An article published on August 7, 2017 reported on the occurrence of polycyclic aromatic hydrocarbons (PAHs) in polystyrene (PS) food contact materials (FCMs). Si-Qi Li and colleagues from the Shenzhen Key Laboratory of Circular Economy, Peking University, Shenzhen, China, measured 16 priority PAHs (as designated by the U.S. Environmental Protection Agency (EPA)) in 21 types of PS-made food contact articles bought in local supermarkets of Shenzhen. The presence of PAHs in PS FCMs could be due either to generation during production, or sorption during use.
Among the 16 PAHs measured, eight low-ring PAHs could be detected, while high-ring PAHs (>4 rings) were not found. According to the authors, this could be because more chemical steps are required for formation of high-ring PAHs compared to low-ring PAHs. The eight PAHs detected were naphthalene (Nap, CAS 91-20-3), acenaphthylene (Acy, CAS 208-96-8), acenaphthene (Ace, CAS 83-32-9), fluorene (Fle, CAS 86-73-7), phenanthrene (Phe, CAS 85-01-8), anthracene (Ant, CAS 120-12-7), and pyrene (Pyr, CAS 129-00-0). Of these, Nap and Phe had a 100% detection rate and the highest concentrations, collectively accounting for 59-99% of the total PAH concentration detected in each product. Fle was detected in more than 75% of the samples, Flu and Pyr in more than 35%, and Acy, Ace, and Ant in 10-20% of the samples.
The total concentration of all detected PAHs ranged from 18.9±5.16 ng/g in a colorless fruit form to 476±52.0 ng/g in an instant noodle container made of PS foam. These levels are in agreement with those previously measured by Rochman et al. (2013) in virgin PS pellets (79-97 ng/g), but much higher than those reported for other FCM-relevant plastics, indicating that PAH contamination may be particularly relevant for PS FCMs. In particular, measured PAH concentrations were below a 1 ng/g limit of detection for polyethylene terephthalate (PET), below a 2 ng/g limit of detection for polyvinyl chloride (PVC), below a 13 ng/g limit of detection for polyethylene (PE), and 2-6 ng/g for polypropylene (PP) plastics.
Li and colleagues further observed that PAH levels were higher in expanded PS products compared to the extruded ones. This was attributed to the utilization of blowing agents during the production of the former material, since these additives may contain short-chain aliphatic hydrocarbons which can generate PAHs under certain conditions. Further, higher concentrations of PAHs were seen in colored products compared to the colorless products, likely because unsaturated bonds and chromophores could facilitate the conversion of short-chain hydrocarbons into aromatic hydrocarbons.
When migration into water was simulated based on a statistical Monte Carlo procedure, probability distributions showed that migration was likely to be lower than 10 µg/kg; however, according to the authors, higher values were possible although less likely. In addition, using water as a simulant could have underestimated the risk of PAHs migration into fatty foods.
The authors concluded that their work confirmed that PS FCMs may be both a source and a sink for PAHs, and provided “valuable data needed for updating dietary intake values for the impurities other than styrene monomer and plastics additives in PS FCMs.”
Li, S.-Q., et al. (2017). “PAHs in polystyrene food contact materials: An unintended consequence.” Science of the Total Environment 609:1126-1131.
Rochman, C. M., et al. (2013). “Polystyrene plastic: a source and sink for polycyclic aromatic hydrocarbons in the marine environment.” Environmental Science & Technology 47:13976-13984.
Van, A., et al. (2012). “Persistent organic pollutants in plastic marine debris found on beaches in San Diego, California.” Chemosphere 86:258-263.