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

Cancer Charlatans

photodynamic therapyWhat makes people defend the indefensible? A prime example of this conundrum is the case of Antonella Carpenter, a 71 year old “alternative practitioner” who was convicted of conducting a fraudulent scheme to cure cancer in Tulsa, Oklahoma and is likely looking at spending the rest of her life in prison. She is not a physician but has some training in physics and claims that she can cure cancer by injecting a tumour with a saline solution of food colouring and walnut hull extract followed by heating the area with a laser. She calls her treatment “Light Induced Enhanced Selective Hyperthermia,” for which she claims 100% efficacy without any side effects. Any claim of 100% efficacy is a hallmark of quackery since no drug of any kind works in such a foolproof fashion. Even worse, she sometimes told patients they had been cured. As is often the case, quacks unearth some legitimate process and then twist it out of proportion to hatch a money-making scheme.

In this case, the legitimate process is “photodynamic therapy.” The treatment of cancer involves some process by which cancer cells are destroyed while normal cells suffer less damage. Unfortunately, it isn’t possible to avoid collateral damage completely and cancer treatment via radiation or drugs is always burdened with side effects. In photodynamic therapy the idea is to introduce a chemical, known as a photosensitizer, that when activated by light interacts with oxygen to convert it into a very reactive form known as “singlet oxygen” that then attacks any organic compound it encounters with the result being cell death. The photosensitizer can be introduced intravenously followed by the tumour being exposed to long wavelength light via optical fiber. Alternately, the photosensitizer can be injected directly into a tumour and then the area exposed to light. In either case singlet oxygen is produced only within the tumour, minimizing damage to normal tissue. The process is applicable to certain types of tumours and is certainly not a cure-all for cancer.

It is this therapy that has been mentally mangled by Antonella Carpenter, who according to investigators cheated cancer patients out of their money and gave them false hope. In spite of any evidence of her treatment having any efficacy, supporters have sprung to her side, claiming that she was wrongly convicted by a kangaroo court. Here are some of the phrases they are pumping out: “The greedy and vindictive genocidal maggots who control the Cancer Industry and have the FDA and courts in their back pocket”…. “the medical mafia is hard at work twisting the truth and vilifying Dr. Antonella Carpenter and any other non-Allopathic practitioners and natural or alternative treatments as quackery”…. “Dr. Carpenter was vindictively targeted by the Medical Mafia and their Gestapo goons at the FDA for successfully curing dozens of cancer patients.” No. The truth is that she was targeted for subjecting cancer patients to a treatment that had no chance of working and was claiming she had cured them. That is evil.

Joe Schwarcz PhD

In the beginning there was…Persil

persilThe world’s first commercially available laundry powder was Persil, introduced by the German company Henkel in 1907. The name derived from perborate and silicate, two key components in the product. Persil was introduced as an improvement over the action of soap, the traditional cleaning agent first formulated around 1500 BC. Just heat some sort of fat with ashes from a wood fire and you get soap. The ashes supply the alkaline chemicals needed to break down the molecules of fat and convert them into salts of fatty acids which we know as soap. One end of the soap molecule has an affinity for water, the other for oily substances. Washing with soapy water then removes oily residues from a surface. While soap cleans well by emulsifying and removing greasy stains, it does present some problems. It isn’t great on colored stains and it forms a precipitate when used in water that has a high mineral content. This “scum” is hard to rinse away and dulls clothes. Persil addressed both of these problems.

Sodium perborate is an oxygen releasing agent, and oxygen is effective for destroying stains. As the prototype “oxidizing agent,” it can steal electrons from molecules. Since electrons are the glue that hold molecules together, exposure to oxygen can break down complex molecules, such as the ones responsible for stains. This is why traditionally laundry was either hung out to dry or spread out over grassy fields. Not only did this expose the fabric to oxygen, but also to ultraviolet light from the sun which can also break down colored molecules. Sodium perborate did the work of the air and the sun at the same time. The addition of sodium silicate had a “water softening” effect, meaning that minerals like calcium and magnesium responsible for forming a scum with soap were in a sense neutralized. These minerals react with silicates to form precipitates, just as they do with soap, but the difference is that these precipitates are readily rinsed away and tend not to deposit on the fibers of the cloth being washed. Silicates have great suspending and anti re-deposition qualities. Today’s detergents are chemically far more complex than the original Persil, and Persil itself has a range of products to cater to different needs, but it will always retain its place in history as the “first self-acting laundry detergent,” and the image of the White Lady introduced in 1922 and featured on numerous placards and signs remains an advertising classic.

Joe Schwarcz

A Rotten Apple Spoils The Whole Barrel. Really.

rotten apple

You’ve heard the expression that a rotten apple spoils the whole barrel. Wonder why? The ripening and subsequent rotting of an apple can be linked to its internal production of a gas called ethylene. As in other fruits, ethylene stimulates a large number of enzymatic processes which are in general responsible for ripening. An increase in concentration of this gas enhances tissue respiration (oxygen uptake) which leads to a slightly increased internal temperature. This then leads to a breakdown of chlorophyll and the synthesis of other pigments. The starch in the fruit is converted to simple sugars and at the same time the compound pectin, a component of fiber which cements cell walls together, begins to disintegrate, softening the tissue. A rotting apple can stimulate this process in other apples. Usually undesired, unless you want to ripen bananas.  Put a green banana in a bag with a ripe, cut-up apple and watch it turn yellow. This ripening process can be carried out “commercially” as well; easily perishable produce such as bananas and tomatoes which must travel a long distance are often picked before they are ripe and are treated with ethylene gas on the way to their destination.

Joe Schwarcz


You Asked: Why is sodium sulphite added to laundry and dish-washing detergents?

laundrySodium sulphite is not added for cleaning purposes, at least not as far as the laundry is concerned. It is added to protect the washing machine or dishwasher from corrosion.  Iron reacts with oxygen to form ferric oxide which is better known as rust.  This reaction proceeds more readily at high temperatures, as found in washing machines.  Where does the oxygen come from?  It is dissolved in water.  The surface of water is in contact with air, so some oxygen can always dissolve.  Oxygen also is a byproduct of photosynthesis which of course occurs as aquatic plants grow.  The amount of oxygen that dissolves depends on the temperature (less dissolves as the temperature increases), the pressure (less dissolves at higher altitudes) and the amount of other substances already dissolved in the water (freshwater holds more oxygen than salt water).  Oxygen in water is a good thing for fish who fulfil their oxygen needs by extracting the gas as water passes through their gills, but it is not so good for metals in washing machines which will corrode.  Sodium sulphite is an oxygen scavenger.  It reacts with oxygen to form sodium sulphate and effectively lowers the dissolved oxygen content thereby protecting the insides of washing machines from rusting.


Joe Schwarcz

Soft drink bottles are made of a plastic called polyethyleneglycol terephthalate, or PET. While this plastic is fine for storing soft drinks, why is it not recommended for storing home-made wine?

While PET has a very low permeability when it comes to carbon dioxide, it readily allows oxygen to pass through. And oxygen is the enemy of wine! When we talk about storing soft drinks, permeability to carbon dioxide is the critical factor. A beverage that loses carbonation loses its appeal. In this case oxygen permeability is not an issue. While oxygen passing into a plastic soft drink bottle from the air may react with some of the flavor components, the effect would be minor given that we don’t store soft drinks for extended periods. But of course we do store wine to age it. And this is where oxygen becomes a problem. Grape juice contains a variety of compounds called polyphenols which can react with oxygen and produce a variety of colors and flavors. This really is the same chemistry that occurs when an apple is cut and exposed to the air. Reaction between polyphenols and oxygen produces the brown discoloration. Not only will the apple slices look different, they will also taste different. The same thing can happen with wine. White wine is more susceptible to such changes because it lacks some of red wines colored compounds, the anthocyanins, which can act as antioxidants. Sulfur dioxide is also an effective antioxidant, which explains why compounds such as sodium bisulfite are used to preserve wine. Burning sulfur inside wine barrels to produce sulfur dioxide is an age-old method of preservation. Now back to our plastic bottles. As we have seen, empty soft drink bottles are too permeable to oxygen and are not appropriate for storing wine. But wine can be purchased in plastic containers, although I suspect a true eonophile would look warily upon this method of marketing. So how do the marketers solve the problem of oxygen permeability? By sandwiching a layer of an oxygen-impermeable plastic between layers of food-grade polyethylene or polypropylene. Ethylene-vinyl alcohol copolymer is ideal for this purpose since it allows very little oxygen to pass through. A bit of ingenious chemistry. So while it is not a good idea to store your wine in old soda bottles, it is quite acceptable to purchase wine in plastic containers.

Joe Schwarcz

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