Radiostrontium activity concentrations in milk in the Republic of Croatia for 1961 - 2001 and dose assessment

Results of systematic measurements of Sr-90 activity concentrations in milk for the period 1961 - 2001 are summarized. An exponential decline of radioactivity followed the moratorium on atmospheric nuclear testing. The highest activity of Sr-90 deposited by fallout, being 1060 Bq/m2, was recorded in 1963, while the peak Sr-90 activity concentration in milk, 1.42 +/-0.17 Bq/L, was recorded in 1964. The values in year 2001 for fallout deposition and milk were 7.7 Bq/m2 and 0.07 +/- 0.03 Bq/L, respectively. The reactor accident at Chernobyl caused higher Sr-90 levels only in 1986. Sr-90 fallout activity affects milk activity, the coefficient of correlation between Sr-90 fallout activity and Sr-90 activity concentrations in milk being 0.80. The transfer coefficient from fallout deposition to milk was estimated to be 2.5 mBqy/L per Bq/m2. The dose incurred by milk consumption was estimated for the Croatian population, the annual collective effective dose in 2001 being approximately 2.0 man-Sv.