How do socio-demographic factors influence plastic pollution?

Plastic pollution in the environment, which was virtually non-existent in 1950, now amounts to between 36 and 115 million tonnes, depending on estimates, and is predicted to continue rising dramatically in the coming decades. Understanding the current and future influence of socio-demographic factors such as gross domestic product (GDP), population size and urbanisation rates, on this phenomenon globally is crucial as it could guide current and future public policies aimed at combating and limiting plastic pollution.

The environmental Kuznets curve: a graphic model that is still controversial

Based on the Kuznets curve, devised in 1955 by economist Simon Kuznets to describe the relationship between a country's economic development and its inequality levels, scientists have proposed an environmental Kuznets curve (EKC) linking a country's pollution levels to its GDP. Introduced in 1994, the EKC presents a bell-shaped evolution. According to this theory, the poorest countries, with limited industrial activity, are the least polluting. In contrast, developing countries with highly active industries but insufficient means to control pollution are the biggest polluters. Finally, in wealthy countries, which have reached a stage where the basic needs of their inhabitants have been met, the curve reverses. Environmental issues become more prominent and these countries have the resources to address them.

Applied to various environmental factors, such as CO2 emissions or energy consumption, the EKC has not yet been validated for plastic pollution. Through their research, Mateo Cordier and Huijie Yan from the laboratory of Cultures, Environments, Arctic, Representations, Climates (CEARC - Univ. Paris-Saclay/University of Versailles-St-Quentin, UVSQ) and the College of Policy Science at Ritsumeikan University (Japan)and Takuro Uehara, from the College of Policy Science (Ritsumeikan University, Japan), have been working to remedy this shortcoming.

A statistical model to study plastic pollution trends

To investigate this, the three researchers used the STIRPAT statistical model, which estimates environmental pressure from plastic pollution using data on population (age, size, density and city size), economic growth (GDP), technological progress (the proportion of services and industry in the economy) and governance (anti-corruption policies and control of industrial lobbying). This empirical model makes it possible to test the contribution of each factor to the overall phenomenon, based on actual data.

World Bank data validates the environmental Kuznets curve

The team applied its STIRPAT model to a World Bank database which catalogues all plastics produced by 217 countries and territories and assesses their plastic waste management practices. Their study focused on mismanaged waste. As Mateo Cordier explains, "this is where the researcher's subjectivity comes into play. As we were focusing on the oceans, we defined mismanaged plastics as those likely to end up in the sea." This included open-air and uncontrolled landfill sites, as well as all waste dumped directly into the environment.

Based on this data, the researchers demonstrated that their statistical model supports the EKC hypothesis, meaning there is a link between a country's pollution levels and its economic development. Wealthy nations are financially and culturally capable of managing their plastic waste, so they produce little mismanaged plastic. The same applies to poor countries, which consume and produce less plastic. However, as Mateo Cordier points out, "emerging countries produce large amounts of mismanaged plastic because their middle classes consume a lot of plastic, but these countries do not yet have the financial resources or the political or civic will to manage their waste properly." »

A dataset with biases to be considered

This result is not without bias, due to the data on which the study was based. Firstly, the environmental impact of what is considered well-managed waste is not neutral. For example, waste incineration generates CO2 and toxic particles harmful to human health and recycling is not an infinite process. Some recycling methods even release of microplastics into the environment (such as when plastic waste is recycled into clothing, road surfaces, etc.). Additionally, the study only accounted for macroplastics from street-collected waste, such as household or commercial waste, leaving out industrial, agricultural and fishing industry waste due to a lack of data. "This means we've probably overlooked half the problem, because the amount of waste produced by economic sectors is enormous," comments Mateo Cordier. Moreover, the World Bank does not provide data on the export of plastic waste from rich to poor countries.

Taking into account the total flow of plastics and waste from economic sectors might result in a graph that no longer follows the environmental Kuznets curve. Mateo Cordier suggests: "It would be interesting to recreate these curves by considering total plastic waste. We would then see that in rich countries, it's a disaster. We know that incineration and recycling are not very good solutions, something our study doesn't reveal." »

No reduction in plastic pollution by 2050

Using their statistical model, the team sought to predict the evolution of plastic pollution from 2023 to 2050 by creating a series of scenarios based on different factors (growth, population and urbanisation). The results indicate that, regardless of the scenario, global plastic pollution will not decrease. In addition to GDP, factors such as corruption, commercial and industrial lobbying, population size, age and urbanisation also have a major influence on plastic pollution. For instance, in a scenario of rapid urbanisation, plastic pollution increases sharply.

A scenario in which economic growth is halved reveals a surprising trend. "We expected to show that slowing growth would improve the situation, but globally, that's not what we see," laments Mateo Cordier. This result is likely due to the influence of lower-middle-income countries on the global evolution of plastic pollution. "These countries need revenue to generate taxes that can finance public services and collect and treat waste. Moving away form the growth paradigm might work for wealthy countries, but not for poor or lower-middle-income countries," says the CEARC researcher. He continues: "However, if instead of focusing on so-called ‘well-managed’ and ‘mismanaged’ waste, we looked at total plastic waste, we might show that slowing economic growth reduces total annual plastic waste production." Indeed, Mateo Cordier and his colleagues demonstrated in 2020 that a 1% growth in GDP per capita leads to a 0.02% increase in total plastic waste production (both well- and mismanaged).

A useful model for guiding public policy

In conclusion, this study can help guide public policy towards better integration of plastic waste management into urban planning. For instance, in a report for the French Ministry of Ecological Transition, Mateo Cordier applied the model to France in order to assess the impact of corruption on the trend in plastic pollution. The results were striking: "If corruption and the influence of commercial and industrial lobbies were reduced by 25%, plastic pollution would significantly reduce," asserts the researcher. Having clear figures provides politicians with a solid foundation to make informed efforts to curb the rise in plastic pollution.

Bibliographic references
Cordier M., Uehara T., Baztan J., Jorgensen B., 2020. Plastic pollution and economic growth: the influence of corruption and the lack of education. Preprint ResearchGate.

Cordier M., Uehara, T., Baztan, J., Jorgensen, B., Yan, H., 2021. Plastic pollution and economic growth: the influence of corruption and lack of education. Ecological Economics 182, 106930.

Yan, H., Cordier, M., & Uehara, T., 2024. Future projections of global plastic pollution: Scenario analyses and policy implications. Sustainability, 16(2), 643.