Today, there are approximately 40 former forest nurseries in Sweden with potentially high DDT concentrations. It would be both costly and unsustainable to excavate large amounts of the agricultural soil if the risks of negative impacts on human health and the environment are negligible. Therefore, it’s preferable to assess site-specific risks.
From the 1950s through to the 1980s, Sweden’s National Forestry Board operated a forest nursery in Kårehogen, Sweden to grow spruce trees. Several different pesticides were used in the process, including DDT. The concentration of DDT there is higher than the Swedish generic guideline value for soil (NV-KM).
The TRIAD is based on the chemistry, (eco)toxicology and ecology lines of evidence (LOE). The purpose is to assess if there is a link between the concentration and toxicity of the contaminant and ecological outcomes.
To investigate whether the soil ecosystem in Kårehogen was negatively affected by DDT, Golder compared on-site results to a reference area. The results for the various LOEs including the results of statistical analyses were evaluated through a qualitative method (cause-effect analysis) and a quantitative method (risk index calculations).
The surveys (performed by sub-contractors) included analysis of DDT levels in soil and earthworms (chemistry LOE), effects on reproduction of earthworms and springtail insects (toxicology LOE), and the carbon and nitrogen mineralization and species composition of earthworms, springtails and roundworms (ecology LOE).
The results showed insignificant risk of negative impacts on the soil ecosystem function (excluding hot-spots), and the assessed livestock, birds and larger mammals. The risk was also assessed to be insignificant for residents or visitors under the current circumstances. Although a theoretical risk exists for small mammals and children at certain circumstances if consumption habits changes compared to today. Further investigations are, however, needed to assess if there is an actual risk.
This project confirmed that the TRIAD method is appropriate for assessing the site-specific risks to soil ecosystem function posed by the prior use of DDT at the site. However, a suitable reference area or good concentration gradient is required. The quantitative evaluation method is considered useful for prioritizing risks between areas, while the qualitative method is useful to determine if there is a level of risk or not.
The results from this project will be evaluated against other contaminated forest nurseries.