What does "reasonable certainty of no harm" mean anyway? [Safe Chemicals Act]

One of the areas of concern in the new Safe Chemicals Act of 2010 bill is the new "safety standard." The main chemical industry trade group said in its initial response that "the proposed decision-making standard may be 'legally and technically impossible to meet.'"

According to the Senate version of the bill, the standard is a "reasonable certainty of no harm," which is defined as:

‘‘(23) REASONABLE CERTAINTY OF NO HARM.—
The term ‘reasonable certainty of no harm’ means, in establishing whether a chemical substance or mixture meets the safety standard under this subchapter, that aggregate exposure and cumulative exposure of the general population or of any vulnerable population to the chemical substance or mixture presents a negligible risk of any adverse effect on the general population or a vulnerable population.

But if one looks at it closely there is a lot in that one paragraph.

Aggregate exposure: Presumably this would include exposures to a particular chemical or mixture from all sources. But how does one assess that based on the "minimum data set" that is specified in the bill? (more on the minimum data set in future pieces)

Cumulative exposure: So not single exposures but perhaps multiple exposures over time. This would be particularly relevant for chemicals that are persistent or bioaccumulate, and also for chemicals to which people get exposed to over and over.

General or vulnerable populations: So there would have to be specific ways to protect vulnerable populations, which would entail adding additional safety factors to whatever safety margin is assessed. Since children tend to be more sensitive and have less developed immune systems, special safety margins would be necessary to protect them.

Negligible risk: Okay, here is a key question that needs to be addressed. What does "negligible" mean? Some risk is always going to happen. We assume the acceptable risks of driving and flying and even eating new foods. So where is the line drawn for "negligible" when it comes to exposure to chemicals?

All of these pieces of the standard need still to be defined. The bill stipulates that the EPA "shall use the best available science when conducting an assessment," and goes on to say they "shall consider the most recent recommendations of the National Academy of Sciences on ways to better protect people, including pregnant women, infants, children and other vulnerable populations from harm by exposure to toxic substances when assessing such potential risks." This should give EPA the flexibility to accept, and request, studies that are currently still under development, such as those mentioned in the "Toxicity Testing for the 21st Century" report.

The bill also stipulates that an assessment "shall address health or environmental impacts including potential or demonstrated cancer and noncancer endpoints," so the potential is there to also address "new" issues such as endocrine disruption.

All of these will likely be discussed during this period of meetings and negotiations between law makers and industry and advocacy representatives.