Buckle up, we're headed into the science lab this week! But for good reason. It's time to talk about wool and microfiber pollution.
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We know that wool requires far less laundering than its synthetic counterparts. But at some point, most of us end up tossing that sweater or pair of leggings into a sink or a very wool-friendly washing machine. What happens then?
All textiles release fiber fragments, or microfibers, during the wash. In the normal course of affairs, those microfibers find their way into our lakes, rivers, and oceans. Microplastics—by which I mean synthetic microfibers—have been found in everything from beer and honey to our drinking water. Only now are we beginning to grasp the scope of microplastic pollution and the harm it has done, not just to the planet, but to the very workings of our bodies.
A new report estimates that there are already 24 trillion pieces (and counting) of microplastics on the ocean floor. According to the IWTO, by 2030, synthetic fibers will make up some 73% of what we wear. Of that, 85% will be polyester. Our microplastic problem is only going to get worse.
That's plastic. What about wool? What happens to those miocrofibers once they reach our waterways? Will they biodegrade? If so, how quickly?
And what happens to wool fibers that have been treated for machine-washability by being coated with the polyamide-Epichlorohydrin resin called Hercosett-125? Does that basically plasticize the wool? Should we avoid it?
A report from Ag Research, published in April 2020, provided some rather astonishing findings.
A Watershed Study
The goal of the Ag Research study was to determine what happens to microfibers after they reach a marine environment. How quickly do they biodegrade, and what do they leave behind? The assumption being that the more they leave behind, the greater threats they pose to the environment.
Going into this, the researchers already knew that wool fibers do biodegrade in a marine environment. There are bioorganisms in the ocean that are quite happy to consume the wool. This appetite has evolved over the nearly 10,000 years that wool has been around. It is not a new or foreign substance.
That's the good news. But questions remain.
First of all, how quickly do those bioorganisms consume the wool? Second, how does wool measure against other microfibers in our oceans? And finally, what kind of residue remains in the water after the fibers have been consumed?
Setting up the Test
To find out, they took lightweight, moderately worn samples of regular and machine-washable Merino, as well as viscose rayon, polyester, nylon, and polypropylene. The samples were all shredded to ensure that their original fabric structure didn't interfere with the biodegradation. To provide a baseline, they also tested readily biodegradable Kraft paper pulp.
They gave the paper pulp a biodegradability score of 100. So, 100 is the best. Relative to that,
- nylon scored 0.8
- polypropylene scored 1.8
- polyester scored 6.3
- the untreated Merino scored 20.3
Viscose rayon leapt ahead at 64.5, being derived from readily biodegradable plant cellulose.
But here's the kicker: The wool that had gone through the Hercosett process scored the highest of them all, at 67.3. Machine-washable wool biodegraded three times faster than its untreated wool counterpart.
The report suggests that the wool did so well because the protective cortex had already been partially removed before the Hercosett resin was applied.
But what happens to that resin?
That's the next question, isn't it? What happens to it as the wool biodegrades? Does it just chip off and form even tinier, more lethal microfibers in our water? In which case is machine-washable wool just as bad as polyester?
The report had some helpful insight into the nature of Hercosett 125 and how it may differ from other polyamides.
"It is important to note that the crosslinked polyamide resin used in the machine-wash treatment for wool is very different from common commercial polyamides. This resin is initially water soluble when applied to the wool surface, where its light crosslinking prevents re-solution. In this form the resin is able to swell significantly in water so that it more effectively masks the fibre scales, enhancing machine-washability. This swelling potentially means that it presents a much- reduced barrier to microbial access."
So it's different from other polyamides. But still, let's keep going.
They left the samples in water for 60 days and then screened the residue using scanning electron microscopy and energy-dispersive X-ray spectroscopy. Between these two systems, you can detect pretty much everything in that water.
They stripped the residue down to its very elements. There they found carbon, nitrogen, oxygen, and sulfur.
Stay with me, because here's where it gets interesting.
Polyamide resin contains no sulfur whatsoever. But wool does. And all of the remaining fragments contained more than 2.5% sulfur. Therefore, they were able to conclude that all remaining fragments had been "almost certainly" derived from wool. Not the resin.
"In other words," notes the report, "we did not detect the formation of microplastic polyamide fragments resulting from the biodegradation of machine-washable wool."
Where did the polyamide coating go? It couldn't have just...disappeared, could it? And does this mean we should all go out and buy machine-washable wool and throw it in our washing machines with reckless abandon?
This, I don't know. We'll let the science continue to evolve. But I do consider this a rather unexpected, potentially valuable data point to add to your next discussion about the relative merits of wool.