Plastic for Tea?

This week’s post continues on the focus of how plastic has ended up in humans but also looks into the impacts plastic has on the marine biota found in the oceans – be sure to check out last weeks post first!

We know that there is a lot of plastic within the oceans, 21 x 10^8 tons in the North Pacific alone, and this naturally is having detrimental impacts on the wildlife that inhabit it.

Figure 1. Sea lion entangled in plastic pollution. Source: Quora.

Plastics could be considered as having numerous types of implications on wildlife in the oceans. Marine fauna can become entangled in pollution causing visible physical damage to the organisms; this may include prevention of resurfacing causing asphyxiation and drowning, lacerations or the blocking of blowholes. These impacts can result in individuals being more vulnerable to predators and potential starvation due to limited mobility.

A lesser thought of impact of plastic pollution is the build-up and transportation of microbial communities and other species to new habitats resulting in changes to ecological niches potentially on large scales. This also has economic implications as large amounts of money will have to be spent in reducing the impacts of the invasive species which therefore will prevent investment elsewhere.

The most recent focus has been the impact of ingestion of plastics by wildlife. Due to most plastics being buoyant it can be easily consumed by species, surface feeding bird species are particularly vulnerable to this and it has been reported that plastic has been found in the gut of fish species in several different habitats including estuaries, bays and surface water. Micro-plastics, defined as particles <5mm, are able to travel substantial distances allowing for the impacts of pollution to be felt on a wide scale.

Figure 2. Seabird found with ingested plastic pollution. Source: The New Republic.

Due to their ability to forage over large distances, seabirds are more likely to ingest plastic pollution mistaking it for prey. The feeding habitats of a large number of species involve parents foraging in the ocean and then regurgitating the found food to their young; the implications of this results in the parents unknowingly feeding their children plastic they have picked up in the ocean. This can have numerous impacts on an individual.

Figure 3. Pathways for microplastics in an organism. Source: Worm et al. (2017)

Ingestion of plastic can result in less visible impacts than that of entanglement such as the release of substances such as plasticizers and monomer residues which therefore accumulate within the tissue of the individual. Plastic substances with a smaller surface area seemingly may have a larger impact due to their ability to be transferred across tissue and interact with other chemicals. Figure 3 demonstrates how plastic can have different effects on an organism, all resulting in population decline.

So how does this result in plastic being found in humans? This is extremely similar to the scare that was seen a number of years ago in pesticides being found in people and is a resultant of the same process – bioaccumulation.

Figure 4. Left: Concept of bioaccumulation in a food web. Right: Bioaccumulation in the form of an energy pyramid. DDT represents the accumulating substance, in this case plastic. Source: Streit (1992)

Bioaccumulation can be used in referral to the uptake of a concentration of a substance in an individual; this may be passive or active. The basic premise can be explained using the food web, see figure 4. When one organism feeds upon another organism, whatever is found within that organism is passed up through the food chain; in this case the substance involved is plastic. This means that the plastic that is being produced by us has come full circle and sits on our dinner plates.

The thought that reaches my mind when looking at this topic, and one that I struggle to find an appropriate answer to, is that seabirds and other species have been found to have ingested plastic since the 1960s, so why is it now when humans are next in line to feel the implications that something is started to be done about it?

Next week in the last of this miniseries I want to address a more hopeful topic in the form of what is being done on a large scale to reduce the amount of plastic found in the oceans.