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Aluminum zirconium chloride hydroxide is an inorganic substance which will rapidly dissociate into aluminum, zirconium, chloride and hydroxide ions upon dissolution in the environment. The chemistry of the relevant metals aluminium and zirconium in aqueous solutions is complex. Depending on concentrations, pH and other ions being present, Al and Zr do not exist as simple metal cations, but instead form various species, most relevantly hydroxides and hydroxide-oxides.

Zirconium is one of the 20 most abundant elements in the earth's crust (at approximately 0.03%). Zirconium displays under most environmental conditions, a very low mobility, mainly due to the low solubility of the hydroxide Zr(OH)4. This limits the concentration of dissolved Zr in most natural solutions (fresh water, seawater as well as soil and sediment porewater) to <0.05 μg/L. Depending on the pH of the environmental medium, different zirconium species exist in solution, including Zr4+, and various hydroxides. At pH 7, a Zr(OH)2(CO3)22-complex may form, but the complex is unstable and Zr(OH)4forms with decreasing pH. The hydro-bicarbonate (Zr(OH)4-HCO3-H2O) complex may be the most significant Zr complex in natural water (http://www.gtk.fi/publ/foregsatlas, accessed on 12.03.2013).

Results of the solubility testing (OECD Series on Testing and Assessment No. 29) seem to confirm the lack of zirconium solubility at environmentally relevant levels. At a loading of 1 mg Aluminum Zirconium Chloride Hydroxide/L (corresponding to 0.19 µg Al and 0.10 mg Zr) of water or environmental OECD test medium at pH 6 and pH 8, respective dissolved zirconium concentrations were below the detection limit of ca. 0.3 µg/L at all time-points while dissolved Al levels ranging from 0.01 – 0.12 mg/L were measured.

Thus, regarding the environmental fate and toxicity of Aluminum zirconium chloride hydroxide, it can be assumed that environmental fate and toxicity (if any) will not be driven by zirconium. Therefore, full read-across to other aluminum substances considering a typical aluminum content of ca. 19.4% is justified.

While data on short-term toxicity of dissolved aluminum are available for three throphic levels (algae, daphnia, fish), reliable long-term data are available for algae and fish only. The table below presents an overview of the reliable toxicity data of dissolved aluminum.

 

Short-term effects on fish

Species

endpoint

set up

pH

result

(mg/l)

Aluminum substance tested

Danio rerio

LC50-96h

static

7.7-4.2

1

Aluminum sulphate

Danio rerio

LC50-96h

semi-static

7.4-8.0

> 0.247

Aluminum sulphate

Danio rerio

LC50-96h

static

8.3-4.2

1.39

Aluminum chloride, basic

Danio rerio

LC50-96h

semi-static

7.5-8.2

> 0.156

Aluminum chloride, basic

  Short-term effects on aquatic invertebrates

Daphnia magna

EC50-48h

static

8.0-4.6

0.33

Aluminum sulphate

Daphnia magna

EC50-48h

semi-static

7.5-8.0

> 0.176

Aluminum sulphate

Daphnia magna

EC50-48h

static

8.0-5.1

0.214 - 1.26

Aluminum chloride, basic

Daphnia magna

EC50-48h

semi-static

7.4-7.9

> 0.24

Aluminum chloride, basic

Daphnia magna

EC50-48h

static

7.6-7.8

> 0.15

Aluminum chloride, basic

  Effects on algae and aquatic plants

C. pyrenoidosa

EC10-96h

static

5

0.084

Aluminum chloride, basic

P. subcapitata

ERC50-72h

static

7.1-8.4

0.24

Aluminum chloride hydroxide sulfate

P. subcapitata

 ERC10-72h

static

7.1-8.4

0.051

Aluminum chloride hydroxide

  Long-term effects on fish

Salvelinus fontinalis

NOEC-60d

semi-static

6.5-6.6

0.013

Aluminum sulphate

Salmo trutta

LC50-28d

natural streams

5.8-5.9

0.019

Aluminum sulphate

Salmo trutta

LC50-42d

natural streams

5.8-5.9

0.015

Aluminum sulphate

As there are 3 short-term studies and long-term tests for fish and algae, an assessment factor of 50 is used. The long-term fish study gave the lowest NOEC of 13 µg Al/L which is used for the PNEC derivation based on dissolved aluminum.

The PNEC_freshwater would be 13/50 = 0.26 µg/L (dissolved Al).

 

For the marine environment an assessment factor of 500 is used.

The PNEC_marine would be 13/500 = 0.026 µg/L (dissolved Al)

 

These values are likely to be a conservative estimates as the available evidence suggests that toxicity declines at environmental relevant pH, as does the availability of dissolved aluminum species.

It is important to note that were these equilibrium concentrations truly reflect the toxicity of aluminum in solution they would place it alongside, or more toxic than, some of the most potent toxic chemicals that are known. Such a view could clearly not be sustained given the ubiquity of aluminum in all its various forms in the environment.

 

It is therefore reasonable to assume that a small proportion of the added aluminum in the tests without analysis was present in the form of dissolved aluminum – the majority being present as precipitate or complex. This is confirmed by chemical analysis performed in several other studies. Only a very small amount of the added aluminum compound was dissolved. In some studies it was even below detection limit. Secondary effects arising from the presence of the precipitate together with possible pH reduction are likely to have contributed to the effects observed in the tests. This assumption is substantiated by observations noted in some of the test reports.

 

Aluminum salts may present a toxic hazard to environmental species under specific conditions. For example, it is possible that aluminum salts could have toxic effects in circumstances where the following conditions apply and persist:

·        pH is low (< 5.5)

·        oxygen content is very low

·        organic matter content is low

·        natural background concentrations of aluminum are low.

 

Such conditions would need to result in dissolved aluminum concentrations in the order of magnitude where toxicity occurs and would not be expected to arise from the industrial production and use patterns for these aluminum salts.

 

Aluminum species are naturally common throughout the environment. Measured background concentrations and Regulatory Standards for aluminum provide a useful context for considering the results of this assessment:

Background concentrations

The concentration of aluminum in natural waters can vary significantly depending on various physicochemical and mineralogical factors. Dissolved aluminum concentrations in waters with near-neutral pH values usually range from 0.001 to 0.05 mg/l but rise to 0.5–1 mg/l in more acidic waters or water rich in organic matter. At the extreme acidity of waters affected by acid mine drainage, dissolved aluminum concentrations of up to 90 mg/l have been measured (WHO, 1997 in WHO, 2010).

Dissolved Al-baseline concentrations (<0.45 µm) in European surface waters (Data from FOREGS-monitoring program;http://www.gsf.fi/publ/foregsatlas/in EURAS, 2007).

 

 

 

N

Min

Max

Mean ± SD

10thpercentile

Median

90thpercentile

Water

Al, µg/L

807

0.70

3,370

75.5 ± 180

3.0

17.7

209

In the rivers Meuse and Rhine concentrations of 36 and 13 µg/l (dissolved Al) were determined, respectively (RIZA, 2002).

- No Environmental Quality Standard (EQS) have been adopted yet for aluminum. In the Netherlands a MTR (Maximum Permissible Risk) is proposed. This MTR consists of a MTT (Maximum Permissible Addition) and a Cb (background concentration). The MTR is 48 µg/l (dissolved Al), with MTT of 12 µg/l (pH ≤ 6.5) and Cb of 36 µg/l (RIZA, 2002).

- WHO has not set a formal guideline for aluminum in drinking water, but has indicated that an average value of 0.1 mg/l or less should be achievable in large water treatment facilities but where there are practical difficulties in smaller facilities a maximum of 0.2 mg/l is the target value. On this basis the EU has set a value of 0.2 mg/l as an indicator parameter (Council Directive 98/83/EC).

 

"The main source of these background concentrations of aluminum in the aqueous environment are minerals such as gibbsite (Al(OH)3) and jurbanite (AlSO4(OH)•5H2O), especially in poorly buffered watersheds (Driscoll and Schecher 1990; Campbell et al. 1992; Kram et al. 1995). In more buffered watersheds, a solid-phase humic sorbent in soil is involved in the release of aluminum (Cronan et al. 1986; Bertsch 1990; Cronan and Schofield 1990; Cronan et al. 1990; Seip et al. 1990; Taugbol and Seip 1994; Lee et al. 1995; Rustad and Cronan 1995)"(Environment Canada and Health Canada, 2010).

 

Organisms present in waters with higher aluminum concentrations (present in e.g. suspended sediment) are adapted to tolerate such conditions. The extent to which organisms will be affected by further additions of aluminum will be determined by their ecology and physiology – some organisms can tolerate elevated levels of suspended material and surface sediment, others cannot.

Responses to effects arising from other secondary factors such as lowered pH and nutrient complexation will also be dependent upon the susceptibility of resident organisms to perturbations in these parameters and the characteristics of the receiving environment (e.g. buffering capacity and background nutrient concentrations). 

 

Conclusion

Because of the high and varying background concentrations and the very low PNEC for aluminum, which is derived when standard guideline is followed for PNEC derivation, it is not considered accurate and realistic to follow the standard approach.

Any concentration of aluminum in water that can be considered as stable can only be due to the complexing effects of natural constituents in the water, bearing in mind that the amount in water will already be at saturation. This concentration will vary with location. It is not possible to consider that any addition to the aquatic compartment can be stable, and therefore no PNEC can be set for fresh and marine water.

A lab study is not able to assess the inherent complexity of the environment. But that environment will be saturated under all realistic conditions with aluminum in the speciated form appropriate to the conditions, and organisms are evolutionarily-adapted to it, and rely on it. Any release of aluminum which the ecosystem cannot adapt to will result in gross physical effects, outside the scope of REACH.

Consequently, a PNEC can also not be set for aluminum zirconium chloride hydroxide in natural water. In sum, it can safely be assumed that under realistic environmental condictions risks for aquatic organisms are negligible because the bioavailability of aluminum zirconium chloride hydroxide in natural waters is low.

References:

Bertsch, P.M. 1990. The hydrolytic products of aluminum and their biological significance. J. Environ. Perspect. Health 12: 7-14.

Campbell, P.G.C., H.J. Hansen, B. Dubreuil and W.O. Nelson. 1992. Geochemistry of Quebec North Shore salmon rivers during snowmelt: organic acid pulse and aluminum mobilization. Can. J. Fish. Aquat. Sci. 49: 1938-1952.

Cronan, C.S. and C.L. Schofield. 1990. Relationships between aqueous aluminum and acidic deposition in forested watersheds of North America and Europe. Environ. Sci. Technol. 24: 1100-1105.

Cronan, C.S., W.J. Walker and P.R. Bloom. 1986. Predicting aqueous aluminum concentrations in natural waters. Nature (London) 324: 140-143.

Cronan, C.S., C.T. Driscoll, R.M. Newton, J.M. Kelly, C.L. Schofield, R.J. Bartlett and R. April. 1990. A comparative analysis of aluminum biogeochemistry in a northeastern and a southeastern forested watershed. Water Resour. Res. 26: 1413-1430.

Driscoll, C.T. and W.D. Schecher. 1990. The chemistry of aluminum in the environment. J. Environ. Perspect. Health 12: 28-49.

Environment Canada and Health Canada. 2010. Canadian Environmental Protection Act, 1999. Priority Substances List State of the Science Report for Aluminum Chloride, Aluminum Nitrate and Aluminum Sulfate.

Kram, P., J. Hruska, C. Driscoll and C.E. Johnson. 1995. Biogeochemistry of aluminum in a forest catchment in the Czech Republic impacted by atmospheric inputs of strong acids. Water Air Soil Pollut. 85: 1831-1836.

Lee, Y.H., H. Hultberg, H. Sverdrup and G.C. Borg. 1995. Are ion exchange processes important in controlling the cation chemistry of soil and runoff water. Water Air Soil Pollut. 85: 1819-1824.

Rustad, L.E. and C.S. Cronan. 1995. Biogeochemical controls on aluminum chemistry in the O horizon of a red spruce (Picea rubens Sarg.) stand in central Maine, USA. Biogeochemistry 29: 107-129.

Seip, H.M., S. Andersen and A. Henriksen. 1990. Geochemical control of aluminum concentrations in acidified surface waters. J. Hydrol. 116: 299-305.

Taugbol, G. and H.M. Seip. 1994. Study of interaction of DOC with aluminium and hydrogen ion in soil and surface water using a simple equilibrium model. Environ. Int. 20: 353-361.