Transfer of 137Cs to cow's milk: Investigations on dairy farms in Sweden

Abstract

Since 1986, the year of the nuclear accident at Chernobyl, 137Cs activity concentrations in cow's milk on dairy farms were studied in Sweden. Transfer coefficients, F m , of 137Cs from pasture and fodder to cow's milk were determined on farms in the counties of Uppsala, Gävleborg and Västmanland in central Sweden for one month on winter-fodder, and for the first month in 1987 and in 1988 on pasture. The average F m for all investigations (of 10 farms on winter-fodder and 11 farms on pasture in 1987 and 4 farms on pasture in 1988) south of Gävle was estimated to be 0.0055 with a range of 0.0039 to 0.0080. The 137Cs activity concentration in milk decreased with time. In summer 1992 and 1993, 137Cs in milk, on the farms still producing milk, was determined. On these farms, 137Cs activity concentration in milk was found to be < 2–21 Bq kg −1. The effective ecological half-life from 1987 was estimated to be 1.4 ± 0.5 (sd) years for milk from 10 farms with a range of 0.8–2.0 years. One farm where 137Cs in milk decreased at a slower rate, or not at all, used semi-natural and uncultivated pasture, forest meadows. On intensely managed farms, where potassium fertilizer was distributed, ploughing was performed and, in 1986, forage was cut at a higher stubble-height, the decrease of 137Cs in milk was observed to be faster.