Harmful Substances in Plastics
Victor O. Sheftel 2000
Introduction to his book "Indirect Food Additives and Polymers: Migration and Toxicology" 2000
Dr. Victor O. Sheftel is the Chief Environmental Toxicologist of the Ministry of Health, State of Israel, Jerusalem.
Dr. Sheftel received his M.D. degree at the Kiyv Medical Institute, Ukraine. By 1966 he made a doctorate (PhD in hygiene) and after this he was a senior researcher and a team manager at the All-Union Research Institute of Hygiene and Toxicology of Pesticides, Polymers and Plastic Materials (Kiyv, USSR). There he engaged in development of the modern toxicology of plastics and was a leading scientist in this field in Russia.
By 1978 he earned a post-doctoral degree (Doctor of Sciences, equivalent to professor) from the Sysin Research Institute of Environmental Hygiene (Moscow) in the Academy of Medical Sciences of the former USSR.
Dr. Sheftel has published 14 monographs and over 50 scientific papers (in the U.S., Great Britain, Russia, and China), mainly related to the toxicological evaluation of food- and water-contact materials and contaminants, the methodology of regulatory process in this realm, and other actual problems of general and applied toxicology. He has recommended a differential approach to the choice of criteria of reliability in toxicological studies (1992).
In 1990 Dr. Sheftel emigrated to Israel. At present, he deals mainly with the problems of drinking water quality and the development of a unique database of toxic effects of food- and water-contact materials.
As it stands today, it is impossible not only during production but also in everyday life to prevent the population from coming into contact with plastics. In any case, approximately 70 to 80% of food is packaged in various polymeric materials (PM).
Unfortunately, PM appear to be a potential source of the release of chemicals into the environment: they may have a variety of effects on human health as a consequence of' water, air, or skin contamination. The principal hazardous factor associated with the use of PM remains the possible contamination of food.
The absence of acute poisonings with fatal outcome does not prove the safety of synthetic packaging materials. Nevertheless, it must be remembered that we do not completely realize the real contribution of PM to the actual contamination of food.
It is true that pM ingredients do not act like pesticides (or a variety of other highly bioactive substances), and one can hardly expect immediate and pronounced clinical manifestations of their toxic action. The occurrence of acute toxicity due to pM used in contact with food and drinking water is most unlikely, since only trace quantities of toxic substances are likely to migrate. However, it would be a great underestimation to consider pM ingredients (indirect food additives) as presenting no real public health threat. It is well known that chronic effects may be observed as the result of repeated ingestion of' a number of small doses, each in itself insufficient to cause an immediate acute reaction but in the long term having a cumulative toxic effect. Thus, pM and other widely used chemicals have introduced a problem of protracted action of low concentrations of chemicals upon human health.
PM as well as many other materials are likely to be a depot of organic (sometimes also inorganic) compounds which, during the lifespan, are discharged into the environment, polluting various contact media such as food, water, air, skin surface, etc. (whenever food or drinks contact a solid surface, the resulting food contaminants could be called migrants). PM ingredients have a potential to migrate from the packaging or wrapping materials into the food in measurable amounts and thereby become indirect food additives (though these substances are never deliberately added to foods!). These migrants arc appropriately regulated in Parts 175 through 179 of Volume 21 of the Code of Federal Regulations where appropriate regulations covering indirect food additives occupy more than 265 pages. US CFR lays out general safety requirements for all indirect food additives covering the safe use of food-contact pM. Under the Food, Drug, and Cosmetic Act (FD&CA), an industry must show that a new 1'M having indirect contact with food, such as packaging material or can coating material, is safe for the intended use.
The Food and Drug Administration (FDA) assesses the initial safety of packaging materials for food contact. If substances are shown to migrate from the packaging into the food, toxicological studies are conducted in order to establish safety standards. Appropriate toxicological information along with the results of animal toxicity tests is submitted to the Food and Drug Administration for review as a part of a Food Additive Petition.
Thus, testing migration of constituents from PM and articles and toxicological evaluation of these extractable contaminants is essential in selecting materials for use in contact with food by verifying that even if migration occurs, there would be no known toxic hazard to the consumer. EU food legislation as well as FDA requirements underscores that verification of compliance of migration into foodstuffs with the migration limits must be carried out under the most extreme conditions of time and temperature foreseeable in actual use. PM and articles which fail to meet the requisite standards shall not be used in the course of storage, preparation, packing, sale or serving of food for human consumption.
It is known that food contact applications are numerous and include the use of plastics, cellulose, paper, aluminum foil, glass, rubber, printing inks, and coatings. PM, in particular, are widely used in contact with foodstuffs, namely, in food processing equipment, food utensils, and as food packaging.
PM are manufactured by polymerization or polycondensation of one or more monomers and/or other starting substances. As basic polymers, the following compounds are most widely used (21 CFR):
Vinyl resinous substances (Polyvinyl acetate, Polyvinyl alcohol, Polyvinyl butyral, Polyvinyl chloride, Polyvinyl formal, Polyvinylidene chloride, Polyvinyl pyrrolidone, Polyvinyl stearate, a number of Polyvinyl chloride copolymers);
Styrene polymers (Polystyrene, -Methylstyrene polymer, Styrene copolymers with acrylonitrile and -Methylstyrene);
Polyethylene and its copolymers;
Polypropylene and its copolymers;
- Acrylics and their copolymers;
Elastomers (Butadiene-acrylonitrile copolymer, Butadiene-acrylonitrile-styrene copolymer. Butadiene-styrene copolymer, Butyl rubber, Chlorinated rubber, 2-Chloro-1,3-butadiene/ neoprene, Natural rubber. Polyisobutylene, Rubber hydrochloride, Styrene- isobutylene copolymer).
In the manufacture of PM, numerous additives are used depending on the type of produced polymer. These additives include plasticizers, antioxidants, catalysts, suspension and emulsifying agents, stabilizers and polymerization inhibitors, pigments, fillers, etc. These additives are bound either chemically or physically into the polymer and may be present in their original or an altered form. In addition. the polymerization process may leave trace quantities of residual monomer or low-molecular-mass polymer in the PM. It is therefore necessary to specify the purity of the polymer to be used in the preparation of pM intended for food and/or drinking water contact use. Subsequently, PM contain a spectrum of polymers of different molecular mass, side effects and residues of all the auxiliary chemicals.
The migration potency of PM depends predominantly on the presence of unpolymerized monomers. residues of additives, reaction and transformation products of starting ingredients, and destruction products (about 3,000 PM components are listed by EU Commission as conceivable migrants). With time, the structure of PM could be changed as a result of destruction and aging processes, and of leaching or evaporation of pM ingredients or of their interaction products.
All additives are liable to break down during processing; some, such as antioxidants, are intended to do so to fulfill their function. A number of PM release not only additives into the environment but also monomers that could be present in pM as residues or have appeared as a result of destructive processes. As a matter of fact, pM appears to be a complicated and mobile system that is more or less stable, depending on its age, manufacture technology, and conditions of actual use.
Potential migrants encompass a large group of substances with differing molecular mass and physical properties. In some cases it is impossible to assess accurate amounts of ingredients migrating from PM into contact media. Migration levels can be considerably affected by destruction processes aging of plastics, and by the presence of unbound low-molecular-mass compounds. The extent to which migration occurs will depend upon such factors as the contact area, the rate of transfer, the type of PM, the temperature, and the contact time. The migration of substances from PM into food is also related to the type of food packaged in PM. Alcoholic beverages and edible fats and oils will extract substances more readily than dry food such as cereals.
The high-molecular-mass polymer itself does not pose a toxic hazard, being inert and essentially insoluble in food. Monomers are very reactive and biologically aggressive. Some of' them have been shown to cause allergic effects, to damage the liver and reproductive functions, and to induce carcinogenicity.
Plasticizers are used to assist processing and impart flexibility to plastics. They intersperse around the polymer molecules and prevent them from bonding to each other so tightly that they form a rigid substance. Plasticizers may lower the melting point of the plastic, and many have relatively low melting points themselves. Plasticizers can be present in food packaging materials in significant amounts and have the potential to migrate into food. The migration of plasticizers can be aggravated by heat and by the presence of a food into which the plasticizing chemical will dissolve (for example, oil, acid or alcohol).
Migration increases with length of contact time and temperature, and levels of migration are highest when there is direct contact between PM and foods with high fat content at the surface.
In the food packaging and food processing industries the plasticizers most often used arc di(2-ethylhexyl) adipate (DEHA), polymeric species, epoxidized soybean oil (ESBO) and acetyl tributyl citrate (ATBC) in packaging films and di(-2ethylhexyl) phthalate (DEHP), diisodecyl phthalate. and diisooctyl phthalate in closure seals for containers.
Those currently used in polyvinyl chloride (PVC) include phthalates, phosphates, aliphatic dibasic acid esters, and polyesters. The plasticizers most widely used in PVC for food contact applications are DEHA, DEHP, and polymeric species. Different plastics may contain different levels of phthalate plasticizers. ATBC is commonly used in vinylidene chloride copolymers; ESBO is also used in polyvinyl chloride and vinylidene chloride copolymer films.
The main function of stabilizers is to prevent destruction of PM when it is heated or exposed to ultraviolet radiation. Antioxidants are introduced to avoid undesirable oxidation. Stabilizers and antioxidants are not bound to polymeric macromolecules and could be easily leached into contact liquid media. Thermal stabilizers contribute to food contamination with their own residues.
Catalysts and hardeners are usually present in the finished product, they are used to aid in the polymer formation reaction. Catalysts of polycondensation (e.g., alkali and acids) seem to be less aggressive in comparison with catalysts used in polymerization.
A number of PM ingredients listed for use in U.S. and EU Regulations have been shown to migrate into the foodstuffs and simulant media under ordinary conditions at hazardous concentrations. When evaluating safety of a food-contact article it is often impossible to perform worst-case calculations (ie . based on 100% migration) to demonstrate that the regulatory limits will not be exceeded under the intended conditions of use. In such cases, migration testing is required to establish compliance with specific migration limits. Modern chromatography techniques including capillary gas chromatography and high-performance liquid chromatography (HPLC) together with other highly selective detectors (FID, Electron capture, Nitrogen-phosphorous, MS for GC, UV, electrochemical, fluorescent, Mass Spectrometry for HPLC) ensure separation, identification, and precise determination of the majority of toxic substances migrating from plastics to contact media at the levels required for safety evaluation.
Advances in analytical chemistry have made it possible in many cases to decode the complex set of chemicals released from PM. Analytical chemistry has gradually become a method of routine monitoring the safety properties of plastics and can estimate or measure directly PM contamination.
Thus far, the United States and the European Union have developed procedures to assure the public that the food packaging materials in use are as safe as they can be. The majority of these Regulations is a listing of substances that can be used in food-contact applications.
In order to prevent or eliminate the risk of health hazard to a population exposed to PM, U.S. CFR lays out general safety requirements for all indirect food additives covering the safe use of food-contact materials. It regulates the use of these materials and articles in contact with food in accordance with the prescribed conditions. The FDA regulations are not conventional regulations prescribing a course of action, and do not govern manufacturing process, catalysts, or reaction control agents.
EU Legislation on PM and articles intended to come in contact with foodstuffs presents a strict list system according to which all substances used in the manufacture of a food packaging material will eventually have to appear and is published by the European Union authorities. EU legislation prescribes an overall migration limit in food and food simulant media and, in some cases, specific migration limits and maximum permitted quantities of the residual substance in pM and articles. This Legislation includes provisions applicable when checking migration limits, and a positive list of monomers and other starting substances that may be used in the manufacture of materials and articles intended to conic into contact with foodstuffs.
Neither the CFR nor the EU legislation distinctly explains why they are publishing records of those PM ingredients for which there are no established specific migration limits. The positive lists (lists of approved PM ingredients) produce a certain unfavorable effect, creating an illusion that the PM composition of listed ingredients is safe. This illusion, shared by many, is erroneous. Sometimes the legislator must admit reluctantly that "such a list would offer no tangible benefit (bolded by author -V. S.) in terms of safeguarding human health" (Commission Directive 90/128/EEC). Then what benefit can it offer? Positive lists neither contribute to the problem nor help with the solution. Regulators in many countries including the U.S., Canada, Denmark, and Switzerland believe that positive lists appear to be the wrong approach and that we would be better off using a case-by-case system when a clearance is granted only on the basis of the specific conditions and is applicable only to the stated conditions of use (L. Borodinsky, 1997).
Some approaches based on an artificial hypothesis aimed at adopting a level of toxicological insignificance, have been suggested in order to avoid toxicity testing of all migrants that might be present (the overall migration test and the so-called threshold of regulation). Unfortunately, so far there is little scope for these approaches since each such recommendation needs to have a firm experimental base or thorough scanning of the existing literature on migration and toxicity. Nevertheless, in the U.S., a threshold of regulation set at 0.5 ppb has been adopted by the FDA for chemicals used in food packaging materials.
Successful regulation of food-contact materials seems to be possible with the help of the newest analytical methods and achievements of modem experimental and regulatory toxicology. All relevant information should be integrated into the risk assessment process on a case-by-case basis. A correct strategy in toxicology of plastics in many cases comprises precise chemical analysis of potential contamination of food, water, or simulant media under specified conditions. Obtained in this way, analytical results must be compared with available toxicology data and safety standards.
In the Author's opinion (and those who have labored long in the area will notice this), this handbook provides an opportunity to make an advancement in the regulatory toxicology of plastics, specifically to implement the modern toxicology approach instead of the application of an out-of-date limit of total extractives and positive lists.
If you have come to this page from an outside location click here to get back to mindfully.org