  Systematic investigations of 137Cs and 134Cs activity concentrations in
potatoes (Solanum tuberosum) for the post-Chernobyl period (1986-2005) in the
Republic of Croatia are summarized. The correlation between 137Cs activity
concentrations in fallout and potatoes, has been found to be very good, the
correlation coefficient being r2=0.88 with P(t) < 0.001 for 18 degrees of
freedom. As the radiocaesium levels in potatoes decreased exponentially, the
mean residence time of 137Cs in potatoes was estimated by fitting the measured
activity concentrations to the exponential curve. The mean residence time was
found to be 6.8 +/- 1.1 years, the standard deviation being estimated by the
Monte Carlo simulations. The initial observed 134Cs:137Cs activity ratio in
potatoes has been found to be quite variable, but slightly lesser than
theoretically predicted value of 0.5, calculated by applying the known
inventory of these radionuclides in the Chernobyl reactor to the equation for
the differential radioactive decay. This can be explained by presence of the
pre-Chernobyl 137Cs in soil that originated from nuclear fallout. The annual
effective doses received by 134Cs and 137Cs intake due to consumption of
potatoes estimated for an adult member of Croatian population were found to be
very small, as the per caput dose for the entire 1986 - 2005 period was
calculated to be about 2.9 mSv, 134Cs accounting approximately for 1/3 of the
entire dose. Therefore, after the Chernobyl accident consumption of potatoes
was not the critical pathway for human intake of radiocaesium from the
environment in Croatia.
