Microplastics In Ringed Seals From The Baltic Sea - Method development regarding the detection of microplastics in the digestive tract contents of marine mammals

anglais. Plastic pollution is a severe global problem and every year approximately 368 million tons of plastic is produced. Both terrestrial and marine environments are impacted and hundreds of species affected. Marine plastic debris accounts for a weight of 268 940 tons and affects hundreds of marine species through habitat degradation, entanglement and ingestion. Microplastics (MPs) are a type of plastic which have gained traction during the last few decades and are defined as plastic particles with a diameter of 1 μm to 500 μm. They can be of either a primary or secondary nature and come in a wide range of shapes and sizes e.g. fibres, fragments and spheres. Their potential harmful effects if ingested by organisms is not yet fully understood. However, it is known that their biochemical qualities enable them to bind to chemicals which can have harmful effects if ingested, for example endocrine disruptive effects. This study investigated the digestive tract contents of five ringed seals ( Pusa hispida ) from the Baltic Sea, in order to both see if they contained any MPs and to develop an efficient method for detecting MPs. In total, 202 MPs were discovered whereof 143 were fibres and 59 were fragments. The method of using a solution of 30% hydrogen peroxide to dissolve the biogenic matter in the digestive tract contents was successful. Additionally, the study also identified several adjustments which need to be made to the method and gained new knowledge regarding the contamination risk, which needs to be taken into consideration for similar future studies. The fact that MPs were detected in all samples indicates that MPs are a widespread problem and shows the need for further research regarding their potential effects.

anglais. What do you have in common with seals? Did you know that you eat approximately five grams of plastic every week? Yes? No? Either way, don’t you wonder what that plastic might do to you when it is inside your body? Will it damage your stomach or maybe react with important cells? We might not know exactly what the implications of ingesting plastic are, however, that’s why it is important to continue developing efficient methods to detect plastic in different organisms. Here I have looked at the digestive tract contents (pretty much the faeces) of five ringed seals ( Pusa hispida ) from the Baltic Sea and tried to develop an efficient method to detect plastic in these samples. Firstly, you might be thinking, “There’s no way I eat plastic. I don’t swallow plastic bags or bottles!”. However, the plastic that I am talking about might not be the kind that you are used to seeing. Bigger plastics, like bottles, are classified as macroplastics while the type of plastics I’m referring to are called microplastics (MPs). They are only 0,001 mm - 5mm wide and therefore difficult to see without a microscope. Primary MPs are those that have been purposely manufactured to be tiny and are used in everything from facial creams to oil drilling fluids, while secondary MPs are a result of bigger plastic particles breaking down into smaller ones When it comes to marine environments it is estimated that at least 693 marine species have encountered debris, the majority of it being plastic debris. Most of these encounters include animals getting entangled in the plastic such as in old fishing nets. They also include encounters where animals have ingested plastic thinking it was food, which could lead to starvation. I examined the intestines of ringed seals to see if they had encountered any MPs. A solution of hydrogen peroxide was used to dissolve any organic material and all samples were left in the solution for 19-37 days. Two control samples were also made. If I could find plastic in the controls, I knew that all samples probably had been contaminated to some degree. The samples were filtered through sieves with tiny pore sizes and the particles which stuck to the sieves were analysed under a microscope. In total, 202 MPs were detected whereof 143 of them were MP fibres and 59 of them were MP fragments. All detected MPs were of secondary origin. Even though the controls had been contaminated, they contained much fewer MPs than the seal samples and it can therefore be concluded that ringed seals from The Baltic Sea are affected by plastic pollution. As seals are both predators of e.g. fish and prey to e.g. polar bears, it is most likely that plastic is affecting other species within their food web as well. In order to prevent marine mammals, as well as all species, from being negatively affected by MPs, more needs to be done to stop plastic from ending up in the environment. The use of primary MPs also needs to be reduced, or completely stopped and replaced with more environmentally friendly alternatives. Now that we know more and more about the presence of MPs within different species, such as in seals and us humans, it is important to continue researching the potentially harmful effects MPs might have. Future generations of both seals, humans and all other species deserve to live long, healthy lives. We can’t let plastic pollution stop that from happening. Supervisors: Maria Hansson & Josefine Larsson Bachelor’s thesis 15 hp in Biology, 2021 Department of Biology, Lund University