copper sulfate monohydrate is an inorganic compound with the formula CuSO4. It is a blue solid when hydrated – that is, when water molecules are attached – and white when anhydrous, which means it does not hold any water. Hydrated copper sulfate has five water molecules attached to each copper sulfate molecule. This hydrate form is used for fungicides, while anhydrous copper sulfate is most often used as a pigment and in Fehling’s or Benedict’s solutions.

When combined with lime and water (called Bordeaux mixture), copper sulfate works as a protective fungicide during seed treatment before plants grow. It’s also used as a molluscicide, controlling slugs and snails that can damage crops and gardens. It’s also used to line drain or sewage pipes, where it prevents roots from growing inside and creating clogs.

Ingestion of copper sulfate is toxic to humans and animals. Symptoms include nausea, vomiting and diarrhea. Copper sulfate is also toxic to fish when it’s used in lakes or ponds, where it reduces the oxygen levels and causes excess debris.

The EPA hasn’t evaluated this chemical for carcinogenicity. However, long-term exposure to low levels of copper sulfate may cause liver and kidney damage. The sulfate is absorbed from the digestive tract and circulates in the bloodstream, where it collects in the tissues. It’s then excreted in feces. More research is needed to evaluate the effects of chronic exposure.