Long-term behavior of radiocesium in dairy herds in the years following the Chernobyl accident.

The longterm behavior of 137Cs in milk of a Bavarian farm (farm A) deposited as a consequence of the Chernobyl accident has been followed from April 1986 until August 1994. On the basis of activity measurements in milk and feed, transfer coefficients for the different seasons have been estimated in order to see any changes in transfer behavior (aging effect) of 137Cs with time. The influence of different grazing regimes has been tested by comparison of activity concentrations in milk and pasture grass in one farm (farm A with rotational grazing regime) with that of a nearby farm (farm B with continuous grazing regime) over a complete grazing season by frequent measurements in 1993. Though the farms are located only 4 km apart, have similar soils, and were contaminated to the same extent by the Chernobyl fallout, tenfold lower 137Cs activity concentrations in milk have been observed in farm B. This finding seems to be partly due to the influence of a different grazing intensity.