Cobalt and nickel concentrations in the Uppsala clay deposits : solubility and risk assessment

Abstract: Heavy metals create a contamination problem in soils. Examples of heavy metals are Ni, Co, and Cu. Soil environment and minerals existing in the soil such as Fe and Mn oxides affect the presence of these heavy metals. In this thesis, the cobalt and nickel concentrations of selected soil samples from different locations in Uppsala were determined. Then risk assessment was performed based on two different tools, the Swedish guideline model for contaminated soils and the Threshold calculator. The output from these two methods is being discussed. The Swedish model provides generic guideline values for different risk objects such as humans, environment, natural sources, and the soil environment. On the other hand, the threshold calculator is focusing particularly on the ecotoxicological threshold concentration of metals. In addition, the toxicity effect on different soil trophic levels is being calculated. The obtained total concentrations of Co and Ni in the soil samples were compared to the Swedish generic guideline value. If the value exceeds the limitation provided by the Swedish Environmental Protection Agency (SEPA) then a leaching test is required. The leaching test will provide extracted concentrations of Co and Ni in the soil samples. Based on this, the partition coefficient (the Kd value) is obtained. The value of the partition coefficient (Kd) determines the mobility of metal in the soil environment. Derivation of a site-specific guideline value helps to determine a new guideline value for different risk levels and protection objects based on the SEPA risk assessment tool. The above is performed by both methods (risk assessment with SEPA- and threshold calculator). One of the advantages of using the Threshold calculator risk assessment tool is that it focuses only on an ecotoxicological threshold concentration of metals. However, the SEPA provides an integrated guideline for the soil environment, human health, groundwater, and surface water. In the report, I explain more about why the threshold calculation is required. The values obtained by SEPA for the soil environment is replaced by values obtained by the threshold calculator. The new guideline values of Co and Ni are used to find the new value of other parameters, which were impossible to determine by the Threshold risk assessment method alone. This way of determining the protection level presents a new way of combining the two tools to get a more accurate picture of the actual risk of heavy metals in contaminated soils.