Environmental Engineering Reference
In-Depth Information
the styrene emissions are not from food packaging but from automobile
exhaust and industrial uses (e.g., reinforced composites) of styrene. Not
generally taken into account is the exposure inside automobiles (Ayoko et
al., 2008). Styrene ranks 4th in mean concentration of volatile constituents
insidethecabandisoneofthefivecompoundsinthemixataconcentration
greater than 40 µg/m
3
. Also, cigarette smoke (~147 µg/cigarette; Cohen et
al., 2002) contributes significantly to the intake. It is readily oxidized in
air and outdoor measurements usually find concentrations of about 1 ppb
(National Toxicology Program, 2006).
Expandedpolystyrene(EPS)foamwidelyusedinthefoodserviceindustryis
made by steam expansion of PS beads containing pentane or other blowing
agents. The foam is molded during the expansion (or subsequently extruded
through a die to obtain a sheet that can be thermoformed). Polystyrene
products may contain up to 153-458 ppm of residual styrene monomers
(American Chemical Council, 2013), dimers, and trimers (Choi et al., 2005)
as well as traces of the 7,8-oxide of styrene. With food service products, EPS
comes into direct contact with hot/cold food or beverages that can extract
residual styrene from packaging particularly efficiently. This is an obvious
route of ingestion and the amounts migrating into food can be estimated
using the migration kinetics of styrene reported by Lickly in 1995 (Lickly
et al., 1995; Tang et al., 2000). For instance, eggs packaged in PS cartons
for 2 weeks had seven times higher levels of styrene and ethyl benzene
compared to fresh farm eggs (Matiella and Hsieh, 2006). Migration of the
monomer from EPS foam cups into water (pH ~ 5) at 80°C over a 35-120
min of exposure was as high as 0.3-4.2 µg/l (Tawfik and Huyghebaert,
1998). Though reliable quantitative data is not available, there is little doubt
that fatty foods such as meat or dairy products in contact with PS containers
also pick up residual monomer.
However, the levels of migrated styrene and other compounds in packaged
food are low compared to maximum permitted levels. Exposure to styrene
at non-occupational levels causes primarily mild irritation of the eyes and
the respiratory tract. Ingestion or inhalation of styrene results in low acute
toxicity and neither styrene nor its dimer or trimer shows any ED effects
(Date et al., 2002; Hirano et al., 1999). The monomer released into air is
photooxidized readily and has a short half-life of only 3.5-9.0 h (Alexander,
1990). In any event, some common foods are naturally rich in styrene with
