To improve risk estimates at the screening stage of Ecological Risk Assessment (ERA), short duration bioassays tailored to undisturbed soil cores from the contaminated site could be useful. However, existing standardized bioassays use disturbed soil samples and often pH sensitive organisms. This is a problem as naturally acidic soils are widespread. Changing soil properties to suit the test organism may change metal bioavailability, leading to erroneous risk estimates. For bioassays in undisturbed soil cores to be effective, species able to withstand natural soil properties must be identified. This review presents a critical examination of bioassay species' tolerance of acidic soils and sensitivity to metal contaminants such as Pb and Zn. Promising organisms include; Dendrobaena octaedra, Folsomia candida, Caenorhabditis elegans, Oppia nitens, Brassica rapa, Trifolium pratense, Allium cepa, Quercus rubra and Acer rubrum. The MetSTICK test and the Bait lamina test were also identified as suitable microorganism tests.

Metal resistance in populations of Acer rubrum and Betula papyrifera in the industrially contaminated region of Sudbury, Ontario, was compared with resistance in populations from neighbouring uncontaminated regions. In two one-season experiments, seedlings were grown outdoors on contaminated (mainly Cu, Ni) and uncontaminated substrates. Sudbury populations of both species responded less to contamination than populations from uncontaminated regions. In A. rubrum this difference was small. For both species, Sudbury plants were smaller when grown on uncontaminated substrate. B. papyrifera from Sudbury grew better on contaminated substrate than the other populations. There is indication of variation in metal resistance within the populations from the non-contaminated regions. The data shows that trees may develop adaptive resistance to heavy metals, but the low degree of resistance indicates that the development of such resistances are slower than observed for herbaceous species with shorter generation times.

The concentrations of heavy metal (copper (Cu), mercury (Hg), manganese (Mn), nickel (Ni), lead (Pb), and zinc (Zn)) were measured in Acer(A.) pseudoplatanus tree bark to evaluate its suitability as a bioindicator of air pollution in downtown Toronto, Canada. The analysis of digested tree bark samples was carried out by inductively coupled plasma optical emission spectrometry (ICP-OES) for Cu, Mn, Ni, Pb, and Zn, whereas a mercury analyzer was used to quantify Hg without sample pre-treatment. The concentrations of the analyzed heavy metals were found to be 26.4 μg g⁻¹ for Cu, 51.7 μg kg⁻¹ for Hg, 55.3 μg g⁻¹ for Mn, 6.55 μg g⁻¹ for Ni, 26.5 μg g⁻¹ for Pb, and 95.2 μg g⁻¹ for Zn. Analysis of background control tree barks (collected in a remote area) showed that maple tree barks in Toronto were strongly enriched with heavy metals, with their mean accumulation factors ranging between 1.88 (Mn) and 12.54 (Pb). The tree bark was also found to distinguish between impacted areas as the locations close to the roads with elevated vehicular traffic showed higher metal contents. Therefore, it could be concluded that A. pseudoplatanus tree bark is a good bioindicator of atmospheric heavy metal pollution.