guia do novo coronavirus
Imprimir Republish

Cover

Reuse, replace, degrade

Experts call for multiple strategies to tackle plastic pollution

Os canudos plásticos já foram proibidos em várias cidades do Brasil e do mundo

The authorities have plastics in their sights. New laws on plastic manufacturing and marketing have already been passed by dozens of countries. Single-use products such as straws, cups, and packaging, which account for most of the waste that pollutes the natural environment, have already been banned in 27 nations—some Brazilian cities have also adopted the measure—while 127 countries have introduced legislation limiting the use of plastic bags. This data comes from the study “Legal limits on single-use plastics and microplastics,” released in late 2018 by the United Nations Environment Agency.

In addition to encouraging recycling, banning disposable plastics is one of the leading strategies for reducing plastic pollution. Its effectiveness, however, is refuted by the industry, and expert opinion is divided. “A simple ban on straws and other single-use products, despite being a seemingly assertive approach, does not solve the problem,” says Alexander Turra, from the Oceanographic Institute at the University of São Paulo (USP). Bans, unlike awareness campaigns, he says, do not create a link between avoiding the use of straws and the potential environmental benefit. “After plastic straws were banned in Rio de Janeiro, coconut water vendors started offering plastic cups to customers instead.”

Finding substitutes for plastic that cause less damage to nature is a significant challenge. “Imagine what would happen if there was a ban on selling water in plastic bottles,” says chemical engineer José Carlos Pinto, from the Alberto Luiz Coimbra Institute for Engineering Research and Graduate Studies at the Federal University of Rio de Janeiro (COPPE-UFRJ). Replacing them with glass containers would also have an environmental impact. “As well as the destruction caused to obtain the raw material, silica, from sand deposits, the glass manufacturing process creates more pollution than plastic. It would also increase carbon dioxide [CO2] emissions during bottle transport, since glass is heavier than plastic,” he says.

“There is no simple solution to the plastic problem. Replacing it with glass, metal, or paper is no easy task,” explains chemist Luiz Henrique Catalani, from the USP Institute of Chemistry. “To know whether substituting one material for another provides any real benefit, we have to thoroughly evaluate these alternative product chains, including post-use analysis. This evaluation should consider the environmental and energy footprint of each substitute,” says the researcher, who studies the application of polymeric materials in biomedical engineering.

In May, the European Union (EU) approved a series of measures to tackle plastic pollution. As well as banning single-use products from 2021 and setting a target of producing 90% of plastic bottles from recycled material by 2029, EU member states have decided that the industry should bear part of the cost of managing the material after use. Known as extended producer responsibility (EPR), the strategy includes higher taxes on the industry, among other measures.

IPT Biodegradable plastic film made from agro-industrial waste at USP, Ribeirão PretoIPT

“Producers must consider the impacts on nature and society as part of the cost of virgin plastic,” says Gabriela Yamaguchi, engagement director at WWF Brazil. “We argue that this cost should fall on the preconsumption production chain, to encourage selective collection and recycling.” A mandatory reverse logistics process—a system through which manufacturers are responsible for collecting post-use plastics for reintroduction to the chain through recycling or for proper disposal—is another suggestion. In 2015, the Brazilian Plastic Industry Association (ABIPLAST), the Plastivida Socioenvironmental Institute of Plastics, and 20 other business associations signed the General Packaging Agreement with the Brazilian Ministry of the Environment, which aims to increase recycling, including of plastics.

The industry disagrees with the implementation of extended responsibility. “We are against the polluter pays principle, where companies are responsible for disposal of the products. It exempts consumers, retailers, and other links in the chain from any liability,” says chemical engineer Miguel Bahiense Neto, president of Plastivida. “The shared responsibility system we currently use in Brazil is more appropriate. Everyone does their part to increase recycling and prevent post-use plastics from polluting the environment.”

Bioplastics
Another strategy to combat the pollution caused by overproduction and improper disposal of plastics is to create alternative materials to petroleum-based polymers, such as bioplastics. The global production capacity of these resins, made from renewable biomass sources, mainly of plant origin (cassava, maize, agricultural residue, etc.) is 2 million tons per year. This volume is growing, but it is still small compared to the 400 million tons of plastics synthesized from oil, natural gas, and coal.

A common feature among bioplastics is their biodegradability, which means they can be degraded by living biological agents such as fungi and bacteria within six months. There are some, however, that are not biodegradable, such as petrochemical company Braskem’s Green Plastic, which is made from sugarcane. But it does offer environmental benefits. “Green Plastic was the world’s first polyethylene made from a renewable source. It captures 3.09 tons of CO2 for every ton of resin produced, contributing to the reduction of greenhouse gas emissions into the atmosphere,” says Gustavo Sergi, renewable chemicals director at Braskem.

When it comes to degradation, OXO-biodegradable polymers must also be mentioned. “They contain substances that accelerate oxidative degradation [by the action of oxygen], causing rapid erosion of the material, but not necessarily complete degradation. The problem is that most of these substances contain transition metals, some of which are highly toxic to the environment,” explains Catalani of USP. “These plastics have been banned in many countries. Manufacturers are trying to gain a foothold in developing nations where legislation is still weak.”

Léo Ramos Chaves Biodegradable polymer: alternative to petroleum derivativesLéo Ramos Chaves

Researchers around the world are working on alternatives to synthetic plastics. During her master’s degree and PhD at USP’s Ribeirão Preto School of Philosophy, Sciences, and Languages and Literature (FFCLRP), chemist Bianca Chieregato Maniglia created biodegradable plastic films from the residues of babassu oil production and turmeric pigment extraction. “These films could potentially be used as bioactive packaging because they contain phenolic compounds that confer antioxidant and antimicrobial properties, helping to preserve food,” says agro-industrial engineer Delia Rita Tapia Blácido, who supervised the research.

Another advantage of the biofilm is that its raw material is agro-industrial waste. “These low-cost materials are usually disposed of as trash. But they have potential for technological applications,” says Maniglia. Manufacturers of cosmetics, food, and textile products have already shown interest in the biopolymer, which is in the final stages of development. “Our material still can’t compete with conventional plastic, mainly because it absorbs a lot of moisture. But we’re working on it.”

At UNICAMP, researcher Rodrigo Leandro Silveira and physicist Munir Salomão Skaf, director of the Center for Research in Engineering and Computational Sciences, one of FAPESP’s Research, Innovation, and Dissemination Centers (RIDCs), were part of an international team that developed an enzyme called PETase, which facilitates the degradation of PET used in plastic bottles. Half of Brazil’s annual production of this plastic, estimated at 520,000 tons, is not recycled and will end up in landfills, dumps, or elsewhere in the natural environment.

“Our role in the study was to analyze the action of the enzyme, which we did using computational models,” says Silveira. He explains that enzymes are not static but dynamic structures. “The simulations demonstrate how they move,” says the researcher. PETase enables the polymers to degrade within just a few days. “A soda bottle has been degraded by the enzyme in 96 hours—normally this process would take hundreds of years. PETase transforms PET into its smaller molecules. There are no macroscopic particles or pieces of plastic left at the end,” explains Skaf, noting that it will take time for PETase to become a commercial product.

Last year, another important discovery relating to polymers was announced in the journal Science. Scientists at Colorado State University, led by Eugene Chen, announced that they had made progress toward creating a plastic that can be converted back to its original state and recycled endlessly without generating any waste. “The aim of the research was to synthesize new polymers that can be easily chemically degraded to their molecular components. These, in turn, can be reused to remake the same plastics. Like the study on PETase, it is important research with great potential to help address plastic waste pollution,” says Silveira.

Projects
1. Synthetic and natural frameworks applied to regenerative medicine (nº 18/13492-2); Grant Mechanism Thematic Project; Principal Investigator Luiz Henrique Catalani (USP); Investment R$2,617,149.54.
2. Utilization of agro-industrial waste in bioactive films (nº 09/14610-0); Grant Mechanism Regular Research Grant – Junior Researcher; Principal Investigator Delia Rita Tápia Blácido (USP); Investment R$473,476.36.
3. Hybrid QM/MM simulations of feruloyl esterases: Mechanism for splitting lignin-carbohydrate complexes in plant cell walls (nº 16/22956-7); Grant Mechanism Grant for Research Abroad; Principal Investigator Munir Salomão Skaf Scholarship Beneficiary Rodrigo Leandro Silveira; Investment R$219,048.74.

Scientific article
CHEN, E. et al. A synthetic polymer system with repeatable chemical recyclability. Science. Apr. 27, 2018.

Republish