Dodecaaluminium trimolybdenum dodecaoxide

Toxicity to aquatic algae and cyanobacteria

Description of key information

EC50 (72h) > 100 mg/L (nominal) for Desmodesmus subspicatus (OECD 201)
NOEC (72h) = 10 mg/L (nominal) for Desmodesmus subspicatus (OECD 201)
measured concentrations after 72 h: 0.39 mg Mo/L (for 10 mg/L nominal), 5.08 mg Mo/L (for 100 mg/L nominal), Al not detectable

Additional information

In a GLP guideline study by Muckle (2013) conducted according to OECD 201, Desmodesmus subspicatus were exposed to a nominal concentration of 100 mg/L. Because the treatments showed significant inhibition and one of the validity criteria algal growth wasn’t met, the study was repeated as a full test. The second experiment was performed using five concentrations in the range of 4.6, 10, 22, 46 and 100 mg/L nominal concentration. In the second experiment, all validity criteria were met. One day before the start of the test, a filtered test solution was prepared (24 h shaking, membrane filtration).

At the beginning and at the end of the test, the concentration of molybdenum (Mo) as component of the test item in the test solutions was determined using an atomic absorption spectrometer (AAS). The obtained measured concentrations show that the test item was present in the solution and sufficient dissolution was achieved. After 72 h, concentrations of 0.19, 0.39, 0.85, 1.54 and 5.08 mg Mo/L were measured, respectively. The recovery after 72 hours was in a range between 84% and 117% of the start concentration. Therefore, the test item can be stated as stable under test conditions. During validation of the analytical method Al could not be determined in algal test medium after storage of the solution under test conditions for 72 hours.

The EC50 for growth rate was determined to be >100 mg/L based on nominal concentration. For the endpoint AUC, the difference between the nominal concentration 22 mg/L and the control can be considered as not significant (level of significance: 97.5 %) as the calculated t-value was smaller than the limit of significance. Therefore the nominal concentration 22 mg/L is stated as NOEC for this endpoint. For the endpoints growth inhibition and yield, the differences between the nominal treatment 10 mg/L and the control can be considered as not significant as algal growth in the treatments was higher than in the control. Therefore, the nominal concentration 10 mg/L is stated as NOEC for these endpoints.

Besides, there are reliable data available for different analogue substances.

The environmental fate pathways and ecotoxicity effects assessments for aluminium metal and aluminium compounds as well as for molybdenum metal and molybdenum compounds is based on the observation that adverse effects to aquatic, soil- and sediment-dwelling organisms are a consequence of exposure to the bioavailable ion, released by the parent compound. The result of this assumption is that the ecotoxicological behaviour will be similar for all soluble aluminium and molybdenum substances used in the presented ecotoxicity tests. As aluminium molybdenum oxide has shown to be only slightly soluble in water (pH 4.5, 7d) and poorly soluble in ecotoxicity test media (pH 7.5-8.5, 96h), it can be assumed that under environmental conditions in aqueous media, the components of the substance will be present in a bioavailable form only in minor amounts (Mo) or hardly, if at all (Al). Within this dossier all available data from soluble and insoluble aluminium and molybdenum substances are taken into account and used for the derivation of ecotoxicological and environmental fate endpoints, based on the aluminium ion and molybdenum ion. All data were pooled and considered as a worst-case assumption for the environment. However, it should be noted that this represents an unrealistic worst-case scenario, as under environmental conditions the concentration of soluble Al³⁺and MoO₄^2-ions released from aluminium molybdenum oxide is negligible (Al) or low (Mo), respectively.

Aluminium

The algae data from the 2009 and 2010 CIMM datasets demonstrate that elevated pH and elevated DOC are protective against aluminium toxicity, whereas hardness appeared to have a minimal effect.  The evidence of both pH and DOC effects are consistent with the Al BLM. Multiple linear regression models (MLRM) based on nominal DOC, and pH were developed to predict nominal EC10 and EC50 values for the algae dataset. The EC50 and EC10 MLRMs performed reasonably well for the dataset. The EC50 MLRM produced an adjusted R²of 0.747, and the EC10 MLRM produce an adjusted R²of 0.987 (see Figures 7.1.1.3-2, and 7.1.1.3-3, respectively).

Literature Review: Six chronic toxicity studies to a freshwater microalga (Pseudokirchneriella subcapitata) were identified in the literature as Klimisch 1 or 2 studies. Additional algal studies with Pseudokirchnerella subcapitata were performed at CIMM to evaluate acute and chronic toxicity to algae and for evaluation of water chemistry effects for modelling purposes. All endpoints from CIMM (2009; 2010a) were reported on the basis of nominal Al concentrations because total Al was not measured in these studies. However, CIMM (2010b) compared nominal to measured total Al concentrations in an identical set of algal test solutions prepared to match all water quality conditions and nominal Al exposure concentrations as used in the previous studies (2009; 2010a). In these new test solutions, average total Al concentrations were within 10% of nominal Al concentrations. A linear regression between total and nominal Al concentrations demonstrated a strong relationship with an r²value of 0.99 (Figure 7.1.1.3 -1). Therefore, nominal Al concentrations can be considered a reliable estimator of total Al concentrations in these studies. EC_r10s were calculated using raw data provided from each study using the statistical program Toxicity Relationship Analysis Program (TRAP) version 1.10 from the US EPA National Health an Environmental Effects Research Laboratory (NHEERL). All other endpoints were as reported in each study. EC_r10s and EC_r50s ranged from 0.051 to 3.15 mg Al/L and 0.024 to 4.93 mg Al/L, respectively. Water quality data for these studies suggest a direct relationship between toxicity and pH, hardness, and DOC. Studies that experimentally manipulated water quality were reported by CIMM 2009 and 2010a. One toxicity study to a higher plant (Lemna minor) was included (Table 8). No toxicity was observed in this study, so both NOEC and EC10 values were > 45.7 mg Al/L.

Molybdenum

Freshwater:

Acute toxicity

The reliable ErC₅₀-values that were determined by De Schamphelaere et al. (2008) for the green algae P. subcapitata were situated between 295 and 1568.9 mg Mo/L. Rodriguez (2008) reported reliable ErC₅₀values that ranged from 289.2 to >419.9 mg/L for the same species. The acute data confirmed the findings of the chronic data (see further), i.e. that the CIMM algal strain was the most sensitive strain. The geometric mean of the 4 CIMM-data points is 333.1 mg/L and is considered as a reliable acute toxicity value for hazard assessment purposes (e.g. classification).

No reliable EC₅₀-values were reported for any other freshwater algal species.

	72h-ErC50(mg Mo/L)
	P. subcapitataCIMM	P. subcapitataUGhent
OECDCIMM, tested at CIMM	289.2 (254.1 – 340.1)	362.9 (316.8 – 415.9)
OECDUGhent, tested at CIMM	369.3 (297.2 – 495.6)	> 419.9
OECDCIMM, tested at UGhent	390.9 (312.4 -489.2)	1568.9 (1431.2 – 1719.8)
OECDUGhent, tested at UGhent	295.0 (247.8 – 351.3)	1094.5 (1019.6 – 1174.8)
Mean: Geomean:	336.1 333.1

Chronic toxicity

For Pseudokirchneriella subcapitata, a 72h-ErC₁₀of 156 mg Mo/L was reported by ECTX (2007a) but this value was based on nominal exposure concentrations.

The table listed hereunder gives an overview of the results of an algal exchange and testing program between Ghent University and CIMM (Centro de Investigación Minera y Metalúrgica) with the green algae Pseudokirchneriella subcapitata. Tests that were performed with the algal strain from CIMM resulted in four 72h-ErC₅₀ values that were situated between 61.2 and 88.7 mg Mo/L, i.e. only a difference of a factor of 1.4 between the lowest and highest value which can be considered as natural biological variation among ecotoxicity tests that are conducted with the same species and same test substance. These four effect levels also indicate that the origin of the test medium or the test facility had little or no influence on the outcome of the test. Comparable results (62.5 – 99.3 mg Mo/L) were also obtained with the UGhent strain tested at CIMM. The tests conducted with this strain at the University of Ghent, however, produced 72h-ErC₁₀ levels that were ± a factor of 4 to 5 higher that the other six tests, but were in line with the test result that was generated by De Schamphelaere et al. (2008a) at the same testing facility, and using the same strain.

 

	72h-ErC10(mg Mo/L)
	P. subcapitataCIMM	P. subcapitataUGhent
OECDCIMM, tested at CIMM	88.7 (69.2 – 106.0)	62.5 (2.5 – 133.8)
OECDUGhent, tested at CIMM	77.3 (58.1 – 95.5)	99.3 (63.5 – 137.5)
OECDCIMM, tested at UGhent	61.2 (36.5 -102.7)	318.6 (278.9 – 363.9)
OECDUGhent, tested at UGhent	72.6 (48.3 – 109.5)	366.2 (294.4 – 455.5)
Mean: Geomean:	75.0 (CV:11.4%) 74.3	211.7 (CV: 153.0%) 164.0

     

Based on these findings, the following was concluded:

- Similar 72h-ErC₁₀-values were produced by the two testing facilities and using test media from these two facilities, with the P. subcapitata strain originating from CIMM.

- All test results are in line (maximum difference of a factor of 2.5) with the outcome of the accepted test result that was generated by ECTX (2007a).

- Comparison of the research results given in Rodriguez (2008) and De Schamphelaere and Janssen (2008), however, indicates that the CIMM-algal strain may be more sensitive than thestrain. From a conservative point of view it was therefore decided that only the 72h-ErC₁₀values obtained with the former strain should be taken into account for the derivation of a NOEC for P. subcapitata, i.e. excluding the effect levels that were obtained with the UGhent strain. The geometric mean of these four values is proposed as the chronic no-effect level for this species, and is 74.3 mg/L.

It should be noted that the geometric mean of all relevant and reliable data would result in a geometric mean that is higher than the proposed chronic no-effect level of 74.3 mg Mo/L, and this value can therefore be considered as a more conservative value.

Marine:

Acute toxicity

The reliable 72h-ErC₅₀-value determined by Aquasense (2009) for the algae P. tricornutum was 356.9 mg Mo/L. Le Page and Hayfield (2010) reported an unbounded 72h-ErC₅₀of > 938 mg Mo/L. Both marine EC50-values were higher than the geometric mean value of 333.1 mg Mo/L for the freshwater green alga P. subcapitata which was put forward as an reference value for acute molybdenum toxicity to algae.

Chronic toxicity

For the micro-alga Dunaliella tertiolecta the 72h-EC₁₀value of 881 mg/L (endpoint: growth rate) is retained for assessment purposes (Le Page and Hayfield, AstraZeneca, 2010). For biomass, the 72h-EC₁₀was 513 mg/L. Although this value is lower than the EC₁₀for growth rate, the latter endpoint is considered ecologically more relevant, and is preferred over biomass in the OECD guideline for algal testing. The 72h-NOEC value for both biomass and growth rate was 938 mg/L, which is higher than both EC₁₀values.

For the diatom Phaeodactylum tricornutum the 72h-EC₁₀value of 169.9 mg/L (endpoint: growth rate) is retained for assessment purposes (Le Page and Hayfield, AstraZeneca, 2010). The 72h-NOEC value for this endpoint was 150 mg/L. The EC₁₀value, however, is preferred over the NOEC value as the latter is a test design-dependent value.