Native American Exposure to ¹³¹Iodine from Nuclear Weapons Testing in Nevada

ABSTRACT

A great deal of work has been done to reconstruct doses from Nevada Test Site fallout, yet the unique exposures of Native American communities continue to be neglected. It is possible to estimate the exposures of these communities through a process of collaborative information gathering and analysis. This article builds on a previous exercise that demonstrated the substantial doses received through the consumption of contaminated game. The updated model includes new information on the deposition of ¹³¹iodine, an assessment of the neonatal thyroid doses received through breast milk, an exploration of the effect of population mobility on dose estimates, and estimates of thyroid cancer risk. All thyroid dose estimates from the rabbit exposure pathway are comparable in magnitude to National Cancer Institute comprehensive dose estimates that assume exposure to contaminated milk from backyard cows and goats. Dose estimates from the rabbit exposure pathway are larger than estimated doses from store-bought milk by an average factor of six. Taking historical population mobility patterns into account may result in slightly lower estimates of dose. The quantification of this exposure pathway is considered be an advance toward a more appropriate dose reconstruction for communities with diets high in wild game.

Key words:

• Native American
• radiation
• nuclear weapons testing
• thyroid cancer
• dose reconstruction.

ACKNOWLEDGMENTS

This research was supported by funds from the National Institute of Environmental Health Sciences (NIEHS), the Centers for Disease Control and Prevention (CDC), and the Agency for Toxic Substances and Disease Registry (ATSDR). All community information was collected and provided by the Native Community Action Council board and staff.

Notes

¹It is important to note here that the thyroids of rabbits and other small mammals were routinely consumed; methods of cleaning the animals minimized waste by removing only intestines (Frohmberg et al. 2000).

²Institute of Medicine recommendations (NAS 1999) against estimating doses at the county or subcounty level do not apply in our study area. Nye County is within the region of “close-in measurements of environmental radiation” where ample data from portable survey instruments are available (NCI 1997a).

³Based on measurements of individual radionuclides in fallout clouds Hicks tabulated the conversion of external gamma radiation exposure rate (mR/hr) to radionuclide ground deposition (nCi/m2) (Hicks 1981 and 1982; NCI 1997a).

⁴ Dunning and Schwarz (1981) provided median dose coefficient estimates of 5.3 × 10⁻⁶ Sv/Bq (newborns) and 3.0 × 10⁻⁷ Sv/Bq (adults). Harvey et al. (2003) give median estimates of 5.31 × 10⁻⁶ (newborns) and 2.15 × 10^{− 6} (5-year olds). These compare with values of 3.7 × 10⁻⁶ (newborns), 2.1 × 10⁻⁶ (5-year olds) and 4.3 × 10⁻⁷ Sv/Bq (adults; ICRP 2000) and the EPA adult value of 4.8 × 10⁻⁷ Sv/Bq (USEPA 1993).

⁵Both sources of the thyroid dose coefficient (Dunning and Schwarz 1981; Harvey et al. 2003) assumed a relative biological effectiveness of ¹³¹I beta radiation of 1 and reported the dose coefficients in units of Sv; this was a change in unit but not in value. We use units of absorbed dose for compatibility with published risk estimates.

^a Distributions of parameters in unit of percent (interception by vegetation and rabbit thyroid absorption) were truncated at 100% so that values greater than 100% were not generated.

^b Martin (1965) calculated interception to be about 8%. We recalculated the deposition (nCi m⁻² mR⁻¹ h) based on Hicks (1981), and together with exposure rates (mR h⁻¹) and ¹³¹I collected from plants (both reported by Martin) we estimated the interception parameter described in this table.

^a Confidence intervals are provided by the online dose calculator; the NCI dose estimates have an average GSD of 5.

^b NCI dose estimates for the goat milk exposure pathway were unusually low for the Apple 2 test, apparently as the result of a calculation error.

^c Neonatal dose estimates for a normal amount of cow milk (not from a backyard cow) were roughly twice as large as those for breast milk.