Oral reference doses (RfDs) for sodium tungstate dihydrate

We derived subchronic and lifetime (chronic) reference doses (RfDs) for sodium tungstate dihydrate (ST) based on a recent chronic study by NTP (2021) using model selection procedures that are consistent and appropriate as per current EPA (2012) guidelines and models. For ST, we derived an RfD of 0.2 mg/kg-day for subchronic exposures and 0.02 mg/kg-day for chronic (lifetime) exposures. In terms of equivalent tungsten (W) RfD, the subchronic RfD is 0.1 mg/kg-day, and the chronic RfD is 0.01 mg/kg-day. Furthermore, based on this NTP (2021) study, ST is judged to have either "suggestive evidence of carcinogenic potential" or perhaps is "not likely to be carcinogenic to humans." However, in either case, a linear dose-response assessment is deemed unreasonable based on EPA (2005) guidance. Based on the derived chronic RfD for tungsten, the regional screening levels (RSLs) for children in residential soil and tap water are estimated to be 780 mg/kg and 200 μg/L, respectively.