## 1 Introduction
Swelling results in significantly higher diffusion coefficients, leading to increased migration values [29]. Therefore, migration tests applied within laboratory simulations to evaluate regulatory compliance appear to be often too severe and not representative for the majority of the real food packaging application of PS, which are mostly refrigerated dairy products (such as yogurt and creams) with single side contact and a shelf life of up to approx. 40 days. On the other hand, only limited data have been published on the levels of styrene in yogurt and dairy products packed in PS directly taken from the market (retail surveys). Reported concentrations of styrene in the available literature vary considerably and are sometimes controversial (Table 1). \begin{table}
\begin{tabular}{c c c c} \hline
**Yogurt 1** & **Sour Cream** &
\begin{tabular}{c} **Butter/Margarine 2/** \\ **Fat Cream** \\ \end{tabular} & **Reference** \\ \hline
36–44 & & & [14] \\
2–9 & & & [30] \\
4–240 & & & [31] \\
4 & & 8–9 & [32] \\
3–35 & & & [33] \\
9–78 & 4–246 & 22–59 & [35] \\ \(<\)1–16 & & & [36; 37] \\
8–12 & & 49–51 & [38] \\
11 & 28 & 74–102 & [39] \\
1–46 & & 5–16 & [40] \\ \(<\)1–100 & \(<\)1–5 & \(<\)1–20 & [41] \\
19 & & 2–18 & [42]3 \\ \(<\)1–200 & \(<\)1–70 & [43] \\ \hline \end{tabular} \({}^{1}\) Including plain (natural) and also flavored products, with different fat content. 2 It should be mentioned that margarine containers are likely not made of PS but of acrylonitrile-butadiene-styrene (ABS) resins. 3 Food samples (composites) were collected without taking account of the packaging material.  
\end{table} 
Table 1: Levels of styrene (\(\mu\)g/kg) in yogurt and other dairy products packed in PS from retail reported in literature as mean or range values. Comprehensive information/description of the analyzed products (packaging and food content) which were sampled at retail level is frequently missing in the retrieved studies. Particularly difficult is the evaluation/distinction of the source of styrene; since measured concentrations could arise not only from migration of the monomer from the food packaging (styrene plastics) but also through natural occurrence in food. Indeed, styrene has been identified as natural constituent/fermentation product or as environmental contaminant in a wide variety of foods without contact with PS packaging. Levels of styrene in food vary widely, from traces or intermediate levels in fruits, cheese, coffee, beef and oat to high levels in some moldy cheese and stored milled olives and very high levels (up to 40 mg/kg) in cinnamon [42; 44; 45]. In view of the above, the aim of the present study was to assess the level of styrene in yogurt and dairy products packed in polystyrene and to identify the possible main factors influencing migration of this monomer in real packed foods taken from the market. A limited number of samples collected from the Italian and German markets were investigated (seventeen in total); several characteristics for each product were reported, such as the residual levels of styrene, the area/weight and the food contact area of the packaging; the fat content, the net weight and a description of the food as well as of the production process and of the storage time/temperature conditions until analysis. This allowed for an evaluation and comparison of the results obtained in the present study with the literature data on styrene migration into food.