Two weeks ago contractors working for the U.S. Environmental Protection Agency (EPA) accidentally breached a containment wall at Colorado’s Gold King mine, spilling three million gallons of toxic waste that turned the Animas River mustard-yellow. People who live near the river in Colorado, New Mexico, Utah, and the Navajo Nation are still asking questions. Are heavy metals buried at the bottom of the river? Will they kill insects, fish, and birds? Is it safe to swim or drink the water?
Unit 6 of The Habitable Planet, “Risk, Exposure and Health,” explains how scientists assess risks to human health when people are exposed to harmful substances. Many of these risks happen at low levels every day: we inhale air pollutants, or consume traces of pesticides on our food. Other exposures, like the Animas River spill, happen suddenly and then dwindle away, but may leave residues behind.
Risk assessment is a multi-step process that asks a series of questions:
- Is there a hazard – i.e., have people been exposed to something that we know is harmful?
- How much of the harmful substance(s) is needed to cause harm?
- What actual exposure has happened? How much of the harmful substance(s) have people come in contact with? By what pathway (for example, drinking water, inhalation or skin contact), and for how long?
- Based on what we know about the substance(s) and the exposure that has occurred, or is likely to occur, what harmful results do we expect?
EPA is collecting water samples from the Animas River and from shallow drinking water wells near the river to test for unsafe levels of 24 types of heavy metals which are common contaminants in drainage from old mines. Some heavy metals are serious health threats: lead causes neurological damage, cadmium can harm kidneys, and arsenic exposure can increase the risk of several types of cancer.
As the plume of mine waste flows south into Lake Powell in Arizona, Colorado and New Mexico have lifted restrictions on using river water, although they have warned residents not to drink untreated water. It may take years to measure long-term impacts on soils, insects, fish, wildlife, and human health. Scientists are just starting to report and assemble findings about how the BP spill in 2010 may have affected ecosystems in the Gulf of Mexico, and many questions still surround that much larger research effort.
What would your students want to know if a toxic spill happened in their neighborhoods? (Has anything like the Animas spill happened in your area?) Who would they trust to measure the impacts? What kinds of tests would make them feel safe? There’s no single right answer to questions like this, but events like the Animas spill can launch thoughtful debates about risk and exposure in everyday life.