Plastics and the Ocean. Группа авторов

plastics will hold in the future generations, that likely underestimate future plastic production; the per capita use of plastics in high‐income countries such as the US are expected to increase by 19% by 2050 (Kaza et al. 2018).

      More sophisticated predictive models estimate even a higher volume of future production of 1100 MMT (World Economic Forum 2016), 1800 MMT (Ryan 2015), or 4000 MMT (Rochman et al. 2013) by 2050. While accurate projections of production volumes are always difficult to estimate, it is reasonable to expect this volume to be at least 1000 MMT by 2050.

Manufacturing plastic resin at this unprecedented scale will entail a set of unique global environmental challenges. Instead of the current demand of 4% of annual fossil fuel production, plastics will then require 20% of the production, and result in 15% of the global carbon emissions (World Economic Forum 2016). Particularly worrisome are the estimated unmanageable increases in global CO₂ emissions in that scenario. This carbon footprint is primarily associated with manufacturing, use, and disposal of plastics and is referred to as “embodied carbon” or “aggregate emissions”. Zheng and Suh (2019), based on 2015 production data, reported annual lifecycle emissions of 1.8 GTCO_2–e from plastics, that amounted to only 3.8% of the global emissions in 2015. With the entire chemical industry accounting for only about 15% (Edenhofer et al., 2014) share of global emissions, this is a reasonable figure considering the societal value of plastics. The future forecast, however, is bleak, with an estimated 6.5 GTCO_2–e annually emitted by 2050 or nearly three times the present value attributed to plastics (Zheng and Suh 2019). This could even reach 8.0 GTCO_2–e if all post‐use plastics are incinerated for energy recovery. That much of carbon emissions will not only be challenging to manage but will certainly make it difficult for the world to abide by the legally binding treaty agreed to by 197 parties (including the US) at the 2015 Paris Agreement, to hold global warming well below 2.0 °C (preferably to 1.5 °C) over the pre‐industrial levels. With the global average temperature being only 0.8 °C short of this limit in 2020, achieving this goal will be a challenge in any event. Dire effects consequent to human failure at controlling climate change, including heat waves, ice‐free Arctic summers, sea‐level rise, declining coral reefs, loss of biodiversity, and lower crop yields, are already evident (IPCC 2018).

Figure 1.4 Global plastic resin production versus the population.

While the above discussion centered around CO₂, it is by no means the worst greenhouse gas responsible for warming; methane, nitrous oxide, and fluorocarbons are much more efficient as greenhouse gases.⁴ Offsetting combustive CO₂ emissions by potentially better controlling the emission of greenhouse gases in other application areas may be of some help. With plastics, over 60% of the emissions arise from feedstock extraction or the resin production stage (either from oil extraction or fracking⁵ for natural gas extraction), making material recycling an attractive strategy to reduce CO₂ emissions. While carbon emissions were used here to illustrate the problems of embedded impacts, it is certainly not the only negative environmental impact of plastic manufacturing. Externalities include acidification of water, water pollution, marine aquatic toxicity, photochemical oxidants, eutrophication potential, human toxicity, and ozone depletion potential (Stefanini et al. 2020).

      A major consequence of higher production of plastics will be the increase in the post‐consumer plastic waste stream, already ineffectively managed worldwide (Jambek et al. 2015; Lebreton and Andrady 2019). This burgeoning plastic waste not only impacts the municipal solid waste (MSW) stream that we poorly manage but also contributes to the unsightly urban litter. Unlike paperboard or wood, plastics do not biodegrade in any appreciable timeframe (see Chapter 11) and will persist as urban litter over an extended period of time. Cities with a high population density, such as Mumbai in India (76 800 persons/sq. mile), Karachi in Pakistan (49 000 persons /sq. mile), and Seoul in Korea (45 000 persons /sq. mile), will be particularly affected by the future plastic litter problem. A recent model based on population density (LandScan data), the GDP, and country‐level plastic consumption data, identified future global “hot spots” for plastic waste generation, assuming a “business as usual” scenario (Lebreton and Andrady 2017). Worst affected regions in the next decades were identified as South Asia, East Asia, and South East Asia on a regional basis and China, India, and the Philippines on a country basis.

      Geyer et al. (2017) estimated 42% of the plastics entering the waste stream at present to be packaging‐related. The MSW in affluent countries is already rich in plastic packaging waste (Kaza et al. 2018). The fraction of all plastics in the MSW stream in the US has grown from negligible levels in 1970 to 16.3% by weight (357 MMT) by 2018, with PET, PE, and PP making up 32% of the total plastic waste. Plastic waste generation (PWG) per capita varies with the affluence of the country. Compared with the PWG of 88 ̶ 98 kg/year per capita for affluent countries such as Korea and the UK, less wealthy countries like India, China, and Pakistan generate only 13–19 kg/year per capita. The US has the highest PWG of 130 kg/year per capita (Law et al. 2020).

      Proliferation of single‐use plastic packaging, including beverage bottles, single‐serve sachets, dessert cups, and disposable bags, has exacerbated the situation, especially in the more affluent countries (Geyer et al. 2017). How the generated plastic waste is managed also varies geographically, depending on the availability of adequate infrastructure. In affluent countries, a combination of landfilling and incineration is used, with the US relying heavily on landfilling.

      1.2.1 Plastics in the Ocean Environment

In the 1970s, yet another dimension of plastic waste came to light with the discovery of plastic litter in the marine environment. The very first observations of plastics in the ocean dates back to 1972 (Carpenter and Smith 1972) and was followed by reports in the 1970s and 1980s on the high concentrations of plastics in the North Pacific (Day et al. 1990; Merrell 1980), North west Atlantic Ocean (Coltonet al. 1974), Mediterranean Sea (Morris 1980), and the Spanish Costa del Sol (Shiber 1982). A study of the ocean influx of plastics for the year 2010 (Jambeck et al. 2015) estimated that of the 270 MMT of plastics produced that year, about 32 MMT that ended up mismanaged waste was generated in coastal regions (constituting 50 km from the coastline). And assuming 3% of this waste to reach the ocean, the global marine influx was calculated to be between 4.8 and 12.7 MMT. The fraction of mismanaged waste plastics would not only be much higher today, compared to that in 2010 but the original estimate excluded plastics influx from marine activity such as fishing and riverine transport. Riverine transport of plastics from land into the ocean was identified as an important route in accumulating plastics waste (Leberton et al. 2017; Leberton and Andrady 2017; Schwarz et al. 2019), with the 20 top‐polluting rivers accounting for as much as 67% of the annual input of plastic debris (i.e., 1.15–2.41 MMT annually) into the ocean (Lebreton et al. 2017). Plastic debris from commercial fishing activity also contributes a significant amount of gear‐related debris (dolly ropes, net fragments, or floats) into the ocean, estimated at 0.6 MMT per year (Boucher and Friot 2017). Gear‐related plastics are mostly PE and PP that are positively buoyant, as well as nylons (PA) used, for instance, in gill netting, that sinks in seawater. Also included in this category are the crab pots deployed in large numbers each season. With a significant fraction of 12–20% of them lost each season, ending up as ghost‐fishing gear in the ocean. Ten thousand such pots are lost annually in Puget Sound alone.

Figure 1.5 Estimated plastic waste in