Recently, PBS NewsHour ran a two-part investigative story that must have seemed to have all the elements of a compelling piece. There was a relatively unknown but apparently widespread carcinogen and a great hook—it was tied to the story of contaminated water behind the film Erin Brockovich. Issues relating to public health threats demand careful and thorough reporting. Unfortunately, those qualities were at times absent from the PBS story.

The story focused on hexavalent chromium (Cr6+) in drinking water. Most chromium is trivalent, which isn’t very soluble in water. When oxidized to hexavalent chromium, however, it becomes mobile. Unlike the trivalent variety, hexavalent chromium is carcinogenic. It's much worse if inhaled, but there’s evidence that it is dangerous when ingested as well. As the NewsHour story noted, recent sampling has shown that hexavalent chromium is present in drinking water across the country. Does that mean we have a public health crisis on our hands, caused by shockingly widespread contamination? Let’s slow down and get some context.

Meet the metal

Hexavalent chromium occurs naturally. That’s a rather important fact never mentioned in the NewsHour story, which describes the water as “tainted” by industrial chemicals. Chromium, like many elements, is present in Earth’s crust. Some types of rock have more than others, but it’s actually a little bit more common than copper or zinc—the average concentration in the upper crust is something like 90 parts per million. Oxidize some of that chromium to the hexavalent state, and it can be mobilized into groundwater. If hexavalent chromium is showing up in wells nearly everywhere we look, it might be because it’s naturally present rather than a ubiquitous, human-introduced contaminant.

This story has many California connections, from the town of Hinkley that Erin Brockovich fought to protect to the California EPA’s high-profile examination of hexavalent chromium health risks. But the connections extend to geology. Serpentinite—California’s state rock—is one of the best rocks in which to look for chromium ore.

California also has collected a lot of data on the occurrence of chromium in drinking water. Of 6,565 public water supply wells sampled across the state, hexavalent chromium was detected (meaning that the concentration was greater than 1 part per billion) in nearly half. It’s mostly present in the 1 to 8 parts per billion range, but it can be higher. In Hinkley, California determined that anything up to 3 parts per billion should be considered background rather than a result of the contamination there (contamination produced much higher concentrations).

While it can sound scary to hear that a potentially hazardous compound was detected in your water, it’s the concentration that determines the risk. The NewsHour story focused on a study of hexavalent chromium in water around a chromium ore mining operation in China. The 1987 study found a statistically significant increase in certain cancer rates for the villages with higher concentrations of hexavalent chromium in their water. Ergo, the story implies, the hexavalent chromium in your water may be giving you cancer, too.

But the concentrations in those Chinese villages were astronomical—as high as 20,000 parts per billion. A summary in the journal Epidemiology describes it as “perhaps the highest exposure to hexavalent chromium in water that will ever be experienced by a population large enough to estimate risks of cancer.” A pair of studies on populations in the US with low-level exposures failed to find much of a correlation—although one did find a slight link to lung cancer. (Again, the risk from inhalation is better understood.) Laboratory studies with rats have indeed shown hexavalent chromium in water to be carcinogenic, but extrapolating this sort of result down to small doses is often tough.

A 2010 Environmental Working Group study sampled water from 35 US cities and reported that hexavalent chromium had been detected in 31 of those cities. But at what concentrations? Only one city had concentrations greater than 2 parts per billion—Norman, Oklahoma at 12.9 parts per billion. A recently completed study that followed up on the results in Madison, WI found concentrations of up to 2 parts per billion in municipal wells—and chromium as high as 30,000 parts per billion in bedrock samples from those wells. The evidence points to a natural source for the hexavalent chromium in the water.

The EPA drinking water standard for total chromium is 100 parts per billion, but that standard is currently being reviewed. California has chosen a “Public Health Goal” of 0.02 parts per billion. We often think of such standards as the line between safe and unsafe exposures, but the real world isn’t so cut-and-dried. The eventual drinking water standard will only be set as close to the Public Health Goal “as is economically and technically feasible.” And the Public Health Goal for hexavalent chromium is based on a one-in-a-million cancer risk. That is, “for every million people who drink two liters of water with that level of [hexavalent chromium] daily for 70 years, no more than one person would be expected to develop cancer from exposure to [hexavalent chromium].”

All these complexities—natural sources, levels of exposure, etc.—were largely left out of the NewsHour report.

At one point in the NewsHour story, Erin Brockovich talks about a crowd-sourced map of cancer clusters she has organized. Her assertion that hexavalent chromium in drinking water is likely the cause of most of the cancer hotspots went completely unchallenged. And the concept itself relies on the dubious assumption that the clusters have local causes. (In reality, cancer clusters are often statistical flukes.) It also assumes that hexavalent chromium is the result of industrial contamination rather than occurring naturally across broad regions.

As anthropogenic groundwater contaminants go, hexavalent chromium isn’t terribly common—unlike petroleum or chlorinated solvents. It’s hard to imagine that industrial releases of hexavalent chromium could be impacting such an astounding number of public wells. If the hexavalent chromium is naturally occurring, the discussion about what’s acceptable and what to do about it becomes a lot more nuanced. Nuance is not what the NewsHour report delivered.

Muddying the waters

It isn’t the first story ever to lack appropriate context, so why has it drawn my ire? Stories like this scare the bejeezus out of people. In a blog post accompanying his story, reporter Miles O’Brien reveals that he had the tap water in his apartment tested while working on this story. When the results showed a concentration of 0.19 parts per billion, he started filtering his water for fear of the cancer risk. After all, as he puts it, “That is ten times more [hexavalent chromium] than the Cal/EPA public health goal.” (A related post helps readers select an expensive filtration system of their own.)

The Environmental Working Group study mentioned above that found hexavalent chromium in 31 cities claims that “[a]t least 74 million Americans in 42 states drink chromium-polluted tap water, much of it likely in the cancer-causing hexavalent form.” Still thirsty? How many people are going to start buying bottled water because of this—water that simply comes from a well somewhere else and might contain just as much hexavalent chromium?

Apart from frightening people who already lead stress-filled lives, claims like this can undermine the actual science (as well as the journalists reporting it). We’ve all heard someone dismiss a health report with, “Whatever, they say everything gives you cancer.”

This particular presentation also chose a common storyline: it pitted plucky environmental watchdogs against corporate mouthpieces. While it may make for good TV, it’s not the best way to establish the facts. What if the corporate lobbyist is right about something? What if the environmental advocate is mistaken? It’s ultimately the journalist’s responsibility to find the experts who can present both the evidence and the uncertainty, rather than letting interested parties have their say unchallenged.

In this shallow, adversarial context, emotions often come to the forefront. And places where contamination has occurred, like Hinkley, provide examples of how damaging these emotions can be. Residents can feel scared, frustrated, and helpless. They’re suddenly exposed to a torrent of new information they have to absorb. They want to protect themselves and their families, and they’re wary of dishonesty and corruption. Trust breaks down, and misunderstanding runs amok.

The story mentions that residents of Hinkley are now terrified that they’re being poisoned with arsenic and manganese, as well—something they blame on the facility that caused the hexavalent chromium contamination. There’s a pretty good chance that these elements had naturally been present all along but hadn’t been tested for or drawn attention before.

It’s so difficult to inject complex facts and rational evaluation into charged issues like this, which makes it all the more critical that media reports take care to do so. While the NewsHour story raises fair questions about industry interference with the development of a hexavalent chromium public health standard, it also fans the flames of chemophobia. The intent was undoubtedly to inform, but the result was confusion.

When Ars asked NewsHour to comment on these concerns, a spokesperson for the program responded, "The Newshour’s two-part report on chromium 6 in drinking water supplies examined arguments about levels of safety and about the EPA’s process for making that determination. We included different points of view in our reports: those of affected residents, environmental activists, industry spokespeople, and scientists. The EPA refused to grant an interview, and we did our best to represent the agency’s position. Any specific comment should be viewed in the context of the entire report."

But that approach—letting everyone have their say, without any critical evaluation—is part of the problem. This is not a question of differing points of view, but one of carefully sifting the knowns and unknowns. Presenting opposing perspectives and leaving the viewer to decide is not the way to communicate science, and it doesn't excuse broadcasting misleading or incomplete information.

This article mistakenly referenced the book "A Civil Action" as the basis for the film "Erin Brockovich". The book, which became a movie of the same name, was written about a lawsuit over chlorinated solvent contamination in Woburn, Massachussets.

Note: While I am employed by the Wisconsin Department of Natural Resources, views expressed are my own and should in no way be construed as representing the department.

Thanks to my colleague Randy Maass for help researching this story.