Oral reference doses (RfDs) for sodium tungstate dihydrate

Area of Science:

• Toxicology and Environmental Health
• Chemical Risk Assessment
• Occupational Health

Background:

• Sodium tungstate dihydrate (ST) is a chemical compound requiring toxicological evaluation.
• Previous risk assessments may not fully incorporate recent study findings.
• Establishing clear reference doses (RfDs) is crucial for public health protection.

Purpose of the Study:

• To derive subchronic and chronic (lifetime) reference doses (RfDs) for sodium tungstate dihydrate (ST).
• To calculate equivalent tungsten (W) RfDs based on ST exposure.
• To assess the carcinogenic potential of ST and determine appropriate dose-response models.

Main Methods:

• Utilized model selection procedures consistent with EPA (2012) guidelines.
• Analyzed data from a recent chronic study by the National Toxicology Program (NTP, 2021).
• Derived RfDs for ST and equivalent tungsten (W) for subchronic and chronic exposures.
• Evaluated carcinogenic potential and dose-response relationships based on EPA (2005) guidance.

Main Results:

• Derived a subchronic RfD for ST of 0.2 mg/kg-day and a chronic RfD of 0.02 mg/kg-day.
• Equivalent tungsten (W) RfDs are 0.1 mg/kg-day (subchronic) and 0.01 mg/kg-day (chronic).
• ST shows suggestive evidence of carcinogenic potential or is not likely to be carcinogenic; linear dose-response is unreasonable.
• Estimated regional screening levels (RSLs) for children: 780 mg/kg in soil and 200 μg/L in tap water.

Conclusions:

• Established new, scientifically-grounded RfDs for ST and tungsten (W) for different exposure durations.
• The derived RfDs and RSLs provide critical data for environmental and health risk assessments.
• Findings guide regulatory decisions regarding safe exposure limits for sodium tungstate dihydrate.