As noted in the editor's note below, a university investigation has concluded that the results of this paper were based in part on data that was completely fabricated. As a result, the paper has now been formally retracted.

EDITOR'S NOTE: The paper this report was based on contained fraudulent data and is in the process of being retracted.

The advent of plastics has given humanity a prominent materials footprint on the world. Plastics provide lots of benefits, such as convenience and low cost, but proper recycling or disposal of plastics is an ongoing challenge.

Most conventional plastics do not undergo appreciable biological degradation. Plastic that is not properly disposed of ends up in the environment, where it breaks down into smaller and smaller pieces. In the ocean, plastic often ends up in fragments less than five millimeters in size.

This microplastic debris can be ingested by marine biota, and it 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 investigation published in Science, researchers from Sweden explored the influence of plastic microparticles on the development and survival of a fairly typical fish.

Tracking microplastic pollution

On the Swedish coast, microplastic particle pollution is abundant. 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 pollutant that has already been shown to alter behaviors and disturb chemical pathways of freshwater fish.

They evaluated the effect of three test conditions: the control condition lacked plastic pollutants; 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 perch) were provided the same feeding conditions.

The team placed 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 monitored 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 yielded a modest decrease in hatching with a rate of 89 percent. Clearly, the presence of the polystyrene microplastic adversely affects these fish larvae.

Plastic pollutant effects on young fish

The team continued to follow the effect of exposure to microplastic during the hatchlings' first week of development. Exposure to microplastics during this period resulted in behavioral changes that were visible in 10-day-old fish larvae. Fish exposed to microplastics had decreased activity, shorter swimming distances, and spent more time motionless than fish living in clean water.

Young fish are highly vulnerable to predation. But most organisms have certain biological mechanisms that warn them of (and protect them from) predators. They may avoid predators by sensing chemical cues in the water—an olfactory threat response. The olfactory sense in larval fish is very sensitive to changes in the environment, though its exact response to microplastic pollutants has not been studied.

To test the innate fear responses of the 10-day-old perch, the scientists injected a chemical alarm cue and watched how the fish reacted. Fish reared in the presence of microplastics exhibited weaker threat responses compared to the fish reared in the absence of microparticles. Those exposed to high microplastic concentrations didn’t exhibit any antipredator response when exposed to chemical threat cues.

The scientists took this test one step further by throwing the perch in with a natural and common predator of larval perch, juvenile pike. Survival of the perch was monitored every 2 to 6 hours over a 24-hour period. Exposure to microplastic significantly reduced the survival rate. Every single one of the larvae reared in the high microplastic concentration was consumed by the pike compared to only half of the control larvae.

By two weeks after hatching, the plastics had slowed down the growth of fish, too. The smallest fish (8.35 ± 0.07 mm) were those reared in the highest microplastic concentrations, while fish reared in the absence of plastic pollutants were the longest (9.17 ± 0.1 mm). Those reared 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 lots of microplastics consumed only the polystyrene particles (7.15 ±1.2). Fish living at average microparticle concentrations consumed fewer microplastic particles (1.4 ± 0.35), plus they ate some of the actual fish food that was available in the surroundings. Not surprisingly, fish raised in environments lacking microplastic pollutants consumed only the fish food.

Clearly, microplastic particles polluting our oceans are detrimental to fish such as the perch, especially during the early stages of their life. The scientists argue that their findings may provide an explanation for the decline in coastal keystone species, including both the perch and the pike.

Science, 2016. DOI 10.1126/science.aad8828 (About DOIs).