## 4 Discussion  
The concentration of BPA in PET bottles containing rPET for drinking water and soft drinks was monitored over a period of five years, with a total of 375 analyzed bottles (Table 1). The results showed mean annual values between 0.715 mg/kg and 4.14 mg/kg. The concentrations increase significantly from 2021, which can be explained by a higher proportion of post-consumer recyclate in the PET bottles. The median was between 0.450 mg/kg and 0.893 mg/kg, which is significantly lower than the mean value. This indicates that individual (high) outliers trigger an increase in the mean value. The median is therefore more suitable for evaluating the development of BPA in rPET bottles. However, the high concentrations in the outliers should be considered critical and should be observed in further monitoring programs. The results of the quantification of BPA in rPET are in good agreement with the literature data. [PERSON] et al. found BPA concentrations in rPET pellets in the range between 0.394 mg/kg and 10.12 mg/kg (\(n=13\)), while virgin PET contained significantly lower concentrations of BPA (between 0.025 mg/kg and 0.432 mg/kg, \(n=10\)) [9]. [PERSON] et al. found 0.014 \(\pm\) 0.00005 mg/kg in virgin PET and 0.25 \(\pm\) 0.082 mg/kg, 0.33 mg/kg, and 2.35 \(\pm\) 0.08 mg/kg in three rPET samples [38]. [PERSON] et al. found 0.24 \(\pm\) 0.04 (\(n=5\)) and 0.38 \(\pm\) 0.02 mg/kg (\(n=5\)) in washed post-consumer colored and transparent PET flakes [39]. [PERSON] et al. determined BPA in 16 PET bottles from the Chinese market. The BPA concentration was determined to be between 0.0641 \(\pm\) 0.00582 mg/kg and 0.0377 \(\pm\)  
Figure 3: Predicted BPA concentrations in the bottle wall, which correspond to a migration of 1 ug/L (**a**) and 0.012 ug/L (**b**) (EU cube, layer thickness 300 μm, diffusion coefficients calculated from the activation energies of diffusion from experimental migration kinetics or prediction models (E\({}_{\text{A}}\)-based and A\({}_{\text{P}}\) models)). 0.00573 mg/kg (\(n\) = 16). It was not described in the study whether the PET bottles contained recyclates [40]. The annual median values of BPA in the investigated PET bottles are all below 3.57 mg/kg (3% acetic acid), 3.06 mg/kg (10% ethanol), and 2.30 mg/kg (20% ethanol), which are concentrations in the PET bottle wall that correlate with a migration of 0.012 ug/L after storage for 365 days at 25 \({}^{\circ}\)C (Table 6). The concentrations found in rPET bottles will therefore not be exceeded, and the non-intentionally introduced concentrations of BPA do not pose a problem for PET recycling. Assuming that most of the mineral water and soft drinks packed in PET bottles are consumed within around 90 days, the mean values are below the corresponding maximum concentrations in PET, which are 7.16 mg/kg (3% acetic acid), 6.17 mg/kg (10% ethanol), and 4.65 mg/kg (20% ethanol), and are therefore below the TDI-implied migration level of 0.012 ug/L. However, the very high outliers are far higher. It is therefore meaningful and recommendable to check the BPA in the individual batches used in the production of rPET bottles. In addition, the entry route of BPA into the rPET cycle should be clarified. [PERSON] et al. [40] also determined the migration at different temperatures. The migrated amount of BPA after storage for 7 days at 4 \({}^{\circ}\)C and 25 \({}^{\circ}\)C were determined to be between 0.26 \(\pm\) 0.07 and 18.7 \(\pm\) 2.58 ng/L and between 0.62 \(\pm\) 0.10 and 22.6 \(\pm\) 4.97 ng/L (\(n\) = 16), respectively. When stored at 70 \({}^{\circ}\)C for 7 days, the BPA concentration ranged from 2.89 to 38.9 ng/L. The migration values show a high scatter range, but based on the concentrations in the PET bottles of 0.0641 \(\pm\) 0.00582 mg/kg and 0.0377 \(\pm\) 0.00573 mg/kg, the predicted migration from the activation energies determined in this study is within these concentration ranges. [PERSON] et al. also measured the migration of BPA into 3% acetic acid and 20% ethanol [9].