Environmental Toxicity | Pesticide Info

Well over 50 years ago, a scientist named Rachel Carson predicted that the “smooth superhighway” of chemical-intensive agriculture this country was speeding along could only lead to disaster. As she asked in Silent Spring,

“Why would anyone believe it is possible to lay down such a barrage of poisons on the surface of the earth without making it unfit for all life?”

Pesticides wreak havoc on the environment, threatening biodiversity and weakening the natural systems upon which human survival depends. PAN works with partners around the world to promote agricultural systems that protect and strengthen, rather than contaminate, natural ecosystems.

Insect populations under threat

A scientific study released in 2019 found that the chemical-intensive farming system in the United States has made U.S. farmland 48 times more toxic to insects than it was 20 years ago and growing evidence shows insect populations around the world are teetering on the edge of collapse. Current research underscores the urgent need to shift our food system away from its reliance on pesticides.

Neonicotinoid pesticides, introduced by Bayer Crop Science in 1985, provide the biggeste threat to pollinators and other insects. By the late 1990s use of “neonics” was growing fast, and today Bayer’s imadocloprid, the first neonic introduced, is among the most widely used pesticides in the world.

Neonics are systemic insecticides. The chemicals are drawn up by the roots and distributed to all parts of a living plant, including its flower and pollen. For years, scientists have known that these chemicals can harm bees and other insects, weakening their immune systems, disrupting reproduction and interfering with nervous system functions. Even worse, neonics can last from months to years in the environment. Insects are experiencing an ever growing “acute toxic load” and the dramatic increases in exposure over time are illustrated in the graphic below.

A few other key findings from the 2019 study:

Neonics are responsible for 92 percent of the increased lethal toxicity to insects
Neonic use on corn and soy contributes to the toxic load more than any other crop
Neonics contributing most to toxicity are imidacloprid and clothianidin (manufactured by Bayer-Monsanto) and thiamethoxam (a product of Syngenta-ChemChina).

It is also clear that use of these pesticides does not help farmers; EPA researchers have found that soy seeds coated with neonics resulted in zero increases in yield. Seed treatments make up nearly 90 percent of all neonic use in the US.

For more information on how pesticides are harming honeybees and other vital pollinators, see our Pesticides & Pollinators resource page.

Endangered species at risk

Some pesticides seep through the soil into groundwater; others are washed by rain into creeks, rivers, and lakes where they can poison fish and other aquatic organisms. Depending on the type of chemical, contamination can last for days, weeks, months – even decades.

Pesticide runoff remains largely unregulated, and government agencies have shown little initiative in protecting complex aquatic ecosystems. Fortunately, when tainted runoff threatens a species already listed as endangered, the government can be forced to act. In the pacific northwest, creeks that are home to endangered salmon now require substantial buffer zones from toxic pesticides.

In 2018, a national report from the National Marine Fisheries Service (NMFS) found that organophosphate pesticides (OPs) malathion, diazinon and chlorpyrifos threaten the health of aquatic wildlife, notably orca and salmon. The NMFS study found that dozens of threatened or endangered species — and their critical habitats — were in jeopardy.

Both chlorpyrifos and malathion were found to be especially damaging. The study found these pesticides were “likely to jeopardize the continued existence of 38 of the 77 listed species” and negatively impacted “37 of the 50 designated critical habitats” where those species live. The Center for Biological Diversity has taken legal action to force EPA to protect threatened and endangered species from the most dangerous pesticides.

Frogs, birds and bats too

In the 1990s, the Syngenta corporation funded Dr. Tyrone Hayes of UC Berkeley to study the environmental impacts of atrazine. When Dr. Hayes discovered ovaries growing in the testes of male frogs raised in atrazine-contaminated water, Syngenta refused to let him publish his findings. Hayes repeated the experiment with independent funding, and today continues research on atrazine’s dramatic impacts on amphibians.

More than 75 million pounds of Syngenta’s atrazine are used on U.S. farms every year, making it the second most-used pesticide in agriculture. The herbicide now contaminates water supplies throughout the Midwest at levels above those found to turn male tadpoles into female frogs in laboratory experiments.

Atrazine’s effect on amphibians is shocking: 10% of male frogs raised in atrazine-contaminated water developed into females. Genetically, the frogs are still males, but morphologically they are completely female — they can even mate successfully with other males and lay viable eggs.

Switzerland, where Syngenta is based, banned atrazine in 2007 and committed to stop exports by 2021 due to concerns about human health and environmental effects. In stark contrast, EPA officials moved forward with reregistration of atrazine for use in the U.S. in fall 2020.

Bird populations are at risk from pesticides as well. Scientists now say insecticides are a primary culprit for declines in prairie bird populations in many Midwestern states in the U.S. Minnesota birds are hardest hit with 12 species in decline, followed by Wisconsin with 11, and Illinois, Michigan, Montana, Nebraska and New York with nine affected species each.

The neonicotinoid pesticides known to harm pollinators have also been identified as a key driver of these declines.

Scientists now believe that, like amphibians, bats have become more susceptible to deadly disease (in this case, White Nose Syndrome) because their immune systems are weakened by pesticides. A growing body of evidence points towards pesticide exposure – even at “safe levels” – as a key contributor to these and other problems for wildlife.

Ecotoxicity data limitations

The majority of ecotoxicity studies focus on acute (immediate) toxicity. A pesticide with low acute toxicity may still pose significant chronic hazards (cancer, reproductive and developmental toxicity, endocrine disruption, genetic effects, etc.) or cause behavioral changes that affect species survival. However, the availability of studies on the chronic (long-term) toxicity of pesticides to plants and animals is limited.

There are a number of reasons ecotoxicity hazard ratings can be incomplete or not representative of the true hazard posed by a particular pesticide:

Laboratory conditions under which studies were conducted may not mimic actual environmental conditions.
In laboratory studies, only a single chemical is present in the test solution. In the environment, multiple pesticides are often present simultaneously, which can lead to additive or synergistic effects.
Many species have not been tested, or the species that have been tested are not necessarily representative of those that inhabit a particular geographic area.
Fewer studies have been conducted on newly registered chemicals, resulting in the appearance that they are less hazardous than those that have been on the market for a longer time and have been more thoroughly studied.

Chronic toxicity data for bees is available for some chemicals, and it is well known that population-level effects on bees may occur even if a pesticide has low acute toxicity. For example, certain pesticides interfere with bee reproduction, ability to navigate, or temperature regulation, any of which can have an effect on long-term survival of bee colonies.

Neonicotinoids, pyrethroids and keto-enol pesticides are some types of pesticides causing one or more of these effects. In Pesticide Info pesticides are designated as “Bee Toxins” if they appear as such on the PAN International list of Highly Hazardous Pesticides, a designation based on peer-reviewed literature as well as EPA and/or European Union reports on pesticide toxicity to bees.

For more information and step-by-step instructions for searching EPA’s ECOTOX database, see our Ecotoxicity Resources page.