Strontium-90 in alfalfa (Medicago sativa) around the Hanford site in southeastern Washington State : An evaluation of surveillance data

From 1988–1994, 90Sr concentrations in alfalfa (Medicago sativa) grown in areas receiving irrigation water from the Columbia River downstream of Hanford have exceeded concentrations observed in alfalfa grown nearby using other irrigation water sources. Surveillance data indicate that the relationship is not linked to atmospheric releases from Hanford. Attributing the apparent differences in 90Sr concentrations to irrigation water is equivocal. Evaluations of 90Sr in Columbia River water fail to consistently show a statistically significant (P > 0.05) contribution at locations immediately downstream of Hanford. Modeling of past 90Sr fallout accumulation in soil indicates that the potential contribution from Hanford liquid effluents entering the Columbia River, subsequently used as irrigation water from 1972 to 1992, would account for ~ 2% of 90Sr in soil. The remaining 98% arises from historic atomic weapons testing fallout. Radiological doses modeled for an alfalfa-cow's milk-human pathway indicate that the maximum 50 year effective dose equivalent to a standard man who consumes 270 l of milk per year was 0.9 μSv, which is < 0.03% of the 3 mSv annual dose resulting from natural sources of radiation exposure.