Plastic Food Container Safety

Abstract

Plastic containers are a huge part of modern life. Perhaps their use is nowhere more significant than in the storage of foods. Stored food comes in contact with plastics, plasticizers, intentional additives, and inadvertent contaminants. Plastic food containers are asserted to be safe, and the resin used in their manufacture is assigned a number to help understand their recyclability. These containers are not totally inert and leach varying levels of metals and chemicals into the foods they store—especially if subjected to elevated temperatures. The safest containers appear to be those made from resins with the ID numbers 2, 4 (except food wraps), and 5. This editorial looks at the various types of plastics used in the manufacture of food containers, their typical contaminants, their toxicity, and the median amount of migration of contaminants into food.

Introduction

One of the most common questions I receive after lecturing on the health-damaging effects of plasticizers is, “Everything is in plastic! Are any of them safe?” While plastics have indeed proven hugely useful in many applications, ever growing research shows that the body load of most plastic components directly correlates with many chronic diseases. Research is now eliciting mechanisms of damage. The research is also showing that the problem is more than just the plasticizers in food wraps and storage containers—many other chemicals found in food containers can contaminate the food. This editorial looks at the health risks of commonly used plastics in storage containers. This is not a review of toxins in all forms of food packaging that may contain toxins, such as per- and polyfluoroalkyl substances (PFAS) in cardboard food plates and microwave pizza, and bisphenols in can lining.

Global plastics production has reached approximately 500 million metric tons a year.¹ Since approximately 40% of this plastic is used for packaging (not just food containers), the high levels in humans of the chemicals associated with plastics is not surprising. Determining how much of these chemicals leak into food is challenging, since there is a huge amount of research, much of it contradictory.

The Types of Plastics Used in Food Containers

The presence of toxic chemicals in food containers is both intentional and inadvertent due to contamination. While almost everyone is aware of the problem of bisphenols, phthalates, and PFAS, one comprehensive study of plastic packaging identified 906 chemicals that have been assessed for toxicity and possibly another 3377 with unknown toxicity.² The authors of the study assert that 148 of the 906 have significant human toxicity. Table 1 lists the functional categories and names of the most common chemical classes in plastic packaging.

Table 1.

The Most Common Chemical Groups in Food Containers²

Function	Chemical group
Accelerator	Dithiocarbamate, thiazole, thiuram
Biocide	Carbamate, phenolic, metal-containing, paraben
Colorant	Azo dye, pigment
Fire retardant	Boron, organophosphate
Plasticizer	Chlorinated paraffin, phthalate, bisphenols (added by Editor)
Foaming	Alkane
Monomer or intermediate	Acrylic, amine, bisphenol, zinc-containing
Solvent	Limonene, naphtha-related
Stabilizer	Tin, organophosphate, hindered phenol, benzotriazol
Surfactant	Nonylphenol, octylphenol, amines, PFAS

As I read the appalling list of chemicals found in containers that leak into food, I am struck by several observations:

1. We buy organic foods to avoid foods contaminated with chemicals, but many chemicals, such as the highly neurotoxic organophosphates, get into the food anyway from the packaging.

2. The list of chemicals in the groups is very long, and many of the chemicals have had little to no research done on them.

3. There is no research that looks at the cumulative or synergistic effects of just a few, much less the whole list, of almost 1000 chemicals that are documented to be in most food containers.

The unavoidable conclusion is that plastic food containers can be contaminated. The questions then are, How contaminated are the various types of plastic food containers? How much of these contaminants leak into the food? How can we avoid as many of the contaminants as reasonably possible?

Federal Guidance

The federal government has produced charts to help educate consumers on the types of plastics used for storage and their relative toxicity.

Conveniently, plastic containers have a number on them to help in their recycling, which lets us know which chemical they are made of, as shown in Table 2. Note that all of these are FDA approved for use in food storage with the implication they are safe. Note also that there are more than 7 resin ID codes, but the others are not common and are not addressed here.

Table 2.

Chemical Composition of Plastic Food Containers

Resin No.	Plastic name	Abbreviation	Example use
1	Polyethylene terephthalate	PETE/PET	To store water, soda, detergents, peanut butter
2	High-density polyethylene	HDPE	To store milk, water, detergents, shampoo
3	Polyvinyl chloride	PVC	Clear food packaging, cling wrap, plastic squeeze bottles, vinyl pipes, shower curtains
4	Low-density polyethylene	LDPE	To store bread, frozen food
5	Polypropylene	PP	To store yogurt, cream cheese, maple syrup; prescription bottles
6	Polystyrene	PS	Disposable cutlery, egg cartons
7	Polycarbonate, bioplastic polylactide, or a combination	Other	Lids, medical storage, sports drinks, large water jugs

Independent Review of Plastic Container Safety

While these plastics are asserted to be safe, the high levels of plasticizers and other chemicals found in the human population means we need to determine where they are coming from. The logical questions are as follows:

1. What are the toxicities of the plastics used in food containers?

2. Do the other chemicals in the containers leak into the foods?

3. How much of these chemicals is leaked into the foods?

As I looked at the research, several important modifying factors became clear:

• Chemical characteristics of the stored food—water or oil, alkaline or acid, alcohol

• Single use or reusable containers

• Virgin or recycled plastic

• Presence of coloring agents

• Exposure to elevated temperatures

• Quality of the manufacturing techniques

One very interesting study did microassays to assess several measures of toxicity of plastic consumer products—both those used for food storage and those for other uses.³ The researchers found that 74% of the 34 plastic extracts contained chemicals triggering at least one toxic end point, including baseline toxicity (62%), oxidative stress (41%), cytotoxicity (32%), estrogenicity (12%), and antiandrogenicity (27%). Figure 1 summarizes their findings. It is important to note that this figure does not differentiate between consumer plastics, food-grade plastics, and food-safe plastics. Despite the lack of distinction, this study provides useful insight into the toxicities of most of the plastics and contaminants in food containers. Food should NEVER be stored in plastics that have not been specifically determined to be safe for this use.

Figure 1.

Toxicity of Commonly Used Plastics³

While it would be nice to simply use these results to assess the toxicity of plastic food containers, as mentioned above, the study included food containers as well as other plastic products and did not address the significant problem of inconsistent manufacturing processes and the type of food stored in a specific type of plastic. Nonetheless, this study provides useful insights.

ID 1. Polyethylene Terephthalate (PETE or PET)

Polyethylene terephthalate is a thermoplastic polymer resin of the polyester family. It is widely used in clothing, containers for liquids and foods, thermoforming for manufacturing, and many other industrial uses. As can be seen in Figure 1, it has very low inherent toxicity.

A big challenge with PETE is that it is not a single molecule and, in contact with food, is chemically modified. PETE oligomers are a class of substances with unlinked monomers, variable chain lengths, linear or branched chains, and incomplete polymerization and suffer thermal or hydrolytic degradation of polymer chains during manufacture and after contact with food. PETE/PET containers do indeed contain a large number of chemicals other than polyethylene terephthalate.⁴ Many studies have looked at PETE migration into food. For example, one study looked at the migration of 3 common PETE monomers into food by testing the migration of water, 4% acetic acid, 20% alcohol, and n-heptane from 56 containers collected from open markets.⁵ The researchers estimate an insignificant 0.0384 mg/kg body weight for each of the 3 monomers. However, when other molecules are measured, the picture becomes more complicated and worrisome. A review study compiled the available data from many studies looking at migration of chemicals into water.⁶ Table 3 summarizes their results. The studies included migration at refrigeration temperature, room temperature, and temperatures as high as 80°C. Migration increased with temperature and carbonation. I find it particularly interesting that none of the metals and chemicals found were the plastics that make the containers; that is, these are intentional additives and unintentional contaminants.

Table 3.

Mean Concentrations of Metals and Chemicals Migrating into Water Stored in PETE Containers⁴

Antimony	0.003-0.4 μg/L at or below room temperature; 3.5 μg/L at 40°C
Formaldehyde	1.0-60.0 μg/L
Acetaldehyde	1.4-70.0 μg/L
Glyoxal	<0.05-5.9 μg/L
Acetone	5.1-125.6 μg/L (concentration range)
Phthalates (those at very low levels not included)
DEP (Diethyl phthalate)	0.08-0.21 μg/L
DBP (Dibutyl phthalate)	0.04-50 μg/L

Bottom line: Marginally safe. Most PETE containers are likely safe. However, inconsistent manufacturing, exposure to elevated temperatures, and the many possible chemical contaminants make the safety of these kinds of containers unpredictable.

ID 2. High-Density Polyethylene (HDPE)

High-density polyethylene is a thermoplastic polymer of the monomer ethylene. As can be seen in Figure 1, it has very low inherent toxicity. It is used in the production of plastic bottles, corrosion-resistant piping, and plastic lumber. While there is contamination from these types of plastic containers, the amount appears small, and the migration of HDPE into food is limited.⁷ Another problem is possible PFAS. Perfluorinated compounds can be added to HDPE containers to make them more chemically resistant. The EPA published concerns that some of these can leak into food.⁸ Frustratingly, the quantitative research is very limited.

Bottom line: Safe. However, not safe to reuse for food if HDPE containers have been used to store nonfood items and not safe if PFAS are used in their manufacturing.

ID 3. Polyvinyl Chloride (PVC)

A key problem with PVC food containers is that they contain phthalates. Body load of phthalates directly correlates with many chronic diseases such as diabetes, infertility, attention deficit hyperactivity disorder, and loss of IQ in children.⁹ Consumer Reports found high levels of phthalates in food.¹⁰ While they did not differentiate between the types of plastic containers, their data clearly show the highest levels of phthalates in fast foods and those foods stored in plastic containers. A review article asserted that the amount of phthalates in PVC, PETE, polyvinyl acetate (PVA), and polyethylene food containers ranges from 10% to 60%!¹¹ The FDA conducted an extensive review of phthalates in PVC packaging and determined the amount ranges from 1% to 53% (!) and that some phthalates do indeed migrate into foods.¹²

Bottom line: Avoid. These PVC containers contain varying levels of phthalates, and the phthalates migrate into food.

ID 4. Low-Density Polyethylene (LDPE)

Low-density polyethylene is a thermoplastic polymer of ethylene. It is flexible, tough, resistant to chemicals, and widely used in food storage. While this type of plastic has low inherent toxicity, some forms have contaminants, and LDPEs are a major source of microplastics.¹³ (I’m working on a microplastics editorial.) LDPE containers appear to be safe.¹⁴ However, polyethylene wrap film contains 1 to 500 ng/g of phthalates, and these phthalates leach into food.¹⁵

Bottom line: Safe, except when used as food wrap.

ID 5. Polypropylene (PP)

Polypropylene is a thermoplastic made by polymerization of propylene. It is part of a group of molecules defined as polyolefins. As with the other resins used in food container production, it has low toxicity but can also be contaminated with a wide range of chemicals. As with other plastic containers, extremes of temperature (both hot and cold) increase migration of PP contaminants into food.¹⁶ Research is emerging that microwaving foods stored in PP results in both migration of chemicals into foods and changes to the chemical structure of food components.¹⁷

Bottom line: Safe, but not when heated.

ID 6. Polystyrene (PS)

Polystyrene is a polymer of styrene. Polystyrene is one of the most widely used plastics, with several million tons produced every year. Styrene is considered a possible carcinogen.¹⁸ However, carcinogenesis is likely only a problem in industrial settings. Polystyrene is considered safe for food use when it is a solid material. However, heating can cause chemicals to leach from PS foam and into food. Food in PS containers should not be microwaved, unless the containers are specifically designated as microwave safe. Dairy products are often stored in PS containers. Research has shown styrene clearly leaks into food in proportion to length of storage and, to a lesser degree, the fat content of the food.¹⁹

Bottom line: Marginally safe. Do not heat.

ID 7. Polycarbonate, Bioplastic Polylactide, or Combination (Other)

Bisphenol A (BPA) release from polycarbonate baby bottles caused considerable public attention in the recent past.²⁰ The uproar resulted in removal of BPA from most baby bottles. Unfortunately, some manufacturers simply replaced BPA with other bisphenols.²¹ Bioplastic substitutes such as polylactide (PLA) are intriguing. However, Figure 1 shows a lot of toxicity for PLA. The research is still emerging on these materials and is showing encouraging and worrisome results.

Bottom line: Unpredictable. Not recommended.

More Issues

Heating and Time

Considerable research shows that the longer a food is in a container and the more the food is heated while in the container the higher its levels of contaminants, such as phthalates. This effect depends upon the container type and the food.²² The clear message is that if the only way to obtain a food is plastic packaging then repackage it in glass or other safe containers as soon as possible,

Recycled Plastics

Obviously, recycling of plastics is extremely important for the environment. However, using recycled plastics for food containers is problematic. It has been asserted that recycling plastics has a net human-health benefit.²³ However, that does not mean recycled plastics should be used in food containers. Unfortunately, recycling increases the risk of contamination. Greenpeace published a comprehensive report on the dangers of recycled plastics.²⁴

Food-Safe vs. Food-Grade

Although food-safe and food-grade tend to be used interchangeably, they are two different terms with meaningful differences. Food-grade means safe when in contact with food. Food-safe, is a more limited ranking as they are only safe to contain specific foods. For example, a plastic safe for a dried food may not be safe for oily or liquid foods.

Microplastics

Another issue is leakage of microplastics into food from plastic food containers. An recent, and worrisome, study in NEJM found microplastics in carotid plaques.²⁵ Polyethylene was detected in carotid artery plaque of 58.4% of patients with a mean level of 21.7.5 μg per milligram of plaque and 12.1% also had polyvinyl chloride with a mean level of 5.24 μg per milligram of plaque. They followed these patients for a mean of 34 months and found that those with microplastics in their atheroma had 4.54 increased risk of a composite of myocardial infarction, stroke, or death from any cause.

Conclusion

This is one of the most frustrating editorials I have written, The huge inconsistency between the many studies results in my not being able to reach the level of certainty I normally try to attain. Nonetheless, I think there is useful conclusions and important guidance we can provide our patients.

1. The specific plastics that define these containers are relatively inert and have minuscule leakage into the foods—if properly manufactured.

2. However, there appears to be substantial variation in manufacturing quality, and the containers are not only made of their defined plastics—they also contain a widely varying number of intentional and inadvertent chemicals and metals. While some of the chemicals in plastic containers are nontoxic, many have well documented toxicity in humans, and many more have undetermined toxicity. Varying amounts of these chemicals inconsistently leak into the foods, depending upon plastic type, manufacturing technique, temperature exposure, length of storage, and chemical composition of the food.

3. The amount of chemicals leached into foods increased greatly if the containers are heated

4. There is a high probability that plastic food containers are a significant source of the high levels of plasticizers and other chemicals found in humans.

As I looked at the research, I saw a pattern of 2 distinct research groups: those expressing a high level of concern about the many chemicals in food packaging and their toxicity, and the other asserting that only small amounts of the chemical contaminants migrate into the foods, and therefore, the chemicals are not a problem. Most of the FDA guidelines I looked at typically assert these chemicals are safe, because the amount of chemicals leached into food is small and below their defined lowest level of toxicity.

When properly manufactured, protected from heat, and containing the appropriate foods for the type of plastic, these storage containers are reasonably safe. Unfortunately, these criteria are often, and unpredictably, not met. A problem with the assertion that the leakage levels are low and below the toxic level—as is typically asserted for many toxins—is that researchers do not consider the additive effects of the many other exposures, the huge variation in individual susceptibility to being damaged by specific toxins and the years-long cumulative effects. If these storage containers are so safe, why do we see the chemicals found in these containers in humans at high-enough levels to cause chronic disease?

Guidance

Avoid plastic containers as much as possible. My ranking (and only if food-grade) of probability of leaching chemicals into the foods they contain:

Lowest: 2 (HDPE), 4 (LDPE) solid containers, 5 (PP) Intermediate: 1 (PETE/PET), 6 (PS) Highest: 3 (PVC), 4 (LDPE) food wrap, 6 (PS) when heated, 7 (Other)

Biography

Joseph Pizzorno, ND, Editor in Chief, IMCJ; co-author, Textbook of Natural Medicine; Founding President, Bastyr University; Member, Board of Directors, Institute for Functional Medicine.