From a Sierra Club insider:
With junk science, it is easy to scare people. There are many things that are bad for us that are present at low levels in the environment -- for example, mercury, lead, radiation, or tobacco smoke. The junk science approach to trace toxins is to claim that if a high level of the bad thing would cause X people to get sick, then a level 10,000 times smaller must cause 1/10,000 as many people to get sick. Given 300 million people in the country, this math can give you thousands of people getting sick from low levels of mercury, lead, radiation, or secondhand tobacco smoke. This approach is known as the linear no threshold hypothesis.
So considering this approach, don't you think this toxic substance should be banned or controlled?