OEHHA released a draft revised REL for mercury in November 2007 (OEHHA, 2007). The revised Acute REL is 0.0006 mg/m3 (600 ng/m3) and is based on the same study and effect level, but the uncertainty factor was increased from 1000 to 3000. OEHHA increased the intra-species uncertainty factor from 10 to 30, using the default factor of 3 to account for inter-individual kinetic variability and a factor of 10 to account for greater susceptibility of children and their developing nervous systems. A factor of 30 for intraspecies uncertainty is highly unusual; typically a single uncertainty factor does not exceed 10. Due to the use of an unconventional uncertainty factor for intraspecies variability and because of the interim status of the draft Acute REL, the 0.0006 mg/m3 value, was not considered for use as a benchmark health value for this report.