The versatility and resistance of plastic allowed for its massive use during the second half of the 20th century. Plastic is hardly degradable and—because waste management is often inefficient—around 55% ends up either in landfill or in nature. Plastic mismanagement thus durably pollutes the environment. Although several studies have pointed out the effect of microplastic and nanoplastic pollution on global health, few have focused on the effect of macroplastics on the proliferation and propagation of infectious diseases and thus on human and livestock health. Plastic debris that holds water can encourage arthropod-borne disease by providing a habitat for some vectors’ immature stages and shelter to anthropophilic and medically important species, potentially increasing local vector populations with implications for disease burden. Similarly, by acting as a stagnant water reservoir, waste plastic promotes the development of pathogenic bacteria (such as leptospirosis) and harmful algae. These microorganisms can produce biofilms, coating plastic fragments that can then colonise new water bodies. These concerns point to the need for a transdisciplinary approach to understand and potentially prevent plastic debris from influencing local vector-borne and waterborne diseases.
Plastic, considered a miracle product of the 20th century, has become the curse of the 21st century. Its large-scale production only dates back to the 1950s.
Its annual production exponentially increased from 2 million metric tons (Mt) in 1950 to 381 Mt in 2015.
The versatility and resistance offered by this synthetic material made it highly attractive for many applications such as in the food sector, where single-use plastic helps to reduce food waste generation by improving food safety and shelf life of the products.
This low-cost and effective product allowed for a globalised economy, in which fabrication happens further and further away from the consumer, facilitated by more and more wrapping and packing materials.
As a consequence, the packaging sector is the largest producer of plastic waste, accounting for nearly half of plastic waste generation.
In 2015, of the 302 Mt of plastic waste generated, 141 Mt were solely attributed to this sector. The plastic waste generated is often of single-use, and is characterised by a short use lifetime, usually less than 6 months.
In 2015, 20% of global plastic waste was recycled, 25% was incinerated, and 55% was either put into landfills or discarded in nature.
Mismanagement of plastic waste is generally most evident in middle-income countries, especially in tropical areas (with the addition of China). These countries have usually faced a rapid development and many import large volumes of plastic waste from high-income countries; however, their waste management systems are not able to cope with these large volumes of plastic.
If current production and plastic waste management practices continue, about 12 000 Mt of plastic waste will end up in landfills or in the natural environment by 2050.
Global plastic waste mismanagement is causing a serious predicament as it interacts with wildlife in several ways.
It can constrict or trap animals, be ingested, or directly affect the environment by its presence, such as by reducing oxygenation in the water, lowering light penetration, or covering coral reefs.
Due to its resistance, it is not—or is barely—degradable and instead breaks down into smaller particles that are easily carried away into aquatic environments.
The ever-growing problem of microplastics and the marine environment is well documented.
Many studies focus on microplastic and nanoplastic’s effects as endocrine disruptors, or in a broader sense their influence on both human and wildlife health.
For example, microplastics were found ontogenically transferred from the larvae to the adult mosquito and fragments could be transmitted through the bite of a female mosquito.
The most noticeable and reported consequences of plastic pollution are the great Pacific garbage patch, and casualties amongst turtles and large mammals after plastic entanglement or ingestion.
Most research articles focus on the effect of plastic debris in marine or aquatic environments.
Surprisingly, there are few studies on macroplastics and their effects in terrestrial environments. In this article, we emphasise the potential role of plastic pollution on infectious disease risk. Several studies have targeted the effect of rubbish and solid waste accumulation on infectious disease risks taking a One Health approach.
However, they often lacked standardised procedures and rarely provide information on waste composition.
Plastic pollution and accumulation are rarely taken into account in infectious diseases studies. However, such pollution can directly influence arthropod-borne diseases by generating suitable habitats for their vectors (figure). The most obvious examples are Aedes aegypti and Aedes albopictus mosquitoes, transmitting chikungunya, dengue, yellow fever, and Zika viruses along with numerous other arboviruses.
Both species are known to be highly anthropophilic and to develop in plastic containers, tyres, buckets, plastic teacups, and plastic bottles and are usually found near households, as observed in Argentina, India, La Reunion Island, Malaysia, the Philippines, and Thailand.
Since these species develop in plastic waste, and considering the large distribution of these highly anthropophilic vector species—mainly across tropical regions, many of which lack effective plastic waste management systems—it is now believed that more than half of the world’s population is at risk of Aedes-borne viruses where plastic waste could influence transmission. Japanese encephalitis virus vectors, mainly belonging to the Culex genus, do the same appropriation of plastic waste for their immature aquatic stages. In addition to providing suitable breeding sites for these species, the pools of water generated by discarded plastic are usually small, and host very little insect diversity. Plastic waste might thus help to decrease predation of mosquito larvae, increasing their survival rate and density.
Indirectly, the accumulation of plastic debris can clog water drainage, leading to a flood of stagnant waters after heavy rains. Resulting pools can serve as a breeding ground for disease vectors such as Anopheles mosquitoes, potentially increasing the malaria burden of an area.
Not only do discarded plastics provide a suitable breeding ground for their larvae, but they also can provide shelter for other haematophagous arthropods, such as triatomine bugs responsible for Chagas disease.
Beside arthropod-borne diseases, stagnant pools of water generated by plastic waste can promote waterborne diseases such as trematodiasis, dracunculiasis (also known as Guinea worm disease), schistosomiasis (also known as bilharzia), lymphatic filariasis, and onchocerciasis.
For schistosomiasis, freshwater snails, such as Bulinus spp or Biomphalaria spp act as intermediate hosts, and can lay their eggs in discarded plastics.
Similarly, macroplastic debris can generate suitable habitats for these molluscs, with the potential to locally increase the disease burden. The same is observable for leptospirosis where Leptospira interrogans, which is responsible for leptospirosis, was able to develop a biofilm on plastic in an in vivo model.
Similarly, a plethora of organisms building up complex biofilms can rapidly colonise floating plastic and harmful algae and bacteria such as Vibrio spp (responsible for cholera) can develop on plastic debris.
Since this material is resilient for a long time in the environment, it can act as a vessel in propagating infectious bacterial and algae species.
Finally, waterborne diseases generated from leftover plastic also affect livestock, potentially holding back agricultural development and local income, and potentially stimulating zoonotic diseases.
For example, locally removed plastic waste led to a substantial increase in survival rate for poultry, a major source of protein in low-income countries, attributed to a decrease of salmonellosis and pasteurellosis (fowl cholera) cases.
Known to also be influenced by climate change, incidence of waterborne diseases is likely to increase substantially with the concomitant increase in plastic debris.
Discarded plastics offer a favourable habitat for vector species, by providing a suitable habitat for the development of their immature stages, locally increasing the density of vectors, and by providing the adults with shelter. In addition, the pools of water that collect in or due to plastic waste can sustain waterborne diseases, such as schistosomiasis, leptospirosis, cholera, or salmonella, causing a burden on both humans and livestock living nearby. Considering the rapidly growing generation of plastic waste, the burden caused by these infectious diseases will probably rise. By 2050, 70% of the world’s population will live in urban areas and without much more effective waste management strategies, especially in tropical areas, more people will likely be exposed to infectious diseases. A global sanitary crisis such as COVID-19 shows how rapidly additional disposable sanitary plastic elements can be created and how subsequent, efficient, waste management strategies have failed. By lacking suitable plastic waste management systems, many middle-income countries might have controlled one disease, but could have put their poorest populations at risk with another major sanitary problem in the form of arthropod-borne or waterborne diseases. Globally, plastics lack a circular economy that would encourage a more responsible and sustainable management.
As plastic pollution affects the environmental–human-animal health triad, any solution will require a One Health approach.
Overall, the influence of plastic waste on infectious disease maintenance and emergence is underestimated. This lack of knowledge and understanding is due to the absence of dedicated transdisciplinary and transboundary approach studies on this problem. Considering the ever-growing nature of the problem, scientific evidence is needed and requires both dedicated funds and plastic-aware epidemiologists.
Pierre-Olivier Maquart, PhD Yves Froehlich, DVM Sebastien Boyer, PhD
Source: The Lancet
