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


plastic bottles“I hate plastics. We should get rid of them.” So began an email I received. The correspondent went on to talk about how plastics are a plague on the environment, how they contain chemicals that contaminate our food supply, disrupt our hormones, cause autism and ADHD and use up valuable petroleum deposits. What prompted the email was some comments I made about different plastics having different properties and how there were some concerns with some but not with others. The disturbing part of the message was the insinuation that I must be in the pockets of the plastic industry since I did not agree that plastics were substances forged in hell. That allegation is easy to answer. I get zero funding from the petroleum or plastics industries. My allegiance is to the scientific method. Where that path leads, I go.

It is true that plastics can be an environmental plague. But plastic shopping bags don’t jump into rivers or trees by themselves, and empty bottles that should be recycled don’t leap into garbage cans unaided. People are the problem. As far as using up petroleum resources, only about 5% of oil goes towards plastic manufacture, and in North America the prime raw material is actually not petroleum but natural gas. I should add that while plastics are mostly made from fossil fuels, this is not the case exclusively. Polylactic acid, widely used today, is made from corn and there is extensive research in the area of “green chemistry” to produce a variety of polymers from plant products.

What about the bit about contamination of our food supply? Anytime two surfaces come into contact, there is an exchange of chemicals. Indeed, it is possible that trace amounts of plastic chemicals with endocrine disruptive properties may end up in our food supply, but the dose is so small that any sort of harmful effect is very unlikely. Heat increases the release of chemicals, so it is better to use glass or ceramic for warming up food, although plastics labeled as microwave safe contain no easily leached components. As far as ADHD and autism go, the fact is that nobody knows the cause. There is much speculation ranging from genetics and microbiome imbalances to environmental contaminants but plastic ingredients would come way down the list. It is true that we can definitely live without plastic microbeads in cosmetics and even without synthetic fabrics, although resorting to cotton poses a whole range of other problems. But the suggestion to get rid of plastics is simple-minded nonsense that amounts to lack of seeing the forest for the trees.

Our life today depends on plastics. They are vital components of our airplanes, our cars, our buildings, our TV sets, our food production and drug manufacturing equipment, as well as numerous consumer goods ranging from shampoo bottles to shower curtains and toothbrushes. Yes, you could make toothbrushes from wood and pig bristles, but nylon is a lot better. Modern medicine could not function without plastics. Intravenous tubing, blood bags, burn dressings, artificial limbs, heart-lung machines, artificial joints, pacemakers, MRI machines, CAT scanners and x-ray equipment and white dental fillings rely on plastics. And just try to make a computer without plastics. Right now you are reading this on a computer or cell phone that could not function without plastics. Mr. McGuire in the Graduate was right: “I want to say one word to you. Just one word. Benjamin: Yes, sir. Mr. McGuire: Are you listening? Benjamin: Yes, I am. Mr. McGuire: Plastics!”


Joe Schwarcz

Dateline NBC: Endocrine Disruptors

Dateline NBCWell…finally the Dateline piece on “hormone disruptors,: for which I was interviewed aired on March 24th. It was not as bad as it could have been, but not as good either. In the end I got 58 seconds clipped out of a 3-hour long interview! They didn’t manage to include my comment that reducing extremely low levels to even lower ones has no clinical significance. I even gave an analogy: if you drink a cup of coffee you expect to find caffeine in the urine. If you then abstain it will vanish. Drink again and it’s back. So what? All you have shown is exposure which does not equate to risk. The presence of a chemical is not the same as presence of risk. But when you report results in percentages you can mislead easily. For example your chance of winning the lottery is trivial but if you buy two tickets you increase your chances by 100%. Sounds impressive but it is irrelevant in practical terms. So reducing very low levels of BPA or phthalates in the blood by 100% similarly has no practical significance. Furthermore testing the urine is not very meaningful because it indicates what is being eliminated! It is what is left in the blood and tissues that is critical. And with BPA as we know from the recent Teeguarden study, there is virtually nothing detectable in the blood because it is quickly eliminated. As for the mouse studies they talked about, yes there are biological effects at exposures greater than human exposure. But of course the human is not a giant mouse. Rodents have different enzyme systems and metabolize BPA differently. Unfortunately they gave much more air time to Rick Smith of “Environmental Defense” and his alarmist crony with their implied message that that “hormone disruptors” are undermining our health. I had made it clear that “hormonal activity” and “hormone disruption” are not equivalent. I also pointed out that there are some 11,000 compounds that are known to have endocrine activity and if any one of these were investigated to the same extent as BPA or the phthalates, similar issues would crop up.  I was glad they put in my comments about triclosan, which I really think should not be in soaps or toothpaste, because I was concerned that they would portray me as some sort of apologist for the chemical industry, which of course I am not. Although they didn’t include my discussion about how this was an environmental issue and not an “endocrine disruption issue.” As was to be expected the public was left with the overall impression that there is reason to worry and that Rick is the knight in shining armour who is set to slay the fire breathing dragon, namely the chemical industry. Well, that armour is actually pretty rusty. Anyway, at least I made it onto Dateline. Maybe next time I can get 60 seconds on 60 Minutes. On the positive side, the comments on my personal Facebook page have been overwhelmingly positive.

Joe Schwarcz

Retinyl Palmitate

According to the Environmental Working Group (EWG), a non-profit, environmental advocacy group, we should all be wary of retinyl palmitate. This compound is commonly added to a range of skin care products, including sunscreens, because of its ability to give skin a more youthful appearance. Actually, retinyl palmitate itself doesn’t have much physiological activity, but enzymes commonly present in the skin convert it first to retinol (vitamin A), then to retinaldehyde ,and finally to retinoic acid. The latter is the active agent, enhancing collagen formation and increasing the rate of cell division. Since collagen is an important structural protein in skin, and since more rapid turnover of cells leads to a larger number of more youthful cells, retinoic acid can be instrumental in improving the appearance of the skin. (more…)

The Environmental Cost of Meat

We know what we should be doing if we want to be environmentally conscious. Recycle, compost, use public transport more, insulate better, shop with reusable bags. But here is something that is probably even more effective. Eat more vegetables and less meat. How can that have anything to do with the environment? Easy. Eating meat is a very inefficient way of consuming plant food. That of course is what it amounts to; animals eat plants and we eat them. Eating the plants directly has less of an impact on the environment since about two and a half pounds of grain are needed to produce a pound of meat. The extra grain needed to feed animals means more fertilizer used, more pesticides used, more transportation and more refrigeration. To clear land needed to raise animals and feed them often means that rainforests are destroyed. Then there is the problem of greenhouse emissions. Animals release methane both from their digestive tract and from their manure. Methane is a potent greenhouse gas. There is also the issue of nitrous oxide that is emitted from the ammonia based fertilizers used to grow feed. Cows and sheep are the biggest culprits, while pigs and chickens are not as bad when it comes to methane emission. Indeed some estimates suggest that livestock are responsible for as much as 18% of the greenhouse gases that cause global warming, more than cars, planes and all other forms of transport combined. And that estimate does not come from crazed vegetarian hippies, it comes from the Food and Agriculture Organization of the United Nations. (more…)

Biodiesel Complications

One thing you can count on in science is that virtually every issue is more complicated than it first seems. Take biodiesel as an example. It can be made from virtually any plant oil by reacting it with methanol. It produces roughly the same amount of carbon dioxide as does petroleum-based diesel when it burns, but since whatever crop is used to produce the oil takes up carbon dioxide from the air through photosynthesis when it grows, there is a smaller contribution to the greenhouse effect. Plus of course plants are a renewable source of energy while petroleum will eventually run out. But while crops do indeed take up carbon dioxide from the air, growing them causes another greenhouse gas, nitrous oxide, to be produced. Nitrous oxide actually is two to three hundred times as potent a greenhouse gas as carbon dioxide. It forms when bacteria in the soil react with nitrogen containing compounds, both those applied as fertilizer and those produced by crops such as legumes that are capable of converting nitrogen from the air into compounds they can use as nutrients. Incidentally, whether the fertilizer is synthetic or good old-fashioned manure has little impact on nitrous oxide production. Since trees do not produce much nitrous oxide, one study has already concluded that greenhouse emissions could be cut by a third if cars were run on conventional fuel and trees were planted on the land that would otherwise be used to grow crops destined for biodiesel production.

But biodiesel production is hot on the environmental agenda and Brazilian rain forests are being cleared at a frightening rate to make room for fields of soybeans to supply the oil needed for the growing biofuel industry. To be sure, not all the clearing is for soybeans, most of it is to create pastureland to raise animals, a financially lucrative proposition. Both of these have an environmental impact, but calculations show that fields of soybeans may have a greater effect on climate than pastures. How can this be? Clearing of trees causes less rainfall since in a rainforest evaporation of water from trees is a major cause of cloud formation. But replacing trees with soybeans results in less rain than replacing them with pasture. That’s because soy plants reflect sunlight more efficiently than fields of grass meaning that there is less heating of the surface, less moisture rising into the air, fewer clouds and less rain. Right now we can only guess at what a fourfold reduction in rain caused by soybean fields when compared with pastureland will mean, or indeed what the eventual global consequences of cutting down rainforests will be. It is unlikely to be a pretty picture. Switching to biodiesel from petroleum diesel may not be as “green” a process as commonly portrayed. As I said, issues always get more complex on further scrutiny.

Dirt and Allergies

They could be just a slight annoyance, like sneezing a few times when you fist step outside or they could be so deadly that even just touching a substance will send you into complete respiratory shock within seconds. Though they have a wide range of ways to manifest themselves, they are known by a common name – allergies. And today we in the west are more susceptible to them than ever.

As our hygiene and cleanliness improves it seems we become more susceptible to allergies. It’s as if our immune system is yearning for action, but having no enemies in the form of infectious agents or parasites to battle, it targets harmless substances present in the environment. This constitutes an allergic reaction. Central to this reaction are specialized proteins known as antibodies. Specifically, IgE (immunoglobulin E) antibodies are implicated. They are made when a foreign substance enters the body and then attach themselves to immune cells called mast cells where they lie in wait, ready for action should the intruder appear again. When the allergen does appear, the antibodies recognize it and bind to it. This disturbs the structure of the mast cell, causing it to “wake up” and release various disease-fighting molecules. The prime one is histamine. This molecule, when released, makes local blood vessels more permeable and unleashes the symptoms of an allergy. There’s sneezing, sniffling, watery eyes and all the rest as the body tries to rid itself of the troublesome allergen.

Today our hygiene-obsessed society is focussed on the use of antibacterial soaps, sponges, pillows and even toys. Some people carry around a special germ-killing lotion and slather it on at the first sign of ‘contamination’. Sounds like something out of a sci-fi movie. You greet someone, shake hands and then immediately proceed to cleanse yourself of them with some goo. But this could end up causing more harm than good. Not only does this over-use of antibacterial products breed drug-resistant forms of microorganisms, it may also be contributing to the rising incidence of allergies in our society.

When we’re born, our immune system is considered ‘naive.’ White blood cells, such as the helper T cells, haven’t yet fully developed. There are actually two types of these T cells. Th1 cells fight mostly small invaders like bacteria and viruses which directly attack our cells while Th2 cells are designed to fight the bigger enemies, such as parasites and worms which may lurk in-between cells. It turns out that these Th2 cells are also the cells that initiate IgE production. Therefore it is not surprising that allergy-prone people tend to have more Th2 cells while those without allergies have more Th1 cells. This may be because of the lack or the presence of microorganisms in the environment of a growing child. Here’s the theory then: if there aren’t many ‘bugs’ around, a child doesn’t make as many Th1 cells and so ends up making an excess of Th2 cells which tend to overreact to normally harmless substances such as pollen, dust or certain foods by stimulating IgE production. At birth the Th2 cells are the most likely to be triggered into activity. And if the Th1 cells aren’t sufficiently stimulated, by microorganisms as found in dirt, for example, allergies can result. Th1 cells produce signals that reduce Th2 responses and Th2 cells produce signals that reduce Th1 responses. In other words, there is a delicate balance between these two types of cells. (more…)

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