New method of analyzing microplastic particle pollution may facilitate environmental impact assessment

Over the past decade, a growing number of researchers have studied plastic pollution, one of the world’s most pressing environmental hazards. They have made progress, but still face challenges, such as the comparability of results, especially for microplastics.

For example, there is no standard methodology for sample collection and analysis. Most studies present conclusions based on particle counts as if they were environmentally equivalent regardless of size, volume, mass, or surface area.

An article by three Brazilian researchers published in Environmental Science and Pollution Research aims to contribute to progress in this field by proposing a new perspective on particle morphology.

Using a theoretical approach, the authors argue that including morphological features in the analysis can reveal significant differences between samples of microplastic particles, demonstrating that samples initially considered equivalent because they contain the same number of particles actually have different environmental impacts due to variations in size of the particles. and shape.

Microplastic particles (MPs) are man-made polymers between 0.001 and 5.0 millimeters or 1-5,000 micrometers (μm) in length and are found in all kinds of environments. Few MP pollution studies have been published in Brazil, especially regarding inland water areas.

“Most of the research done on MPs reports the number of particles in terms of the unit adopted for the sample type, ranging from volume in the case of water, to mass when the analysis includes soil and sediment, and individuals for living organisms. We have been researching MPs in the lab for several years and have confirmed that size matters and makes a difference. We measure the particle size in all samples. In this study we found samples with a similar number of MPs but significant variations in particle size and very different levels of plastic pollution based on particle mass and volume,” Décio Semensatto, first author of the paper, told Agência FAPESP. He is a professor at the Institute of Environmental, Chemical and Pharmaceutical Sciences of the Federal University of São Paulo (ICAQF-UNIFESP).

The other authors of the article are Professor Geórgia Labuto and Cristiano Rezende Gerolin, former researcher at UNIFESP.

According to Semensatto, the group is completing a paper on the Guarapiranga Reservoir, a source of drinking water for São Paulo and two nearby towns, Itapecerica da Serra and Embu-Guaçu. “We collected samples in the wet and dry seasons and found more MPs in one season than the other, with an even greater difference in the mass of each sample and the total volume of plastic. Using only particle numbers as a parameter only focuses on one dimension and ignores this fact that different particle sizes have different effects on ecosystems,” he said.

Comparisons

According to the recent article, the researchers analyzed seven samples with 100 MPs each. These will be considered equivalent based on conventional pollution measurements. However, the comparisons made showed that their impact on the environment would be very different. In one sample, MPs were larger in volume, mass, and specific surface area. It therefore had more plastic than the others and was likely to produce a greater number of even smaller particles when broken down by physical and chemical degradation.

In another comparison, they analyzed samples with 100 MPs and 10 MPs respectively, noting that if only the number of particles was considered, the conclusion would be that the former had ten times more plastic than the latter, although both had the same total mass and volume of plastic, while particle size and specific surface area were greater in the former.

The authors also highlight the issue of particle morphology or shape. Samples containing fibers had lower volume, mass and surface area, for example.

“We are also exploring the issue of surface specificity, which is very relevant, especially when studying MPs as carriers of other contaminants, such as metals or pharmaceuticals,” Semensatto said. “Particle size affects the surface area available to absorb these pollutants. In addition, MPs also form a plastic sphere that serves as a substrate for organisms and disperses these organisms to other environments, with implications for global health.”

The plasticosphere is the community of bacteria, fungi, algae, viruses and other microorganisms that have evolved to live in man-made plastic.

“By considering particle volume, mass and specific surface area, we can better understand how MPs pollute water bodies and transport other polluting agents, including microorganisms,” Semensatto said. “Analysis of all sample characteristics brings new possibilities to the fore and extends the comparability of results.”

The sheer scale of the problem

Global plastic production reached 348 million metric tons in 2017, up from just 2 million tons in 1950. The global plastics industry is valued at US$522.6 billion and its capacity is expected to double by 2040, according to a report by The Pew Charitable Trusts and SystemIQ, in collaboration with the Universities of Oxford and Leeds in the UK.

Plastic production and pollution affect human health and fuel greenhouse gas emissions. Plastic can be ingested by or cause accidents involving more than 800 marine and coastal species. About 11 million tons of plastic waste enter the oceans every year.

In 2022, 175 countries represented at the UN General Assembly adopted a historic resolution to sign by 2024 a legally binding commitment to end global plastic pollution. To this end, they created an intergovernmental negotiating committee, which held its first session in December.

“With this study, we aimed to contribute to academic efforts to develop routines and methodologies to tackle plastic pollution,” Semensatto said. “Our paper suggests a discussion within the academic community. The proposal is open for debate. We invite other scientists to measure MPs and report their morphological features, as a contribution to the discussion of their environmental significance.”

In this context, a team at UNIFESP linked to Semensatto is working with the Environmental Society of the State of São Paulo (CETESB) to develop protocols for the collection of water samples and the analysis of MPs in the coastal area of ​​the state. The main goal is to find a way to compare the results so that MPs can become part of continuous environmental monitoring, which is not currently the case in São Paulo.

This project is carried out under the auspices of Rede Hydropoll, a network of researchers at various institutions involved in the study of water source pollution.