Ethene, homopolymer, oxidized, hydrolyzed, distn. residues, from C16-18 alcs. manuf.

Bioaccumulation: aquatic / sediment

Description of key information

The data requirement for bioaccumulation studies in aquatic and terrestrial organisms is waived on the evidence of technical difficulties, ready biodegradability and the absence of toxicity in aquatic organisms and mammals. A bioconcentration factor for icosan-1-ol and docosan-1-ol was calculated from the estimated log Kow value of 7.75 using the parabolic recalculated Connell and Hawker equation; the BCF is 31,800 L/kg. However, predicted BCFs for long chain alcohols are considered to be overestimates by orders of magnitude due to the natural ability of biochemical systems in organisms to metabolise alcohols.

Additional information

Ziegler Bottoms are characterized as comprising of two primary constituents; icosan-1-ol and docosan-1-ol. Together these primary constituents represent a structural class of components (alcohols) that constitute approximately 82% of the composition of Ziegler Bottoms. Study data, where available, for each of these primary constituents has been evaluated and considered together. In a conservative approach the most sensitive study result from across the two constituents has been identified and used to address the Ziegler Bottoms endpoint in question. 

The REACH requirement in Annex IX for a study on bioaccumulation in aquatic species is not needed if the substance has a low potential for bioaccumulation and/or a low potential to cross biological membranes. The waiver argumentations are based on the technical difficulties associated with conducting bioaccumulation studies, the ready biodegradability of the test substance, the low toxicity in aquatic organisms and the low toxicity in mammals resulting in the unlikely potential for secondary poisoning, as presented in more detail below:

Study not technically feasible

The requirement to conduct bioaccumulation studies for icosan-1-ol and docosan-1-ol is waived due to technical difficulties in performing such a test. Guideline (standard) studies of bioaccumulation in fish would be confounded by the technical difficulties of maintaining the test alcohols (icosan-1-ol and docosan-1-ol) in solution, as was demonstrated in long-term invertebrate studies reported in the OECD SIDS Report for Long Chain Alcohols (2006). Severe difficulties were encountered when studies were conducted with >C15 alcohols, which are similar to constituents of the Ziegler Bottoms, as biodegradation in the test system was almost complete within the 24-hr test media renewal period.

Biodegradation

Icosan-1-ol and docosan-1-ol are both readily biodegradable. The most recent reliable study (OECD 301B) using icosan-1-ol reported results of 87.9% (CO₂) in 28 days confirming the readily biodegradable (P&G, 2009). The finding is consistent with very high levels of removal in other types of test systems where very fast degradation and metabolism in microorganisms and a range of trophic levels has been identified for alcohols in the range C6-24. Ready biodegradability means that the test substance will rapidly be unavailable for uptake and bioaccumulation in biological organisms.

Toxicity to Aquatic Organisms

Generally the short-term aquatic toxicity of the two primary constituent substances (icosan-1-ol and docosan-1-ol) is low. According to the OECD SIDS Report for Long Chain Alcohols (2006) long-term toxicity is also considered to be very low and below the limit of solubility for alcohols >C15 in chain length.

Toxicity to Mammals

There is no requirement in REACH to conduct a secondary poisoning assessment in view of the lack of toxic effects in mammals. Chronic and sub-chronic mammalian toxicity studies have shown that long chain alcohols (LCA) are of low toxicity. Furthermore, combined repeated-dose studies with developmental endpoints, as well as reproductive and developmental studies, showed no effects at the highest dose tested. This evidence indicates that the test substance is not considered to be toxic (in PBT terms) to mammals and secondary poisoning is unlikely to occur in the environment.

Summary

The data requirement for bioaccumulation studies in aquatic and terrestrial organisms is waived on the evidence of technical difficulties, ready biodegradability and the absence of toxicity in aquatic organisms and mammals. A bioconcentration factor for icosan-1-ol and docosan-1-ol was calculated from the estimated log Kow value of 7.75 using the parabolic recalculated Connell and Hawker equation; the BCF is 31,800 L/kg. However, predicted BCFs for long chain alcohols are considered to be overestimates by orders of magnitude due to the natural ability of biochemical systems in organisms to metabolise alcohols (OECD SIDS Initial Assessment Report (2006); Veithet al(1979) and Connell and Hawker (1988)).

References

SIDS Initial Assessment Report on Long Chain Alcohols (2006). Organisation for Economic Cooperation and Development (OECD).

Veith GD, Defoe DL and Bergstedt BV (1979). Measuring and estimating the bioconcentration factor of chemicals in fish. J. Fish. Board Can. 36: 1040-1048.

Connell DW and Hawker DW (1988). Use of polynomial expressions to describe the bioconcentration of hydrophobic chemicals by fish. Ecotox. Environ. Safety 16: 242-257.

Additional Rationale for Testing Waiver

All the reviewed data indicate that log K_ow-based QSARs overestimate BCF because they take no account of biotransformation and metabolism of alcohols by a wide range of biota from bacteria to mammals (Veenstra et al., 2009; Mudge, 2008). These observations have recently been critically assessed using cellular biotransformation assays of ethoxylated alcohols and other aliphatic surfactants which confirm that metabolism of the alkyl chain can lower BCF by orders of magnitude (Dyeret al., 2008; Cowan-Ellsberry et al., 2008). For the more soluble chain lengths, evaluated in non-guideline BCF studies on linear alcohols and guideline studies for branched alcohols, predicted BCFs are overestimated by at least an order of magnitude (Fisk et al., 2010).

 

There is ample experimental in vivo evidence of metabolism in various trophic levels. Rapid biotransformation into tissue lipids has been demonstrated by Mankura (1987) in fish (carp). Biotransformation of linear structures has been demonstrated to be faster than for multiply-branched structures (Menzel et al., 2001) in accordance with expectations based upon the metabolic pathways. Predicted bioconcentration factors, using methods which take account of the expected metabolism in vivo, estimate low BCF values. Experimental studies using structural analogues show low BCF values. All linear alcohols in this chain length range are readily biodegradable in reliable standard studies.

 

These considerations suggest that it is unlikely that bioaccumulation would be exhibited in nature. It is therefore concluded that the long-chain alcohols in this category are non-bioaccumulative. This conclusion is considered to be sufficiently well-supported to justify no need for further testing in fish, since vertebrate testing for the purposes of REACH registration should be avoided where adequate existing evidence exists, and in view of the expected severe technical difficulties in conducting such a test.