Written and illustrated by: Nia Johnson

Edited by: Sophie Hill, Henry Ertl, Jessica Li, and Jennifer Baker

Have you ever wondered how we are able to feed nearly 8 billion people globally? Presently, agricultural lands make up the world’s largest biome, covering over 1/3 of the ice-free land area. According to the United Nations Food and Agriculture Organization, these 5 billion hectares of land produce around 550 billion tons of crops annually. This is equivalent in weight to 110,000 Empire State Buildings each year! Agriculture is not only a major source of income for 40% of the world’s population, but it also makes up 30% of GDP in low-income countries. While technological advances and agricultural expansion are projected to keep up with the rising pressures of human population growth (about 10 billion people by 2050), the unintended impacts of modern agriculture have advocacy groups and scientists alike concerned about the long-term consequences.

History of human agriculture

Humans first began cultivating agriculture roughly 10,0000 years ago, allowing for rapid population growth and urbanization. Initially, farming practices were mainly focused on small-scale, subsistence farming, which relied on traditional methods and techniques passed down through generations allowing for centralized populations. However, as the world population began to rise rapidly in the late 19th and early 20th century, there was a crucial need to increase food production to meet the demands of a growing population. In the 1960s, this led to the Green Revolution, the development of modern agricultural practices that focus on increasing crop yields and efficiency. Between 1961 and 2014, grain harvested per person increased from 6,400 to 8,600 pounds. One of the main drivers of this shift was the introduction of man-made technologies, including pesticides. 

Pesticides (from the Latin word “pestis”, which means disease, plague, and destruction) are designed to target and kill unwanted organisms that threaten crop yields such as weeds, insects, rodents, and fungi. These synthetic chemicals allow farmers to grow more food on less land, decreasing the cost for consumers. Currently, over 5.6 billion pounds of pesticides are used world-wide each year, enough to fill more than 2,000 Olympic-sized swimming pools! In comparison to historical practices, however, the intensification and expansion of modern agriculture has novel unintended impacts on both human and environmental health.

Unintended effects of pesticides on human health

Each year, an estimated 385 million agricultural workers are exposed to pesticide poisoning globally. This poisoning is associated with many forms of cancers, including those of the brain, pancreas, testicles, colon, and lymph nodes. Even more commonly, pesticides have been detected in the drinking water systems of 38 states, impacting nearly 50 million Americans annually and disproportionally affecting black and brown communities. Pesticides can be particularly dangerous for children because they cause abnormal brain development. As chemical compounds created to alter normal biochemical functions, many pesticide classes are being classified as cancer risks to humans by the World Health Organization (WHO). In response to such classifications from the WHO, agrochemical companies have focused on reducing direct exposure to humans. However, human health effects are not the only unintended consequences of pesticides. Pesticide use has also been linked to significant changes in natural ecosystems that neighbor agricultural fields. 

Unintended effects of pesticides on ecological health

Non-crop ecosystems that neighbor agricultural fields are important reservoirs of biodiversity. Pesticide use often results in drift, the unintended migration of these chemicals to these neighboring ecosystems. Drift has been shown to significantly alter the diversity and evolution of natural species. Additionally, major shifts in biodiversity can ultimately have negative impacts on crop yields since field edges provide key services like pollination and pest control. For example, field edges provide habitat for bees, butterflies, moths, and other pollinators that transfer pollen, allowing crops to produce fruits and seeds. Other insect species that live at field edges such as beetles and spiders help to control populations of agricultural pests such as aphids, which damage crop yields and transfer diseases that target plants. Pesticide drift is also linked to dwindling bird and amphibian populations, as these species regularly visit field edges to consume unwanted plants and insects, further contributing to pest management. Overall, the effects of drift on the delicate balance of ecosystem dynamics could ultimately harm the same agricultural fields that sourced the pesticide drift.

While pesticides can modify most parts of the ecosystem, almost 50% of the pesticides used in agriculture are herbicides that target “weeds,” or unwanted plants. The U.S. has some of the most well-documented accounts of herbicide drift incidents that occur in states where herbicide-tolerant crops are planted (see figure), though incidents are underreported. Research tells us that communities that neighbor agricultural fields can be exposed to herbicide drift at rates between 1% and 5% of the normal field application rate. Further, glyphosate, the most commonly used herbicide in the world, has been found in 70% of stream samples collected across the U.S. by the Geological Survey National Water Quality Network for Rivers and Streams.

Research has shown that herbicide drift can have major consequences on the makeup of populations in weed-plant communities that neighbor agricultural fields. Often, the plant populations in these border communities develop herbicide resistance at relatively fast evolutionary rates (less than 20 years) due to consistent herbicide exposure. From the plants’ perspective, herbicide resistance may be advantageous in this environment, but research suggests that it may come at a cost of developing fewer viable seeds and shorter roots. There is also evidence that herbicide drift can modify plant species’ makeup because not all species are affected in the same way. For example, when exposed to drift, some species produce fewer flowers, which may lead to fewer overall seeds produced. Other species flower later in the season, which may affect seed maturation. These changes in plant community structure can also have indirect effects on non-plant species they interact with (i.e., herbivores, predators, and microorganisms).

Herbicide drift can also have cross-species impacts. For instance, herbicide use can be linked to declines in pollinator visitation and development (including bees, butterflies, and moths) and arthropod abundances (including spiders, beetles, and centipedes) for plant habitats exposed to drift. Herbicides also affect microorganisms, influencing nutrient availability in the soil, and plant physiology, influencing how susceptible plants may be to being eaten by herbivores (referred to as herbivory). This is because plants have limited resources to invest into defense. In response to a novel threat, like herbicide drift, plants may allocate more resources to defend against herbicide damage, reducing the resources available for defense against herbivory. These physiological changes have been linked to increases in the abundance of agricultural pests such as whiteflies, which are known vectors for several hundred species of crop pathogens that are continuously evolving. 

The delicate balance of energy and nutrients in living systems is influenced by rates of feeding, metabolism, and growth of all living community members. As such, herbicide drift has the potential to drastically shift major components of ecological dynamics. Changes in how energy and nutrients are transferred throughout the food web could have unprecedented long-term effects on the evolution of communities and ecosystems adjacent to agricultural fields.

A path towards more sustainable food production

There is still much to uncover about how pesticides influence ecological interactions and subsequent evolutionary responses. From what we know already, however, it is clear that we must urgently find a balance in agriculture to feed a growing human population while preserving both the natural world and human life. Although pesticides enable increased agricultural yields and profits, they also decrease biodiversity and harm human health – even at levels deemed safe by the agrochemical industry. Comprehensive regulation of pesticides requires detailed review, as independently funded research and industry funded research often report contradictory results. Some believe the path forward is to convert to completely organic (i.e., pesticide-free) agriculture, while others believe there should be a tiered process of pest management with pesticides as the last resort. Regardless of the approach, most experts agree that integrating a focus on ecosystem balance in decision-making is necessary for the health of the entire system, including the ecological and socioeconomic dimensions. Some countries such Sweden, Canada, and Indonesia have already demonstrated that pesticide use can be reduced by 50% to 65% without sacrificing crop yields and quality through this integrated decision-making process.

Agricultural lands and practices are projected to expand and magnify in response to population growth in the coming decades. Thus, there is a critical need to fully examine the nuanced effects of pesticide use. Farmers and policymakers should consider the global economic and social perspectives as well as the ecological and evolutionary perspectives of modern agriculture. Today, we are faced with the challenge of meeting the needs for a growing population while supporting the synergistic harmony of an ever-changing planet. As new technologies are developed, we must prioritize solutions in which food production becomes more sustainable for the longevity of both natural and human systems.

Nia Johnson M.S. is a PhD candidate in Ecology and Evolutionary Biology, where she studies the impacts of modern agriculture on plant-herbivore interactions and adaptations in Regina Baucom’s lab. She is a Howard Hughes Medical Institute Gilliam Graduation Fellow and the Rackham Merit Fellow, originally from Atlanta, Ga. Prior to moving to starting graduate school, Nia was a grade school science teacher as a Teach for America corps member. She earned her BS in 2015 from Howard University with a concentration in plant biology. Nia has a broad interest in understanding reciprocal influences between human activity and the natural world.

One thought on “The Pesticide Paradox: How Modern Agriculture is Both Feeding and Poisoning the World

  1. >>> 550 billion tons of crops
    Divided by 8 billion people that’s… 68.75 tons per person on the planet… or 376 pounds per person per day.

    >>> 10 billion people by 2050

    All the developed countries except Israel are currently below replacement level birth rates (2.1 births per woman). The only reason they’re not in population decline is because of immigration. Except for Japan (1.45 bpw): they’re in population decline even with immigration (and have been since 2000). (In 2020 the US birth rate fell to 1.64 bpw.)

    Oh, and as of 2002 India is now at 2.05… that’s below replacement levels… for the first time in their history.

    Birth rates in the developing countries are following the trends set by the developed countries: as they become more developed their birth rates are declining also… but none have fell below replacement levels yet.

    One of the World Health Organization’s population predictions is that world population will peek before 2100 at less than nine billion.

    We won’t be nine billion: Jørgen Randers at TEDxMaastricht (https://youtu.be/x6qG3l8liSU).


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