Erin Brockovich (2000): Does the Science Hold Up?

Erin Brockovich is twice divorced, unemployed and raising three children alone. She talks her way into a job as a file clerk at a small law firm. Sorting a pro bono real-estate file, she notices medical records filed alongside property documents for homes in Hinkley, a small town in the Mojave Desert. She starts asking why.

Her digging turns up two things. Pacific Gas and Electric had used hexavalent chromium, a chemical that stops metal corroding, at its Hinkley compressor station. And the company had been talking to residents about buying their homes.

She goes door to door, wins the trust of hundreds of residents, and gathers their accounts into a mass action. In 1996 PG&E settles with more than 600 Hinkley plaintiffs for $333 million.

Spoilers below. This page discusses the settlement that ends Erin Brockovich, and what the film asks you to conclude from it.

Start with the part that holds up completely.

California's Lahontan Regional Water Quality Control Board records the facts on its own cleanup page. PG&E used hexavalent chromium to fight corrosion in cooling-tower water between 1952 and 1966. The wastewater went into unlined ponds at the site. Some of it percolated down to the groundwater. The Board describes the affected groundwater as at least eight miles long and two miles wide, and PG&E remains under orders to stop the plume expanding and clean it up.

So the corporate-conduct story the film tells is substantially true. A utility discharged a recognised human carcinogen into unlined ponds, it reached drinking-water aquifers, residents were not properly told, and a legal assistant with no credentials drove the accountability.

The film then takes one more step, and that step is where this page begins.

IARC classifies chromium (VI) compounds as Group 1, carcinogenic to humans. The US National Toxicology Program lists them as known to be human carcinogens.

Both rest on the same evidence. It comes from groups of workers followed over time. The jobs were chromate production, chromate pigment work and chrome plating. The cancer is lung cancer. The route is breathing the chemical in. NTP also found a raised risk of a rare cancer of the nose and sinuses in those workers. For other sites, it says the data were unclear.

That is not the exposure in Hinkley. Hinkley was drinking water.

On swallowing it, IARC found little evidence of a link with stomach cancer. It counted about as many estimates above the no-effect line as below it. It also set aside a single study of polluted drinking water in China, saying one study of that kind is not enough on its own.

The picture has moved since the film, and it has moved towards more concern rather than less.

A National Toxicology Program study put it in the drinking water of rats and mice for two years. It was reported after the film came out. In rats at the top dose, tumours turned up in the lining of the mouth or on the tongue. In mice at the two top doses, tumours turned up in the small bowel. In both species, more of the chemical meant more tumours.

EPA finished its own review in 2024. Its finding: chromium-6 is likely to cause cancer in people who swallow it. That rests on the animal work above. The same review keeps the older finding that breathing it in does cause cancer in people.

Notice the two phrasings. "Carcinogenic to humans" for inhalation. "Likely to be carcinogenic" for ingestion. That gap is deliberate. Drinking it is a real hazard, and it justifies regulation. It also sits on a weaker evidence tier than the lung link. Both things are true at once.

The California Cancer Registry assessed cancer incidence in the census tract containing Hinkley three times, through its Desert Sierra program.

The first covered 1988 to 1993. It found 114 cancers against 91.2 expected. The authors did not treat that as a real excess. They put much of it down to undercounting a growing population. Extending the count to 1998 gave 173 against 167.2 expected. A third look, covering 1996 to 2008, gave 196 against 224.2. That last one is slightly below what was expected.

Other epidemiologists have criticised those results. The criticisms are worth knowing, because they apply to almost every cancer-cluster investigation you will ever read about.

• Exposure misclassification. The count pools everyone in a large census tract. The Center for Public Integrity reported that the tract covers about 137 square miles and roughly 3,500 people. The families who sued lived in about 13 homes, in roughly one square mile. Diluting the worst-hit homes into the whole tract can hide a real effect.
• Statistical threshold. The registry applied a 99% confidence level. The epidemiologist Richard Clapp told the same reporters there was at least 95% certainty that the cluster was not a fluke, which is the standard most epidemiologists use.
• Study period. The third assessment starts in 1996, the year of the settlement, by which point homes in the worst-affected neighbourhood had been demolished and residents had moved away.

The registry's author has said his aim was to correct a popular notion that people in Hinkley had a high rate of cancer. That is a fair aim, and a null result at tract level is genuine evidence against a large community-wide excess. It is not evidence that no individual's cancer was caused by the water. And it is not a study of the exposed group. No study assigning individual exposures and following those individuals appears to have been published. That absence, rather than any null result, is the honest reason this is unresolved.

Anderson v. Pacific Gas and Electric settled in 1996 for $333 million on behalf of more than 600 residents. It settled before any court ruled on causation.

People cite the size of the payment as though it were proof. It is not. What a company pays to settle reflects the risk of losing, the cost of fighting hundreds of claims, the threat of punitive damages, and the damage to its name. All of those can be severe even where the evidence on cause is weak.

The claim made in the litigation was also far broader than the toxicology supports. It covered a wide range of cancers plus conditions that are not cancer. The ingestion evidence points mainly at the gut.

Clusters are one of the hardest things in epidemiology and one of the easiest things to write a story about.

Small populations produce noisy numbers. Clusters appear by chance, and they get found because somebody went looking. And the two available narratives — corporate villainy proven, or worried residents debunked — are both more satisfying than the truth. The truth is usually that the exposure was real, the harm is plausible, and the study that would settle it was never done.

If that pattern is useful to you, how to read cancer statistics and news headlines covers the general version. For an exposure where the human evidence is strong, asbestos is the contrast case. Air pollution and cancer risk shows what a well-characterised environmental exposure looks like.

There is still no federal drinking-water limit specific to hexavalent chromium. EPA regulates total chromium at 100 parts per billion.

California went its own way. Its total chromium limit has stayed at 50 parts per billion since 1977. An earlier chromium-6 limit was thrown out by a Sacramento court in 2017. The reason was cost, not science: the court made no finding about whether the limit protected health. The State Water Board then set a new chromium-6 limit of 10 parts per billion. It adopted that on 18 April 2024, effective from 1 October 2024. The smallest water systems have four years to comply. California also has a health goal of 0.02 parts per billion, set in 2011. A health goal is not enforceable, and it does not have to account for what treatment costs.

Cancer Explained sells nothing and takes no sponsorship. If this page helped you hold two true things at once, you can help keep that kind of writing available. Support our work.

Erin Brockovich is a great film and a bad citation. The contamination was real. The chemical is a genuine carcinogen. And the causal claim at the film's centre was settled around rather than proven. Holding all three at once is harder than picking a side. It is also the only honest position available.

• IARC Monographs Volume 100C — Chromium (VI) compounds
• NTP Report on Carcinogens — Chromium Hexavalent Compounds
• EPA IRIS — Hexavalent Chromium
• Lahontan Regional Water Quality Control Board — PG&E Hinkley Chromium Cleanup
• California State Water Resources Control Board — Hexavalent Chromium (Chromium-6)
• California Cancer Registry — Community Cancer Assessment in Hinkley, 1988-1993, updated 2000
• California Cancer Registry — Preliminary Assessment of Cancer Occurrence in the Hinkley Census Tract, 1996-2008
• Center for Public Integrity — Cancer-cluster study seeking to debunk 'Erin Brockovich' has glaring weaknesses

This page discusses Erin Brockovich for education. It is not medical advice, and nothing here is a judgement of anyone's real medical care. Spotted an error? Please email [email protected].