For those of you who are currently sitting at a desk chewing on their plastic pen (or other plastic object). Stop. Think carefully about what you are doing (I have to remind myself about this on a daily basis). You are currently/potentially breaking off teeny tiny pieces of plastics which, if you are unlucky, will find their way into your mouth, and end up in your stomach. You know the old fable that if you swallow chewing gum it will say in your stomach for several years (It’s a myth). Well the same could be said about plastic. In fact it will more than likely exit your body given a day or two. Lets face it, gum and plastic pieces are small, your body cant dissolve or utilize it, so it will try to get rid of it. However, what if the plastic gets stuck, or you eat enough plastic that it has a nasty effect on your body?
This is the basis for theory behind microplastic ingestion in the wild. In most cases ingestion is accidental and plastic is mistaken for food, although some studies have found that plastics can be targeted specifically by animals (more about this later). In some extremely polluted areas, the numbers of microplastic may outweigh natural prey items.
There are so many studies which look at microplastics ingestion in the wild. Most studies of microplastic come from the analysis of stomach contents. Below I am going to discuss are a few highlights, once you start getting into the material you will see that there are several other studies, these are some of the more recent ones. Some of the links you have to have access to journals, although most are available free online. I might be biasing your reading a little with two of them….
- Fish: Lusher et al. 2014, Foekema et al. 2014
- Birds: Acampora et al. 2014
- Mammals: Bravo Rebolledo et al. 2014
- Turtles: Tourinho et al. 2010
- Invertebrates: Murray & Cowie 2011
So we cut up all of these organisms (normally by-catch species, or those washed up on beaches), and find microplastic in their stomachs but what does this mean? The more species we look at, the more we find ingestion plastic. Is this a case of seek and you shall find? On a positive note: in all of the papers I have mentioned above, microplastics are not the cause of death.
Were the organisms feeding directly on microplastics?
This is often hard to determine from wild studies, in the case of the Humbolt squid (Dosidicus gigas) plastic pellets were found in their stomachs (Braid et al. 2012). However they are a predatory species which feeds at depths >200 m. The route of ingestion is unknown, they could have been feeding directly on pellets that had sunk, or they ate organisms that had already eaten pellets.
What’s great about laboratory studies is you can control for the plastics you are looking for and directly expose organisms. However sometimes the levels of exposure are greater than the microplastic level in the wild. Laboratory studies have shown ingestion in marine species. For example:
So why is the study of microplastic uptake important?
Microplastic exposure doesn’t just stop at the individual that has eaten the microplastics. There have been a number of studies addressing the fate of ingested microplastics, and research is still continuing. Below are a quick run down of the fate of microplastics.
1) The first option for microplastics is to pass directly out of the organism, either by excretion or the production of pseudofaeces (think of it like the animals make themselves sick). If this happens then it can be assumed that microplastics are not having any long-lasting effect on the individual.
3) Micropalstics might have negative effects on organisms. Adverse effects of microplastic ingestion have been noticed in laboratory studies. Microplastics can reduce feeding activity and compromise the fitness of a invertebrates. Stephanie Wright’s PhD research has been based around this topic. Her paper on laboratory exposure of worms to microplastic is extremely interesting.
3) Animals with microplastics inside them, may subsequently be eaten by animals from higher in the food chain. Microplastics can therefore pass to other animals.
A question for you:
If microplastics are ingested by fish and bivalves that we, as humans, consume on a regular basis….does this mean microplastics could end up inside us? From here on in: what I say needs to be taken lightly, until we can provide results.
– The answer is technically, Yes. However this is assuming that microplastics are present in the tissue of individuals that we eat. In the case of most fish species, we gut them before eating. The risk is practically non-existent. Although there are some species of fish and mollusc that we eat whole (mussels, pilchard etc). Microplastics might be in there tissues. The word MIGHT is important, because for all we know microplastics may have been egested (as laboratory studies have already shown), and the presence of microplastics will be related to how recently the individual has fed. Gut passage time for fish is relatively fast, and the likelihood of plastics hanging around in the gut of healthy fish is minimum. Furthermore, most shellfish are depurated before sold to the consumer, depuration would in theory allow for microplastics to be passed out of individuals.
-But what if the microplastics have transferred into tissues that we do eat, like skin….well currently there are no conclusive reports in this respect. It is more than likely the plastics will pass through our digestive system in the same way as the chewing gum and plastic example I gave earlier. So there is no need to worry ………. YET.
…..I will come back to the issue of chemicals associated with plastics in another post.
Published by Amy Lusher