Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:10:p6
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 10 (pt 6/11)
Character Range: 2250097–2253255

In addition, US EPA has classified mercuric chloride as Group C—possible human carcinogen, based on increased incidence of squamous cell papillomas of the forestomach and marginally increased incidence of thyroid follicular cell adenomas and carcinomas from long-term oral studies in rats.

    10.4.2     Review of Available Values/Information

10.4.2.1     Inorganic Mercury
Most information on the toxicity of inorganic mercury compounds comes from studies of mercuric chloride. As the water solubility and bioavailability of many other inorganic compounds, notably mercurous compounds, are much less than those of mercuric chloride, such compounds are likely to be less toxic. These issues should be considered further in a site-specific assessment, where relevant.

Carcinogenicity studies in experimental animals are available for mercuric chloride where no carcinogenic effect was observed in mice or female rats, though marginal increases in the incidence of thyroid follicular adenomas and carcinomas and forestomach papillomas were observed in male rats exposed orally. Mercuric chloride binds to DNA and induces clastogenic effects in vitro; in vivo, both positive and negative results have been reported, without a clear-cut explanation of the discrepancy. The overall weight of evidence is that mercuric chloride possesses weak genotoxic activity but does not cause point mutations (WHO 2011b). US EPA (IRIS 2012) evaluation of mercuric chloride indicates that a linear low-dose extrapolation is not appropriate as kidney tumours seen in mice occurred at doses that were also nephrotoxic.

On this basis, a threshold approach is considered appropriate, based on the most sensitive effect associated with mercury exposure. The following threshold values are available from Level 1 Australian and International sources:
Source              Value                                                 Basis/Comments
Australian
ADWG (NHMRC 2011)   Guideline established on the basis of methyl mercury
FSANZ (2003)        PTWI = 0.003 mg/kg/week                               Value for total mercury referenced from JECFA 1989, based on methyl mercury.
International
WHO (2011b)         TDI = 0.002 mg/kg/day                                 The current WHO DWG (2011a, consistent with the review conducted in 2003) has derived a guideline of 0.006 mg/L, based on a TDI of 0.002 mg/kg/day derived from a NOAEL of 0.23 mg/day associated with kidney effects in a 26-week study in rats and an uncertainty factor of 100. A similar TDI was derived on the basis of a LOAEL of 1.9 mg/kg/day associated with renal effects in a 2-year rat study and an uncertainty factor of 1000.
JECFA (WHO 2011a)   PTWI = 0.004 mg/kg                                    Review of mercury by JECFA indicated that the predominant form of mercury indoors, other than fish and shellfish, is inorganic mercury and, while data on speciation is limited, the toxicological database on mercury (II) chloride was relevant for establishing a PTWI for foodborne inorganic mercury. A PTWI was established on the bases of a benchmark dose approach, where the BMDL10 of 0.06 mg/kg/day for relative