Strontium-90 activity in monthly milk samples from Greece

The present study evaluated after the Chernobyl nuclear accident the activity of 90Sr in commercial bovine milk sampled monthly from 1987 to 1994. Monthly mean activities (0.04 to 1.25 Bq/L) were comparable with those reported for other countries of the European Union (0.05 to 0.9 Bq/L), but maxima were higher, and the range of values was wider. Milk samples were also compared against samples of bovine milk in Greece that were collected before the Chernobyl accident during the period from 1969 to 1983 (0.04 to 1.37 Bq/L) and from 1985 to 1986 (0.04 to 0.30 Bq/L). The data were fit exponentially utilizing the chi-square statistic. The goodness of fit for the curve was 65%. Based on this result, the effective half-life of 90Sr in milk was estimated to be 308 +/- 57 d, which is very short compared with the physical half-life of 10,410 d for 90Sr. Since the second half of 1992, the decay curve of the measured mean activity approximated a threshold of 0.09 +/- 0.03 Bq/L, which is close to the low limit of detection by beta-scintillation.