Quantity of plastic waste input into the ocean from China based on a material flow analysis model 1

: Marine plastic waste has been an important global environmental issue in recent years, and quantifying the amount of global marine plastic waste input is vital for control and mitigation. However, determining an accurate quantity of oceanic plastics is challeng-ing because comprehensive monitoring data are difficult to obtain on national and global scales. To understand the contribution of China in global marine plastic waste input, we used a material flow analysis (MFA) method, which is included in lifecycle assessment and combines statistical data from China ’ s official statistics, reports, and NPO (nonprofit organi-zation) to establish an MFA model. The model assesses the lifecycle of plastics, which starts with primary plastic, passes the stage of plastic product, and eventually becomes plastic waste. With the MFA model, the annual amount of plastic waste entering the ocean from China from 2011 to 2020 can be calculated. In 2011, 0.65 million tonnes of plastic waste entered the ocean from China, and the quantity rose slowly until 2016. A rapid decline appeared in 2018 because of China ’ s governmental managements and the quantity will continue to decrease until 2020. Our results indicate the amount of oceanic plastics has a strong correlation with government control measures.


Introduction
Since the 1960s, plastics have become one of the most commonly used artificial materials and a source of major environmental pollution (Smith 2014;Galloway and Lewis 2016) as a result of their inherent properties and poor management. Plastic debris is found in oceans, lakes, harbors, and polar regions, and it can harm a variety of organisms (Donohue et al. 2001;Derraik 2002;Barnes et al. 2009;Free et al. 2014). Most marine plastic waste includes disposable straws, lunchboxes, plastic bottles, and other food packaging. According to a regional survey in Thailand, the top four marine plastic wastes are plastic bags, plastic bottle caps, plastic ropes, and plastic straws. Similar plastic waste categories are found in China. Plastic garbage can enter the ocean by direct littering near rivers (Lebreton et al. 2017) or beaches, followed by tidal or wind transport (Kershaw and Rochman 2015), and even during the transport of products or after traffic accidents (Barnes et al. 2009). After entering the oceans, plastic waste will eventually float in the sea or sink into the deep seabed (Thompson et al. 2004;Van Cauwenberghe et al. 2013;Law et al. 2014). So far, plastic waste has been found in more than 100 species of organisms including marine life such as whales, dolphins, fish, invertebrates, and birds (Allsopp et al. 2006). Quantitative research on the sources and fates of marine plastic debris plays an important guiding role in mitigating and minimizing the effects of this pollution on the environment. Eriksen et al. (2014) calculated the quantity of macroplastics with a modelling approach, and concluded that the annual plastic debris input into the North Pacific is 9.64 × 10 4 t (9.64 × 10 7 kg), while the input into the South Pacific is 2.1 × 10 4 t (2.1 × 10 7 kg). Lebreton et al. (2017) estimated that 1.15-2.41 × 10 6 t of plastic waste enters the ocean every year through riverine input. Schmidt et al. (2017) calculated that the global plastic debris input into the ocean is between 0.41 and 4 × 10 6 t per year from rivers. Jambeck et al. (2015) estimated that in 2010, 4.8-12.7 × 10 6 t of plastic waste has entered oceans from coastal areas globally.
As the world's largest plastic producer and consumer (PlasticsEurope 2017), it is necessary to determine China's contribution to the input of marine plastic waste. We used a model to calculate and predict the amount of plastic waste entering the ocean from China on a time scale of 10 years.

Methods
In this study, a material flow analysis (MFA) model was established using data from each stage in the lifecycle of plastics. The amount of mismanaged plastic waste was multiplied by the rate of plastic entering the ocean to calculate the total amount of plastic waste that entered the ocean from China between 2011 and 2017. We then predicted the amount of plastic that entered the ocean from 2018 to 2020, and found that strong governmental control measures could dramatically decrease marine plastic waste input.
Lifecycle assessment is a systematic method used to determine the impacts of products on the environment through the stages of a product's life from raw material through material processing, distribution and use, and recycling or disposal. Material flow analysis can quantitatively analyze the flows and stocks of materials within a defined system (Van Eygen et al. 2017). The main components of a MFA model include the raw materials, pathways, intermediates, and final sinks of a material. A MFA model must obey the law of conservation of mass (Brunner and Rechberger 2004), and all inputs, stocks, and outputs of a material within the model are balanced.
We connected processes from primary plastic to the plastic garbage generated in China, and finally calculated the amount of plastic waste entering the ocean from China. The complete MFA model, specific coefficients, and data for evaluating plastic waste entering the ocean is presented in Bai et al. (2018). Figure 1 is a simplified schematic model of plastic waste entering the ocean from China. The "Input" refers to several components correlated with plastic products from the initial form to the end of service life. When plastic products end their life or are discarded, they become plastic garbage. Recycled plastic garbage, in turn, can become plastic waste. The "Output" stands for plastic waste that is mismanaged and could enter the ocean.

Source of data
The sources of data used in the model include national official statistics, publications, and field surveys. By collecting data from the National Bureau of Statistics of P.R.C., General Administration of Customs of P.R.C., National Development and Reform Commission, and other governmental agencies, we obtained national official statistics. Data from reports and publications compiled by market research firms and plastic industry associations like the China Plastic Processing Industry Association and China Scrap Plastics Association are used in this model. We investigated the status of disposal and management of plastic waste in Wenzhou, Zhejiang province, which is a typical coastal city in China. Thus, the quantity of plastic waste that enters the ocean through several major pathways from coastal areas in China can be calculated.

Results
The amount of plastic waste entering the ocean annually during 2011-2020 from China is shown in Fig. 2. In 2011, inputs to the ocean were 6.5 × 10 5 t, and this amount rose slowly until 2016, with a maximum quantity of 8.

Discussions and conclusions
Comparing the amount of plastic waste input from China in 2010 estimated by Jambeck et al. (2015), which was (1.32-3.53) × 10 6 t, to the amount of plastic waste predicted in this study in 2011 (6.5 × 10 5 t), it is clear there are large discrepancies. Our estimation is 20%-50% lower than that calculated previously (Jambeck et al. 2015). The overestimation of marine plastic waste input from China will lead to a global overestimation of the total quantity of oceanic plastics. According to the results of our estimation, laws and regulations about mismanaged plastic waste have great influence on oceanic plastics input. To get a more precise prediction and calculation of marine plastic waste input, the impact of governmental management plans needs to be taken into consideration when establishing models.
This study is the first to estimate and predict the amount of plastic waste entering the oceans annually from China. Our results suggest that the input of plastic waste increased prior to 2016 and then decreased dramatically after that time. Inputs will likely continue to decrease in the near future as a result of China's efforts in domestic waste management and control. Several uncertainties exist in this study. In particular, we did not include climate and seasonal variations that could affect runoff and, thus, the amount of plastic entering the ocean (Morishige et al. 2007;Vianello et al. 2015;Lebreton et al. 2017). Additionally, the effect of dams was not considered, which also could influence the input of plastic debris (Lehner et al. 2011). These factors will be taken into account in future modeling efforts.