With production of plastic products increasing globally, plastics have been identified as a large component of marine and beach litter. Scientists have studied the abundance and distribution of microplastics, plastic particles less than 5 millimeters in length, in marine and freshwater surface sediments – tiny pieces of matter that float at the top of water. However, less is known about how the abundance and distribution of microplastics varies between different environments.
A research team from Simon Fraser University, Canada, recently analyzed samples of surface sediment from 16 sites within Lambert Channel and Baynes Sound in British Columbia, Canada. They found microplastics at all the sites and identified three main types: microfibers, microbeads and microfragments. The greatest number of all three types of microplastics was found in Henry Bay and Metcalfe Bay, both regions of intense shellfish aquaculture within Baynes Sound.
I spoke with co-author L.I. Bendell about the research findings and their greater implications for these regions, as well as other areas that could be affected by microplastic pollution.
What drew you to studying microplastics in the surface sediments of Baynes Sound and Lambert Channel? Was there a reason why you chose these sites specifically?
LIB: I have been studying this region of the west coast of British Columbia since 1998, for 20 years. This region was recently characterized (in 2012) as being an Ecological and Biological Sensitive Area, an ESBA. The EBSAs were developed as a management tool and are intended to identify areas in need of enhanced management that supersedes the management needs of individual species. The three core criteria for an EBSA include: unique, rare and distinct features; aggregation, including areas where most individuals of a species are aggregated for some part the year; and fitness consequences, defined as areas that are used by species for life history activity (ies) and that make a significant contribution to the fitness of individuals of those species. An EBSA would meet one or more of these core criteria. Baynes Sound and Lambert Channel meet all three criteria.
The question that came forward was: what impact are the plastics, both macro- and micro-, having on this sensitive ecosystem? One of the focuses of my research has been to add to the body of literature on how industrial practices alter the function of intertidal regions, with an emphasis on sediment geochemistry and nutrient cycling. Hence, the rationale for the study: what are the numbers of microplastics in intertidal sediments, what types are they, and are they in amounts that could interfere with the normal functioning of the sediment?
How would you describe the distinct types of microplastics you studied? Does each type have different implications for the ecosystem in which it is found?
LIB: We found three main types of microplastics: fibers, fragments and beads. Fragments are secondary plastics, as they have been broken down from their original form through mechanical abrasion and UV exposure into items that are less than 5 millimeters in diameter. Fibers are primarily of textile origin. Microbeads can be either primary, that is they are introduced into the ecosystem as a microbead, or secondary, where their origin, like the microfragment, is from a larger item breaking down in the marine environment.
The main concern for microfragments and microbeads is that they can be ingested by benthic organisms. Microfibers, which are also ingested, can also entangle small crustaceans such as zooplankton.
Of the 16 sites you studied, you found that Henry Bay and Metcalfe Bay had the highest concentration of microplastics. What implications could this have for the shellfish farming industry at those locations?
LIB: At these sites, we recovered extremely high numbers of microbeads. The primary concern is the ingestion of the microbeads by oysters that are farmed in the same region.
Was there anything that surprised you in this study?
LIB: We found that the amounts of microbeads that were present were in the same amounts as key sediment components, such as silt and organic matter; about 3 to 4 percent. Silt and organic matter are the primary sediment components that govern trace metal availability to benthic organisms and hence to intertidal foodwebs. We now have a third sediment component that could potentially provide an additional vector for the transfer of metals through intertidal food webs.
What are the next steps for research in this area?
LIB: The next steps are to determine 1) the role of microbeads in the sorption of trace metals within intertidal sediments, 2) the amounts of microbeads that are being ingested by intertidal organisms such as oysters, and 3) whether the metals associated with the ingested microbeads are accumulating within the organism. This has important health implications both for the oyster and other shellfish, but also for humans that consume shellfish.
Reference: Kazmiruk TN, Kazmiruk VD, Bendell LI (2018) Abundance and distribution of microplastics within surface sediments of a key shellfish growing region of Canada. PLoS ONE 13(5): e0196005. https://doi.org/10.1371/journal.pone.0196005
Image Credit: Denman Island community member; LI Bendell