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Short-term toxicity to aquatic invertebrates

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Description of key information

The pH significantly alters the speciation and therefore bioavailability of the aluminium such that acutely toxic concentrations occur below a pH of 6 but that above 6 the bioavailable concentration necessary to achieve immobilisation in an acute study cannot be achieved.

Key value for chemical safety assessment

Additional information

Eight valid studies are available of which two on a hydrated form of the reference substance:

Aluminum sulphate

Two short term studies with Daphnia magna on the 14 hydrate are available (Schafers 2003). One test was static without pH adjustment. The test substance concentrations ranged from 10 to 160 mg/l (nominal) equivalent to Total Al concentrations from 0.907 to 14.5 mg/L.

In this test an EC50 was found of 0.33 mg/l (dissolved Al) equivalent to 4.3 mg/L Total aluminium but there was a significant difference in pH between concentrations with the highest concentrations (>4.3 mg/L Total Al) at a pH <6 and lower concentrations (<4.3 mg/L Total Al) at pH of approximately 6.5 -7.5.

The second test was semi-static with pH adjustment limiting the range of pH between 7.5 and 8. The test substance concentrations were the same as the static test, ranging from 10 to 160 mg/l (nominal), equivalent to Total Al concentrations from 0.907 to 14.5 mg/L.

this resulted in dissolved aluminum concentrations of 0.107 to 0.176 mg/l. The pH was between 7.5 and 8.0. No effects were found in this test, therefore, at environmentally relevant pH, the EC50 is greater than 0.176 mg/l (dissolved Al), which was the maximum soluble concentration under the test conditions and the highest Total aluminium concentration of 14 mg/L.

One supporting study from Kimball (1978) is available on the 16 hydrated salt. The nominal concentrations found that led to the 48 h LC50 are in line with those from the other studies.

Polyaluminium chloride hydroxide sulphate (CAS 39290 -78 -3)

Four short-term studies with Daphnia magna are available, one by Thiebaud (2000) and three by Thomas (1996a, b, c). All were static at a neutral pH between 7.0 and 8.0. The first study (Thiebaud, 2000) was performed using two methods following OECD 202 with modifications according to the OECD guidance on testing for difficult substances. The WAF method was employed and the loaded solutions allowed either to stand for four days to precipitate out and then decanted into test vessels without including the precitpitate or were prepared and the loaded solutions were filtered immediately and used for the study on the same day. The analytical data only makes sense when the values from T0 and T48 are inversed, however, this does not impact the validity of the study as the EC50 was greater than the maximum loading rate of the test substance used and thus greater than the solubility limit of the dissolved aluminium concentration measured in the study. The pH remained between 7.0 and 7.79 over the study in both filtered and unfiltered (precipitated) solutions.

In three further studies (Thomas, 1996a, b, c), the toxicity of the test substance to Daphnia magna was tested according to the OECD 202 guideline in a limit test using M7 medium to reduce EDTA. The nominal test concentration was 100 mg/L, with a range finder performed at 0.1, 1 and 10 mg/L. Concentrations of 0.005 mg/L Al3 + were found as backgroud noise in M7 medium.

Analysis was performed on the limit test and control by an outside laboratory a week after the end of the biological study although samples were acidified a priori to prevent loss of material. Some probable minor contamination due to residual Al concentrations in the acid and analytical reagents was observed but were due to analysis, not included in the in Vivo part of the study and so was accounted for in the final concentrations.

The conclusion is that no effects on daphnids were observed after 48 hours exposure to the maximum solubility of the aluminium salt at a pH of between 7.4 and 7.95 further to addition of a nominal concentration of 100 mg/L of test material in any of the studies (equivalent to 5.2, 5.5 and 9.0 mg/L Total aluminium) equivalent to dissolved aluminium concentrations ranging from 0.15 to 0.55 mg/L as Al3+.

 

Polyaluminum hydroxide chloride, solution (CAS 1327 -41 -9)

Two short-term studies with Daphnia magna are available (Schafers, 2004). One test was static without pH adjustment.

The test substance concentrations ranged from 10 to 160 mg/l (nominal) corresponding to measured Total Al concentrations from 0.907 to 14.5 mg/L. This resulted in dissolved Al concentrations ranging from <0.1 to 1.44 mg/L at a pH of approximately 5.1-8.0.In this test an EC50 was found for Total aluminium of 3.45 mg/L with dissolved aluminium concentrations of between 0.214 (the background concentration found in the control) and 1.26 mg/l (the highest dissolved concentration observed, but the only group where pH was <6 throughout the study).

The second test was semi-static with pH adjustment. The pH was between 7.4 and 7.9. The test substance concentrations were the same as in the static test, ranging from 10 to 160 mg/l (nominal) equivalent to Total Al concentrations from 0.907 to 14.5 mg/L.

All measured dissolved Al concentrations were below detection limit after the background concentration present in the control was subtracted. A clear dose-response curve was found when looking at the nominal and Total Al concentrations with an EC50 of 98 mg/L (equivalent to a Total Al concentration of 8.9 mg/L), but as no concentration relationship based on dissolved aluminum concentrations could not be determined, the EC50 for this cannot be calculated. The background concentration was 0.240 mg/l (dissolved Al) therefore, EC50 is greater than 0.240 mg/l (dissolved Al). Conclusion Of the eight available valid studies, six found no effects at the end of the study, with Total aluminium concentrations of at least 8.9 mg/L (up to 14.5) and dissolved concentrations measured at a minimum of 0.24 mg/L (up to0.55 mg/L) elemental Al. All these studies were performed under standard Guideline conditions at pHs between 7.5 and 8. In the two remaining studies effects were found with Total alumuinium concentrations between 3.45 and 4.3 mg/L and dissolved aluminium concentrations at approximately 0.33 mg/L. In this case the pH was not corrected to Guideline recommended values in the study and significant reduction of pH below 6 occurred in solutions where immobilisation was observed. Thus it can be concluded that the pH significantly alters the speciation and therefore bioavailability of the aluminium such that acutely toxic concentrations occur below a pH of 6 but that above 6 the bioavailable concentration necessary to achieve immobilisation in an acute study cannot be achieved.