The Chemistry of Microplastics

Microplastics have gained significant attention due to their contamination of marine environments and potential harm to wildlife. Defined as plastic fragments smaller than 5 mm, research has been conducted for over two decades. A specific subset, known as nanoplastics—particles 1 micron or smaller—raises particular concern. These tiny particles can float in water, remaining suspended rather than sinking, thus potentially disrupting the behavior of small marine organisms. A major hurdle in understanding microplastics is the sheer variety of plastics; laboratory findings may not accurately reflect real-world conditions. The diverse nature of plastics complicates waste management efforts.

Plastics in Use Today

Many of the plastics we encounter are synthetic, produced through industrial processes rather than sourced from natural materials like rubber or tortoiseshell. Chemically, plastics consist of long chains of atoms, created from repeated units known as monomers. Imagine a string of beads, where different beads represent different building blocks, resulting in varied plastic properties. Typically, the polymer backbone is carbon-based, derived from fossil fuels, with additional elements altering its characteristics. Additives are often included to change color or enhance performance, adding to the recycling complexity.

Plastics can be categorized into two primary types: thermosets and thermoplastics. Thermosets do not undergo recycling but will eventually decompose under sunlight or heat, or when subjected to specific bacteria. Polyethylene terephthalate (PET), a common material for plastic bottles, is the most recycled thermoplastic. Despite its prevalence, PET's recycling isn't simpler than other plastics; it’s merely more common due to its cost-effectiveness. The chemical structure of PET is relatively intricate, featuring chains of carbon and oxygen atoms. In contrast, polyethylene (PE) has a straightforward hydrocarbon chain and is available in various densities. Interestingly, the high-density version (HDPE) is utilized for items like flimsy plastic bags and milk bottles. Polyvinyl chloride (PVC), another thermoplastic, is typically rigid and used in applications such as piping and window frames.

Barriers to Recycling

Although thermoplastics should theoretically be easy to recycle, logistical challenges complicate the process. Estimates suggest that only 16% of plastics are recycled, with the remainder ending up in landfills, incinerators, or being improperly discarded. Factors like problematic additives, lack of recycling infrastructure, and high costs can hinder recycling efforts. In the UK, many single-use plastics bear a triangular recycling symbol accompanied by a number indicating the plastic type. Local recycling programs typically accept only certain types; for instance, Manchester’s municipal scheme only processes numbers 1 and 2, even though numbers 3–6 are thermoplastics that could be recycled. This limitation likely stems from the absence of recycling facilities for these types. Additionally, lightweight plastics, like film and plastic bags, can jam recycling machines, while heavier variants are easier to manage. Some plastics, bonded with materials like cardboard in coffee cups, are also challenging to recycle.

A significant amount of plastic waste from the UK and USA is sent to countries like China and India for processing, often due to lower labor costs. While sorting waste in these regions can be beneficial, the environmental cost of transporting millions of tonnes of plastic waste raises concerns about associated greenhouse gas emissions.

The Benefits of Plastic

Despite the challenges, plastic has numerous advantages. Its lightweight nature makes it easier to transport compared to other packaging materials, which can lead to reduced greenhouse gas emissions. Furthermore, plastic packaging can extend the shelf life of food by maintaining a protective atmosphere. In healthcare, plastic plays a vital role in personal protective equipment and sterile packaging for medical devices. For instance, when conducting a COVID-19 lateral flow test, the cleanliness of the equipment is paramount. Additionally, plastic is utilized in constructing double-glazed window frames, enhancing insulation compared to older models.

The water industry also relies heavily on plastic, employing large underground pipes to deliver clean water and remove sewage. These pipes, manufactured to high standards, have been in service for over 80 years. However, plastic pollution remains an issue in this sector. Non-water industry plastics can break down and infiltrate water treatment systems, often originating from unexpected sources like roadway paint. While filters are employed to remove plastics from drinking water, they do not address plastics in sludge, which complicates potential uses for fertilizer or as feedstock for anaerobic digestion.

Rethinking Plastic Usage

The core issue is not the existence of plastic itself but rather the manner in which we utilize it. Waste management would improve significantly if packaging were not composed of mixed materials, such as cardboard fused with paper or different types of plastics. Some researchers are investigating methods to create plastics with reduced feedstock.

To enhance recycling efforts, improved infrastructure is essential. Currently, users must separately sort various plastics while also locating appropriate recycling facilities. Economic factors often dictate that sending plastic to landfills is cheaper than recycling it, suggesting a need for initiatives that incentivize recycling, perhaps through a credit system similar to carbon credits.

Further research is necessary to understand the impact of different plastics in the environment, but it’s clear that we should strive to utilize existing plastics more effectively. Given their durability, why limit their use to a single application? Challenges arise when plastic bottles degrade under certain conditions, which complicates their reuse. Developing methods to assess plastic integrity could enable the sterilization and refilling of these bottles.

Historically, food weigh-houses were commonplace in the UK, but the shift toward pre-packaged food has been driven by convenience and shelf-life improvements. However, this trend does not apply universally. For example, purchasing dried beans or fresh milk often negates the need for pre-packaged options.

As the energy sector transitions away from fossil fuels, companies reliant on this resource must consider the future of plastic production. Should we preserve fossil fuels and explore bio-based alternatives, or do we have sufficient plastic already in circulation to meet our needs?