The Perchlorate Index: Putting the Facts in Perspective

The following table is meant to offer some perspective on how much perchlorate would need to be present in drinking water to compare with the amounts found in thyroid medicine that contains perchlorate, as well as the amounts of naturally occurring compounds found in everyday foods. These compounds (thiocyanates1 and nitrates2) have essentially the same effect on the thyroid as perchlorate, while still being part of a healthy and safe diet. This table also provides a snapshot of what the U.S. Environmental Protection Agency (U.S EPA) and the State of California have proposed for a drinking water standard for perchlorate.

Quantities are provided in terms of "parts per billion" (ppb). In simplest terms, one part per billion is roughly equal to one half teaspoon of water in an Olympic sized pool (660,000 gallons).

Please note that these figures do not represent levels of perchlorate actually found in the environment.

Where perchlorate has been detected in water supplies, it is typically found at levels below 50 ppb, well within the levels that research has shown have no measurable health effects.

 

Comparative Levels of Perchlorate Exposure Perchlorate ppb equivalent*
Level of perchlorate in medicine used to treat thyroid problems (no longer used in the U.S. but still prescribed in Europe and elsewhere) 70,000-300,000 ppb
Level of perchlorate required daily for a period of years to cause adverse health effects in people, based on recent human studies 20,000 ppb or more*
Level of perchlorate intake equivalent to one 3.5 ounce serving of cauliflower or Brussels sprouts (based on the effect on the thyroid of thiocyanates present in the vegetables) 8,000 ppb
Level of perchlorate in drinking water below which no measurable effects occur in humans 200 ppb daily
Level of perchlorate intake equivalent to the current federal drinking water standard for nitrate 90 ppb
Level of perchlorate equivalent to one 3.5 ounce serving of broccoli (based on the effect on the thyroid of nitrates present in the vegetable) 100 ppb
Level of perchlorate equivalent to drinking an 8 oz. glass of milk (based on thiocyanate in the milk) 16-80 ppb
Proposed EPA Reference Dose – or "safe" level – for perchlorate in drinking water in 1998 that was considered by a scientific and medical peer review panel to be overly strict 32 ppb
California's level at which water utilities must inform the local government of perchlorate's presence in water 4 ppb
California's proposed Public Health Goal – or "safe" level – for perchlorate in drinking water (currently the subject of controversy and is now the subject of a peer review by a panel of scientists being convened by the University of California.) 2-6 ppb
U.S. EPA's recently proposed Reference Dose – "safe" exposure level – for perchlorate in drinking water 1 ppb

* All conversions based on concentration of perchlorate in a daily amount of drinking water (about 2 quarts)

1 Thiocyanate, a salt-like substance, is found in foods such as milk, cabbage, broccoli, cauliflower and Brussels sprouts. It has essentially the same effect on the thyroid as perchlorate, in that it can block the uptake of iodide.

2 Nitrates – salt-like substances composed of nitrogen and oxygen – have essentially the same effect on the thyroid as perchlorate, in that they can block the uptake of iodide. Nitrates occur at some level in most drinking water, as well as in processed meats and garden vegetables like carrots and celery.