This article was first published in聽
There is probably no quote more often cited in discussions of toxicity than that of 16th-century Swiss physician and alchemist Paracelsus, namely that 鈥渙nly the dose makes the poison.鈥�
I invoke this cornerstone of toxicology with great regularity these days since I am flooded with questions about pesticide residues, the safety of artificial sweeteners, food dyes, parabens in cosmetics and fluoride in water. And most recently, 鈥渂lack plastic!鈥�
Many of you asked whether the black plastic spatulas and serving spoons that lurk in kitchen drawers should be discarded. Why? Because of the massive publicity given to a paper published in the journal Chemosphere with the title 鈥淔lame retardants contaminating household items add to concern about plastic recycling.鈥� The basic message was that 鈥渉armful flame retardants used in electronics were found in black plastic household products, including toys and kitchen utensils, likely due to recycled content.鈥�
The use of the term 鈥渉armful鈥� begs for numbers. How does actual exposure compare with doses that have been determined to be harmful by actual studies? We will get back to that, but first let鈥檚 set the stage. Why do black plastic items appear in the marketplace at all, and why do flame retardants end up in items that have no need for them? Your kitchen spatula is not at risk of bursting into flames when you flip your omelette.
The 鈥渂lack鈥� in black plastics is 鈥渃arbon black,鈥� a pigment produced by charring organic matter such as wood in the absence of air. When added to plastics, it is embedded in the matrix of the polymer, does not leach out and is approved for use in food contact materials. Why is it added? Carbon black improves heat resistance, increases strength and rigidity, and blocks ultraviolet light that can degrade plastics. Its addition also allows different coloured plastics to be mixed and recycled into uniformly coloured items.
Then there are esthetic considerations. Consumers tend to evaluate black items as being more luxurious, and producers like that leakage from foods packaged in black containers is less visible.
Now for the dark side of black plastics. These days the problem of plastics polluting the environment is a hot topic both among scientists and the public, as it should be. Our oceans are inundated with plastic waste, our beaches are marred with plastic trash, and nanoplastics circulate in our blood. Recycling is an obvious way to reduce the amount of plastic that ends up in the environment, but therein lies a problem. Most black plastic items end up in a landfill because they cannot be sorted from other plastics as they scoot by on the conveyor belt in a recycling facility.
In most such facilities, sorting is done with the aid of infrared light. Different plastics absorb and reflect infrared light to different extents and can therefore be identified as they travel along a conveyor belt. Jets of air then blow the different plastics into appropriate containers for recycling, but black plastic does not reflect infrared light, making it 鈥渋nvisible鈥� to the detector. As a result, these items fall into a bin at the end of the conveyor belt, destined for a landfill. They cannot be recycled because they are composed of a variety of plastics. Polypropylene, polystyrene and polyethylene terephthalate, the common polymers in black plastic, can all be recycled, but they require different technologies and therefore have to be separated, which is a huge challenge with black plastics.
Still, there is a demand for black plastics, and since it is not available from recycling facilities, it has to be made from raw materials, meaning more plastic being produced and a greater environmental burden. However, there is another possible source. Discarded electric and electronic equipment, ranging from cellphones and television sets to computers, ends up being dismantled for valuable metals, and the black plastic used in casings and circuit boards is sold to whoever may want to purchase it. That is usually companies in Asia that melt it down and convert it into consumer items.
The problem is that the black plastic in electronics contains flame retardants given that we do not want our computers and TVs catching fire. But neither do we want flame retardants in our bodies from exposure to kitchen utensils and toys. Yet, they have been detected in sushi trays, kitchen utensils, toys and hairbrushes, all items that do not have flame retardants purposely added.
Now for the obvious question. What risk do flame retardants in these items pose? It is a legitimate question in face of the vast literature on their toxicity and the fact that some, such as decabromodiphenyl ether, also known as BDE-209, have been banned by some regulatory agencies. What if children play with black plastic toys? What if we use a black spatula tainted with flame retardants to turn over food in a frying pan?
Researchers at the University of Birmingham investigated these questions. They found that no transfer of flame retardants occurs when black plastic items are handled. However, immersion of bits of black plastic in olive oil at 160 C for 15 minutes was found to transfer flame retardants to the oil. Hardly a mimic of using a spatula in a frying pan and, of course, when we fry not all the oil used ends up in our body.
Nevertheless, based on this study, scientists at the non-profit organization Toxin-Free-Future estimated a daily intake of 34,700 nanograms of BDE-209 from the use of contaminated utensils and compared this with the 鈥渞eference dose (RfD),鈥� which is 7,000 nanograms per kg body weight per day. The RfD is based on laboratory and animal studies and is the dose that is not likely to be associated with any health risk. For a 60-kg adult, they calculated this to be 42,000 nanograms a day and opined that this was frighteningly close to the 34,700 nanograms of daily intake. But they made a mathematical error: 7,000 times 60 is not 42,000, but 420,000. The supposed exposure is not close to the reference dose. It is one-tenth of it.
For me, this risk would not be enough to discard a black plastic kitchen item if I had one, and neither would I like the prospect of it going into landfill. That being said, there should be no flame retardants in such items. Novel methods, including some based on artificial intelligence, are being developed to identify plastics on the recycling conveyor belt that will allow black plastics to be sorted and recycled, eliminating the need to resort to using plastics from electronic waste.
The evaluation of risk often involves calculations that have to be done carefully. A small error can cause large worries.
