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Long-term toxicity to aquatic invertebrates

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Endpoint:
long-term toxicity to aquatic invertebrates
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Peer reviewed data with high level of detail.
Qualifier:
according to
Guideline:
OECD Guideline 211 (Daphnia magna Reproduction Test)
GLP compliance:
yes
Analytical monitoring:
yes
Remarks:
No detail on analytical method given in the OECD SIDS
Details on sampling:
Test solution renewals were made daily, with confirmatory analysis on both renewed and initial test solutions;
Details on test solutions:
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.
Test organisms (species):
Daphnia magna
Test type:
semi-static
Water media type:
freshwater
Total exposure duration:
21 d
Nominal and measured concentrations:
- Nominal concentration: 0 (control), 0.030, 0.065, 0.139 and 0.300 mg/L
- Measured concentration (mean total): -, 0.002, 0.0078, 0.019 and 0.063 mg/L
- Measured concentration (mean initial): -, 0.015, 0.056, 0.104 and 0.241 mg/L
Details on test conditions:
DIFFICULT SUBSTANCE PROPERTIES
To account for the rapid (and extensive) biodegradation and the low water solubility of the tested alcohol, 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 alcohol 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 alcohols as this reduced the transfer of alcohol-degrading or consuming microbes (as compared to flowthrough
systems, where it becomes increasingly difficult to discourage acclimation and biofilm 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;
- 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;
- Dilution water and test vessels were autoclaved prior to use each time.
Duration:
21 d
Dose descriptor:
EC10
Effect conc.:
0.012 mg/L
Nominal / measured:
meas. (not specified)
Conc. based on:
test mat.
Basis for effect:
reproduction
Duration:
21 d
Dose descriptor:
NOEC
Effect conc.:
0.008 mg/L
Nominal / measured:
meas. (not specified)
Conc. based on:
test mat.
Basis for effect:
reproduction
Duration:
21 d
Dose descriptor:
EC10
Effect conc.:
> 0.063 mg/L
Nominal / measured:
meas. (not specified)
Conc. based on:
test mat.
Basis for effect:
mortality
Duration:
21 d
Dose descriptor:
NOEC
Effect conc.:
> 0.063 mg/L
Nominal / measured:
meas. (not specified)
Conc. based on:
test mat.
Basis for effect:
mortality
Details on results:
DETAIL ON FINDINGS AND OECD CONSIDERATIONS
Effect of long chain aliphatic alcohols 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. However, for survival and reproduction, the NOEC and EC10 values increase from C14 to C15. This is almost certainly due to exceeding the boundary of water solubility. It must be appreciated that significant uncertainty exists in identifying the true exposure concentrations in the region of the water solubility of a substance. Interpretation of toxicity responses observed above the solubility limit is aggravated by artefacts and that testing should only occur at or below the limit.

The toxicity findings are considered due to a mixture of both toxicity and physical effects that occur above the water solubility limit. Studies with (C14 and) C15 were especially difficult as the predicted water solubilities for these alcohols are very low. Theory and practice in aquatic toxicology are established for testing that occurs at or below the level of solubility. Above the level of solubility physical effects enter into observed responses of the organism, but do not reflect influence of the chemical entering the body, target tissues or cells. Thus, interpretation is confounded and the observed responses of the test organism include a mixture of both physical effects (e.g., entrapment of particles in feeding structures, oil droplets and micro-emulsions coating organism surfaces, etc.) and toxicity. It is a reality that separating these profiles is not possible. However, it is possible to evaluate whether test observations adhere to theory and thus allow the organism to assist in the inference of solubility being exceeded or not. An example of this would be the expectation that a monotonic increase in toxicity would be observed as hydrophobicity of a chemical series increases.

Survival of Daphnia magna in chronic toxicity studies followed a pattern close to expectations until C15 with increasing effect with increasing hydrophobicity. In the study on C15 alcohol, Daphnia magna all survived even at the highest exposure concentration of 63 μg/L (mean measured concentrations) or 240 μg/L (mean initial concentration), therefore the conclusion of this study is that the actual NOEC and EC10 would lie above these values. These responses do not conform to a pattern of monotonic decline with increasing hydrophobicity and may suggest that the test chemical does not penetrate cell membranes of the organism. While the actual regression statistics for the NOEC (Q)SAR may not provide an immediate interpretation of statistical significance (p <0.61) the response is interpretable and can be considered biologically relevant.

The response of Daphnia magna with regards to reproduction (young per female) is somewhat more sensitive than survival. Again, as with mortality, the expectation that C15 belongs within the same structure-activity relationship appears unlikely. The effect on Daphnia magna in the C15 study is less than that for C14. In plots of reproduction NOEC and EC10 values based on total mean concentration there is a clear deflection of apparent toxicity upward relative to C14. It is clear in both plots of reproduction NOEC and EC10 values based on initial mean concentrations that the C15 response is near or above its water solubility. When the survival endpoint is considered the measured responses for both C14 and C15 occur near the solubility limit. Because stress is apparent in these studies near the limits of practical solubility, the effect on reproduction must also include relevant aspects of these factors.

CONCLUSIONS
1. The new chronic data generated are the best that can be achieved reasonably, yet involve real complications to due to exceptionally rapid biodegradability and the need to test as close as possible to limits of solubility for the long chained aliphatic alcohols.
2. The apparent toxicity of C15 alcohol is measurably less than C14 alcohol based on survival and reproduction endpoints.
3. The only method by which to make sense of the upward deflection in the toxicity profile for this series of long chain alcohols is to understand the relationship between toxicity, measured responses (which can combine toxicity and physical effects), and solubility.
4. The C15 toxicity data are a mixture of both toxicity and physical effects that occur above the water solubility limit. A similar situation can be inferred to a lesser extent for C14.
5. Reproduction is the more sensitive parameter and should be used to express toxicity and develop the (Quantitative) Structure-Activity Relationship ((Q)SAR).
6. NOEC and EC10 give similar (Q)SARs, although EC10 appears to be more consistently robust in (Q)SAR regression analyses. However, because the NOEC is more universally accepted in regulatory submissions, the NOEC will be used.
7. Use of the C15 data in an (Q)SAR should be questioned. This relates to the water solubility of C15. When C15 is not included the slope of most (Q)SARs approach -1 consistent with the expectation of non-polar narcotic mode of action for alcohols (Veith et al., 1983).
8. The ACR <10 for 73% and <100 for 100% (see Table A.X. 5) suggesting a non-specific narcotic ecotoxicological mode of action (ECETOC, 2003).
9. The rapid biodegradability of these alcohols further complicates interpretation such that the real exposure-response profile lies somewhere between that expressed by total mean measured exposures and initial mean measured exposure.

RESULTS BASED ON MEAN MEASURED INITIAL CONCENTRATIONS:
- 21-d EC10 (reproduction): 0.074 mg/L
- 21-d NOEC (reprooduction): 0.056 mg/L
- 21-d EC10 (mortality): >0.240 mg/L
- 21-d NOEC (mortality): 0.240 mg/L
Reported statistics and error estimates:
The OECD workshop on the statistical analysis of aquatic toxicity data concluded that regression analysis (ECx) was preferable to ANOVA (NOEC) for a number of reasons and that the latter should be phased out (OECD, 1998). Reasons for this recommendation include among others: data, such as the strength of the exposure response, are wasted in NOEC determinations, outcomes or conclusions are directly driven by choice of exposure concentrations, and the statistical outcome cannot be linked to population models. ECx estimations are generally found to be more robust for the development of structure-activity-relationships than those developed from NOECs. The influence of the choice of test concentrations on the structure-activity regression is highly diminished in the former and these can be more easily related to acute structure activity based on a similar modelling platform (for example, models already used to estimate the acute EC50).
Endpoint:
long-term toxicity to aquatic invertebrates
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
See 'Attached justification'
Reason / purpose:
read-across source
Key result
Duration:
21 d
Dose descriptor:
EC10
Effect conc.:
0.006 mg/L
Remarks on result:
other: as determined from read-across to C14 alcohol, linear
Duration:
21 d
Dose descriptor:
NOEC
Effect conc.:
0.002 mg/L
Remarks on result:
other: as determined from read-across to C14 alcohol, linear
Details on results:
The molecular weight of C14 may be considered to be representatvie for the entire C13-15 alcohol. Therefore, no correction for molecular weight difference was performed.

Description of key information

Very toxic to aquatic organisms based on long-term (chronic) toxicity study data.

Key value for chemical safety assessment

Additional information

High quality data is available for C15 linear alcohol (CAS 629-76-5) which is one of the components of alcohols C13 -15 -branched and linear. The toxicity of C15 linear alcohol was investigated in a study according to OECD 211 and in compliance with GLP criteria (OECD SIDS, 2006). In this study, daphnids (D. magna) were exposed to the test substance for 21 days under semi-static conditions (daily renewal). Saturated stock solutions of the C15 linear alcohol 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. All practicable methods, more extensive than is usually necessary, were implemented to increase the stability of exposures at and below the level of solubility in each study. Measures were also taken to reduce as much as possible the presence of bacteria in the test systems to avoid biodegradation of test substance. Nominal tested concentrations were 0 (control), 0.030, 0.065, 0.139 and 0.300 mg/L. Daily confirmatory analysis was performed on both renewed and initial test solutions. Measured concentration (mean total) were determined at 0.002, 0.0078, 0.019 and 0.063 mg/L.The response of daphnids with respect to survival and reproduction (young per female) was recorded regularly throughout the test. For survival the 21 -d EC10 and NOEC values were both determined at >0.063 mg/L. For reproduction the 21 -d EC10 and NOEC values were 0.012 and 0.0078 mg/L. All effect concentrations presented here are based on mean total concentrations.