As the global population surpassed the 8 billion mark in November 2022, the looming challenge of feeding an expected 10 billion people by 2050 becomes increasingly daunting. Technological innovations, such as using plastics in agriculture, over the past two decades have expanded the capacity to produce food for the growing populace while balancing environmental impacts and the need for sustainable transitions.
However, agriculture remains a major environmental stressor, often conflicting with the United Nations Sustainable Development Goals (SDGs). It's a sector that contributes 29% of greenhouse gas emissions, consumes 30% of the world's energy, utilizes 33% of the available land, extracts 70% of groundwater, and is responsible for 75% of deforestation. Moreover, the interconnected web of these environmental pressures exacerbates global warming, which adversely affects crop yields. To meet the food demand, there must be a balance between agricultural intensification with ecosystem preservation and fostering technological innovation.
In recent decades, plastics have emerged as a critical component of modern plant agriculture, playing a pivotal role in achieving sustainability goals. However, by delving deeper into this symbiotic relationship between agriculture and plastics, it is also imperative to consider the potential long-term consequences of their use, according to a recent research report in Communications, Earth & Environment.
Plastic, a broad term encompassing materials derived from organic polymers enhanced with various additives, serves as the linchpin of this discussion.
These additives imbue plastics with specific properties, ranging from flame resistance and antistatic qualities to coloration and UV protection. Conventional polymers like polyethylene (PE), polypropylene (PP), and polyvinyl chloride (PVC) are renowned for their environmental persistence, thanks to the chemical stability of their polymer structures. Agricultural plastics predominantly comprise these conventional polymers and have the propensity to fragment into micro- and nanoplastics (MNP) that accumulate in soils, permeate ecosystems, and impact biota.
In contrast, biodegradable polymers are designed to undergo microbial metabolic processes, wherein the polymer carbon is converted to carbon dioxide and microbial biomass in oxygen-rich conditions. The biodegradability of a polymer depends on its physicochemical properties and the environmental conditions in which it degrades. Biodegradable polymers, whether from non-renewable petrochemical or renewable bio-based sources, may transiently produce MNP fragments during degradation.
Plastics have found multifaceted applications in agriculture, with their utilization surging over the past 70 years to an estimated 12.5 million tons annually. This widespread integration of plastics into agriculture has led to the accumulation of substantial quantities of macro-, micro-, and nano-plastics in soils and surrounding environments. The omnipresence of plastics in agriculture poses a growing threat to soil functions and the broader natural ecosystem, emphasizing the urgency of adopting more sustainable practices.
In a remarkable turn of events in March 2022, 175 countries united to initiate negotiations for a global and legally binding plastics treaty (UNEA-5.2) with a mission to eradicate plastic pollution by 2024. This international policy instrument aspires to tackle the ecological and human health hazards associated with the entire plastic lifecycle, including its implications in agriculture. The treaty is expected to mandate regular reporting by governments and non-government stakeholders on their efforts to reduce plastic pollution.
Plastics have introduced a plethora of environmental and societal benefits in plant agriculture. Plastic mulch films, constituting roughly 50% of all agricultural plastics, are instrumental in crop production. They offer a myriad of advantages, including weed and pest control, moisture conservation, temperature regulation, and enhanced nutrient uptake, all of which translate into increased yields, improved resource efficiency, and reduced pesticide usage. In regions like China, plastic mulch films have proved indispensable, saving millions of hectares of arable land.
Conventional plastic mulch films, primarily composed of low-density PE but sometimes PVC or ethylene-vinyl acetate copolymers, play a significant role in agriculture. However, their incomplete collection post-use and the leaching of chemical additives can lead to the accumulation of plastic residues and adverse effects on soil productivity.
The widespread use of plastics in agriculture has repercussions on soil functions, affecting their physical, chemical, and biological properties. Conventional plastic residues can impede water infiltration, reduce water holding capacity, disrupt microbial communities, and decrease soil fertility. This, in turn, can adversely impact plant growth and yields, particularly when plastic concentrations are high.
Plastics in agriculture coexist with various global stressors, including climate change, chemical pesticides, and invasive species, creating a complex web of interactions and unpredictable outcomes for soil ecosystems. Soil erosion represents a potential route for plastics to enter water bodies, emphasizing the need for erosion control measures.
Plastics' entry into the food chain, primarily through plant uptake and root crop consumption, poses questions about food safety and its impact on human health. Effects on crop growth, soil microfauna, and macrofauna have been observed in laboratory settings, albeit often at higher concentrations and in hydroponic systems.
Aging and fragmentation of plastics enhance the release of additives, creating a chemical burden on soils. The release of these chemicals varies widely, from centuries for hydrophobic phthalates to days for more polar phthalates. These additives, including endocrine-disrupting substances, may accumulate in edible plants and enter the human food chain, raising concerns about food safety.
The intricate relationship between plastics and agriculture presents a conundrum. While plastics have ushered in remarkable benefits, their environmental impact and long-term sustainability pose challenges that demand our attention.
Addressing these challenges requires a holistic approach, including technological advancements, regulatory measures, and societal changes. As we navigate this path, it is essential to strike a balance between reaping the advantages of plastics in agriculture and safeguarding the health of our planet and its inhabitants.
