Biodegradable materials have gained space on shelves and in discussions about sustainability. Despite this, it is not always clear how each of them breaks down. Some, for example, only decompose in specific locations, such as industrial composting plants.
The idea that “everything degrades one day” tends to sow confusion since, in fact, all materials degrade over the years, under the effect of the sun, heat or oxygenation. However, this does not mean that it is biodegradable.
Biodegradation involves chemical, environmental and temporal criteria. To receive this classification, the material must be transformed by living organisms and reintegrated into nature without leaving toxic substances in the environment.
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What defines a biodegradable material?
A material is considered biodegradable when microorganisms such as bacteria and fungi are able to “eat” the material and transform it into simple substances, such as carbon dioxide, water or organic matter. In other words, it must become something that nature can reintegrate without harm.
Certain international and Brazilian standards determine, for example, that at least 90% of the carbon present in the material must be converted into CO2 within 180 days. Additionally, the process cannot leave toxic residue in the soil or water.
“A material only truly delivers on its promises if it meets standardized biodegradation criteria, which include defined time frames and no toxicity at the end of the process,” explains environmental engineer Pedro Montenegro, from Rio de Janeiro.
This means that the material must serve as food or participate in the chemical reactions of these microorganisms. If degradation occurs due to sunlight, heat, air, or weather, it is not biodegradation, but rather physical or chemical decomposition, a process that does not guarantee safe reentry into the environment.
Biodegradable materials are products that break down with the help of microorganisms and return to the environment without causing harm.
Why don’t some materials break down as easily?
Some materials have very stable chemical structures, making them difficult for microorganisms to break down. This is the case for synthetic polymers, such as polyethylene and polypropylene, used in everyday objects.
Chemistry professor Walter Ruggeri Waldman, from the Federal University of São Carlos (UFSCar), in São Paulo, explains that synthetic polymers were created to last and give firmness to products. This is why they do not fall apart easily.
“Synthetic polymers are part of equipment, such as automobile parts, household appliances and construction materials. The current challenge is to develop materials that are resistant to use, but biodegradable only at the end of their lifespan,” emphasizes Waldman.
Even when subjected to wear and tear from the sun or air, only a portion of these materials are ready to be biodegraded. In addition, the presence of additives used to add color, flexibility or resistance also hinders the work of microorganisms and can release toxic substances into the environment.
Ideal conditions for biodegradation
Biological decomposition depends on specific environmental factors. Temperature, humidity, soil type, presence of oxygen and diversity of microorganisms determine whether the process progresses or not. In cold regions the pace may be slower. In tropical regions, heat accelerates biological action.
Therefore, some materials classified as biodegradable only decompose in industrial facilities, which maintain controlled conditions of temperature, oxygenation, and periodic mixing of the material. In domestic composters, these requirements are rarely met.
Why doesn’t the biodegradable label always guarantee rapid decomposition?
Even when a product is labeled “biodegradable,” that doesn’t mean it will break down in any environment. Most urban waste is sent to landfills, where there is a lack of oxygen and a low diversity of microorganisms capable of biodegradation.
Under these conditions, the process may take much longer than provided for by the regulations or simply not take place. Additionally, the label states that the material can biodegrade, but only if exposed to appropriate conditions, which are typically those of industrial composting.
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