, respectively, in the gastro-intestinal phase. Significant positive correlations were observed between concentrations extracted with UBM and total MTE contents. Stepwise multiple regression analysis showed that human bioaccessibility was also affected by some physico-chemical soil parameters (i.e. total nitrogen, carbonates, clay contents and pH). The unified test presents some valuable data for risk assessment. Indeed, the incorporation of oral bioaccessible concentrations into risk estimations could give more realistic information for health risk assessment.