Comparison of milk and ethanol/water mixtures with respect to monostyrene migration from a polystyrene packaging material.

Measurement of styrene monomer migration from polystyrene cups into milks containing 0-5, 3-5 or 10 % fat, as well as into four water/ethanol mixtures, containing 0, 15, 50 or 100 % ethanol, indicated that water, the simulant prescribed for milk under EC legislation (Directive 85/572/EEC) does not exhibit the required physico-chemical properties for an adequate simulation under practical migration conditions. Styrene migration was found to depend strongly upon the fat content of the milk and on the ethanol concentration in the simulant. Pure water gave migration values considerably lower than all of the three milks. 50 % ethanol was shown to correlate approximately with 3-5 % fat milk. Measurement of gas/liquid partition coefficients for styrene in the simulants confirmed the findings of the migration test. Higher migration values were found for lower gas/liquid partition coefficients and vice versa. From the kinetic data, an indication of the mechanism of the migration process into m ilk was obtained, leading to the conclusion that the migration rate limiting step is the penetration of the aqueous phase.