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Boron orthophosphate (CAS 13308-51-5) is an inorganic boron phosphate salt. The substance does not undergo biological degradation and in general, abiotic degradation of the substance as such is an irrelevant process for inorganic substances that are assessed on an elemental basis. Boron and phosphorus are both natural elements present in all environmental compartments. The elements boron and phosphorus are persistent in environment. When exposed to water Boron orthophosphate would likely undergo sedimentation due to low water solubility. Boron orthophosphate transforms to undissociated boric species and borates, as well as (di) hydrogenphosphate, which are the naturally occurring forms of boron and phosphorous in environment. However, no further degradation is possible. The only significant mechanism expected to influence the fate of boron in water is adsorption-desorption reactions with soil and sediment (Rai et al., 1986).

Boron is ubiquitous in the environment and an essential micronutrient 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 will normally occur in low concentrations (U. S. EPA 1975), e. g. in natural freshwater ecosystems, surface water concentrations are usually less than 0.1 mg/L and concentrations of more than 1 mg/L will be rarely exceed (United States Department of the Interior 1998). But boron compounds can be degraded or transformed to boric species and borates, the main compounds of ecological significance (Sprague 1972), which both show remarkable stability in natural aquatic systems. The chemical form of boron found in water is dictated by pH and other constituents (Sprague 1972), but in most freshwater systems (pH<9) undissociated boric acid will occur (Hem 1970, Maier and Knight 1991). Boron, if not taken up by plants and animals, will tend to accumulate and will be bioavailable over extended periods of time (Perry et al. 1994). Thus, boron compounds tend to accumulate in aquatic ecosystems (U. S. EPA 1975), but do not seem to biomagnify through the food chain (Wren et al. 1983; Saiki et al. 1993). BCF < 100 was calculated for boron in freshwater plants, fish and invertebrates (Thompson et al. 1972). Experimental BCF between 52 and 198 were determined for fish (Tsui and McCart 1981) and a BCF = 0.3 was calculated for fathead minnows (Pimephales promelas) and green sunfish (Lepomis cyanellus) (Suloway et al. 1983). Therefore, boron will not bioaccumulate in aquatic organisms.

Orthophosphates are also formed by natural hydrolysis of human urine and faeces, animal wastes, food and organic wastes, mineral fertilisers, bacterial recycling of organic materials in ecosystems, etc. Phosphates are bio-assimilated by the bacterial populations and the aquatic plants and algae found in these different compartments and are an essential nutrient (food element) for plants, and stimulate the growth of water plants (macrophytes) and/or algae (phytoplankton) if they represent the growth-limiting factor.

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). Boron adsorption is also reported on clay minerals (Hingston 1964) and on hydrous oxides of Fe and Al (Sims and Bingham, 1968). The adsorption of Boron from solution by Ca forms will be described as a function of pH and boron concentration in solution. Adsorption coefficients were estimated to be 2.94, 11.8 and 15.1 µmole/g for Ca-kaolinite, Ca-montmorillionite and kaolinite (Keren & Mezuman 1981). 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.

The availability of inorganic phosphorus in soils depends on precipitation-dissolution and sorption-desorption processes (Cornforth, 2005). Phosphorus ions are mainly immobilised in soils by adsorption to organic matter or by reaction with aluminium or iron to aluminium- and ironphosphates. Sato et al. (2009) observed that Phosphorus released from calciumphosphate was adsorbed to aluminium and iron-oxyhydroxides.

The air compartment is considered not relevant for Boron orthophosphate. Due to its physico-chemical properties, Boron orthophosphate is not distributed or transported to the atmosphere as the substance is usually not emitted to air.

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.

Cornforth, I. S. (2005). The fate of phosphate fertilisers in soil. Department of Soil Science, Lincoln University online: www. nzic. org. nz.

Hem, J. D. (1970). Study and interpretation of the chemical characteristics of natural water, 2d ed. U. S. Geological Survey Water-Supply Paper 1473.

Hingston, F. J. (1964) Reactions between boron and clays.Aust. J. Soil Res. 2, 83-95

Keren, R. and U. Mezuman (1981).Boron adsorption ny clay minerals using a phenomenological equation. Clays and Clay Minerals. Vol. 29, No. 3, 198-204.

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

Perry, D. M., Suffet, I. S. et al (1994) Boron environmental chemistry, distribution, bioaccumulation, and toxicity in aquatic systems and recommendations for establishment of a boron water quality criterion for natural waters in the San Joaquin Valley, California. Final report for contract number 1-192-150-0, submitted to the California Regional Water Quality Control Board, Central Valley Region, and the California Environmental Protection Agency. 270 p.

Rai, D., J. M. Zachara, A. P. Schwab, R. Schmidt, D. Girvin, and D. Rogers (1986). Chemical attenuation rates, coefficients, and constants in leachate migration. Vol. 1. A critical review. Report to Electric Power Research Institute, Palo Alto, CA by Battelle, Pacific Northwest Laboratories, Richland, WA. Research Project 2198-1. (As cited in ATSDR, 1992.)

Saiki, M. K., Jennings, M. R., and Brumbaugh, W. G. (1993). Boron, molybdenum, and selenium in aquatic food chains from lower San Joaquin River and its tributaries, California. Arch. Environ. Contam. Toxicol. 24: 307-319.

Sato et al. (2009) Biogenic calcium phosphate transformation in soils over millennial time scales. Journal of Soils Sediments (2009) 9:194–205

Sims, J. R. and Bingham, F. T. (1968) Retention of boron by layer silicates, sesquioxides and soil minerals. II. Sesquioxides. Proc. Soil Sci. Soc. Amer. 32, 364-369

Sprague, R. W. (1972) The ecological significance of boron. U. S. Borax Research Corporation, Anaheim, California. 58p.

Suloway, J. J., Roy, W. R., Skelly, T. M. Dickerson, D. R. Schuller, R. M. and Griffin, R. A. (1983). Chemical and toxicological properties of coal fly ash. Champaign, Illinois, Illinois State

Thompson, S. E., Burton, C. A., Quinn, D. J., et al. 1972. Concentration factors of chemical elements in edible aquatic organisms. Report to U. S. Atomic Energy Commission by Lawrence Livermore Laboratory, Unviversity of California, Livermore, CA. UCRL-50564. Cited In: ATSDR, 1992.

Tsui, P. T., and McCart, P. J. 1981. Chlorinated hydrocarbon residues and heavy metals in several fish species from the Cold Lake area in Alberta, Canada. Intern J Environ Anal Chem 10: 277-285. Cited In: ATSDR, 1992.

United States Department of the Interior (1998) Guidelines for Interpretation of the Biological Effects of Selected Constituents in Biota, Water and Sediment. National Irrigation Water Quality Program Information Report No. 3.

U. S. EPA (United States Environmental Protection Agency). 1975. Preliminary investigation of effects on the environment of boron, indium, nickel, selenium, tin, vanadium and their compounds. Vol. 1. Boron. U. S. Environmental Protection Agency Rep. 56/2- 75-005A. 111pp. Cited In: Eisler, 1990.

Wren, C. D., MacCrimon, H. R. and Loescher, B. R. (1983). Examination of bioaccumulation and biomagnification of metals in a Precambrian shield lake. Water Air Soil Pollut 19: 277-291.