Another Big Science Fail Over Pollution
Is plastic polluting the world’s oceans? Yes, but not nearly as much as hundreds of studies had claimed. Measure, don’t assume!
When told by the media that humans are destroying the planet, always ask how they know. A team reporting today decided to look at ocean water carefully in a thousand separate locations. What they actually measured contradicts previous scientific claims.
The claim that bioplastic fibers are fouling the ocean with artificial chemicals is common. Plastics are destroying fish stocks, marine life, coral reefs, whales and the health of the biosphere. How do scientists know? They just know. They quote each other. It must be true. Plastic is especially bad because it takes so long to degrade. And it comes from that evil stuff, fossil fuel.
It’s important to state up front that plastic pollution is a big problem that needs to be addressed, and no attempt will be made here to excuse it. Large masses of plastic bottles and other waste are showing up in certain ‘gyres’ of circulating currents. Whales are being found dead with large amounts of plastic in their guts, and sea turtles have been found with plastic straws stuck in their noses. Mylar balloons have been found stuck in whale stomachs, the animals having mistaken them for jellyfish. This is terrible by anyone’s standards.
But measurement matters. How much of the claimed microfiber material is really plastic? Eight authors from 4 countries went looking, and reported their findings in the AAAS open-access journal Science Advances, “Microfibers in oceanic surface waters: A global characterization.”
Microfibers are ubiquitous contaminants of emerging concern. Traditionally ascribed to the “microplastics” family, their widespread occurrence in the natural environment is commonly reported in plastic pollution studies, based on the assumption that fibers largely derive from wear and tear of synthetic textiles. By compiling a global dataset from 916 seawater samples collected in six ocean basins, we show that although synthetic polymers currently account for two-thirds of global fiber production, oceanic fibers are mainly composed of natural polymers. µFT-IR characterization of ~2000 fibers revealed that only 8.2% of oceanic fibers are synthetic, with most being cellulosic (79.5%) or of animal origin (12.3%). The widespread occurrence of natural fibers throughout marine environments emphasizes the necessity of chemically identifying microfibers before classifying them as microplastics. Our results highlight a considerable mismatch between the global production of synthetic fibers and the current composition of marine fibers, a finding that clearly deserves further attention.
This is actually good news, because it means that (1) synthetic fibers—mostly polyester, although produced in much larger quantities (2/3 of global fiber production)—account for only 8.2% of ocean fibers, and (2) the vast majority of ocean fibers are biodegradable, or at least they degrade faster than plastics. They are ‘natural’—i.e., originating from plant or animal material.
The authors do not minimize the ecological damage of fibers nor the concern about increasing production of fibers. It is a serious issue, and we are all contributing to the problem. Just washing one sweater can produce 10 million fibers! “Shedding of fabric materials, wear and tear, and increased consumption have led to the accumulation of these fibers in the natural environment,” they say. These fibers are showing up everywhere – and some of the fibers end up in our own lungs.
Large numbers of fibers are discharged into wastewater from washing clothes, with each garment releasing up to 107 fibers per wash, and enter the environment through wastewater effluent, aerial deposition, or through the application of contaminated sludge on agricultural soils. As a consequence, fibers are now the most prevalent type of anthropogenic particle found by microplastic pollution surveys around the world, including human exposure studies. Substantial concentrations have been detected in surface and subsurface waters, in sea ice, deep-sea and coastal sediments, as well as in terrestrial and freshwater ecosystems. Given their abundance, it is not surprising that fibers have been detected in food, drinking water, and human lungs, as well as in the digestive tracts of many aquatic and terrestrial organisms.
Under the best of circumstances, fibers made of biodegradable material might still have synthetic dies that are harmful to wildlife. The question before the research team, though, is how much of the fiber is plastic with very long degradation times? The team sampled almost a thousand locations of seawater over wide areas and examined the contents for fibrous material. They counted fibers, looked at the color, composition, length and density of each piece. They found out that most of it, by far, is cellulose. What makes cellulose? Plants! Here’s where bad assumptions led to bad science:
Most fibers floating in the world’s oceans are not plastic but dyed cellulose. This is in agreement with recent studies showing that cellulosic fibers account for more than 60–80% of all fibers in seafloor sediments, marine organisms, wastewater, fresh water, ice cores, and airborne fiber populations. Before these studies, cellulosic fibers (natural and regenerated) have been likely included in the synthetic realm by hundreds of studies, inflating “microplastic” counts in both environmental matrices and organisms. This error has resulted either from the assumption that all colored fibers are synthetic—although without proper chemical identification, visual identification of synthetic fibers has been criticized—or from the assumption that man-made cellulosic fibers can be considered synthetic and included in microplastic counts because they are extruded and processed industrially.
The next question they consider is, what is the fate of this fibrous cellulose? Some sea organisms eat it! Even the “synthetic” cellulose is part of their food supply.
“Semi-synthetic” cellulosics are a readily available source of carbon for microorganisms, and their biodegradability seems to be similar to, if not faster than, cotton yarns, and considerably faster than synthetic polymers such as polyester. Therefore, as already highlighted by other authors, extruded cellulosics such as viscose/rayon, lyocell, and acetate should not be considered synthetic, irrespective of their origin.
The authors were surprised by this, given how widespread is the assumption that humans are foiling the planet with plastic. They do make a distinction, though, between the microfiber material and plastic bottles made of polyethylene and polypropylene, the main products of the plastics industry. That material is long-lived, and constitutes a serious pollutant. Some environmental groups are developing technologies to collect and degrade that kind of plastic. Nevertheless, the results were unexpected:
The high proportion of animal- and plant-based fibers throughout the world’s oceans is unexpected, given the dominance of synthetic fibers in current global production (62%, compared to 8% in our samples). Cellulosic and animal fibers accounted for 80 and 12% of our samples, despite comprising only 36% and less than 2% of global production, respectively…. if anything, cellulosic fibers should be underrepresented rather than overrepresented in surface water samples. The causes of this apparent shortage of synthetic fibers in environmental samples are currently unknown, and more research is needed to elucidate this pattern.
But if cellulose is biodegradable, why does it dominate fibrous material in ocean water? Some of it may have a lifetime that is artificially extended by processing. They mention “a dyed cotton waistcoat recovered from a deep-ocean shipwreck showed almost no sign of degradation after years of submersion.” That being said, rates of degradation of various materials are little known, and may depend on the particular environment: depth, temperature, and ecology.
Suffice it to say that cellulose, wool, and other plant animal fibers are not pollutants in themselves. Undoubtedly biological microfiber, like wool, cotton, and plant cellulose, has been entering the ocean for millennia before humans accelerated it. Even oil seeps and methane leaks have occurred long before the oil industry. One might recall how quickly microbes degraded some oil spills.
Another question regards the fate of cellulose and ‘natural’ fibrous material. The authors suggest that much of it should sink to the ocean bottom and be buried in sediment. But how much is ingested, or suspended in the water column? We don’t know.
With the exception of polypropylene, all natural and synthetic polymers found in our study have densities greater than seawater and should sink. Their widespread occurrence in surface waters could thus be explained by a constant atmospheric deposition to the ocean surface, coupled with retention mechanisms within the sea surface microlayer and complex turbulence and resuspension processes about which we know very little.
This paper underscores the need for scientists to be careful. They must not assume things, or depend on other published papers, which may have made assumptions, and believed earlier papers’ assumptions, and so on back up the line. It is common for papers to contain numerous references to earlier work, but how many scientists really examine the quality of the work they refer to? There’s no substitute for going out and measuring. Even then, scientists must ask sufficient questions to avoid jumping to conclusions:
- What is the degradation time for each kind of material?
- What effect does temperature have on degradation?
- What is the fate of each material: ocean bottom, water column, or ingestion?
- How does current production of fibrous material in the oceans compare with pre-anthropogenic production?
- Do any of these materials benefit organisms, for instance, as a source of food?
- How do the materials flow through the food web? Do any organisms suffer?
- How do the rates of production and the rates of degradation compare?
- Which geographic locations have the highest concentrations, and why?
- Which materials are the worst culprits, so that environmental policies can concentrate on minimizing them?
This surprising study has lessons for all kinds of science. Sometimes political biases can get ahead of facts (see yesterday’s article about the retracted hydrochloroquine study that had been published in two leading journals, and was widely cited, even by the World Health Organization). The authors pointed out that hundreds of studies made unwarranted assumptions, and miscounted microplastics by lumping natural fibers in with them. They conclude,
The use of natural fibers is being advocated as a strategy to reduce inputs and risks of microplastics into the environment. However, animal and cellulosic fibers are greatly underrepresented in environmental pollution literature. Research on the prevalence, fate, and impacts of microfibers is relatively young and often unbalanced in favor of plastic polymers. More information is needed on the degradation of natural fibers relative to synthetic polymers. Here, we show that natural and synthetic fibers are ubiquitous in the world’s oceans and that their abundance and composition are not homogeneous among ocean basins. As already demonstrated in freshwater and atmospheric deposition and in marked contrast to global production patterns, around 80–90% of fibers in our samples are of natural origin. Understanding the ecological impacts and biodegradation rates of natural and synthetic fibers in a range of environmental conditions is crucial for assessing their potential impacts on environments and ecosystems worldwide.
A common problem in calculus is to solve for impacts of “sources” and “sinks” — illustrated by a bathtub with the drain open and the spigot running. Depending on the rate of source input (the spigot) and the rate of output (the drain), students can figure out if the water will rise or fall, and how fast. The problems become more complicated when there are multiple inputs, such as here, when different kinds of material are entering the oceans at different rates, each with their own degradation times. The problems may become intractable when sources of error in the input and output rates become excessive. If input is growing faster than output, that could lead to a crisis. If output exceeds input, there is less worry, because the situation will heal itself. A steady state could also be occurring. But who can tell? These are matters “about which we know very little.”
One rarely sees this kind of nuance in popular articles about pollution. There is much we don’t know about the multitude of factors entering the equation. One thing we do know: politicians and reporters can often miss the nuance if they have a political axe to grind, and talk in glittering generalities to push their agenda. How many environmental groups decrying plastic pollution, posting out-of-context photos of dead seabirds or turtles on the beach with plastic in their guts, knew that over 90% of fibers in the oceans are of natural origin? If they could be this inaccurate about something measurable in real time, how much more inaccurate could they be about claims of climate disasters a century in the future, or evolutionary happenings hundreds of millions of years ago? (see article about Extinctions, 28 May 2020).
Again, nothing in this article should minimize one’s concern about ocean pollution; it should just add clarity and context, so that policies do not exceed knowledge. Hopefully the articles from yesterday and today lead our readers to be more careful about confident-sounding pronouncements in the science media.