Seasonal variation in the activity concentration of 137Cs in Swedish Roe-deer and in their daily intake

Abstract

The seasonal variation of the activity concentration of 137Cs in roe-deer ( Capreolus capreolus) from the central part of Sweden was studied in order to test whether there is a relationship with any variation in the seasonal intake of 137Cs from different plant species. Muscle samples of roe-deer were collected by local hunters in 1986 (June–Septemb er), 1987 and 1988. In 1986, samples were collected in the contaminated regions of central Sweden. In 1987, samples were collected in the Gävle Commune. In 1988, samples were collected from two study areas in central Sweden: Gävle and Harbo. The ground deposition in the Gävle area was 30 000–120 000 Bq m −2, and in the Harbo area 35 000–45 0 00 Bq m −2. The calculated daily intake of 137Cs was based on knowledge of the feed composition taking into account the seasonal shift in diet for roe-deer and the activity concentrations of 137Cs in the most important feed plants. Radiocesium in the plants which typically constitute roe-deer diet has been regularly measured in the Harbo region since the Chernobyl accident. In these plants, there was only a minor variation of 137Cs content during these years and a mean 137Cs activity concentration was therefore used in subsequent calculations. An increase in the activity concentration of 137Cs in roe-deer was observed in August and September of 1986, 1987 and 1988. For example, the activity concentration of 137Cs seemed to have increased in Gävle in 1988 from levels of 1000–3000 Bq kg −1 during January–July to 11 800 Bq kg −1 in August. The seasonal variation of the activity concentration of 137Cs in roe-deer observed in Harbo in 1988 was similar to that seen in Gävle in 1988, with pronounced maximum values in August and September. The calculated daily intake of 137Cs corresponds well to the activity concentrations of 137Cs in roe-deer, except in April. Intake of fungal species seems to be an important cause of the maximum values of early autumn.