Microplastics: How They Affect Marine Ecosystems, Organisms, and Us

Figure 1. Microplastic pollution in aquatic environments and impacts on food chains. This infographic illustrates the multiple sources of common microplastic pollution and how it infiltrates environments. PHOTO COURTESY OF WU ET AL.

Marine litter is human-created waste that enters marine ecosystems, and often this highly non-biodegradable litter is fragmented and never truly broken down--creating micropollutants (Gomiero et al. 2018). Micropollutants can be inorganic (as in heavy metals, fibers, and plastics) or organic (such as hormones and other Endocrine Disrupting Chemicals, pharmaceuticals and personal care products, and pesticides) (Lazarri et al. 2000). While all pollutants create formidable risk to ecosystems and human populations, inorganic micropollutants like microplastics present a greater risk because of excessive human utilization of inorganic material. One of the main issues with high plastic usage is that plastics lack long-term integrity, for polyethylene terephthalate (PET), polypropylene (PP), and polystyrene (PS), common in most plastics found in the marine environment, are compact and therefore highly resistant to biodegradation (Gewert et al. 2015). This results in fragmentation of plastics into micropollutants, and they can have detrimental effects on ecosystems and organisms.

Microplastics can be categorized into two types: primary and secondary. Primary microplastics result from the direct input of man-made emissions, adding new micro-sized plastic material to the environment in manufacturing. Primary plastics are produced in three ways: as polymers intentionally produced like personal care products (facial cleansers, body cleansers, exfoliants, and cosmetics), industrial or commercial products and other specialty chemicals with plastic microbeads; as inherent collateral products of other industrial activities; or as accidental or deliberate spillage like pellets lost from plastic factories and transport (Cole et al. 2011, Rochman et al 2015, Gomiero et al, 2018). Secondary microplastics occur when larger plastic items degrade (mostly from UV radiation) and consequently fragment. This fragmentation leads to small, residual plastic pieces as they start to break down (Cole et al. 2011; Wright et al. 2013; Gomiero et al. 2018). 

They mainly consist of PET, PE, PP, and PS, with PET being the most common plastic found in household items of which heavily infiltrate marine ecosystems (Cole et al. 2011; GESAMP, 2015; Gomiero et al. 2018). 80% of the primary and secondary plastics in the ocean originate from land-based sources, with 20% originating from fisheries and shipping (Andrady 2011, Henderson and Green 2020). Since these plastics are continually broken down into microplastics, it presents a widespread and uncontrollable contamination of the marine environment (Henderson and Green 2020).

Figure 2. PE microbeads in personal care products. PHOTO COURTESY OF WU ET AL.

There are estimated to be a minimum of 5.25 trillion of these microplastic particles in the world’s oceans, weighing approximately 269,000 tons (Eriksen et al. 2014). Because of their particulate size and high abundance in the water from excessive use of plastics in mainstream society, it poses the potential for microplastics to have a very large, and possibly irreversible, impact in terrestrial and marine ecosystems. 

Around 693 different wildlife species have been negatively impacted by marine debris--either through ingestion, entanglement, transport or habitat degradation (Gall and Thompson 2015, Henderson and Green 2020). Directly ingested microplastics can persist for over 48 days in the circulatory system and allows predators to consume microplastics if their prey has consumed them in the past 48 days. This can provide complications such as bowel blockages and choking hazards for many marine organisms that either kill them immediately or prevent them taking in enough nutrients, slowing down their growth and development (Farrell and Nelson 2013, Setälä et al. 2016). 

Also, microplastics exhibit a level of toxicity once in the tissues and can serve as storage for toxic chemicals that cause severe effects on the organism's body. Many plasticizers, colorants, stabilizers, and flame retardants are added to many plastics during manufacturing. These additives are toxic for organism consumption, and in the case of common additives such as nonylphenol and brominated flame-retardants, they can be endocrine disruptors and carcinogens. The additives or contaminants that are released from the plastic are then taken up into the body, causing mutations in various cells. In the case of Artemia, it caused malformations in their limbs (Engler 2012; Fries et al. 2013; Bergami et al. 2016).

Additionally, pollutants such as industrial chemicals, pesticides and metals can in some cases adhere to the microplastics already in the oceans, making them even more toxic. And when small organisms like zooplankton and bivalves directly ingest the plastic, the chemicals follow and can subsequently move up the food chain for other larger organisms to consume for indirect consumption. 

Overall, direct ingestion may detrimentally affect foraging strategies, feeding behaviors, reproductivity and fecundity, and ecosystem functioning by altering the structures and functions of tissues and organelles (Bergami et al. 2016, Peng et al. 2017, Harmon 2018). Add these effects can carry through the food chain--and up to humans.

It has been demonstrated that microplastics can transfer from lower trophic level organisms to their predators. While the actual passing of plastics can immediately harm one individual, bioaccumulation of microplastic toxins can pass through the food chain as well and broadly impact other trophic levels.  Microplastics can transfer their adsorbed and absorbed trace metals, organic pollutants, and additives throughout food webs. 

The shellfish that we eat is particularly jeopardized by microplastics, for the way they feed makes them very susceptible to trapping the plastics in their bodies. They accumulate great amounts of plastics for humans to ingest since they feed by filtering water into their gills for particulate food. Shellfish are filter feeders and clear large volumes of water in this food extraction process and are, therefore, excellent bioaccumulators of “stuff”, and, everything that comes through the water, they collect. In the shellfish we eat (mussels, clams, etc.), microplastic accumulation often occurs in the digestive gland, which plays a role in assimilation, excretion, and detoxification of contaminants (Gueguen et al. 2011). Due to a lack of enzymatic pathways available to break down plastics in filter feeders, Andrady 2011 asserts that microplastics are unlikely to be digested or absorbed, and, therefore, the plastics stay in their tissues (Andrady 2011). 

While significant consumption risks are only really to those residing in fishing communities, for pregnant and breast-feeding women, and for very young children, the presence of microplastic toxins accumulating in human digestive tissues suggests possible effects and bioaccumulation in lower trophic level organisms. Therefore, indirect ingestion holds an equal, if not greater, effect to direct digestion in regard to broader health implications for marine organisms and us.

Loss of marine biodiversity constrains the environment's ability to recover from disturbances. Therefore, it impairs the capacity of the ocean to provide an increasing global population with essential ecosystem services--such as food provision, primary productivity, carbon cycling, and water quality (Worm et al. 2006). 

So how do we solve this problem? How can we preserve the organisms we rely on and prevent such a devastating loss of resources and services? While microplastics still threaten ecosystems and organisms, many have developed and encouraged solutions to reducing them and their impacts. 

One reduction strategy is introducing bans or limits to decrease microplastic integration in ecosystems and effectively reduce microplastics. Bans like these are implemented in countries like the United States (in California), U.K, Canada, and New Zealand but are under negotiation in other countries as well (Wu et al. 2016). Additionally, researchers have addressed innovating ways to utilize more biodegradable materials in place of common plastics, to better filtration methods in wastewater treatment facilities, and to improve solid waste infrastructure (inherently improving the reducing, reusing, and recovery of plastics) (Wu et al. 2016, Das et al. 2017). 

Biodegradable/ biocompatible plastics such as polylactide (PLA) and polyhydroxyalkanoates (PHA) can easily replace traditional, commercial plastics for many applications and further decrease the input on microplastics in the environment. 

Furthermore, laboratories have discovered that bacteria can fully degrade petroleum-based plastic pollutants, for biodegradation and bioremediation strategies can be effective in removing plastics completely from ecosystems. Bacillus and Enterobacter asburiae can degrade PE and Exiguobacterium can degrade PS (Yang et al. 2014; Yang et al. 2015). Ideonella sakaiensis catalyzes the degradation of PET fibers into carbon monomers by eating them (Yoshida et al. 2016). 

Many solutions! Why aren’t we doing them? One answer--money. Lack of funding to research to apply these strategies is very lowly allocated. Most importantly, the Trump administration has continually dismissed the science community and de-emphasized the importance of our environment. This is exemplified in his recent 26 percent cut to the Environmental Protection Agency (EPA). Trump’s budget would eliminate 50 EPA programs and impose massive cuts to research and development, as stated by The Hill.

Like a lot of environmental solutions, the most we can do is contribute our time and money. Be conscious consumers and purchase personal care products without plastics in the ingredients and/or without excessive plastic packaging (look for polyethylene terephthalate (PET), polypropylene (PP), and polystyrene (PS) in your ingredients). Call your representatives to push legislation that funds environmental research and/or subsidizing ecological preserves. VOTE! Tuesday is coming up quickly, and it’s too late to mail-in you absentee ballots. Either drop them off at a polling center or vite (safely) in person. Each and every vote counts, and it starts with you to help our environment!

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https://thehill.com/policy/energy-environment/482352-trump-budget-slashes-funding-for-epa-environmental-programs

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