Ending the year on a positive note!

Check out this awesome TED talk by Boyan Slat, founder of The Ocean Cleanup: he is such an inspiration, not just because of his age (18 years old!!), but for making an insurmountable task like cleaning up the oceans seem so possible, almost easy even! A great note to end the year, in my mind.

Happy New Year!!!



Continuing with plastic pollution, I wanted to bring your attention to macroplastics - and as you've probably guessed, these are simply larger pieces of plastic when compared to microplastics. Most authors refer to macroplastics as those that aren't microplastics i.e. anything bigger than between 1-5mm depending on the author (see my first post on microplastics), although Gregory and Andrady (2003) also include another class of plastics identified as mesoplastics. These include plastics such as virgin resin pellets. For the purpose of this post, I will consider macroplastics to be anything that can be seen with the naked eye. Examples include bottles and caps, cups, rope and beer can rings (Andrady 2011).

Much like microplastics, effects of macroplastics include ingestion and contamination. However, macroplastics also cause entanglement. Below is a review of these three effects:

1. Ingestion

The results of the ingestion of macroplastics are clearly seen in the Midway video in the first post [Figure 1]. Indeed, according to Rios et al. (2007), nearly half of all marine bird species are known to ingest plastic.
Animals consume plastic either directly, by mistaking it for prey, or indirectly when they consume prey that has ingested plastic. Among the problem associated with the ingestion of macroplastics are satiation and malnutrition, blockage of the intestine and internal wounding from sharp objects, all of which may be fatal to the animal (Gregory 2009).

Figure 1. Photo showing the stomach contents - most of it plastic -
of a decaying albatross found on Midway Atoll (Daily Telegraph Australia)

However, not all ingestion from macroplastics leads to death. Tomás et al. (2002) looked at 54 juvenile loggerhead turtles in the Mediterranean. They found that despite plastics accounting for 3/4 of all debris found and low feeding discrimination among the turtles, there was no clear evidence of intestine blockage or them dying because of plastic ingestion (Tomás et al. 2002).

2. Contamination

This is the same issue with microplastics (again see post below) - toxic compounds dissolved in the ocean may adsorb onto the surface of plastic and depending on the compound, may cause severe health issues, and may also make their way up through the food chain (Cole et al. 2011).

3. Entanglement

Figure 2. A selection of photos depicting various forms of entanglement; clockwise from top left: green sea turtle entangled in a gillnet (National Geographic); seal with a deep cut around its neck from a fishing line (BBC); turtle with a six-pack ring around its middle (Ocean Crusaders); another entanglement in a gillnet, but this time the victim is a grey whale (Oceana)

Turtles, some pinnipeds (seals, sea lions and fur seals), cetaceans and birds have all been affected by entanglement. This is usually due to the nets but can also be with smaller items such as bottle cap or six-pack rings [Figure 2 and references therein].
Entanglement causes limited movement and thus a reduction in how well the animal can travel and hunt/find food. This may lead to starvation and inability to feed their young (Gregory 2009).

I hope those images don't upset you too much, but I thought the best way to convey the gravity of marine pollution and the effects of entanglement was to approach it using photos. After all, an image is worth a thousand words...


Microplastics part 3: Effects

This is my final post on micrplastics and this time I'm looking into the two most significant effects and potential threats of these minute fragments of plastic:

1. Ingestion

One of the major potential threats of microplastics to marine fauna is ingestion. Figure 1 shows potential transport pathways of plastic particles, as well as their interaction with the biota (Wright et al. 2013).
Among the different methods of ingestion by aniamls, microplastics may be taken up either actively and passively. The former describes the voluntary selection of microplastics due to their similar appearance in both size and shape to the food normally consumed by the animal. Passive ingestion refers to indiscriminate feeding, whereby the animal doesn't differentiate between types of food. Animals may also ingest microplastics through scavenging or indirectly when they consume prey that had previously ingested plastic particles (ibid).
A study by Farrell and Nelson (2013) investigated the effectiveness of trophic transfer. The authors added 0.5μm fluorescent microspheres to water that contained mussels. Once the mussels had filtered these microspheres from the water, they were fed to crabs. The results showed the approximately 0.28% of microspheres that had been filtered by the mussels were transferred to the crabs (Farrell and Nelson 2013), demonstrating that there is evidence for trophic transfer.

Figure 1. Potential transport pathways of microplastics and their interaction with the biota (Wright et al. 2013)

However, some animals manage to avoid the ingestion of microplastics altogether. Interestingly, some bivalves have developed a way to sift through particles before ingesting them, and thus unlike passive feeders actually discriminate between these particles (Wright et al. 2013).

2. Contamination

Another threat is the contamination of toxic compounds from their adsorption to the surfaces of microplastics. Because of their small size, microplastics have a large surface area : volume ratio, indicating that they are more likely to adhere pollutants onto their surfaces (Cole et al. 2011). There have been a number of studies published on the types of chemicals found on micorplastics, including trace metals (such as chromium, lead and cadmium) (Holmes et al. 2012), brominated flame retardants (Engler 2012) and Persistent Organic Pollutants (POPs) including organic compounds such as organochlorine pesticides, Polychlorinated Biphenyl (PCBs) and Polycyclic Aromatic Hydrocarbons (PAHs) (Mato et al. 2011). The biggest concern about POPs is that they are known mutagens and/or carginogens and endocrine disruptors (Cole et al. 2011), which suggests that ingestion of these may cause problems, especially if there is significant transfer across the trophic level.

The sources and effects of microplastics are vast and complex, but hopefully I've provided with you with an informative overview over the last few posts. Next up - macroplastics!


Canvas Bags

Taking a break from microplastics with a little help from the brilliant Tim Minchin. Enjoy!