Risk factors and assessment strategies for the evaluation of human or environmental risk from metal(loid)s – A focus on Ireland

Elevated human exposure to metals and metalloids (metal(loid)s) may lead to acute sickness and pose a severe threat to human health. The human body is exposed to metal(loid)s principally through food, water, supplements, and (occasionally) air. There are inherent background levels of many metal(loid)s in regional soils as a consequence of geological sources. Baseline levels coupled with anthropogenic sources such as regional application of biosolids may lead to increased levels of certain metal(loid)s in soil, leading to potential transfer to water sources and potential uptake by plants. The latter could potentially transfer into the feed-to-food chain, viz. grazing animals, and bio-transfer to food products resulting in human exposure. This study addresses health concerns due to excessive intake of metal(loid)s by conducting a traditional review of peer-reviewed journals between 2015 and 2019, secondary references and relevant websites. The review identified the most researched metal(loid)s as Cu, Zn, Pb, Cd, Ni, Cr, As, Hg, Mn, Fe in the environment. The potential uptake of metal(loid)s by plants (phytoavailability) is a function of the mobility/retainability of metal(loid)s in the soil, influenced by soil geochemistry. The most critical parameters (including soil pH, soil organic matter, clay content, cation exchange capacity, the capability of decomposition of organic matter by microbes, redox potential, ionic strength) influencing metal(loid)s in soil are reviewed and used as a foundation to build a framework model for ranking metal(loid)s of concern. A robust quantitative risk assessment model is recommended for evaluating risk from individual metal(loid)s based on health-based indices (Daily Dietary Index (DDI), No Observed Adverse Effect Level (NOAEL), and Lowest Observed Adverse Effect Level (LOAEL)). This research proposes a risk assessment framework for potentially harmful metal(loid)s in the environment and highlights where regulation and intervention may be required.