As noted in the editor’s comment below, a university study concluded that the results of this article were based in part on data that was completely fabricated. As a result, the document has now been formally withdrawn.
EDITOR’S NOTE: The article on which this report was based contained fraudulent data and is currently being withdrawn.
The advent of plastics has given humanity a prominent footprint on the world. Plastics offer numerous benefits, such as convenience and low cost, but the proper recycling or disposal of plastics is an ongoing challenge.
Most conventional plastics do not undergo appreciable biodegradation. Plastic that is not properly disposed of ends up in the environment, where it breaks down into smaller and smaller pieces. Plastic often ends up in the ocean in pieces less than five millimeters in size.
This microplastic waste can be ingested by marine biota and affects life both physically and chemically. But little is known about the overall effect of plastic pollution on marine animals or the mechanisms that would drive any effects. In a recent study published in Scienceresearchers from Sweden investigated the influence of plastic microparticles on the development and survival of a fairly typical fish.
Tracking microplastic pollution
There is a lot of pollution from microplastic particles on the Swedish coast. When sampling zooplankton from the least polluted areas, the team found as many as 150 plastic particles per cubic meter. The most polluted areas were dramatically worse with 102,000 plastic particles per cubic meter. The team decided to evaluate the effects of polystyrene, a common plastic contaminant that has already been shown to alter the behavior and disrupt the chemical pathways of freshwater fish.
They evaluated the effect of three test conditions: the control condition contained no plastic contaminants; one test condition mimicked the average microplastic concentrations found of 10,000 particles per cubic meter; and the third concentration represented highly polluted areas with a concentration of 80,000 particles per cubic meter. During the studies, all fish (the researchers used Eurasian bass) were given the same feeding conditions.
The team laid fertilized eggs from the perch (P. fluviatilis from the Baltic Sea) in a small glass aquarium under one of the three polystyrene concentrations described above. They followed the eggs over a three-week period and counted the number of successful hatches. The fish that were not exposed to the microplastics had the highest hatching rates (96 percent). The lowest hatching rate (81 percent) was seen when fish were exposed to the highest concentration of polystyrene.
The intermediate microplastic concentration produced a modest reduction in hatching at a rate of 89 percent. It is clear that the presence of the polystyrene microplastic has a negative impact on these fish larvae.
Plastic pollutant effects on juvenile fish
The team continued to monitor the effect of microplastic exposure during the boy’s first week of development. Exposure to microplastics during this period led to behavioral changes that were visible in 10-day-old fish larvae. Fish exposed to microplastics had reduced activity, shorter swimming distances and spent more time immobile than fish living in clean water.
Juvenile fish are very vulnerable to predation. But most organisms have certain biological mechanisms that warn them against (and protect them from) predators. They can avoid predators by sensing chemical cues in the water – an olfactory threat response. The sense of smell in larval fish is very sensitive to changes in the environment, although the exact response to polluting microplastics has not been studied.
To test the innate fear responses of the 10-day-old bass, the scientists injected a chemical alarm signal and watched the fish react. Fish reared in the presence of microplastics showed weaker responses to threats compared to fish reared in the absence of microparticles. Those exposed to high concentrations of microplastic showed none each antipredator response when exposed to chemical threat signals.
The scientists took this test a step further by throwing in the perch with a natural and common predator of the larval perch, the juvenile pike. Perch survival was monitored every 2 to 6 hours over a 24 hour period. Exposure to microplastic significantly reduced the chance of survival. Each larva cultured in the high concentration of microplastic was eaten by the pike compared to only half of the control larvae.
Two weeks after hatching, the plastic had also slowed the growth of the fish. The smallest fish (8.35 ± 0.07 mm) were those grown in the highest concentrations of microplastic, while those grown without plastic contaminants were the longest (9.17 ± 0.1 mm). Those raised in the moderate microplastic conditions came in between the two (8.89 ± 0.12 mm).
The scientists noticed something that could easily explain this growth difference: They found that newly hatched larvae actually prefer to consume microplastic particles over natural, free-swimming food sources. The fish living in environments with a lot of microplastics consumed only the polystyrene particles (7.15 ± 1.2). Fish living in medium microparticle concentrations consumed fewer microplastic particles (1.4 ± 0.35), plus they ate some of the real fish food available in the environment. It is therefore not surprising that fish raised in environments lacking microplastics consumed only the fish food.
It is clear that microplastic particles polluting our oceans are harmful to fish such as bass, especially during the early stages of their lives. The scientists claim their findings could explain the decline of coastal rock species, including both perch and pike.
Science2016. DOI 10.1126/science.aad8828 (About DOIs).