Effect of milking method and season on phthalate content in cow milk from organic production

Dibutyl phthalate (DBP) and diethylhexyl phthalate (DEHP) content was determined by the high-performance liquid chromatography in the milk samples either mechanically or manually taken from 10 dairy cows in January, April, July and October (altogether 344 milk samples were collected). Milking method and season accounted for 23 and 77%, and 33 and 36% of the explained variability of DBP and DEHP content, respectively. Content of DBP in mechanically collected samples was higher in comparison with manually collected milk: 10.0 vs. 6.7 mg kg(-1) milk (P < 0.05). Irrespective of the milking method, DBP content differed significantly (P < 0.05) between samples collected in January (6.6 mg kg(-1)), July (4.2 mg kg(-1)) and October (20.0 mg kg(-1)). In the case of DEHP, only differences between April and October milk were found out (0.03 vs. 0.96 mg kg(-1); P < 0.05). Concentration of DBP in both mechanically and manually collected milk increased according to a polynomial function from spring to autumn (P < 0.01). Thirty times higher average DBP content than DEHP content was contrary to expectation. A migration of DBP in milk apart from the milking equipment (probably by contaminated silage) was more important in comparison with DEHP.