This research conducted by France Collard, a doctoral student in the Functional and Evolutionary Morphology Laboratory of the University of Liege studies the presence of microplastics in the digestive system of three commercialized species of fish from the North Sea, the Channel and the Mediterranean. The three species concerned are the herring, sardine and anchovy respectively. The researchers focussed only the experiment of a new method of detection and isolation of these particles in fish stomachs. The next step will confirm the results of this study by precisely identifying the type and number of microplastics ingested as well as the way the fish swallow them. For the moment, the method suggested by France Collard is an opportunity to greatly improve research on the detection of marine pollution by microplastics (1). The research also led to another astonishing discovery: fish stomachs contain as many fibres of cellulose as plastic!

Worldwide levels of plastics production was estimated at 299 megatons in 2013. It is considered that 10% of these plastics end up in the seas and oceans. Marine pollution by plastics is now well-known to the wider public. This is particularly so given the fact that this degradation of the marine environment has led to the spectacular and monstrous spectre of a “seventh continent”. Waste matter that cannot be seen by the naked eye must be added to the overall pollution count. While this state of affairs is already very worrying, there is also the added problem of ingestion of these plastics by marine animal species (mammals, fish, turtles and birds). Very little research on fish has been done into this question which is surprising given that plastic was first produced on an industrial scale as far back as the nineteen-fifties. It is true that these environmental concerns are a relatively recent development. Indeed, on starting her thesis three years ago, France Collard, a researcher at the Functional and Evolutionary Morphology Laboratory and the Laboratory of Oceanology at the University of Liege, could only rely on “seven or eight studies worldwide on the ingestion of plastics by fish. I chose to study the relationship between microplastics and fish, because, despite the economic and ecological importance of fish, almost nothing was known about this phenomenon. In the first instance we didn’t even know whether they ingested plastic or not, whether this had an impact on them, whether they chose to ingest it or whether they were lured and saw the plastic as normal prey”. Many questions remain unanswered or are the subject of theories. For example, what happens to plastic once it has been ingested? Is it digested or not?  « Based on what I have seen in fish stomachs, I can say that there is very little plastic which leads me to believe that it is not digested and is excreted naturally. Of course, if the plastic is too big, it can block the digestive tract. This has not been reported in fish but rather in marine mammals, turtles and birds”. But the problem is not limited to the digestive mechanism alone. In fact, plastic is a material that acts like a magnet for pollutants such as PCB and DDT. “When the fish ingests the plastic, it also ingests pollutants. Once these are in the digestive system they are released from the plastic and find their way into the organs and tissues of the fish. With regard to PBDE, it has been demonstrated that in one species of fish in particular, this compound made its way into the muscles and other tissues”.

But before reaching this stage of analysis, it is first necessary to prove that the particles found are indeed plastic. This is very difficult in the circumstances because here we are dealing with microplastics which are less than five millimetres in size. Observation by the naked eye, even with a stereomicroscope, is therefore hazardous and yet this is the most commonly used method by scientists today. “This is a problem. Some scientists take the easy way out. If they see colours or unusual shapes, they class these as microplastics. From another viewpoint, it is true that it is difficult to analyse such small objects”. Whether difficult or not, France Collard has been working on perfecting an effective method for the detection and isolation of microplastics in fish stomachs and has done so with great success.  For this, it was necessary to degrade all the organic matter (preys) in the stomach so that only suspect particles remained. These were then chemically analysed in order to determine whether they were indeed plastic.

(1) Detection of anthropogenic particles in fish stomachs : an isolation method adapted to indentification by Raman spectroscopy, Collard France, Bernard Gilbert, Gauthier Eppe, Eric Parmentier, Krishna Das, 20 août 2015, in Archives of Environmental Contamination & Toxicology, http://hdl.handle.net/2268/1847