1,1'-(ethane-1,2-diyl)bis[pentabromobenzene]

Endpoint summary

Description of key information

Two recent guideline studies according to OECD 305 and GLP with dietary exposure were performed following the substance evaluation decision. These studies are regarded as the key studies to determine the bioaccumulation potential of EBP in aquatic organisms. The first study (Schneider et al, 2020a) was initially planned to be a range finding preliminary study, but then evolved to a full study that had additional elements built in. The results were submitted in January 2019, but the final audited report only became available in December 2020 due to delays in the QA group of the contract house and the Covid-19 situation.

This study was designed to investigate if there is a considerable difference in uptake of radiolabled EBP (radiolabel in the aromatic ring) from the gut at two different concentration levels (100 and 1000 micro-g/g diet). In addition a lipophilic reference substance with a known high BCF, PCB-153, was included in the same diet as a positive control and benchmark chemical and to test if the test system was behaving as expected. The dose levels of PCB-153 were 100 and 10 micro-g/g diet. A control that is not taken up from the gut, chromium trioxide was also included in both treatment groups following an expert advice. The guts were removed before determination of the substance concentrations in the whole fish to make sure that the absorbed substance only was considered for the calculation. The gut contents were analyzed separately for the parent substance and possible metabolites. In the high dose group the exposure was also continued for 56 days in order to account for a possible slower uptake and retarded accumulation.

Bluegill were exposed to a commercial diet treated at a nominal concentrations of 100 µg/g EBP + 10 µg/g PCB for 28 Days and 1000 µg/g EBP + 100 µg/g PCB for 56 Days and a control group fed with untreated diet only. The calculation of the BMF parameters was based on the EBP equivalent concentrations determined by LSC in the diet and in fish tissues and mean measured concentrations of PCB in the diet and fish tissues. Results from the pilot dietary exposure indicate that EBP at concentrations of 100 and 1000 µg/g does not bioaccumulate in whole fish tissue and is primarily retained in the gut tract. Further analysis of the gut tract samples collected from fish sampled during the uptake phase in Treatment Group 2, indicate that there was no metabolism of EBP. There was minimal uptake of EBP in whole fish tissues and concentrations during depuration were below LOQ by Day 1 of depuration. The lipid-corrected growth-corrected kinetic BMF values for EBP were 0.003 and 0.001 in Treatment Groups 1 and 2, respectively. Indicative lipid-corrected steady-state BMF values for the EBP in Treatment Groups 1 and 2 were 0.003 and 0.001, respectively. Statistical analysis indicated that there was no significant difference in tissue concentrations on days 14 to 28 in group 1 (low dose) and between tissue levels on days 28 to 56 in the high dose group.

Results from the uptake and depuration phase indicate that EBP did not bioaccumulate in fish tissue. Analysis of gut track tissue show that the test material was retained in the gut and that no metabolism occurred. 

In the low dose group of PCB tissue concentrations increased between day 1 and 14 but there was no statistically significant further increase in PCB tissue concentrations between day 14 and 28. In the high dose group the tissue concentrations further increased between day 14 and 56 and indicative steady state was not reached during the prolonged uptake phase for the reference substance. PCB slowly depurated from whole fish tissue with measured concentrations at the end of depuration being 57 (high dose group) to 75% (low dose group) of end of uptake measured concentrations.  The lipid-corrected growth-corrected kinetic BMF values for PCB-153 were 0.201 and 1.329 in Treatment Groups 1 and 2, respectively.  Indicative lipid-corrected steady-state BMF values for the PCB-153 in Treatment Groups 1 and 2 were 0.143 and 0.381, respectively. However, statistical analysis showed that steady state was not reached do this substance during the uptake phase of 28 and 56 days respectively. Thus the positive control showed bioaccumulation and magnification as expected.

The results indicate that EBP did not biomagnify and did not bioaccumulate in fish under the conditions of this study.

The results also demonstrated that the uptake was not concentration-dependent and for the main study only one concentration (1000 micro-g/g diet to maximize exposure) was be tested. With longer duration of the uptake phase no increase in tissue concentration was observed. Thus for the main study the uptake phase was chosen as 28 days.

For the main study a group co-dosed with PCB-153 and group with treatment of EBP only at the same dose level without the reference substance and several reference substances with different BMF/BCF values were included as benchmarks. This design should exclude influence on the bioavailability and absorption efficiency by the control substance if dosed at the same time, because this could not be completely excluded by this pilot study, although the reference substance showed the expected accumulation behavior.

In the main study Schneider et al , 2020b, key study 2, Bluegill were exposed to five treatment groups which consisted of a commercial diet treated at nominal concentrations of 1000 µg/g EBP + 100 µg/g PCB-153 (Treatment Group 1), 1000 µg/g EBP (Treatment Group 2), 100 µg/g PCB-153 (Treatment Group 3), 100 µg/g Solvent Blue (Treatment Group 4) and 100 µg/g ο-Terphenyl (Treatment Group 5) for 28 Days and a control group fed with untreated diet only. The calculation of the BMF parameters was based on the EBP equivalent concentrations determined by LSC in the diet and in fish tissues and mean measured concentrations of PCB-153, Solvent Blue and ο-Terphenyl in the diet and fish tissues.

Results from the dietary exposure indicate that EBP does not bioaccumulate in whole fish tissue and is primarily retained in the gut tract. There was minimal uptake of EBP in whole fish tissues and rapid depuration. Tissue concentrations in group 1 and 2 did not significantly increase between day 14 and 28 of uptake. Mean measured concentrations during depuration were below LOQ by Day 3 of depuration in Treatment Groups 1 and 2. The lipid-corrected growth-corrected BMF values for EBP were 0.0003 and 0.0014 in Treatment Groups 1 and 2, respectively, and were comparable to the low BMF values estimated in the preliminary study. The definitive BMF values for EBP correlate with the BMF value obtained in the preliminary pilot study, 0.0010 and support the conclusion that EBP does not bioaccumulate in fish tissue.

The preliminary study (Schneider et al 2020a) used two concentrations of EBP (100 and 1000 µg/g. The uptake phase in the high dose group was prolonged in the preliminary study to 56 days to account for a possible slower uptake and retarded accumulation

At the end of uptake phase in the preliminary study, guts were removed and analyzed separately confirming that there was minimal uptake of EBP in tissue and EPB was retained in the gut tract. Additional evaluation during the preliminary study indicates that EBP does not metabolize in the gut tract. The data in both the preliminary and definitive studies demonstrate that the test substance is retained in the gut with minimal uptake into tissue, stays unchanged in the feces and is rapidly eliminated even after the prolonged exposure in the preliminary test.

PCB-153, was found to accumulate in whole fish tissue sampled during the uptake phase. In both PCB-153 treated groups the tissue concentrations increased between day 14 and 28 of uptake indicating that steady state was not reached. PCB-153 slowly depurated from whole fish tissue with measured concentrations at the end of depuration being 40 to 59% of measured concentrations at the end of uptake. The lipid-corrected growth-corrected BMF values for PCB-153 was 3.78 and 6.40 in treatment Groups 1 and 3, respectively. The definitive values for PCB-153 agree with the BMF value obtained in the preliminary pilot study, 1.33. Both studies indicate a BMF greater than 1 and demonstrate that PCB-153 bioaccumulates in the fish tissue. The lipid corrected BMF values obtained from the definitive study, 0.760 and 0.602, were slightly higher than the published value of 0.410. 

The lipid and growth corrected kinetic BMF values in Treatment Group 1 (1000 µg/g EBP + 100 µg/g PCB-153) were 0.0003 for EPB and 3.78 for PCB-153. These BMF values come from the same fish and offer a relative comparison of EPB to a known chemical that bioaccumulates. Within the same fish we see that EBP is not bioaccumulating while PCB-153 shows substantial bioaccumulation. The difference (3.76 or 6.40 vs 0.0003 or 0.0014) is greater than approximately three to four orders of magnitude, demonstrating the negligible bioaccumulation of EBP. Additionally, PCB-153 can be considered as a benchmark that demonstrates the fish used in this study were in good condition and responded as expected with BMF values that were comparable to other acceptable studies.

Solvent Blue, was found to accumulate in whole fish tissue sampled during the uptake phase. No statistically significant difference in the mean tissue concentrations and no increasing trend was observed between day 14 and day 28. Solvent Blue depurated from whole fish tissue with measured concentrations at the end of depuration being 12% of measured concentrations at the end of uptake. The lipid-corrected growth-corrected BMF values for Solvent Blue was 0.304. The BMF value obtained from this study was comparable to the literature value of 0.316. The published BCF value for Solvent Blue in carp was 5300 Solvent Blue can also be considered as a benchmark in the study that represent moderate bioaccumulation but still above the vB criterion. The difference between BMF values for Solvent Blue and EBP (0.304 vs 0.0003 or 0.0014) is approximately 2 to 3 orders of magnitude greater and again is demonstrating the negligible bioaccumulation of EBP.

ο-Terphenyl, was found to accumulate in whole fish tissue sampled during the uptake phase. No statistically significant difference in the mean tissue concentrations and no increasing trend was observed between day 14 and day 28. ο-Terphenyl depurated from whole fish tissue with measured concentrations at the end of depuration being 11% of measured concentrations at the end of uptake. The lipid-corrected growth-corrected BMF values for ο-Terphenyl was 0.314. The BMF value obtained from this study was higher than the literature value of 0.0912. The published BCF value for ο-Terphenyl in carp was 1200 (Inoue Y et al. 2012) and was slightly lower than the range of values based on the dietary data. However, literature estimates of BCF and BMF values for o-terphenyl are highly variable, and the pattern of variation suggests that both experimental factors and species may play a large role in this variation. Thus, the literature estimates of BCF for o-terphenyl range between 590 and 12993. In hindsight, evidence that the BCF of o-terphenyl should be below 2000 is weak, but there were difficulties finding an appropriate benchmark substance with a BCF below 2000. Overall, ο-Terphenyl can also be considered as a benchmark in the study that represents a more moderate bioaccumulation. The difference between growth and lipid corrected kinetic BMF values for ο-Terphenyl and EBP (0.314 vs 0.0003 or 0.0014) is also approximately 2 to 3 orders of magnitude greater and again is demonstrating the negligible bioaccumulation of EBP. These results demonstrate EBP has an extremely low potential for bioaccumulation compared to known reference substances.

Additional information

Terrestrial bioaccumulation is not expected based on the rat ADME study, negligible water and organic solvent solubility of the substance, high binding to particulates, and an in vitro study showing negligible solubility in cell culture media. Substances must first be in solution to be absorbed, and EBPs low solubility will limit its uptake. Particulate binding reduces bioavailability. Rat oral pharmacokinetic studies using 14C-EBP demonstrated elimination in the feces as the parent molecule and background levels of radioactivity in the blood, plasma, bile, tissues and urine. EBP’s solubility in octanol is <0.002 mM x MW, which according to REACH Guidance, indicates a low potential for bioaccumulation.  

     

 Guerra et al. (2012) did not detect EBP in 13 peregrine falcon eggs collected in Spain from 2003 to 2006. McKinney et al. (2011)did not detect EBP in adipose of polar bears collected in East Greenland and Svalbard between 2005 – 2008.  Tlustos et al. (2010)reported decabromodiphenylethane was not detected in milk, eggs, fat and liver samples sampled in Ireland by the Food Safety Authority of Ireland. Analyses were performed by the Food and Environment Research Agency, York, UK. A total of 100 composite samples were prepared after collection of individual sub-samples at the production or processing stage. These included 30 milk samples, 20 egg samples, 38 samples of carcass fat taken from beef cattle, pigs, lambs, chickens and ducks, and 12 samples of liver (bovine, porcine, ovine, equine and avian). Samples were supplied by officers of the Department of Agriculture, Fisheries and Food at production level (slaughterhouse – fat and liver, farm/dairy tanker – milk, packing station – eggs. Analysis was via GC-HRMS using 13C-labelled surrogates.   The authors noted that a recent survey in the UK had also not detected the substance.   

 

Recent monitoring results from European studies in birds, eggs and fish muscle and liver were reviewed in the exposure assessment report (Fisk et al, 2019) attached to this dossier. Levels were either below detection or quantification limit or in the pg/g range.   

 In addition to birds’ eggs and fish muscle and liver, data are also available for shellfish at the local marine scale (<0.84 pg/g ww - 20.1 pg/g ww and 29 ± 50 pg/g), zebra mussel and zooplankton (both <LOD) at the local scale, and bird liver (<0.025 ng/g ww), seal blubber  

  (<0.12 - 0.30 ng/g ww, more than 80% < MDL) and polar bear adipose tissue (<0.13 ng/g ww) at the continental background scale. Data are also reported for tree bark (<LOD – 3.9 ng/g lipid) weight, or 0.13 ng/g using reported lipid %). As for the previous Nordic data, all concentrations reported in recent literature were either <LOD or in the range of pg/g.  

  Al these data do not indicate that EBP is not biomagnifying in environmental species and support the findings that it is not bioaccumulative.