[LUM#18] Plastic Is a Tragedy
Overfishing, global warming, ocean acidification… Times are tough for fish, whose numbers are dwindling in the oceans. Added to these threats is another: plastic. Researchers have studied the effects of exposure to microplastics and have shown that these tiny particles have consequences for marine life that are inversely proportional to their size…
“When we think of plastic pollution, we often see images of turtles or fish choking on large pieces of debris, but there’s another problem with plastics: they break down into particles that are sometimes barely visible—micro- and nanoplastics—which can affect fish metabolism, partly because they carry additives and pollutants,” explain Marie-Laure Bégout and Xavier Cousin, researchers at the Marbec* laboratory. A cocktail of various substances, including perfluorooctane sulfonic acid, used as a flame retardant in plastics; benzophenone-3, which acts as a UV filter in sunscreens; and benzo(a)pyrene, found in petroleum derivatives. “These pollutants are found from the surface to the bottom of the water because they are present on plastics that float, such as polyethylene, but also on denser, more
plastics that sink to the bottom, such as PVC, ” explains Xavier Cousin.
To better understand the effects of these substances, researchers exposed a fish—the marine medaka—to plastic particles, some coated with these three pollutants and others uncoated, in a laboratory setting. “This allowed us to study their effects at concentrations similar to those found in the fish’s natural environment throughout its entire life cycle, ” explains Xavier Cousin.
Slower growth
First finding: a 20–35% reduction in fish growth. “These effects are much more pronounced after 4 months of exposure than after 2 months, which underscores the importance of conducting long-term studies to assess the toxicity of microplastics, ” explains Xavier Cousin. The reduction in growth is more pronounced in females, “probably because their energy requirements are higher than those of males during reproduction, ” adds Marie-Laure Bégout.
Reproduction—a process that appears to be a prime target for these disruptors. Researchers have found that exposed females lay fewer eggs, a phenomenon that can lead to a drop of up to 50% in the usual reproduction rate. “In marine medaka, exposure to nearly all microplastics causes a delay in the onset of egg-laying and a decrease in the number of eggs produced per female per day, ” the researchers add. They also found that the effects varied depending on the type of plastic and pollutant and could even affect the larvae of the next generation. “When fish are exposed to PVC-type plastic containing benzophenone-3, behavioral abnormalities are observed in the offspring at the larval stage.”
Risk Assessment
While all these consequences are enough to lead to serious ecological disruptions, the results of this study likely still underestimate the reality: “In the lab, the fish are pampered, but in their natural environment they are exposed to other pressures: predation, fishing, and other pollutants. Microplastic pollution adds to these factors, all of which are likely to cause problems for fish, ” laments Marie-Laure Bégout.
Every year, 8 to 10 million metric tons of plastic end up in the oceans. 10% of this floats in the form of micro-debris that can potentially carry all kinds of pollutants. “We therefore recommend including this mode of pollutant transfer in the ecotoxicological risk assessment of microplastics,” the researchers conclude. “Understanding the mechanisms underlying biological disruptions will also make it possible to assess the extent to which these effects can be generalized to all types of microplastics, in order, for example, to prioritize the control of
emissions.”
Eternal Fragments
Will this polyethylene plastic bag—which we just let blow away into the sea—eventually disappear? “It will take several hundred years to degrade completely, but it breaks down quickly into smaller and smaller particles,” replies Matthieu George. Together with his colleague Pascale Fabre, the researcher at the Charles Coulomb** laboratory is studying the degradation processes of these polymers. “Under the combined effects of water, UV radiation, and the mechanical stress exerted by waves, a piece of plastic bag will take about 10 years to degrade into tiny fragments—the so-called microplastics smaller than a millimeter,” explains Matthieu George. Unfortunately, once this size is reached, the fragmentation process stops, and these plastic particles can persist for… an eternity. “They are now found absolutely everywhere in the oceans, from north to south and from the bottom to the surface. This invisible pollution is far worse than visible plastic pollution, because these microplastics aren’t going to disappear, and we can’t recover them from the water,” laments the researcher. What about biodegradable plastics? “They’re not a miracle solution, because the ocean environment is not at all conducive to their degradation, which only occurs under very specific conditions, ” emphasizes Matthieu George. So how can we rid the oceans of plastic? “While some research is underway to develop new materials, we shouldn’t expect a miracle solution; the only way forward is to prevent these plastics from entering the seas and oceans by reducing their production and improving waste collection,” the researcher concludes.
*Marbec (UM, IRD, CNRS, Ifremer)
**L2C (UM, CNRS)
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