Humans have made 8.3 billion tons of plastic. Where does it all go?
Plastic materials are impossible to avoid. From water bottles and shampoo containers, snack wrappers and Tupperware, to polyester clothes and electronics, we use and eventually throw out most plastics.
Landfills and the natural environment are the final destinations for more than three quarters of non-degradable plastic trash, according to a new global estimate. If current trends in plastic production and waste management continue, the plastic debris housed in landfills and natural environments — currently 4.9 billion metric tons — will more than double by 2050, scientists reported Wednesday in Science Advances.
"It's quite sobering," Roland Geyer, an industrial ecologist at the University of California Santa Barbara and the report's senior author, said. "We're making enormous quantities of plastic … and we're not very good at plastic waste management. Around 60 percent of all the plastics we've ever made are on the planet somewhere."
How much we've made
To figure out how much plastic has been made to date, the researchers consolidated global plastic production data from trade associations and market research companies. Mass production of plastic started in 1950, and since then trade associations have kept tabs on production stats, so the team was able to capture plastic's entire lifetime.
As of 2015, the grand total of all plastic ever made since 1950 amounts to 8.3 billion metric tons.
Since the birth of plastic, production has escalated. Manufacturing of the most common kinds — polymer resins found in packaging like packing peanuts and plastic bags, polyvinyl chloride (PVC) piping and synthetic fibers like polyester — swelled from 2 million metric tons in 1950 to 380 million metric tons in 2015. This uptick corresponds to a compound annual growth rate approximately 2.5 times the rate of the global gross domestic product during the same time period.
And, the production speed is increasing. Of the plastic manufactured since 1950, half was made in just the last 13 years. In other words, just over 400 million metric tons sustained us for 50 years. But, since 2002, we've doubled that yield, Geyer said.
Where does it all go?
To model how long plastics are used by people before being jettisoned, Geyer and team perused published literature on plastic product lifetimes in eight industry sectors: packaging, electronics, transportation, textiles, industrial machinery, consumer goods, building and construction and miscellaneous. Some products — like the PVC piping used in construction — have decades-long lifespans, whereas others, like consumer goods, only last a few years.
The researchers found most plastics are kept for short time periods. Despite rampant production, only 30 percent (2.5 billion metric tons) of all plastics ever made are currently being used. Part of this trend is because nearly half of polymer plastics becomes packaging material.
An overwhelming majority of packaging plastics are acquired and discarded within the same year. In 2015, 146 million metric tons of polymer plastics went into use as packaging, but 141 million metric tons were thrown out.
In contrast, 65 million metric tons of non-fiber plastics were consumed in construction in 2015. But because of their longer useful lifetimes, only 12 million metric tons, or 5 percent, of waste was created by construction.
The fate of plastic waste
Plastic waste has three fates — recycling, thermal destruction and landfills. Each carries unique consequences.
The researchers modeled how much waste each kind of plastic generated by feeding the production numbers through a model that accounted for the plastic's lifespan in a given industry. They then matched this waste generation data to global recycling, incineration and discard rates found in World Bank and EPA waste management records and other agency reports.
Since 1950, cumulative plastic waste has amassed to 6.3 billion metric tons. Twelve percent (800 million metric tons) has been incinerated and nine percent (600 million metric tons) has been recycled. The remainder — more than three-quarters of plastic waste and more than half of all plastic ever made — ended in landfills or natural environments. The team also found less than 10 percent of plastic waste is recycled in the U.S.
Burning plastic eradicates it. But burning at low temperatures, as often happens in developing countries, releases noxious chemicals and creates a significant public health risk. In developed countries, the environmental and health impacts of waste incineration rely on the incinerator design and emissions technologies.
Once plastic makes way into landfills and the open environment, it doesn't go anywhere. Most plastics are not biodegradable and those that are were excluded from this analysis because of their low production volume of 4 million metric tons. Sunlight breaks degradable plastic down into microscopic bits, known as "microplastics." But, many of the environmental impacts of these microplastics on natural environments, including freshwater and marine ecosystems, remain unknown.
Our plastic future?
Using their model and historical trends, Geyer and his collaborators extended their projections to 2050. They found that discarded plastic waste would grow from 4.9 billion metric tons to 12 billion, assuming consistent production, use and waste management trends.
"It's a disconcerting number," Dan Hoornweg, a material scientist at the University of Ontario Institute of Technology, who was not involved in the study, said. "This is a great study. It's sort of an early first round of just how much stuff is there."
Geyer and Hoornweg recognize the value and inherent contribution plastics make in modern society and even its environmental benefits. For example, plastics provide environmentally responsible strategies to alleviate food waste and transportation costs.
Another example involves Air Canada's in-flight booze bottles, Hoornweg said. When Air Canada made the switch from glass to plastic bottles, the plastic couldn't be recycled. But the amount of jet fuel saved by the exchange was enormous, Hoornweg said.
Hoornweg also cautions this type of work is rarely as cut and dry as it might seem. Many factors are at play. One is that plastics are a fraction of the stuff we throw in the garbage. Geyer too asserts that the numbers might be off by about 10 percent. "They're not super precise, but they're robust,"Geyer said. "We're in the ballpark."
To develop a truly comprehensive waste management plan, Hoornweg said communities need strategies to address and track other waste too, such as metals and hazardous materials.