Measurements of 131I, 134Cs and 137Cs in environmental samples in Bulgaria after the Fukushima accident

This work reports results from measurements of ¹³¹I, ¹³⁴Cs and ¹³⁷Cs in environmental samples in Bulgaria after the Fukushima accident. Measurements performed in the period from 25 March to 2 May by high volume air sampling on glass fiber aerosol filters showed ¹³¹I concentrations in the range 31-2240 μBq/m³. Caesium-134 and ¹³⁷Cs were also detected in the air samples with concentrations in the ranges 33-456 μBq/m³ and 38-637 μBq/m³, respectively. Measurements of rainwater showed concentrations of ¹³¹I in the range 0.09-1.15 Bq/l. ¹³¹I was also found in raw milk (0.14-0.38 Bq/l) and in grass (0.33 Bq/kg). The measured concentrations are consistent with those in other European countries and do not require special actions for public protection. The measured peak concentrations in the air in Bulgaria were higher than those reported for Northern Greece and were reached on the same day (4-5 April) [3]. Long-term (15 days) air sampling have shown detectable concentrations of airborne activity concentrations of ¹³⁴Cs and ¹³⁷Cs with stable ¹³⁷Cs to ¹³⁴Cs ratio in the range 1.1 - 1.3. The results of the rainwater measurements indicate that washout was the dominant atmosphere scavenging mechanism during the rainfalls. Under these conditions roof sampling of rainwater in the early stages of the rain was found to be very appropriate for detection of trace quantities of ¹³¹I in the atmosphere. Dedicated comparison between roof sampling through a drain pipe and direct sampling shows that the roof sampling is more efficient as it appears to be more sensitive to ¹³¹I in the air.