Belgian-American chemist Leo Baekeland developed Bakelite, the first fully synthetic plastic, in 1907. The heat-resistant material was used primarily as an electrical insulator. Polyvinyl chloride, polystyrene, polyethylene and nylon entered industrial production from the 1930s onward. These plastics were lightweight, moldable, waterproof and hygienic, and could be manufactured to a consistent standard. By the 1950s, plastic had become a global mass-market product.

The original goal was not to create disposable products but to develop inexpensive, versatile materials that did not depend on scarce natural resources. Plastics became a waste problem through their mass use in short-lived products. Packaging and disposable goods drove volumes sharply higher during the second half of the 20th century.

When Durability Becomes an Issue

The qualities that make plastics useful also create the waste problem. They are lightweight, moldable, durable and inexpensive. But that resilience becomes a liability when exceptionally long-lasting materials are used for short-lived products. According to the OECD, almost two-thirds of global plastic waste comes from products used for less than five years. Packaging accounts for the largest share, at 40%.

In 2019, the US generated 221 kg of plastic waste per person. The average in European OECD countries was 114 kg. Global plastic production doubled between 2000 and 2019, while waste collection and treatment failed to keep pace in many countries.

Industrialized countries generate large amounts of waste, but they also trade in discarded materials and have developed profitable industries around waste disposal and recycling.

Poorer countries without comprehensive waste collection or recycling systems, by contrast, lose a larger proportion of the plastic they use to the environment. Natural materials that enter the environment as waste can usually be broken down by enzymes and microorganisms and returned to natural cycles. Many synthetic plastics lack structures that biological processes can attack. They do not decompose. They persist.

Most visible plastic waste in the oceans therefore originates in inadequate collection and disposal. Waste accumulates in open dumps or is washed into waterways by rain. Rivers then carry it into the sea. Lost fishing nets and lines from fishing and shipping are another source.

The Problem with Microplastics

Many plastics consist of long, chemically stable polymer chains that water and microorganisms can barely attack. Sunlight, oxygen and waves break bottles, films and nets into smaller pieces, but the plastic does not disappear. It simply fragments into ever smaller particles.

Microplastics are particles measuring less than 5 mm. They develop from larger objects or enter the environment as plastic pellets, tire wear, road markings and textile fibers. According to the OECD, its member countries account for 14% of all plastic entering the environment but 35% of microplastic pollution.

Microplastics and even smaller particles spread through the water column, settle in sediments and are ingested by animals. Large objects can be recovered. Removing microscopic particles is barely possible. A visible waste problem thus becomes a long-term burden dispersed throughout the ecosystem.

Visible and Invisible Damage

According to UNEP, plastics account for at least 85% of marine litter. The consequences are particularly severe for wildlife. Animals become entangled in nets and lines or ingest microplastics with their food. The particles can then re-enter the human food chain. Plastic waste also covers habitats and transports organisms over long distances.

The ingestion of microplastics by organisms has been demonstrated, although the long-term effects on animal populations and humans are harder to determine. Particles can release additives and carry other substances on their surfaces. Their effects depend on their size, shape, type of plastic, dose and surroundings.

The complete degradation of plastic must be measured not in years but in decades or centuries. A conventional plastic shopping bag is frequently said to take 10 to 20 years to decompose fully in nature. The estimate for a beverage bottle is about 450 years and for fishing line about 600 years. These are only rough estimates.

The US National Oceanic and Atmospheric Administration (NOAA) says the time required for complete degradation is often unknown. In many cases, such figures describe only how long plastic takes to fragment until it is no longer visible. The problem has not disappeared at that point.

What Waste Incineration Changes

Controlled waste incineration destroys the polymer chains in plastic. Waste that is properly collected and either securely deposited in landfills or incinerated therefore remains within a controlled waste-management system rather than entering the environment.

Incineration does not, however, keep the material within a circular economy. The raw material is lost and the process produces carbon dioxide and solid residues. Modern plants clean flue gases and recover energy, which is the principal advantage of thermal treatment. In cement plants and other industrial facilities, for example, waste can replace some of the fuel required to generate process heat.

For non-recyclable residues, controlled thermal treatment is a safer final destination than an open dump or a body of water.

Why Recycling Is Not Enough

The global recycling rate of 9% already reveals the limitations of recycling as a universal solution. Only 15% of plastic waste was collected for recycling worldwide in 2019, and about 40% of that amount was rejected as residue during processing.

Recycling makes sense when waste becomes a usable raw material again. Separated residues that no one can reuse remain waste, even if they have been collected properly.

The complexity of some packaging prevents effective recycling. Waste-sorting plants reach their limits with packaging containing different polymers, colors, adhesives and additives. Multilayer packaging generally combines several materials, while some plastics lose quality each time they are processed. Virgin material is often cheaper and more predictable and offers more consistent quality. Mechanical recycling therefore works best with large, clean, single-material waste streams rather than small-scale, multilayer waste.

Chemical processes that break plastics down into their constituent materials also exist. They require large amounts of energy, however, and do not automatically produce new material of consistent quality.

A 2020 study demonstrated the breakdown of polyethylene terephthalate (PET), the plastic used in many beverage bottles, with the help of an enzyme. The additional substances and pretreatment required nevertheless limit the process.

Other research approaches embed enzymes in polyester to break down the plastic. Heat and moisture later activate the splitting of the polymer chains, greatly accelerating decomposition. Scientific trials achieved almost complete breakdown into the original building blocks.

In bio-based plastics, the carbon comes entirely or partly from biomass. This does not automatically make them biodegradable. Polylactic acid (PLA), a commonly used bio-based plastic, usually decomposes only under industrial composting conditions. The necessary temperature and microbial activity are absent in the sea. Controlled disposal is therefore still required to prevent it from accumulating in the environment.

Stopping Plastic Before It Reaches the Sea

Preventing plastic from entering the world’s oceans means intervening much earlier. The technical measures available to limit the problem begin long before a piece of plastic reaches the sea.

Products can use less material and consist of components that are easier to separate. Deposit-return and take-back systems give products value after use and return them more frequently to the recycling system. Plastic manufacturers can help finance collection and treatment. In countries with incomplete waste collection, regular services and secure landfills can reduce the direct flow of waste into waterways. River barriers and the recovery of ghost nets at sea can remove plastic before it fragments into microplastics.

UNEP calculated in 2023 that existing technologies could reduce global plastic pollution by 80% by 2040. The scenario combines reuse, improved recycling, the replacement of problematic plastic compounds and the safe treatment of waste. Even then, however, about 100 million metric tons of short-lived plastics would still require controlled disposal each year by 2040.

There is no universal plastic that combines durability in use with rapid degradation once it enters the environment, and there is unlikely to be one. Tackling plastic pollution therefore requires different solutions for different materials and uses.

Clean, single-material waste can be mechanically recycled, while other plastics can be broken down using chemical or enzymatic processes. Biodegradable materials may offer an alternative where some release into the environment is difficult to prevent. What cannot be recycled must be safely disposed of, in many cases through incineration.

Ultimately, the most effective solution is also the simplest: keeping plastic out of the environment in the first place.