Commentary Articles
Contaminants of Food
Contaminants of Food Prioritisation Scheme to Identify Manufactured Organic Chemicals as Potential Contaminants of Food Steven J. Wearne, Martin G. de M. Gem, Nigel Harrison, Peter P. Collier 1, Frank Fairweather 1, Michael Fielding 1, Franklin 1, James R. Startin ~, Roger J. Tregunno 1, Heather W a l t o n l
Andrew
Food Safety Directorate, Ministry of Agriculture, Fisheries and Food, Ergon House, c/o Nobel House, 17 Smith Square, London, United Kingdom SWIP 3JR
Corresponding
author:
Dr. Steven J. Wearne
Abstract A scheme has been developed to rank 70 industrial organic chemicals in order of their priority for further study as potential contaminants of food. Numerical scales were developed for the following seven key criteria concerning environmental issues, food and toxicity: - Production volume - Pattern of usage - Possible fate in the environment - Likelihood of chemical entering the food chain - Mechanism of entry into the food chain - Persistence and accumulation in the food chain - Toxicity. Each chemical was assigned a score for the above criteria, which were combined to give an overall ranking for the chemicals. This scheme has been endorsed by the MAFF Steering Group on Chemical Aspects of Food Surveillance. It will be used in the assessment of relative priorities for further non-statutory surveillance for these contaminants in the UK food supply. Key words: Organic environmental chemicals, manufactured; industrial organic contaminants of food; food, contaminants; assessment, contaminants of food; toxicity and food; prioritisation scheme, contaminants of food
1 Introduction The UK Government aims to ensure that consumers in the UK have access to a safe and nutritious food supply. Work towards these aims involves a wide range of regulatory and other activities, an important element of which is the nonstatutory surveillance of food. The results of surveillance are used to estimate the exposure to food chemicals of av-
1 Members of the WorkingParty on Organic Environmental Contaminants in Food, Sub-Groupon Priorities
ESPR - Environ. Sci. & Poltut. Res. 3 (2) 83-88 (1996) 9 ecomed publishers, D-86899 Landsberg, Germany
erage and upper range (97.5th percentile) consumers in the population and of individuals in particular groups (e.g. diabetics, infants), to assess the safety or nutritional value of food. Surveillance of organic environmental contaminants conducted by the UK Ministry of Agriculture, Fisheries and Food since 1986 initially aimed to estimate the dietary intake of polychlorinated biphenyls and polynuclear aromatic hydrocarbons. M u c h of the later work in this area has been directed towards dioxins in food (MAFF, 1992). These well-established groups of contaminants will continue to be monitored. There are, however, a large number of other organic chemicals which are emitted by industrial processes and which have the potential to enter the food supply chain by a variety of routes (ECKARD, 1980). It would be an impossible task to monitor all of these organic chemicals (OECD Existing Chemicals Programme, 1985) and a scheme for the prioritisation of these chemicals for future surveillance would provide a flexible management tool to supplement expert judgement. A variety of prioritisation schemes have been developed to assess chemicals that may be released to the environment (ARMSTRONG and NEWHOOK, 1992; ECETOC, 1988; HERRCHEN et al., 1993; MOCKE et al., 1986; MI3CKE et al., 1989; SAMPAOLOand BINETTI, 1989). This paper describes a simple and pragmatic prioritisation scheme for ranking those industrial organic chemicals that may enter the food chain as a result of long-term, multi-source releases from industrial and other activities and, once in the food chain, accumulate to levels of toxicological significance. Other management tools are available for assessing the potential food chain impacts of localised or short-term chemical releases. The scheme may be easily revised, to take account of new information that m a y become available on those chemicals already included in the ranking, or to assign relative priorities to other potential industrial organic contaminants of food.
83
Contaminants of Food
2
Commentary Articles
Approach
A shortlist of 70 organic chemicals and closely related groups of organic chemicals has been developed using expert judgement. The list is based mainly on those chemicals produced in the UK in quantities in excess of 1000 tonnes per annum, and an assessment of which compounds were known to be or could reasonably be expected to be toxic to humans. Further prioritisation of this shortlist of organic chemicals is based on three areas: The possibility for release of the chemical in significant amounts to the environment; its potential to enter, persist and accumulate in the food supply; and safety concerns. This assessment is further broken down into a set of seven criteria to which numerical scales can be assigned: Environment:
production volume pattern of usage possible fate in the environment Food: likelihood of chemical entering the food chain mechanism of entry into the food chain persistence and accumulation in the food chain Safety concerns: toxicity Each organic chemical included in the shortlist is given a score for each criterion. The relative importance of each of the criteria is reflected by the difference between the maximum and minimum scores for that criterion. For example, the toxicity of a potential contaminant is important in assessing any risk or hazard associated with its presence in food. Accordingly, the maximum and minimum scores for this criterion differ by a factor of ten. The pattern of usage is less important and scores only differ by a factor of four. The range of scores used for each criterion in this scheme are given in Table 1.
Table 1:
3 3.1
N u m e r i c a l Scales for P r i o r i t i s a t i o n C r i t e r i a Production volume (Score P)
The score for this criterion is based on the assumption that the amount of chemical released to the environment in the UK is related to the quantity produced in the UK, with allowances made for imports and exports. With the exception of a relatively few organic chemicals, UK production figures are not available in the open literature. Additional data on production volumes and production capacity have been obtained from commercial reports (SRI International, 1985; PARPINELLI,1986; Sema-Metra Conseil, 1986). To provide numerical scores in a suitable range, the logarithm (to base 10) of the annual UK production volume or capacity, plus any known imports and less exports, is used as the score. The minimum score for this criterion is 1, for chemicals with an annual UK production volume or capacity of 10 tonnes or less. The maximum score is 6, for chemicals with an annual UK production volume or capacity of over 1,000,000 tonnes. If no information on UK production was available, a default value of 4 is used for chemicals known to have an annual EU production volume of over 1,000 tonnes (European Council, 1993) and a default value of 2 is used for other chemicals.
The range of scores for each of the criteria included in the prioritisation scheme
Criterion
Production volume (score P) Pattern of usage (score U) Possible fate in the environment (score R) Likelihood of chemical entering the food chain (score E) Mechanism of entry into the food chain (score M) Persistence and accumulation in the food chain (score B)
Toxicity (score T)
Range of scores 1 to6 1 to4 1 to5
1 to5 1 to5 1 to5 1 to 10
Standard physico-chemical, persistence and other data required by this scheme are available in the literature for many industrial organic chemicals. There are likely to be some gaps in the information available for some of the chemicals to be assessed and default values for each of the criteria have been proposed for use as necessary. Default values have been set low to ensure that the most highly ranked chemicals are those for which data are available and
84
indicate definite adverse characteristics (e.g. persistence, toxicity). Other risk assessment systems set default values high, to give a conservative approach that ensures unknown potential risks are not underestimated. However, the scheme described in this paper seeks to identify the highest priority chemicals to which resources should be allocated, rather than seeking to identify all compounds that may present a risk. On these grounds, the use of low default values is justified as it will lead to a high ranking for those chemicals where there is a known risk. Clearly, these are the substances on which surveillance of food should focus first.
3.2
Pattern of usage (Score U)
This criterion is included to take account of the different potentials for release into the food chain that could arise from different uses of an industrial organic chemical. Each chemical is given a score of between 1 and 4 based on the general category of use of the organic chemical (--~ Table 2). Low scores are given to uses that occur in an enclosed process with no or little fugitive emissions and that are subject to the greatest control. High scores are given to highly diffuse uses, such as would arise from the use of organic chemicals as adjuvants in pesticide formulations, or uses subject to little or no control. If a chemical has more than one use, then the use with the highest score is taken. No knowledge is needed of the details of the industrial processes involved. 3.3
Possible fate in the environment (Score R)
At equilibrium, an industrial organic chemical that has been released into the environment will exist at different ESPR - Environ. Sci. & Pollut. Res. 3 (2) 1996
Commentary Articles Table 2:
Contaminants of Food
Scoresfor pattern of usage
Use
3.4 Score (U)
As an intermediate in the manufacture of other chemicals
Industry (e.g. mining; steel or polymer manufacture) Light industry and skilled trade use (e.g. dye houses) Consumer and dispersed use (e.g. retail cleaning agents)
1 2a 3
a) Default value
concentrations in air, water, soil, and other environmental media. The concept of fugacity, a measure of the tendency of a substance to escape from a given phase, is a useful descriptor of the equilibrium between these phases. A variety of fugacity models are available to model the concentrations of a substance in different environmental compartments following its release. For each substance of interest, this scheme uses a fugacity calculation (MACKAYet al., 1992) to estimate the proportion of a standard relase (100,000 kg) that would partition between a variety of environmental compartments (air, water, soil, aquatic biota, suspended sediment and bottom sediment). A Level I calculation requires only the use of standard physico-chemical data for each organic chemical. Where data on the halflives of the substance of interest in air, water, soil and bottom sediment are also available, a Level II calculation is performed. Non-equilibrium conditions such as those resuiting from incidents involving localised, short-term, accidental releases of relatively large quantities of industrial organic chemicals are excluded from this scheme and are managed using different tools. For each of the six phases, the fraction of the release predicted to reside in that phase at equilibrium is multiplied by a factor reflecting the relative importance of that phase in contributing to concentrations of the organic chemical in food. A factor of 5 is used for water, soil and aquatic biota; a factor of 2 is used for air; and a factor of 1 is used for suspended sediment and bottom sediment. These factors assume that a substance in water or soil may reach the food chain more easily than if it were in air. Although the absorption of compounds such as volatile halocarbons by fatty foods from air does occur (GROB et al., 1990), this is a simple physical process and does not provide the potential for accumulation and biomagnification that is offered by the uptake of organic environmental contaminants from soil or water by plants, fish or animals (section 3.6). The products (proportion of release x weighting factor) for the six phases are summed and this total is used as the score, R, for this criterion. The maximum score of R is 5, which would be given to an organic chemical partitioning entirely to water, soil and/or aquatic biota. The minimum score is 1, which would be given to an organic chemical partitioning entirely to sediment. A default value of 2 is used if physico-chemical data are not available. ESPR - Environ. Sci. & Pollut. Res. 3 (2) 1996
Likelihood of chemical entering the food chain (Score E)
The likelihood of an organic environmental contaminant entering the food chain from environmental routes is determined by the availability of the chemical in the environment. A major factor controlling the availability of chemicals, once released to the environment, is the rate of degradation of the chemical in the phases in which it is found. The Level II fugacity calculation (section 3.3) calculates a residence time from degradation rates and the partitioning of the substance of interest between environmental phases. This residence time, a measure of the persistence of the chemical in the environment at equilibrium, is used as the basis for the score for this criterion, E (--~ Table 3). This scheme does not assess the potential effects on the food supply chain of the products of environmental degradation of organic industrial chemicals. Where degradation products have been identified, they may be assessed as organic contaminants in their own right. Table 3"
Scoresfor rates of degradation in environmentalmedia
Residence time
Score (E)
Less than 1 hour
1 2a 3 4 5
1 to 10 hours 10 to 100 hours 100 to 1000 hours Greater than 1000 hours
a) Default value
The highest possible score of 5 is assigned to an organic chemical with a residence time greater than 1000 hours. The lowest score of 1 is assigned to a chemical with a residence time of less than 1 hour. If no degradation data are available, a default value of 2 is used. 3.5
Mechanism of entry into the food chain (Score M)
The mechanism and rate of entry into the food chain is difficult to quantify, as there may be multiple routes of entry for some organic chemicals, dependant on complex mechanism not readily amenable to simple mathematical analysis. An empirical approach is taken and the score for this cirterion, M, is based on the number of reported food contamination incidents, taken from a recent full-scale literature survey for reported occurrences of industrial organic contaminants in food in Western Europe and North America undertaken by the Leatherhead Food Research Association, and supplemented by a regular in-house review of the open literature for surveillance conducted by industry, research organisations and other food agencies (-~ Table 4). An "incident" is defined as the report of a given contaminant in one or more samples of a given foodstuff or raw material. Any one report or paper may identify a range of contaminated foodstuffs and may therefore represent a number of "incidents". A small group of organic chemicals
85
Contaminants of Food Table 4:
Commentary Articles
Scoresfor the number of reports of contamination of food
Number of reports
Scoresfor bioconcentration factors and bioaccumulation potential (log Kow)
Score (M)
Less than 4 4to 10 11 to 30 31 to 100 More than 100
are reported frequently and are the subject of more than 100 incidents; many other substances are reported occasionally. There are limitations in the use of this information. First, most surveys will have been conducted as a result of existing concerns over potential food contamination and will tend to introduce a bias in favour of those substances widely regarded as potential contaminants (e.g. tetrachloroethylene). This limitation is not necessarily disadvantageous, as it will tend to accentuate the differences between high-scoring and low-scoring chemicals. Second, the number of reports will depend to some extent on the limits of detection used in the various papers reviewed. The maximum score of 5 is assigned to a substance that was the subject of more than 100 incidents. The minimum score of 1 is assigned to a chemical reported in fewer than 4 incidents, or not at all. 3.6
Table 5:
Persistence and accumulation in the food chain (Score B)
Most organic chemicals are more soluble in organic phases than in water. Depending on the extent of their lipophilicity and the ease by which chemicals are taken up from soil and air by plants or ingested by animals and fish, there can be a large potential for bioaccumulation and for biomagnification up the food chain. Bioaccumulation potential is scored using either an experimentally determined bioconcentration factor (BCF) which will generally relate to fish or invertebrate species, or a bioaccumulation potential expressed in terms of the octanol-water partition coefficient of the chemical (Kow). Where data are available, the BCF, determined for a species of relevance to the food supply chain, is preferred as it refers to an actual, measured bioconcentration effect and will take some account of the distribution, metabolism and excretion of the chemical in a relevant species. The relationship between the bioaccumulation of a compound in fish and the logarithm of the partition coefficient of the compound has been shown to be linear (ISNARDand LAMBERT,1988) and where an experimentally determined BCF is not available, the score B is based on log Kow. The ranges used to score the BCF and log Kow are shown in Table 5. The scores assigned to chemicals for this criterion range from lto5.
Bioconcentration factor Less than 10 10 to 100 100 to 1,000 1,000 to 10,000 Greater than 10,000
log Kowa Less than 2
1
2to3 3to4 4to5 Greater than 5
2b
Toxicity (Score T)
A numerical score for this criterion was derived from a screen of available human and animal toxicity data, based 86
3
4 5
") Logarithm (base 10) of the octanol-waterpartitioncoefficient b) Default value
on a method discussed by international experts in an Informal Working Group on Priority Setting (VAN DER ZANDT, 1992). Certain modifications to this method were made for the purposes of this paper, such as using a score of 5 rather than 7 as a default score, scores of 7 and 6 for respiratory and skin sensitisation and a score of 8 for equivocal carcinogenicity, mutagenicity or reproductive toxicity. The scores assigned to chemicals for this criterion range from 1 to 10 and the derivation of scores for individual chemicals was assisted by the risk phrases defined in Annex VI of EC Directive 67/548/EEC, as amended (European Commission, 1967; Health and Safety Commission, 1994) (--) Table 6). This scheme gives higher priority to carcinogenicity, mutagenicity and effects on reproduction over other systemic effects in scoring the available toxicological evidence. The overall score for a chemical for this criterion is the highest score obtained for any aspect of the toxicity of that chemical covered in Table 6. The score assumes that any metabolites will be no more toxic than the parent compound. Where available, recently generated toxicity data and evaluations are likely to include information on the toxicity of metabolites. Alternatively, theoretical models of biological transformation (STORMANNand JASTORFF,1993) may allow potential toxic metabolites to be identified and assessed as organic contaminants in their own right.
4
Calculation of a T o t a l Score and R a n k i n g of Chemicals
The individual scores assigned to a chemical for each of the seven above criteria need to be combined to generate an overall, total score. These scores for each chemical can then be used to rank the chemicals. The method of calculation of the final score must acknowledge the implicit dependence of overall concerns on a combination of factors. For example, the toxicity of a compound will only play a large role in determining priorities if the compound is released to the environment and is persistent enough to transfer to and accumulate in food. The total score is calculated as follows: Total s c o r e = P x U x R x M x E x B x T
3.7
Score (B)
... [1]
The scores and relative rankings of the 70 chemicals or closely related chemicals considered by MAFF to date are summarised in Appendix 1 ( ~ p. 88). ESPR - Environ. Sci. & Pollut. Res. 3 (2) 1996
Commentary Articles
Table 6:
Contaminants of Food
Scores for toxicity
Toxicological evidence"
Score (1")
Human evidence or strong evidence in animals of carcinogenicity, heritable genetic damage or reproductive toxicity (R45, R49, R46, R47, R60 or R61)
10
Animal evidence of carcinogenicity, in vivo mutagenicity or reproductive toxicity, or human evidence of somatic cell genetic damage (R40, R62, R63 or R64)
9
Positive in at least one in vitro test for mutagenicity or positive in an in vivo reproductive screening test or animal evidence of carcinogenicity, mutagenicity or reproductive toxicity which is equivocal or of uncertain relevance to man
8
Evidence for respiratory sensitisation (R42) or oral toxicity at _
Contaminants of Food
Contaminants of Food Prioritisation Scheme to Identify Manufactured Organic Chemicals as Potential Contaminants of Food Steven J. Wearne, Martin G. de M. Gem, Nigel Harrison, Peter P. Collier 1, Frank Fairweather 1, Michael Fielding 1, Franklin 1, James R. Startin ~, Roger J. Tregunno 1, Heather W a l t o n l
Andrew
Food Safety Directorate, Ministry of Agriculture, Fisheries and Food, Ergon House, c/o Nobel House, 17 Smith Square, London, United Kingdom SWIP 3JR
Corresponding
author:
Dr. Steven J. Wearne
Abstract A scheme has been developed to rank 70 industrial organic chemicals in order of their priority for further study as potential contaminants of food. Numerical scales were developed for the following seven key criteria concerning environmental issues, food and toxicity: - Production volume - Pattern of usage - Possible fate in the environment - Likelihood of chemical entering the food chain - Mechanism of entry into the food chain - Persistence and accumulation in the food chain - Toxicity. Each chemical was assigned a score for the above criteria, which were combined to give an overall ranking for the chemicals. This scheme has been endorsed by the MAFF Steering Group on Chemical Aspects of Food Surveillance. It will be used in the assessment of relative priorities for further non-statutory surveillance for these contaminants in the UK food supply. Key words: Organic environmental chemicals, manufactured; industrial organic contaminants of food; food, contaminants; assessment, contaminants of food; toxicity and food; prioritisation scheme, contaminants of food
1 Introduction The UK Government aims to ensure that consumers in the UK have access to a safe and nutritious food supply. Work towards these aims involves a wide range of regulatory and other activities, an important element of which is the nonstatutory surveillance of food. The results of surveillance are used to estimate the exposure to food chemicals of av-
1 Members of the WorkingParty on Organic Environmental Contaminants in Food, Sub-Groupon Priorities
ESPR - Environ. Sci. & Poltut. Res. 3 (2) 83-88 (1996) 9 ecomed publishers, D-86899 Landsberg, Germany
erage and upper range (97.5th percentile) consumers in the population and of individuals in particular groups (e.g. diabetics, infants), to assess the safety or nutritional value of food. Surveillance of organic environmental contaminants conducted by the UK Ministry of Agriculture, Fisheries and Food since 1986 initially aimed to estimate the dietary intake of polychlorinated biphenyls and polynuclear aromatic hydrocarbons. M u c h of the later work in this area has been directed towards dioxins in food (MAFF, 1992). These well-established groups of contaminants will continue to be monitored. There are, however, a large number of other organic chemicals which are emitted by industrial processes and which have the potential to enter the food supply chain by a variety of routes (ECKARD, 1980). It would be an impossible task to monitor all of these organic chemicals (OECD Existing Chemicals Programme, 1985) and a scheme for the prioritisation of these chemicals for future surveillance would provide a flexible management tool to supplement expert judgement. A variety of prioritisation schemes have been developed to assess chemicals that may be released to the environment (ARMSTRONG and NEWHOOK, 1992; ECETOC, 1988; HERRCHEN et al., 1993; MOCKE et al., 1986; MI3CKE et al., 1989; SAMPAOLOand BINETTI, 1989). This paper describes a simple and pragmatic prioritisation scheme for ranking those industrial organic chemicals that may enter the food chain as a result of long-term, multi-source releases from industrial and other activities and, once in the food chain, accumulate to levels of toxicological significance. Other management tools are available for assessing the potential food chain impacts of localised or short-term chemical releases. The scheme may be easily revised, to take account of new information that m a y become available on those chemicals already included in the ranking, or to assign relative priorities to other potential industrial organic contaminants of food.
83
Contaminants of Food
2
Commentary Articles
Approach
A shortlist of 70 organic chemicals and closely related groups of organic chemicals has been developed using expert judgement. The list is based mainly on those chemicals produced in the UK in quantities in excess of 1000 tonnes per annum, and an assessment of which compounds were known to be or could reasonably be expected to be toxic to humans. Further prioritisation of this shortlist of organic chemicals is based on three areas: The possibility for release of the chemical in significant amounts to the environment; its potential to enter, persist and accumulate in the food supply; and safety concerns. This assessment is further broken down into a set of seven criteria to which numerical scales can be assigned: Environment:
production volume pattern of usage possible fate in the environment Food: likelihood of chemical entering the food chain mechanism of entry into the food chain persistence and accumulation in the food chain Safety concerns: toxicity Each organic chemical included in the shortlist is given a score for each criterion. The relative importance of each of the criteria is reflected by the difference between the maximum and minimum scores for that criterion. For example, the toxicity of a potential contaminant is important in assessing any risk or hazard associated with its presence in food. Accordingly, the maximum and minimum scores for this criterion differ by a factor of ten. The pattern of usage is less important and scores only differ by a factor of four. The range of scores used for each criterion in this scheme are given in Table 1.
Table 1:
3 3.1
N u m e r i c a l Scales for P r i o r i t i s a t i o n C r i t e r i a Production volume (Score P)
The score for this criterion is based on the assumption that the amount of chemical released to the environment in the UK is related to the quantity produced in the UK, with allowances made for imports and exports. With the exception of a relatively few organic chemicals, UK production figures are not available in the open literature. Additional data on production volumes and production capacity have been obtained from commercial reports (SRI International, 1985; PARPINELLI,1986; Sema-Metra Conseil, 1986). To provide numerical scores in a suitable range, the logarithm (to base 10) of the annual UK production volume or capacity, plus any known imports and less exports, is used as the score. The minimum score for this criterion is 1, for chemicals with an annual UK production volume or capacity of 10 tonnes or less. The maximum score is 6, for chemicals with an annual UK production volume or capacity of over 1,000,000 tonnes. If no information on UK production was available, a default value of 4 is used for chemicals known to have an annual EU production volume of over 1,000 tonnes (European Council, 1993) and a default value of 2 is used for other chemicals.
The range of scores for each of the criteria included in the prioritisation scheme
Criterion
Production volume (score P) Pattern of usage (score U) Possible fate in the environment (score R) Likelihood of chemical entering the food chain (score E) Mechanism of entry into the food chain (score M) Persistence and accumulation in the food chain (score B)
Toxicity (score T)
Range of scores 1 to6 1 to4 1 to5
1 to5 1 to5 1 to5 1 to 10
Standard physico-chemical, persistence and other data required by this scheme are available in the literature for many industrial organic chemicals. There are likely to be some gaps in the information available for some of the chemicals to be assessed and default values for each of the criteria have been proposed for use as necessary. Default values have been set low to ensure that the most highly ranked chemicals are those for which data are available and
84
indicate definite adverse characteristics (e.g. persistence, toxicity). Other risk assessment systems set default values high, to give a conservative approach that ensures unknown potential risks are not underestimated. However, the scheme described in this paper seeks to identify the highest priority chemicals to which resources should be allocated, rather than seeking to identify all compounds that may present a risk. On these grounds, the use of low default values is justified as it will lead to a high ranking for those chemicals where there is a known risk. Clearly, these are the substances on which surveillance of food should focus first.
3.2
Pattern of usage (Score U)
This criterion is included to take account of the different potentials for release into the food chain that could arise from different uses of an industrial organic chemical. Each chemical is given a score of between 1 and 4 based on the general category of use of the organic chemical (--~ Table 2). Low scores are given to uses that occur in an enclosed process with no or little fugitive emissions and that are subject to the greatest control. High scores are given to highly diffuse uses, such as would arise from the use of organic chemicals as adjuvants in pesticide formulations, or uses subject to little or no control. If a chemical has more than one use, then the use with the highest score is taken. No knowledge is needed of the details of the industrial processes involved. 3.3
Possible fate in the environment (Score R)
At equilibrium, an industrial organic chemical that has been released into the environment will exist at different ESPR - Environ. Sci. & Pollut. Res. 3 (2) 1996
Commentary Articles Table 2:
Contaminants of Food
Scoresfor pattern of usage
Use
3.4 Score (U)
As an intermediate in the manufacture of other chemicals
Industry (e.g. mining; steel or polymer manufacture) Light industry and skilled trade use (e.g. dye houses) Consumer and dispersed use (e.g. retail cleaning agents)
1 2a 3
a) Default value
concentrations in air, water, soil, and other environmental media. The concept of fugacity, a measure of the tendency of a substance to escape from a given phase, is a useful descriptor of the equilibrium between these phases. A variety of fugacity models are available to model the concentrations of a substance in different environmental compartments following its release. For each substance of interest, this scheme uses a fugacity calculation (MACKAYet al., 1992) to estimate the proportion of a standard relase (100,000 kg) that would partition between a variety of environmental compartments (air, water, soil, aquatic biota, suspended sediment and bottom sediment). A Level I calculation requires only the use of standard physico-chemical data for each organic chemical. Where data on the halflives of the substance of interest in air, water, soil and bottom sediment are also available, a Level II calculation is performed. Non-equilibrium conditions such as those resuiting from incidents involving localised, short-term, accidental releases of relatively large quantities of industrial organic chemicals are excluded from this scheme and are managed using different tools. For each of the six phases, the fraction of the release predicted to reside in that phase at equilibrium is multiplied by a factor reflecting the relative importance of that phase in contributing to concentrations of the organic chemical in food. A factor of 5 is used for water, soil and aquatic biota; a factor of 2 is used for air; and a factor of 1 is used for suspended sediment and bottom sediment. These factors assume that a substance in water or soil may reach the food chain more easily than if it were in air. Although the absorption of compounds such as volatile halocarbons by fatty foods from air does occur (GROB et al., 1990), this is a simple physical process and does not provide the potential for accumulation and biomagnification that is offered by the uptake of organic environmental contaminants from soil or water by plants, fish or animals (section 3.6). The products (proportion of release x weighting factor) for the six phases are summed and this total is used as the score, R, for this criterion. The maximum score of R is 5, which would be given to an organic chemical partitioning entirely to water, soil and/or aquatic biota. The minimum score is 1, which would be given to an organic chemical partitioning entirely to sediment. A default value of 2 is used if physico-chemical data are not available. ESPR - Environ. Sci. & Pollut. Res. 3 (2) 1996
Likelihood of chemical entering the food chain (Score E)
The likelihood of an organic environmental contaminant entering the food chain from environmental routes is determined by the availability of the chemical in the environment. A major factor controlling the availability of chemicals, once released to the environment, is the rate of degradation of the chemical in the phases in which it is found. The Level II fugacity calculation (section 3.3) calculates a residence time from degradation rates and the partitioning of the substance of interest between environmental phases. This residence time, a measure of the persistence of the chemical in the environment at equilibrium, is used as the basis for the score for this criterion, E (--~ Table 3). This scheme does not assess the potential effects on the food supply chain of the products of environmental degradation of organic industrial chemicals. Where degradation products have been identified, they may be assessed as organic contaminants in their own right. Table 3"
Scoresfor rates of degradation in environmentalmedia
Residence time
Score (E)
Less than 1 hour
1 2a 3 4 5
1 to 10 hours 10 to 100 hours 100 to 1000 hours Greater than 1000 hours
a) Default value
The highest possible score of 5 is assigned to an organic chemical with a residence time greater than 1000 hours. The lowest score of 1 is assigned to a chemical with a residence time of less than 1 hour. If no degradation data are available, a default value of 2 is used. 3.5
Mechanism of entry into the food chain (Score M)
The mechanism and rate of entry into the food chain is difficult to quantify, as there may be multiple routes of entry for some organic chemicals, dependant on complex mechanism not readily amenable to simple mathematical analysis. An empirical approach is taken and the score for this cirterion, M, is based on the number of reported food contamination incidents, taken from a recent full-scale literature survey for reported occurrences of industrial organic contaminants in food in Western Europe and North America undertaken by the Leatherhead Food Research Association, and supplemented by a regular in-house review of the open literature for surveillance conducted by industry, research organisations and other food agencies (-~ Table 4). An "incident" is defined as the report of a given contaminant in one or more samples of a given foodstuff or raw material. Any one report or paper may identify a range of contaminated foodstuffs and may therefore represent a number of "incidents". A small group of organic chemicals
85
Contaminants of Food Table 4:
Commentary Articles
Scoresfor the number of reports of contamination of food
Number of reports
Scoresfor bioconcentration factors and bioaccumulation potential (log Kow)
Score (M)
Less than 4 4to 10 11 to 30 31 to 100 More than 100
are reported frequently and are the subject of more than 100 incidents; many other substances are reported occasionally. There are limitations in the use of this information. First, most surveys will have been conducted as a result of existing concerns over potential food contamination and will tend to introduce a bias in favour of those substances widely regarded as potential contaminants (e.g. tetrachloroethylene). This limitation is not necessarily disadvantageous, as it will tend to accentuate the differences between high-scoring and low-scoring chemicals. Second, the number of reports will depend to some extent on the limits of detection used in the various papers reviewed. The maximum score of 5 is assigned to a substance that was the subject of more than 100 incidents. The minimum score of 1 is assigned to a chemical reported in fewer than 4 incidents, or not at all. 3.6
Table 5:
Persistence and accumulation in the food chain (Score B)
Most organic chemicals are more soluble in organic phases than in water. Depending on the extent of their lipophilicity and the ease by which chemicals are taken up from soil and air by plants or ingested by animals and fish, there can be a large potential for bioaccumulation and for biomagnification up the food chain. Bioaccumulation potential is scored using either an experimentally determined bioconcentration factor (BCF) which will generally relate to fish or invertebrate species, or a bioaccumulation potential expressed in terms of the octanol-water partition coefficient of the chemical (Kow). Where data are available, the BCF, determined for a species of relevance to the food supply chain, is preferred as it refers to an actual, measured bioconcentration effect and will take some account of the distribution, metabolism and excretion of the chemical in a relevant species. The relationship between the bioaccumulation of a compound in fish and the logarithm of the partition coefficient of the compound has been shown to be linear (ISNARDand LAMBERT,1988) and where an experimentally determined BCF is not available, the score B is based on log Kow. The ranges used to score the BCF and log Kow are shown in Table 5. The scores assigned to chemicals for this criterion range from lto5.
Bioconcentration factor Less than 10 10 to 100 100 to 1,000 1,000 to 10,000 Greater than 10,000
log Kowa Less than 2
1
2to3 3to4 4to5 Greater than 5
2b
Toxicity (Score T)
A numerical score for this criterion was derived from a screen of available human and animal toxicity data, based 86
3
4 5
") Logarithm (base 10) of the octanol-waterpartitioncoefficient b) Default value
on a method discussed by international experts in an Informal Working Group on Priority Setting (VAN DER ZANDT, 1992). Certain modifications to this method were made for the purposes of this paper, such as using a score of 5 rather than 7 as a default score, scores of 7 and 6 for respiratory and skin sensitisation and a score of 8 for equivocal carcinogenicity, mutagenicity or reproductive toxicity. The scores assigned to chemicals for this criterion range from 1 to 10 and the derivation of scores for individual chemicals was assisted by the risk phrases defined in Annex VI of EC Directive 67/548/EEC, as amended (European Commission, 1967; Health and Safety Commission, 1994) (--) Table 6). This scheme gives higher priority to carcinogenicity, mutagenicity and effects on reproduction over other systemic effects in scoring the available toxicological evidence. The overall score for a chemical for this criterion is the highest score obtained for any aspect of the toxicity of that chemical covered in Table 6. The score assumes that any metabolites will be no more toxic than the parent compound. Where available, recently generated toxicity data and evaluations are likely to include information on the toxicity of metabolites. Alternatively, theoretical models of biological transformation (STORMANNand JASTORFF,1993) may allow potential toxic metabolites to be identified and assessed as organic contaminants in their own right.
4
Calculation of a T o t a l Score and R a n k i n g of Chemicals
The individual scores assigned to a chemical for each of the seven above criteria need to be combined to generate an overall, total score. These scores for each chemical can then be used to rank the chemicals. The method of calculation of the final score must acknowledge the implicit dependence of overall concerns on a combination of factors. For example, the toxicity of a compound will only play a large role in determining priorities if the compound is released to the environment and is persistent enough to transfer to and accumulate in food. The total score is calculated as follows: Total s c o r e = P x U x R x M x E x B x T
3.7
Score (B)
... [1]
The scores and relative rankings of the 70 chemicals or closely related chemicals considered by MAFF to date are summarised in Appendix 1 ( ~ p. 88). ESPR - Environ. Sci. & Pollut. Res. 3 (2) 1996
Commentary Articles
Table 6:
Contaminants of Food
Scores for toxicity
Toxicological evidence"
Score (1")
Human evidence or strong evidence in animals of carcinogenicity, heritable genetic damage or reproductive toxicity (R45, R49, R46, R47, R60 or R61)
10
Animal evidence of carcinogenicity, in vivo mutagenicity or reproductive toxicity, or human evidence of somatic cell genetic damage (R40, R62, R63 or R64)
9
Positive in at least one in vitro test for mutagenicity or positive in an in vivo reproductive screening test or animal evidence of carcinogenicity, mutagenicity or reproductive toxicity which is equivocal or of uncertain relevance to man
8
Evidence for respiratory sensitisation (R42) or oral toxicity at _
