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Boron orthophosphate (CAS 13308-51-5) will be hydrolytically transformed in the ionic forms in water (B3+ and PO43-) which will further associate with the ionic forms of H2O. Therefore a separate assessment of the toxicity of boron and the PO43- ions is considered justified.

Boron is ubiquitous in the environment and essential for many organisms, e.g. for plant growth. Plants may require boron to stimulate ascorbate metabolism, which was demonstrated in recent studies (Mastromatteo E., Sullivan F. 1994). Boron retention in soil depends on boron concentration in the soil solution, soil pH, texture, organic matter, cation exchange capacity, type of clay and mineral coating on the clay (Butterwick et al., 1989). The degree of boron fixation is influenced by moisture content, wetting and drying cycles and temperature.

Boron may be found in four forms in soil: organically bound, water-soluble, adsorbed and fixed in clay and mineral lattics (Adriano 1986). The highest concentration of Boron can be found in arid, saline soils. In sandy soils, boron could be leached more readily than in clay soils and is therefore less likely to accumulate (Adriano 1986). Boron can bind with clays, suspended matter, and sediments of aquatic systems (Maier and Knight 1991). As less than 5 percent of the soil boron is available for plant uptake (Butterwick et al. 1989), a high uptake is not expected for plants.

Phosphate is applied to soil as a fertilizer for a variety of crops. Phosphate has low potential for adsorption to solid particles (as it will be rapidly transformed in water into its dissociated forms). Phosphate is an essential nutrient for terrestrial organisms. Therefore bioaccumulation and toxicity are considered not relevant for phosphate.

One experimental study is ongoing investigating the effects of Boron orthophosphate (CAS 13308-51-5) on mortality, behavior, body weight and reproduction of Eisenia andrei. Until now the range finder test with Eisenia andrei is available. Testing this representative species of the soil fauna evaluates the exposure to the test substance via soil pore water, surface contact as well as by ingestion of soil particles. The available range finder study was performed according to OECD 222 and did not result in any adverse effects on mortality, behavior, body weight and reproduction. Thus, a NOEC (56 d) ≥ 1000 mg/kg dw was derived for reproduction.

In addition, indirect exposure of soil via irrigation or atmospheric transport is considered to be negligible, as the air compartment is considered not relevant for Boron orthophosphate.

The available studies on the acute toxicity of Boron orthophosphate on aquatic organisms determined no effects of the substance on fish, aquatic invertebrates or algae. Toxic effects on terrestrial organisms are therefore not expected.

The available data for toxicity to activated sludge microorganisms support the proposal of Boron orthophosphate having a low toxicity to soil microorganisms. No inhibition of respiration rate of a microbial sewage treatment plant community was observed in the available study according to OECD 209. The Guidance Document (ECHA, 2012, page 122) states that a test on soil microbial activity will only be additionally necessary for a valid PNEC derivation if inhibition of sewage sludge microbial activity has occurred and this is clearly not the case. Based on the available information, effects on soil microorganisms are not expected to be of concern, and consequently, no further testing is required.

Based on the available data terrestrial toxicity testing is also not deemed necessary.

 

References:

Adriano, D.C. (1986). Trace elements in the terrestrial environment. Springer-Verlag, New York. 533 p.

Butterwick, L.N. De Oude, and K. Raymond (1989). Safety assessment of boron I aquatic and terrestrial environments. Ecotoxicol. Environ. Safety 17: 339-371.

Maier, K.J., and A.W. Knight (1991). The toxicity of waterborne boron to Daphnia magna and Chironomus decorus and the effects of water hardness and sulfate on boron toxicity. Arch. Environ. Contam. Toxicol. 20: 282-287.

Mastromatteo, E. and Sullivan, F. (1994) Summary: International Symposium on the Health Effects of Boron and Its Compounds. Environ Health Perspect 102 (Suppl 7): 139 – 141