It's not clear whether mercury from the Seattle plants winds up concentrated in surrounding neighborhoods. One kind of mercury from smokestacks spreads into the atmosphere, while other kinds are more likely to come back to earth nearby.
There's no evidence that people in the area are at additional risk, Ash Grove Cement spokesman Scott Matter wrote in an e-mail response to questions.
"Operations at Ash Grove and other facilities are closely monitored by EPA and other regulatory agencies," he said.
State and local health and environmental agencies said they knew of no studies looking at the mercury from the Seattle cement plants. The amount of mercury coming from the plant isn't directly monitored by agencies. They rely on annual estimates from the companies.
Yesterday Blogging Georgetown wrote about the West Seattle Blog writing about this same issue.