DECIDING WHEN TO INTERVENE

Introduction

The Ontario Ministry of the Environment has developed a protocol for determining when sediment is contaminated to a level that requires remedial action. The protocol is based upon sediment guidelines, combined with a risk assessment approach.

The first step is comparison of sediment contaminant concentrations with sediment quality criteria. The Provincial Sediment Quality Guidelines (PSQGs) are a set of numerical guidelines, using a tiered approach, that were developed for the protection of sediment-dwelling (benthic) organisms. The Guidelines also protect against biomagnification of contaminants through the food chain from sediment contaminant sources.

Provincial Sediment Quality Guidelines (PSQGs)

The PSQGs define three levels of eco-toxic effects and are based on the chronic, long-term effects of contaminants on benthic organisms. The essence of the guidelines and their significance are summarized below. Details are provided in Persaud et al. (1993).

The No Effect Level. This is intended as the level at which contaminants in sediment do not present a threat to water quality and uses, benthic biota, wildlife, or human health. The No Effect Level (NEL) is principally designed to protect against biomagnification through the food chain. Partitioning approaches in conjunction with Provincial Water Quality Objectives (PWQOs) are used to set these guidelines, since with appropriate safety factors PWQOs/Gs are designed to protect against biomagnification.

A PSQG NEL is derived through the equation: PSQG = K_OC x PWQO/G

where:

PSQG = sediment quality guideline normalized to the sediment organic carbon content (TOC) of 1%
K_oc = organic carbon partitioning coefficient
PWQO/G = Provincial Water Quality Objective/Guideline

The Lowest Effect Level. The Lowest Effect Level (LEL) is the level that can be tolerated by the majority of benthic organisms. It is derived using field-based data on the co-occurrence of sediment concentrations and benthic species. The procedure used is based on the Screening Level Concentration (SLC) method described in Neff et al. (1986).

The calculation of the SLC is a two step process and is calculated separately for each parameter. In the first step, the individual SLCs (Species SLCs) are calculated for each benthic species. The sediment concentrations at all locations at which that species was present are plotted in order of increasing concentration. From this plot, the 90th percentile of this concentration distribution is determined. The 90th percentile was chosen to provide a conservative estimate of the tolerance range for that species. This would serve to eliminate extremes in concentrations that may be due to specific and unusual sediment characteristics.

In the second step, the 90th percentiles for all of the species present are plotted, also in order of increasing concentration. From this plot, the 5th percentile is calculated and this level becomes the LEL guideline.

The Severe Effect Level. This level represents contaminant concentrations in sediment that could potentially eliminate most of the benthic organisms. The procedure used is identical to the calculation of the LEL except that the 95th percentile of the SLC (the level below which 95% of all SSLCs fall) is calculated in the second step of the SLC calculation, and this level becomes the Severe Effect Level (SEL) guideline.

Table 1: Provincial Sediment Quality Guidelines for metals and nutrients (values in mg/kg dry weight unless otherwise noted)

Parameter	No Effect Level	Lowest Effect Level	Severe Effect Level
Arsenic	-	6	33
Cadmium	-	0.6	10
Chromium	-	26	110
Copper	-	16	110
Iron (%)	-	2	4
Lead	-	31	250
Manganese	-	460	1100
Mercury	-	0.2	2
Nickel	-	16	75
Zinc	-	120	820
TOC (%)	-	1	10
TKN	-	550	4800
TP	-	600	2000

Metal concentrations determined using Aqua-Regia digestion
"-" = denotes insufficient data/no suitable method
TOC = Total Organic Carbon TKN = Total Kjeldahl Nitrogen TP = Total Phosphorus

Table 2: Provincial Sediment Quality Guidelines for Organic Compounds (values in mg/kg dry weight unless otherwise noted)

Compound	No Effect Level	Lowest Effect Level	Severe Effect Level*
Aldrin	-	0.002	8
BHC	-	0.003	12
alpha-BHC	-	0.006	10
beta-BHC	-	0.005	21
gamma-BHC	0.0002	(0.003)	(1)
Chlordane	0.005	0.007	6
DDT(total)	-	0.007	12
op+pp-DDT	-	0.008	71
pp-DDD	-	0.008	6
pp-DDE	-	0.005	19
Dieldrin	0.0006	0.002	91
Endrin	0.0005	0.003	130
HCB	0.01	0.02	24
Heptachlor epoxide	-	0.005	5
Mirex	-	0.007	130
PCB(total)	0.01	0.07	530
Anthracene	-	0.220	370
Benz[a]anthracene	-	0.320	1,480
Benzo[k]fluoranthene	-	0.240	1,340
Benzo[a]pyrene	-	0.370	1,440
Benzo[g,h,i]perylene	-	0.170	320
Chrysene	-	0.340	460
Dibenzo[a,h]anthracene	-	0.060	130
Fluoranthene	-	0.750	1,020
Fluorene	-	0.190	160
Indeno[1,2,3-cd]pyrene	-	0.200	320
Phenanthrene	-	0.560	950
Pyrene	-	0.490	850
PAH (total)**	-	4	10,000

- = Insufficient data to calculate guideline
* = Numbers in this column are expressed as mg/kg organic carbon and are converted to bulk sediment values by multiplying by the actual TOC concentration of the sediment (to a maximum of 10%). For a sediment sample with a PCB value of 30 mg/kg and a TOC of 5%, the PCB SEL is converted to a bulk sediment value for a sediment with 5% TOC by multiplying 530 x 0.05 = 26.5 mg/kg and gives the SEL guideline for that sediment. The measured value of 30 mg/kg is then compared with the bulk sediment value, and is found to exceed the guideline.
** = PAH (total) is the sum of 16 PAH compounds: Acenaphthene, Acenaphthylene, Anthracene, Benzo[k]fluoranthene, Benzo[b]fluorene, Benzo[a]anthracene, Benzo[a]pyrene, Benzo[g,h,i]perylene, Chrysene, Dibenzo[a,h]anthracene, Fluoranthene, Fluorene, Indeno[1,2,3-cd]pyrene, Naphthalene, Phenanthrene and Pyrene.

Application of the PSQGs

The PSQGs shown in Tables 1 and 2 are used in making decisions in relation to a number of sediment-related issues ranging from dredged material disposal to determination of remedial action for contaminated sediment.

In an area as geologically diverse as Ontario, local natural sediment levels of the metals may vary considerably and in certain areas, such as wetlands, the organic matter content and nutrient levels may be naturally high.

Metals. In areas where local background levels are above the LEL, the local background level will form the practical lower limit for management decisions. In some waterbodies, surficial sediment upstream of all discharges may be acceptable for calculation of background values. Where it cannot be shown that such areas are unaffected by local discharges, the pre-colonial sediment horizon is used. Site-specific background for metals is calculated as the mean of 5 replicate samples from surficial sediment that has not been directly affected by man's activities or from the pre-colonial sediment horizon. Alternatively, the mean background values for the Great Lakes Basin as calculated in the guidelines may be used.

Nutrients. Areas of high natural organic matter content, such as marshes and other types of wetlands, can be readily distinguished from those resulting from anthropogenic sources. In such cases, for the nutrients listed in Table 1, the local background would serve as the practical lower limit for management action.

It is also recognized that long-range sources such as atmospheric deposition have contributed to accumulation of organic compounds in areas remote from any specific source. Therefore, in those areas where specific sources cannot be determined, the practical lower limit for management action is the Upper Great Lakes deep basin surficial sediment concentration.

If the sediment concentration exceeds the local background value, the next step is to determine whether the sediment poses a threat to aquatic life. The severity of this effect is determined using a number of biological assessment techniques.

If the concentration of the contaminant in the sediment exceeds the SEL, then the MOE Sediment Bioassay tests for acute toxicity, described in Bedard et al. (1992), are required.

Assessment of contaminated sediment

Initial sediment assessment. The most important preliminary piece of information necessary for sediment evaluation is chemical data, which are compared against the PSQGs as well as background levels. The importance of sediment assessment is that it provides a good indication as to whether any further effort is required in studying sediment contamination in a given area. From a sediment management standpoint, the LEL is the point at which low-level concerns arise in relation to future worsening of the situation if existing sources are not controlled. This level would rarely warrant concerns from a remediation standpoint unless dealing with a spill in areas where the background sediment is below the LEL.

The SEL is the level that raises major concern from an environmental management standpoint. The urgency of a management response can be established by obtaining additional information through laboratory sediment bioassays on the toxicity of the sediment.

Based on comparison with the PSQGs and background levels, there are three possible outcomes from a sediment evaluation:

• The sediment is clean (i.e., all parameters tested are below the LEL) and no further action is required unless the situation changes as a result of new discharges or material spills.
• The concentrations of contaminants in sediment are above the LEL and further testing is warranted. This will necessitate gathering additional information of a quality and quantity that would facilitate a thorough review of the site and may include both chemical and biological tests.
• The sediment has been shown to have contaminant levels at or above the SEL and biological assessment is required. The detailed studies must include laboratory biological testing for potential toxic effects as described in the PSQG document. Determination of biological cleanup targets may also be necessary.

Degree of chemical contamination. After the initial assessment, the extent and degree of sediment contamination is assessed through mapping, which will permit delineation of "hot spots" and areas of lesser degrees of contamination. It is especially important to determine the outer boundaries of the affected area, as well as the depth of sediment contamination, since this will define the area of any future remediation and permit calculation of volumes of material to be dealt with.

A second but equally important aspect of sediment characterization is determination of the physical characteristics of the area. In many cases, areas of contaminated sediment may act as sources of contaminated material to adjacent or downstream areas through resuspension of material. The potential for resuspension of contaminated material through erosion (i.e., through fluctuations in discharge, currents, wave patterns, and physical obstructions such as lakefill structures, dams, and weirs) needs to be carefully assessed. Characteristics such as seasonal and yearly net sediment erosion or deposition, which may affect subsurface contamination, should be determined since this will have a major impact on the determination of a remediation plan.

The biological significance of the chemicals. An assessment of the severity of biological effects of contaminants in sediment is normally required as part of the protocol for sediment that exceeds the LEL or the SEL. Biological assessment is also necessary, since the decision to remediate is usually based on biological effects.

The nature of the effects can be broken down into two main categories: effects on individuals and effects on communities. This is achieved through a number of components such as:

• Benthic community structure and functional analysis
• Fish community studies
• Sediment bioassays (including testing with water column organisms)
• Uptake studies (e.g., caged fish and caged mussel studies)
• Tissue resides in in-situ organisms (e.g., sport fish, young-of-the-year fish, in situ benthic organisms)

A number of evaluation techniques are available to carry out a comprehensive biological assessment. These include:

• Benthic and fish community structure - functional group analysis. These studies consider the effects of contaminants at the population or community level. While generally unable to pinpoint a cause-effect relationship, they can provide a useful measure of overall ecosystem health.
• Sediment bioassays. These use benthic organisms such as chironomids, mayflies, oligochaetes, and fathead minnows to assess chronic and acute toxicity of sediment. These studies can be designed to examine mortality, reproductive impairment, mutagenicity, and a range of sub-lethal effects on individuals. They are most effective, however, in determining the potential toxicity of contaminated sediment (usually as a measured effect over a certain exposure period). The specific causative agent is difficult to isolate, especially when dealing with mixtures of contaminants. The sediment used in these tests is usually disturbed, which in most cases heightens the biological availability of the contaminants in the sediment and also through release to the water column. As a result, this test can be considered as representing the worst case scenario.
• Uptake studies. These use caged mussels, leeches, and/or caged fish placed on, or suspended just above, the sediment to determine the levels of contaminants in the water column at the study site. Similarly, this approach can be applied in the laboratory through the exposure of cultured juvenile fathead minnows to test and control sediment. Both field and laboratory studies can provide a good indication of the release of contaminants to the water column from sediment. This information, therefore, is an indirect measure of the impacts of contaminants in sediment on water use impairments.
• Contaminant residues in in situ organisms. Analysis of benthic organisms and fish tissue for contaminant residues can be used to determine availability of contaminants from sediment. In most cases, sediment ingesting organisms are chosen, whether benthic organisms or bottom-feeding fish, since these are most likely to accumulate contaminants directly from the sediment. This provides a measure of the availability of contaminants to biota, and the potential for transfer of contaminants through the food chain. Coupled with the mussel studies, it can provide an indication of the relative importance of the water and sediment pathways for bioaccumulation. Analysis of sport fish and comparison with consumption guidelines provides a measure of direct danger to humans through consumption of contaminated fish. Levels are designed to protect human consumers, but also provide an indication of the availability of contaminants from sediment and other sources such as prey.

A number of different biological tests are necessary at any one site in order to provide a good indication as to whether the study area presents a danger to organisms, including humans, since no single indicator can provide all the necessary information for management decision-making. This type of information will also assist in determining where to concentrate any remedial actions.

The source or origin of contaminants. Concurrent with environmental data gathering, efforts should be made to obtain information on contaminant input to the area. The usual sources of contaminants can be grouped into municipal (which will likely contain the widest range of chemicals), industrial, urban runoff, agricultural, mining, and atmospheric fallout. Knowledge of the sources will provide a good framework of the type of chemical analysis required and will also aid decision-making on remediation. In some instances it may be necessary to test material emanating from such sources to determine their current toxic impact.

Establishing the need for remediation. Once the information has been gathered and the data evaluated, the need for remediation should be assessed. This is based on evaluating the considerations listed below:

Sources:

• Presence of active contaminant sources to the area
• Types of contaminant sources - point sources or non-point (diffuse) sources

Contaminant concentrations:

• Sediment contaminants exceed LEL for 1 or more contaminants
• Sediment contaminants exceed SEL for 1 or more contaminants

Contaminant characteristics:

• Types of contaminants - i.e., nutrients, metals, persistent organics
• Presence of contaminants as a mix of metals and organics

Biological effects:

• Characteristics of benthic community - benthic organisms are abundant and evenly distributed, or the benthic invertebrate community is species poor and consists mainly of pollution tolerant organisms
• In situ and laboratory biological tests and sport fish data show uptake of contaminants
• Sediment results in chronic effects on aquatic organisms, or is acutely toxic

Physical factors:

• Sediment type - i.e., presence of fine-grained material (sand/clay/mud)
• Physical characteristics of area - i.e., depositional or erosional
• Presence of factors that may alter the physical nature (e.g., lakefills, flow changes, etc.) of the site

In instances where some or all of the biological effects studies yield negative results, then the reasons for such findings must be fully explored. In cases where significant adverse effects have been noted in sediment bioassays, effort should be directed towards determining whether this is in fact due to chemical factors, rather than physical factors, such as unsuitable sediment type. For example, a combination of contaminated sediment and unsuitable sediment type could result in stresses on the test organisms which, individually, would not have elicited such a severe response.

The types of adverse effects are evaluated on a case-by-case basis. The only clear-cut case is where sediment is acutely toxic. Where chronic effects and/or bioaccumulation are the primary biological effects, the need for remediation must include other considerations. These are often based upon identified use impairments and use restorations.

Setting a goal

The setting of cleanup goals can be guided by use impairments to be restored. The International Joint Commission (1985) in its "listing/delisting" criteria for Great Lakes Areas of Concern has identified several use impairments. These include:

• Restrictions on fish and wildlife consumption
• Tainting of fish and wildlife flavor
• Degraded fish and wildlife populations
• Fish tumors or other deformities
• Bird or animal deformities or reproductive problems
• Degradation of benthos
• Restrictions on dredging activities
• Restrictions on drinking water consumption or taste and odor problems
• Added costs to agriculture or industry

Sediment alone may not contribute directly to this extensive list of use impairments, but through the slow release of contaminants in some areas, may be a source of chemicals to the water column. To progress from a contaminated sediment problem to the restoration of designated uses in an area will require a strategy that involves a phased approach, likely over several years, to achieve significant improvements. It is imperative that any cleanup aimed at use restoration be based on a realistic schedule that allows sufficient time for source controls to take effect and the practical constraints of removing or covering over contaminated sediment.

Factors to consider in setting cleanup goals include:

• The size of the area affected needs to be clearly defined since it will have a significant bearing on the remedial option chosen from both a cost and technology perspective.
• The uses the area is put to and the potential for this area to affect adjoining areas through the spread of contaminated sediment must be considered. Uses may include protection of fisheries and benthic organisms. There is a need to consider both the toxic and bioaccumulative potential of contaminants. In previous sections, the need to look at a range of tests was indicated. This becomes critical at this stage since the severity of the effect will play a major role in arriving at the final decision.
• From a human health perspective, compounds that are persistent and pose a threat to water supplies or fish and wildlife will be weighted differently from compounds that do not pose similar threats. In some cases recreational/aesthetic considerations may be the driving force in a cleanup study.
• The potential for recontamination must be examined from the point of view of existing and proposed land use and source controls. Existing and new industries must incorporate features that will not lead to sediment contamination.
• There is a need to consider whether sediment removal will create additional problems, such as the exposure of historical contamination in deeper layers of the sediment. Care must be taken to ensure that the full depth of the problem has been adequately defined.
• The physical environment of the area needs to be considered. The potential for resuspension of contaminated sediment, with resultant contamination of adjacent or downstream areas, will be an important factor in developing a remediation plan.

With the exception of spills, which must be cleaned up immediately, the most urgent need in environmental management is to protect the ecosystem from further abuse. Thus, source control must be the foundation of remedial action.

Conclusion

Consideration of remedial action in an area of contaminated sediment requires the development of a cleanup goal. This goal should be based on the "desired state of the environment" or developed in support of certain "attainable" uses. Where feasible, chemical guidelines provide a very convenient tool for setting cleanup goals, though these must be used with care, since most chemical guidelines have been developed for broad use and may require some adjustment when applied to specific sites. The final goal could also include intermediate goals, since the achievement of the goal can be phased over time or over a sequence of activities.

The ideal cleanup goal for restoration of contaminated sediment will always be the level that provides for the protection of all sediment uses. To this end, the cleanup target should be derived with heavy reliance on biological tests, rather than guideline levels. In many cases, the practical limits to cleanup will be dictated by the local background or ambient values, since cleanup to levels lower than these will be impractical and counterproductive. However, even cleaning up to this level will not always be feasible, especially when the area under consideration is large or where there are ongoing sources of contamination. Such areas may require a multi-phased approach, spread out over time, to achieve source control before any remediation work is undertaken.

In addition to these technical considerations, the final decision as to the proper course of action must also be based on considerations of social and economic criteria.

References

Bedard, D., Hayton, A. and D. Persaud. 1992. Laboratory Sediment Biological Testing Protocol. Ontario Ministry of Environment. Toronto, Ontario. 26 pp.

International Joint Commission (IJC). 1985. Report on Great Lakes Water Quality. Great Lakes Water Quality Board. 212 pp.

Neff, J. M., Bean, D. J., Cornaby, B. W., Vaga, R. M., Gulbransen, T. C. and J. A. Scanlon. 1986. Sediment Quality Criteria Methodology Validation: Calculation of Screening Level Concentrations from Field Data. Battelle Washington Environmental Program Office for U.S. EPA. 60 pp.

Persaud, D., Jaagumagi, R. and A. Hayton. 1993. Guidelines for the Protection and Management of Aquatic Sediment Quality in Ontario. Ontario Ministry of Environment and Energy Report. 30pp.