Model of the seasonal variations of fungi ingestion and 137Cs activity concentrations in roe deer

This paper presents experimental data on 137Cs activity concentrations in roe deer during 1989–1994 in Harbo, Sweden. The data indicate that 137Cs levels in roe deer are rather constant in the period outside the mushroom season and increase between 2.4 and 4.9 times in autumn and summer. A data set of rumen analyses obtained in the same area is used to estimate the 137Cs daily intakes by roe deer. The time dependence of the calculated daily intakes resembles the kinetics of the activity concentrations in roe deer and supports the hypothesis that the autumn increase of 137Cs concentrations in roe deer is due to the increase of the ingestion rate of mushrooms. A model of the seasonal variations of fungi ingestion and 137Cs activity concentrations in roe deer is presented. The model parameters were estimated from experimental data on 137Cs activity concentrations in roe deer meat and feeds in combination with data of rumen composition. The time when the maximum ingestion rate of mushrooms takes place and the maximum ingestion rate of mushrooms are the model parameters that influence mostly the model predictions. An independent estimation of the ingestion rates of mushrooms, made from experimental values of the rumen composition measured in 1990, was compared with values predicted by the model. An agreement, within a factor of 1.5, was observed.