Mathalon, A., Hill, P. Microplastic fibers in the intertidal ecosystem surrounding Halifax Harbor, Nova Scotia. Mar. Pollut. Bull. (2014), http://dx.doi.org/10.1016/j.marpolbul.2014.02.018
Microplastics are the tiny pieces of plastic, at least <5mm but usually < 1mm (hence the “micro”), that result largely from the breakdown of larger plastic debris in our oceans, but are also from production and waste of certain products. Today, you can find microplastics in the form of ‘spheres, pellets, irregular fragments, and fibers’ virtually anywhere you look for them as a byproduct of the society we live in. Two of the most prevalent places they are found are along the coast, particularly an urbanized coast, and in mid-ocean gyres (for more on that, read here!). The statistics of plastic production are staggering as plastics are virtually used by most people every single day. It is estimated that in 1950 around 1.5 million tones of plastic were produced; compared to current estimates that we have produced approximately 240 – 280 million tones of plastic every year since 2008. On top of that, approximately 50% of this production gets thrown away after only being used once! Included in these figures are the plastics we think of more traditionally, such as plastic used in packaging for products, in single use plastic shopping bags, in single use water and soda bottles, etc… Yet, what is also included in these figures are things you might not traditionally associate with the term ‘plastic’ and furthermore, plastic pollution. Examples of these are little tiny polyethylene microbeads that might be in your facewash as an ‘exfoliant’ or small polyester fibers that have washed out of your clothing. Previous studies have found that a single washing of a synthetic clothing garment (e.g. your favorite outdoor fleece) can release as many as 1900 or more microfibers into the wash stream. The problem is that when we wash our synthetic clothes or wash our faces with tiny microbeads, that water goes to a wastewater treatment plant that is essentially not equipped to remove tiny pieces of this size. This inevitably means they end up in the marine environment.
There are a number of reasons to be concerned about the concentrations of microplastics including their potential to be ingested by marine life due to their small size, but also their potential to sorb organic contaminants and subsequently transfer them to the marine organisms whose organs they now reside in (check out this piece by Carrie!). Not to mention their aesthetic appeal is not at the top of everyone’s wish list for “views at the beach.” The study we’re looking at today was performed by researchers in Halifax, Nova Scotia who investigated microplastic fibers in the intertidal region around Halifax Harbor (Fig. 1).
What they Did
Three different types of samples were collected from three different sources. The first was sediment from three different beaches, two of which are relatively protected and one of which is exposed. Samples were taken from the high, mid, and low tide line and were analyzed to see if there were any correlations between tidal range, protected v. exposed beaches, and grain size. The second sample set was of fecal casts from polychaete worms, which are deposit feeders; and the third sample set was from blue mussels (Mytulis edulis) from both beach sites as well as from aquaculture/farmed sites (purchased from a grocery store).
Looking for microplastics in some of these samples can be a bit challenging. One of the first procedures is to apply multiple hydrogen peroxide (H2O2) treatments to the samples to remove any organic matter present. Once the organic matter is removed, the microplastics are separated out with a concentrated saline (NaCl) solution. The idea is that most of the microplastics are less dense than the solution and will float to the surface. In addition to all of the samples, blanks are added to the sample set to ensure confidence in laboratory results.
What they found
All samples analyzed contained microplastic fibers. The sediment samples from the beach had around 20 – 80 microplastics/10g sediment. The exposed beach had the most fibers at the high tide line, versus the protected beaches had the most fibers at the low tide line. This makes sense when considering wave and wind energy on an exposed beach vs. protected shoreline. There was no correlation found between grain size and microplastic fibers found. The polychaete worm fecal casts showed similar microplastic concentrations to the beaches they were collected from, with an average of around 45 microplastics per 10g. This implies that the worms are essentially eating (and excreting) the microplastics at the same levels that surround them. One of the biggest differences was observed between wild mussels collected from the beaches and farmed mussels purchased at the store. Initially, it was thought that the farmed mussels might have lower concentrations than the beach mussels because they are farmed further offshore and away from the urbanized harbor, however, the number of microplastics per farmed mussel was significantly higher than the number per wild mussel (Fig.2). Reasons for this were suggested to be the fact that the mussels are farmed on a polypropylene line, or there is some other pathway of plastic contamination from the farm site to the market. On a side note, it is mentioned that the presence of microplastics in aquaculture is currently unregulated.
In short, microplastic fibers can be found virtually anywhere you choose to look. The scientists mention the need for extreme caution in a laboratory setting due to microplastic fiber contamination. Suggestions for future work are focused on further investigation into the role of organic contaminant sorption to these plastics and the resulting interactions with these plastics as they are passed up the trophic food web.