Impacts: Microplastics, the silent killer

Hello all!

In a follow up from my previous post, I will elaborate more on microplastic debris pollution in the marine environment, which accumulate in organisms over time without directly causing death.

Microplastics: the silent killer

"Of the 5.25 trillion particles of plastic we estimated were in the oceans [...] 95% were smaller than a grain of rice," said Stiv Wilson.

Microplastics and their effects are critical to understanding the magnitude of impact on marine life.  As plastics do not decompose readily, they accumulate in the environment over a long period of time and concentrate toxic pollutants. Pollutants include additives used in the plastic compounding process during the manufacturing process, toxicity from intermediates in the degradation of plastic (eg. styrene) and the persistent organic pollutants (POPs) in seawater that may be absorbed into the microplastic fragments. These are ingested by aquatic organisms, with the impacts briefly listed below:

1. Reduced health and ecological function of the individual: exposure of microplastic fragments to zooplanktons such as copepods and bivalve larvae has shown to cause reduced algal ingestion rates in the example of the copepod Centropages typicus.

2. Increased mortality rates: prolonged exposure to microplastics has also been observed to lead to increased mortality rates in the copepod Tigriopus japonicus over successive generations.

3. Catastrophic ecological transfers: POPs within microplastics and their impacts may be transferred across trophic levels within the food chain, observed within the planktonic food web between copepods and mysid shrimps.

4. Human health dangers from toxic accumulation: in the case of 'nanoplastics' (0.001μm to 0.1μm) with their current undetectable dimensions, they may de-aggregate in the gastrointestinal tract to be absorbed by the body, or that they may translocate across the gut epithelium (lining of the intestines) resulting in toxicity exposure to humans.

Nonetheless, there are still challenges as the impacts of microplastics are still fairly inconclusive at this stage. Adverse effects of plastic transfer and potential bioaccumulation in organisms are still fiercely debated at present as they have only been observed under extreme laboratory conditions in the abovementioned studies; current technology does not allow for the quantification and measurement of nanoplastics in organisms, and therefore there are uncertain effects on human health. In the best estimate on impacts of human health, it was also studied to be negligible, as the majority of microplastics are found in digestive tracts of marine animals, which are often disposed of before human consumption. Even in consumption of bivalves in whole (eg. mussels), a worst case estimate of exposure to microplastics would be 7 µg, considered a negligible amount relative to the total dietary intake of persistant, bioaccumulative and toxic substances (PBTs) by humans.

Summary

Macroplastics and their immediate impacts on marine organisms (recall: "serial killer") are clear disruptions to the natural ecological balance, and an obvious telltale sign that our plastic consumption inflicts direct harm on the environment. Microplastics and their impacts are much less conspicuous, as they have only been evident under extreme laboratory conditions which do not represent the fatigue of the oceans. Unfortunately, the present lack of direct health risk from ingesting minute quantities of microplastics or nanoplastics as written above also serves little to discourage individuals from irresponsible use of plastics.

Nevertheless, it is important to consider the projected increase of plastic waste in the future (recall: introduction post), which may concomitantly possibly magnify the presently undetected impacts of plastic consumption in humans through the 7-step causal chain I constructed in Figure 10.  The micro-nanoplastic problem is especially important given that the particle distribution will increasingly shift towards microplastics and nanoplastics in aquatic environments with fragmentation over time.

Figure 10. Flowchart representing the causal chain of increased plastic waste in the environment, with accompanying ecological effects on aquatic organisms and impacts on human health highlighted in red (Source: Author).

The causal chain drafted above also serves as an effective summary for our discussion in this week's entry. In my following post, I will talk more about the impacts of microplastics from microfibre and microbeads, something I came across in social media lately.

See you!

Impacts: Macroplastics, the serial killer

Hello all!

Last week, I spoke briefly about microplastics from the degradation of plastic bags, which may be a less familiar concept compared to macroplastics. I coined the headers 'serial killer' and 'silent killer' as catchphrases, which succinctly summarise the impacts of both macroplastics and microplastics on aquatic organisms respectively.

Macroplastics: the serial killer

Macroplastics in the form of mesoplastics (>5mm in size) and macroplastics (>25mm in size), kill millions of marine animals every year. Impacts are briefly listed below:

1. Death from entanglement: entanglement may lead to debilitation and subsequently starvation; ingestion by marine species also cause these animals to face a reduced quality of life and lowered reproductive performance. Other taxa that have been affected similarly include penguins, dolphins, and fur seals (see Figure 7).

2. Death from consumption: sea turtles mistake plastic bags for jellyfish (see Figure 8), a situation which obstructs the passage of food, possibly leading to death from starvation. Sea turtles are extremely vulnerable due to their inability to regurgitate their food intake from the downward-facing spines in their throat.
3. Ecological implications (ripple effect): sea turtles naturally keep the jellyfish population in check, and a reduction of sea turtles in the ocean may indirectly promote the jellyfish population, which feeds on fish larvae and therefore reduce fish populations in the ocean.
4. Facilitate spread of pathogens: due to the durability and floatibility of plastic, microorganisms may hitchhike and accumulate on plastic up to years, introducting pathogens into marine ecosystems observed in the coral reefs and introducting non-native species (eg. algal blooms) across marine environments.
5. Economic losses: piles of macroplastic waste that may make their way onto shorelines are visually appalling to the observer, and has been studied to lead to reduced tourism from negative emotions as they devalue the experience of beachgoers (see Figure 9). They also lead to decreases in income from recreational tourism due to its interference with the shipping and fishing industries.
6. Choke urban drainage systems: plastic bags were the culprits to choking urban drainage systems, causing devastating floods in Bangladesh in 2002. Bangladesh thereafter became the first country in the world to legislate a ban on thinner plastic bags, although the country continues to struggle with enforcing the ban.

Figure 7. Seal entangled by plastic, which may potentially lead to death. Photo: LiveScience (2017)

Figure 8. Animation (click to open in a separate window if it does not load) of a sea turtle unable to differentiate between jellyfish and plastic bags. Source: Conserve Turtles (2017)

Figure 9. Freedom Island, an artificial island in Manila Bay, Philippines, showing clearly the impact of plastic waste in our oceans that have washed up onto shorelines. Photo: Dianna Cohen, Plastic Pollution Coalition (2017)

In this post, I have spoken about the visually appalling effects from imcroplastics. In the following week, I will speak more about microplastics with their unseen ecological impacts, before summing up these two entries with my thoughts.

Introduction: Life Cycle of Plastic Bags

Hello all!

In my second week on plastic waste, I would first summarise the life cycle of plastic bags from its construction, using an improvised and basic flowchart seen in Figure 5.

Life Cycle of Plastic

Figure 5. Life Cycle of Plastics (Improvised from sources: 1, 2)

Plastics are very widely used in products and production processes, such as in the form of packaging, textiles, in automotive parts, and paints. They are formed from long chains of organic polymeric molecules, with the most widely-used synthetic polymer being polyethylene (PE). Generally, polyethylene bags are made using plastic pellets which are subjected to high pressure, melted in a hopper, and extracted through a vertical tube to form a long continuous plastic film of desired thickness. Individual bags are then created by cutting and heat-sealing the bags.

Within PE, there are three types of molecules used for plastic bags: linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE) and high-density polyethylene (HDPE). Generally, the higher the density, the greater the molecular weight and the stronger the resulting plastic bag. These three uses account for a combined 38% of global plastic production.

Figure 6. Different types of plastics and their uses (Source: UNEP on Twitter)

Figure 6 shows the different PE types and their typical uses in plastic bagging. Although the image may indicate that LDPE forms the bulk of marine plastic litter given their lightweight properties, over the course of my research I conclude that thickness of the bags in consideration of impacts - the thinner the plastic bag, the lower its quality and the lower its re-usability. Subsequently, some of these lightweight plastic bags may make their way to water bodies from land-based sources such as beach litter and their buoyancy encourages ocean-driven surface transport. Over time, the plastic waste undergoes fragmentation when subject to UV-radiation and warm temperatures as they traverse the oceans, and may form microplastics (defined as plastic particles <5mm in size) which can stay in the ocean for thousands of years.

This knowledge would later be helpful in assisting our understanding on the adverse effects (ecological, environmental and social costs) of marine plastic litter in our oceans. See you!

Introduction: Why Plastic Waste?

Hello all!

Having enrolled in the 'Global Environmental Change' module, I have chosen to zoom in the pertinent issue of plastic waste. Plastic pollution has increasingly received attention, owing to the growing accumulation of plastic waste that has materialised in the Great Pacific garbage patch. Based on the current consumption of plastic, plastic waste has been anticipated to increase by 10 times by 2025. Regionally, 8% of the manufactured plastic bags in the European Union are littered to the ocean, forming the bulk of marine litter.

Personal Thoughts

In my journey of blogging, although I will examine plastic waste and its impacts on the environment as a whole, I will focus disproportionately on plastic bags. This choice originates from the recent summer spent back home in Singapore, where I realised that consumer habits when it came to plastic bagging differed very much. I arrived in London the first time a mere 2 weeks before the '5p Plastic Bag Charge' was implemented on all single-use plastic carrier bags in large shops, which had me reducing my plastic bag use drastically. Incidentally, supermarkets in Singapore were in discussion to implement a similar move come 2018, to reduce the burden of plastic waste disposal on our only landfill. The news came as a pleasant surprise for me, especially as I had gotten used to living with less plastic in London.

Figure 1. Article on Singapore's highest-selling paper, The Straits Times, on the plans of implementing a plastic bag charge. But it certainly did trigger some angry reactions, as seen in the following 3 figures.

Figure 2. Angry netizen #1.

Figure 3. Angry netizen #2.

Figure 4. Angry netizen #3.

In my opinion, single-use carrier bags are commodities we could do with less - we could pay for one  reusable plastic bag, use free handmade tote bags, or even our school bags to store groceries. The only inconvenience is travelling around with a reusable bag, and unfortunately this inconvenience could outweigh our care for the environment, possibly due to an unawareness of the full impact on the Earth from plastic waste as seen from Figures 2, 3 and 4. These opinions made me realise that before implementation of industry-wide moves, it is first quintessential to encourage responsibility and care for the environment. In the following weeks, I will explore these thematic areas:

1. Life cycle of a plastic bag from its construction to its destruction.

2. Environmental, ecological and social costs of plastic waste (especially plastic bags).

3. Legislations around plastic bags and how to tighten these regulations.

4. Proposed alternatives: biodegradable plastics, paper bags, and recyclable bags.

*5. How will I respond to these Facebook comments?

I hope that my blog would positively reshape mindsets around plastic packaging to move towards a cleaner Earth. See you next week!