Distribution of 40K, 137Cs, and 90Sr from Cow Milk to Cottage and Livno Cheese in Bosnia and Herzegovina: Physicochemical Associations, Regional Variation, and Radiological Safety

This study investigated the distribution of 40K, 137Cs and 90Sr during the processing of cow milk into cottage cheese from central Bosnia and Herzegovina and Livno cheese from the southwestern production area, with particular emphasis on physicochemical composition and regional differences. Raw milk (n = 15 per group), corresponding cheeses (n = 15 per group), and composite whey samples (one per cheese type) were analyzed for protein, fat, dry matter, water content, 40K, and 137Cs, as well as titratable acidity in milk samples. In a random second-stage subset, because of the cost and complexity of the radiochemical method, 90Sr was determined. Mean activity concentrations in milk used for cottage and Livno cheese production were 42.31 and 40.77 Bq/L for 40K, 0.030 and 0.057 Bq/L for 137Cs, and 0.015 and 0.030 Bq/L for 90Sr, respectively. Corresponding cheese means were 26.45 and 28.23 Bq/kg for 40K, 0.038 and 0.087 Bq/kg for 137Cs, and 0.073 and 0.369 Bq/kg for 90Sr. Processing retention factors showed limited transfer of 40K and 137Cs into cheese, whereas 90Sr was retained mostly in the curd. Significant regional differences were observed for 137Cs in both milk and cheese, whereas 40K did not differ significantly between regions. Differences between regions for 90Sr were also indicated, but these results should be interpreted cautiously because it was analyzed only in a limited second-stage subset. These findings show that radionuclide behavior in artisanal dairy systems is jointly shaped by radionuclide chemistry, cheese technology, and local environment, highlighting the need for site-specific food-chain assessment.