Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:3:p1
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 3 (pt 1/5)
Character Range: 2111058–2114005

3                   Boron

3.1              General
Several comprehensive reviews of boron in the environment and its toxicity to humans are available and should be consulted for more detailed information not presented in this summary (ATSDR 2010; WHO 1998; US EPA 2004b). The following provides a summary of the key aspects of boron that are relevant to the derivation of a soil HIL.

Boron is never found in its elemental form in nature. The most common boron-containing ores are alkali and alkaline earth borates, including borax (Na4B4O2.10H2O), kernite (Na2B4O7.4H2O), colemanite (Ca2B6O11.5H2O), and ulexite (NaCaB5O9.8H2O), and borosilicate minerals. Common boron-containing compounds used in commerce also include borax pentahydrate, boric acid and boron oxide (ATSDR 2010).

Boron and boron compounds are used in the production of products such as fibreglass, soaps, detergents, enamels, frits, glazes, fertilisers, herbicides and fire retardants. They are also used in industries such as metallurgy, chemical synthesis and in nuclear applications (ATSDR 2010).

The toxicological database is largest for boric acid and borax and most of the toxicological information for inorganic borates in animals and humans is derived from studies on boric acid and borax (Mangas 1998).

Boron is an essential micronutrient for most plants and there is evidence that it is also essential for animals, including humans (ATSDR 2010).

3.2              Previous HIL
The derivation of the previous HIL (HIL A = 3000 mg/kg) for boron is presented by Mangas (1998). In summary, the HIL was derived on the basis of the following:
    * Intakes of boron from other sources were estimated with dietary intakes considered most significant for the general population. Background intakes from dietary exposure (based on US data) and soil (background) were estimated to be 3.23 mg/day for an adult and 1.62 mg/day for infants (half the adult intake).
    * A provisional tolerable daily intake (PTDI) of 14 µg/day was derived for boron based on a NOAEL of 9.6 mg/kg, body weight of 70kg and an uncertainty factor of 48.
    * Ingestion of both soil and dust has been considered, assuming 100% is bioavailable and is absorbed.
    * Dermal absorption has been considered to be low, with a conservative assumption of 1% adopted.
    * Inhalation of boron in dust has been considered both outdoors and indoors, with 10% bioavailability of inhaled boron assumed and the amount of boron in indoor dust assumed to be 75% of that outdoors.

3.3              Significance of Exposure Pathways
Ingestion of soil and dust is considered the most significant pathway of exposure for inorganics in soil. The consideration of bioavailability and inclusion of other exposure pathways in the derivation of a soil HIL has been further reviewed as noted below.

    3.3.1         Oral Bioavailability
While bioavailability (inhalation only) has been considered in the previous HIL,