Aluminium sodium dioxide

Toxicity to aquatic algae and cyanobacteria

Additional information

A study on the toxicity of sodium aluminate to algae is available (CIMM 2010). However, as results of this study refer to the toxicity of aluminium as studies with other compounds do, a weight of evidence is applied and data are read-across to various aluminium compounds based on an analogue approach.

In two studies the toxicity of aluminium to Pseudokirchneriella subcapitata was tested using sodium aluminate and aluminium nitrate as sources for aluminium (CIMM 2010). Studies were conducted according to OECD 201. In the study using sodium aluminate, tests were conducted at a single pH of 8 and a water hardness of 10.6 mg/L as CaCO3. pH was adjusted using HEPES 5mM buffer. Endpoints were based on inhibition of growth. The following effect values were determined: EC50s (growth rate) for total and dissolved Al of 1703.8 and 1799 µg/L, respectively; NOEC and LOEC for total Al of 600 and 1000 µg/L, respectively.

The study using aluminium nitrate was conducted at pHs of 7.7 and 8 and at a water hardness of 24.3 mg/L as CaCO3. Two parallel test series were run not stabilising and stabilising pH by using HEPES 5mM buffer. Endpoints addressed were biomass and growth rate. For total Al EC50 (growth rate) was 1282 µg/L in the unbuffered test. In the buffered tests at pH 8 and 7.7 EC50s were slightly higher with 1476.6 and 1417.9 µg/L, respectively. As regards dissolved Al the three respective EC50s were 292.4, 515, and 229.8 µg/L. NOEC for growth rate based on total Al was determined to be 400 µg/L for each test (without buffer, pH 8, pH 7.7).

Three further studies were conducted by CIMM (2009) according to method 821-R-02-013, EPA 2002 and OECD 201 in which Pseudokirchneriella subcapitata were exposed to aluminium nitrate at different test regimes. In one study algae were exposed at three different pH values: 6, 7, and 8 in AAP medium. EC50s were determined for biomass and ranged from 24 to 316.8 µg/L (total Al) and 5.4 to 150.6 µg/L. In terms of nominal Al concentration, Al toxicity to P. subcapitata shows a negative correlation with pH, whereas in terms of the dissolved Al, toxicity is higher at pH 6.0 and pH 7.0, and then it decreases sharply going from pH 7.0 to pH 8.0. The second study followed the same protocol, however, the influence of phosphate on the toxicity was tested by adding different concentration of this nutrient to the test series. EC50s were determined based on biomass and ranged from 24 – 2622.4 µg/L (total Al) and 20.1 – 86.3 µg/L (dissolved Al).Total Al concentration showed an important decrease in the toxicity of Al to P. subcapitata as the concentration of phosphate increased, with the EC50 increasing by ten fold between 1x and 8x phosphate. In the case of the Dissolved Al, there was also a “protective” effect of phosphate at the 4x and 8x levels, but lower than in the case of the total Al and, also, this effect was lower at the 8x level compared to the 4x level. The behaviour of dissolved Al concentrations as a function of phosphate concentration was demonstrated. Dissolved Al remained constant throughout the phosphate concentration range and phosphate does decrease dissolved Al toxicity. In the third study algae were exposed to a set of parameters, including three p levels of 6, 7, and 8, three different water hardness of 24.3, 60, and 120 mg/L as CaCO3, and DOC levels of 0, 2, and 4 mg/L. pH was adjusted using 5mM MES, MOPS, and HEPES buffers. EC50s for growth rate were determined and ranged between 345.6 - 4980 µg/L (total Al) and 16.9 - 699.9 µg/L (dissolved Al). Although not all determined effect values support a strict correlation between decreasing toxicity and increasing water hardness and DOC at both pH levels, an overall clear tendency is to observe that there is a protctive effect by these parameters.

Two limit tests were conducted by NIVA (1996a, 1996b) using aluminium oxide and aluminium hydroxide as source chemicals for aluminium. Both tests were conducted according to GLP standards and OECD guideline 201 using Selenastrum capricornutum as test species. pH in both studies was about 7.8. EL50s and NOELRs for growth rate were determined to be >100 and ≥100 mg/L, respectively (nominal for Al2O3 and Al(OH)3). EC50s and NOECs were determined to be > 52 and ≥ 52 µg/L (dissolved Al for Al2O3) and > 4 and ≥ 4 (dissolved Al for Al(OH)3), respectively.

In a further non-GLP non-guideline study with Selenastrum capricornutum Call et al (1984) determined the EC50 for biomass at pH 7.6 and 8.2 to be 0.46 and 0.57 mg/L, respectively.