Microplastics part 2: Sources

Below is an overview of the sources of microplastics:

1. Degradation and Fragmentation

Larger plastic debris already present on the ocean surface or on beaches may undergo degradation and ultimately fragment. Degradation is a process by which a polymer undergoes a chemical change that significantly reduces its average molecular weight (Andrady 2011). Plastics, also known as synthetic polymers (Moore 2008) can undergo degradation through the actions of sunlight (photodegradation) and high temperatures (thermodegradation) (Andrady 2011). Some microorganisms have been found to degrade plastics, a process called biodegradation (Sivan 2011).
Oxidation via UV-B radiation from the Sun is especially effective at degrading certain polymers, such as Low and High Density Polyethylene (LHDE and HDPE respectively), polypropylene and nylon (Andrady 2011).
Plastic debris on beaches degrades quicker than that found on the surface of the water because the temperature is higher, which accelerates the process (Andrady 2011). By reducing the molecular weight of plastic, degradation renders plastic brittle and thus it fragments (Browne et al. 2007). These newly formed microplastics are then easily carried into the ocean through wind and wave action (Andrady 2011).

2. Plastic resin pellets

Resin pellets are the raw material from which some plastics are made (Cole et al. 2011). These pellets are generally less than 1mm in diametre and may be accidentally released during manufacturing or ocean transport (Ogata et al. 2009).

3. Industrial and domestic cleansers

Both industrial and domestic cleaning products are also a source of microplastics. Amazingly, these contain a range of synthetic compounds from polyethylene and polystyrene, which measure less than 1mm in diametre, to polyester and acrylic, which range between 0.25 and 1.7mm (Brown et al 2007). These particles make their way to wastewater treatment facilities via household or industrial drainage systems. Being so small, they are not caught by the filtration system and thus end up in the ocean (Cole 2011).
According to Fendall and Sewell (2009) polyethylene microplastics are found in the majority of facial cleanser nowadays. These products are often marketed as "micro-beads", "microbead formula" or "micro exfoliates". The authors tested four supermarket-bought facial cleansers for the size of these micro-beads and found that they varied in both size and shape [Figure 1]. The modal size (the most frequent size found) of the micro-beads in three out of the four cleaners was smaller than 100μm (i.e. 0.1mm), suggesting that these are small enough to easily enter the oceans via wastewater treatment facilities.

Figure 1. Microplastics particles in four different supermarket-bought facial cleansers seen under the microscope with 500μm scale bar for reference. Note the different shapes: granular particles (g), ellipses (e) and threads (t) (Fendall and Sewell 2009)

4. Fibres

Synthetic compounds are also found in clothing (Browne et al. 2007). Browne et al (2011) reported that a single item of clothing may shed more than 1900 fibres during one wash cycle. These fibres make they way through to wastewater treatment facilities but similarly to micro-beads, they are too small to be intercepted and thus end up in the ocean.

Next up, the effects of microplastics!



If you watched the Midway video in my first post, you'll have noticed that much (if not all) of what the birds ingested came from plastic. Likewise, the video I posted a few weeks back by the Australian Marine Conservation Society highlighted the extent of plastic pollution in the oceans very effectively.

Plastic pollution is clearly a mammoth problem. Indeed, along with phosphorous pollution, the United Nations Environment Programme (UNEP - mentioned in my previous post on Eutrophication) lists plastic pollution in the oceans as one of the two main emerging issues in its 2011 Year Book (UNEP 2011).
The more I read about plastic pollution in the literature, the more I realised I could not tackle the issue in one post alone - there's simply too much information. As a result, I have decided to break down all this info into bite size chunks beginning with...


As the name suggests, microplastics [Figure 1] are characterised by their small size. However, there seems to be no common consensus in the literature regarding a size "limit". For example, UNEP defines microplastics as plastic fragments measuring less than 5 millimeters in length (ibid), whereas Browne et al. (2007) consider them to be less than 1mm. Gregory and Andrady (2003, in Andrady 2011) place microplastic in the micrometer (μm) range, with anything big enough to pass through a 500μm sieve but small enough to be caught in a 67μm sieve, i.e. any plastic between approx. 0.06 and 0.5mm.

Figure 1. Microplastics on a petri dish (Sea Education Association)

My next post will cover the sources of microplastics and some of these may surprise you - at least they did me - so stayed tuned!



Following on from my post on tumors in sea turtles (see below), I wanted to investigate eutrophication further.

During my research, I came across a paper written by a group of high school students in Alaska describing eutrophication on marine ecosystems and its effect on their villages. It's an impressive piece of work (albeit it with some minor errors), especially considering the students had never heard of eutrophication prior to starting the project (Matthias et al. 2011)!

Eutrophication is a complex issue involving many factors. Below are some of the key facts courtesy of the Alaskan High Schoolers:

Eutrophication is the enrichment of a body of water due to the influx of nutrients, particularly those that are nitrogen and phosphorous-based. A major contributor of this input is the anthropogenic (over)use of fertilisers, which infiltrate rivers and streams and eventually discharge into the ocean (Matthias et al. 2011). According to the 2011 United Nations Environment Programme Year Book (UNEP 2011) "the global use of fertilisers that contain phosphorous, nitrogen and potassium increased by 600 per cent between 1950 and 2000". UNEP estimate that about 22 million tonnes of phosphorous enter the marine environment from land every year, mainly due to inefficient farming methods and "failure to recycle wastewater".

Nitrates and phosphates (nitrogen and phosphorous-based compounds) are required in algal and plant growth. When excess nutrients enter coastal waters, nutrient concentrations in these waters increase leading to a surge in algal growth, a phenomenon known as algal blooms [Figure 1]. When the organisms die they sink to the bottom of the ocean and are decomposed by bacteria, a process that requires oxygen. Consequently, these areas are depleted of oxygen becoming hypoxic (oxygen-poor) and in some cases anoxic (oxygen-free). This often results in the death of fish and other aquatic organisms (Matthias et al. 2011).

Figure 1. Satellite image of an algal bloom in the Baltic Sea (National Geographic)
Areas in which the deep water oxygen concentration is so low it cannot sustain sea life are called dead zones [Figure 2].
Figure 2 shows the location and size of dead zones around the world. It is perhaps unsurprising that the majority of these zones are found along the coastlines of developed countries, where population is high and the use of fertilisers is abundant (NASA 2008).

Figure 2. Location and size of marine dead zones (NASA 2008)

Of course, areas that are naturally low in oxygen are not uncommon in oceans and in such zones, marine life has adapted to these conditions. However, increases in both global population and global demand for meat and dairy suggests the use of fertilisers is likely to escalate thus exacerbating the problem (NASA 2008).

Moreover, problems linked to eutrophication are not only confined to marine species but affect communities and economies that rely on fishing and tourism (Matthias et al. 2011). I don't believe anthropogenic eutrophication can be stopped, but it can be slowed with adequate management strategies aimed at reducing the amount of nutrients entering both freshwater and marine ecosystems.


Give Frank A Break

Heading to the other side of the world for this post...

Here is a short video courtesy of the Australian Marine Conservation Society and comedian Frank Woodley. It's wonderfully shot and thoroughly thought-provoking:

In addition to the video, the Society lists some steps that can be taken to tackle the problem of plastic pollution, from simply being mindful about what and how we consume to appealing to Australian state and territory governments to implement a "Cash for Container" scheme. The scheme is already active in South Australia and is proving successful: the state recycles double the amount of drink containers compared to the national average (Australian Marine Conservation Society 2014).

Despite there being a number of similar schemes in the UK dedicated to materials such as aluminium (see Think Cans), there are no such programmes for plastics. The charity Campaign to Protect Rural England published a report in 2010 investigating "the environmental and financial implications of the introduction of a UK-wide deposit refund scheme", which would have comprised glass and plastic bottles and cans (Hogg et al. 2010). However, it seems nothing has been put into place yet as my research into the outcome of the report quickly met a dead-end. It's a shame, as I think we're a fairly recycling-friendly nation, so there's little reason why such a scheme could not work.