Aluminium tris(dihydrogen phosphate)

Bioaccumulation: aquatic / sediment

Link to relevant study record(s)

Reference

Endpoint:

bioaccumulation in aquatic species: fish

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

REPORTING FORMAT FOR THE ANALOGUE APPROACH

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
In water aluminium orthophosphates will dissociate into their ionic forms (Al3+ and PO43-, which will further associate with the ionic forms of H2O). It is therefore considered acceptable to assess the aluminium and phosphate ions as separate entities.
The aluminium ion is considered to be toxic to fish under certain circumstances. The bioavailability and hence toxicity of aluminium is predominantly influenced by water quality parameters, in particular pH. The fate of Al3+ ion is of the most importance when considering whether a classification for aquatic toxicity of aluminium orthophosphates is required. In pH conditions of around neutral (as would be maintained via the use of appropriate buffers in a laboratory study) the Al3+ ion would be expected to react with the water molecules forming a weak acid (Al(OH)3)which would ultimately precipitate out of the water column rendering it not bioavailable and thus non-toxic to aquatic organisms. Since aluminium sulphate is soluble in water it is considered that the behaviour in water will be similar to the target substance and as such the data is relevant for assessing the toxicity of aluminium.

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
The water solubility of aluminium sulphate-14-hydrate is stated as being approximately 600 g/L, therefore the solubility of aluminium tris(dihydrogen phosphate) is very similar (522 g/L) at 20±0.5°C).

3. ANALOGUE APPROACH JUSTIFICATION
On the basis of the discussion presented above the results of acute toxicity studies on aluminium sulphate-14-hydrate have been used and are justified on the basis that Al3+ ion is of concern with regards to potential toxicity and therefore the results of such a study are relevant for read-across to the target substance.
This study is submitted as part of a weight of evidence approach in accordance with REACH Annex XI, Section 1.2. When considered alongside the additional data provided for this endpoint it is considered that the ecotoxicity of the substance to be registered is adequately assessed.

4. DATA MATRIX
See full read-across justification attached under Section 13 of this dossier and summary of data included in the endpoint summary under Section 6.1 of this dossier.

Reason / purpose for cross-reference:

read-across source

Reason / purpose for cross-reference:

read-across: supporting information

Type:

BCF

Value:

215 dimensionless

Basis:

whole body w.w.

Remarks on result:

other: at pH 5.3

Remarks:

Conc.in environment / dose:200 µg/L

Type:

BCF

Value:

123 dimensionless

Basis:

whole body w.w.

Remarks on result:

other: at pH 6.1

Remarks:

Conc.in environment / dose:200 µg/L

Type:

BCF

Value:

36

Basis:

whole body w.w.

Remarks on result:

other: at pH 7.2

Remarks:

Conc.in environment / dose:200 µg/L

Reported statistics:

Statistical analyses of percent mortality (arcsine transformed values), fish weight and whole-body residues of aluminum were performed with Statistical Analysis Systems’ analysis of variance (ANOVA) programs on the mainframe computer system of the University of Missouri, Columbia, Missouri. Contrasts among means were performed by least significant difference (LSD) tests. The two compartment model of Blau et al. was used to determine the residue dynamics of aluminum in whole-body tissues of brook trout at each pH tested. The BIOFAC computer program of Blau and Agin was used to derive uptake and clearance
rate constants, biological half-lives, bioconcentration factors (BCF) and the time to 90% steady state for aluminum in whole-body tissues of brook trout.

Mean aluminum exposure concentration, whole-body residues (wet weight basis), weight and mortality

(+ standard deviations in parentheses) for brook trout exposed at acidic and neutral pH for 56 d.

Mean pH and days of exposure	Aluminum exposure concentration [µg/L]	Aluminum tissue concentration [µg/g]	Weight [g]	Mortality [%]
pH 5.3 (0.5)
3	251.5 (41.7)	58.4 (7.6)	0.25 (0.02)	2.0 (0.0)
7	239.0 (30.2)	46.4 (15.8)	0.21 (0.01)	11.5 (3.3)
14	214.0 (45.3)	30.3 (14.3)	0.21 (0.01)	21.0 (2.8)
28	198.1 (48.5)	33.8 (5.6)	0.19 (0.02)	42.5 (13.4)
56	206.8 (9.0)	37.3 (18.0)	0.24 (0.07)	73.0 (16.9)
pH 6.1 (0.3)
3	323.5 (23.3)	18.5 (6.2)	0.26 (0.04)	0.0
7	266.8 (68.9)	40.7 (19.3)	0.21 (0.03)	0.0
14	223.5 (86.9)	23.2 (10.1)	0.20 (0.03)	3.5 (0.7)
28	211.9 (77.8)	21.6 (10.9)	0.20 (0.03)	27.5 (12.0)
56	217.1 (70.9)	16.6 (10.3)	0.44 (0.06)	48.0 (33.9)
pH 7.2 (0.1)
3	415.0 (8.5)	12.5 (1.9)	0.27 (0.02)	0.0
7	305.0 (127.4)	8.3 (3.0)	0.28 (0.03)	0.0
14	278.2 (108.8)	12.8 (7.1)	0.40 (0.03)	0.0
28	253.6 (103.1)	9.0 (5.2)	0.58 (0.08)	0.0
56	261.6 (95.7)	3.8 (0.7)	1.50 (0.24)	1.0 (1.4)

 

The estimated time to 90% steady state for aluminum in the fish was 1.5 d at pH 5.3, 4.2 d at pH 6.1 and 1.7 d at pH 7.2. Estimated steadystate bioconcentration factors for aluminum, which were inversely related to pH, were 215 at pH 5.3, 123 at pH 6.1 and 36 at pH 7.2. The maximum observed factors were 232 at pH 5.3, 153 at pH 6.1 and 46 at pH 7.2. Brook trout eliminated aluminum from tissues more rapidly at pH 5.3 than at pH 6.1 and 7.2. Mortality was generally higher in brook trout exposed to aluminum at pH 5.3 than in those exposed at pH 6.1 and 7.2. Mortality was lowest (<3%) for the fish exposed to aluminum at pH 7.2.

 

Description of key information

Bioaccumulation of aluminium tris(dihydrogen phosphate) (CAS 13530-50-2) is not expected.

Additional information

Aluminium tris(dihydrogen phosphate) (CAS 13530-50-2) is a well soluble inorganic phosphate salt and will dissociate to soluble dihydrogen phosphate (H2PO4-) in sewerage systems, sewage treatment plants and in the environment.

While BCFs indicate the potential for bioaccumulation there may be a number of complications in interpreting measured BCF values for metals and inorganic metal compounds. A general bioaccumulation assessment does not apply to phosphorus, as it is biological essential and the internal concentration will be well-regulated in living organisms.

BCFs for aluminium can be found to range from quite low to quite high values, this variance can largely be explained by the difference in exposure conditions in the different studies. An important factor influencing the bioconcentration of aluminium in fish is the water quality (e.g. pH and total organic carbon). Basically, metals do not biomagnify unless they exist in organic form. The available evidence clearly demonstrates a lack of aluminium biomagnification across several trophic levels in aquatic and terrestrial food chains respectively. Aluminium is the most abundant metallic element in the earth's crust, with a proportion of around 8% by weight, and the third most abundant of all elements. Based on its ubiquitous occurrence existing data clearly demonstrate that the present natural background concentration outweighs the anthropogenic contributions of aluminium to the environment. 

Studies on the bioaccumulation potential of the aluminium tris(dihydrogen phosphate), are not available. Bioaccumulation and secondary poisoning are considered not relevant for aluminium tris(dihydrogen phosphate). The conclusion is supported by a study on the pH dependence of aluminium accumulation in brook trout (Cleveland et al. 1991). The fish were exposed to a nominal aluminium concentration of 200 µg total aluminium/L at pH values of 6.1, 3.6 and 7.2 for 56 days. The determined BCF values increased with decreasing pH and thus a pH invers dependency of aluminium accumulation in fish was demonstrated. The determined BCF values were 215 at pH 5.3, 123 at pH 6.1 and 36 at pH 7.2 respectively. During the 28-day depuration phase the aluminium elimination was more rapid at pH 5.3 than at pH 6.1 or 7.2. The biological half-life of aluminium in brook trout was 0.46 day at pH 5.3, 1.26 day at pH 6.1 and 0.52 day at pH 7.2. Though the determined BCF values increased with decreasing pH the demonstrated bioaccumulation potential of aluminium under acidic conditions is low and decreases further at neutral conditions.