Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:10:p9
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 10 (pt 9/11)
Character Range: 2258662–2262105

adults.
EA (2009)           PTWI = 0.0016 mg/kg/week                            Value adopted is referenced from JECFA for all routes of exposure.
                    (PTDI = 00023 mg/kg/day)
RIVM (2001)         TDI = 0.0001 mg/kg/day                              Derived on the basis of a NOAEL of 1.3 µg/kg/day for developmental effects in humans (and hair concentrations), and an uncertainty factor of 10.
ATSDR (1999)        MRL = 0.0003 mg/kg/day                              Chronic oral MRL derived on the basis of a NOAEL of 0.0013 mg/kg/day (adjusted) associated with CNS effects in humans (and hair concentrations), and an uncertainty factor of 4.5.
US EPA (IRIS 2012)  RfD = 0.0001 mg/kg/day                              RfD (last reviewed in 2001) based on a BMD of 0.0009 to 0.0015 mg/kg/day (adjusted) based on CNS effects in humans (and blood concentrations), and an uncertainty factor of 10.

The PTWI derived for methyl mercury from JECFA (WHO 2004) is considered to be based on the most recent detailed review of available studies in relation to exposure to methyl mercury. The TRV established by JECFA is within the same range of values previously established by US EPA and ATSDR and is recommended for use in the derivation of a soil HIL for methyl mercury. No dermal or inhalation specific data is available and hence the PTWI is recommended to be adopted for all routes of exposure.

    10.4.3     Recommendation
On the basis of the discussion above, the following toxicity reference values (TRVs) have been adopted for mercury in the derivation of HILs:

10.5          Calculated HILs
On the basis of the above, the following HILs have been derived for mercury (refer to Appendix B for equations used to calculate the HILs and Appendix C for calculations):

    10.5.1     Inorganic Mercury
HIL Scenario            HIL (mg/kg)                      Percentage Contribution from Exposure Pathways
Ingestion of Soil/Dust  Ingestion of Home-grown Produce  Dermal Absorption of Soil/Dust                  Inhalation (dust)
Residential A           40                               66                                              21                 13  <1
Residential B           120                              56                                              --                 44  <1
Recreational C          80                               72                                              --                 28  <1
Commercial D            730                              48                                              --                 52  1

-- Pathway not included in derivation of HIL

    10.5.2     Methyl Mercury
The previous HIL A for methyl mercury was 10 mg/kg. Direct calculation of the revised HIL on the basis of the above assumptions results in the calculation of an HIL A of 7 mg/kg. Given the level of uncertainty and variability in the estimation of intakes from other sources (background, particularly from fish) and the difficulty in obtaining reliable analytical data, the existing HIL A of 10 mg/kg has been retained. The HILs for other exposure scenarios have been calculated directly on the basis of the assumptions outlined in this document.
HIL Scenario            HIL (mg/kg)                      Percentage Contribution from Exposure Pathways
Ingestion of Soil/Dust  Ingestion of Home-grown Produce  Dermal Absorption of Soil/Dust                  Inhalation (dust)
Residential A           10