Review(Micro)plastic crisis: Un-ignorable contribution to global greenhouse gas emissions and climate change
Graphical abstract
Introduction
Plastics are one of the most common materials in the global economy. It has become an inevitable part of the material world and is constantly flowing in various human activities, from plastic packing (plastic bags and bottles), clothes, and equipment parts to building materials. Global plastic production has increased from 2 million tons in 1950s to 348 million tons in 2017 (PlasticsEurope, 2018) and 359 million tons in 2018 (PlasticsEurope, 2019), and China is the largest global plastic producer, followed by Europe and North America (Fig. 1). In general, plastics are synthetic organic polymers, which possess a backbone consisting entirely of C–C bonds, and the raw materials mainly come from fossil fuel, coal, oil and natural gas. Massive production, widespread applications and mismanagement of plastics increase their chances of entering the environment. Because plastics are difficult to be decomposed naturally, they have accumulated in land, freshwater and oceans for many decades. People have become increasingly aware of and concerned about the emergency crisis of plastics in the environment over the past decade, especially microplastics and nanoplastics (Hu et al., 2019a, Hu et al., 2019b, Shen et al., 2019d, Thompson et al., 2004). This concern has expanded to the impact of microplastics and nanoplastics on ecosystems and human health. New evidence has emerged that microplastics not only accumulate in the environment, but also in our food (Gündoğdu, 2018, Gerd and Elisabeth, 2014, Karami et al., 2017, Rochman et al., 2015, Yang et al., 2015) and water supplies (Kosuth et al., 2018, Mintenig et al., 2019, Oßmann et al., 2018, Pivokonsky et al., 2018), even in our bodies. These microplastic and nanoplastic particles can be transferred along the food chain to higher trophic level organisms, or into the human food chain through other pathways (Yang et al., 2015). Because of the large size of microplastics, most microplastics will accumulate in the intestinal tract of animals, but a small amount of microplastics can enter the circulatory system through the abundant lymph nodes in the intestinal tract. For the larger size of microplastics, it is difficult to penetrate into the organs. In the current literature, the toxicity evaluation of microplastics in vivo and in vitro is less. But for nanoplastics, they can cross the intestinal barrier into the circulatory system and eventually lead to systemic exposure (Bouwmeester et al., 2015). Because of its stable nature, nanoplastics are easy to accumulate in tissues and cells, causing metabolic disorders and local inflammation. Especially in patients with intestinal diseases, the changes of tissue permeability caused by inflammatory infection will significantly increase the transport and absorption of nanoplastics, thus furtherly increasing the risk of exposure (Shen et al., 2019c). Therefore, the pollution of microplastics and nanoplastics should be seriously considered, and the potential toxicity of microplastics and nanoplastics to human health should be fully studied.
Recently, the hidden crisis of (micro)plastics, on the other hand, is also emerging in this growing concern: the un-ignorable contribution of plastics to global greenhouse gas emissions and climate change. With the rapid expansion of global plastic production, plastic industrials have become the most important and rapidly growing source of industrial greenhouse gas emissions. Evidence showed that according to the distribution of about 4% of crude oil as the raw material of plastics, greenhouse gas emission from well-to-refinery in 2015 were estimated 68 million tons CO2 equivalents (CO2e) by determining the weighted average carbon intensity of oil well energy production in global 8966 on-stream oil fields in 90 countries (Masnadi et al., 2018). Greenhouse gas emissions not only come from the production and manufacturing process, but also from the extraction and transportation of raw materials of plastics, to plastic waste management, to plastics entering the environment (Hamilton et al., 2019). Geyer et al. (2017) reported that 72 plastic manufacturing facilities in the United States emitted about 17 million tons of CO2e in 2014 during plastic manufacturing. Emissions during from well to manufacturing are controlled by the production facilities themselves, usually depending on the efficiency, configuration and service life of equipment, etc. Additionally, when plastics are discarded, the impact of plastics on global climate will not stop. Actually, most of its impacts on climate occur after the end of its life span (Royer et al., 2018). Currently, recycling, incineration and landfill are used to manage most plastic waste. Evidence has shown that the net emissions from plastic packing waste incineration were estimated to be 16 million tons in 2015 (Fig. 2). And with the continuous plastic production, the net emissions from plastic packing waste incineration will increase to 84 and 309 million tons by 2030 and 2050, respectively (PlasticsEurope, 2016).
Since the Great Industrial revolution, the concentration of greenhouse gas in the global atmosphere has continued to rise. The concentrations of CO2, CH4 and N2O have increased by 41%, 160% and 20% (Working Group I of the IPCC, 2013), respectively, compared with those before industrialization, which has caused serious global warming effects. During 1951–2010, greenhouse gases increased the global average temperature by 0.5–1.3 °C, and their continued emissions will lead to further global warming. It is expected that the global average surface temperature will increase by 0.3–0.7 °C by 2035 compared with 1986–2005, while it will increase by 0.3–4.8 °C in 2018–2100 (Moss et al., 2010). Global warming caused by the increase of greenhouse gas concentration has become a major environmental issue of concern to all mankind. Therefore, in October 2018, the Intergovernmental Panel on Climate Change’s issued a special report, which proposed that global warming should be limited to 1.5 °C in order to avoid series of impacts of global climate change (IPCC, 2018). It means that to have any opportunity to keep within 1.5 °C, the global CO2 emission level in 2030 needs to be reduced by about 45% compared with 2010, and carbon neutralization requires to be achieve by removing CO2 to balance the remaining carbon budgets around 2050 (Hausfather, 2018). They furtherly reported that under this circumstance, the total warning of the reaming carbon budget cap is only 420 gigatons CO2e not more than 570 gigatons in the carbon budget of 800 gigatons CO2e of energy and industrial sectors by 2100. The accumulative greenhouse gas emissions from cradle to grave of plastics may exceed 56 gigatons by 2050 (approximately accounting for 10%–13% of the total remaining carbon budget). Rapid plastic production expansion and emissions growth will exacerbate the climate crisis.
Moreover, a new study has confirmed that greenhouse gases are released during the degradation of environmental plastics (Royer et al., 2018). Although the emission by environmental degradation is relatively small compared to plastic incineration (about 2122 tons CO2e per year), it is a continuous process. With the increase of plastic production and plastic waste, its impact will become more and more significant. The widespread presence of plastics in the ocean may have a negative impact on the carbon fixation. Ocean plants and animals play a key role in microbial carbon pump, which capture carbon from the atmosphere and transport it to the deep sea to prevent it from reentering the atmosphere. Evidence showed that the plastic pollution can reduce the ability of phytoplankton to fix carbon via photosynthesis (Nolte et al., 2017, Sjollema et al., 2016). Plastic pollution can also reduce metabolic rates, reproductive success rates and zooplankton survival rates, and zooplankton transfer carbon to the deep sea (Galloway et al., 2017, Long et al., 2017). Microplastics can also interfere with the operation of marine primary food chain/web (Shen et al., 2019a).
Despite limited information on greenhouse gas emissions consequence of plastics, the available data point to a fact that the climate impacts of greenhouse gas emissions from plastics are urgent. It is necessary to formulate emission reduction strategies and implement corresponding policies globally. The effect of “(micro)plastics & greenhouse gas emissions” on global climate has become a hot issue in the research of (micro)plastics. In this paper, greenhouse gas emissions of plastic from cradle to grave and the effects of (micro)plastics on carbon fixation capacity of the ocean are systematically discussed from different perspectives. Some future research needs and challenges are also proposed in order to provide valuable reference for the formulation of relevant policies and scientific research.
Section snippets
Methods and analysis
In this paper, many published data were collected to make a preliminary assessment of contribution to global greenhouse gas emissions and climate change in plastic life cycle from cradle to grave. Greenhouse gas emissions at each stage of the plastic life cycle were introduced. Un-ignorable contribution of (micro)plastics to global greenhouse gas emissions and climate change were discussed from the following three aspects: (1) direct contribution to greenhouse gas emissions from plastics; (b)
Plastic waste management
There are several ways to manage plastic wastes: recycling, incineration, sanitary landfill and others. Plastic packing is one of the most problematic types of plastic waste, accounting for approximately 40% (PlasticsEurope, 2016), because it is usually designed for single use and ubiquitous in garbage and extremely difficult to be recycled. The flexible increasing use and multi-layer packing poses challenges to collection, separation and recycling. Although some plastics can be recycled, there
Potential emissions during plastic manufacturing
Olefins are important raw material for plastic production. In 2014, the global ethylene production was 134 million tons and propylene is the second most common raw material after ethylene, with an estimated demand of 89 million tons in 2014 (Plotkin, 2015). Olefins are monomers and can bind together to form long chains. In order to become plastics, olefins are stitched together to from extremely long chains of molecules or polymers. Plasticizers are also usually added in the production process.
Perspectives and challenges
The impacts of plastics on global climate change have attracted more and more attention all over the world. Raising public awareness of the plastic pollution crisis and increasing public concern have simulated many strategies for mitigating plastic pollution. Due to the increase in global plastic production and plastic waste, greenhouse gas emissions have intensified. However, lack of efficient and standard technologies and methods for determination and monitoring of greenhouse gas emissions
Conclusions
The increasingly serious impact of the plastic crisis on marine ecosystems has attracted worldwide attention. There is growing evidence that cradle to grave of plastics poses risks not only to the environment, but to human health. Despite challenges and uncertainties, the impact of the existing plastic economy on climate is real, significant and cannot be ignored. The impact of plastics on global climate change cannot be neglected. Plastic industrials are one of the fastest growing sources of
Declaration of competing interest
The authors have no conflict of interest to declare regarding this article.
Acknowledgements
The study is financially supported by the Program for the National Natural Science Foundation of China (51521006) and the Program for Changjiang Scholars and Innovative Research Team in University (IRT-13R17).
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