Potential routes for plastic losses from landfills involve environmental mechanisms like wind, flooding, leaching and runoffs
Most plastic waste ends up in landfills and takes a long time to break down. Photo: iStock India produces 9.3 million tonnes of plastic each year and the amount produced has quadrupled in the last five years. The COVID-19 pandemic has increased plastic manufacture in e-commerce, food delivery services and fast-moving consumer goods (FMCG) businesses.
The primary issue is the accumulation of uncollected plastic waste — constituting 40 per cent of the total — which ends up in landfills, causing blockages in water bodies and pollution on streets. When plastics reach a landfill site or an open dumpsite, they are typically in the form of macroplastics (larger in size), which later convert into microplastics as well. Therefore, both forms can be found at the landfill site.
Microplastics generated from the breakdown of large plastics have also sparked significant global concerns regarding their potential impact on both the environment and human health
Most plastic waste ends up in landfills and takes a long time to break down. In specific environmental conditions, plastic materials undergo changes that make them lose some of their properties. Factors like molecular weight, crystallinity, functional groups, mobility, structure substituents, and added additives all affect how plastics degrade.
We still don't fully understand how long it takes for these plastics to decompose and completely turn into carbon dioxide in landfills. Polymers can break down through chemical, photodegradation and biological processes, potentially contributing to the creation of secondary microplastic pollution.
Plastics in landfills initially break down with the help of bacteria in the presence of oxygen, but they later enter anaerobic conditions. This transition affects the degradation process through the formation of acid and methane from organic waste.
Even without light and oxygen, plastics in landfills continue to break into smaller pieces, known as nanoplastics, due to factors like fluctuating temperatures (up to 60 to 90 degrees Celsius), varying pH levels (4.5–9), deep-seated fires, physical stress, compaction and limited microbial activity. Each of these factors speeds up the breakdown of plastics.
While most polymers and plastics in landfills remain unchanged, some may degrade through biological (biotic) or non-biological (abiotic) processes into fragments that either persist as produced or biodegrade into gaseous products and water. In aerobic environments, the gaseous products mainly include carbon dioxide.
Potential routes for plastic losses from landfills involve environmental mechanisms, which include processes like wind, flooding, leaching, and runoff, as well as the impact of living organisms, such as their removal by animals, according to a 2022 study. Engineered landfills that are sanitary and well-managed are equipped with physical barriers to prevent losses through various mechanisms.
These locations are typically chosen for their environmental attributes, which significantly decrease the likelihood of plastics escaping into the environment. In contrast, open dumps lack effective barriers to prevent plastic losses. They lack fencing to hinder the movement of macroplastics through winds, runoff or floods and lack liners to impede the movement of microplastics through leachate.
In the presence of elevated pore pressure resulting from the accumulation and extrusion of waste, the movement of leachate and landfill gas may induce diverse aging effects on plastic waste, involving processes such as rinsing, immersion, collision, and corrosion, the 2022 study had found. As a part of the landfill stabilisation process, the gradual settling of waste can lead to its creeping, mechanically breaking down plastic waste through friction and shear force.
The properties of plastics that influence their transport from landfills through flooding include mass, density, shape and size. In general, plastics possess a higher surface to volume ratio, which makes them more likely to float in water compared to other denser materials in municipal solid waste (MSW). The majority of plastic products has smooth surfaces, resulting in lower interlayer friction within the MSW, which enhances their potential for mobility.
Indian Institute of Technology, Kharagpur presented a novel framework to categorise urban centres into different risk levels based on a trivariate risk assessment model where 496 Indian urban centres with populations larger than 100,000 inhabitants were studied. Results showed that nearly 11 per cent of these cities present severe and very high-risk levels of plastic losses from their existing dumpsites, Mumbai and Delhi being at the major risk.
The study also reported that environmental losses of plastics from mismanaged landfills (including open dumps, sanitary and well managed landfills) have been estimated or modelled to be 5 per cent up to 47 per cent as per the studies conducted across the globe.
Plastic waste pollution from dumpsites and landfills
Source: Wojnowska-Baryła, I., Bernat, K., & Zaborowska, M. (2022). Plastic waste degradation in landfill conditions: the problem with microplastics, and their direct and indirect environmental effects. International Journal of Environmental Research and Public Health, 19(20), 13223.
Leachate contamination: Rainwater or other liquids percolating through waste in landfills can create leachate, a liquid that can contain various pollutants, including microplastics and harmful chemicals. If not properly managed, leachate can migrate into the surrounding soil and water, leading to pollution.
Microplastic (typically polyethylene, polystyrene, and polypropylene) concentration in raw and treated landfill leachate varied between 0–382 and 0–2.7 items per litre as reported by a recent study conducted by North Carolina Agricultural and Technical State University, the US.
Wind dispersal: Lightweight plastic particles, such as microplastics or small plastic fragments, can be carried by the wind. Inadequately covered or managed landfills, particularly in developing economies such as India, may release plastic particles into the air, contributing to pollution in nearby regions.
Surface runoff: Rainwater can wash over the surface of landfills, picking up plastic debris and contaminants. This runoff may flow into nearby water bodies, introducing plastics and associated pollutants into aquatic ecosystems.
Flooding events: During heavy rainfall or flooding, landfills may become inundated, causing plastic waste to be carried away by floodwaters. This can result in the spread of plastics and contaminants to downstream areas.
Biological transport: Animals, attracted to landfills for food or shelter, may carry plastic waste away from the landfill site. This can contribute to the dispersal of plastics into surrounding regions.
Lack of engineering controls: In poorly managed or unengineered landfills, where physical barriers and containment systems are insufficient, there is a higher risk of plastic pollution. Open dumping without proper waste containment measures can lead to widespread environmental contamination.
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