2017 Study Abstract
The tremendous increases in production of plastic materials has led to an accumulation of plastic pollution worldwide. Many studies have addressed the physical effects of large-sized plastics on organisms, whereas few have focused on plastic nanoparticles, despite their distinct chemical, physical and mechanical properties. Hence our understanding of their effects on ecosystem function, behaviour and metabolism of organisms remains elusive. Here we demonstrate that plastic nanoparticles reduce survival of aquatic zooplankton and penetrate the blood-to-brain barrier in fish and cause behavioural disorders. Hence, for the first time, we uncover direct interactions between plastic nanoparticles and brain tissue, which is the likely mechanism behind the observed behavioural disorders in the top consumer. In a broader perspective, our findings demonstrate that plastic nanoparticles are transferred up through a food chain, enter the brain of the top consumer and affect its behaviour, thereby severely disrupting the function of natural ecosystems.
The amount of plastics in the world’s water bodies is rapidly increasing and this material degrades in size over time and will eventually break down into plastic nanoparticles. Due to their small size, they easily enter the basis of natural food chains, although it is unclear how these particles affect aquatic ecosystems. We show here that 52 nm positively charged amino modified polystyrene nanoparticles are toxic to Daphnia and that fish feeding on Daphnia containing plastic nanoparticles change their behaviour in terms of activity, feeding time and the distance they need to swim to consume their provided food. Furthermore, the behavioural changes depend on the size of the particles. However, fish receiving 180 nm particles were differently affected as they were the fastest feeders and had the highest activity. In nature, the particles likely become aggregated with biological or inorganic material, but we here show that the nano-size effect remains after passing through the Daphnia digestive system. For example, Ward et al. exposed the blue mussel Mytilus edulis and the oyster Crassostrea virginica to polystyrene nanoparticles, aggregated nanoparticles and micro-particles and found a higher ingestion rate for the aggregated nanoparticles. Wegner et al. exposed the mussel Mytilus edulis to polystyrene nanoparticles both as nano-sized particles and as aggregated polystyrene nanoparticles. They found a reduced filtering rate and an increased production of pseudofeces. In this context, our results point to an acute need for a deeper understanding of the size-dependent toxicity effects of nanoparticles when released into nature. How these particles affect organisms higher up in the food web, such as fish, as well as how they affect birds and mammals are unclear. In 2015, the estimated amount of plastics being released into the ocean was between 4.8 and 12.7 million tons, with a steady increase the coming years. Eventually this plastic will degrade in size and reach the nanometer size range.
Here we demonstrate how plastic nanoparticles are transported up the food chain and are detected in brain tissue of the fish top consumer whereas no polystyrene were detected in the control group. Moreover, we also here report macroscopic changes in the brain structure and water content in fish that have received plastic nanoparticles. By using hyperspectral microscopy, we were able to detect polystyrene particles in fish brain tissue and thereby we have, for the first time, demonstrated that the plastics nanoparticles can be transported across the blood-brain barrier in fish. Moreover, this result suggests a mechanistic link between the observed behavioural changes and the presence of plastic nanoparticles in the brain tissue. In the present study, we observed changes in the brain which may have been caused by specific interactions between the plastics and the brain tissue, although we cannot rule out that other organs may also be affected. Our study lasted for two months, but during the first half of the experiment we observed no changes in behaviour of the nanoparticle fed fish, suggesting that fish are affected by the particles that are accumulated in the fish. In nature, the Daphnia and fish are likely exposed to low concentrations of plastic nanoparticles during their whole life-time, which allows accumulation processes to act for a much longer time period than in our study, since fish, such as crucian carp, may live for more than 10 years. However, our results also imply that effects on biota from plastic nanoplastics are dependent on both concentration and size of the particles, which opens up for manufacturers to adjust production of nanoparticles to sizes that are less hazardous to organism metabolism and thereby ecosystem function.
The main conclusion from our study is that plastic nanoparticles are transferred through three tropic levels, suggesting that they are likely to be transferred even further up the food web to ultimately reach humans, the top-level consumer. Hence, in a broader perspective, our results may have implications for human wellbeing, although such consequences of the accelerating disposal rate of plastics is yet not well recognized or understood.
- Brain damage and behavioural disorders in fish induced by plastic nanoparticles delivered through the food chain, Nature Scientific Reports, doi:10.1038/s41598-017-10813-0, 13 September 2017.
- Nanoparticles featured image : Food chain from algae-zooplankton-fish, nanoparticles (53 nm mass (dark blue), 53 nm surface area (light blue) and 180 nm (red)) credit nature.