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Keywords:

  • Bioaccumulation;
  • Biomagnification;
  • Field measurements

Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. WORKSHOP OBJECTIVES
  5. KEY FINDINGS
  6. REFERENCES

Once they are released into the environment, a number of chemicals are known to bioaccumulate in organisms, sometimes to concentrations that may threaten the individual or their predators. However, use of physical or chemical properties or results from laboratory bioaccumulation tests to predict concentrations sometimes found in wild organisms remains a challenge. How well laboratory studies and field measurements agree or disagree, and the cause of any discrepancies, is a subject of great interest and discussion from both a scientific and a regulatory perspective. A workshop sponsored by the ILSI Health and Environmental Sciences Institute, US Environmental Protection Agency, and the Society of Environmental Toxicology and Chemistry assembled scientists from academia, industry, and government to compare and contrast laboratory and field bioaccumulation data. The results of this workshop are summarized in a series of 5 articles published in this issue of Integrated Environmental Assessment and Management. The articles describe: 1) a weight-of-evidence approach that uses fugacity ratios to bring field measurements into the assessment of biomagnification potential for legacy chemicals; 2) a detailed comparison between laboratory and field data for the most commonly measured bioaccumulation endpoint, the biota–sediment accumulation factor; 3) a study that identifies and quantifies the differences between laboratory and field metrics of bioaccumulation for aquatic and terrestrial organisms; and 4) 2 reports on trophic magnification factors: the 1st addresses how trophic magnification factors are determined and interpreted and the 2nd describes how they could be used in regulatory assessments. Collectively, these articles present the workshop participants' current understanding and assessment of bioaccumulation science and make a number of recommendations on how to improve the collection and interpretation of bioaccumulation data. Integr Environ Assess Manag 2012;8:13–16. © 2011 SETAC


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. WORKSHOP OBJECTIVES
  5. KEY FINDINGS
  6. REFERENCES

New and existing substances are screened by regulatory agencies at national and international levels according to persistent (P), bioaccumulative (B), and toxic (T) pollutants criteria, such as that from the Stockholm Convention (UNEP 2001), Environment Canada (Environment Canada 2003), the US Environmental Protection Agency (USEPA 1976), and the European Chemicals Agency (ECHA 2008). Substances exceeding these criteria are referred to as PBTs and are potentially subject to regulatory controls or further characterization to determine their harmfulness. The bioaccumulative potential (B) of a chemical, which is a measure of the tendency for a chemical to form unacceptable residues in organisms, is currently assessed by regulatory agencies through use of the n-octanol–water partition coefficient (KOW), bioconcentration factor (BCF), and/or bioaccumulation factor (BAF) endpoint metrics. In general, threshold values of 1000 to 5000 and 100 000 are used for the BCF–BAF and KOW, respectively (Gobas et al. 2009). In support of these criteria, standardized protocols have been developed for measuring the KOW (USEPA 1995; OECD 2004, 2006) and the BCF (OECD 1996; USEPA 1996a, 1996b; ASTM 2007). Many of the measurements performed with standard methods have provided useful data on bioconcentration and/or bioaccumulation, i.e., chemicals identified as bioaccumulative on the basis of laboratory BCF–BAF data and/or KOW are indeed bioaccumulative in the field. However, results from numerous field studies have shown widely differing levels of agreement between laboratory and field measurements of bioaccumulation potential for other chemicals (e.g., Borgå et al. 2004; Weisbrod et al. 2009; Burkhard et al. 2012a; Selck et al. this issue2012). As documented by Arnot and Gobas (2006), BAFs from field samples can differ by up to several orders of magnitude from laboratory BCF measurements for some chemicals.

From both a regulatory and industry perspective, there is concern about whether the existing PBT criteria, which may not be reflective of the current state of the science, may lead to either false positive or false negative conclusions on the bioaccumulation potential of individual chemicals. False positive conclusions may lead to the unnecessary allocation of resources to further characterize a chemical, whereas false negative conclusions may lead to decisions that are not protective of environmental organisms. A recent review resulting from an international Pellston workshop (Klecka et al. 2009) reported that the “B” criteria used by the Stockholm Convention on persistent organic pollutants (UNEP 2001) and many national risk assessment programs (EC 2003) were unable to identify or predict the actual bioaccumulation of several substances in organisms in the environment (Gobas et al. 2009; van Wijk et al. 2009; Weisbrod et al. 2009). Current deliberations by Stockholm Convention members include the use of field studies of bioaccumulation in their assessments of candidate persistent organic pollutants to supplement KOW and laboratory-based BCF–BAF data (see meeting documents, UNEP 2006).

Given the growing use of field bioaccumulation data, a need exists for a better understanding of the magnitude and causes of the variability between laboratory and field measurements of bioaccumulation potential. Furthermore, approaches are needed for incorporating additional metrics such as the biota–sediment accumulation factor (BSAF), biomagnification factor (BMF), biota–suspended solids accumulation factor (BSSAF), and trophic magnification factor (TMF) as a means of broadening the assessment of bioaccumulation potential beyond the metrics currently used (such as KOW, BCF, and BAF). Some of these additional metrics can be measured in the laboratory (BSAF and BMF), whereas all of them can be measured in field studies.

WORKSHOP OBJECTIVES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. WORKSHOP OBJECTIVES
  5. KEY FINDINGS
  6. REFERENCES

A Lab–Field Bioaccumulation workshop, involving more than 35 scientists from government, academia, and industry from North America, South America, Europe, and Asia, was held in November 2009 in New Orleans, Louisiana, USA. This workshop was the 4th in a series of workshops on bioaccumulation issues and science organized over the past 5 y by various partners, including the ISLI Health and Environmental Sciences Institute, the Society of Environmental Toxicology and Chemistry, Society of Toxicology, European Commission Joint Research Centre, and US Environmental Protection Agency. The November 2009 workshop had 3 breakout groups, and their objectives were to: 1) examine how laboratory and field measurements of bioaccumulation endpoints compare, 2) discuss the reasons why laboratory measurements may not align with field data, and 3) explore the main sources of variation in field bioaccumulation measurements and TMFs. The following 5 articles in this issue of Integrated Environmental Assessment and Management provide the key findings and recommendations from this workshop.

KEY FINDINGS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. WORKSHOP OBJECTIVES
  5. KEY FINDINGS
  6. REFERENCES

Comparing Laboratory and Field Measured Bioaccumulation Endpoints (Burkhard et al. 2012a, 2012b)

One of the key issues with comparing laboratory and field data, especially among the various bioaccumulation metrics, was to determine a standard basis for this comparison. This working group recommended that fugacity ratios serve as this standard metric. Using this approach, field measurements and other laboratory measurements (i.e., BSAFs and BMFs) can be used, along with a chemical's BCF–BAF and KOW, in a weight-of-evidence assessment of “B” potential for nonionic organic chemicals. This approach also provides a basis for direct comparison of all laboratory and field bioaccumulation measurements (i.e., values for BCF, BAF, BSAF, BMF, BSSAF, and TMF). The working group concluded that the use of both field and laboratory bioaccumulation measurements in “B” assessments will improve confidence in “B” classification decisions.

Laboratory sediment bioaccumulation tests are extensively used in regulatory applications; however, the level of agreement between laboratory measured BSAFs and field-derived BSAFs for infaunal invertebrates has not been systematically assessed. Based on a large database of BSAF values, the analysis by the working group found that 1) laboratory BSAFs for the oligochaete Lumbriculus variegatus are typically within a factor of 2 of the BSAFs for field-collected oligochaetes, and 2) laboratory BSAFs for bivalves can provide reasonable estimates of field BSAF values (with a factor of 2 to 3), if certain precautions are taken, such as ensuring that steady-state BSAF values are being compared.

Understanding the Sources of Differences in Laboratory and Field Metrics of Bioaccumulation (Selck et al. this issue2012)

The 2nd working group focused on understanding and quantifying the sources of variability between laboratory and field metrics of bioaccumulation. They found that probabilistic models could be used 1) to improve our understanding of the underlying processes controlling bioaccumulation, 2) to direct sampling methods to improve accuracy of bioaccumulation measures in field samples (i.e., pinning down main drivers of variation in “B”), and, 3) eventually as a significant tool in PBT assessment (i.e., after validation). These conclusions were demonstrated using models that simulated the field accumulation of contaminants in mayflies, polychaetes, yellow perch, and little owls (represented by Athene noctua). The model simulations explained from 65 to more than 100% of the variation in empirical data. A few of the main conclusions include:

  • As few as 3 to 12 of 56 parameters explained more than 95% of the variation in bioaccumulation for the 8 organism–chemical simulations performed.

  • Accurate “B” assessment for benthic species requires knowledge of the chemical's bioavailability in the sediment.

  • Accurate “B” assessment for higher predatory species such as yellow perch and little owls requires knowledge of how the composition of, and chemical concentrations in, the diet vary.

  • Food is the main contributor to the uptake of hydrophobic contaminants, specifically those with log KOW greater than approximately 5, for benthic, pelagic, and terrestrial organisms. Given the potential importance of dietary exposure as a bioaccumulation pathway, the appropriateness of the BCF as the only “B” metric for hydrophobic contaminants, as opposed to its use in conjunction with additional metrics such as BAF and TMF that include dietary uptake, was discussed.

In order to validate and implement models in bioaccumulation assessment, there is a need for a range of activities that demonstrate the added value of models for ecological risk assessment of bioaccumulative chemicals. Relevant activities include 1) comparative bioaccumulation studies in the laboratory and field for the same chemicals, 2) studies to determine the actual bioavailable chemical concentrations in food items, including the distribution and effects of black C and other sediment components (labile organic matter, inorganic matter, and others) in natural sediments on chemical absorption efficiencies in a range of organisms, and 3) development of models for compounds other than neutral organics (e.g., hydrophilic organics, metals, and so forth). By focusing on these issues, we will significantly improve data for model parameterization and refinement and increase confidence in model outputs (specifically by model validation).

Trophic Magnification Factors in Bioaccumulation Assessment (Borgå et al. this issue2012)

It is recognized that TMFs, calculated from the slope of log-transformed concentrations of a contaminant versus trophic level (using stable N isotopes), can be used to understand whether a chemical does (TMF > 1) or does not (TMF < 1 or = 0) biomagnify through food webs. This approach shows considerable promise for improving our understanding of the “B” potential for a diverse range of chemicals. The report by Borgå et al. (this issue2012) describes how the approach has been used thus far and its advantages over other metrics used to measure biomagnification. However, it is clear that a number of factors must be considered when designing TMF studies and evaluating their data both within and across sites to ensure that this approach meets its full potential. This working group concluded the following:

  • Although not well understood, physical, chemical, and biological characteristics of ecosystems and their organisms may affect TMFs. These characteristics, as well as statistical and analytical issues, should be considered when studies are designed.

  • Although this approach has been used for almost 2 decades, several knowledge gaps exist, including 1) an understanding of what the intercepts of TMF relationships represent, 2) the usefulness of TMFs for terrestrial systems, and 3) the variability in TMFs across diverse ecosystems. Standardized approaches to TMF studies would improve our ability to use these data to assess the “B” potential of chemicals.

Using Trophic Magnification Factors and Related Measures in Regulatory Assessments (Conder et al. 2012)

The final working group examined the use of field-derived TMFs and other measures of bioaccumulation in conducting a holistic weight-of-evidence assessment of bioaccumulation potential in a regulatory context. This group concluded the following:

  • TMF values are useful as a holistic quantification of bioaccumulation potential in a regulatory context, but the strength of each study design and its results should be evaluated in the context of statistical power, food web characteristics, and comparative results for known bioaccumulative chemicals.

  • Caveats to the use of TMFs include the lack of information on the transfer from abiotic compartments to lower trophic levels, as well as the compression of information about single predator–prey relationships into a single TMF value.

  • When insufficient field data are available, multiple supporting lines of bioaccumulation evidence (e.g., trophic-level normalized BMFs and BAFs, modeling, and quantitative–structure activity relationships) can be used to provide information analogous to that provided by a TMF.

These articles represent a culmination of the key concepts and ideas explored by the participants at the workshop and a critical analysis of the state of the science for evaluating laboratory and field bioaccumulation data. The workshop organizers and participants hope that the information presented in these articles will serve as a starting point for future discussions on the refinement of bioaccumulation assessment and as a springboard for the research necessary to address the data gaps identified in the articles.

REFERENCES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. WORKSHOP OBJECTIVES
  5. KEY FINDINGS
  6. REFERENCES
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