Risk assessments of contaminated sediments from the perspective of weight of evidence strategies – a Swedish case study

Figures & data

Figure 1. Framework for Ecological Risk Assessment. Adapted from U.S. Environmental Protection Agency (USEPA) 1998.

Table 1. Overview of the ERAs included in the present study.

ERAs	Overview
A	Harbor sediments were known to be substantially contaminated from historical industrial activities and boat traffic. The contaminants included Ar, Cd, Cu, Hg, Ni, Pb, Zn, PCBs, dioxins and TBT. The overall purpose was to limit environmental effects and remove the outflow of contaminants from the harbor; the aim of the ERA was to establish the extent of the contamination in order to develop remediation alternatives.
B	Lake sediments were known to be contaminated with dioxin from historical industrial activities. The aim of the ERA was to ensure that contaminants did not pose a considerable environmental risk.
C	Lake sediments were suspected to be contaminated by a onetime oil leakage from a neighboring industrial site. The aim of the ERA was to determine what contaminant pressure the area would be able to withstand, in order to determine the need for potential mitigating management.
D	Same site as for ERA C. The lake sediments were now known to be contaminated with PAHs. The purpose was to assess the risk of effects and potential spread of PAHs from the sediment.
E	The sediments in a river bay, close to an estuary, were known to be contaminated with mercury from former pulp industry. The aim of the ERA was to assess the need of mitigation of environmental risks in situ and the spread to surrounding water bodies in order to device a management plan.
F	Sediments in a stream were suspected to be contaminated, mainly with pyrite ash. The purpose of the ERA was to assess the risks to human health and the environment and provide the basis for a management plan. The aim was to achieve levels of metals in the water column at background levels and the colonization of a gastropod community in the area.
G	Lake sediments in a bay were known to be contaminated with PAHs from the use of creosote in neighboring industrial and harbor activities. The aim of the ERA was to conduct an in-depth assessment, focusing on biological risks. The aim was to provide information to determine the need and scope of mitigating management.

Figure 2. General framework for ERA of contaminated sediments, based on frameworks from strategies described by Algar et al. 2014; Anderson et al. 2008; Breedveld et al. 2015; and den Besten et al. 2003, with details of what lines of evidence (LOEs) are assessed at each step in each country. *The ERA can proceed directly to management if the costs for tier 2 outweighs the cost for a continued assessment.

Table 2. Decision matrix adapted from Van Elswijk et al. (2001) and Anderson et al. (2008b ) . The matrix indicates the need of remediating actions or additional investigations. The white symbol indicates that adverse effects are unlikely and the black indicates likely or definite adverse effects.

Sediment contaminants	Toxicity	Benthos alterations	Biomagnification (Canada only)	Course of action
○	○	○	○	No further actions are needed.
•	○	○	○	No further actions are urgent.
•	○	•	•	Test additional field parameters.
•	○	•	○	Assess cause of benthos alteration.
•	•	•	•	Management actions are urgent.

Table 4. The boxes indicate that an ERA has described the use of measurements equivalent to a LOE as described in the strategy documents (Table 3). A filled box indicates a non-negligible risk; an empty box indicates negligible risk.

Lines of evidence
		Environmental risk assessment (A-G)
	A	B	C	D	E	F	G
Contaminant concentrations in sediment	▪	▪**	▪	–	▪	▪	▪
Bioaccumulation and Biomagnification	□	□	–	–	▪	□	–
Human exposure	□	□	–	–	□	□	–
Benthic community structure	▪	–	–	–	▪	▪	▪
Biomarkers	–	–	–	–	□	–	▪
Contaminant transport	▪	–	–	□	▪	□	▪
Sediment toxicity	–	–	–	–	–	–	▪
Tier*	2	2	1	2	2	1–2	2
Conclusion	Risk	No risk	Risk	No risk	Risk	Risk	Risk
Mitigation recommended	Yes	No	No	No	Yes	Yes	Yes^‡
Calculated cost for recommended action in millions of US dollars^$	55	0	0	0	8 − 86	Up to 0.3	NA

* The tiers are based on whether or not the assessment is based on suspected but not confirmed risks (Tier 1) or if a risk is known but is yet to be quantified (Tier 2). ^$In millions of US dollars at the exchange rate of 2019-04-10.

** ERA B detected contaminant concentrations in lake sediments equal to or lower than average concentrations in Baltic Sea sediments and concluded that there was a negligible risk. However, the concentrations were also compared to, and exceeded, SQGs.

‡ Additional investigations were recommended as well as mitigation.

Table 3. The lines of evidence (LOEs) and the environmental variables and assessment criteria prescribed for ERA of contaminated sediments by four nations. Depending on country, the LOEs are prescribed to be conducted either in specific tiers, in general or in addition to the general LOEs. Assessment criteria are criteria that, if exceeded, indicate risk.

LOE	Canada	The Netherlands	Norway	The US
Contaminant concentrations	1^st tier	1^st tier	1^st tier	General LOE
Environmental variables assessed	Contaminant concentrations	Contaminant concentrations normalized according to national standards.	Average contaminant concentrations.	Contaminant concentrations
Assessment criteria	Biomagnifiable contaminants above detection limit. Conservative SQG predicting effect on >5% of benthic fauna and/or concentrations >20% compared to in reference area.	National SQG for human health and ecological effects.	National SQG for ecological effects.	Case specific. Low weight in WOE compared to LOEs assessing biological responses.
Sediment toxicity	2^nd tier	2^nd tier	1–2^nd tier	General LOE
Environmental variables assessed	Four optional taxa and endpoints.	2 species – fecundity, development and mortality. Bacteria luminescence with Microtox test.	3 species – growth inhibition, mortality and larval development. 2^nd tier: 1 out of 2 species – mortality. Bacteria luminescence with Calux test.	Species and endpoints based on protection endpoints. Whole sediment preferred to porewater extracts.
Assessment Criteria	One or more sediment endpoints >20% difference from reference. Lower weight than field surveys.	Statistical significance p < 0.05. Criteria for moderate and strong effects for mortality, fecundity and bioluminescence.	Tier 1: >5% effect Tier 2: >20% mortality	Case specific
Biomagnification or bioaccumulation	1 -3^rd tier	2^nd tier	2 - 3^rd tier	General LOE
Environmental variables assessed	Sediment concentrations in tier 1, case-specific exposure models in tier 2 and field measurements in tier 3.	Laboratory tests or field measurements.	Calculations complemented by measurements in tier 3.	Modeling, followed by measurements if needed.
Assessment Criteria	Tier 1: Biomagnifiable contaminants in concentrations exceeding criteria. Tier 2: Case-specific conservative models for potential biomagnification.	National criteria for human exposure	≥10% of human TDI*	Case specific
Benthic community	2^nd tier	2^nd tier	Optional in 3^rd tier	General LOE
Environmental variables assessed	Highest weight in WOE. Replace if not appropriate due to site characteristics.	Case specific	Case specific	Case specific
Assessment Criteria	Statistically significant difference from reference area.	Statistically significant difference from reference area.	Case specific	Case specific
Human health	1^st and 2^nd tier	2^nd tier	2^nd tier	Additional line of assessment
Environmental variables assessed	Biomagnification	Biomagnification and dermal contact	Biomagnification and dermal contact
Assessment Criteria	Tier 1: Biomagnifiable contaminants present above background concentrations. Tier 2: Conservative models indicate potential biomagnification.	National criteria for human exposure	≥10% of human TDI*	Case specific
Contaminant transport	Optional in 3^rd tier	2^nd tier	2^nd and 3^rd tier	Additional line of assessment
Environmental variables assessed	Case specific	Modeling contaminant fluxes from sediment to groundwater or surface water.	Biodiffusion and resuspension modeling followed by complementary measurements.	Case specific
Assessment Criteria	Case specific	National criteria	Local criteria	Case specific
Biomarkers	Optional in 2^nd and 3^rd tier	–	Optional in 3^rd tier	General LOE
Environmental variables assessed	Case specific		Case specific	Pathology of resident/exposed organisms
Assessment Criteria	Case specific	–	Case specific	Case specific
In situ toxicity test	-	–	–	Additional LOE
Environmental variables assessed	–	–	–	Case specific
Assessment Criteria	Case specific	–	–	Case specific
Toxicity identification evaluation	Optional in 3^rd tier	–	–	Additional LOE
Environmental variables assessed	Sediment toxicity	–	–	Case specific
Assessment Criteria	Toxicity	–	–	Case specific
Critical body residue	Optional in 3^rd tier	–	–	–
Environmental variables assessed	Substances suspected to cause toxicity in tissue.
Assessment Criteria	Case specific	–	–	–

* Total Daily Intake.

References for each LOE: Contaminant concentrations (den Besten et al. 2003; Anderson et al. 2008, 8–9; Algar et al. 2014, 131–135; Breedveld et al. 2015, 7–8, 15). Sediment toxicity (den Besten et al. 2003; Anderson et al. 2008, 12; Algar et al. 2014, 132–133, 135; Breedveld et al. 2015, 3, 7–8, 18, 26). Bioaccumulation and biomagnification (den Besten et al. 2003; Anderson et al. 2008, 8, 12, 28; Algar et al. 2014, 110–111, 131–133; Breedveld et al. 2015, 32). Benthic community (den Besten et al. 2003; Anderson et al. 2008, 3, 8, 13, 15, 29; Algar et al. 2014, 6, 8, 133; Breedveld et al. 2015, 46–47). Human health (den Besten et al. 2003; Anderson et al. 2008, 2, 8; Algar et al. 2014, 110; Breedveld et al. 2015, 8, 12, 26, 38–39). Contaminant transport (den Besten et al. 2003; Anderson et al. 2008, 28; Algar et al. 2014, 25–77; Breedveld et al. 2015, 8, 26, 31, 43–44). Biomarkers (Anderson et al. 2008, 28; Algar et al. 2014, 133, 146; Breedveld et al. 2015, 46). In situ toxicity (Algar et al. 2014, 141). Toxicity identification evaluation (Anderson et al. 2008, 29–30; Algar et al. 2014, 131). Critical body residue (Anderson et al. 2008, 29–30).

Table 5. Measurements and benchmarks used in seven Swedish ERAs to assess risk.

LOE/ERA	A	B	C	D	E	F	G
Sediment contaminants	Background concentration^1	Background concentrations^1 and Canadian SQG.	Guideline values for soil.^5		Background levels.	Guideline values for soil.^8	Canadian SQG.
Contaminant transport	Concentrations in water compared to background concentrations.^1 Modeled transport to adjacent water body, compared to that of other sources.			Passive samplers in water column compared to Dutch guidelines.^6	Concentrations in water compared to background concentrations.^1 Modeled transport to adjacent water body, compared to that of other sources.	Concentrations in water compared to background concentrations.^1	Measures of local sedimentation rates to determine natural attenuation.
Bioaccumulation	Background concentrations^1				Guidelines for consumption of fish. Background concentrations for gastropods.	Gastropod tissue concentrations compared to reference area. Fish tissue concentration compared to background concentrations. No reference
Human health	Dutch SQG for sediment concentrations. Guidelines for consumption of fish.	Fish tissue concentrations compared to EU consumption guidelines.			Concentration in water compared to background concentrations and guidelines for consumption. Fish tissue concentrations compared to EU consumption guidelines.^7	Fish tissue concentration compared to guidelines for consumption.
Benthic community					Benthic community structure compared to reference area	Abundance of gastropod Radix balthica compared to reference area.	Benthic community structure compared to historic reference and index of stress tolerance.
Biomarkers							PAH metabolites and EROD compared to a reference area.
Toxicity test							Microtox bioluminescence test compared to clean sediment control

References used by the ERAs: ¹Swedish Environmental Protection Agency (SEEPA) 2007; ² Reference no longer available; ³No references given; ⁴Canadian Council of Ministers of the Environment (CCME) 2002; ⁵Swedish Environmental Protection Agency (SEEPA) 2009; ⁶VROM (Ministerie van Volkshuisvesting Ruimtelijke Ordening en Milieubeheer) 2000; ⁷EU (Council of the European Union) 2001; ⁸No given reference but likely Swedish Environmental Protection Agency (SEEPA) 2009.

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