What’s An MCL, Anyway

Is California Close To Setting Standards For This Toxic Chemical?

I spoke with The Hill about the struggles of the past year—and the ass backwards process of protecting our air, land, and water. If you have a moment give it a read. Let me know what you think.

One of the topics we discussed was of course, hexavalent chromium, also called chromium-6.

I came across this chemical back in 1991 when working in Hinkley, California. PG&E used chromium-6 to prevent corrosion at a natural gas compressor station, from which wastewater percolated into the town’s groundwater.  

I didn’t realize it at the time but this chemical is a problem nationwide. In 2016, a report from the Environmental Working Group (EWG) found that about two-thirds of the American population—218 million people—were drinking water contaminated with potentially unsafe levels of that same chemical, chromium-6.

The EPA classifies chromium-6 as a known carcinogen, yet no federal standard exists for it in our drinking water. Instead, the EPA only monitors general chromium in water, which includes the two most common forms: chromium-3, a naturally occurring metallic element, and chromium-6, the toxic version used by industry. We don’t differentiate between the two at the federal level and that’s a big problem.

Where do water regulations come from?

The U.S. EPA, of course. As part of the Safe Drinking Water Act (SDWA), the agency has issued a number of drinking water regulations that help strengthen public health protection.

We have what’s called Maximum Contaminant Levels (MCLs). An MCL is the legal threshold limit on the amount of a substance allowed in public water systems as per the SDWA. The limit is usually expressed in a concentration of milligrams or micrograms per liter of water.  

The EPA has three criteria, according to the law, when determining what to regulate:

  1. a contaminant may have an adverse health effect on people

  2. a contaminant is known to occur or there is a high chance that the contaminant will occur in public water systems often enough and at levels of public health concern

  3. regulation of the contaminant will result in a meaningful opportunity for health risk reductions for people served by public water systems

Hexavalent chromium has been an industry standard, used nationwide by giant corporations such as Lockheed Martin and Boeing and found seeping into water supplies near coal ash dump sites across the country. In fact, chromium-6 was the single most common corrosive inhibitor used in cooling towers in the United States until the 1990s.

Millions of gallons of this toxic chemical were used everywhere from schools to hospitals to courthouses to food-processing plants to refrigerated warehouses.

California Dreamin’

The country has yet to set a maximum contaminant level for chromium-6 in drinking water. But California may finally do so, after previous attempts were thwarted by the Superior Court of Sacramento County.

“We ask that chromium-6 be treated as the crisis that it is for those remaining exposed to it through their water,” said Kyle Jones, policy director of Community Water Center, during an October 5 meeting of the state Water Resources Control board (WRCB).

“If you are at a home where drinking water can give you cancer, you are living with an ongoing crisis with no end in sight,” he added. “And so, we’re continuing to grow increasingly concerned with the reasons that this MCL has been delayed, and are calling on the board to ensure that a proposed regulation is released by the end of this year, and that finalization and implementation is expedited so that community members . . . can be protected. Anything else is an environmental injustice.”

A Little MCL History

In July 2014, California became the first state in the nation to regulate this substance and establish an MCL for chromium-6 in drinking water. The MCL was 10 ppb.

For reference, the rest of the country uses a federal standard of 100 ppb for total chromium, including other types like chromium-3, which is nontoxic. Those federal standards were created at a time when hexavalent chromium was not linked to cancer, but subsequent studies have shown a direct correlation.

One piece of research that helped set the standards in California was from the National Institutes of Health.

A 2007 study from The National Toxicology Program found that:

sodium dichromate dihydrate, a compound containing hexavalent chromium, causes cancer in laboratory animals following oral ingestion. Researchers found significant increases in tumors at sites where tumors are rarely seen in laboratory animals. Male and female rats had malignant tumors in the oral cavity. The studies conducted in mice found increases in the number of benign and malignant tumors in the small intestine, which increased with dose in both males and females.

But in September 2017, California dropped its MCL. The Superior Court of Sacramento County invalidated the standard, saying that “the state failed to properly consider the economic feasibility of complying with the MCL.”

The Safe Drinking Water Act requires the state to determine that the cost of treatment offsets the public health benefits. In this case, the court did not rule on whether the MCL was economically feasible or that it adequately protected public health, it simply found that the department did not adequately document whether the MCL was cost-effective.

The challenge came from the Solano County Taxpayers Association and the California Manufacturers & Technology Association, a trade group whose mission is to improve and enhance a strong business climate for California’s thirty thousand manufacturing, processing, and technology-based companies. The city of Vacaville, California, estimated that the standard would cost about $7.5 million to enforce.

“As if the current challenges we’re facing with the water supply in California aren’t bad enough, along comes this unnecessary regulation, which will place steep cost burdens on taxpayers without a benefit to public health,” Ourania Riddle of the taxpayers’ association said in 2016.

The state water board is in the process of adopting a new standard rather than appealing the court’s decision.

WRCB Vice Chair Dorene D’Adamo said that while the MCL was not on the board’s October 5 meeting agenda, setting a standard for hexavalent chromium remains a top priority for the board.  

Following the meeting, a WRCB spokeswoman said the board anticipates unveiling a chrome-6 MCL regulatory proposal in “spring 2022,” and finalizing it approximately one year later.

The health issues associated with ingesting this chemical are myriad. In addition to cancer and reproductive harm, short and long-term exposures can lead to eye and respiratory irritation, asthma attacks, nasal ulcers, dermal burns, anemia, acute gastroenteritis, vertigo, gastrointestinal hemorrhage, convulsions, ulcers, and damage or failure of the liver and kidneys.

It’s been five years… The research has been clear for years. The time to protect our public health is now. California, let’s set a standard for chromium-6 and be a leader in this country. EPA, you’re next.


Tell me what you think in the comments below!