1,4-Dioxane gets around.
It’s on laboratory shelves, a reagent familiar to bench scientists. Some drugmakers use it to purify pharmaceutical ingredients. Filter makers employ it to create tiny pores in membranes.The chemical’s commercial heyday was in the second half of the 20th century, when it stabilized chlorinated solvents used for metal degreasing.
Since then, the chemical’s reputation has dimmed.
In toxicity studies, laboratory rodents given 1,4-dioxane in their drinking water developed liver cancer. The US National Toxicology Program classifies the synthetic compound as “reasonably anticipated to be a human carcinogen.” Likewise, the US Environmental Protection Agency deems this synthetic chemical a likely carcinogen. In addition, 1,4-dioxane doesn’t readily biodegrade in the environment, the EPA says.
Consequently, production of the compound has dropped, at least in the US. BASF, the last US manufacturer of 1,4-dioxane, halted production at a plant in Louisiana in 2018 and closed the facility a year later, the company tells C&EN in a statement. BASF, however, still imports it from Germany to supply its US customers, and other companies could do similarly.
But even as use of 1,4-dioxane declines, it’s not truly going away. The consequence of legacy and ongoing uses—plus the compound’s tendency to appear as an impurity in consumer and commercial products—is that 1,4-dioxane is more widespread as a contaminant in drinking water than most other synthetic chemicals, says Thomas K. G. Mohr, author of a technical book about investigating and remediating 1,4-dioxane pollution. Water monitoring data collected in 2010–15 show that more than 7 million people in the US across 27 states had utility-supplied tap water that had detectable 1,4-dioxane, according to the Environmental Working Group (EWG), an advocacy organization.
The problem of 1,4-dioxane pollution isn’t unique to the US. However, the US situation reveals a number of regulatory barriers. There is no federal limit on 1,4-dioxane in drinking water. And getting it out of water is challenging.
1,4-Dioxane, a cyclic ether first reported synthesized in 1863 (Ann. Chim. Phys. 1863, 67, 257; Ann. Chim. Phys. 1863, 69, 317), poses a cancer risk when it’s released to the air and people breathe it, but the chemical doesn’t stick around in outdoor air. It degrades quickly in the atmosphere, with a half-life of less than 5 h, according to the EPA. The compound reacts with photochemically produced hydroxyl radicals to form breakdown products such as aldehydes and ketones. As the US Clean Air Act requires, the EPA regulates 1,4-dioxane as part of a family of substances classified as hazardous air pollutants.
But in water, it dissolves completely, even at high concentrations. It also does not evaporate readily. These properties make 1,4-dioxane difficult to remove from water.
For example, polluted groundwater is commonly treated with pump-and-treat systems in which water is drawn from the ground, aerated or filtered through granulated activated carbon to excise chlorinated solvents and other contaminants, and returned to the aquifer. But this technology doesn’t work effectively on 1,4-dioxane.
An expensive, energy-intensive treatment called advanced oxidation processes does the job, though only a few water utilities have it. The technology combines ultraviolet light, which photolyzes organic compounds, with hydrogen peroxide, an oxidant. A study published earlier this year suggests that using hypochlorous acid instead of H2O2 makes this process even more efficient at ridding water of 1,4-dioxane (Environ. Sci.: Water Res. Technol. 2020, DOI: 10.1039/D0EW00316F).
Many communities that depend on wells for public drinking water have aquifers tainted with worrisome levels of 1,4-dioxane. This contamination arose from past unregulated industrial practices, in which spent or unwanted solvents were legally dumped into unlined ponds or leaked from underground storage tanks. Some 1,4-dioxane leached out of landfills. In any case, 1,4-dioxane infiltrated aquifers.
Some areas in particular face serious challenges from high levels of contamination. In New York, for example, 1,4-dioxane taints public wells across much of Long Island. It came from manufacturing operations that used the solvent 1,1,1-trichloroethane stabilized with 1,4-dioxane from the 1950s through the mid-1990s, according to water commissioners there. Spills and the unregulated past practice of direct disposal of solvents to the ground led to the pollution. Water districts on Long Island are adopting newer technology to remove the chemical from tap water.
The situation near Ann Arbor, Michigan, is somewhat different. Between 1966 and 1986, 1,4-dioxane filtered into groundwater from lagoons that held wastewater from the manufacture of medical and industrial filtration equipment at Gelman Sciences, now defunct. An underground plume of 1,4-dioxane is headed toward the Huron River, the main source of drinking water for Ann Arbor. A successor company to Gelman, Pall Life Sciences, is treating the tainted groundwater.
Both Long Island and the Ann Arbor area have similar geological formations—both are situated on glacial outwash plains, Mohr says. In this type of substrate, pollutants released to the soil “move every which way fast,” he says.
Plumes of 1,4-dioxane from former industrial operations also taint groundwater in arid Southern California. Some water suppliers have shut down wells or blended water from different wells to dilute 1,4-dioxane concentrations.
In other locations, utilities are just as worried about the presence of 1,4-dioxane in sewage. Many cleaning products, laundry detergents, and shampoos, for example, include 1,4-dioxane as an unintentional impurity from surfactants, which are key ingredients in such products that get rinsed down the drain. Although the amounts are small in individual products, they add up when multiplied by many households and commercial establishments such as car washes and hospital laundries.
For utilities that recharge aquifers by injecting treated wastewater underground or discharging it into infiltration basins, all that 1,4-dioxane coming from drains presents a problem. Sewage treatment plants are engineered to reduce biomass and eliminate pathogens from wastewater—not to remove hydrophilic compounds like 1,4-dioxane, Mohr says. Sewage plants remove less than 3% of 1,4-dioxane from the wastewater they treat, the EPA says in a 2019 draft assessment of the chemical.
To prevent contamination of aquifers that get recharged, the California State Water Resources Control Board requires that recycled water contain no more than 1 µg/L of 1,4-dioxane. California utilities that recharge aquifers treat wastewater with reverse osmosis and advanced oxidation processes.
The top four US dischargers of 1,4-dioxane into rivers or public sewage systems in 2019 were from pharmaceutical and plastics plants, according to data filed with the Environmental Protection Agency.
Albany Molecular Research Inc. (AMRI)
▸ Rensselaer, New York
▸ 23,378 kg
▸ To sewage system, then the Hudson River
▸ Decatur, Alabama
▸ 10,453 kg
▸ To sewage system, then the Tennessee River
APG Polytech, a subsidiary of Taiwan-based Far Eastern New Century
▸ Apple Grove, West Virginia
▸ 8,922 kg
▸ To the Ohio River
DAK Americas, a subsidiary of Mexico-based Alpek
▸ Moncks Corner, South Carolina
▸ 8,057 kg
▸ To the Cooper River
Source: US EPA Toxics Release Inventory, 2019.
Note: The largest environmental release of 1,4-dioxane in 2019 was reported from Huntsman International’s Houston plant. This facility sent 197,713 kg of 1,4-dioxane for disposal in an underground injection well.
1,4-Dioxane can be a problem in rivers as well as groundwater. Utilities typically send treated wastewater into rivers, and a handful of US industrial plants still flush the chemical down the drain.
It’s unclear how many industrial sites have wastewater permits from a state or the EPA that include a limit on their 1,4-dioxane discharges. Some wastewater permits do specify limits on the chemical, says Heather Barbare of the 1,4-dioxane team of the Interstate Technology and Regulatory Council (ITRC), a group of state regulators. She points to the EPA’s Toxics Release Inventory (TRI), which provides information about facilities with the largest discharges.
TRI data for 2019 show that five facilities collectively discharged tens of thousands of kilograms of this chemical into rivers or local sewage systems. Four are facilities that manufacture poly(ethylene terephthalate) (PET)—the clear plastic of beverage bottles—or other polyesters, producing 1,4-dioxane as a by-product. The fifth is a drug ingredient maker.
In most US watersheds, consumers’ and industry’s legally discharged 1,4-dioxane gets diluted to levels that aren’t of health concern to downstream communities’ drinking water, Mohr and Detlef Knappe, a North Carolina State University engineering professor, tell C&EN.
But that’s not true for North Carolina’s Cape Fear River. The river, which flows into the Atlantic Ocean near the city of Wilmington, provides drinking water to more than a million people, according to the EWG.
Knappe says discharges of about 23 kg per day of 1,4-dioxane into the Cape Fear River watershed lead to worrisome levels of the chemical in drinking water drawn downstream, which also includes a stew of per- and polyfluoroalkyl substances (PFAS). The river empties at about 282 m3/s. This is small compared with other US rivers, such as the Tennessee River’s output of 1,925 m3/s, meaning that the Cape Fear can’t dilute 1,4-dioxane discharges as much as other waterways.
A 2016 study showed that three wastewater treatment plants contributed almost all the 1,4-dioxane found in the watershed, says Knappe, who has studied persistent synthetic chemicals in the Cape Fear River. Those facilities treat wastewater from a variety of industries, including a PET manufacturing plant in Asheboro and an industrial waste handler in Greensboro, he says. Levels of 1,4-dioxane in the Cape Fear River have dropped since 2014 when Knappe alerted North Carolina officials to the contamination. He says the drop is probably due to a decrease in industrial discharges of the chemical.
Knappe sees a tension between upstream sewage treatment plants that can’t easily remove 1,4-dioxane that is legally discharged and downstream utilities that want to keep the potential carcinogen out of drinking water. Neither wants to resort to expensive advanced oxidation processes to remove the chemical.
There’s no federal limit on 1,4-dioxane in tap water. The EPA has a nonbinding health advisory level for 1,4-dioxane in drinking water of between 0.35 and 35 μg/L. The numbers correspond, respectively, to a lifetime cancer risk of 1 in a million and 1 in 10,000. The World Health Organization, meanwhile, has a suggested threshold of 50 μg/L.
The EPA is taking a detailed look at risks from 1,4-dioxane under the federal chemical control law, the Toxic Substances Control Act. In its 2019 draft version of that assessment, which the agency is expected to finalize by the end of 2020, the EPA determined that the chemical may pose an unreasonable risk to some workers. If finalized, this finding could lead to regulation, but the EPA may refer the issue to the Occupational Safety and Health Administration.
But the EPA chose not to address in the assessment the general public’s exposure to the chemical in drinking water. The EPA says in a fact sheet it can “adequately assess and effectively manage risks from 1,4-dioxane” to the general public using other federal statutes, including the Safe Drinking Water Act (SDWA). Such regulation would take years to implement.
In the meantime, a number of states are working to address 1,4-dioxane contamination in drinking water. Those actions are all over the map, according to data compiled by the ITRC. A handful of states have enforceable limits on the chemical in drinking water. Others have legal cleanup levels for aquifers. Some adopted the EPA’s advisory levels, while some have no numeric standards.
New York, with a large affected population living on Long Island, has taken the biggest regulatory action. In July, the state adopted the first enforceable limit for 1,4-dioxane in drinking water in the US, setting it at 1 µg/L. New York requires all public water systems, regardless of size, to test and monitor for the compound. Last year, the state enacted a law intended to keep more 1,4-dioxane from entering its drinking-water supplies by restricting levels of 1,4-dioxane in cosmetics and personal care and cleaning products. Companies that make those products, in response, are changing their manufacturing processes to eliminate the formation of 1,4-dioxane.
Some other states are following New York’s lead. In September, New Jersey’s Drinking Water Quality Institute recommended the state adopt an enforceable maximum contaminant level for 1,4-dioxane of 0.33 µg/L. The institute—a panel of academics, environmental health specialists, and public water utility representatives—endorsed the use of advanced oxidation processes to remove the contaminant from drinking water.
California, too, has begun steps toward restricting 1,4-dioxane in consumer goods and setting an enforceable limit in drinking water.
This mixture of state actions and their varying numeric levels is confusing, says Tasha Stoiber, senior scientist at the EWG. She and other environmental and health advocates want the EPA to set an enforceable federal drinking-water standard for 1,4-dioxane and are urging utilities to test their drinking water regularly for the presence of the chemical.
But the multiyear process that the EPA must go through to regulate contaminants under the SDWA makes a federal standard for 1,4-dioxane unlikely in the short term. Since Congress revised the process in 1996, the EPA hasn’t regulated any contaminants—except for those ordered by Congress—in drinking water. Earlier this year, the EPA opted not to set a drinking-water limit for perchlorate, an ingredient in rocket fuel that interferes with thyroid functioning, saying state regulation of the compound sufficiently protects public health. This could prove a precedent for 1,4-dioxane, Mohr says.
Regardless of whether the EPA or states set limits, Stoiber contends, it’s easier and less expensive to stop environmental releases of 1,4-dioxane than it is to treat drinking water to get it out.
This story was updated on Nov. 10, 2020, to correct the name of the North Carolina town that has a poly(ethylene terephthalate) manufacturing plant. The town is Asheboro, not Fayetteville.