row of bottles with their caps prominently shown, montage with woman drinking from a bottle

Chemicals in Cap Gaskets

As described in the report with results listed in test results, we tested gaskets from the caps of 273 glass-bottled beverages from 146 brands, the large majority having metal caps or lids. The gasket materials identified by the testing are listed below. 

Polymers Detected    

PVC (65.7% of tested gaskets): Polyvinyl chloride, also called "vinyl," is a plastic with a highly toxic environmental footprint. High levels of plasticizer chemicals must be added to PVC to make a flexible cap gasket. Typcially, 20-40% of the weight of the gasket is plasticizer. The plasticizer molecules are not bound to the PVC, so they may migrate into a food or beverage or onto surfaces the PVC touches.

Polystyrene copolymer (19.4% of tested gaskets): Polystyrene is mixed with other polymers to form a synthetic rubber that does not require plasticizer additives.

PEVA (10.6% of tested gaskets): Polyethylene vinyl acetate is a relatively safe choice for cap gaskets.

Polyethylene (2.9% of tested gaskets): Polyethylene is a relatively safe choice for cap gaskets.

PDMS (0.4% of tested gaskets): Polydimethylsiloxane, also called "silicone" plastic, was found rarely in cap gaskets and most often in plastic caps.

Polypropylene (0.4% of tested gaskets): Polypropylene was rare in cap gaskets. It is a relatively safe choice.

Mix of PE and PDMS (0.4% of tested gaskets).             

Plasticizers Detected (in PVC only)

Phthalates (34.3% of all; 51.7% of PVC gaskets): Ortho-phthalate esters are a class of plasticizer that pose significant health hazards.

ESBO (23.0% of all; 35.0% of PVC gaskets): Epoxidized soybean oil is commonly used to soften PVC used in the gaskets for lug-style caps and is very common in the lids of baby food jars. It is known to migrate into food, typically at levels below regulatory thresholds.

DOTP (6.6% of all; 10.0% of PVC gaskets): Dioctyl terephthalate is also known as di(ethylhexyl)terephthalate, abbreviated DEHT. It is a common and safer alternative to phthalates, although some data gaps regarding endocrine disruption remain.

Adipate (1.5% of all; 2.2% of PVC gaskets): Adipates are a class of alternative plasticizer with a better hazard profile than phthalates. DEHA, or di(ethylhexyl)adipate, was found in some cap gaskets in our study.

ATBC (0.7% of all; 1.1% of PVC gaskets): Acetyl tributyl citrate is an alternative plasticizer with a better hazard profile than phthalates.