Evaluating the effectiveness of gentle remediation options (GRO) on a DDT-contaminated site - A case study of the Kolleberga plant nursery site

Abstract

Due to the extensive use of pesticides in the mid-nineties, DDT (Dichlorodiphenyltrichloroethane) and its metabolites (DDE and DDD) are still present in the soil, posing a risk to different ecosystems. In Sweden, it's estimated that there are about 750 contaminated sites with DDT with a high risk of harming humans or the environment. Kolleberga forest nurseries are one of these contaminated sites. Due to its large area and high soil volume, environmentally friendly options such as Gentle Remediation Options (GRO) were suggested as a good alternative for their low cost and sustainability. This thesis is part of an ongoing research project conducted by Chalmers University to evaluate the effectiveness of different GRO strategies at Kolleberga plant nursery. The specific objectives of this thesis are i) to evaluate the ability different of GRO strategies to manage the risks of DDT using statistical methods, and ii) to carry out a detailed risk assessment study for two potential future land use scenarios for the site to evaluate the level of the risk and potential remediation needed. A literature review was conducted to understand the history of DDT contamination, available sustainable remediation techniques, DDT health risks to both the environment and humans; and source to potential receptors pathways (exposure and spreading). Statistical analysis (ANOVA) was conducted using IBM SPPS software to evaluate the effectiveness of phytostabilization and phytoextraction (GRO techniques) to manage the risks posed by DDT in the soil at the Kolleberga plant nursery. The results from the statistical analysis conclude that biochar had a significant impact (i.e., lower DDT concentrations) on the soil pore water concentration. This reduction was also seen in DDT uptake in earthworms. However, this study observed that there is no significant impact on the uptake of DDT in biomass for both grass and legume (phytostabilization) and the stabilization effect of biochar. Pumpkin roots (among leaves, stems & roots) could extract DDT significantly when biochar is added, however, no significant effect of pumpkin alone was observed, even though uptake is higher than grass and legumes. There is no influence of biochar on DDT to DDD or DDT to DDE transformation. Also the plant treatments alone do not significantly impact the degradation process. The ineffectiveness of GRO strategies might be due to soil and weather conditions at the site, anyway, biochar is found effective. Therefore, aided phytoremediation could be recommended to treat the Kolleberga plant nursery. An ecological risk assessment was carried out for two future land use scenarios (a planned tree nursery and a horse-riding center). For the first scenario, a qualitative method was conducted using the available data for DDT uptake in earthworms and assumptions regarding DDT bioavailability. While for the second scenario, a quantitative method was used using exposure equations developed specifically for horses. The results of this study concluded that the implementation of GRO, specifically aided-phytostabilization using biochar reduced the uptake of DDT in earthworms and so reduced the possibility of secondary poisoning to other mammals and predators. The site can be considered safe for keeping horses as the exposure levels of DDT pose no risk to both humans and horses even when they feed on grass planted on the site. However, more studies and research are still needed to further analyze the risks for other animals (predators and mammals), especially in the case of keeping grazing animals at the site for meat production and to produce other animal products such as meat, eggs, and dairy for human consumption.