1,6,7,8,9,14,15,16,17,17,18,18-dodecachloropentacyclo[12.2.1.16,9.02,13.05,10]octadeca-7,15-diene

Endpoint summary

Description of key information

Dechlorane Plus has been assessed as vPvB and inserted to SVHC candidate list based on weight of evidence expert judgement although the member state authorities commented that the most available data within the lead dossier as well in the literature were not conducted in line with OECD Guidance.

The registrant emphasizes that relevant and reliable studies are lacking to assess the biodegradation potential of DP - a substance with very low water solubility.

Additional information

The substance is highly insoluble in water and thus hydrolysis of Dechlorane Plus cannot be sufficiently tested. In a screening study the rate of oxidation of Dechlorane Plus in water was estimated resulting in a first-order rate constant with 1/10000000000 / sec corresponding to an oxidation half-life in water of 2100 years. Findings of DP in the environment (see section 5.5) do support this assumption. Study results do indicate a potential for photodegradation in water but degradation rates seen were within the error margin of the study and thus should only be considered indicative.

 

Dechlorane Plus was investigated for biodegradation in two non-standard tests. Whereas in a first study no biodegradation was observed within 21 days (Boudreau et al., 1973), in a second experiment by Chou et al. (1979) radiolabelled Dechlorane Plus was investigated for biodegradation. Degradation was determined as loss of radioactivity following 2 and 6 weeks of exposure to sewage sludge. No loss of radioactivity was seen after 2 weeks of incubation at aerobic and anaerobic conditions. After 6 weeks of incubation, the recovery of radioactivity at aerobic conditions was 42.9% at the low concentration and 0.16% at the high concentration when compared to 92.1% in the sterile negative control at the high concentration.

Volatilisation of the test substance causing reduction of radiolabelled material is unlikely, given the physico-chemical properties of the substance (melting point >300 °C and vapour pressure considered negligible), but adsorption to sludge or bacteria cannot be excluded. Also the position of radiolabelling in the molecule is not described. Thus, the findings have to be seen with caution and cannot be considered as proof for biodegradation. Hence, the substance is considered non-biodegradable. Studies on biodegradation in water and/or soil are not available.

 

From all publications assessed so far no consistent findings on accumulation of DP in the food chain can be derived. Bioconcentration studies using fish did not show high levels of bioaccumulation, but their relevance to highly insoluble substances such as Dechlorane Plus is limited. Bioaccumulation was observed in some freshwater predator/prey sets and also in marine oysters that could be considered very bioaccumulative. However, the results mainly reported in peer-reviewed literature did not indicate strong bioaccumulation or indicated no accumulation in the food webs investigated and many predator/prey sets. Several literature sources demonstrate, that bioaccumulation of DP is lower than for example for mirex, polychlorinated biphenyl ethers or Dechlorane 602.

 

The highest values found for Dechlorane Plus from all studies assessed were:

BCF: 2907 (Boudreau, 1973 using acetone as vehicle and thus of limited relevance)

Half-lifes in fish: 53.3 days and 40.4 days for the syn- and anti-isomer, respectively (Tomy, 2008, exposure via feeding of rainbow trouts under flow-through conditions).

BMF: 12 and 11 for syn- and anti-DP, respectively (Tomy, 2007 for trout/alewife set in Lake Ontario, whereas other predator/prey sets showed values ≤1)

log BAF: 4.4 (Wu, 2010 for water snake)

BSAF (freshwater sediment): 0.88 (0.33 - 2.8) for syn-DP, and 0.33 (0.086 - 1.0) for anti-DP (Wang, 2012)

BSAF (marine sediment): 4.6, ranging from 1.0 to 7.9 (Jia, 2011)

 

Remark: The vPvB classification and subsequent inclusion into SVHC candidate list is based on detailed analysis of Tomy et al. study. The registrant has re-calculated this values due to inconsistencies. Based on BMF values re-calculated from the data of Tomy et al., which are clearly below 1 Dechlorane Plus cannot be considered to be a vB substance. Contrary to the conclusion drawn by Tomy, results do not indicate a biomagnification, but may rather point to a relatively slow depuration of DP isomers.

 

An adsorption/desorption study was not performed as the substance is highly insoluble in water. However, in a study by Chou et al. (1979) the sorption to sediment was assessed and as expected high sorption to sediment was found in aqueous system. With a sorption partition coefficient determined being 4.5 ± 1.9 *10E6 (the particulate matter was assessed form the blank control and considered for calculation).

 

DP is found in all environmental compartments (air, water, sediment and soil) but in rather low concentrations when compared to other flame retardant such as Mirex or brominated flame retardants (orders of magnitudes lower). High peak concentrations are found close to manufacturing sites for DP and e-waste recycling sites in China. Besides those, low levels can be found in urban and highly industrialized areas and even lower concentration, close to quantification limits, in rural areas.

 

Although in some publications a difference in syn- and anti-DP accumulation is postulated, most studies do not support this hypothesis. The slight variations seen may be due to the fact that syn/anti-DP ratios are different in the two manufacturing plants on one hand and on the other hand variations over time in the manufacturing plants may have existed due to optimization of production processes. Also, thermal stress in e-waste recycling sites (plastic is incinerated there) may alter the syn/anti-DP ratio leading to variations in findings. Only the results from Möller et al. do indicate that the syn/anti-DP ratio may change upon exposure to UV-light in air and that the syn-isomer is more stable to UV-light than the anti-isomer. As transport via air is the dominant route for DP distribution, this also may have affected some findings, especially at concentration found close to quantification limits, usually far away from point sources. However, in other compartments (water, sediment, soil, biota) the syn/anti-DP ratio appears to be not significantly affected.