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Unexpected Stories from Science’s Past
February 1, 2024 Environment

Rings of Fire

Arsenic cycles through racism and empire in the Americas.

Black and white photo of girl with a cotton plant
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Arsenic is a byproduct of Earth bubbling from the inside out. Before there was life, and therefore before the possibility of toxicity, arsenic spewed from holes and crevasses in Earth’s crust and bonded with sulfur, iron, and other metals.

Arsenic was an abundant and bioavailable nutrient for organisms that craved metal ions during the anaerobic stages of evolution. It offered biogeochemical pathways for organisms to survive in these environments without oxygen. Some of the earliest microbes on Earth evolved with arsenic released from volcanoes, plate tectonics, and deep-sea vents. They breathed the stuff. It’s perhaps no coincidence, then, that arsenic sits in group 15 of the periodic table as a metalloid, dualistic in nature: metal and nonmetal, life giver and taker.

Oxidized arsenic became toxic to most living things with the arrival of oxygen-breathing organisms around two billion years ago. During the Great Oxidation Event, cyanobacteria began to fill Earth’s atmosphere with oxygen. Life had to develop strategies to combat toxic elements, including arsenic (III), which oxidized into more bioavailable forms, such as arsenate (V). Given the “broad-scale sensitization of microbial life” to arsenate, “protective mechanisms” against the metalloid spread throughout the tree of life. Its toxicity now connects life through pathways of resistance.

Color illustrations of rocks and crystals
Examples of arsenic ore, from an English translation of Johann Kurr’s Das Mineralreich in Bildern (The Mineral Kingdom), 1859.

The cells of cyanobacteria, fungi, and plants share many things in common; one of them is an aversion to arsenic. Humans, like other animals, are also biologically wired to reject arsenic. However, our societies began to accept arsenic as an essential element for modern world-building during the Industrial Revolution. How these industrial societies transformed this geological byproduct into a source of economic and political power had a lot to do with who was exposed to the benefits of arsenic and who was exposed to its harm. In the Americas, unnatural arsenic exposure increased under settler colonialism and slavery.

Detail of a German-language tectonic map by Max Fritz, 1926. Red and purple dots mark volcanic eruptions and earthquakes, respectively, and indicate the western portion of the Ring of Fire.

Arsenic contamination follows natural and unnatural pathways in the region. Geographically, arsenic deposits concentrated along the same geological processes that created the Pacific coastal rim of the Americas, from Alaska to Argentina. Millions of years of magmatic activity from the Ring of Fire volcanoes formed the concentration of arsenic deposits in Latin America, western Canada, and the U.S. West.

Untold amounts of arsenic from these deposits have slowly seeped and eroded into river basins, mineral ores, and alluvial aquifers. While most living things on Earth evolved to resist trace amounts of arsenic, life in this part of the world has encountered even higher concentrations. Did the Ring of Fire and its countless arsenic deposits inform life and death in modern Latin America? Mummified bodies from Chile reveal that people have suffered chronic arsenic poisoning for at least 7,000 years.

When hundreds of arsenic scientists and scholars met in Mexico City in 2006 to discuss 100 years of arsenic contamination in Latin America, they acknowledged naturally occurring arsenic as the principal culprit. They noted how colonial mining for silver and gold created new forms of contamination and exposure. However, they agreed that the historical and persistent use of arsenic pesticides was the region’s second primary source of arsenic contamination.

In 500 years, the colonial unearthing of arsenic has continued to put selective pressure on certain organisms in the Americas. The realization that arsenic killed many of the same pests that monoculture attracted to plantations transformed large-scale agriculture and the global arsenic cycle during the export boom in the Americas that lasted from the 1870s to 1930s. Across the hemisphere, planters and politicians looked to chemistry to maintain agricultural production and white supremacy during the gradual abolition of slavery.

Black and white photo of men with hand tools working in a tunnel
Mining silver at the Sirena Mine in Guanajuato, Mexico, undated.

Mining has subsumed the afterlife of many volcanoes. After carrying metals to Earth’s crust, fusing them with arsenic and sulfur along the way, dormant volcanoes make great substratum for mines. Around the turn of the 20th century, the expansion of mining for semiprecious metals in the defunct volcanoes of Mexico and the U.S. West was coupled with significant damage to the vegetation and animal life surrounding the smelters that extract metals from ores.

After mines physically reduced forests into clearings and mountains into terraced valleys, these smelters used vast energy to further separate rock from metal and metal from byproducts, including sulfur and arsenic. As smelter waste, arsenic and sulfur were “driven off in the air”; they traveled for miles in every direction, contaminating waterways, killing animals, and decimating farmland. Farmers on both sides of the border alerted authorities about arsenic in smelter fumes. Ranchers and foresters were concerned, too. But these concerns went unheeded at first. In 1902, just a year after the United States started collecting white arsenic in Mexico, at least 30 residents died and hundreds more were poisoned in Mapimí, Durango, when a mine’s smelter began leaking arsenic into the town’s water supply.

Old photo of a dusty mining scene
A smelter at the Ojuela Mine near Mapimí, Durango, ca. 1900.

Miners loathed arsenic. Smelters penalized them if the arsenic content of ores exceeded the percentage specified in the contract. Farmers and ranchers complaining about the environmental damages caused by arsenic-rich smelter fumes only gave miners another reason to hate arsenic. It diminished the worth of ores and increased the cost of mining.

However, arsenic also held nuisance value from its capacity to cause harm. As Adam Romero argues, insecticides turned industrial byproducts into profits, agriculture a sink for toxic waste. During World War I, arsenic’s use in poisonous gases and explosives raised its price and convinced smelter operators to collect the element and sell it to chemical companies. After the war, many of these companies increasingly manufactured insecticides. The entire industry was fed on violence and racist ideas that black labor and Indigenous land also held “nuisance value”—harmful unless controlled. American business interests pried these first-generation agrochemicals from Mexican and Indigenous lands then cast them at black sharecroppers and tenet farmers back home.

Black and white landscape photo of mining complex with smoking stacks
Copper mill at the Bingham Canon mine in Utah, 1905.

Unlike many insecticides used today, arsenic-based insecticides, such as calcium arsenate, lead arsenate, and sodium arsenite, cannot kill insects through contact alone. They must be eaten, chewed, and digested before any insect keels over. And if they don’t taste good, insects won’t eat them. Arsenic poisoning is a nonstarter if the insect species doesn’t chew; it’s a miserable defense against mosquitos or scales. But contact can be hazardous for plants.

Raw white arsenic, the base for all arsenic insecticides, is more effective as an herbicide than as an insecticide. Because arsenic’s phytotoxicity, or corrosive impact on plant tissues, makes it a tremendous weed killer, farmers in the early 20th century had to watch what they dusted. Soap- and nicotine-based concoctions were more common as insecticides for delicate crops, such as strawberries and tomatoes. For cotton growers, however, arsenic was king.

Black and white photo of a man standing in a field
Dusting cotton with lead arsenate in Victoria, Texas, June 1910.

Cotton (Gossypium), for all its softness, is not the least bit delicate and is ideal for arsenates. For one thing, cotton is a nonedible crop. For another, the cotton boll’s external shell protects its pillowy fibers as they develop. Once harvested, these fibers go through a great deal of processing before reaching consumers. These facts helped chemical promoters convince cotton planters to adopt arsenic poisons.

As a historical product of harsh and inhumane conditions, the cotton plantation was readymade for additional harm. The settler notions that autonomous black labor and Indigenous land were harmful to the economics and politics of the United States helped justify the use of poison to maintain cotton production after slavery. Labor on cotton plantations remained predominantly black and marginalized by the time the boll weevil (Anthonomus grandis) arrived in the early 1920s. Weevil infestations destroyed a third of U.S. cotton in 1921 and wiped out $600 million in value (nearly $11 billion in today’s dollars). This calamity accelerated arsenic use to protect cotton profits and sustained mechanisms of controlling black labor and land-use patterns after slavery.

Close-up black and white photo of an insect on a plant surface
A boll weevil on a boll, from the USDA publication Cotton or Weevils, 1929.

The weevil was a funny-looking scapegoat for the decline of cotton profits. Its long snout is perfect for penetrating cotton bolls and hanging excuses for lousy behavior. Southern cotton planters did not blame the exhaustive nature of cotton plantations or the industry’s expansion into Northern Mexico for encouraging the weevil to cross into the United States; they criticized Mexico and Mexican farming practices.

One writer described the weevil as an immigrant “mother [who] crossed the Rio Grande” and raised a big family that “has spread over a large area of the South.” Naming it the “Mexican cotton boll weevil” was as derogatory as it was etymological. Depending on the year, between 50% and 75% of the arsenic used to combat weevils in the United States came from mines in Mexico. But did Mexico get any credit for providing the modern chemical “solution”? No.

For cotton planters, blaming Mexico for weevils was easy, but there was no consensus on how to address the issue. Howard Ambruster, author of Arsenic, Calcium Arsenate, and the Boll Weevil (1923), believed that “in the last twenty years, there have probably been more official and private controversies in the South about the best way to handle the boll weevil than there were about the slavery question and the Civil War.”

Illustrated map of southern United States
Map showing the spread of boll weevils from 1892 to 1922, from Cotton or Weevils, 1929.

Black people made a more common scapegoat for the failures of the South. Anti-black racism was at the heart of many controversies regarding arsenic use on cotton fields. Politicians and planters often disagreed on how to endorse insecticide use with black labor. Some cotton planters blamed the weevil for reducing opportunities for black farmers to grow cotton economically. They saw the cost of arsenates as more of a barrier for black sharecroppers than the poor prices they received for their cotton. Rather than blame the rise of the Ku Klux Klan or racist restrictions on black land ownership, some white Southerners accused the weevil of forcing black people off the land.

In 1925 a researcher for the army’s Chemical Warfare Service wrote that a black family with 20 acres could afford to poison their fields if they harvested 250 pounds of cotton per acre. But white landowners rarely allowed black families to hold the most productive land. After the peak of black farming between 1910 and 1920, anti-black policymakers and organized criminals such as the Ku Klux Klan steadily worked to eliminate black land ownership altogether.

Black and white panorama photo of cotton farm with workers
An unknown cotton farm photographed by John Coovert, 1907.

As if black people did not have enough to fear, many planters ignored their concerns over using arsenic. To mask and dilute the poison, one Arkansas planter suggested mixing arsenic with molasses because “the weevil and the negro both like it.” He wasn’t alone in his thinking. One of the largest cotton holders from South Carolina, David R. Coker, argued before Congress that using young black children to apply molasses-arsenic spray was the most effective way to combat the weevil. Coker furiously advocated for more arsenic solutions, with little care for black life and health from his seat on the National Boll Weevil Control Association.

While equal in their disregard for black folks’ health, many planters did not believe black farmers could use arsenic properly. They thought and felt entitled to say that the “negro tenant and sharecroppers [did] not know how to dust, cannot dust, and will not dust as directed.” They used innumerable phrases and stereotypes to convince themselves that black people were not intelligent enough to poison fields. Some even suggested that since the “intelligent” black folks fled north, the remaining population wasn’t smart enough to use arsenic.

For Ambruster, the leading expert on calcium arsenate use against boll weevils, the education of Southern black people was as big an obstacle to the insecticide industry as chemical engineering and marketing. He did not trust black farmers to educate themselves. He suggested the government and chemical companies teach black folks how to use arsenic. In 1920 the U.S. Department of Agriculture made a film to show planters how to teach their black field hands. A few years later, the Armour Chemical Company of Chicago and Georgia conducted a year-long experiment to see if black farmers could cultivate cotton with calcium arsenate.

Black and white photo of two men drive mule teams through a field
A USDA agent monitors a cotton-dusting demonstration in Kershaw County, South Carolina, 1924.

The experiment was an exercise in authority and control. The company, in the words of the Atlanta Constitution, “took the attitude toward its sharecroppers and colored tenants that any sensible landlord ought to take.” The chief of research gave 72 black sharecroppers and tenant farmers orders, and they “either had to follow them or get out.”

The demands were numerous. The company forced the farmers to use specific varieties of cotton and at least 500 pounds of fertilizer per acre. Planting had to start at designated times and in defined ways. The company gave each farmer an arsenate duster, taught them how and when to use it, and provided enough poison for the year.

The chief researcher acknowledged that farmers enjoyed their harvests more than the constant oversight, but controlling production was just as crucial as controlling black farmers. It was not by accident that the only three farmers who did not improve their harvests failed on account of being imprisoned. The company tried to debunk racist notions that black people couldn’t use agrochemicals with the equally racist idea that black farmers needed constant surveillance. Armour’s demonstration was a violent act of social control that put black lives and land at risk.


While volcanic eruptions infrequently release tons of arsenic into the atmosphere, capitalist interests within the United States disrupted the arsenic cycle like a volcano erupting on repeat. Instead of rising magma causing these eruptions, the imperial and racial relations of agrochemical expansion set these new arsenic cycles into motion.

From 1870 to 1914, arsenic was one of the essential substances that connected the Age of Empire and the Second Industrial Revolution. It is unlikely life on Earth has been subjected to this degree of chronic and widespread arsenic exposure since the Great Oxidation Event. But not all life on Earth; the selective pressure of arsenic exposure disproportionately impacted Latin America, where arsenic exposure reached new heights while following newly established pathways during the region’s so-called “export boom” from 1870 to 1930. This era witnessed the expansion of foreign-owned plantation economies to produce sugar, coffee, rubber, and other goods for export to the United States and Europe.

Black and white photo of a man on a spraying tractor in a field
Spraying beans in Pittsford, New York, 1932.

Agrochemical arsenic has traveled with settler colonialism and the U.S. empire since the 1870s. During Western expansion in the United States, settlers turned to Paris green (copper [II] acetoarsenite) to combat the Colorado potato beetle (Leptinotarsa decemlineata) in the 1860s and Rocky Mountain locust (Melanoplus spretus) in the 1870s. Settlers from Kansas to Nebraska used so much Paris green to combat the great locust swarms of 1874–1875 that they eventually drove the entire species into extinction.

Arsenic served as an extension of U.S. empire into many regions. In addition to maintaining the political economy of unjust cotton production in the South, arsenic helped U.S. leaders spread the politics of agrochemical use throughout the Americas. Concurrent with U.S. cotton planters’ actions in the post-emancipation South, planters across the Americas started introducing arsenic into their export-oriented plantations and orchards.

The association between arsenic and empire exploded in the early 1920s. The British maintained a global arsenic network that tied colonies and cotton together. They sequestered raw arsenic in Canada, South Africa, Australia, and Rhodesia, refined it in the United Kingdom, and exported it to Hong Kong, New Zealand, and India.

Dusting crops in Bridgeton, New Jersey, 1942.

The United States relied on geological deposits in the northeastern edge of the Ring of Fire but quickly outpaced the British arsenic empire. U.S. companies, including the American Smelting and Refining Company (ASARCO) and the American Metals Company, owned some of the most profitable mines in Mexico. They began selling raw white arsenic duty-free to a dozen or so chemical companies that manufactured insecticides, exporting it by boat from the Port of Tampico or by rail through Laredo or El Paso.

The United States imported only 272 tons of arsenic in 1922, though the quantity jumped to 1,402 tons in 1923 and 2,551 tons in 1924. For the next two decades, U.S. companies imported between 8,500 and 13,000 tons of arsenic annually, amounting to more than three-fourths of all arsenic processed in the United States. Together, the cotton-arsenate nexus quickly made the United States and Mexico the two largest arsenic producers in the world.

Black and white photo of men in protective equipment in front of a brink wall
Workers outside the American Smelting Company’s arsenic plant in San Luis Potosí, Mexico, 1940.

Arsenical insecticides helped U.S. business interests extend farther into Latin America. With a new surplus of arsenic in North America, ASARCO and other U.S. companies established agrochemical trade networks across Central and South America to sell lead arsenate and calcium arsenate for cotton and fruit cultivation. Before the rise of DDT during the Green Revolution, planters in Brazil, Colombia, Argentina, El Salvador, and Nicaragua purchased tons of U.S. arsenates between 1937 and 1944. In the aftermath of World War II, U.S. foreign policy built on these arsenical channels to further export chemical- and capital-intensive modes of industrial agriculture.

Like agrochemical racism in the United States, agrochemical inequality in U.S. foreign policy was born in the 19th century. U.S. and Mexican government officials collaborated on pest management as a form of border management in the 1890s. The first walls erected on the U.S.-Mexico border in 1911 aimed to quarantine cattle ticks. But in the context of the Mexican Revolution (1910–1920), these fences were intended to keep out more than cattle and ticks.

U.S. border officials adopted policies for spraying harmful disinfectants on Mexican crops and migrant workers entering the United States. Chemicals enabled the United States to extend white supremacist practices into Mexico and on the border. U.S. officials determined why and how Mexican laborers would be disinfected and expected Mexicans to defer. If Mexican vegetable packers did not spray crops just as U.S. officials taught them, then border officials could reject the produce. Even if Mexicans followed orders, U.S. officials could refuse to pay a fair price.

Black and white pesticide ad with a photo of a dead boll weevil
Advertisement for toxaphene, a pesticide marketed by the Hercules Powder Company to control boll weevils, 1952.

The U.S.-Mexican arsenic cycle also influenced why the Green Revolution started in Sonora, Mexico. While a surplus of agricultural products led to plummeting prices in most of the United States in the 1920s, the U.S.-Mexican borderlands witnessed sustained population growth in California, Arizona, Sonora, and Sinaloa. California’s agricultural expansion was the driving force behind this development. Still, it relied heavily on experiments with arsenic-based insecticides performed elsewhere.

California landholders and the U.S. Department of Agriculture conducted a series of tests in Sinaloa in the late 1920s and early 1930s to determine how best to use arsenic on tomatoes and which cotton varieties grew best in the area. Following models from the U.S. South, Californians toyed with aerial dusting in Sinaloa as early as 1926. However, Californians often experimented with more significant quantities of arsenic in Sinaloa than they would at home, helping establish a pattern of agricultural practices in Mexico that would be unacceptable in the United States. And despite blaming Mexico for the cotton boll weevil, Californian interests occasionally introduced agricultural pests from California into Mexico and took no responsibility.

The arsenic-cotton nexus helped normalize agrochemical use. By 1969, 27 of Mexico’s 45 insecticide-producing enterprises were in cotton-producing regions. The same areas of Sinaloa dedicated to arsenic experiments in the 1920s and 1930s experienced acute poisonings from subsequent generations of insecticides in the 1970s and 1980s. The pioneering study Circle of Poison (1981) highlighted Sinaloa as a site of widespread U.S.-driven agrochemical violence and proved the state held one of the world’s highest pesticide poisoning rates. Doctors serving plantations growing tomatoes for U.S. consumption witnessed two to three poisonings a week from exposure to pesticides. Another report in Mexico suggested that nearly one Indigenous migrant farmer died every day from pesticide exposure.

Illustrated produce label for tomatoes
Crate label for Esperanza brand tomatoes grown in Sinaloa, Mexico, ca. 1900s.

Although the agrochemical culprit was no longer arsenic, the historical pattern of imperial and racialized arsenic cycles persisted as a defining factor in the social nature of agrochemical inequalities. Arsenic helped U.S. officials assert control over Mexican counterparts and informed power imbalances between the United States and Mexico that persist today. As of 2019, U.S. companies continue to manufacture and export to Sinaloa more than 100 agrochemicals that are illegal to use in the United States.

Despite its lower market share since the 1940s, arsenic did not simply go away. Arsenic maintained the first and longest monopoly over the insecticide industry, and it never fully relinquished its influence.

This is partially because arsenic contamination persists in soil and water for generations, but it is also due to its persistent use as a preservative and herbicide. Railroads and telephone companies still favor arsenic (chromated copper-arsenate) as a wood preservative on railroad ties and utility poles. During the Vietnam War, the U.S. military sprayed an organic arsenic herbicide called Agent Blue (cacodylic acid) on nearly 400,000 hectares of mangrove forests and rice paddies. The commercial form of Agent Blue was so profitable and useful on cotton fields, golf courses, and backyards that the EPA deregulated it in 2004. Five years later the agency reversed course and announced it would phase out organic arsenic pesticides by 2013, with the exception of MSMA (monosodium methanearsonate), an herbicide used on cotton plantations.

Color photo of worker in surgical mask spraying flowers in greenhouse
A worker sprays pesticides in a gerbera greeenhouse in Villa Guerrero, Mexico, March 2020. Villa Guerrero is part of the country’s so called flower belt, where residents have experienced health problems, including birth defects and infertility, associated with agrochemical exposure.

Biogeochemist Stephen Porder argues in Elemental (2023) that humans’ relationships with the elemental cycles most important to life—hydrogen, oxygen, carbon, nitrogen, and phosphorus—have shaped Earth’s past and future. We haven’t yet figured out how to enjoy the benefits of our innovations without paying the costs of their harmful byproducts. Arsenic shares a kinship with two of those life-affirming elements on the periodic table, nitrogen and phosphorus. Could something similar be said for the cycles of elements that became most toxic to life, such as arsenic?

The disruption of the global arsenic cycle since the 19th century has left a legacy of environmental violence across the Americas. American exceptionalism rarely exists, but the Americas—and the United States in particular—have played an exceptional part in the spread and standardization of agrochemical use.

Naturally occurring arsenic in the Ring of Fire set the geological stage for its unnatural extraction and extension, but arsenic contamination zones are no longer geological facts alone; many are the historical and living remnants of U.S. empire and racism.

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