Many communities around the country face environmental health threats from multiple sources. However, when government agencies estimate the health risks from toxic chemical exposures, they only consider the risk from a single chemical emitted from a single location for a defined period of time. This approach, while simpler to study and draw conclusions from, fails to capture the reality of chemical exposures that communities face.

It is crucial to consider the potential health impacts from exposure to multiple chemicals because when multiple chemicals target similar organs or biological pathways, then simultaneous exposure to them can make their effects worse. A study from a group of 350 cancer scientists found that exposure to multiple chemicals that don’t cause cancer on their own could lead to biological changes that ultimately do cause cancer. Exposure to multiple chemicals – even at low doses – can have unexpected impacts on human health and need to be considered when evaluating the risk to the public from chemicals in the environment.

The Environmental Protection Agency has acknowledged the need to consider the accumulation of risks from multiple environmental threats when evaluating the potential harm to human health, and it has even developed a framework to do so. However, it is difficult to implement because crucial information is often missing, difficult to obtain, or impossible to obtain in situations where people are being exposed to toxic chemicals. Even with advancements in mathematical modeling that can make it more feasible to estimate the cumulative risk from multiple chemical exposures, this approach can never perfectly replicate the entire, exact pattern of exposure that communities face, which means it can’t always accurately assess the potential for those exposures to harm human health.

Communities often struggle to understand the health impacts of all the chemicals they are exposed to, but that’s not simply because of a limitation in their knowledge or their data. There is a fundamental limitation in our ability to accurately calculate the health impacts of simultaneous exposure to multiple chemicals. Because exposure to multiple chemicals can have complex impacts on human health, the government should do more to protect communities from these exposures. Strategies like being more conservative in setting “safe” thresholds of chemical exposures, making industries accountable for demonstrating that their exposures aren’t harmful before they’re allowed to expose communities, and taking more decisive action after exposures occur would all help protect communities from the health threats of exposure to multiple chemicals.