A Deep Dive into Sediments : Exploring approaches to assess environmental risks and achieving environmental goals in management of contaminated sediments in Sweden

Abstract: Contaminated sediments are common, especially near urban and industrialized areas, and they can have negative ecological effects. In three studies, I explore the challenges for environmental management of contaminated sediments, focusing on environmental risk assessment (ERA) in Sweden. I investigate the scientific basis and ecological relevance of the knowledge that is produced in, and evaluated from, assessments. I then relate that knowledge to environmental goals set for general management, but also within individual assessments.Study I identified environmental goals set by society that ERA of contaminated sediment sites should address through a survey conducted among governmental agencies working with contaminated sediment. To investigate to what extent the practice of ERA addressed the goals which had been identified in the survey, the study also analyzed seven cases of ERA, from 2008-2015. Study II reviewed established strategies for assessing risks from contaminated sediments, from four countries. Then, with the ERAs included in study I, the Swedish ERA practice was characterized and contrasted to the review. Study III investigated to what extent dumping dredged sediment at sea was used as an alternative to manage dredged sediments. The study further investigated how courts, in 14 cases from 2015-2020, evaluated environmental risk when considering to allow dumping.The five environmental goals identified as most relevant focused on ecosystem services and management of environmental resources. While the ERAs occasionally addressed these goals, their priorities were not well aligned with that of the agencies (I). In studies II-III, the case-specific goals were not clearly addressed with the methods used. The results indicate that there is a focus on contaminant concentrations and sediment mobility. Four out of the seven ERAs in study II, and none in study III, measured potential effects from contaminants. The ERAs in study II surveyed benthic species and one conducted a toxicity test. When characterizing risk, there was also a frequent use of references not related to toxicity (II-III). Furthermore, uncertainties were not quantified and rarely discussed. Transparency was lacking regarding what weight individual types of measurements had in characterizing risk (II). In study III, sediment accumulation and contaminant concentrations were the decisive factors. However, in evaluating concentrations, the courts’ reasoning was inconsistent. The ERA practice in Sweden does not clearly produce the information needed to effectively characterize or evaluate risk in line with case specific or societal goals and risk underestimating the risks from contaminated sediments.Additional development and research could improve the capability to produce information for efficient management. Issues that should be addressed are, for example, requirements and guidance for designing case specific ERAs, including setting measurement and assessment endpoints in line with the ERA goals; additional types of measurement of contaminant effects; a system for criteria when characterizing risk; and requirements and guidance for how to consider future changes of site-specific conditions, such as climate change.This thesis highlights some of the potential and limitations in the Swedish practice to inspire management in how to incorporate existing best available methods as well as point to additional research needs.