Glossary of Terms
Perchlorate - A salt-like substance made up of chlorine and oxygen. It is found in nature and it can be man-made. It is widely used today by the military, NASA and the commercial space industry as an ingredient in solid rocket fuels and explosives. It's also used in safety flares, fireworks, auto air bag inflators, lubricating oils and aluminum refining. Perchlorate also is naturally present in some fertilizers, typically used in organic farming. In addition, perchlorate has a long history of use as a medicine for certain thyroid gland disorders.
Parts per billion (ppb) - A measurement expression used to describe the concentration of a substance in air, water or soil. In water, one part per billion is roughly equal to one half teaspoon of water in an Olympic-sized pool (660,000 gallons).
Thyroid gland - A gland at the base of the neck that produces various hormones, which the body uses for normal growth, development and metabolism.
Iodide - A substance (a particular state of iodine) the thyroid gland uses in the manufacture of hormones. Most Americans eat a diet with at least twice the recommended daily allowance of iodide, much of which comes from common table salt (i.e., "iodized" salt). The thyroid gland keeps a substantial reserve of iodide to compensate for times when the amount of iodide in the body fluctuates.
Iodide Uptake - The process by which the thyroid gland absorbs iodide from the blood stream.
"No Effect" Level - The dosage below which a compound has no measurable effect on human health.
Action Level - The level set by a regulatory agency at which water system operators are required to notify local government agencies. The current Action Level for perchlorate in California (Set by Department of Health Services) is 4 ppb. Federal EPA advises 4-18 ppb and other states may have other values set.
Public Health Goal (PHG) - A level set by a regulatory agency to be protective of human health. This level may be overly protective if there is inadequate understanding of the contaminant in question, however PHG values are set very conservatively by using uncertainty factors to always be protective even if the science on the contaminant is not completely understood. The amount of perchlorate in drinking water that the California Environmental Protection Agency (Cal/EPA) considers "safe" if consumed every day. This goal must be set before a state standard for perchlorate in drinking water can be established (see Maximum Contaminant Level).
Reference Dose (RfD) - The amount of perchlorate in drinking water that the U.S. Environmental Protection Agency (U.S. EPA) considers "safe" if consumed every day for a lifetime of exposure. This is essentially a goal the U.S. EPA sets before establishing a national drinking water standard (see Maximum Contaminant Level).
Maximum Contaminant Level (MCL) - This is a term for both the national and State drinking water standards covering any regulated contaminant. The Maximum Contaminant Level must be as close to the Reference Dose (national) or Public Health Goal (California) as possible but must take into account several other factors, including the economic and technological feasibility of meeting that standard and the accuracy and limits of detection of analysis methodology.
Substances Commonly Found in Food
Nitrates - Salt-like substances composed of nitrogen and oxygen that 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. Nitrates much like perchlorate can occur naturally or be manufactured. Nitrates are an essential component of fertilizers.
Thiocyanate - A salt-like substance composed of sulfur, carbon, and nitrogen that 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.
Biological Treatment - A process that uses microorganisms to break down perchlorate into other components. In this process, water is treated in a tank, using microorganisms, or in the ground, using native organisms. Small amounts of carbon sources, such as alcohol or corn syrup, are also placed in the water. The microorganisms then convert the perchlorate and carbon into two primary components: carbon dioxide and chloride.
Ion Exchange - A technology that uses a resin to absorb perchlorate and remove it from water. The water with perchlorate or other contaminants is pumped through a system containing resin "beds," which are two to six feet in diameter and one to six feet high. Negatively charged perchlorate is captured on the positively charged resin, releasing harmless chloride (a component of table salt) in its place and affording the opportunity for safe and appropriate disposal.