A guest post by Erica K. Brockmeier
The following post is one of a series generated from research presented at the SETAC Europe Annual Meeting in Brussels, Belgium (7-11 May 2017). Each post features the latest research findings from SETAC scientists on emerging topics of interest.
What are microplastics and why should we care about them?
Microplastics are pieces of plastic or polymer debris that are very small in size, ranging from a shard as narrow as the width of a hair to a piece as large as a marble. Microplastics include pieces of plastic that are broken down from larger items, such as single-use water bottles, or ‘microbeads’ that are added to certain soaps and exfoliators.
Even though microplastics are small, there are concerns they can cause serious damage. Animals that confuse microplastics for food can end up with internal lacerations, inflammation, and nutrient deficiency caused by eating too much inedible material. Microplastics are also widely spread across the globe—scientists calculated that up to 90% of marine birds have ingested microplastics.
Plastic waste can be found everywhere. Coupled with predictions that plastic production could increase to 33 billion tons each year by 2050, it appears that microplastics are not going away anytime soon. Major news outlets regularly highlight the pervasive nature of this waste, including the story of the recent discovery of over 37 million pieces of plastic garbage on a South Pacific island.
Environmental toxicology researchers at the SETAC Brussels meeting (May 2017) presented a range of studies exploring the impacts of microplastics and addressing the challenges that we face in combating this pervasive, persistent, and tiny pollutant. In this post we highlight some of the findings presented during the sessions “Challenges and best practices in monitoring of micro- and nanoplastic abundance and environmental distribution” and “Microplastics, nanoplastics and co-contaminants: Fate, effects, and risk assessment for biota, the environment and human health.”
Microplastic monitoring: Where does it come from and where does it go?
One of the challenges for researchers is that microplastics comprise a large and diverse group of materials, including various sizes, shapes, materials, and sources. Some microplastics are formed by the breakdown of larger materials, while others are added into household products (e.g., microbeads), so it’s difficult to trace the fate of these materials.
Beate Baensch-Baltruschat from the German Fedreal Institute of Hydrology conducted a survey of plastic monitoring in European freshwater ecosystems. She found that rivers and streams are important for following the movement of plastics since these waterways are a major route for microplastics on their journey to the ocean. The survey looked at active sampling efforts by ten countries across Western and Central Europe. Monitoring data collected by these surveys revealed that there is a wide range of microplastic sizes, with larger particles (0.1 mm to 10 mm) more prevalent in surface waters and smaller particles found primarily in sediments.
Jes Vollertsen (Aalborg University) noted the problem of how the transport of microplastics during stormwater runoff events was not well-understood. To explore the issue, his research group sampled water and sediment from stormwater retention ponds in Denmark to examine microplastic levels. Their survey found that stormwater can hold up to 10 micrograms of microplastics per liter, and that nearly half of this plastic waste builds up in the sediment while the other half slowly discharges out of the pond water over time. Both Vollertsen and Baensch-Baltruschat’s work highlight the importance of monitoring and tracking microplastic movement in different types of environments.
Fabienne Lagarde from the Institute of Molecules and Materials studied how mussels were impacted by microplastic contamination along the Atlantic coast of France. Lagarde and her team identified 73 microplastics across all of the mussels they sampled over two sites, seasons, and habitats (wild caught versus cultivated environments). Eighty-five percent of the particles were polyethylene and polypropylene. Polyethylene is primarily found in single-use plastics such as bags and bottles, while polypropylene is made for more durable materials like plastic pipes and furniture. While microplastic levels did not differ significantly between seasons, sampling sites, or habitats, Lagarde’s results highlight the pervasive nature of microplastic contamination. Over 140,000 tons of mussels are produced in France every year, so studies like this are crucial for understanding potential risk to seafood consumers.
Some microplastics are in the form of fibers, shed from synthetic clothing during laundering. When these plastic microfibers enter the waste stream, pieces that are too small to be filtered out (microfibers) are discharged into the environment. Imogen Napper (Plymouth University) measured microfibers released from wash cycles with synthetic materials and found that a typical 6-kg wash of polyester-cotton blend clothing releases 137,000 fibers into wastewater. Even more microfibers are released from polyester materials (nearly 500,000) and acrylic clothing (728,000 fibers). Napper proposed a straightforward solution of including filters on washing machines to collect microfibers in order to reduce the large number of them that are discharged into the environment.
Microplastic effects: Are microplastics harmful to marine wildlife?
Inger Lise Nerland from NIVA discussed her work examining the impacts of polyethylene microbead exposure on Mediterranean mussels. Nerland exposed mussels to microbeads isolated from toothpaste for 3 weeks. The study was designed to reflect what happens in an actual environmental exposure by weathering the microbeads (allowing the material to break down naturally in seawater) before the exposure started. Nerland and her group found that not only did mussels ingest the microbeads, but that mussels with plastic particles had a higher number of blood cells in their gills, thinner gill tissues, and clumps of blood cells in their digestive system. This study provides more support for the hypothesis that microbead exposure can cause damage to the wildlife they come in contact with.
Theresee Karlsson (University of Gothenburg) looked at how single-use polyethylene bags break down in seawater. These single-use bags are very lightweight, yet somehow scientists find polyethylene deep in ocean sediments. Karlsson cut single-use bags into pieces of various sizes and placed the bags in stainless steel cages. Karlsson’s study showed that the amount of time that plastic pieces were left to degrade influenced the growth of microorganisms, or biofilms, on the plastic. The presence of biofilms changed the density of the plastic waste due to a build-up of calcium and silica. The example of how polyethylene bags change in density when they are bound by biofilms demonstrates how plastic waste cannot be classified in any broad, all-encompassing manner—even waste that starts off as the same material can have a completely different fate based on how it interacts with the environment.
Adam Porter from the University of Exeter highlighted his work demonstrating the importance of marine snow—organic matter, such as decaying animal and plant material, that falls from the surface levels of the ocean into the deep sea. This ‘snow’ is responsible for moving nutrients from the ocean’s surface down to the organisms living in the depths of the ocean. Porter’s work provides evidence on how marine snow affects the movement of microplastics. Porter measured microplastic sinking rates in artificial water columns both with and without artificial marine snow and also measured the difference in microplastic uptake in mussels. This study found that marine snow can bring lightweight microplastics to lower parts of the water column, and that mussels consumed more microplastics if marine snow was present. Porter’s work highlights the importance of considering deep sea organisms studying effects of microplastics in the marine environment.
Ricardo Beiras (University of Vigo) described how microplastics can bind other chemicals, becoming inadvertent vehicles for chemical exposure. Polymers and plastics contain many additives that can absorb other chemicals, so animals who consume microplastics might accidentally also be eating toxic chemicals. Beiras exposed sea urchin larvae to microplastics that were incubated with a toxic chemical (nonylphenol). While the plastic particles did absorb nonylphenol and the larvae did eat the plastic particles, Beiras did not find any evidence that nonylphenol was transferred to the larvae through the microplastics.
There is still a lot of work to be done to gain a better understanding the environmental fate and impacts of microplastics. Several sessions held at SETAC Brussels brought together researchers from numerous fields to share their work. This post represents just a small part of the global effort to understand and mediate the impacts of plastic pollution for both environmental and human health.
For those who want to help in the effort to reduce microplastics, you can start by using your own shopping bag instead of a single-use bag at the grocery store and look for alternatives to cleaning products containing microbeads.