(The following is the first in a weekly series of 50 upcoming Tr-Ash Talk blogs discussing the dangers of coal ash. Earthjustice hopes that by December 2011, the third anniversary of the TVA coal ash spill, the EPA will release a coal ash rule establishing federally enforceable regulations ensuring the safe disposal of this toxic waste.)

Arsenic, one of the most potent poisons known to man, is found in coal ash. It is well documented that coal ash leaks dangerous quantities of arsenic to drinking water when dumped in unlined pits and ponds. In fact, in an EPA analysis the agency acknowledges that people living near unlined coal ash ponds can face as much as a one-in-50 chance of getting cancer from drinking water contaminated by arsenic. This risk is 2,000 times greater than the EPA’s goal for reducing cancer risk to one-in-100,000. Yet, four renowned arsenic experts found that this EPA risk assessment underestimates the risk of cancer from arsenic by a factor of over 17 times.

In a letter to EPA, medical toxicologist Dr. Michael Kosnett along with three senior scientists explain that the EPA relied on an outdated “cancer slope factor” (CSF) that is 17.3 times less than the updated CSF for arsenic. The scientists therefore recommend revision of the EPA’s risk estimates.

The outdated cancer slope factor used by the EPA, which was first published in 1988, is based on a study of skin cancer in a population ingesting arsenic in drinking water. Arsenic is now known to cause bladder and lung cancer, as well.  Outrageously, multiple offices of EPA and the broader scientific community acknowledge that the 1988 cancer slope factor greatly underestimates actual cancer risk.  In fact, in an EPA analysis dated April 2010, the agency explicitly states that the 1988 “skin cancer based risk assessments no longer represent the current state of the science for health risk assessment for arsenic.”

Clearly, the EPA must update its risk assessment for coal ash to reflect the greater danger posed by arsenic in ash.  Failure to use the best available science in its upcoming rulemaking on coal ash would be a fatal mistake – and an injustice to the thousands of communities living near coal ash dumps.