Selenium levels in cow's milk from different regions of Australia

Homogenised cow's milk samples were collected each season in 1990 and 1991 from 19 selected dairy factories in different regions across Australia. Fresh cow's milk samples were also collected every month in 1990 and 1991 from 24 selected dairy farms in Queensland. Selenium (Se) analyses were performed by spectrofluorimetry after complexing with 2,3-diaminonaphthalene. The study found a wide variation of Se levels in homogenised milk from dairy milk factories. Statistical analysis using unpaired t-test showed that Se levels in summer were significantly higher (P < 0.001) than in other seasons. Mean concentrations in summer, autumn, winter and spring for 1990 and 1991 were 23.8 +/- 4.6, 20.9 +/- 4.4, 20.7 +/- 4.2 and 20.6 +/- 4.8 micrograms/L, respectively. A two-way ANOVA analysis also indicated that regions and season have a significant influence (P < 0.001) on Se levels and that there is an interaction between regions and seasons. High Se levels in each region tend to be associated with high Se levels in summer milk. A wide variation of Se levels was also found in raw milk collected from dairy farms. Mean concentration was 22.0 +/- 6.0 micrograms/L, with a range of 6.7 to 47.6 micrograms/L. When the values of Se levels in homogenised milk for each season were used to estimate the contribution of milk to daily intake of different populations groups, it was found that infants have the highest intake (10.0-12.2 micrograms/day) which meets the Australian Recommended Dietary Intake.