A Tiered Risk Assessment Approach for Assessing Soil Contamination in an Area Adjacent to a Chemical Complex

Inadequate solid waste management and liquid effluent discharged into neighbouring waterways in the past caused serious environmental problems to the area surrounding the Estarreja Chemical Complex (ECC), which is located in northwest Portugal. Nevertheless, a comprehensive environmental risk assessment (ERA) procedure has yet to be undertaken. Starting with Tier 0, data collection and mapping, this work aims to design a tiered ERA for this region. Initial findings suggest that the legacy of ECC past activities may harm the ecosystem, particularly around the main ditch used to transport effluents to the Ria the Aveiro lagoon. Therefore, a Tier 1 was followed, with efforts focused on the vicinity this ditch. This step, in addition to identify the risks due to the presence of contaminants in soils, intended to optimize the approach for larger-scale assessment. This study involved the collection of 23 composite soil samples, which were subjected to comprehensive analysis to assess their fundamental soil characteristics, including pH, organic matter content, electrical conductivity, and water holding capacity. The chemical Line-of-evidence (LoE) included the determination of 34 inorganic elements (Aqua regia digestion and determination by ICP-MS or AES) and of 200 organic compounds (TerrAttesT®). The ecotoxicological LoE included a set of assays with terrestrial and aquatic organisms: seed germination of three terrestrial plants, earthworm avoidance, microalgae and aquatic plant growth inhibition, inhibition of the bioluminescence of an aquatic bacteria, acute immobilisation of a crustacean. The estimation of environmental risk associated with the presence of contaminants in soils was further conducted based on these two LoE. The occurrence rate of samples surpassing the established soil screening values, as well as the magnitude of the values, suggest the continued presence of contamination at the site. However, the impact on terrestrial and aquatic ecosystems appears to be less severe than initially anticipated, with several species showing no significant effects. The inconsistencies between the two LoE indicated a high level of uncertainty, thereby requiring further investigation at Tier 2. Thus, a Tier 2 analysis was conducted to evaluate the chemical availability of contaminants in the soil and perform other ecotoxicological assays, which involved measuring biomass production, earthworm reproduction and biomarkers of exposure. The obtained findings allowed a more comprehensive understanding of the (bio)availability of contaminants in soils and enduring consequences of soil pollutants, while also elucidating any apparent inconsistencies from the preceding Tier.