Radiocaesium activity concentrations in potatoes in Croatia after the Chernobyl accident and dose assessment

Systematic investigations of (137)Cs and (134)Cs activity concentrations in potatoes (Solanum tuberosum) for the post-Chernobyl period (1986-2005) in the Republic of Croatia are summarized. The correlation between (137)Cs activity concentrations in fallout and potatoes, has been found to be very good, the correlation coefficient being r = 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 (137)Cs 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 (134)Cs:(137)Cs activity ratio in potatoes has been found to be quite variable, but slightly lesser than the 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 (137)Cs in soil that originated from nuclear fallout. The annual effective doses received by (134)Cs and (137)Cs intake due to consumption of potatoes estimated for an adult member of the 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 microSv, (134)Cs 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.     

Radiocaesium Activity Concentrations in Wheat Grains in the Republic of Croatia for 1965–2003 and Dose Assessment

Results of systematic, long-term measurements of ¹³⁷Cs activities in wheat for the period 1965–2003 are summarized. Radiocaesum fallout activities affect wheat activity concentrations, the coefficient of correlation being 0.91. In the observed period, the highest activity of ¹³⁷Cs deposited by fallout, 6321 Bq m⁻², was recorded in 1986, i.e., in the year of Chernobyl accident, causing peak ¹³⁷Cs activity concentration in wheat of 38.0 ± 13.0 Bq kg⁻¹. After the Chernobyl nuclear accident the ¹³⁴Cs:¹³⁷Cs activity ratio in wheat was ≈0.5, and did not differ from the value found in other environmental samples. The transfer coefficient from ¹³⁷Cs fallout deposition to wheat was calculated to be 8.6 × 10⁻³ Bq y kg⁻¹ per Bq m⁻², indicating the low transfer of radiocaesium from fallout to wheat. The upper limit for the collective effective dose for the Croatian population due to ¹³⁷Cs and ¹³⁴Cs ingestion by wheat and wheat products consumption for period 1965–2003 was estimated to be 665 person-Sv, the upper limit for the annual collective effective dose in 2003 being only about 0.061 person-Sv.     

226Ra in Tap and Mineral Water and Related Health Risk in the Republic of Croatia

The presence of 226Ra in drinking water may sometimes make important contribution to natural background radiation exposures. The paper describes the study of 226Ra content in drinking water of Croatia: tap water from the public supply system of several major towns and bottled mineral water from two selected mineral water springs. 226Ra was determined by alpha-spectrometric measurement after radiochemical separation. The radiation doses originating from drinking tap water and bottled mineral water were estimated. The annual dose from consumption of bottled mineral water was compared to that received from ingestion of public system tap water. The study showed that 226Ra content for investigated categories of waters is below the levels at which any unacceptable dose due to ingestion would arise.     

Radiocaesium Activity Concentrations in Milk in the Republic of Croatia and Dose Assessment

Results of systematic measurements of radiocaesium activities in milk after the Chernobyl nuclear accident are summarized. ¹³⁷Cs fallout activity affects milk activity, the coefficient of correlation being 0.89. The ¹³⁷Cs activities in milk in Croatia are log-normally distributed, reflecting the exponential decrease of activity. After the Chernobyl nuclear accident the ¹³⁴Cs:¹³⁷ Cs activity ratio in milk was 0.5, and did not differ from that for other environmental samples. The dose due to radiocaesium ingestion by milk consumption was estimated for the Croatian population, the annual collective equivalent dose being approximately 205 manSv in 1986 and 1.5 manSv in 1994.