Good riddance to plastic bags?
Despite student's success, breaking down bags may not be the answer
But finding a place to put all of those pesky plastic grocery store bags is becoming an enormous problem. They don't biodegrade easily and are only recycled in some Canadian municipalities. Estimates are that they can last in a landfill anywhere between 50 and 1,000 years.
Recently, an Ontario science student appeared to have found the answer to the plastic bag problem — and one of the world's current great environmental conundrums.
Daniel Burd, a 17-year-old from Waterloo, Ont., won the Canada Wide Science Fair's highest honour and a $10,000 prize for an experiment in which he came up with a way to use bacteria to speed the decomposition of a plastic bag in a soil solution, a situation similar to what would exist in a landfill.
Burd hypothesized that some sort of bacteria would break down polyethylene, which is commonly used to make plastic bags. In a laboratory, he combined soil from a Waterloo landfill site, strips of polyethylene bags, and a solution to encourage bacteria to develop. He found that two types of bacteria — Sphingomonas and Pseudomonas — were most effective at breaking down the plastic, and by isolating them and increasing the temperature, he was eventually able to break down the plastic by 43 per cent.
Draws widespread media attention
"This is a huge, huge step forward .… We're using nature to solve a man-made problem," Burd told The Record newspaper in Waterloo. He said he hopes that eventually landfills could include "recycling stations" for plastic bags, in which people would be able to compost the bags using his method.
To test his hypothesis, Burd took a few soil samples from a local landfill and mixed them with polyethylene, the substance used to make plastic bags, as well as a solution to encourage bacterial growth.
After concentrating the solution several times and incubating it for 12 weeks, Burd took the resulting bacterial culture and tested it on strips of polyethylene.
After six weeks, the strips had lost more than 17 per cent of their weight compared to a set of control strips. Burd concluded that a combination of two types of bacteria — Sphingomonas and Pseudomonas — was most effective at breaking down the polyethylene.
After isolating these two bacteria, combining them with some sodium acetate and incubating the solution at 37 C, Burd was able to degrade the plastic by 43 per cent in six weeks. He figures the solution would entirely break down plastic bags in a matter of three months.
— The Canadian Press
His work garnered widespread media attention and was widely cited in science blogs such as those published by Wired and the Christian Science Monitor last week.
"These are great lab findings, but whether or not they can be extrapolated and work in the field depends on the other million variables that are going on," said Myrna Simpson, an associate professor of environmental science at the University of Toronto.
For one, Simpson said that while the two types of bacteria isolated in the lab were actively munching on the plastic, in the real world, that may not be the case.
"In nature, there is going to be competition between several organisms. Even if one organism is dominant in the lab, especially in the soil environment, you are going to have a number of organisms and they are going to be competing for water and nutrients."
Simpson said some species that are active in the lab may not act the same in nature. For example, "if you take a person to a buffet, they are going to eat like crazy, but are they eating because the food is there? If you take them somewhere else, they may not eat to the same extent."
As well, Burd made it easier for the bacteria to break down the plastic because it was shredded into pieces, she said. It would be difficult, if not impossible, for bacteria to break down a whole plastic bag, Simpson said. However, if the bags were shredded first at "recycling stations," it could work, she theorized.
Don't usually break down very large polymers
Roberta Fulthorpe, a professor in the department of physical and environmental science at the University of Toronto and a biodegradation expert, said what is unusual is that these two types of bacteria, while well-known for their biodegradation qualities, usually have difficulty breaking down very large polymers, like polyethylene. Polymers are large molecules composed of repeating structural units that are held together. (Plastics, as well as proteins and DNA, are all well-known polymers).
Fulthorpe said it is possible, however, that Sphingomonas and Pseudomonas have evolved to the point that they can decompose larger polymers such as polyethylene. "Bacteria will find a way to break down almost anything."
For example, when bacteria break down dry cleaning fluid, they create vinyl chloride, which is toxic.
"He [Burd] didn't really look at how the structure was changing. Is it creating something else that's worse?" asked Simpson.
Fulthorpe said that if this process were to eventually be industrialized, "it is very exciting. There is all kinds of things you could do to increase the rate [of degradation]."
Elizabeth Edwards, a professor of chemical engineering at the U of T, said that research into biodegradation of plastics has existed for about three decades, but the problem is that plastic bags are made up of a number of different materials besides polyethylene. Even with polyethylene bags, she says, "each differs considerably in biodegradability. The reality is that the polyethylene used most commonly are those that are least biodegradable."
Could encourage more bag use
Environmental organizations said although Burd's work is positive because it's getting people talking about solutions to the plastic bag problem, they worry that this type of experiment could give people the idea that it's OK to continue to use plastic bags with abandon.
"At the end of the day, this kind of a breakthrough might have the unfortunate side effect of encouraging the greater use of disposable plastic bags," said Pierre Sadik, senior policy advisor for the David Suzuki Foundation. Sadik says the production of plastic bags involves the use of non-renewable energy, along with toxic chemicals.
But could this be helpful for the bags already in existence in landfills and the ocean? Sadik says no.
Most of those bags are "basically irretrievable," because they are metres underground, mixed with other garbage in the landfill, or in the ocean, where it's not possible to collect them. But he added that the bags currently in use in stores and in people's homes could potentially be processed using Burd's research as a basis, if municipalities and other jurisdictions set up a program to divert the plastic.
Plastic Bag Facts
- 500 billion plastic bags are used worldwide each year.
- Municipalities in eight Canadian provinces offer plastic bag recycling, but often not in big cities, such as Toronto and Ottawa.
- Only one to three per cent of the world's plastic bags are actually recycled, according to the Wall Street Journal.
- In Ireland in 2002, a highly successful plastic bag tax reduced the consumption of the bags by 90 per cent.
- Human plastic waste is evident on a large scale in the Great Pacific Garbage Patch, a giant clot of debris twice the size of Texas floating in the Pacific Ocean.
Sources: Wires, myplasticbag.ca, reusablebags.com
Jean Langlois, national campaigns director for the Sierra Club of Canada, says for this approach to work, people would have to separate out garbage bags, but unfortunately, most people still use disposable plastic bags to throw out their garbage in the landfill. "Separating it is going to inherently be a problem."
The best thing for municipalities to do is to mandate the use of biodegradable plastic bags, which are engineered from the start to biodegrade in the landfill, he said. They are commonly found now in green-bin recycling programs for organic waste.
"The No. 1 value [of Burd's study] is that it gets people talking about this problem, which is great," said Langlois.
But he added: "The take-home message is we still don't know how to get rid of these things so we should avoid using them."