Pyrethrins are a class of naturally occurring compounds derived from chrysanthemum flowers. They have been used for thousands of years as insecticides and insect repellents. There are also human-made chemicals similar in chemical structure to pyrethrins – called pyrethroids – that are used as more potent insecticides. Today, pyrethrins and pyrethroids are commonly used as household insecticides on gardens, crops, pets, livestock, and humans. They can be found in bug bombs, home bug sprays, pet shampoos, and lice shampoos.

When pyrethrins enter the environment, they are quickly degraded, which makes them among the safer insecticides. However, pyrethroids are more persistent in the air, water, and soil. Even if pyrethrins and pyrethroids are not widely contaminating an environment, people can absorb, inhale, and ingest these chemicals through normal use of certain household products. When people use pyrethrin- or pyrethroid-containing products like lice shampoo or mosquito repellent directly on their bodies, pyrethrins or pyrethroids can be absorbed through the skin. This can also happen if people bathe their pets with these shampoos without using gloves. When pyrethrin- or pyrethroid-containing bug bombs or sprays are used in the home, people can become exposed by breathing the air. When pyrethrin- or pyrethroid-containing insecticides are sprayed on crops, people can become exposed when they eat those crops. People whose jobs require applying insecticides to crops, fumigating homes, or bathing animals are more likely to be exposed to pyrethrins or pyrethroids at high levels.

Pyrethrins and pyrethroids interfere with the normal functioning of the brain. Absorption, ingestion, or inhalation over just a short period of time can cause headache, nausea, dizziness, mood changes, convulsions, and even unconsciousness. These symptoms can last for days after exposure has ended. In studies of laboratory animals, exposure caused fertility problems as well. While pyrethrins and pyrethroids may be safer than other insecticides, they can cause serious harm to human health.

Hydraulic fracturing (commonly known as fracking) is a technique that uses pressurized liquid to fracture bedrock in order to the extract the oil or gas inside.  Materials in the fracking fluid keep these cracks open so the oil or gas beneath can flow freely and be collected. After injection into the rock, some fracking fluid remains underground and some flows back to the surface.

Fracking fluid usually consists of water, sand or beads, and a mixture of chemicals. While many of the chemicals are not publicly known, some of the ones that are known can have harmful effects on human health. With up to millions of gallons of liquid being used to fracture a single well, these chemicals can be dangerous even if they constitute a small percentage of the fracking fluid. People can be exposed to these chemicals through contamination of drinking water supplies, physical contact with the flowback waste, or inhaling chemicals after they evaporate into the air from open-air waste pits.

Research has shown that living close to fracking wells is associated with adverse health outcomes, including poor birth outcomes like preterm birth (PTB) and low birth weight (LBW). However, not all this research is in agreement about these effects on birth outcomes because there are other confounding factors that can make drawing conclusions difficult. For example, most fracking wells are in rural areas, and rural communities have higher rates of many health conditions including PTB and LBW when compared to urban communities. Another confounding factor is that fracking wells have different mixtures of chemicals, so the health effects of living near a well may depend on the specific chemicals used in that well.

A recent study set out to clarify the link between living near active fracking wells and rates of PTB and LBW on a national scale. This study used publicly available, national, county-level 2014-2018 data from the US Census, Centers for Disease Control, US Department of Agriculture, WellExplorer, March of Dimes, and the National Birth Defects Prevention Network to analyze the association between exposure to fracking wells and the rate of PTB and LBW. It controlled for many socioeconomic and geographic factors that may impact PTB and LBW, thereby more directly analyzing the specific link between fracking wells and birth outcomes than previous studies. The factors this study controlled for included: race, ethnicity, poverty level, education level, percentage of population with health insurance, access to maternal care, marriage rates, drug-related death rates, population density, percentage of a county that is agricultural land, and amount of agricultural pesticides used in a county.

The study found that density of active fracking wells was associated with a higher average county-level PTB and LBW. For wells known to use chemicals that target the hormones estrogen or testosterone, well density had an even bigger effect on county-level PTB and LBW. This is one of the first studies to assess these associations on a national scale and to demonstrate that the chemical ingredients in fracking wells can have a major impact on PTB and LBW. Importantly, these findings are not a result of socioeconomic or geographic factors like race, poverty, health insurance, or population density. This study is one of the strongest yet in demonstrating that fracking wells are linked to the poor birth outcomes of preterm birth and low birth weight. 

Carbon disulfide is a colorless liquid chemical that readily evaporates at room temperature. It occurs naturally during composting and volcanic eruptions, but most carbon disulfide is manufactured by humans for industrial purposes. Most manufactured carbon disulfide is used in the production of rayon, a semi-synthetic fiber used to make clothing. Other uses of carbon disulfide include manufacturing of cellophane, certain pesticides, and vulcanized rubber.

While carbon disulfide enters the environment from naturally occurring sources, most of it comes from emissions from industrial facilities that make or use it. Most carbon disulfide that enters soil or surface water quickly evaporates into the air. This means that the primary way people become exposed to carbon disulfide is through breathing contaminated air. People who work at rayon manufacturing facilities are the most likely to become exposed, but people who live near these facilities have been known to be exposed as well. When pesticides manufactured with carbon disulfide break down in the environment, the carbon disulfide can be released. People who work with these pesticides or live near where they’re applied can become exposed at high levels too.

Long-term inhalation of carbon disulfide causes serious nervous system dysfunction, including tremors, abnormal movement, decreased sensitivity to pain, and vision impairment. It can also cause elevated cholesterol and cardiovascular disease. Short-tern inhalation of high levels of carbon disulfide can also cause serious neurological dysfunction including psychosis, paranoia, mood changes, and hearing problems. Adverse health effects associated with carbon disulfide inhalation have been known since the early 1900s.

The evidence is clear that carbon disulfide exposure is dangerous to human health, and its use can be replaced in many industries. For example, there are ways to produce rayon that don’t use carbon disulfide, but they are not widely used because they are more expensive. Regulations that stop carbon disulfide use in these industrial processes would protect human health without having to end production of these useful consumer goods.

Uranium is a naturally occurring element found ubiquitously in rock, soil, and water. It is often mined and processed because a certain type of uranium is useful in making fuel for nuclear power plants. This process creates what is called enriched uranium.

While uranium is present in low levels in all rock, soil, and water, there are ways people can become exposed to it at high levels. One of these ways is through living near facilities that mine, process, or manufacture enriched uranium. Another way is through oil and gas production. When bedrock is fractured to extract the oil and gas inside, chemicals like uranium that are embedded in the bedrock can be released into the resulting fluid. This fluid – which is often called flowback, wastewater, produced water, or brine – can then enter the surrounding soil, surface water, or groundwater. In some places, this brine is used as a de-icer and is deliberately put on roads and sidewalks in icy winter conditions. This means people can be exposed to uranium in both unintentional and intentional ways.

If uranium enters groundwater, people in surrounding areas can be exposed to it in their drinking water. When uranium is present in high concentrations in the soil, vegetables – especially root vegetables like potatoes and turnips – absorb this uranium, and people can be exposed by eating these vegetables.

Uranium is dangerous to human health because it is radioactive, which means it is unstable. Radioactive elements will emit energy or radiation and convert into another element. This radiation can cause cell death, organ failure, and cancer. Because of this radiation, uranium exposure causes broken bones and kidney damage. The Environmental Protection Agency has determined that uranium probably causes cancer in humans. In studies of laboratory animals, it also caused lung damage, fertility problems, and birth defects. Effects of uranium exposure on children may be more severe because their bodies are growing.

In addition to these direct effects of uranium exposure, when uranium emits radiation it is converted into an element called radium, which is also harmful to human health. Radium exposure can cause bone, blood, liver, and breast cancer. When radium emits radiation it is converted into an element called radon, which is also dangerous. These direct and indirect effects make uranium very dangerous, and processes that can release it from the environment must be more tightly monitored and controlled to protect human health.

For more information, CHEJ has previously written about fracking, radiation risks from fracking, the presence of radium in brine, and radon.

Diethylene glycol (DEG) is a clear liquid with a sweet taste. It is an effective solvent for resins and adhesives, making them function better. For this reason, DEG is used in many industrial and consumer product settings. It is used in the manufacturing of polymers like polyester and polyurethane to help make them more flexible. It can also be used in dyes and oils for textiles, inks, and adhesives. It can be a component of brake fluid, antifreeze, and wall strippers. DEG can also be found in personal care products like makeup, creams, lotions, and deodorants.

With so many uses, DEG is a chemical many people can be exposed to. People who work in facilities that manufacture materials with DEG are most likely to be exposed. People who live near these facilities may be exposed through improper waste disposal or contamination of drinking water. The general public can also be exposed to DEG through common household and consumer products that contain it. DEG does not absorb well through the skin, so the most common route of exposure is through ingestion. This can happen through accidentally drinking contaminated water or DEG-containing products.

DEG ingestion is very dangerous, and even deadly, if not treated. People who ingest it may initially seem drunk. As the body metabolizes DEG, they can then develop nausea, vomiting, diarrhea, and abdominal pain. A few days after ingestion, kidney failure and irregular heartbeats are very common. About one week after ingestion, there can be impairment of brain function, loss of motor control, coma, and death.

Because DEG has useful chemical properties and is inexpensive, companies have inappropriately added it into products like medicines, toothpaste, and alcohol as a substitute for other ingredients. Between 1937 and today there have been dozens of instances worldwide of DEG poisoning through contaminated products that have resulted in mass deaths. In 1937, DEG added to a medicine caused 105 deaths in the US, which lead to the establishment of the Food and Drug Administration’s authority to regulate the safety of food, drugs, and cosmetics. The fact that mass deaths through DEG poisoning have continued since then in the US and elsewhere makes clear that additional oversight and regulation is needed to protect people from DEG exposure and poisoning.

Arsenic is a naturally-occurring element found in the Earth’s crust. It has some industrial uses through which people can become exposed to it. In some places, like northern New England, arsenic is present in bedrock, and drinking water wells drilled in these areas can expose people to arsenic in their water. Arsenic is classified as a human carcinogen, meaning exposure to it can cause cancer. Skin, liver, bladder, and lung cancer are the most commonly reported cancer types. In northern New England states (Maine, New Hampshire, and Vermont), mortality rates from bladder cancer are much higher than they are across the US as a whole, and it is thought that the reason is long-term exposure to arsenic in well water. Some wells in these states have arsenic levels over 1,000 times the safe limit set by the US Environmental Protection Agency (EPA).

Arsenic exposure through well water is a serious concern, but the full extent of the problem in northern New England isn’t known. This is because it is difficult to test all drinking water sources in a large, rural geographic area, and because about half of homes in Maine and New Hampshire receive water from private wells which are not subject to regulation by the government. A recent study called the All About Arsenic (AAA) program used citizen science to collect data on arsenic in well water in Maine and New Hampshire and help raise community awareness about mitigating arsenic exposure.

Citizen science is scientific research conducted with the participation of the general public. Research has shown that citizen science can generate new knowledge, create learning opportunities for participants, strengthen community relationships, promote participation in civic life, and address environmental health concerns. In the AAA program, the researchers recruited teachers from a large geographic area in Maine and New Hampshire and paired them with scientist partners from nearby colleges. They developed water sample kits for the teachers’ students to use to collect water samples from their homes and their neighbors’ homes. Samples were analyzed for metals by scientists and results were shared with the teacher and student participants. Teachers and students then prepared community education materials so that classmates, parents, neighbors, local news, and local elected officials would know and understand the results.

The AAA program recruited a total of 31 teachers and 4,859 middle and high school students. Students collected 3,070 drinking water samples from 2016-2022, and 15% exceeded the EPA’s limit for arsenic in drinking water. These samples represented a significant increase in wells in Maine and New Hampshire that now have data regarding their arsenic levels. In some towns, the AAA program more than doubled the number of samples the states previously had. In other towns the AAA sampled, the states previously had no data. In one town, before the AAA program it was not known that arsenic levels exceeded the EPA’s limit. Consistent with the idea that the source of arsenic in these samples is from bedrock, samples that receive water from drilled wells tended to have higher arsenic concentrations.

The AAA researchers used surveys and interviews to follow up with some households whose water was sampled. Of 72 households surveyed, 29 (40%) took actions to mitigate their exposure to arsenic in their water after receiving their sampling results. Some survey respondents said they had no prior knowledge about arsenic in their well water. Mitigating actions included upgrading their systems, installing point-of-use filters, and using bottled water for drinking. Interviews with households confirmed that the AAA program had direct public health and educational impacts on those that participated in the study. Interviewees specifically mentioned that health risks to their families and children were their main concerns that drove their decision-making after receiving their sampling results.

The AAA program provides valuable insights beyond simply generating more data. It shows that are ways to collect data and disseminate information in communities – like large rural areas – that have been previously underserved by public health agencies. It also demonstrates that communities can and should be crucial partners in every stage of the process, not simply as study subjects. The AAA program involved teachers and students in study design, sample collection, sample analysis, communication of results, and community education, reflecting a true citizen science partnership. Finally, the study demonstrates that there is more environmental exposure to toxic chemicals than we have previously been aware of. Data collection alone won’t change this, so taking action to protect communities is essential. The AAA program shows that when given information about their potential arsenic exposure, many residents took action to protect themselves. However, relying on individual residents to spend time and money on their own arsenic mitigation strategies cannot be the only solution. Using data like that collected in the AAA program, local, state, and federal agencies must monitor, regulate, and provide mitigation equipment for private water wells like they do for public wells. This will be the best way to keep communities safe from arsenic in their drinking water.

CHEJ has previously written about other sources of arsenic exposure here.

Toxaphene is a pesticide made up of a mixture of hundreds of different chemicals. It is a yellow, waxy solid that smells like pine. In the 1970s it was the most commonly used pesticide in the United States, used primarily in southern states on cotton crops. Toxaphene use was banned in the US in 1990, and banned internationally in an environmental treaty in 2001.

Although toxaphene is no longer in use, it is still in the environment today. There are hazardous waste sites containing toxaphene, and at least 68 Superfund sites are known to have it. When it enters the environment, it is most likely to be found in air, soil, or sediment at the bottom of bodies of water. It can travel long distances in air, leading to contamination of large geographic areas. Toxaphene doesn’t break down easily, so once it’s in the environment it persists for a long time. Toxaphene also bioaccumulates, so it builds up in the fatty tissues of fish and mammals that ingest it.

Today, people living near waste sites contaminated with toxaphene are the most likely to become exposed to it through breathing contaminated air, touching contaminated soil, or drinking contaminated water. Eating fish or mammals from contaminated areas can also lead to toxaphene exposure. High exposure through any of these scenarios can lead to brain, liver, kidney, and lung damage. In extreme cases, it can cause seizures and death. In studies of laboratory animals, toxaphene exposure caused liver cancer. The US Environmental Protection Agency determined that toxaphene probably causes cancer in humans as well. Banning toxaphene use was a good way to prevent widespread exposure, but toxaphene’s persistence in the environment means that people are still exposed to it today.

Copper is a chemical element and a metal. It is naturally occurring and is found in rocks, soil, water, and air all over the planet. Because it is soft, malleable, and a
good conductor of heat and electricity, it is useful for many purposes. Copper is thought to be the first metal humans collected and smelted to create things, dating back to 5000 BC. Today it is used in wiring, plumbing, cookware, dietary supplements, and pesticides. It is also combined with other metals to make brass, bronze, and sterling silver.

While copper exists naturally in the environment, it can also be released into the air, soil, or water by humans through sources like industrial waste, municipal solid waste, and fossil fuels. In air, copper generally attaches to particles and can travel long distances from its source. In soil, copper can be taken up by plants through their roots. In water, copper can attach to sediments and be taken up by clams andoysters. Once copper is in the environment, it does not break down. For humans, animals, and plants, copper is a required nutrient that is crucial for energy production. Humans generally consume enough copper through eating and drinking. However, exposure to too much copper is detrimental. People who work in or live near facilities that use copper may inhale, ingest, or touch copper dust orparticles at high levels. Many new homes are built using copper pipes, which can contaminate the tap water with copper, especially if the water flowing through those pipes is more acidic than normal. Drinking this water can then cause exposure to high levels of copper.

Exposure to too much copper can have adverse health effects. Ingesting it from food or water can cause nausea, vomiting, diarrhea, and abdominal pain. In extreme cases, this can lead to liver or kidney failure. Inhaling copper that’s attached to particles in the air can cause nose and throat irritation leading to lung damage. Skin contact with high levels of copper can cause rashes and discoloration. Studies in laboratory animals have found that ingesting high levels of copper can cause liver, kidney, blood, brain, and reproductive defects. Copper is an illustrative example of how nutrients essential for survival can become dangerous environmental toxins at high doses.

Aniline is a yellow liquid that smells like rotten fish and easily catches fire. It was first discovered in the 1800s and used as a synthetic dye for textiles. Aniline is now also used in the production of products like herbicides, agricultural chemicals, antioxidants, varnishes, rubber, polyurethane, and explosives. Aniline may enter the environment through its industrial use and disposal. It tends to stick to soil, and through soil it can ultimately migrate into groundwater.

If aniline enters soil or water, food or drinking water can become contaminated, and people consuming them may become exposed. Exposure to aniline this way is usually minimal, but can happen at high levels in areas near sites that contain aniline. Those most at risk of aniline exposure are people who work in places that make products using aniline where they may ingest, inhale, or touch the chemical.

When aniline enters the body, it impairs the blood’s ability to transport oxygen. Without oxygen, organs cannot function normally, which can lead to dizziness, headaches, decreased heartbeat, and a bluish discoloration to the skin. These symptoms can occur after a brief exposure, and they become more severe as the amount or length of time of exposure increases. Extreme exposure can result in coma and death. In studies of laboratory animals, long-term aniline exposure caused spleen cancer. For this reason, the Environmental Protection Agency classifies aniline as probably causing cancer in humans. Because aniline easily catches fire, it is also dangerous because accidents or spills at sites that contain aniline can cause risk of explosion. These explosion and human health risks make aniline a dangerous chemical whose use and disposal should be closely monitored and regulated.

Evaluating the cumulative impacts of exposure to multiple chemicals is perhaps the most difficult task facing toxicologists. The standard approach is to evaluate these risks by conducting a risk assessment or risk evaluation which relies heavily on data from exposure to a single chemical. But this only provides a limited assessment of the risks. Over the years there has been a growing recognition that this approach has many flaws (see previous issues of Toxic Tuesday) and limited application to real world exposures to multiple chemicals at low concentrations. EPA has recognized the need to develop tools to evaluate cumulative risks, but has failed to develop a clear road map for how to do this.

A cumulative risk assessment would analyze the combined risks to health or the environment from exposure to multiple agents or stressors (USEPA 2003). This process includes evaluating the risks posed by exposure to multiple toxic chemicals simultaneously and over time as well as the influence on health of stressors such as genetics, lifestyle choices, income and air quality.

Evaluating cumulative risks requires knowledge of what chemicals a person was exposed to, the concentration of each of the substances in the mixture and how long a person was exposed to each of these substances. It also requires knowledge of how these chemicals in combination react to each other and how these chemical interactions in mixtures potentially impact human health. It also necessitates knowledge about the health status of each person exposed. There is both a natural variability as well as unique susceptibility among a group of people that influences health outcomes. For example, people who are sick or who have existing health conditions such as a weak heart or compromised immune system can influence how a person responds to a mixture of chemicals. Socioeconomic factors such as poverty, unemployment rates, education levels and income also influences how people in a community respond. All of these factors combined would have to be considered to assess the cumulative health impact resulting from exposure to multiple chemicals simultaneously.

What’s become very clear over the years is that the scientific community knows very little about most of these factors. Consequently, risk assessors need to make many assumptions about information that is not known or at best uncertain. This is especially true when it comes to information about exposures (concentration and for how long) as well what level of exposure actually triggers harm in the body. The lack of knowledge and understanding of the molecular interactions have made it very difficult for scientists to forecast what will happen when people are exposed to multiple chemicals at low concentrations over time and why the field of toxicology has struggled to address multiple chemical exposures.

This failure has left community leaders and people in communities exposed to multiple chemicals simultaneously frustrated by the lack of answers and the lack for action by government agencies when addressing multiple chemical exposures. It may also be frustrating for government agencies because they are dependent on a tool (risk assessment) that relies on an antiquated approach that cannot answer the questions that people are asking.

EPA and other public health agencies need to be honest and truthful with the public about what they don’t know about chemical exposure risks. Scientists actually don’t know very much about what happens to people exposed to low level mixtures of toxic chemicals. While this reality may not be reassuring, the truth allows everyone to better understand what they are facing.

There is an alternative that should be considered. EPA should follow the lead of what the government did to take care of Vietnam Veterans who were exposed to Agent Orange and the soldiers exposed to emissions from the burn pits in Iraq and Afghanistan, among others. In these cases, soldiers do not have to prove that their illnesses were caused by their exposure to toxic chemicals. If they can show that they were exposed and that they have an illness associated with the chemicals they were exposed to, that’s sufficient for them to get health care and other compensation.

Communities exposed to toxic chemical mixtures shouldn’t be held to a different standard given that the uncertainties about toxic exposures are driven by the same scientific unknowns. In the absence of a basic understanding of what adverse health effects might result from exposures to the mixtures of toxic chemicals released into a community, the government should take steps to address the needs of the community, whether it’s by providing health care for those who were exposed or establishing a medical monitoring program to follow these people, or both.

These steps will begin the long and difficult process of acknowledging what we know and don’t know about exposes to low level mixtures of toxic chemicals and begin to learn what happens to the people exposed in these situations.