California’s New Perchlorate MCL

The State of California has now set a drinking water standard, formally known as a maximum contaminant level (MCL), for perchlorate of six parts per billion (ppb). This new standard is far below what a National Academy of Science (NAS) panel determined to be necessary.

NAS found that levels as high as 245 ppb had no effect, but took an extra precaution to suggest that one-tenth of that amount, 24.5 ppb, would be a safe amount for even the most sensitive subpopulations, including newborns, pregnant women and their fetuses.