Expanded Polystyrene (EPS), commonly known by the trade name Styrofoam, is a lightweight foam used widely for disposable cups and containers. The safety of drinking from these containers is nuanced and depends heavily on the beverage itself. For cold, non-acidic drinks, regulatory bodies consider the risk very low. However, conditions like heat, alcohol, or high acidity accelerate the transfer of chemicals from the foam into the liquid. This chemical migration is the primary safety concern for consumers.
The Chemical Composition of Expanded Polystyrene
A Styrofoam cup is approximately 98% air and only 2% plastic polymer. This plastic component is polystyrene, a polymer made up of long chains of the aromatic hydrocarbon known as styrene. Polystyrene is derived from linking thousands of styrene monomers through polymerization. Trace amounts of the unreacted styrene monomer remain within the finished foam product. This residual styrene is the primary chemical of concern for food or beverage contact. Federal agencies, including the U.S. Food and Drug Administration, have determined that the minute amounts of styrene typically present in EPS are not a health concern under normal use conditions. However, this chemical compound allows for potential leaching into the liquid.
Accelerants for Chemical Leaching
The transfer of residual styrene into a beverage is called chemical leaching, and it is significantly influenced by environmental factors. High temperatures are the most potent accelerant for this migration, as heat increases molecular movement within the polymer structure. Hot beverages like coffee, tea, or soup cause chemical bonds to break down more readily, rapidly increasing the amount of styrene that contaminates the liquid.
The drink’s chemical composition also plays a major role in styrene release. Styrene is a lipophilic compound, meaning it dissolves more easily in fatty, oily, or alcohol-containing liquids. Consequently, alcoholic beverages and highly acidic drinks, such as some fruit juices, facilitate the breakdown of polymer bonds faster than neutral, cold water. Studies show that even a single serving of a hot beverage in a foam cup can result in a measurable uptake of styrene.
Health Implications of Styrene Exposure
Once consumed, the leached styrene monomer is absorbed and metabolized by the body. The primary health concern is its classification by the National Toxicology Program (NTP) as “reasonably anticipated to be a human carcinogen.” This classification is based on sufficient evidence of carcinogenicity observed in animal studies and limited evidence from human epidemiological studies.
Large-scale occupational studies of workers exposed to high levels of styrene, such as in the reinforced-plastics industry, suggest an increased risk for specific cancers. These include lymphohematopoietic cancers, like leukemia, and some evidence points toward esophageal and pancreatic cancers. The neurological system is also a potential target for chronic exposure. High-dose occupational exposure has been linked to effects like changes in color vision and slowed reaction times.
The styrene concentrations that caused these neurological effects were thousands of times higher than the levels typically found in the environment. The long-term effects of chronic, low-level exposure from sources like foam cups are still under scientific investigation. Developmental concerns also exist, as styrene’s metabolites can be found in breast milk, though data on the direct effect on infants remains inconclusive.
Safer Alternatives for Beverages
Moving away from foam cups eliminates the risk of chemical leaching and supports sustainable choices. Reusable options are the most practical way to ensure beverage safety. Containers made from glass, ceramic, and stainless steel are chemically inert and will not leach compounds into drinks, regardless of temperature or acidity.
For disposable situations, several alternatives present a lower leaching risk than foam:
- Biodegradable paper cups, often lined with plant-based plastic like polylactic acid (PLA).
- Polypropylene (PP) or polyethylene terephthalate (PET) plastic alternatives.
Glass and metal remain the safest choices for minimizing chemical contact.