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Keywords:

  • Bioaccumulation;
  • Biomagnification;
  • Chlorinated paraffins;
  • PBT;
  • Trophic magnification

ABSTRACT

  1. Top of page
  2. ABSTRACT
  3. INTRODUCTION
  4. PHYSICOCHEMICAL PROPERTIES AND MODELING
  5. BIOCONCENTRATION/BIOACCUMULATION FACTORS
  6. BIOMAGNIFICATION FACTORS
  7. TROPHIC MAGNIFICATION FACTORS
  8. METABOLISM OF CHLORINATED PARAFFINS
  9. CONCLUSIONS
  10. Acknowledgment
  11. REFERENCES

Chlorinated paraffins (CPs) are high molecular weight organochlorine compounds that have been used in a variety of industrial applications for many years. Medium-chain chlorinated paraffins (MCCPs) (CAS 85535-85-9; Alkanes, C14–17, chloro) are currently under investigation as potential persistent bioaccumulative toxic (PBT) compounds. In this article, the bioaccumulation potential of MCCPs is assessed using a tiered framework proposed after a recent Society of Environmental Toxicology and Chemistry (SETAC) Pellston Workshop in 2008. The framework proposes the use of physicochemical properties and modeling assessment, bioconcentration/bioaccumulation (BCF/BAF) assessment, biomagnification (BMF) assessment, and trophic magnification factor (TMF) assessment. It is hoped that use of this framework could harmonize and improve the efficiency and effectiveness of the chemical substance evaluation screening process for PBT properties. When applied to MCCPs, the following conclusions were made: empirical physiochemical data is available negating the use of models; laboratory BCFs range from 1000 to 15 000 (growth-corrected lipid normalized values) for 2 MCCP structures; field BAFs were an order of magnitude higher than the trigger criterion for “B status possible”; although results may not meet acceptance criteria for field studies, laboratory-derived BMFs for a number of C14–17 chlorinated alkanes were less than the trigger value of 1 (based on whole-body concentrations) whereas field-derived BMFs were less than 1 (based on lipid corrected values [generally used for field data] excluding one measure for sculpin, [Cottus cognatus]-Diporeia that was based on only one detectable sample); and finally, TMFs were less than the trigger criterion value of 1, which are considered the most convincing evidence for bioaccumulative properties of a compound and the “Gold Standard” measure of bioaccumulation. This article also discusses the uncertainties surrounding the published data, especially concerning field data where limited sampling points are available and the difficulty in assessing the bioaccumulative potential of MCCPs as mixtures of different congeners. In conclusion, although some laboratory bioaccumulation values have a potential for concern, the majority of field values are more favorable when assessing the bioaccumulative potential of MCCPs. Definitive conclusions on the PBT assessment of MCCPs can be eased with further testing in both areas of P and B in the laboratory in conjunction with further monitoring of biota in the field to derive more robust field data. Integr Environ Assess Manag 2014;10:78–86. © 2013 SETAC


INTRODUCTION

  1. Top of page
  2. ABSTRACT
  3. INTRODUCTION
  4. PHYSICOCHEMICAL PROPERTIES AND MODELING
  5. BIOCONCENTRATION/BIOACCUMULATION FACTORS
  6. BIOMAGNIFICATION FACTORS
  7. TROPHIC MAGNIFICATION FACTORS
  8. METABOLISM OF CHLORINATED PARAFFINS
  9. CONCLUSIONS
  10. Acknowledgment
  11. REFERENCES

Chlorinated paraffins (CPs) also known as polychlorinated alkanes (PCAs) are high molecular weight organochlorine compounds that have been used for many years in a variety of industrial applications, including use as high temperature lubricants, plasticizers, flame retardants, and additives in adhesives, paints, rubber, and sealants. The first large scale use of CPs is reported as lubricant additives in 1932 and usage increased steadily through to the 1990s (Muir et al. 2000).

Individual commercial CP products are complex mixtures of congeners with varying C-chain lengths and chlorination levels. They are manufactured by the direct chlorination of different n-alkanes. Commercial CP products are grouped by C-chain length of the n-alkane feedstock used in their manufacture. Those manufactured from n-alkanes with chain lengths C10–13 are referred to as short-chain chlorinated paraffins (SCCPs), those manufactured from n-alkanes with chain lengths C14–17 are referred to as medium-chain (MCCPs), and those manufactured from n-alkanes with chain lengths C18–20 or C >20 are referred to as long-chain (LCCPs). SCCPs (CAS 85535-84-8; Alkanes, C10–13, chloro) are currently subjected to controlled use in many applications due to their potential to be persistent bioaccumulative toxic (PBT) compounds and, more recently, regulatory attention has shifted to the evaluation of MCCPs (CAS 85535-85-9; Alkanes, C14–17, chloro) as PBT compounds (EU 2005, 2007; Environment Canada 2008).

The bioaccumulative potential of MCCPs is not easily categorized in relation to the current regulatory criteria, and a considerable amount of relevant data has been generated in the last 10 years. Commercial MCCPs are mixtures of many different congeners, each with potentially different environmental behavior (Sijm and Sinnige 1995). Various national and international regulatory schemes exist to evaluate the impact of chemical substances on the environment and it is recognized that, although there exist some common approaches in these schemes, there is currently no uniform assessment of PBT or very persistent, very bioaccumulative (vPvB) properties of chemicals in the European Union (EU) and the rest of the world. Further harmonization is needed to present a consistent approach among international frameworks (Moermond et al. 2011). Although the criteria can differ between the different schemes, all aim to identify chemicals with a high potential to accumulate in organisms, in combination with high environmental persistence and (in most cases) high toxicity.

Bioaccumulation is broadly defined as a process by which the concentration of a chemical in an organism exceeds that in the respiratory medium (e.g., water for fish, air for mammals), or in the diet, or both (Gobas et al. 2009). Highly bioaccumulative substances are perceived as problematic because potentially hazardous concentrations may be achieved in organisms, including humans, at the top of food chains, even though the “source” (e.g., water) concentrations are not directly toxic to exposed organisms. In regulatory frameworks, bioaccumulation is traditionally assessed using metrics such as the octanol-water partition coefficient (Kow) and bioconcentration factors (BCFs) determined from laboratory studies, but it is now recognized that such factors may not be good descriptors of the biomagnification potential of some substances, especially for hydrophobic substances (Gobas et al. 2009; Swackhamer et al. 2009; Howard and Muir 2010; Borga et al. 2011; Selck et al. 2011). Table 1 lists the criteria used by different regulatory agencies to classify bioaccumulation (taken from Gobas et al. 2009).

Table 1. Criteria used by regulatory agencies to classify bioaccumulation (taken from Gobas et al. 2009)
Regulatory agencyBioaccumulation endpointCriteriaProgram
  1. BCF = bioconcentration factor; CEPA = Canadian Environmental Protection Act 1999; EU = European Union; REACH = Registration, Evaluation, and Authorization of Chemicals; TRI = Toxic Release Inventory; TSCA = Toxic Substances Control Act; UN = United Nations; US = United States.

  2. a

    Government of Canada (1999, 2000).

  3. b

    REACH Annex XII (European Commission 2001).

  4. c

    Currently being used by the US Environmental Protection Agency in its TSCA and TRI programs (USEPA 1976).

  5. d

    Stockholm Convention on Persistent Organic Pollutants (UNEP 2001).

Environment CanadaKow≥100 000CEPA 1999a
Environment CanadaBCF≥5000CEPA 1999
Environment CanadaBAF≥5000CEPA 1999
EU “bioaccumulative”BCF≥2000REACHb
EU “very bioaccumulative”BCF≥5000REACH
US “bioaccumulative”BCF1000–5000TSCAc, TRI
US “very bioaccumulative”BCF≥5000TSCA, TRI
UN Environment ProgramKow≥100 000Stockholm Conventiond
UN Environment ProgramBCF≥5000Stockholm Convention

Until recently, BCFs for the aqueous environment were measured in the laboratory using the Organisation for Economic Co-operation and Development (OECD) 305 Test Guideline (OECD 1996). This guideline has recently been reviewed and updated (OECD 2012). The new guideline contains the option to use a new minimized aqueous exposure test, a revised full aqueous exposure test, or a new standardized dietary exposure test for poorly water soluble substances. Although other bioaccumulation metrics, such as laboratory and field biomagnification factors (BMFs), biota to sediment bioaccumulation factors (BSAFs), and trophic magnification factors (TMFs) are being considered more in a weight of evidence (WoE) approach to assessment, they are not often used in a regulatory context (Gobas et al. 2009). Although the various regulatory schemes attempt to set both quantitative and qualitative criteria to define the level of bioaccumulation deemed to be hazardous, interpretation of these criteria in relation to the different types of scientific data that are, or are not, available for a particular substance is often difficult. In response to this difficulty, Gobas et al. (2009), as part of a SETAC Pellston Workshop in 2008, considered all factors relevant to the identification of PBTs and persistent organic pollutants (POPs), reviewed the state of the science, and proposed a framework for the evaluation of bioaccumulation in relation to the regulatory situation. It was hoped that use of this framework could harmonize and improve the efficiency and effectiveness of the chemical substance evaluation screening process. It has several advantages over current screening methods, including the minimization of incorrect categorizations and the more effective use of available data.

This article aims to review the bioaccumulation potential of commercial MCCPs in the aquatic environment using the tiered framework proposed by Gobas et al. (2009). Although these authors describe a “top-down” approach, starting with the “definitive” assessment of relevant food webs for TMF (defined below), they indicate that in practice, for screening of chemicals, the framework is likely to be used in reverse order; this sequence is used here: physicochemical properties and modeling assessment, bioconcentration/bioaccumulation (BCF/BAF) assessment, BMF assessment, and TMF assessment. The potential metabolism of MCCPs is also considered. The definitions used below are those given by Gobas et al. (2009).

PHYSICOCHEMICAL PROPERTIES AND MODELING

  1. Top of page
  2. ABSTRACT
  3. INTRODUCTION
  4. PHYSICOCHEMICAL PROPERTIES AND MODELING
  5. BIOCONCENTRATION/BIOACCUMULATION FACTORS
  6. BIOMAGNIFICATION FACTORS
  7. TROPHIC MAGNIFICATION FACTORS
  8. METABOLISM OF CHLORINATED PARAFFINS
  9. CONCLUSIONS
  10. Acknowledgment
  11. REFERENCES

As stated by Gobas et al. (2009), quantitative modeling predictions based on physicochemical properties are only of significant value if empirical bioaccumulation data are not available. For MCCPs, there are a large number of empirical studies and, as a consequence, such modeling serves only to indicate in which areas measured data are needed. For lipophilic substances, the most relevant physicochemical property for use in assessing bioaccumulation potential in water-respiring organisms is the octanol-water partition coefficient (Kow), which acts as a surrogate to indicate the chemical's tendency to partition from the ambient water into the lipid compartment of organisms. Although a Kow can be a useful predictor of bioaccumulation, it can lead to an overestimation if metabolism/biotransformation occurs. MCCPs are hydrophobic compounds with relatively high Kow values (typically cited as log Kow 5.5 to 8.2 but dependent on chain length and chlorination level) (EU 2005). Furthermore, because of the complexity of MCCP mixtures, and the difficulty of their analysis, the Kow values themselves are of uncertain accuracy (Sijm and Sinnege 1995).

Although bioaccumulation, particularly bioconcentration, has been shown (as a general rule) to increase with increasing Kow up to a log Kow of approximately 6, there is considerable evidence (of particular relevance to MCCPs) for a decline above this level (Bintein et al. 1993; Meylan et al. 1999), possibly related to a decrease in the permeability through biological membranes due to increasing molecular size. Thus for MCCPs, different models provide very different estimates of bioaccumulation, dependent on the model used, the particular congeners specified, and the Kow value selected (EU 2007). Furthermore, the bioaccumulation of a substance is heavily dependent on its metabolism by the organism, which for MCCPs is relevant but for which the rate is uncertain (Sijm and Sinnege 1995; Fisk et al. 1996).

BIOCONCENTRATION/BIOACCUMULATION FACTORS

  1. Top of page
  2. ABSTRACT
  3. INTRODUCTION
  4. PHYSICOCHEMICAL PROPERTIES AND MODELING
  5. BIOCONCENTRATION/BIOACCUMULATION FACTORS
  6. BIOMAGNIFICATION FACTORS
  7. TROPHIC MAGNIFICATION FACTORS
  8. METABOLISM OF CHLORINATED PARAFFINS
  9. CONCLUSIONS
  10. Acknowledgment
  11. REFERENCES

Bioconcentration factors

Gobas et al. (2009) defined a BCF as the ratio of the steady-state chemical concentrations in an aquatic water-respiring organism (CB, g chemical/kg wet weight) and the water (CW, g chemical/L) determined in a controlled laboratory experiment in which the test organisms are exposed to a chemical in the water (but not in the diet) (units: L/kg wet weight).

It is now accepted that to standardize measurements of bioaccumulation for easy comparison, metrics such as BCF, BAF, and BMF should be normalized to a known lipid content. However, definitions given by Gobas et al. (2009) for BCF, BAF, and BMF seem to indicate (via the units presented as wet weight) that data should be used as whole-body concentrations in the framework. The majority of data discussed in this section and the Biomagnification factors section is based on lipid normalized values reported in the literature but for comparative reasons, where possible, the data has also been transformed into whole-body concentrations.

Before 2000, a number of studies had reported BCFs in fish for MCCPs, all of which were below 1000 (EU 2005). However, these studies were criticized on the grounds that the exposure (water) concentrations used were in excess of the solubility of the substance and therefore may have overestimated exposure and thus underestimated the BCF. Furthermore, most of the studies preceded, and therefore were not consistent with, standardized procedures (e.g., OECD Guideline 305). In response to these criticisms, and as part of the European Risk Assessment Regulation an OECD-compliant study was carried out (Thompson et al. 2000) to determine the BCF in rainbow trout (Oncorhynchus mykiss), exposed to a 51% chlorinated MCCP, monitored using 14C-radiolabeled chlorinated n-pentadecane (≈C15H26Cl6). The exposure period was 35 days followed by 42 days depuration.

The maximum BCF reported was 1100 at a nominal exposure concentration of 1.0 μg/L (mean measured 0.93 μg/L), calculated by the kinetic method (whole-body, extrapolated to steady-state). Because this was based on radiolabeled residues and may therefore have included metabolites of the parent substance, this value can be considered as a worst-case estimate. The study was carried out to the then current OECD test guideline and no growth correction or lipid normalization was carried out (as now recommended; OECD 2012). Further analysis of the original data for growth correction and lipid normalization to the now recommended 5% (OECD 2012) gives a BCF of 1000. (Lipid normalization was calculated using a representative 10% fish lipid content [estimated from in-house data] because no lipid measurements were determined in the original study.) The resulting BCF of 1000 is lower than the BCF criterion specified in the current regulatory schemes for the EU (BCF 2000), Canada, and the United Nations Environment Program (BCF 5000) and lower than the indicator for “B status possible” (BCF 5000) recommended by Gobas et al. (2009).

A further study has been conducted to determine the BCF in rainbow trout (O. mykiss) of a lower single-chain length material with a relatively low chlorination level (45% chlorinated [14C]-n-tetradecane; ≈C14H25.5Cl4.5) (Vaughan and Hurd 2010). The exposure period was 35 days followed by 42 days depuration. A whole-body BCF of 6600 was reported and a maximum BCF obtained of 9100 at a nominal exposure concentration of 0.50 μg/L (mean measured 0.34 μg/L), calculated by the kinetic method. Further manipulation of the data to conform with the 2012 OECD 305 test guideline recommendations gives a lipid normalized growth corrected kinetic BCF of 15 000, well in excess of the 5000 B status possible recommended by Gobas et al. (2009). As for the previous study, this study was based on the analysis of radiolabeled residues and may therefore have included metabolites of the parent substance that may have been incorporated into lipid or protein tissue in the fish. At the end of the study, analysis of fish taken from the end of the depuration phase for parent compound indicated significant metabolism, with a mean metabolite percentage of 21% reported (range 17%–30%, nonextractable residues considered as bound metabolites in fish tissue) (Leonards and van Beuzekom 2010), although the mean percentage of metabolites observed may also have been underestimated. Fish samples were only available for analysis at the end of the depuration period, therefore metabolites and parent compound may have been excreted. Because the potential metabolites are likely to be more polar and may have different depuration rates to the parent compound, the ratio of parent–metabolite may have been different at the end of depuration compared to the end of uptake. The level of metabolites may therefore have been underestimated if they had depurated at a faster rate than the parent compound, see “Metabolism of chlorinated paraffins” for further discussion.

A study of the bioconcentration in carp (Cyprinus carpio) of a 49% chlorinated tridecane (C13H23.2Cl4.8), separately monitoring Cl5 (50% Cl), Cl6 (54% Cl), and Cl7 (58% Cl) components in water and fish using high performance liquid chromatography mass spectrometry (LC/MS) has been reported. The fish were exposed to nominal concentrations of 1.0 and 10 μg/L of the test substance for 62 days. Preliminary data (UNEP 2009) provides whole-body steady-state BCFs of 1700, 2000, and 2800 for Cl5, Cl6, and Cl7, respectively at the higher exposure concentration (1500, 1600, and 2300, respectively, at the lower exposure concentration). The similarity of the BCFs at the different exposure levels indicates that the dosing system had achieved full dissolution of the components at both concentrations. In addition Cl4, Cl8, and Cl9 components were monitored, but the levels were considered too low to provide accurate BCFs; approximate values after 62 days were 300, 2600, and 1800, respectively for the higher exposure concentration. Depuration was also monitored but the data have not been reported. These data suggest that bioconcentration increases with increasing chlorination of the tridecane, up to Cl7 (58% Cl), with a possible slight decline thereafter. The increase cannot be attributed to increasing hydrophobicity, because the authors also reported that measured solubilities of the congeners increased with increasing chlorination −50, 70, and 90 μg/L for Cl5, Cl6, and Cl7, respectively. Therefore, the increasing BCF might suggest that metabolism of the components of the parent substance was decreasing with increasing chlorination.

All available whole-body fish BCFs obtained for representative single-chain length materials over the range C10 to C17 using procedures compatible with OECD Guideline 305, are plotted against chain length in Figure 1. The plot shows percentage chlorination level and distinguishes between analysis based on the radiolabel (14C) or parent compound. Results are shown for studies previously mentioned above and a further study on a C11 58% Cl material (Madeley and Maddock 1983b).

image

Figure 1. Plot showing all available whole-body fish bioconcentration factors obtained for representative single chain length materials over the range C10 to C17 plotted against C number. The plot shows the percentage chlorination level and distinguishes between analysis based on the radiolabel (14C) or parent compound. Results are shown for studies previously mentioned above and a further study on a C11 58% Cl material (Madeley and Maddock 1983b).

Download figure to PowerPoint

The recent BCF for 45% chlorinated tetradecane (C14) appears to be unusually high compared with those obtained for C13 and C15 substances, which might suggest that substantial metabolism occurs below a “critical” level of chlorination. In that case, determinations by radiochemistry would increasingly overestimate the BCF with decreasing chlorination level. The potential for metabolism of chlorinated paraffins is discussed further later.

Bioaccumulation factors

Defined as the ratio of the steady-state chemical concentrations in an aquatic water-respiring organism (CB, g chemical/kg wet weight) and the water (CW, g chemical/L) determined from field data in which sampled organisms are exposed to a chemical in the water and in their diet (units: L/kg wet weight).

Field data relevant to a BAF assessment of C14–17 chlorinated alkanes, based on this definition, are provided by Houde et al. (2008).

Houde et al. (2008) report concentrations of C14–17 chlorinated alkanes in biota and water samples from Lake Ontario and Lake Michigan. Bioaccumulation factors are calculated between water and 4 species of fish and plankton from Lake Ontario, but are expressed as lipid normalized values. As described above, these values have also been corrected to whole-body (wet weight) units, as specified in the framework definition, using the mean lipid content of the samples as given in the article.

Mean whole-body (total C14–17 chlorinated alkanes) BAFs range from 35 000 L/kg wet weight (lipid normalized Log BAF = 6.5) for water-Diporeia to 958 000 L/kg wet weight (lipid normalized Log BAF = 7.3) for water-sculpin (Cottus cognatus). These values are considerably in excess of the framework criterion of 5000 indicative of B status possible (Gobas et al. 2009), and markedly different from the laboratory BCF data discussed above. However, it should be noted that these BAFs are based on water samples taken at different locations and at different times to the biota samples. Thus, it is possible that the biota concentrations reflect exposure to temporally or spatially varying ambient levels, in particular in relation to local sources of contamination. Indeed, Houde et al. (2008) (Supplemental Data) show that the measured water concentration of C14–17 chlorinated alkanes varied from 47 pg/L in 2002 to <0.5 pg/L in 2004, at the same sample location. Furthermore, the biota were sampled from the western, industrialized (Toronto, Hamilton, etc.) end of Lake Ontario, whereas the water samples were taken in the central and eastern areas of the lake. Each fish species value was based on only 2 samples (except for lake trout [Salvelinus namaycush], 7 samples) and the water concentration was based on only 4 samples of which 2 were below the detection limit. Therefore, the results quoted in Houde et al. (2008) do not fully meet acceptance criteria given for field studies. Parkerton et al. (2008) stated that guidance for the conduct of field bioaccumulation studies is lacking, and further efforts are needed to describe best practices for field investigations. Field samples should sufficiently represent the habitat and exposure regime of the selected organism, and samples should be taken at the same locations over a period of time (Weisbrod et al. 2009). Further acceptance criteria for field measurements are given in Burkhard et al. (2011).

BIOMAGNIFICATION FACTORS

  1. Top of page
  2. ABSTRACT
  3. INTRODUCTION
  4. PHYSICOCHEMICAL PROPERTIES AND MODELING
  5. BIOCONCENTRATION/BIOACCUMULATION FACTORS
  6. BIOMAGNIFICATION FACTORS
  7. TROPHIC MAGNIFICATION FACTORS
  8. METABOLISM OF CHLORINATED PARAFFINS
  9. CONCLUSIONS
  10. Acknowledgment
  11. REFERENCES

Laboratory-derived BMFs

Defined as the ratio of the steady-state chemical concentrations in a water- or air-respiring organism (CB, g chemical/kg wet weight) and in the diet of the organism (CD, g chemical/kg dry weight) determined in a controlled laboratory experiment in which the test organisms are exposed to chemical in the diet (but not the water or air) (units: kg dry weight/kg wet weight).

Laboratory biomagnification data are available for rainbow trout (O. mykiss) fed diets artificially contaminated with various C14–17 chlorinated alkane congeners (Fisk et al. 1996, 1998, 2000). These studies reported BMFs based on lipid corrected (note not lipid normalized)/growth corrected concentrations in both the fish and the diet and thus have also been corrected back to the units of whole fish (wet weight) and whole diet (dry weight), as per the definition above, based on the lipid concentrations reported for the fish and their food.

After this transformation to whole-body, the BMFs for 4 C14 congeners (ranging from 42%–55% chlorination) and 2 C16 congeners (34% and 69% chlorination) ranged from 0.10 to 0.96, with a mean of 0.38, with no clear relationship between BMF and chain length or chlorination level. It should be noted that these BMFs were based on the uptake and depuration kinetics, and were therefore predicted values at steady-state. The lipid corrected/growth corrected values reported in Fisk et al. (1996) for the 2 C16 congeners ranged from 0.44 to 1.07, whereas the values reported for 3 of the 4 C14 congeners in Fisk et al. (1998) are less clear. Here, 3 separate BMFs are reported for each congener. First, BMF equilibrium, calculated using the same equation for the lipid corrected–growth corrected BMFs reported in 1996 and 2000, range from 1.9 to 3.0, but BMFs are also reported based on both an assumed assimilation efficiency of 0.5 (range, 1.7–5.0) and an assumed steady-state (range, 0.74–2.8). The authors discuss the uncertainty surrounding some of the calculated assimilation efficiencies with some efficiencies calculated at >100%, hence the use of an assumed assimilation efficiency. The last of the 4 C14 congeners reported in Fisk et al. (2000) had lipid corrected/growth corrected BMF values ranging from 0.27 to 0.43 for the 2 concentrations tested.

Biomagnification factors >1 would indicate probable B status for a chemical that may undergo biomagnification, whereas BMFs <1 indicate possible trophic dilution. Biomagnification factors for C14–17 chlorinated alkanes as discussed above are all <1 based on whole-body concentrations as described in the framework, although some lipid corrected/growth corrected BMFs, as reported in the literature are >1.

It should be noted that, as well as not being consistent with the definition given in the framework, there is uncertainty on the scientific rationale for the lipid correction of laboratory biomagnification studies, as used by Fisk et al. (1996, 1998, 2000) Some uncertainty has been expressed over the relevant basis to express laboratory BMFs and the use of this data needs careful consideration (EU 2005).

Field-derived BMFs

Defined as the ratio of the steady-state chemical concentrations in a water- or air-respiring organism (CB, g chemical/kg wet weight) and in the diet of the organism (CD, g chemical/kg wet weight) determined from field data in which sampled organisms are exposed to chemical in air, water, and diet (units: kg wet weight/kg wet weight).

Data on field analyses from food web components of Lake Ontario and Lake Michigan were used to derive BMFs for C14–17 chlorinated alkanes in Houde et al. (2008). Houde et al. (2008) contains much of the data in EU (2005) but contains additional analyses for certain types of samples. Similarly, regarding BMFs, Muir et al. (2003) can be considered to be superseded by Houde et al. (2008). In all cases, the BMFs reported by Houde et al. (2008) are equal to or exceed those given in Muir et al. (2008).

Table 2 shows BMFs reported by Houde et al. (2008) that are lipid-corrected (ng/g lipid in predator ÷ ng/g lipid in prey) as generally used for field data, and whole-body BMFs as calculated from the raw data provided in Houde et al. (2008) for total C14–17 chlorinated alkanes in the different organisms. For C14–17 chlorinated alkanes, BMFs are given between lake trout, S. namaycush and 3 species of potential prey fish (alewife [Alosa pseudoharengus], rainbow smelt [Osmerus mordax], and sculpin [Cottus cognatus]) and also between sculpin (C. cognatus) and a benthic invertebrate (Diporeia), both for individual C14, C15, and C16 isomer groups and for total C14–17 chlorinated alkanes (mean of the 3 groups). For Lake Michigan, all C14–17 chlorinated alkane chain lengths were below detection in rainbow smelt, (O. mordax) and C16 isomers were below detection in all of the biota samples. For total C14–17 chlorinated alkanes, the lipid-corrected BMFs were <1 for all lake trout S. namaycush–prey fish comparisons with a maximum for Lake Ontario of 0.25 (lake trout [S. namaycush]–alewife [A. pseudoharengus]) and a maximum for Lake Michigan of 0.94 (lake trout [S. namaycush]–sculpin [C. cognatus]). For sculpin (C. cognatus)–Diporeia, the BMF was 0.88 in Lake Michigan, but 8.7 in Lake Ontario. Biomagnification factors for the individual chain length groups were also all ≤1.0 except for sculpin, (C. cognatus)–Diporeia in Lake Ontario. However, the authors noted that for Diporeia in Lake Ontario, the values were based on a detectable concentration of C14–17 chlorinated alkanes in only 1 sample.

Table 2. BMF values for total C14–17 chlorinated alkanes from Houde et al. (2008)
BMF values Lake trout (Salvelinus namaycush)—alewife (Alosa pseudoharengus)Lake trout (Salvelinus namaycush)—smelt (Osmerus mordax)Lake trout (Salvelinus namaycush)—sculpin (Cottus cognatus)Sculpin (Cottus cognatus)—Diporeia
  1. BMF = biomagnification factor.

  2. a

    Based on analysis of 1 Diporeia sample.

  3. b

    BMF could not be calculated because of nondetected values.

  4. c

    Whole-body BMF values calculated from the raw data provided by Houde et al. (2008).

  5. d

    Whole-body concentrations in Diporeia not given. Estimated from lipid-based BMF and lipid content.

Lipid-correctedLake Ontario0.25 ± 0.260.14 ± 0.160.11 ± 0.108.7a ± 7.7
 Lake Michigan0.22 ± 0.10b0.94 ± 0.170.88 ± 0.71
 Mean of lakes0.240.534.8
Whole-bodycLake Ontario0.690.220.2225.7a
 Lake Michigan1.00b1.932.18d
 Mean of lakes0.841.0813.9

As discussed previously for BAF data, field samples should sufficiently represent the habitat and exposure regime of the selected organism and multiple samples should be taken over a prolonged period. Use of a single sample in field monitoring will contribute to an unbalance of the design and will result in considerable leverage of the sample data point (Borga et al. 2011). Thus, the sculpin (C. cognatus)–Diporeia values for Lake Ontario may not be representative, especially considering that the BMF for the same pairing in Lake Michigan was <1. Furthermore, commenting on essentially the same data, Muir et al. (2002) state that further work was needed to confirm whether or not these represent realistic BMFs based on actual feeding by sculpin (C. cognatus) on Diporeia. For example, Brandt (2004) showed that the contribution of Diporeia to the sculpin's diet varied geographically and seasonally and that for certain of the Great Lakes there has been a decline in the Diporeia populations in recent years, contributing to this variability. Houde et al. (2008) also suggest that the high concentrations in sculpin (C. cognatus) indicate that sediment may be a source of contamination for these fish, noting that for C10–13 chlorinated alkanes in Lake Ontario, the chain-length distribution in sculpin (C. cognatus) was very similar to that in sediments. Although it is expected that sediments may be a reservoir for hydrophobic substances such as MCCPs, biota-sediment accumulation factors (BSAFs) are not directly discussed in the referenced literature or considered using the Gobas framework as a critic for the aquatic bioaccumulation potential of MCCPs. However, the effects of MCCP exposure from sediments are considered via field BMFs and TMF analysis.

It should be noted that there was high variability reported for the biota concentrations of C14–17 chlorinated alkanes, in particular for lake trout (S. namaycush) (Lake Ontario 24 ± 26 ng/g wet weight; Lake Michigan 5.6 ± 4.8 ng/g wet weight). Considering this, and the difference between the lake trout (S. namaycush)–sculpin (C. cognatus) values for the 2 lakes, there is no convincing evidence for BMFs >1 between lake trout (S. namaycush) and prey fish species. The uncertainties regarding the sculpin (C. cognatus)–Diporeia values have already been described.

TROPHIC MAGNIFICATION FACTORS

  1. Top of page
  2. ABSTRACT
  3. INTRODUCTION
  4. PHYSICOCHEMICAL PROPERTIES AND MODELING
  5. BIOCONCENTRATION/BIOACCUMULATION FACTORS
  6. BIOMAGNIFICATION FACTORS
  7. TROPHIC MAGNIFICATION FACTORS
  8. METABOLISM OF CHLORINATED PARAFFINS
  9. CONCLUSIONS
  10. Acknowledgment
  11. REFERENCES

Defined as the average factor by which the normalized chemical concentration in biota of a food web increases per trophic level. The TMF is determined from the slope (m) derived by linear regression of logarithmically transformed normalized chemical concentration in biota and trophic position of the sampled biota.

Houde et al. (2008) report TMFs, calculated as per the above definition, for C14, C15, and C16 groups and for total C14–17 chlorinated alkanes for Lake Ontario. The values were based on regressions between log concentrations in biota on a lipid basis and the trophic level (derived from δ15N values). Trophic magnification factors could not be calculated for Lake Michigan due to nondetected values in numerous species. Trophic magnification factor values for Lake Ontario ranged from 0.14 (C16) to 0.29 (C14), with a value of 0.22 for total C14–17 chlorinated alkanes, although the uncertainty discussed earlier for field studies also apply in this case. Concentrations of C14–17 chlorinated alkanes were observed to be lower in lake trout (S. namaycush) than their prey based on a lipid basis, indicating possible biotransformation in higher organisms (Houde et al. 2008).

Data derived from field studies, and in particular TMF values, are considered to be the ultimate indicator of a compound's potential to bioaccumulate in the natural environment. Field measurements integrate multiple exposure routes and processes that may enhance (biomagnifications) bioaccumulation, mitigate (biotransformation, bioavailability) bioaccumulation, or both (Weisbrod et al. 2009). Trophic magnification factors are therefore considered to be the Gold Standard holistic measure of a compound's bioaccumulation potential and are suggested to be the most reliable tool for assessing the bioaccumulation potential of commercial compounds that have been in use for a long time (Gobas et al. 2009; Weisbrod et al. 2009; Swackhamer et al. 2009; Borga et al. 2011; Burkhard et al. 2011; Conder et al. 2011). Swackhamer et al. (2009) also describe a TMF as essentially an “average BMF” value considering all of the trophic levels in a given food web.

Gobas et al. (2009) considered that a TMF >1 represented the most conclusive evidence of the bioaccumulative nature of a chemical. Trophic magnification factor values seen from Lake Ontario are <1, therefore, with regard to aquatic (water-respiring) food webs, C14–17 chlorinated alkanes are below this threshold, and should not be considered bioaccumulative. Because C14–17 chlorinated alkanes have also been used for many years, they can be considered to have reached steady-state in the environment. This assumption is pertinent when considering the lack of TMFs available for Lake Michigan due to nondetected values in numerous species.

METABOLISM OF CHLORINATED PARAFFINS

  1. Top of page
  2. ABSTRACT
  3. INTRODUCTION
  4. PHYSICOCHEMICAL PROPERTIES AND MODELING
  5. BIOCONCENTRATION/BIOACCUMULATION FACTORS
  6. BIOMAGNIFICATION FACTORS
  7. TROPHIC MAGNIFICATION FACTORS
  8. METABOLISM OF CHLORINATED PARAFFINS
  9. CONCLUSIONS
  10. Acknowledgment
  11. REFERENCES

The potential for metabolism of CPs by fish has been noted in a number of studies. Madeley and Maddock (1983a) reported BCFs for an MCCP (52% chlorinated) in rainbow trout (O. mykiss) that were 40% to 60% higher based on radioactivity than those based on parent compound analysis. Madeley and Maddock (1983b) also reported evidence of metabolism of trout during uptake of an SCCP (58% chlorinated). Concentrations of the parent compound in the liver and viscera on day 35 were only 12% and 18% of the concentrations determined by radiochemistry, respectively. Fisk et al. (2000) determined the percentage biotransformation of various single chain length radiolabeled CPs in rainbow trout (O. mykiss) after 40 days of dietary uptake and 40 days of depuration, by comparing toluene extractable (parent) and nonextractable (metabolized) radioactivity. Nonextractable compounds were considered to have been metabolized because they are considered to be more polar. Nonextractable compounds may also have been incorporated into tissues. Biotransformation decreased with increasing chlorination level for C12 compounds (uptake) and C16 compounds (depuration). Although the greatest degree of biotransformation was observed for a C10 congener, there was otherwise little relationship to chain length. Data for the various chlorinated alkanes are shown in Table 3 (approximate, read from graph; Fisk et al. [2000]).

Table 3. Percentage biotransformation for various chlorinated alkanes, taken from Fisk et al. (2000), approximate read from graph
Chlorinated alkaneChlorination (%)Biotransformation (%)a
Day 40 uptakeDay 40 depuration
  1. a

    Biotransformation shown for juvenile rainbow trout (O. mykiss) at 2 time points, first time point at the end of a 40 day uptake/accumulation phase (through dietary exposure) and the second time point at the end of a subsequent 40 day depuration phase were fish were fed undosed food.

C-12 Cl-6.7593534
C-12 Cl-9.8682333
C-14 Cl-6.7553144
C-16 Cl-3.4353538
C-16 Cl-13.4693327

In the most recent BCF study of a 45% chlorinated [14C]-n-tetradecane (Vaughan and Hurd 2010), significant biotransformation was observed (mean metabolites measured at 21% of parent compound, range 17%–30%, [nonextractable residues considered as bound metabolites in fish tissue]) in rainbow trout (O. mykiss) at the end of the depuration phase (Leonards and van Beuzekom 2010). Indeed, biotransformation may also have been significantly underestimated, because fish were only available at the end of the depuration phase by which time metabolites and parent compound may have been excreted at different rates. Metabolism has been observed in modified biodegradation tests, discussed below, which also indicates a possible underestimation of metabolism in the recent fish study.

Fisk et al. (2000) estimated trout biotransformation rates for a wide range of CP structures from the measured depuration rate from feeding studies, by subtracting the “minimal” (zero biotransformation) depuration rate, as a function of Kow, derived from recalcitrant organochlorines such as PCBs. They concluded that these CP biotransformation rates showed a strong negative correlation with both chlorination level and chain length.

Of relevance to the potential for metabolism of C14–17 chlorinated alkanes by fish is their susceptibility to degradation and mineralization by microorganisms. (Although fish and microorganisms do not possess identical chemical pathways, some common pathways may be conserved, thus the presence of microbial breakdown suggests that MCCPs may also be susceptible to transformation in fish.) The EU Risk Assessment Report on MCCPs (EU 2005) describes a number of nonstandard studies showing some degree of biodegradation of MCCPs, which confirms their susceptibility to biochemical transformation, and concluded that the potential for biodegradation appears to increase with decreasing chlorination. This trend appears to be confirmed by a recent study of (unlabeled) 45% chlorinated n-tetradecane (prepared to correspond with the radiolabel used for the recent BCF study). The test procedure (Closed Bottle Test) incorporated modifications for the testing of poorly soluble substances (acceptable under REACH guidance) and showed that this low-chlorination material satisfied the criteria for “readily biodegradable” (van Ginkel and Belle 2010). Further work by van Ginkel et al. (2011) reported testing of CPs using the Closed Bottle Test with C14 alkanes with varying chlorination levels that confirm the decreasing biodegradation potential at higher chlorination levels. However, >60% biodegradation was observed within 60 days for C14 (41.3%, 45.5%, and 50.0% Cl) and still relatively high degradation for 55% Cl (close to 60% biodegradation) and 60% Cl (40% biodegradation) after 84 days.

CONCLUSIONS

  1. Top of page
  2. ABSTRACT
  3. INTRODUCTION
  4. PHYSICOCHEMICAL PROPERTIES AND MODELING
  5. BIOCONCENTRATION/BIOACCUMULATION FACTORS
  6. BIOMAGNIFICATION FACTORS
  7. TROPHIC MAGNIFICATION FACTORS
  8. METABOLISM OF CHLORINATED PARAFFINS
  9. CONCLUSIONS
  10. Acknowledgment
  11. REFERENCES

The SETAC Pellston Workshop in 2008 proposed an improved framework for assessing the bioaccumulation potential of chemical substances (Gobas et al. 2009). Chemicals should be assessed using data in a tiered framework—physicochemical properties and modeling assessment, BCF/BAF assessment, BMF assessment, and TMF assessment. Metabolism of MCCPs was also considered. When applied to MCCPs and to C14–17 chlorinated alkanes, the following conclusions can be made: although the physicochemical properties of MCCPs suggest that an evaluation of bioaccumulation potential is appropriate, current models based on such data do not accurately predict the available empirical data.

A laboratory study of the bioaccumulation of a commercial MCCP from water by rainbow trout (O. mykiss), monitoring a representative C15 (51% chlorinated) component, provided a kinetic BCF of 1100, below any regulatory criteria. This study was cited as reliable in EU (2005) and used for the EU Risk Assessment. After a recent revision of the OECD 305 bioaccumulation test guideline, growth correction and lipid normalization to 5% is now recommended. (It is interesting to note that historically, regulatory cut off values for BCFs were based on nongrowth corrected or lipid normalized values and because the practice of growth correction and lipid normalization is now accepted as standard, whether it is now appropriate to re-evaluate these cut off limits.) Further analysis of the original data to incorporate growth correction and lipid normalization gives a BCF of 1000, still below any regulatory criteria. However, a recent study of a low-chain length, low chlorination substance (C14, 45% chlorinated) gave a higher BCF (kinetic BCF 9100 and a 5% lipid normalized growth corrected kinetic BCF of 15 000) as measured by radiochemistry, although significant metabolism, which may be underestimated has not been taken into consideration and may account for this discrepancy. Metabolism (biotransformation) of C14–17 chlorinated alkanes by fish has been noted in a number of studies, with evidence that the degree of transformation increases with decreasing chlorination level.

Field BAFs (comparing water concentrations with levels in biota subject to water and dietary exposure) for C14–17 chlorinated alkanes are published for Lake Ontario. These values were over an order of magnitude higher than the framework criterion of 5000 (B status possible) when calculated as whole-body concentrations and higher again when normalized for lipid content. However, the sample sizes were small and taken at different locations and at different times to the biota samples. Thus, it is possible that the biota concentrations reflect exposure to historically or spatially different ambient levels.

Laboratory-derived BMFs for a number of C14–17 chlorinated alkanes were all less than the trigger value of 1 when expressed on a whole-body basis. Lipid and growth corrected values are higher but there is some confusion with a number of different BMFs reported. Field-derived BMFs for Lake Ontario and Lake Michigan have been derived from the same data as used to derive the field BAFs and therefore suffer the same issues of small sample size with high variability, and differing sample locations and times. However, between lake trout (Salvelinus namaycush) and 3 prey fish species, there were no lipid based BMFs >1 and no convincing evidence for BMFs greater than the criterion of 1 after conversion to whole-body values.

Trophic magnification factors, considered the most convincing evidence for bioaccumulative properties by Gobas et al. (2009) and the Gold Standard measure, were observed to be less than the criterion of 1, with a maximum of 0.29 for individual chain lengths and a value of 0.22 for total C14–17 chlorinated alkanes in Lake Ontario. Trophic magnification factors could not be calculated for Lake Michigan due to nondetected values in numerous species (although the TMF data again suffers from the same issues of small sample size with high variability discussed above), the present of nondetected values in numerous species is pertinent when considering that MCCPs have been used for many years and thus could be considered to have reached steady-state in the environment.

In conclusion, although some laboratory bioaccumulation values have a potential for concern, the majority of field values are more favorable when assessing the bioaccumulative potential of MCCPs. It is difficult to assess the bioaccumulative potential and indeed environmental impact of compounds such as MCCPs, which consist of mixtures of different congeners, with potentially hundreds of congeners in a single mixture. Each component of a mixture may have varying ecotoxicological or toxicological properties. This is confounded by the difficulties seen analyzing chlorinated alkanes (including MCCP congeners) in the environment, when it is not always possible to determine the exact composition (in terms of C-chain length and Cl content) present in each sample (UNEP 2011). The difficultly in drawing definitive conclusions on the PBT assessment of MCCPs can be eased with further testing in both areas of P and B in the laboratory. If field measurements are now considered to be the most convincing evidence for a compounds bioaccumulative potential, focus should also be applied in the field to provide more confidence in measures such as TMFs. As well as discussing acceptance criteria for field bioaccumulation measurements, Burkhard et al. (2011) also discusses an approach to convert bioaccumulation data to dimensionless fugacity (or concentration normalized) ratios. This approach is proposed to facilitate the interpretation of bioaccumulation data from different sources and could be considered as the next step for decision making in a chemicals management context.

Acknowledgment

  1. Top of page
  2. ABSTRACT
  3. INTRODUCTION
  4. PHYSICOCHEMICAL PROPERTIES AND MODELING
  5. BIOCONCENTRATION/BIOACCUMULATION FACTORS
  6. BIOMAGNIFICATION FACTORS
  7. TROPHIC MAGNIFICATION FACTORS
  8. METABOLISM OF CHLORINATED PARAFFINS
  9. CONCLUSIONS
  10. Acknowledgment
  11. REFERENCES

We would like to thank Alan Sharpe and Gary Roberts (Brixham Environmental Laboratory, UK) for reviewing an earlier draft of this manuscript and their helpful suggestions. We would also like to thank Euro Chlor, Avenue E Van Nieuwenhuyse 4, B-1160 Brussels, Belgium for their financial support in preparation of this manuscript.

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  1. Top of page
  2. ABSTRACT
  3. INTRODUCTION
  4. PHYSICOCHEMICAL PROPERTIES AND MODELING
  5. BIOCONCENTRATION/BIOACCUMULATION FACTORS
  6. BIOMAGNIFICATION FACTORS
  7. TROPHIC MAGNIFICATION FACTORS
  8. METABOLISM OF CHLORINATED PARAFFINS
  9. CONCLUSIONS
  10. Acknowledgment
  11. REFERENCES
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