Out of sight, out of mind: the trouble with little things

If we can’t see it, then it doesn’t exist, right?

Wrong. In the Dr Seuss story “Horton hears a Who”, the elephant knew that the lives of the Who’s of Whoville, living as they were on a tiny speck of dust, depended on him. He alone believed in their existence, and he alone was aware that this made Whoville prone to unexpected movement, weather, and activity, and even complete changes of location.

Animated elephant Horton finds a speck of dust floating in the Jungle of Nool. Upon investigation of the speck, Horton discovers the tiny city of Who-ville and its residents, the Whos, which he can hear but cannot see. Horton forms a friendship with the mayor of Who-ville, Ned McDodd, and promises to transport Who-ville to safety. However, Horton encounters opposition from his jungle neighbours, who don't want to believe in the existence of Who-ville. Remember: “A person’s a person, no matter how small”

Animated elephant Horton finds a speck of dust floating in the Jungle of Nool. Upon investigation of the speck, Horton discovers the tiny city of Who-ville and its residents, the Whos, which he can hear but cannot see. Horton forms a friendship with the mayor of Who-ville, Ned McDodd, and promises to transport Who-ville to safety. However, Horton encounters opposition from his jungle neighbours, who don't want to believe in the existence of Who-ville. Remember: “A person’s a person, no matter how small”

That’s the trouble with very small things: they move around, they get everywhere. We can try to ignore them, but…

Particulate matter, including micro plastics, might well be something we’re only now waking up to. However, there are already fears of the impact these may be having on the ecosystems around us and, directly, on human health.

Many millions of tonnes of plastic are discarded into the environment every year and are broken down into small particles and fibres that do not biodegrade. These particles, known as microplastics, have now been found everywhere from high mountains to deep oceans. These can carry toxic chemicals and harmful microbes. Studies carried out in the snows of the Arctic Circle and the Alps have found abundant levels of mircoplastic pollution, prompting scientists to warn of significant contamination of the atmosphere and potential health impacts on people. This comes after earlier studies have found particles in cancerous human lung tissue, and the calculation that people eat at least 50,000 microplastic particles per year.

Microplastics, transported by the air, are turning up everywhere, including in snow deposits within the Arctic Circle

Microplastics, transported by the air, are turning up everywhere, including in snow deposits within the Arctic Circle

Transport by winds is a major factor in dispersal of and contamination by microplastics. There is now so much concern on the part of researchers that it is being recommended for microplastics to be included in air pollutant monitoring schemes. Microplastics from polymer-based protective coatings on vehicles, buildings and ships were the most common of those frequently found by the researchers, followed by rubber, polyethylene and polyamides including nylon.

Bear in mind that much of the sampling has been of particles 11 microns and above in size. Scientists are very concerned that there may be many more in the smaller size range, i.e. beyond their detection limits. The very real fear is that these can be taken up by a greater range of organisms and, if they reach nano-scale, they could penetrate cell membranes and translocate into organs much more easily than the larger fraction.

Meanwhile, British researchers have been digging lugworms out of the sand on beaches on Tenerife, Scotland and Cumbria (I know which I’d rather be on). Lugworms will ingest any particles of plastic they comes across while swallowing sand, which can then pass up the food chain to birds and fish.

Lugworms, commonly used as fishing bait, will consume plastic particles

Lugworms, commonly used as fishing bait, will consume plastic particles

So, if you're exposed to more plastics are you going to be eating more plastics? What types of plastics, what shapes, colours, sizes? By identifying the type of polymer, the type of plastic it is and then by matching that with the known uses of those polymers you can sometimes make an educated guess of where that plastic's likely to have come from.

From the Great Pacific garbage patch to riverbeds and streets in the UK, microplastics are among the most widespread contaminants on the planet, turning up from the deepest parts of our oceans to the stomachs of whales and seabirds. The explosion in plastic use in recent decades is so great that microplastics are becoming a permanent part of the Earth's sedimentary rocks - yes, you read that right:

While studying rock sediments off the Californian coast, scientists discovered disturbing evidence of how our love of plastic is leaving an indelible mark on the planet. There has been an exponential increase in microplastics being left behind in our sediment record, and that exponential increase in microplastics almost perfectly mirrors the exponential increase in plastic production.

The plastic we're using is getting out into the ocean and we're leaving it behind in our fossil record - what a legacy! Are we now living in the Age of Plastic?

Ocean sediments are a cemetery for plastic! Our sedimentary record is in danger of being characterised by a seam of plastic.

Ocean sediments are a cemetery for plastic! Our sedimentary record is in danger of being characterised by a seam of plastic.

In August, the World Health Organization (WHO) released a report concluding that while particles in tap and bottled water do not pose an apparent health hazard, more research and evidence is needed. However, perhaps we ought to know the "plastic score" of the animals that are ending up on our dinner plates. After all, these microplastics are small enough to be eaten by plankton and by coral polyps and by filter-feeding mussels, but how are they bio-accumulating up the food chain? By the time you get to a huge fish, is that fish eating plastic itself or is it eating thousands of little fish that are eating thousands of plankton, that are eating thousands of microplastics. Which makes you wonder about the size of the plastic signature in something like a tuna by the time it gets on your dinner plate? That’s certainly not something you’re told - because we just don’t know!

But, before those of us living on a plant-based diet get too complacent, it’s worth considering that plants might be suffering from plastic in the environment too. At the moment the risks are unproven, but this is because it’s so much easier to spot plastic in aquatic systems than soil. There are plenty of reports showing microplastics in many terrestrial ecosystems, and these will not all have the same effect. Although plastic beads are a problem in the food chain in marine environments, they are considered a potential minor effect in soil in terrestrial environments. Fibres might even boost plant growth in changing soil density. Not all effects are expected to be positive though. These same changes in density could affect the microbe community. Plastics can change the soil chemistry. Films could increase water evaporation, drying out the soil. Plastic surfaces could allow toxic substances to accumulate in ways that they couldn’t in organic soil.

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If you thought biodegradable plastic was emphatically good, you might want to think again, too. Large biodegradable plastics breaking down become microplastics and food for microbes. These are a rich source of carbon, which is good for microbes, which need large amounts of carbon to build cells. But, they don’t just need carbon though. They also need other nutrients like nitrogen. So, if a plastic feast provides the carbon, but not enough other elements, then the microbes grab this from elsewhere in the soil, leading to nutrient immobilisation - when microbes grab the nutrients, they’re no longer available for plants to use.

Breaking down microplastics will create nanoplastics. When plastic particles are smaller, there’s a greater chance of uptake by roots. Will these nanoparticles be toxic? As I said earlier, it’s rare for anything to simply disappear.

What, then, is the scale of the problem?

  • Over 400 million tons of plastic are produced globally each year

  • It is estimated that one third of all plastic waste ends up in soils or freshwaters.

  • Most of this plastic disintegrates into particles smaller than five millimetres, referred to as microplastics, and breaks down further into nanoparticles, which are less than 0.1 micrometre in size.

  • Terrestrial microplastic pollution is much higher than marine microplastic pollution – an estimate of four to 23 times more, depending on the environment.

  • Sewage, for example, is an important factor in the distribution of microplastics. In fact, 80 to 90 per cent of the particles contained in sewage, such as from garment fibres, persist in the sludge.

  • Sewage sludge is then often applied to fields as fertilizer, meaning that several thousand tons of microplastics end up in our soils each year.

Some microplastics exhibit properties that might have direct damaging effects on ecosystems. For instance, the surfaces of tiny fragments of plastic may carry disease-causing organisms and act as a vector that transmits diseases in the environment. Microplastics can also interact with soil fauna, affecting their health and soil functions.

Generally speaking, when plastic particles break down, they gain new physical and chemical properties, increasing the risk that they will have a toxic effect on organisms. The more likely it is that toxic effects will occur, the larger the number of potentially affected species and ecological functions. Chemical effects are especially problematic at the decomposition stage, e.g. additives such as phthalates and Bisphenol A leach out of plastic particles. These additives are known for their hormonal effects and can potentially disrupt the hormone system not only of vertebrates, but also of several invertebrates.

In addition, nano-sized particles may cause inflammation; they may traverse or change cellular barriers, and even cross highly selective membranes such as the blood-brain barrier or the placenta. Within the cell, they can trigger changes in gene expression and biochemical reactions, among other things. The long-term effects of these changes have not yet been sufficiently explored. However, it has already been shown that when passing the blood-brain barrier nanoplastics have a behaviour-changing effect in fish.

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Humans also ingest microplastics via food: they have already been detected not only in fish and seafood, but also in salt, sugar and beer. It could be that the accumulation of plastics in terrestrial organisms is already common everywhere, even among those that do not “ingest” their food, e.g. tiny fragments of plastic can be accumulated in yeasts and filamentous fungi.

The intake and uptake of small microplastics could turn out to be the new long-term stress factor for the environment. It’s high time we took this threat seriously, rather than our usual, somewhat complacent, ‘out of sight, out of mind’ attitude.