The Harmful Effects of Pesticides on Humans and Animals

A coughing man holding a spray bottle andexperiencing a harmful effect of pesticides on humans.

What are the harmful effects of pesticides on humans? What can pesticides do to insects and animals?

In Silent Spring, Rachel Carson warns that pesticides will do more damage to your health than good. Common effects of pesticide spraying on insects, animals, and humans can include nerve damage and convulsions, vomiting, diarrhea, fever, difficulty breathing, and mass death.

Find out more about how pesticides are negatively affecting you and other species.

Specific Effects of Pesticides

Though pesticides have yet to devastate human populations the way they have insects, birds, fish, small mammals, and livestock, Carson gives multiple examples of government-sponsored spraying campaigns that resulted in hospitalizations. The 1959 spraying of aldrin over parts of Michigan and the 1954 and 1960 spraying of dieldrin in Illinois both sickened people and killed large numbers of birds, cats, rabbits, and squirrels, despite federal and local Agriculture Departments’ insistence that the chemicals were safe.

(Shortform note: The EPA completely banned the use of aldrin and dieldrin in 1987—prior to that, the chemicals were still being used to control termites. Despite greater attention being paid to pesticides in recent decades, mass poisoning incidents like the ones Carson describes still occur, and at least tens of thousands of people die following exposure every year. These chemicals also continue to wipe out entire animal communities.)

Beyond the documented reactions to pesticides, Carson argues that there’s evidence pesticides can sterilize humans, cause genetic damage, and increase the risk of cancer. She also warns that pesticides may have additional harmful effects that won’t become apparent for years to come. We’ll discuss these harmful effects of pesticides on humans and animals in detail.

Sterilization and Genetic Damage

An effect of spraying that’s not immediately obvious is pesticides’ ability to sterilize or greatly reduce a species’ capacity to reproduce. Birds and fish sprayed with pesticides either fail to lay eggs, or those eggs never develop. Livestock like pigs, cows, or sheep carry fewer babies to term, and those that are born are often sickly and die young. Carson notes that testing of the bodies and the undeveloped eggs has shown that they contain large quantities of chemicals like aldrin and dieldrin. Ultimately, even animals that survive spraying will struggle to build their populations up to former levels and may die out entirely in a few generations. It’s not clear whether pesticides can also impair humans’ ability to reproduce.

(Shortform note: Pesticides’ negative impact on the fertility of birds and insects is now well documented, and the evidence increasingly suggests that certain chemicals can similarly affect humans—particularly men—by disrupting the functioning of the endocrine system. Studies have also linked pesticides to miscarriages and birth defects. Evidence suggests that other environmental pollutants may also interfere with fertility, which could partially account for declining birth rates worldwide in the 21st century.)

Carson believes that these reproductive issues are linked to pesticides’ ability to damage species’ DNA by interrupting cellular division (the process by which cells reproduce) and cellular oxidation (the process by which cells produce energy). Some cells die off, while others produce dangerous mutations in new cells. For example, plants sprayed with lindane produced offspring containing extra chromosomes in their DNA, resulting in plant roots so swollen that further growth was impossible.

(Shortform note: Cellular damage has been observed in a wide number of plant species treated with pesticides over the past half-century, though this generally leads to wilting or the plant dying rather than the overgrowth Carson describes. Recent studies suggest that pesticides can have the same effects on humans, particularly agricultural workers who have direct regular contact with chemicals like 2,4-D, glyphosate, paraquat, and acephate. Though the long-term effects of this damage are not certain, scientists speculate that people exposed may develop chronic diseases of the lung, pancreas, liver, or brain, as well as various cancers.)

Cancer

Carson argues that pesticides’ ability to damage cells and DNA also makes them carcinogenic, or cancer-causing. Cancer cells reproduce out of control to the point that they impair the body’s normal functioning. This can be caused by genetic mutations, interruptions to cellular oxidation, or liver damage (since the liver regulates the body’s hormone levels), all of which are potential effects of pesticide poisoning. Lab testing has shown several chemicals commonly used in pesticides, such as arsenic, benzene, and urethane, to be definitely carcinogenic, as is DDT. Carson points out that cases of liver disease and cancer have been on the rise in the US since the early 1950s, around the same time that pesticide use exploded.

(Shortform note: In the decades since Carson’s own death from breast cancer, several pesticides have been found to “likely” be carcinogenic, though human data is limited. These include lindane, chlordane, dieldrin, and possibly 2,4-D. Though the death rate from cancer has declined in the 21st century, cancer diagnoses are on the rise, particularly among people under the age of 50. The reason for the rise is unclear, though experts suggest that it could be a combination of exposure to pollutants and lifestyle factors like alcohol abuse or poor diet.)

Unknown Effects

Because the widespread use of pesticides was still new at the time of Carson’s writing—about two decades old—Carson repeatedly emphasizes that the worst effects of pesticides may still be unknown, as some health issues can take multiple generations to surface. While the increasing rates of liver disease and cancer may be early warning signs, pesticides may also do long-term nerve damage, impair the body’s ability to store fat, or even cause mental illness. Pesticide poisoning seems to affect some people more than others, and repeated exposures lead to worse reactions—meaning that children may be especially vulnerable, and people who appear healthy now could become seriously ill in the coming decades.

(Shortform note: Though there’s little evidence that pesticides prevent fat storage long-term—in fact, some scientists suspect that pesticides may actually contribute to growing global obesity rates—modern studies have linked pesticides to mood disorders and neurological disorders like Alzheimer’s and Parkinson’s. Beyond pesticides, in recent years many researchers have expressed anxieties similar to Carson’s about microplastics. These tiny plastic particles are present in the body of nearly every person on Earth, and may have negative health effects that will only become apparent years or even decades into the future.)

The Harmful Effects of Pesticides on Humans and Animals