The increasingly frequent use of pesticides to combat pests and pathogens is of growing concern across agricultural systems due to the negative impacts on human populations as well as ecosystems.
Although these impacts are expected to worsen with the expansion of agriculture and the advent of global climate change, emerging solutions may improve the sustainability and environmental outlook of pesticide usage.
Pesticides. Image Credit: Fotokostic/Shutterstock.com
The agricultural challenge of pests and pathogens
Throughout agricultural history, pests and pathogens have been recognized as fundamental challenges for crop production. This is conflated in modern systems due to the extensive specialization of crop types which increases the risk of crop damage in the face of increased pest and pathogen prevalence.
It is estimated that every year, the contribution of pests to global crop losses varies from between 50% in wheat to 80% in cotton. More specifically, insects alone consume 5 to 20% of major grain crops annually around the world, posing a considerable threat to food security. Additionally, these impacts are known to be exacerbated in regions lacking the capacity to prevent, manage, or recover from the damage incurred, which often correlates with socioeconomic status.
Looking forward, the damage of pests is forecasted to increase considerably in the future as damage from insects estimated to increase by 10 to 25% per degree Celsius of warming. This was a finding from a 2018 study by Curtis Deutsh and colleagues, who modeled changes in insect consumption of wheat, rice, and maize under global warming.
In response, the increase in targeting efficiency combined with the reduced costs of pesticides has increased its application across modern agricultural systems to protect major crops from harmful pest species.
The development of pesticides through agricultural history
Chemical pesticides were developed at the onset of agricultural history to counter the persistence of pests, pathogens, and competitive species. Interestingly, remnants of elemental sulfur dusting were found to be used in ancient Mesopotamia to protect crops.
In the present day, nearly 3.5 million tonnes of pesticides are used worldwide every year. China is the major contributing country followed by the USA.
Today’s pesticides have considerable effects and products range from insecticides to fungicides, but herbicides alone account for over 80% of pesticides used. Modern pesticides also encompass diverse target capacities and can incapacitate many pest species from birds through to nematodes.
Interestingly, the results of a study published in the journal Rural Sociology in 2019 show a positive relationship between economic development and pesticide consumption over time. That is, countries with growing economies tend to use increasing amounts of pesticides. However, once countries reached their peak of economic development, they did not reduce the levels of pesticide use, hoping to reduce crop losses further.
However, findings from the work of Erich-Christian Oerke from 2005 demonstrated that despite the increase in global use of pesticides, the number of crops lost has not decreased during the last 40 years. This particularly interesting as the study suggests that the increasing pesticide use primarily benefits the diversity of agricultural systems but not overall crop yield.
Nevertheless, the study concludes by discussing the economic and ecologically acceptable levels of pesticide use due to the numerous detrimental outcomes associated with intensive pesticide usage.
The consequences of pesticide usage
It is now well recognized that chemical pesticides generate considerable losses in non‐target species and cause widespread contamination of soil and water systems. Such widespread issues affect not only surrounding areas, populations, and natural habitats but any ecosystem that may be connected in some way.
For humans, the use of pesticides is linked to thousands of annual accidental poisonings from direct contact with the chemical or indirectly from contact with contaminated material. Organochlorine pesticides in particular are the most harmful and can accumulate through trophic levels before ending up in the plates of consumers. Due to such severe health-related impacts, contaminants are better detectable and their effects more recognizable.
Nevertheless, environmental impacts are still ongoing and receive less attention. These impacts were summarised in a review led by Anket Sharma from 2019, in which the use of pesticides from each country was quantified concerning their impacts on global ecosystems.
In particular, the review synthesized the myriad of harmful impacts on key habitats in various continents, from the Great Barrier Reef through to the North American lakes.
A major source of these impacts has been the increased production and trade of pesticides around the world. In particular, China has rapidly become the largest pesticide producer, exporter, and supplier. China itself has seen a rapid increase in pesticide use that has had considerable repercussions on air, water, and soil pollution, which was investigated in a study by Chinese researchers in 2011.
The study revealed the extent of pesticide-related deaths across China, which has become increasingly serious in past years and is projected to cause major health concerns in the future.
The future of pesticide usage in agricultural systems
The most suitable strategy may be to modify or limit the usage of chemical pesticides by using a combination of sustainable alternatives to reduce crop vulnerability. For instance, employing genetically modified crops that are pathogen-resistant may reduce the need for pesticides. Metabolomics have also been used to refine the targeting of pesticides by identifying pesticides with high selectivity, unique modes-of-action, and acceptable eco-toxicological properties.
Another strategy may be to change the application technique of pesticides such as by using a controlled release system, which was discussed further in a review by Indian researchers from earlier this year. Such a strategy provides more precise control and monitoring of pesticide use and may help lessen the ecological burden of pesticides.
Biopesticides and other nature-based strategies for biological control are also promising candidates to limit pesticide use. Considerable research has been conducted over the past decade to explore such strategies through the use of predators, such as ladybirds, to reduce the burden of insecticides in crops.
However, despite a particularly beneficial outlook, this strategy may have unpredictable ecological risks such as spreading invasive species and causing unwanted crop damage. Nonetheless, this would provide considerable environmental benefits by eliminating the need for chemical pesticides.
Looking forward, new methodologies and techniques are needed to assess the detrimental impacts of chemical pesticides on ecosystems and human health. Efforts should also focus on spreading awareness among the general public to minimize their application and instead promote more suitable alternatives to the intensive use of chemical pesticides.
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