Hexabromocyclododecane

Toxicity to aquatic algae and cyanobacteria

Description of key information

The selection of key information for this endpoint is complicated by the composition of the registered substance (reaction mass of three isomers), the insolubility of the registered substance and the variety of information available (both freshwater and marine algal studies).
Selection of the key information would usually be made upon reliability and so all available studies have been scored according to the criteria of Klimisch et al, 1997, however due to the above differences in test method and principle additional factor concerning the selection of the key information must also be taken into account. These factors are detailed below:
•The registered substance is a mixture of three isomers present at differing qualtities in the various grades of the substance however the γ-isomer is usually present at greater concentrations than the α- and β-isomers.
•The registered substance is more soluble in marine water than freshwater (as shown in the water solubility studies), with each isomer having it's own limit of solubility.
•The water accomodated fraction approach to test solution preparation has been shown to be unsuitable due to undissolved material present in the aqueous fraction even after settling (see water solubility studies).
•The column elution method has been shown to produce test solutions which are disproportionately rich in the α- and β- isomers compared to the registered substance values.
Due to the above concerns the following studies were selected as the key information for this endpoint.
Desjardins et al (2004) - Toxicity study conducted on marine algae
Roberts & Swigert (1997) - Toxicity study conducted on freshwater algae

Key value for chemical safety assessment

EC10 or NOEC for freshwater algae:

8.1 µg/L

EC10 or NOEC for marine water algae:

320 µg/L

Additional information

Freshwater algae

When added to freshwater, the commercial HBCDD product was not acutely toxic to Selenastrum capricornutum when tested at concentrations based on the water solubility of the gamma diastereomer (Roberts and Swigert, 1997). HBCDD's 96 hour EC10, EC50, EC90 and NOEC were all greater than water solubility of the gamma isomer, on which the dose levels were based. The highest nominal dose tested was twice gamma HBCDD’s water solubility. Dose levels were 0, 1.5, 2.2, 3.12 4.6 and 6.8 µg/L (nominal). The mean measured concentration (HPLC with UV/VIS detector) at the 6.8 µg/L dose was 3.7 µg/L. The dose levels were based on the gamma isomer's water solubility of 3.4 µg/L. At this level and the typical proportions of the alpha and beta diastereomers in the commercial product, the alpha and beta diasteromers were not quantifiable in water. Assuming the test article was 80% gamma, approximately 4.6 µg/L of the commercial product would be needed to generate the measured concentration of the gamma diastereomer. Thus, the NOEC for the commercial HBCD product would at a minimum be 4.6 µg/L measured or 8.1 µg/L nominal. Using the WAF methodology, EPS and XPS boards flame retarded with HBCD were not toxic to freshwater algae; the LL50 was > 100 mg board/L.

Marine algae

Walsh et al. (1987) reported the combined effects of media and test chemicals in three species of marine algae.  A commercial HBCDD product was tested in three species of marine algae using six different media. The EC50s were Chlorella sp 96 hr EC50 > 1500 µg/L in all six media; S. costatum72 hr EC50 = 9.3-12 µg/L in the six media; T. pseudonana 72 hr EC50 50-370 µg/L in the six media. In a guideline/GLP-compliant study that used a generator column to generate test article-containing media from a composite of the commercial HBCDD product, Desjardins et al. (2004) reported the EC50 in S. costatum was greater than the sum of the alpha (30.5 µg/L), beta (8.86 µg/L) and gamma (1.61 µg/L) diasteromers measured in the media (EC50 > 41 µg/L) whereas the NOEC was less than the sum of the three (NOEC <41 µg/L). In a second study (Desjardin et al., 2005a) reported no effects in the marine algae Skeletonema constatum in a 72 hour test,when the commercial HBCDD product was added to test water with a co-solvent at concentrations equivalent to the water solubility of the gamma diastereomer (EC50 > 10 µg/L). In a third study using a generator column to produce test water from the commercial HBCDD product, the EC50 (growth rate) was approximately equal to the sum of the measured concentrations of the alpha (35.8 µg/L), beta (15.2 µg/L) and gamma (3.5 µg/L) diasteromers in the media, which in this case was 52 µg/L (Desjardins et al. 2005b). The generator column produced a test media in which all three diasteromers were present at approximately their individual water solubilities. Based on the composition of the test article, approximately 620 µg of the commercial HBCD product would need to be added to one litre of marine water to achieve these concentrations. Thus, the commercial HBCDD's EC50 would be >620 µg/L, while the NOEC would be <620 µg/L. Using REACH Guidance R.10, Table R.10-1, an NOEC can be calculated as follows: assume the LOEC = 620 µg/L given the effect of approximately 20%, then the NOEC=LOEC/2=320 µg/L.