What the Heck is Perchlorate?

With the problems with perchlorate in many areas of the United States that have been in the news and that many, if not all of you, have heard about, you may be wondering what this chemical is and why it’s a problem. So I thought I’d talk a little bit about that, as well as some rather peculiar relationships between perchlorate and another chemical a lot of people in the drinking water and waste water business work with every day – more on that later.
Perchlorate is the most highly oxygenated form of chlorine – a chlorine atom with 4 oxygen atoms attached (see chart below). Usually, the more oxygenated something is, the more unstable and reactive it is. But perchlorate is quite stable, although definitely reactive, and having a stable molecule that packs a lot of oxygen atoms and is normally found as a solid is what makes it so important in manufacturing. Of course, when it dissolves in water is when it’s a problem for many of us.

Perchlorate is valuable as a source of oxygen for combustion, which is why the solid rocket boosters of the space shuttle contain 350 metric tons of the stuff. That’s also why it’s widely used in road flares, fireworks, and other explosives, like the detonators that fill the airbags if your car is in an accident. When perchlorate gets into the groundwater or surface water and then into our drinking water, it can have serious health effects. Perchlorate is an endocrine disrupting compound (EDC) in that it affects the proper uptake of iodine by the thyroid gland, a part of the human endocrine system. Improper thyroid function can lead to osteoporosis, as well as problems with metabolism and body temperature regulation, among other things.
A related, but less highly oxygenated compound that is use every day in many drinking water systems to disinfect the water supply is hypochlorite, generally applied as sodium hypochlorite, a liquid, or calcium hypochlorite, a solid. Hypochlorite is a chlorine atom with one oxygen atom attached (see chart), and is an excellent disinfectant, ensuring that the water we drink is free of the harmful pathogens, such as cholera, that plague so many people in the world. But hypochlorite can change form and add oxygen atoms as it ages, changing into chlorite and chlorate, and eventually becoming perchlorate. That’s one reason it is recommended that hypochlorite is never stored for more than 30 days, because small amounts of perchlorate may be formed given the right conditions.