You Asked: What are “oxo-biodegradable plastic” shopping bags?

question markPolyethylene shopping bags are a big convenience but they also present a big problem. While they can be recycled, many just get carelessly discarded and end up in the environment not only as an eyesore but as a danger to wildlife. Estimates are that only about 3% of plastics that can be recycled actually are. Polyethylene does not degrade easily in the environment and the bags can end up as pollutants for decades. Some clever chemistry can, however, help the situation.

If certain salts of iron, manganese, nickel or cobalt are incorporated into the polyethylene, polypropylene or polystyrenene molecular chains during manufacture, they will catalyze the breakdown of the polymers. But the breakdown requires the presence of oxygen because the mechanism of the degradation involves “oxidation,” which means forming bonds between some of the carbon atoms in the polymer and oxygen atoms supplied by oxygen in the atmosphere. Exposure to ultraviolet light speeds up the reaction

Once the chain has been “oxidized,” the bonds between the oxygen bearing carbons and their neighbours are significantly weakened and begin to break apart. The resulting short chains are then biodegraded by microbes basically to carbon dioxide and water. Depending on the extent of UV and oxygen exposure, and ambient temperature, oxo-biodegradable plastics visually disappear in as little as two months, although the process can take up to a year and a half. These bags will not degrade in a landfill and therefore will not generate methane, a potent greenhouse gas. They cannot be composted, but they can be recycled just like other polyethylene bags. The big advantage is a reduction in all those bags that end up fluttering from trees or floating in the ocean. Of course, until the plastic breaks down, it can still pose a risk to wildlife but there is no doubt that the oxo-biodegradable plastic is preferable to the conventional variety in terms of impact on the environment.


Dr. Joe Schwarcz

Small beads can make for a large problem

dangerScience can make for a strange bedfellow. I had just finished recording a video showing off one of my favourite sweaters and expounding on the ingenuity and the environmental benefit of it being made from recycled polyester bottles when an article appeared on one of my newsfeeds about how “your clothes are poisoning our oceans and food supply.” The message was that the very fabric I was so high on may be unravelling the fabric of society.

I must say I was puzzled by the headline, but on glancing through the story, the details of the problem quickly came out in the wash, as it were. Synthetic fabrics are not exactly inert and release microscopic bits of fiber when washed. The particles may be microscopic, but their number is anything but. Researchers at the University of California found that a synthetic fleece jacket releases hundreds of thousands of microscopic fibers, about 2 grams in total, with each wash. Wastewater treatment removes some of this debris, but most of it ends up in rivers, lakes and oceans where it can be consumed by wildlife. The fibers then can bioaccumulate up the aquatic food chain, right up to people consuming fish. Whether this presents a risk is not known, but bits of plastic are not a desirable dietary component. The clothing industry is sensitive to the problem and is working on coatings for fabric that would reduce shedding. Also in the works are washing machines that prevent the release of microfibers by using pressurized carbon dioxide instead of water.

The shedding of microfibers from synthetic fabrics is not the only way tiny pieces of plastic, invisible to the naked eye, end up in water systems.” Microbeads,” introduced into consumer products such as toothpaste and exfoliating skin products as abrasives, are a bigger concern. Six varieties of the tiny beads are used. Those composed of either polyethylene, polypropylene or expanded polystyrene are more likely to float, whereas the ones made of polyvinyl chloride, nylon or polyethylene terephthalate (PET) are more likely to sink. McGill biologist Anthony Ricciardi has found microbeads in significant numbers in sediment at the bottom of the St. Lawrence River, meaning possible contamination of fish that feed on the riverbed.

Microbeads range in size from 10 millionths of a meter to one millimeter. Their round shape makes them much less irritating than irregularly shaped, abrasive exfoliants like apricot kernels or walnut shells that have sharp edges. Also, because the particles are tiny spheres, they act as little ball bearings, allowing for easy spreadability of creams and lotions as well as a smooth texture and silky feel. There’s more. Imperfections in the skin tend to be visible because of the contrast between how they reflect light compared with the surrounding tissue. Microbeads with their ability to scatter and diffuse light can minimize the appearance of fine lines and improve skin tone. When it comes to toothpaste, though, they make a minimal contribution to polishing the teeth and may actually become embedded in gum tissue. Why are they there? Since the microbeads can be produced in various colours they can also increase the visual appeal of a product.

A single container of face wash can contain hundreds of thousands of the microspheres. While the virtually indestructible plastic beads are not themselves toxic, once they enter the water, they attract potentially toxic substances such as PCBs, triclosan and nonylphenols. Like the microfibers, microbeads can then become part of the aquatic food chain, eaten by fish and then by people. Once consumed, the beads may also leach out plastic additives like colourants, plasticizers and ultraviolet light stabilizers.

Researchers have found fish both in the oceans and the Great Lakes contaminated with microbeads. Besides carrying toxins, the beads can cause internal abrasions and can stunt growth of the fish by giving them a false sense of being full. One-third of fish caught off the south-west coast of England have been found to contain microbeads and  Belgian researchers studying seafood from German farms and French supermarkets found that an average portion of mussels can contain about ninety microplastic particles, and an order of oysters about fifty. The beads have also been found to lodge in the guts of crabs as well as in their gills.

The number of microbeads that end up in the environment is staggering. In New York State alone some 19 tons go down the drain every year. Most wastewater plants are not equipped to filter out such fine particles and while they could be retrofitted, the expense would be prohibitive. Drinking water poses less of a problem because municipal water treatment plants can filter out the tiny particles although a sampling of German beers found microbeads in every bottle, with the water used being the likely source. Both Canada and the U.S. have moved to ban microbeads and manufacturers have started the process of phasing them out. Researchers agree that there are still too many unknowns to fully assess the environmental damage caused by microplastics but given that they do not contribute significant benefits they should be eliminated.

But the problem of plastic waste in the oceans is greater than can be accounted for by microfibers and microbeads. Other tiny particles form from the breakdown of plastic bags, bottles and all sorts of containers that get discarded end up in waste streams that empty into the ocean. “Biodegradable” on a label means that the plastic has been shown to degrade under ideal composting conditions, but these do not exist in the natural environment. Estimates are that the ratio of plastics to fish by weight in the oceans is 1:5 and with our current callous attitude towards “reduce, recycle, reuse,” it is set to increase to 1:1 by 2050.

Given these concerns, I don’t think I can wear my “made from a plastic bottle” sweater with the same pride as before. And I may even feel a bit of apprehension tossing it into the laundry basket.


Joe Schwarcz

Blog authors are solely responsible for the content of the blogs listed in the directory. Neither the content of these blogs, nor the links to other web sites, are screened, approved, reviewed or endorsed by McGill University. The text and other material on these blogs are the opinion of the specific author and are not statements of advice, opinion, or information of McGill.