Trace elements in soils from reclaimed lands and their bioavailability in wild berries

Open-pit mining severely disturbs land by removing vegetation, altering soils, degrading soil structure, and promoting soil erosion and nutrient loss. Waste rock and tailings can release toxic trace elements (TEs), which may be taken up by plants and transferred through the food chain, thereby exposing humans and wildlife to contamination. These long-lasting ecological and health risks highlight the need for soil rehabilitation, vegetation recovery, and ongoing environmental monitoring.

Within this context, reclaimed sites located in a bitumen mining and upgrading area in Alberta, Canada, were selected to: (i) assess the potential bioavailability and transfer of TEs from cover soils to wild berries growing on them; (ii) evaluate the extent to which TEs are enriched in berries from reclaimed lands compared to natural background levels; and (iii) compare TE concentrations in berries with existing thresholds intended for human consumption.

Following metal-free, ultra-clean laboratory procedures, soils and eight species of unwashed berries collected in 2024 were dried and milled, digested in HNO₃, and analyzed using ICP-MS. Phytoavailable TEs in soils were determined following extraction with DTPA. Micronutrients (Cu, Mn, Ni, and Zn), bitumen-enriched elements (Mo, Re, Se, and V), and chalcophile elements (As, Ag, Cd, Pb, Sb, and Tl) were below the remediation guidelines for natural areas in Alberta. Average TE concentrations in these soils were also lower than those reported for soils worldwide and were either lower than or comparable to concentrations in regional parent materials. Based on DTPA soil extracts, it was estimated that 0.1–23% of bitumen-enriched elements, 0.1–75% of chalcophile elements, and 0.1–25% of micronutrients are potentially available for plant uptake.

To distinguish between TE deposition on berry surfaces and root uptake, linear regressions were performed between TE concentrations and conservative lithophile elements (Al, Th, and Y), and Y-normalized TE concentrations in berries were compared with those in soils. These analyses indicate that As, Sb, Pb, Tl, and V are predominantly deposited on berry surfaces (R² > 0.6), whereas Ag, Cd, Cu, Mn, Mo, Ni, and Zn (R² < 0.6) are primarily taken up from the soil. Iron, an essential and abundant element in soils, occurs both internally and on the surface of berries. With the exception of Mn and Mo, TE concentrations in unwashed berries from reclaimed sites were 2-fold (Cd, Cu, Zn) to 38-fold (Y) higher than those measured at remote locations. These differences are attributed to berry species as well as greater dust deposition at reclaimed sites compared to remote areas.

After accounting for the average berry water content (80%), TE concentrations were 7–17 times lower than EU guidelines for safe consumption (30–40 µg/kg for Cd and 100 µg/kg for Pb). However, these results should be interpreted cautiously, as population-related factors such as age, dietary habits, and risk perception must also be considered.