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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.


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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.

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