Probabilistic Ecological Risk Assessment and Effectiveness of Biochar as a Gentle Remediation Option (GRO)

Abstract

The historical use of DDT still impacts the soil where it was once used despite a half-century long ban, and its presence can still potentially be harmful to local ecosystems. One important area where DDT was used was forest nurseries and many are still contaminated above soil guideline values. This thesis aimed to create a probabilistic ERA model to estimate the ecological risk for top predators from DDT-accumulation through diet at the Kolleberga forest nursery in southern Sweden. It also aimed to evaluate the effectiveness of lowering the ecological risks by implementing biochar using data provided by an ongoing pilot experiment at the site. The investigated species were red kite, common buzzard, great spotted woodpecker, common raven, badger and weasel. The thesis is a follow-up study with additional developments from a previous study in the area. The developments were dividing the area into subareas based on the former forest nursery use with different distributions of more recently obtained DDT-concentrations and incorporating home range into the model. Site-specific BAFs for leaves, grass, and earthworms (soft invertebrates) were provided from the ongoing pilot experiment. The parameters where no sitespecific data was available were sourced from literature. The results showed that there is a high probability of exceeding HC5 for many of the analyzed species. Implementing biochar lowered the BAF for all evaluated food groups, but more sitespecific data is needed to evaluate the full effects of its implementation. The risk was seen as high enough to suggest preliminary remediation options. Excavation was seen as suitable for the geographically small hotspot areas while biochar can be used on the field. More site-specific data for BAFs, home ranges, and local diets of the analyzed species would be needed to get more accurate results. Suggested further research includes collection of local home range, dietary, and BAF data, implement a weighting system for home range, extending the model to include more species and performing cost-benefit analyses.