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Scientists study chemicals for their potential to cause cancer, but usually they examine them one at a time.

And yet, we're exposed to mixtures of different chemicals every day.

Dr. William Goodson is a senior scientist with the California Pacific Medical Center Research Institute.

He's the lead author of a new paper in the journal Carcinogenesis. He worked with a team of more than 170 scientists around the world to examine what we know about the potential for mixtures of chemicals to cause cancer.

Here's an excerpt from the paper's abstract:

Lifestyle factors are responsible for a considerable portion of cancer incidence worldwide, but credible estimates from the World Health Organization and the International Agency for Research on Cancer (IARC) suggest that the fraction of cancers attributable to toxic environmental exposures is between 7% and 19%. To explore the hypothesis that low-dose exposures to mixtures of chemicals in the environment may be combining to contribute to environmental carcinogenesis, we reviewed 11 hallmark phenotypes of cancer, multiple priority target sites for disruption in each area and prototypical chemical disruptors for all targets, this included dose-response characterizations, evidence of low-dose effects and cross-hallmark effects for all targets and chemicals.

Why study mixtures?

Goodson says we know very little about the mixtures of chemicals we're exposed to.

Up until now, he says, researchers have focused on whether or not individual chemicals can, on their own, cause cancer. There just haven't been many studies on how chemicals might work together to lead to cancer.

"Because it's more complicated to do," he says.

"And what we're realizing, and what this group spent several days talking about, was that there's reason to think that it doesn't take one chemical to take it all the way from normal to cancer."

Goodson says different chemicals, when combined, might lead to a carcinogenic mixture.

"One chemical can take it part way, another chemical will take it another portion of the way and maybe a second, third, or fourth chemical will take it all the way," he says.

He says this concept is still just theoretical.

"But we think it really needs to be looked at very carefully," Goodson says.

Beginning the process

He says testing mixtures of chemicals is tricky.

"Probably the biggest challenge is trying to figure out which mixtures you're going to test, and that requires making some educated guesses about which ones to look at," Goodson says.

And it won't be cheap.

"It's going to require a lot of effort to put this together," he says. "No company's going to take this on because nobody is going to make money by deciding what mixtures are unsafe. It really requires a funding effort and an organizational effort, really probably on a federal level."

He also noted that many big-name organizations fundraise for cancer research, but there are gaps in the types of research they fund.

"They will talk about prevention, but if you look at their portfolio of research, almost none of them actually do anything looking at chemicals, and certainly not mixtures of chemicals," Goodson says.