Epsilon Archive for Student Projects

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.