Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:10:p2
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 10 (pt 2/11)
Character Range: 2239597–2242500

February 2003, after considering the key findings of the Global Mercury Assessment report, that there is sufficient evidence of significant global adverse impacts from mercury to warrant further international action to reduce the risks to humans and wildlife from the release of mercury to the environment.

10.2          Previous HIL
The derivation of the previous HIL (HIL A for inorganic mercury = 15 mg/kg and for methyl mercury = 10 mg/kg) is presented by Imray & Neville (1996). In summary, the HILs were derived on the basis of the following:
    * Intakes of mercury were considered based on available data that showed dental amalgams and dietary intakes (based on data from FSANZ from 1992) as most significant. The total intake of inorganic mercury (derived from inorganic or elemental sources, both of which add to the body burden of mercury) estimated for a 2-year-old child was 2.1 µg/day. The most significant exposures were derived from dietary intakes and dental amalgams. For methyl mercury, the total intake was estimated to be 2.4 µg/day (approximately 50% of the adopted TI of 5 µg/day, which was based on methyl mercury). The most significant exposures were derived from dietary intakes of seafood. Based on the available data, 20% of the PTWI was considered for intakes derived from soil.
    * A provisional tolerable weekly intake (PTWI) of 300 µg for total mercury, of which no more than 200 µg should be methyl mercury, referenced from the JECFA evaluation, was adopted as the toxicity reference value.
    * Ingestion of both soil and dust has been considered assuming 100% is bioavailable.

10.3          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.

    10.3.1     Oral Bioavailability
The bioavailability of different forms of mercury, by different routes of exposure, is expected to vary considerably (Imray & Neville 1996) with oral bioavailabilities reported in the range 215% for inorganic mercury and 80100% for methyl mercury.  Bioavailability has not been considered in the previous HIL, as insufficient data is available to adequately define the bioavailability of the different forms of mercury from soil. On this basis, a default approach of assuming 100% oral (and inhalation) bioavailability has been adopted in the derivation of an HIL. It is noted that site-specific assessment of bioavailability can be considered where required.

    10.3.2     Dermal absorption
Review of dermal absorption by MfE (2011) has noted that 'Mercury reacts with skin proteins, and as a result penetration does not increase commensurably with increasing exposure concentration but rather approaches a plateau value. Mercury has a