Shortly after entering the field of public health in the early 1970s, Stephen Lester learned there was one thing he should steer clear of studying: how exposure to multiple chemicals at once might be devastating human health.

It was nearly impossible to secure government grant money for mixture studies, due to monumental hurdles in interpreting the results and ultimately determining which chemicals might have caused any documented health issue. If, for example, you exposed a rat in a lab to seven chemicals and the rat developed cancer, you could conclude the mixture causes cancer but are no closer to being able to say which toxin or combination of toxins was responsible. Researchers didnt bother submitting grant applications to do such work.

Little has changed in the 50 years since. Few mixture studies receive funding, and very little data on the effect of chemical mixtures exists. And when disasters strike, scientists assess risk the way theyve been doing it for decades: one chemical at a time even though the reality is that people are often exposed to a cocktail of different chemicals.

You have these risk numbers, and theyre all driven by one chemical exposure at a time, said Lester, a toxicologist and the science director for the Center for Health, Environment and Justice. Those numbers dont have any reality in the world, but yet if you talk to the best scientists in the world, theyll say thats what we have to use because thats what weve got.

In communities like East Palestine, Ohio, where residents were exposed to potentially dozens of different chemicals following the fiery derailment of a Norfolk Southern train in February, environmental agencies are often quick to declare the air, water and soil safe, despite having little grasp of how substances could be interacting to harm human health.

We really know just short of nothing about this, and yet we are making statements to the public that its fine, Lester said.

All the work that weve done, all the science that we know, is not enough.

Something From Nothing

The Norfolk Southern train careened off the tracks Feb. 3 while hauling toxic materials, including hundreds of thousands of pounds of vinyl chloride, a common organic chemical used in the production of plastics that has been linked to several types of cancer . Fearing a potentially catastrophic explosion, the railroad and local authorities temporarily evacuated people in the immediate area, and intentionally vented and burned the vinyl chloride, releasing a thick plume of toxic smoke into neighboring communities.

Since then, the Environmental Protection Agency (EPA) has repeatedly stressed there is little cause for concern , even as residents have continued to report a myriad of lingering health impacts nose bleeds, headaches, respiratory problems, rashes and irregular menstrual cycles that they are convinced are linked to the derailment. The agencies determination relies on testing that, for the most part, has found individual chemicals, including vinyl chloride and benzene, at levels below minimal risk thresholds.

Yet the danger in East Palestine may not be any one chemical but several working in tandem. And the fields of toxicology and epidemiology remain largely incapable of investigating and understanding that threat.