Copper sulfate is an inorganic compound that combines sulfur with copper. It can kill bacteria, algae, roots, plants, snails, and fungi. The toxicity of copper sulfate depends on the copper content. Copper is an essential mineral. It can be found in the environment, foods, and water. Copper sulfate has been registered for use in pesticide products in the United States since 1956.

Products containing copper sulfate can be liquids, dusts, or crystals. There are several dozen active products containing copper sulfate on the market in the United States. Some of these have been approved for use in organic agriculture.

Copper in copper sulfate binds to proteins in fungi and algae. This damages the cells causing them to leak and die. In snails, copper disrupts the normal function of the skin cells and enzymes.

You can be exposed if you are applying copper sulfate and you get it on your skin, breathe it in, or accidentally eat or drink a product. This can also happen if you get some on your hands and eat or smoke without washing your hands first. You can limit your exposure and reduce risk by following all label instructions carefully.

Copper is an essential element and it is required to support proper health. The human body adjusts its internal environment to maintain copper equilibrium. Copper sulfate is absorbed into the body if eaten or inhaled. It then rapidly enters the bloodstream. Once inside, copper moves throughout the body. It then binds to proteins and enters different organs.

Excess copper is excreted and not often stored in the body. Copper can be collected in the liver but it can also be found in stomach secretions, bone, brain, hair, heart, intestine, kidneys, muscle, nails, skin, and spleen. Copper is mainly excreted in the feces. Small amounts can also be eliminated in hair and nails. In one study, researchers found it takes 13 to 33 days for half of a large copper dose to be eliminated from the body.

Whether copper sulfate causes cancer in animals is uncertain. The U.S. Environmental Protection Agency (U.S. EPA) has not published a cancer rating for copper sulfate. This is due to a lack of evidence linking copper or copper salts to cancer development in animals that can normally regulate copper in their bodies.

One study looked at long-term work-related exposures to copper sulfate. They found an increased risk of kidney cancer. Another study found that decreasing copper can inhibit cancer growth. Animal studies have provided conflicting results.

Studies in humans of long-term non-cancer effects to copper sulfate were not identified. However, Wilson's disease may provide insight into potential health effects over long periods of time. Wilson's disease is a rare genetic disorder in which the body retains too much copper. The effects include infertility, higher miscarriage rates, loss of menses and hormonal imbalances in women. In men, the testes don't function properly. Exposure to copper sulfate does not cause Wilson’s disease.

In one study, mice were fed very large amounts of copper sulfate before and during pregnancy. Some baby mice died during gestation or did not develop normally.

Children may be especially sensitive to pesticides compared to adults. However, there are currently no data to conclude that children have increased sensitivity specifically to copper sulfate.

The U.S. EPA considers copper to be practically nontoxic to bees and moderately toxic to birds. Studies with several aquatic species have found copper to be highly to very highly toxic to fish and aquatic life. Trout, koi and juvenile fish of several species are known to be particularly sensitive to copper.

Fish kills have been reported after copper sulfate applications for algae control in ponds and lakes. Oxygen depletion and increased debris have been cited as the cause of most fish deaths. This is sometimes due to the sudden death and decay of algae and plants after an application. Even small concentrations of copper can be harmful to fish and water organisms. Always follow label instructions to protect the environment.