Heavy metal distribution, bioaccessibility, and phytoavailability in long-term contaminated soils from Lake Macquarie, Australia

This study was conducted to investigate the distribution, bioaccessibility, and phytoavailability of heavy metal(loids) in long-term contaminated soils within the vicinity of a lead (Pb) and zinc (Zn) smelter in Lake Macquarie, NSW, Australia. Thirty-two representative surface (0–100 mm) soils were collected from the region surrounding the smelter. The soils were analysed for aqua regia extractable heavy metals (Cu, Zn, Cd, Pb), bioaccessibility using a simplified physiological-based extraction technique (SBET), and phytoavailability using 1 m NH4NO3 extractions, together with key soil properties known to influence metal speciation and availability. The area was found to be potentially contaminated with heavy metals (Cu, Zn, Cd, Pb) with many soil samples exceeding the Australian Health Investigation Levels for ‘Standard’ residential areas. Lead bioaccessibility ranged from 32 to 100% of the total Pb concentration, with bioaccessibility increasing as metal loading increased. Heavy metal phytoavailability was strongly related to soil pH for Cu (r2 = 0.84, P < 0.001), Pb (r2 = 0.70, P < 0.001), and Cd (r2 = 0.66, P < 0.001), implying that the phytoavailability of these heavy metal was mainly governed by soil acidity. Most significantly, the presence of multiple metals was found to influence metal phytoavailability. For example, the presence of Pb significantly influenced the phytoavailability of Cd (r2 = 0.89, P < 0.001) and Zn (r2 = 0.78, P < 0.001) in mixed heavy metal contaminated soils.