A Preliminary Assessment of As and F Uptake by Plants Growing on Uncontaminated Soils

In Australia, the regulatory framework for assessing the risk of soil contamination assumes there is minimal risk from the natural enrichment of potentially toxic elements in soil. When this assumption is applied to land cleared for anthropogenic purposes, non-adapted biota including humans, domestic animals and garden plants can be exposed to these soils. While the impacts of natural arsenic (As) and fluorine (F) in waterways are widely reported, little is known about the biological impacts of natural As and F in non-aquatic soils. We investigated four field sites with naturally elevated soil As and F around Melbourne, Australia. All sites were assessed for As and F in soil, tree and herb (grasses and forbs) foliage. Soil concentrations of As and F ranged from near to above mean ambient background concentrations for Victoria. Soil As and F under trees were consistently higher than under herbs, suggesting deeper tree roots resulted in translocation and accumulation of As and F from deeper soil layers. While surface soil enrichment by plants is known for nutrients, there is less information about enrichment of potentially toxic elements. No clear relationships between soil and foliar As/F concentrations were found. However, there was a range of As and F accumulations in foliage across the four sites: from low to concentrations representative of contaminated sites and above regulatory guidelines. We demonstrated that soils naturally enriched in As and F can be bioavailable and accumulated in plant foliage. Thus, we suggest reassessment of the assumption in Australian guidance that naturally elevated concentrations of potentially toxic elements are not bioavailable and pose minimal risk.