Using environmental conservation units as reference for evaluating contamination in river basins

Risk assessment of sediment quality relies on using local references as a guiding criterion. However, there are knowledge gaps regarding the criteria for defining (choosing) reference sites free from contamination on the river basins scale. Under this perspective, this study establishes appropriate baselines (backgrounds) for the Várzea River basin - RS, using different criteria based on the average concentrations of the elements Al (10539.4–12454.7 mg kg⁻¹), Ba (6.0–62.0 mg kg⁻¹), B (23.0–140.4 mg kg⁻¹), Ca (990.0–3859.1 mg kg⁻¹), Co (9.6–11.1 mg kg⁻¹), Cu (36.3–234.2 mg kg⁻¹), Fe (46091.0–92750.9 mg kg⁻¹), Li (136.4–147.8 mg kg⁻¹), Mg (149.9–500.2 mg kg⁻¹), Mn (336.4–1894.1 mg kg⁻¹), K (557.0–748.5 mg kg⁻¹), Ag (0.0–70.5 mg kg⁻¹), Na (70.5–1447.4 mg kg⁻¹) and Sr (8.2–1344.0 mg kg⁻¹), which are common in the region's soils, determined from samples collected in highly preserved environmental conservation areas. The study's background results demonstrate that the use of inadequate and/or non-representative local references as an indicator of environmental quality can lead to either overestimation or underestimation of environmental contamination. The Robustness Method proved to be most suitable for assessing environmental quality in this hydrographic basin.