Plastic’s toxic trail: What are these polymers and what do they contain?

Between 2021 and 2024, the number of chemicals reported to be used by the plastic industry has gone up from around 10,000 to 16,000

By Siddharth Ghanshyam Singh
Published: Friday 26 April 2024
A hand sifting through a pile of clear plastic resin pellets. Photo: iStock

Plastic is indispensable for us today. Or so we are told. But what, after all, is it?

In simple terms, all plastics are based on polymers—large molecules formed by the joining of monomers. During polymerisation, mixtures of different monomers are often used to make different polymers.

For example the PET bottle used to package beverages like mineral water bottle, juices and softdrinks is a co-polymer made from Purified terephthalic acid (PTA) and Monoethylene Glycol (MEG) — both of which are high volume products made in the petrochemical industry.

Additional chemicals used in polymerisation processes include initiators, catalysts, and solvents. Virgin plastics are typically produced in granular or pellet form, also called ‘nurdles’. Other forms of virgin polymers may include powder and flakes.

With more than 98 per cent manufactured from the fossil fuel industry, plastics comprise of a carbon-based backbone and thousands of chemicals that are incorporated in the polymer to impart properties such as durability, flexibility, stability, colour, flame retardation and ultraviolet protection.


The monomer that maybe used to make a rigid blue plastic, can also be used to manufacture a flexible white plastic. At the molecular level, the hydrocarbon chain is the same. However, the chemicals used during the production change properties like rigidity, thickness, colour, water repellence, etc. of the polymer.

As per a research published in the journal Environmental Science and Research, a little over 10,500 chemicals are used for making plastics. In addition to monomers, two other classes of chemicals that are extensively used to manufacture plastics are processing aids (catalysts, lubricants, solvents, etc.) and additives (colorants, fillers, etc.).

Source: “Deep dive into plastic monomers, additives and processing aids”, Environmental Science and  Technology, 2021

Overall, 55 per cent of the substances identified are categorised as plastics additives, 39 per cent as processing aids, and 24 per cent as monomers, with significant overlaps between these three categories. In addition, due to a lack of information, 30 per cent of the substances remain non-categorisable regarding their functions.

Year after year, the scientific community has been advancing in this field and putting out updated numbers. Between 2021 and 2024, the number of chemicals reported to be used by the plastic industry has gone up from around 10,000 to 16,000.

According to a 2024 research conducted by Plastchem, more than 4,200 plastic chemicals are ‘of concern’ because they are persistent, bioaccumulative, mobile, and/or toxic (PBMT).

It also notes strikingly that hazard information is lacking for over 10,000 chemicals. Around 25 per cent of the known plastic chemicals lack basic information on their identity, while a mere 6 per cent of these chemicals are currently subject to international regulation through multilateral environmental agreements like the Rotterdam Convention that mandates a prior informed consent (PIC) on trading of some chemicals, Stockholm Convention on persistent organic pollutant (POP) and the Montreal Protocol on ozone-depleting substances.

Several experts believe that the actual number of chemicals used by the plastic industry across the life cycle could be somewhere around 25,000 or even more. This uncertainty is also because most companies do not reveal their recipes for making plastics to protect their trade secrets.

Many of these added chemicals are highly toxic. They include carcinogens, neurotoxicants and endocrine disruptors such as phthalates, bisphenols, per- and poly-fluoroalkyl substances (PFAS), brominated flame retardants, and organophosphate flame retardants. They are integral components of plastic and are responsible for many of the harms caused by plastics to human health and the environment.

Common additives like plasticizers and phthalates are not typically bound to the polymer matrix and leach out from the polymer as mobile components thus entering the human body through various routes such as inhalation, ingestion, and dermal contact.

Every time a plastic in any form (pellets, films, etc.) is exposed to processing (pellet to product, waste recycling, incineration, etc), it undergoes a thermal cycle. At every thermal cycle, non-intentionally added substances (NIAS) are released and become a part of the polymer.

Transparency regarding the chemicals utilised in manufacturing diverse types of polymers and their potential effects on human health and the environment is urgently required. Implementing a labeling system on plastic products to convey the impact of chemicals could be instrumental in addressing concerns related to hazardous substances.

This is the third in a 5-part series. Read the first, secondfourth and fifth parts.

Subscribe to Daily Newsletter :

Comments are moderated and will be published only after the site moderator’s approval. Please use a genuine email ID and provide your name. Selected comments may also be used in the ‘Letters’ section of the Down To Earth print edition.