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Long-term toxicity to aquatic invertebrates

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Testing for long term toxicity to aquatic invertebrates is not considered necessary because:

            The needs associated with a sound understanding of long-term aquatic toxicity to invertebrates are adequately met by the available data on constituents. For the purpose of risk assessment aquatic PNECs have been derived from the available data with each separate constituent.

The relevant long-term toxicity to invertebrates values for each constituent are as follows:

C12: Measured 21-d EC10 value of 0.013 mg/l based on reproduction of Daphnia magna (Schafers 2005).

C13: Predicted 21-d EC10 value has been calculated (QSAR) to lie in the range of 0.018 - 0.14 mg/l based on reproduction of Daphnia magna (Schafers 2009).

C14: Measured 21-d EC10 value of 0.0063 mg/l based on reproduction of Daphnia magna (Schafers 2005).

C15: Measured 21-d EC10 value of 0.012 mg/l based on reproduction of Daphnia magna (Schafers 2005).

 

Discussion of trends in the Category of C6-24 linear and essentially-linear aliphatic alcohols:

Linear LCAAs

Data of an acceptable quality are available for 21-day reproduction studies with Daphnia magna for the single carbon chain length LCAAs 1-octanol (Kuhn et al., 1989), 1-decanol, 1-dodecanol, 1-tetradecanol, 1-pentadecanol (Schäfers, 2005a-d respectively), pentadecanol branched (ABC 1999a) and octadecanol branched (ABC 1999c). The data were obtained generally in accordance with standard test guideline OECD 211. However some modifications to the normal guideline procedures were necessary to reduce losses of test substances due to the extensive and rapid biodegradation of the LCAAs. The following changes to typical protocols were therefore adopted to enable the performance of high-quality and meaningful studies:

Vessels were closed, to reduce entry of bacteria from the atmosphere;

Gentle aeration of test vessels was required as degradative losses of LCAAs resulted in unacceptably low dissolved oxygen concentrations;

Test solution renewals were made daily, with confirmatory analysis on both renewed and initial test solutions;

Static renewal was determined to be the best exposure regime for long chain aliphatic alcohols as this reduced the transfer of LCAAs -degrading or consuming microbes (as compared to flow-through systems, where it becomes increasingly difficult to discourage acclimation and bio film formation; see Brixham Environmental Laboratory, AstraZeneca, 2004);

Saturated alcohol stock solutions were prepared daily for each test concentration. This involved a detailed preparatory method to reduce the possibility of insoluble material being present in the tests (Schäfers, 2005a, b);

Daphnia magna were carefully rinsed with each daily transfer to reduce bacterial cross over to fresh exposure solutions. As Daphnia magna grow in size, this becomes less effective; and,

Dilution water and test vessels were autoclaved prior to use each time (Schäfers et al., 2005a, b, c, d).

 

Algae have been found to metabolize LCAAs and this is an unavoidable occurrence in long-term studies with Daphnia magna fed with algae. No modifications could be made to counter this without conducting further research into an alternative diet.

 

In spite of the guideline modifications significant losses of test substance still occurred. It was therefore necessary to report the results both in terms of the mean of the measured concentrations in the fresh media and the mean of the measured concentrations in the fresh and old media. The test substance renewal interval was 24 hours. Survival and reproduction endpoints have been summarised using standard statistical techniques. Conclusions for each test are presented as both NOEC and EC10. The 1-octanol and 1-octadecanol study are reliability 2, valid with restrictions; the other studies are reliability 1.

 

The effect of LCAAs on Daphnia magna survival is generally less sensitive than the effect on reproduction. A pattern of increased toxicity with increasing chain length is also apparent. In the octanol study, the most sensitive and only reported effect was on time to first brood release which occurred at 1000 µg/L (nominal concentration). For comparison of results across chain lengths and structure activity models the response for survival and reproduction was assumed to be equal to the effect on time to first brood.

 

The data indicates that for survival and reproduction, the NOEC and EC10 values increase from C14 to C15. This is almost certainly due to exceeding the limit of water solubility as would be expected from conventional toxicological theory (Rufli et al. 1998). Under these circumstances a more accurate interpretation of the results might be obtained by setting the exposure to the solubility of the substance (i.e. 49 µg/L). This has the effect of lowering the toxicity values but they are still higher than those for the C14 substance. This pattern is not in keeping with the trend of reducing short-term toxicity values (i.e. higher toxicity) observed between the C8 and C14 alcohols. Similarly, the NOEC identified for C18 is a limit value of >980 µg/L but a lower value would have been obtained if a lower loading had been tested. A more accurate NOEC would therefore be obtained by expressing it as greater than the water solubility of the test substance, which is 10 µg/L. This statement is supported by data on C15 and C15 branched, where the NOEC was not achieved at the solubility limit.

 

It must be appreciated that significant uncertainty exists in identifying the true exposure concentrations in the region of the water solubility of a substance. The water solubility values of the LCAAs category decrease with increasing chain length (see section 1.4 for further details.). In a review of aquatic toxicity testing of sparingly soluble compounds Rufli et al. (1998) point out that interpretation of toxicity responses observed above the solubility limit is aggravated by artefacts and that testing should only occur at or below the limit. For LCAAs with carbon numbers greater than C15 there are significant experimental difficulties in producing, maintaining and quantifying exposures of the test substance due to progressively lower solubility, while exceptionally rapid biodegradability would remain unchanged. This explains why there are no data for such substances.

 

However, based on the trends observed in the available data, it is expected that for linear LCAAs with carbon numbers ≥C15 the NOEC for long-term effects on mortality and reproduction would be above the solubility limit (Schäfers et al. 2009).

 

Multi-constituent LCAAs

No measured data are available for multi-constituent substances of different carbon chain length LCAAs.