[LUM#18] Plastic is dramatic
Overfishing, global warming, water acidification... Times are tough for fish, whose numbers are dwindling in the oceans. Added to these threats is another: plastic. Researchers have explored the effects of exposure to microplastics and show that these tiny particles have consequences for marine wildlife that are inversely proportional to their size...
When we think of plastic pollution, we often see images of turtles or fish suffocating on large pieces of debris, but there is another problem with plastics: they break down into particles that are sometimes barely visible, microplastics 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 floating plastics such as polyethylene, but also on denser, more in
plastics that sink to the bottom of the water, such as PVC," explains Xavier Cousin.
To better understand the consequences of these substances, researchers exposed a fish, the marine medaka, to plastic particles coated or uncoated with these three pollutants in a laboratory setting. "This allowed us to study their effects at concentrations similar to those found in their environment throughout the animal's life cycle, " explains Xavier Cousin.
Growth reduction
First observation: a 20 to 35% reduction in fish growth. "These effects are much more significant after four months of exposure than after two months, which highlights 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 they have higher energy requirements than males during reproduction, " adds Marie-Laure Bégout.
Reproduction, a process that seems to be the primary target of 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 almost all microplastics causes a delay in 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 with added benzophenone-3, behavioral disorders are observed in the offspring at the larval stage."
Risk assessment
While all these consequences are enough to cause serious ecological problems, the results of this study probably still underestimate the reality: "In the laboratory, fish are pampered, but in their natural environment they are exposed to other pressures: predation, fishing, 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 tons of plastic end up in the oceans. 10% float in the form of micro-waste 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 disruption will also make it possible to assess the extent to which these effects can be generalized to all types of microplastics, for example, in order to prioritize the control of emissions
.
Eternal fragments
Will that plastic polyethylene bag that we just threw into the sea eventually disappear? "It will take several hundred years to degrade completely, but it will quickly break down 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 rays, and mechanical stress from waves, a piece of plastic bag will take about 10 years to degrade into tiny fragments, the famous 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... 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 much worse than visible plastic pollution, because these microplastics will not disappear and cannot be recovered from the water, " laments the researcher. What about biodegradable plastics? "They are 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 research is underway to develop new materials, we shouldn't expect any miracles. The only solution is to prevent these plastics from entering the seas and oceans by reducing their production and improving waste collection," concludes the researcher.
*Marbec (UM, IRD, CNRS, Ifremer)
**L2C (UM, CNRS)
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