Opinion on the results of the Environmental Risk Assessment (Report version: final draft of August 1999) of : Octabromodiphenyl ether [CAS N° 32536-52-0] [EINECS N° 251-087-9] carried out in the framework of Council Regulation (EEC) 793/93 on the evaluation and control of the risks of existing substances1 - Opinion expressed at the 16th CSTEE plenary meeting, Brussels, 19th of June 2000.
Terms of reference
The CSTEE has been invited to examine the Environmental Risk Assessment Report for Octabromodiphenyl ether and address the following issues:
1. Does the CSTEE agree with the conclusions of the Risk Assessment Report?
2. If the CSTEE disagrees with such conclusions, the CSTEE is invited to elaborate the reasons for this divergence of opinion.
GENERAL COMMENTS/CONCLUSIONS
Commercial octabromodiphenyl ether is a mixture containing congeners with varying bromine content. These congeners have different properties and will behave differently in the environment. An option to handle this would be to make separate risk assessments for at least the different homologue groups, but the scarce amount of data available makes this impossible. These compounds are very lipophilic and organisms absorb at least some of them slowly, which makes acute effect data less relevant. While some of these compounds are predicted to bioaccumulate and degrade slowly in the environment, available data suggests limited bioaccumulation.
On the basis of the few data available, a potential risk for the environment cannot be excluded. The conclusions of the report suggest the need for further information and testing for: The aquatic compartment to assess the effects on sediment from local sources and to assess the risk to waste water treatment processes; The terrestrial compartment to assess effects on soil organisms from local sources; The secondary poisoning in relation to degradation products. The CSTEE agrees with these conclusions. In addition some more precise information to quantify the effects on water organisms at local level is needed. The CSTEE do not think that the equilibrium partitioning method can be applied for these very adsorptive compounds with very low water solubility, and thus also further information is needed of effects on organisms in the sediment and soil compartments.
The CSTEE has the main following comments to make on the chapters indicated.
SPECIFIC COMMENTS
3.1 Exposure assessment
Octabromodiphenyl ether is used as technical mixtures (31-35% OBDE) containing large amounts of other congeners, in particular hexabromo- (10-12%), heptabromo- (44%) and nonabromodiphenyl ethers (10-11%). In a recent thesis (Andreas Sjödin, "Occupational and Dietary Exposure to Organohalogen Substances, with Special Emphasis on Polybrominated Diphenyl Ethers", Stockholm University, 2000), which was not available to the assessors, the composition of one OBDE product is shown to have higher concentrations of the higher brominated groups. Most of the few toxicity data available refer to commercial mixtures and it is not possible to assess the effects of different congeners.
In the General information on exposure, relatively old data on production and uses are reported and all references are to 1994 or before. The anticipated "worst case" use (2550 tonnes/year) seems to be verified by data from the industry saying that 2500 tonnes were used 1993 (De Poortere, "Brominated Flame Retardants", presented at a Swedish Society of Toxicology Workshop, 2000). The use of OBDE products was estimated to have decreased since that time and for 1999 about 400 tonnes were expected to be used in the EU.
There are only few measurements of OBDE concentrations in the environment reported, and most of these are from industrialised areas. There is a reasonable agreement between those data and the EUSES predicted values. The CSTEE have earlier pointed at the problems with predictions of root crop concentrations, and also for OBDE the levels predicted there are probably far too high.
The exposure to possible transformation products of OBDE has to be taken into account, and the CSTEE does not agree with the statement "the presence of octabromodiphenyl (ether) in fires is unlikely to significantly affect the total release of toxic products" (p 12).
3.2.1 Effects in the aquatic compartment
No data on toxicity to algae are available for commercial OBDE. An EC50>1 mg/L (high above the solubility) was obtained for decabromodiphenyl ether. For pentabromodiphenyl ether a 96h NOEC = 26 microg/L was observed, but growth inhibition was present at lower concentrations in shorter time (24 h EC10=2.7-3.3 microg/L).
A NOEL > 2 microg/L was obtained in a 21-days reproduction test on Daphnia for the commercial OBDE mixture. QSAR data seem not to be in disagreement with this result.
The only available toxicity test on fish indicate a 48h LC50>500 mg/L for the technical mixture, a concentration far above the solubility of these substances. At least some of the components in the commercial mixtures are absorbed slowly and therefore short-term tests are less relevant.
A PNECwater>0.2 microg/L has been estimated by applying a factor of 10 to the 21-days reproduction NOEC on Daphnia.
No data are available on sediment dwelling organisms. According to the equilibrium partitioning method proposed by the TGD, PNECs have been estimated on the basis of the PNECwater. A calculated PNECsed is >5.93 mg/kg but the use of this method for the highly adsorptive OBDE is questionable.
For hexabromodiphenyl ether components, a reasonable worst case has been assumed to calculate a PNECwater = 0.11 microg/L.
3.2.2 Effects in the terrestrial compartment
No effect data for OBDE are available on terrestrial organisms. The PNEC has been derived according to the TGD rules, but this approach is not considered valid for this particular chemical. The derivation of a PNECsoil using the partitioning equilibrium method for a chemical which does not show toxicity for aquatic organisms at the solubility limit is not scientifically valid. The basis for the equilibrium partitioning method is that pore water represents the main (or even the only) exposure route, and this assumption is clearly not valid for chemicals which water solubility is so low that toxicity is not observed at this level. The RAR properly applies and additional safety factor of 10 to consider food exposure, but even under these circumstances the method is not valid, because the lack of toxicity for water exposures is related to the unavailability of the substance to enter into the organisms, and not to lack of toxicity if the substance is able to enter in the organisms by any other route. A basic rule for the application of the partitioning equilibrium method is to observe toxicity or to confirm that the chemical has had the opportunity to reach the target organ.
Therefore although the CSTEE recognised that the RAR has followed the TGD, the suggested PNEC for terrestrial organisms is not considered valid.
3.2.4 Non compartment specific effects relevant to the food chain (secondary poisoning)
Available data indicate that OBDE has a low bioaccumulation potential, but it is higher for lower brominated homologues present in the products. A PNEC = 6.7 mg/kg food has been calculated for secondary poisoning.
The document underlined the possibility of formation of more accumulative and toxic compounds (lower brominated diphenyl ethers, brominated dibenzo-p-dioxins and furans) from degradation or combustion processes. The CSTEE also underlines the possibility for formation of lower brominated diphenyl ethers that are more rapidly absorbed by organisms.
The proposed risk assessment must be re-evaluated by the CSTEE after the submission of the mammalian toxicity data.
3.3 Risk characterisation
3.3.1.1 Water
Calculated local PEC/PNEC ratio for surface water is close to 1, thus, the risk for water is low but cannot completely excluded from available data.
3.3.1.2 Sediments
As for sediments, low PEC/PNEC ratios have been calculated for OBDE, but a local value >1 has been calculated for hexabromodiphenyl ether components. However, the validity of equilibrium partitioning method for this chemical is highly questionable because pore water is not expected to be the main exposure route for sediment dwelling organisms.
3.3.2 Risk characterisation for the terrestrial compartment
For the soil compartment, a relatively high local PEC/PNEC ratio has been observed for octabromodiphenyl ether. However, a PNEC value cannot be derived with the available information and therefore conclusion (i) - there is a need for further information - is the only acceptable conclusion.
The RAR suggests the refinement of the risk characterisation after the submission of the toxicity tests currently ongoing for other brominated homologues. However, the CSTEE considers that the extrapolation from one homologue to the other will only be possible if the produced information allows a clear understanding of the relationships between the toxicity and the bioavailability of each substance. A low level or lack of toxicity for any substance cannot be extrapolated to other homologues and/or exposure routes if it is related to a reduced bioavailability for that particular exposure route. Therefore the assumption of lack of toxicity for any non-tested homologues can only be accepted if there is clear evidence that the tested substance has been able to reach the target organ, or if the bioavailability for the non-tested homologue or exposure route is equal to or lower than the tested homologue and route.
----------------------------------------
1 Regulation 793/93 provides a systematic framework for the evaluation of the risks to human health and the environment of those substances if they are produced or imported into the Community in volumes above 10 tonnes per year. The methods for carrying out an in-depth Risk Assessment at Community level are laid down in Commission Regulation (EC) 1488/94, which is supported by a technical guidance document.
Terms of reference
The CSTEE has been invited to examine the Environmental Risk Assessment Report for Octabromodiphenyl ether and address the following issues:
1. Does the CSTEE agree with the conclusions of the Risk Assessment Report?
2. If the CSTEE disagrees with such conclusions, the CSTEE is invited to elaborate the reasons for this divergence of opinion.
GENERAL COMMENTS/CONCLUSIONS
Commercial octabromodiphenyl ether is a mixture containing congeners with varying bromine content. These congeners have different properties and will behave differently in the environment. An option to handle this would be to make separate risk assessments for at least the different homologue groups, but the scarce amount of data available makes this impossible. These compounds are very lipophilic and organisms absorb at least some of them slowly, which makes acute effect data less relevant. While some of these compounds are predicted to bioaccumulate and degrade slowly in the environment, available data suggests limited bioaccumulation.
On the basis of the few data available, a potential risk for the environment cannot be excluded. The conclusions of the report suggest the need for further information and testing for: The aquatic compartment to assess the effects on sediment from local sources and to assess the risk to waste water treatment processes; The terrestrial compartment to assess effects on soil organisms from local sources; The secondary poisoning in relation to degradation products. The CSTEE agrees with these conclusions. In addition some more precise information to quantify the effects on water organisms at local level is needed. The CSTEE do not think that the equilibrium partitioning method can be applied for these very adsorptive compounds with very low water solubility, and thus also further information is needed of effects on organisms in the sediment and soil compartments.
The CSTEE has the main following comments to make on the chapters indicated.
SPECIFIC COMMENTS
3.1 Exposure assessment
Octabromodiphenyl ether is used as technical mixtures (31-35% OBDE) containing large amounts of other congeners, in particular hexabromo- (10-12%), heptabromo- (44%) and nonabromodiphenyl ethers (10-11%). In a recent thesis (Andreas Sjödin, "Occupational and Dietary Exposure to Organohalogen Substances, with Special Emphasis on Polybrominated Diphenyl Ethers", Stockholm University, 2000), which was not available to the assessors, the composition of one OBDE product is shown to have higher concentrations of the higher brominated groups. Most of the few toxicity data available refer to commercial mixtures and it is not possible to assess the effects of different congeners.
In the General information on exposure, relatively old data on production and uses are reported and all references are to 1994 or before. The anticipated "worst case" use (2550 tonnes/year) seems to be verified by data from the industry saying that 2500 tonnes were used 1993 (De Poortere, "Brominated Flame Retardants", presented at a Swedish Society of Toxicology Workshop, 2000). The use of OBDE products was estimated to have decreased since that time and for 1999 about 400 tonnes were expected to be used in the EU.
There are only few measurements of OBDE concentrations in the environment reported, and most of these are from industrialised areas. There is a reasonable agreement between those data and the EUSES predicted values. The CSTEE have earlier pointed at the problems with predictions of root crop concentrations, and also for OBDE the levels predicted there are probably far too high.
The exposure to possible transformation products of OBDE has to be taken into account, and the CSTEE does not agree with the statement "the presence of octabromodiphenyl (ether) in fires is unlikely to significantly affect the total release of toxic products" (p 12).
3.2.1 Effects in the aquatic compartment
No data on toxicity to algae are available for commercial OBDE. An EC50>1 mg/L (high above the solubility) was obtained for decabromodiphenyl ether. For pentabromodiphenyl ether a 96h NOEC = 26 microg/L was observed, but growth inhibition was present at lower concentrations in shorter time (24 h EC10=2.7-3.3 microg/L).
A NOEL > 2 microg/L was obtained in a 21-days reproduction test on Daphnia for the commercial OBDE mixture. QSAR data seem not to be in disagreement with this result.
The only available toxicity test on fish indicate a 48h LC50>500 mg/L for the technical mixture, a concentration far above the solubility of these substances. At least some of the components in the commercial mixtures are absorbed slowly and therefore short-term tests are less relevant.
A PNECwater>0.2 microg/L has been estimated by applying a factor of 10 to the 21-days reproduction NOEC on Daphnia.
No data are available on sediment dwelling organisms. According to the equilibrium partitioning method proposed by the TGD, PNECs have been estimated on the basis of the PNECwater. A calculated PNECsed is >5.93 mg/kg but the use of this method for the highly adsorptive OBDE is questionable.
For hexabromodiphenyl ether components, a reasonable worst case has been assumed to calculate a PNECwater = 0.11 microg/L.
3.2.2 Effects in the terrestrial compartment
No effect data for OBDE are available on terrestrial organisms. The PNEC has been derived according to the TGD rules, but this approach is not considered valid for this particular chemical. The derivation of a PNECsoil using the partitioning equilibrium method for a chemical which does not show toxicity for aquatic organisms at the solubility limit is not scientifically valid. The basis for the equilibrium partitioning method is that pore water represents the main (or even the only) exposure route, and this assumption is clearly not valid for chemicals which water solubility is so low that toxicity is not observed at this level. The RAR properly applies and additional safety factor of 10 to consider food exposure, but even under these circumstances the method is not valid, because the lack of toxicity for water exposures is related to the unavailability of the substance to enter into the organisms, and not to lack of toxicity if the substance is able to enter in the organisms by any other route. A basic rule for the application of the partitioning equilibrium method is to observe toxicity or to confirm that the chemical has had the opportunity to reach the target organ.
Therefore although the CSTEE recognised that the RAR has followed the TGD, the suggested PNEC for terrestrial organisms is not considered valid.
3.2.4 Non compartment specific effects relevant to the food chain (secondary poisoning)
Available data indicate that OBDE has a low bioaccumulation potential, but it is higher for lower brominated homologues present in the products. A PNEC = 6.7 mg/kg food has been calculated for secondary poisoning.
The document underlined the possibility of formation of more accumulative and toxic compounds (lower brominated diphenyl ethers, brominated dibenzo-p-dioxins and furans) from degradation or combustion processes. The CSTEE also underlines the possibility for formation of lower brominated diphenyl ethers that are more rapidly absorbed by organisms.
The proposed risk assessment must be re-evaluated by the CSTEE after the submission of the mammalian toxicity data.
3.3 Risk characterisation
3.3.1.1 Water
Calculated local PEC/PNEC ratio for surface water is close to 1, thus, the risk for water is low but cannot completely excluded from available data.
3.3.1.2 Sediments
As for sediments, low PEC/PNEC ratios have been calculated for OBDE, but a local value >1 has been calculated for hexabromodiphenyl ether components. However, the validity of equilibrium partitioning method for this chemical is highly questionable because pore water is not expected to be the main exposure route for sediment dwelling organisms.
3.3.2 Risk characterisation for the terrestrial compartment
For the soil compartment, a relatively high local PEC/PNEC ratio has been observed for octabromodiphenyl ether. However, a PNEC value cannot be derived with the available information and therefore conclusion (i) - there is a need for further information - is the only acceptable conclusion.
The RAR suggests the refinement of the risk characterisation after the submission of the toxicity tests currently ongoing for other brominated homologues. However, the CSTEE considers that the extrapolation from one homologue to the other will only be possible if the produced information allows a clear understanding of the relationships between the toxicity and the bioavailability of each substance. A low level or lack of toxicity for any substance cannot be extrapolated to other homologues and/or exposure routes if it is related to a reduced bioavailability for that particular exposure route. Therefore the assumption of lack of toxicity for any non-tested homologues can only be accepted if there is clear evidence that the tested substance has been able to reach the target organ, or if the bioavailability for the non-tested homologue or exposure route is equal to or lower than the tested homologue and route.
----------------------------------------
1 Regulation 793/93 provides a systematic framework for the evaluation of the risks to human health and the environment of those substances if they are produced or imported into the Community in volumes above 10 tonnes per year. The methods for carrying out an in-depth Risk Assessment at Community level are laid down in Commission Regulation (EC) 1488/94, which is supported by a technical guidance document.