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Keywords:

  • Contaminated sediments;
  • Weight of evidence;
  • Toxicity;
  • Benthos;
  • Biomagnification

Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. THE SEDIMENT DECISION-MAKING FRAMEWORK
  5. Step 8: If necessary, conduct further assessments
  6. CONCLUSIONS
  7. Acknowledgements
  8. References

A decision-making framework for determining whether or not contaminated sediments are polluted is described. This framework is intended to be sufficiently prescriptive to standardize the decision-making process but without using “cook book” assessments. It emphasizes 4 guidance “rules”: (1) sediment chemistry data are only to be used alone for remediation decisions when the costs of further investigation outweigh the costs of remediation and there is agreement among all stakeholders to act; (2) remediation decisions are based primarily on biology; (3) lines of evidence (LOE), such as laboratory toxicity tests and models that contradict the results of properly conducted field surveys, are assumed incorrect; and (4) if the impacts of a remedial alternative will cause more environmental harm than good, then it should not be implemented. Sediments with contaminant concentrations below sediment quality guidelines (SQGs) that predict toxicity to less than 5% of sediment-dwelling infauna and that contain no quantifiable concentrations of substances capable of biomagnifying are excluded from further consideration, as are sediments that do not meet these criteria but have contaminant concentrations equal to or below reference concentrations. Biomagnification potential is initially addressed by conservative (worst case) modeling based on benthos and sediments and, subsequently, by additional food chain data and more realistic assumptions. Toxicity (acute and chronic) and alterations to resident communities are addressed by, respectively, laboratory studies and field observations. The integrative decision point for sediments is a weight of evidence (WOE) matrix combining up to 4 main LOE: chemistry, toxicity, community alteration, and biomagnification potential. Of 16 possible WOE scenarios, 6 result in definite decisions, and 10 require additional assessment. Typically, this framework will be applied to surficial sediments. The possibility that deeper sediments may be uncovered as a result of natural or other processes must also be investigated and may require similar assessment.


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. THE SEDIMENT DECISION-MAKING FRAMEWORK
  5. Step 8: If necessary, conduct further assessments
  6. CONCLUSIONS
  7. Acknowledgements
  8. References

Contaminated sediment is a global problem and can be a major impediment to restoration efforts in degraded aquatic environments. Although regulatory agencies and groups around the world are assessing contaminated sediments, to date there is no universal, pragmatic, decision-making framework for such sediments.

This article builds on previous publications regarding weight of evidence (WOE) sediment assessments (Chapman 1996; Krantzberg et al. 2000; Borgmann et al. 2001; Burton et al. 2002; Chapman, McDonald, et al. 2002; Grapentine et al. 2002; Ingersoll and MacDonald 2002; MacDonald and Ingersoll 2002a, 2002b; Reynoldson, Smith, et al. 2002; Suter et al. 2002; Apitz et al. 2005; Simpson et al. 2005). In this article, a requisite framework is proposed, which determines when contamination (defined as a condition in which substances are present where they would not normally be found or where they occur above natural background levels) becomes pollution (defined as contamination that results in adverse biological effects). The framework is explicitly based on ecological risk assessment principles (CCME 1996). Additional detail regarding this framework is available in Chapman (2005), a document that will form the basis for contaminated sediment decision-making in the Great Lakes under the 2002 Canada-Ontario Agreement Respecting the Great Lakes Ecosystem.

The framework is intended to be sufficiently prescriptive to standardize the decision-making process but without using a “cook book” assessment approach that would fail to acknowledge the influence of site-specific conditions on the outcome of the decision-making framework and prevent the appropriate use of best professional judgment. It is intended to be objective, transparent, scientifically rigorous, and readily understandable.

The framework is also intended to be rigid enough, without being inflexible, so that there is consistency between different contaminated sediment assessments, so that site-specific considerations can be appropriately addressed, and so that both localized and regional risks from contaminated sediments are determined. Although the basic framework is not expected to change over time, new knowledge is expected to change and improve the tools that comprise the different lines of evidence (LOE) within the framework. Accordingly, the best available science should be used in applying the framework. This will require suitable state-of-the-art expertise in the various disciplines comprising the framework.

The framework is specific for environmental concerns associated with contaminated sediment, including human health concerns related to biomagnification. The framework, however, is not concerned with human health risk assessment; that is, it does not address situations in which potential human health concerns are associated with dermal contact to contaminated sediment (e.g., swimming and wading), or by other exposure routes (e.g., flooding resulting in aquatic sediments contaminating residential soils or gardens). The framework does not address the issue of unacceptable levels of contaminants that do not biomagnify, such as cadmium (Cd), lead (Pb), and polyaromatic hydrocarbons, in fish or shellfish. In such situations, a screening-level human health risk assessment should be considered to assess potential risks and to inform the public.

THE SEDIMENT DECISION-MAKING FRAMEWORK

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. THE SEDIMENT DECISION-MAKING FRAMEWORK
  5. Step 8: If necessary, conduct further assessments
  6. CONCLUSIONS
  7. Acknowledgements
  8. References

Guidance for implementation

The primary guidance for implementation of this framework is that it be applied with common sense. In other words, it will not be applied inflexibly. In addition, there are 4 other guidance “rules” for the use of this framework:

  • 1.
    Sediment chemistry data, such as sediment quality guidelines (SQGs), will not be used alone for remediation decisions except for cases of “simple contamination where adverse biological effects are likely … when the costs of further investigation outweigh the costs of remediation, and there is agreement to act instead of conducting further investigations” (Wenning and Ingersoll 2002). This first case is intended to apply to small sites with a limited number of contaminants present at extremely elevated concentrations (e.g., levels well above predicted effects).
  • 2.
    Accordingly, any remediation decisions will be based primarily on biology not chemistry.
  • 3.
    LOE (such as information developed from laboratory toxicity tests and models) that contradict the results of properly conducted field surveys with appropriate power to detect changes (see Environment Canada 2002) “are clearly incorrect” (Suter 1996) to the extent that other LOE are not indicative of adverse biological effects in the field.
  • 4.
    If the impacts of a remedial alternative will “cause more environmental harm than leaving the contaminants in place,” that alternative should not be implemented (USEPA 1998).

The framework

The framework is tiered and proceeds through a series of sequential steps. Each step, however, does not need to be completed separately; 2 or more steps can (and, in some cases, should) be completed jointly (e.g., when time and costs constrain sampling and analysis). For example, if available data are insufficient to rule out management action, then sediment toxicity tests can be conducted before chemical analyses are conducted for all chemicals with a SQG. If toxicity tests show that the sediment is not toxic, then there would be no reason to determine chemical concentrations in the sediment related to toxicity.

The linear nature of the framework may vary to accommodate actions such as sample collections or analyses. For example, initial field sampling can involve measurement of all possible LOE (e.g., sediments for chemical analyses and toxicity testing; benthos for chemical analyses and taxonomy) with the recognition that although samples for some chemical analyses and taxonomy can be archived for future evaluation, those for toxicity testing cannot be archived and should be tested as soon as possible and no later than 8 weeks following collection (USEPA and USACE 1998).

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Figure Figure 1.. Decision-making framework for sediment contamination. SAP = sampling and analysis plan; COPC = contaminants of potential concern. For explanation of steps and decisions, see text.

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The framework is conceptually divided into a series of steps and decisions that correspond to different ecological risk assessment tiers: screening assessment comprises steps 1 to 3 and decisions 1 and 2; preliminary quantitative assessment comprises steps 4 to 6 and decisions 3 to 5; detailed quantitative assessment comprises steps 7 and 8 and decisions 6 and 7; and step 9 and decision 8 deal with deeper (than surficial) sediments. The framework is illustrated schematically in its entirety in Figure 1 and in terms of the different ERA tiers (Figures 2 to 5).

As noted by Jaagumagi and Persaud (1996), “Due to the complexity involved in evaluating contaminated sediment, it is essential that scientists with strong expertise in sediment chemistry (chemical fate, transport, and speciation), sediment toxicity testing, benthic community assessment, food chain effects, and environmental statistics assist stakeholder groups in the interpretation of the data. This is especially important in determining differences or effects of sediment contamination compared to reference conditions.”

Step 1: Examine available data

In the 1 st step of the framework, all readily available data are examined to determine:

  • Contaminants of potential concern (COPCs) and their concentrations at surface (e.g., <10 cm) and at depth (e.g., >10 cm);

  • Receptors of potential concern (ROPCs), that is, organisms that may be affected by COPCs;

  • Exposure pathways by which COPCs may reach ROPCs;

  • Any human health consumption advisories;

  • Sediment stability;

  • Appropriate assessment endpoints;

  • Measures of effect and acceptable and unacceptable levels of any effects determined; and

  • Appropriate reference areas and locations and their characteristics.

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Figure Figure 2.. Initial screening assessment (steps 1–3, decisions 1–2). Conservative (worst case) assumptions are used to screen out locations and substances that are clearly not of concern and to focus on those that may be of concern. SAP = sampling and analysis plan; COPC = contaminants of potential concern. For explanation of steps and decisions, see text.

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In addition, the 1st step in the evaluation should determine whether the site, defined in terms of both spatial and temporal scales, has a high level of environmental sensitivity (based on habitat not land use) and whether contamination is only from off-site sources. Sites typically comprise samples from multiple stations and can be delineated based on ecologically defined scales, on contaminant concentrations, or on other site-specific considerations. Information gathered should consider not only surficial sediments (to about 10 cm depth), which are the initial focus because that is where the majority of sediment-dwelling organisms live, but also deeper sediments and their contamination level and the likelihood of them being uncovered or possibly moved so that they could affect surrounding areas. The status of deeper sediments (step 9, decision 8) should be considered as data become available. The outcome of step 1 is an initial conceptual site model (showing the interrelationships of COPCs and ROPCs), which is updated as more information becomes available through further investigation.

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Figure Figure 3.. Preliminary quantitative assessment (steps 4–6, decisions 3–5). Contaminated areas screened in are further investigated in preparation for determining whether there is or is not a problem or whether additional investigations are required.

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Step 2: Develop and implement a sampling and analysis plan

Based on step 1, step 2 involves development of a sampling and analysis plan for review and approval by stakeholders and for implementation at both the site and reference areas. The objective of the sampling and analysis plan is to fill in data gaps related to both COPCs and ROPCs. The sampling and analysis plan should not necessarily be restricted to surficial sediments. A determination is required as to whether there are any COPCs in the sediments that could be toxic or biomagnify up the food chains. Biomagnification is significant if COPCs increase in concentrations through 3 or more trophic levels. Common sediment contaminants that may biomagnify include: organic mercury, PCBs, DDT, and 2,3,7,8-tetrachlorodibenzo-p-dioxin. If mercury is a COPC, then testing should include both total mercury and methyl-mercury concentrations in sediments (mercury only biomagnifies in the methylated form). If PCBs are a concern, then testing should include total PCBs (typically the sum of 7 Aroclors: 1016, 1221, 1232, 1242, 1248, 1254, 1260). If DDT is a concern, then the degradation products dichlorodiphenyldichloroethane (DDD) and dichlorodiphenyldichloroethylene (DDE) should also be measured.

Decision point 1—At the conclusion of step 2, two questions need to be answered. First, are COPCs present in sediments above levels that have been shown to have minimal effects to biota living in the sediments? In other words, could the COPC possibly cause toxic effects? Second, do COPCs present in the sediments comprise substances that could biomagnify and affect the health of biological communities at higher trophic levels or the health of humans consuming contaminated biota?

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Figure Figure 4.. Detailed quantitative assessment (steps 7–8, decisions 6–7). Decisions can be made regarding management actions for specific conditions. In other situations, additional, focused investigations will be required.

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The 1st question is addressed by comparing COPCs to SQGs that predict toxicity to less than 5% of the sediment-dwelling fauna (SQG-low; e.g., the Canadian threshold-effect level or the Ontario lowest-effect level). The specific SQG-low used may vary based on both regional considerations and best professional judgment. The 2nd question is addressed by determining whether or not COPCs that can biomagnify are present at quantifiable concentrations. The 2 possible decision outcomes are summarized in Table 1.

By design, SQGs are typically conservative and generally considered as intentionally overprotective of the aquatic environment (O'Connor 2004). Thus, if sediment COPC concentrations are below SQGs that predict minimal effects (SQG-low), then there is likely negligible ecological risk. These observations are corroborated by Porebski et al. (1999), for example, who found that such SQG-low values nearly always represented levels below which unacceptable biological effects were unlikely to occur in sediment. Because SQGs have no role in evaluating human health risks or biomagnification (Wenning and Ingersoll 2002) and there are no such sediment guidelines, initial (conservative) decisions regarding biomagnification potential are simply based on the presence or absence of quantifiable amounts of substances that may biomagnify.

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Figure Figure 5.. Assessment of deeper (below surficial) sediments (step 9, decision 8). If deeper sediments may pose a risk and could be exposed, the risk posed and the need for management actions must be determined.

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Step 3: Is there a potential risk based on contaminant concentrations?

The 3rd step of the framework involves determining whether the concentrations of COPCs that exceed SQG-low values or that have the potential to biomagnify statistically exceed reference concentrations as determined by comparisons with reference areas. Typically, reference areas represent the optimal range of minimally impaired conditions that can be achieved at sites anticipated to be ecologically similar and acceptable to local stakeholders (Krantzberg et al. 2000).

Table Table 1.. Two possible decisions arising from the consideration of information derived in step 2 of the sediment decision-making framework
ComparisonaDecision
  1. a COPCs = contaminants of potential concern; SQG = sediment quality guidelines (predict toxicity to less than 5% of the sediment-dwelling fauna).

All sediment COPCs < SQG-low, and no COPCs are present that can biomagnifyNo further assessment or remediation of the sediment is required. STOP
One or more sediment COPCs > SQG-low, and/or 1 or more COPCs are present that can biomagnifyConditions pose a potential risk to ecologic receptors and further assessment or remediation of the sediment is required. PROCEED TO STEP 3

Decision point 2—At the conclusion of step 3, two separate questions need to be answered. First, are concentrations of COPCs in sediments (a) above levels that have been shown to have minimal effects to biota living in the sediments (that is, are the COPC levels above SQG-low levels), and (b) not statistically different (p < 0.05) from reference conditions? Second, are the concentrations of COPCs that could biomagnify statistically different (p < 0.05) from those same COPCs in reference areas? In cases in which there is little discriminatory power in statistical significance determinations because of very low variability in the reference areas (i.e., a very small difference from the reference would be statistically significant but of arguable environmental significance), an additional comparison is possible, specifically, are the concentrations of COPCs less than 20% above those same COPC concentrations in reference areas? The +20% comparison is a straight arithmetic comparison of either mean or individual values, depending on site-specific circumstances (α = 0.05; β = 0.10). Reference conditions include background conditions, either measured or determined from historical data. In making these comparisons, the data for a highly contaminated hot spot (e.g., 10-fold greater than the SQGs that predict the likelihood of toxicity) should not be diluted with data from other less-contaminated areas. The 2 possible decision outcomes are summarized in Table 2.

Inorganic and some organic substances occur naturally and may be naturally enriched in some areas (e.g., naturally mineralized areas or oil seeps). The focus of remediation efforts needs to be on anthropogenic (human) contamination, not natural enrichment. The additional possible determination of a difference of 20% between 2 sets of chemistry data is well within the bounds of typical analytical variability and may not represent a true (significant) difference because it is likely a consequence of natural sediment heterogeneity (Jaagumagi and Persaud 1996) and is highly unlikely to be of any environmental concern. The additional use of reference + 20% could be useful to screen out areas of marginal environmental concern and is the same criterion used for sediment toxicity test result comparisons (described later).

Step 4: Is biomagnification a potential concern?

Step 4 involves consideration of whether substances that can biomagnify remain of concern by conservatively modeling the concentrations in the sediments and predicting uptake by sediment-dwelling organisms and predators of those organisms through to top predators to determine whether or not there is a potential risk (Grapentine et al. 2003a, 2003b). Conservative modeling includes, for example, the assumption that maximum contaminant concentrations occur throughout the exposed area, the use of maximum biomagnification factors, and the assumption that fish feeding is limited to the exposure area. These worst-case scenarios, some of which may be unrealistic, are used to identify environmental risks that are either screened out or identified as possibilities to be investigated further. In step 4, the determination of benthic invertebrate tissue concentrations is preferable for predicting concentrations in higher trophic levels.

Decision point 3—At the conclusion of step 4, the question of whether biomagnification is a potential concern at a site is answered. The 2 possible decision outcomes are summarized in Table 3.

Table Table 2.. Two possible decisions arising from the consideration of information derived in step 3 of the sediment decision-making framework
ComparisonaDecision
  1. a COPCs = contaminants of potential concern; SQG = sediment quality guidelines (predict toxicity to less than 5% of the sediment-dwelling fauna).

[Concentrations of all sediment COPCs > SQG-low and that can biomagnify] ≤ reference conditions and are statistically no different than reference area conditionsNo further assessment or remediation of the sediment is required. STOP
[Concentrations of 1 or more sediment COPCs > SQG-low, and/or 1 or more COPCs can biomagnify] > statistically higher than reference conditionsConditions pose a potential risk to ecologic receptors, and further assessment or remediation of the sediment is required. PROCEED TO STEP 4

Step 5: Are the sediments toxic?

In step 5, the remaining COPCs are evaluated using SQG-low and SQG-high values (which predict toxicity to 50% or more of the sediment infauna) to map spatial patterns of sediment contamination. Work entails determining the toxicity of representative areas—including those areas most heavily contaminated and areas moderately and minimally contaminated—and reference areas synoptic with sediment chemistry determinations (the use of subsamples of the same sample for both chemical analyses and toxicity testing). Typically, laboratory sediment toxicity tests are conducted with 3 or 4 appropriately sensitive, standardized sediment-dwelling or sediment-associated test organisms that are reasonably similar to those found (or expected to be found) at the site (based on the available data generated in step 1). The endpoints in sediment toxicity tests involve survival, growth, and reproduction (for acute and chronic endpoints; Reynoldson, Thompson, et al. 2002).

Table Table 3.. Two possible decisions arising from the consideration of information derived in step 4 of the sediment decision-making framework
ComparisonDecision
No potential exists for contaminant biomagnification from the sediments through aquatic food chainsNo further assessment or remediation of the sediment is required regarding biomagnification. PROCEED TO STEP 5
Potential exists for contaminant biomagnification from the sediments through aquatic food chainsConditions pose a potential risk to ecologic receptors and further assessment of biomagnification potential is required. PROCEED TO STEP 5

Decision point 4—Bulk sediment chemical analyses do not consider contaminant bioavailability nor do they provide reliable information on the toxicity of sediment contaminants (reasonably reliable information can be obtained on the non-toxicity of sediment contaminants; see, for example, decision point 1). Thus, a determination is required about whether or not the sediments that were previously assessed as contaminated are toxic to individual organisms and about the extent of any toxicity. The 2 possible decision outcomes are summarized in Table 4.

A difference of 20% between the controls and the test and reference sediments is neither different nor environmentally relevant in short-term (e.g., 10-d), acute tests (Mearns et al. 1986; WAC 1995; Suter 1996; USEPA and USACE 1998; Environment Canada 1998, 1999). Recent experience with longer-term (e.g., 28-d), chronic tests suggests greater differences can occur between the controls and reference and the test sediments without being distinguishable (P.M. Chapman, unpublished data). However, pending publication and more detailed discussion of these findings, the conservative 20% difference is recommended at this time. Thus, if all sediment toxicity endpoints are ≤20% different from the reference, the sediments are not considered toxic even if the difference is statistically significant.

Table Table 4.. Two possible decisions arising from the consideration of information derived in step 5 of the sediment decision-making framework
ComparisonDecision
All sediment toxicity endpoints are <20% different from reference, and the difference from the reference is not statistically significantNo further assessment required for laboratory toxicity. PROCEED TO STEP 6
One or more sediment endpoints are >20% different from reference, and the difference from reference is statistically significantConditions pose a potential risk and further assessment is required. PROCEED TO STEP 6

Step 6: Is it possible and appropriate to assess benthic community data?

Because there can be situations in which assessments of the relationship between the benthic community structure and possible sediment contaminant effects are not realistically possible, step 6 addresses the need for consideration of benthic community impacts as part of the sediment assessment. For example, in shallow harbors, propeller scour, dredging, or other habitat disturbances often alter benthic communities independent of any contaminant effects; dynamic, sediment bed flow conditions can also alter the biological zone as a result of continuous deposition or scour (Chapman, Ho, et al. 2002). Benthic community structure assessments are not meaningful in sediments deeper than about 10 cm because the vast majority of the sediment-dwelling organisms live at depths less than 10 cm, although some organisms (e.g., some bivalves) can burrow much deeper (Chapman 2002).

Decision point 5—At the conclusion of step 6 is the determination of whether or not benthic community assessments are appropriate or possible at a site. If they are, then benthic community assessments should be conducted. Benthos alteration is assessed by identifying and enumerating benthic assemblages and using both univariate (species richness, abundance, and dominance) and multivariate analyses (ordination and principle component analysis) to determine similarities and differences from reference areas and conditions (Chapman 1996; Simpson et al. 2005). The possibility of incorporating information on the structure of communities of organisms actually living in the sediments into the decision-making needs to be determined. Ideally such information can be incorporated (see “rule” 3). The 2 possible decision outcomes are summarized in Table 5.

Step 7: Develop decision matrix

Step 7 involves developing a decision matrix by ranking data from the available LOE: sediment chemistry; toxicity; benthos, if available and appropriate; and bioaccumulation potential. This approach is illustrated in Table 6 (adapted from Grapentine et al. 2002). Samples for sediment chemistry and toxicity are collected synoptically (i.e., subsamples of the same samples); samples for benthos are collected coincidentally (i.e., at the same locations but not on the same samples). Samples for benthos and chemistry analyses can be collected during initial field sampling and archived until needed, reducing field costs. Samples for sediment toxicity, however, cannot be archived for longer than 8 weeks and should be tested as soon as possible following collection (USEPA and USACE 1998). If benthos studies are not reasonably possible, then other LOE are fit into Table 7 using best professional judgment for step 8.

Table Table 5.. Two possible decisions arising from the consideration of information derived in step 6 of the sediment decision-making framework
ComparisonDecision
Are benthic community assessments appropriate or possible?Yes. Conduct such assessments, then PROCEED TO STEP 7
 No. PROCEED TO STEP 7

Decision point 6—At this stage of the framework, a definitive final decision may be possible. Specifically, sufficient information has now been gathered to allow for an assessment of 3 possibilities: (1) the contaminated sediments pose an environmental risk; (2) the contaminated sediments may pose an environmental risk, but further assessment is required before a definitive decision can be made; or (3) the contaminated sediments pose a negligible environmental risk. As shown in Table 7, definitive determinations are possible in 6 of 16 possible scenarios (4 determinations of negligible environmental risk requiring no further actions, and 2 determinations of environmental risk requiring management actions).

A definitive determination of sediment risk is possible, in some cases, with the proviso that sediment stability may still need to be assessed (step 9); in other cases, further assessment is needed but can be guided by the results of the integration of data collected at this stage of the assessment into a WOE. As noted by Wong (2004), SQGs do not provide definitive information for decisions regarding contaminated sediments or remediation; for that, a WOE approach is required. In a WOE approach, sediment chemistry data are given the least weight (rules 1 and 2); benthic community data are given the most weight (rule 3).

Table Table 6.. Ordinal ranking for weight of evidence (WOE) categorizations for chemistry, toxicity, benthos, and biomagnification potential in sedimenta
 
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  1. a SQG = sediment quality guideline. Note that the overall definition of “no significant adverse effects” is independent of sediment chemistry.

  2. b This is a multivariate assessment such as ordination.

Bulk chemistry (compared with SQG)Adverse effects likely: One or more exceeds SQG-highAdverse effects may/may not occur: One or more exceeds SQG-lowAdverse effects unlikely: All contaminant concentrations below SQG-low
Toxicity end points (relative to reference)Major: Statistically significant reduction of >50% in 1 or more toxicological endpointsMinor: Statistically significant reduction of >20% in 1 or more toxicological endpointsNegligible: Reduction of ≤20% in all toxicological end-points
Overall toxicitySignificant: Multiple tests or endpoints exhibit major toxicological effectsPotential: Multiple tests or endpoints exhibit minor toxicological effects and/or one test/endpoint exhibits major effectNegligible: Minor toxicological effects observed in no more than 1 endpoint
Benthos alterationb“Different” or “very different” from reference stations“Possibly different” from reference stations“Equivalent” to reference stations
Biomagnification potential (relative to reference)Significant: Based on step 8Possible: Based on step 4Negligible: Based on steps 4 or 8
Overall WOE assessmentSignificant adverse effects: Elevated chemistry; >50% reduction in 1 or more toxicological endpoints; benthic community structure different (from reference); and/or significant potential for biomagnificationPotential adverse effects: Elevated chemistry; >20% reduction in 2 or more toxicological endpoints; benthic community structure possibly different (from reference); and/or possible biomagnification potentialNo significant adverse effects: Minor reduction in no more than 1 toxicological endpoint; benthic community structure not different from reference; and negligible biomagnification potential

The type of WOE integration of LOE shown in Table 7 is usually applied on a station-by-station basis. Thus, although initial screening (steps 1–3) is intended to screen out areas with relatively low-contaminant concentrations, subsequent more-detailed sampling of these areas may include stations with contaminant concentrations below levels of concern. Mapping of the results is one means of applying the findings on a large sample basis (i.e., to all sample locations) as a tool for expert and stakeholder groups to identify and focus on obvious problem areas and patterns.

Table Table 7.. Decision matrix for weight of evidence (WOE) categorizationa
  1. a Based on Table 6, see text for explanation; a dash means “or.” Separate end points can be included within each line of evidence (LOE); for example, metals, PAHs, and PCBs for chemistry; survival, growth, and reproduction for toxicity; and abundance, diversity, and dominance for benthos.

  2. b Per Table 1, significant biomagnification (

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    ) can typically only be determined in step 8; step 3 only allows a determination that there is either negligible biomagnification potential or possible biomagnification potential. Site-specific situations, however, may already have sufficient evidence available from fish advisories and prior research to consider biomagnification at a site significant; that would be determined in step 1 (examination of available data). So, for example, if significant biomagnification were indicated in scenario 5 above, management actions would be required. The other 3 LOE do allow for definitive determinations in prior steps of this framework.

  3. c Benthos alteration may the result of other factors, either natural (e.g., competition/predation, habitat differences) or human-related (e.g., water-column contamination).

  4. d Dependent on the reason(s) for the observed toxicity.

  5. e Definitive determination is possible. Ideally, elevated chemistry should be shown to be linked to observed biological effects (i.e., it is causal) to ensure management actions address the problem. For example, there is no point in removing polluted sediments before a continuing source of contamination is fully addressed. Ensuring causality may require additional investigations such as toxicity identification evaluation or contaminant body residue analyses. If bulk sediment chemistry, toxicity, and benthos alteration all indicate that pollution is occurring, further assessments of biomagnification should await management actions dealing with the clearly identified problem of contaminated and toxic sediments adversely affecting the organisms living in those sediments. In other words, deal with the obvious problem, which may obviate the possible problem (e.g., dredging to deal with unacceptable contaminant-induced alterations to the benthos will effectively also address possible biomagnification issues).

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Step 8: If necessary, conduct further assessments

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. THE SEDIMENT DECISION-MAKING FRAMEWORK
  5. Step 8: If necessary, conduct further assessments
  6. CONCLUSIONS
  7. Acknowledgements
  8. References

For the 16 possible scenarios described in Table 7, ten scenarios result in a determination that contaminated sediments may pose an environmental risk, but further assessment is required before a definitive decision can be made. For instance, because fish are mobile, their entire feeding area needs to be considered to fully assess the potential for some organic contaminants to biomagnify (e.g., through area curve modeling; Freshman and Menzie 1996). Factors such as site-and species-specific biomagnification, lipid content, age and size, and receptor food preference can also be incorporated. Using more realistic assumptions than those used for the preliminary quantitative assessment should allow for a better determination regarding the toxicological outcome for upper trophic level receptor species. Whereas the preliminary quantitative assessment is solely a modeling exercise based on sediment and benthos, a more detailed quantitative assessment involves other food chain measurements including analyzing fish and, possibly, plankton.

Table Table 8.. Two possible decisions arising from the consideration of information derived in step 9 of the sediment decision-making framework
ComparisonaDecision
  1. a COPCs = contaminants of potential concern; SQG = sediment quality guidelines (predicts toxicity to less than 5% of the sediment-dwelling fauna).

Levels of COPCs in deeper sediments occur below SQG-low, and no substances are present that can biomagnify, or deeper sediments are unlikely to be uncovered under any reasonably possible set of circumstancesNo further assessment or remediation is required. STOP. Management options for polluted surficial sediments should be determined
Levels of COPCs in deeper sediments occur above SQG-low, and/or 1 or more substances are present that can biomagnify, and these sediments may be uncovered under 1 or more reasonably possible set of circumstancesConditions may pose a potential risk; further assessment may be required. REPEAT THE FRAMEWORK FROM STEP 1 (IF NECESSARY)

In step 8, detailed quantitative toxicity assessment involves additional or more extensive studies as appropriate to site-specific circumstances, such as spiked sediment-toxicity tests, toxicity identification evaluations, contaminant body residue analyses, tests with resident organisms, and in situ bioassays.

Decision point 7—Based on the additional investigations performed in step 8, a decision must be reached regarding whether or not an environmental risk exists in the sediment. This is where, in particular, it is critical that the assessment include scientists with strong expertise in sediment chemistry (chemical fate, transport, and speciation), sediment-toxicity testing, benthic community assessment, food chain effects, and environmental statistics for the design, implementation, and interpretation of site-specific studies.

Three outcomes are possible:

  • 1.
    If there is no clear link between elevated chemistry (sediment contaminant concentrations are above SQG-low) and biological effects (sediment toxicity or benthos alteration), then there is no point to sediment remediation. If the contaminants in sediment are not causative, then sediment remediation will not ameliorate the biological effects.
  • 2.
    Observed toxicity or benthos alteration in the absence of elevated chemistry may be the result of unmeasured contaminants or noncontaminant-related factors; either way, certainty about causation is required (e.g., through the use of toxicity identification evaluations studies; Ankley and Schubauer-Berigan 1995; Burgess 2000).
  • 3.
    Modeling biomagnification only indicates whether there is no problem or there may be a problem; if there is a potential biomagnification problem, then more definitive assessments involving field measurements (e.g., contaminant body residue analyses; Jarvinen and Ankley 1999; Borgmann et al. 2001), laboratory studies, or more realistic modeling scenarios are required.

Step 9: If necessary, assess deeper sediments

In the final stage, step 9, consideration is given to assessment of buried sediments. Surficial sediments effectively cover deeper sediments, which may be similarly or differently contaminated. If so, there is a need to determine whether, under unusual but possibly natural or human-related circumstances, these deeper sediments may be uncovered. Such studies typically involve an assessment of both sediment stability and sediment deposition rates (Chapman, McDonald, et al. 2002).

Decision point 8—If deeper sediments are contaminated and could be uncovered (become surface sediments), buried sediments could pose an environmental risk. If buried sediments are unlikely to be uncovered under any reasonably likely set of circumstances (e.g., a 100-y flood), then buried sediments do not require further assessment. Contaminants occurring below 10 cm are not linked by complete exposure pathways to aquatic biota. The 2 possible decision outcomes are summarized in Table 8.

CONCLUSIONS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. THE SEDIMENT DECISION-MAKING FRAMEWORK
  5. Step 8: If necessary, conduct further assessments
  6. CONCLUSIONS
  7. Acknowledgements
  8. References

The basic approach used in this framework—starting with chemical hazard assessment (the use of SQGs), then adding toxicity tests, followed by incorporating environment evaluations—matches current practices and international trends (Krantzberg et al. 2000; Power and Boumphrey 2004; Apitz et al. 2005). The framework can be applied to both large and small sites for both preliminary and more detailed assessments. It fits within the ecological risk assessment paradigm and provides information necessary for the protection of both local aquatic communities and endangered species. Furthermore, the framework differentiates contamination (substances present where they would not normally be found or above natural background levels) from pollution (contamination that results in adverse biological effects). Application of this framework will allow for informed decision-making regarding the need to remediate contaminated sediments by using a consistent overall approach applicable to different sites so that findings can be readily compared and understood, and comparative risks can be more readily evaluated.

Acknowledgements

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. THE SEDIMENT DECISION-MAKING FRAMEWORK
  5. Step 8: If necessary, conduct further assessments
  6. CONCLUSIONS
  7. Acknowledgements
  8. References

Useful review comments on one or more drafts of the framework were provided by Jo-Ann Aldridge, Graeme Batley Caroll Bélanger, Lise Boudreau, Duncan Boyd, Terri Bulman, Rob Campbell, Conrad deBarros, Ken Doe, Tim Fletcher, Lee Grapentine, Susan Humphrey, Pat Inch, Pritam Jain, Haseen Khan, Bruce Kilgour, Tay Kok-Long, Blair McDonald, Mike Macfarlane, Tom O'Connor, Trefor Reynoldson, Lisa Richman, Susan Roe, Roger Santiago, Angel del Valls, Doris Vidal-Dorsch, Paul Welsh, Cecilia Wong, and Mike Zarull. Work on this project was funded by Environment Canada under the Canada–Ontario Agreement with assistance from the Ontario Ministry of the Environment.

References

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. THE SEDIMENT DECISION-MAKING FRAMEWORK
  5. Step 8: If necessary, conduct further assessments
  6. CONCLUSIONS
  7. Acknowledgements
  8. References
  • Ankley GT, Schubauer-Berigan MK., 1995. Background and overview of current sediment toxicity identification evaluation procedures. J Aquat Ecosyst Health 4: 133149.
  • Apitz SE, Davis JW, Finkelstein K, Hohreiter DW, Hoke R, Jensen RH, Jersak J, Kirtay VJ, Mack EE, Magar VS, Moore D, Reible D, Stahl RG Jr., 2005. Assessing and managing contaminated sediments: Part I, developing an effective investigation and risk evaluation strategy. Integr Environ Assess Manag 1: 28.
  • Borgmann U, Norwood WP, Reynoldson TB, Rosa F., 2001. Identifying cause in sediment assessments: Bioavailability and the Sediment Quality Triad. Can J Fish Aquat Sci 58: 950960.
  • Burgess RM., 2000. Characterizing and identifying toxicants in marine waters: A review of marine toxicity identification evaluations (TIEs). Int J Environ Pollut 13: 233.
  • Burton GA Jr, Chapman PM, Smith EP., 2002. Weight-of-evidence approaches for assessing ecosystem impairment. Human and Ecological Risk Assessment 8: 16571673.
  • [CCME] Canadian Council of Ministers of the Environment. 1996. A framework for ecological risk assessment: General guidance. Winnipeg (MN). EN 108–4–10–1996E.
  • Chapman PM., 1996. Presentation and interpretation of Sediment Quality Triad data. Ecotoxicology 5: 327339.
  • Chapman PM., 2002. Integrating toxicology and benthic ecology: Putting the eco back into ecotoxicology. Mar Pollut Bull 44: 715.
  • Chapman PM., 2005. Development of a Canada-Ontario decision-making framework for contaminated sediments in the great lakes (and elsewhere): Final report. North Vancouver, BC, Canada: EVS Environment Consultants-Golder Associates.
  • Chapman PM, Ho K, Munns W, Solomon K, Weinstein MP., 2002. Issues in sediment toxicity and ecological risk assessment. Mar Pollut Bull 44: 271278.
  • Chapman PM, McDonald BG, Lawrence GS., 2002. Weight of evidence frameworks for sediment quality and other assessments. Human and Ecological Risk Assessment 8: 14891515.
  • Environment Canada. 1998. Biological test method: Reference method for determining acute lethality of sediment to marine or estuarine amphipods. Ottawa (ON). EPS 1/RM/35.
  • Environment Canada. 1999. Guidance document on the application and interpretation of single-species tests in environmental toxicology. Ottawa (ON). EPS 1/RM/34.
  • Environment Canada. 2002. Metal mining guidance document for aquatic environmental effects monitoring. Ottawa, (ON).
  • Freshman JS, Menzie CA., 1996. Two wildlife exposure models to assess impacts at the individual and population levels and the efficacy of remedial actions. Human and Ecological Risk Assessment 3: 481498.
  • Grapentine L, Anderson J, Boyd D, Burton GA Jr, DeBarros C, Johnson G, Marvin C, Milani D, Painter S, Pascoe T, Reynoldson T, Richman L, Solomon K, Chapman PM., 2002. A decision-making framework for sediment assessment developed for the Great Lakes. Human and Ecological Risk Assessment 8: 16411655.
  • Grapentine L, Milani D, Mackay S., 2003a. A study of the bioavailability of mercury and the potential for biomagnification from sediment in the St. Lawrence River (Cornwall) Area of Concern. Burlington (ON), Canada: National Water Research Institute, Environment Canada.
  • Grapentine L, Milani D, Mackay S., 2003b. A study of the bioavailability of mercury and the potential for biomagnification from sediment in Jellico Cove, Peninsula Harbour. Burlington (ON), Canada: National Water Research Institute, Environment Canada.
  • Ingersoll CG, MacDonald DD., 2002. Guidance manual to support the assessment of contaminated sediments in freshwater ecosystems, Volume III: Interpretation of the results of sediment quality investigations. Chicago, (IL): U.S. Environmental Protection Agency, Great Lakes National Program. EPA 905-B02–001-C.
  • Jaagumagi R, Persaud D., 1996. An integrated approach to the evaluation and management of contaminated sediments. Toronto: Ontario Ministry of the Environment, Standards Development Branch, Environmental Standards Section.
  • Jarvinen AW, Ankley GT., 1999. Linkage of effects to tissue residues: Development of a comprehensive database for aquatic organisms exposed to inorganic and organic chemicals. Pensacola (FL), USA: Society of Environmental Toxicology and Chemistry.
  • Krantzberg G, Reynoldson T, Jaagumagi R, Painter S, Boyd D, Bedard D, Pawson T., 2000. SEDS: Setting environmental decisions for sediment management. Aquatic Ecosystem Health and Management 3: 387396.
  • MacDonald DD, Ingersoll CG., 2002a. A guidance manual to support the assessment of contaminated sediments in freshwater ecosystems, Vol I: An ecosystem-based framework for assessing and managing contaminated sediments. Chicago (IL): U.S. Environmental Protection Agency, Great Lakes National Program. EPA 905-B02–001-A.
  • MacDonald DD, Ingersoll CG., 2002b. Guidance manual to support the assessment of contaminated sediments in freshwater ecosystems. Volume II: Design and implementation of sediment quality investigations. Chicago (IL): U.S. Environmental Protection Agency, Great Lakes National Program. EPA 905-B02–001-B.
  • Mearns AJ, Swartz RC, Cummins JM, Dinnel PA, Plesha P, Chapman PM., 1986. Inter-laboratory comparison of a sediment toxicity test using the marine amphipod, Rhepoxynius abronius. Mar Environ Res 19: 1337.
  • O'Connor TP., 2004. The sediment quality guideline, ERL, is not a chemical concentration atthe threshold of sediment toxicity. Mar Pollut Bull 49: 383385.
  • Porebski LM, Doe KG, Zajdlik BA, Lee D, Pocklington P, Osborne JM., 1999. Evaluating the techniques for a tiered testing approach to dredged sediment assessment—A study over a metal concentration gradient. Environ Toxicol Chem 18: 26002610.
  • Power EA, Boumphrey RS., 2004. International trends in bioassay use for effluent management. Ecotoxicology 13: 377398.
  • Reynoldson TB, Smith EP, Bailer AJ., 2002. A comparison of three weight-of-evidence approaches for integrating sediment contamination data within and across lines of evidence. Human and Ecological Risk Assessment 8: 16131624.
  • Reynoldson TB, Thompson SP, Milani D., 2002. Integrating multiple toxicological endpoints in a decision-making framework for contaminated sediments. Human and Ecological Risk Assessment 8: 15691584.
  • Simpson SL, Batley GE, Stauber JL, King CK, Chapman JC, Hyne RV, Gale SA, Roach AC, Maher WA, Chariton AA., 2005. Handbook for sediment quality assessment. Canberra, Australia: Environmental Trust.
  • Suter GW II., 1996. Risk characterization for ecological risk assessment of contaminated sites. Oak Ridge (TN): U.S. Department of Energy, Office of Environmental Management. ES/ER/TM-20.
  • Suter GW II, Norton SB, Cormier SM., 2002. A methodology for inferring the causes of observed impairments in aquatic ecosystems. Environ Toxicol Chem 21: 11011111.
  • [USEPA] U.S. Environmental Protection Agency. 1998. EPA's contaminated sediment management strategy. Washington DC: USEPA, Office of Water. EPA823-R-98–001.
  • [USEPA and USACE] U.S. Environmental Protection Agency, U.S. Army Corps of Engineers. 1998. Evaluation of dredged material proposed for discharge in waters of the United States—Testing manual. Washington DC: USEPA, USACE. EPA 823-B-98–004.
  • [WAC] Washington Administrative Code. 1995. Sediment management standards. Title 173, Chapter 204. Olympia (WA), USA: Department of Ecology.
  • Wenning RJ, Ingersoll CG, editors. 2002. Use of sediment quality guidelines and related tools for the assessment of contaminated sediments: Executive summary booklet of a Society of Environmental Toxicology and Chemistry (SETAC) Pellston Workshop. Pensacola (FL), USA: SETAC.
  • Wong C., 2004. Evaluating the ecological relevance of sediment quality guidelines. Poster Presentation at the 31 st Annual Aquatic Toxicity Workshop, 2004 Oct 24–27; Charlottetown (Prince Edward Island), Canada.