1,4-dichlorobenzene (1,4-DCB) – also known as p-dichlorobenzene (p-DCB) – is a colorless solid chemical that readily evaporates into the air. 1,4-DCB does not occur in nature, and it is often produced for use in deodorants or disinfectants because it has a strong odor that humans can smell at very low concentrations. It is commonly used in household products like mothballs and deodorizing sprays. It also has industrial uses as a pesticide ingredient and a precursor to commercial dyes. 1,4-DCB can enter the environment through its household uses, pesticides, and industrial waste disposal. 1,4-DCB mostly enters the environment as a vapor, and people are likely to inhale it in homes and buildings where it is used. Solid 1,4-DCB can also bind to soil and remain there for long periods of time, but people are less likely to be exposed to it in this way.

Inhaling high concentrations of 1,4-DCB can cause irritation or burning sensations in the eyes and nose. It can also cause coughing, nausea, difficulty breathing, dizziness, headaches, and liver dysfunction. Touching products that contain 1,4-DCB can also cause burning sensations on the skin. In studies of laboratory animals, 1,4-DCB exposure caused liver, kidney, and blood defects as well as liver cancer. The US Department of Health and Human Services and the International Agency for Research on Cancer both classify it as being reasonably anticipated to cause cancer.

Because of the danger to human health, the Environmental Protection Agency has set a maximum 1,4-DCB concentration that can be present in drinking water without observing adverse health effects. The European Union has gone even further, banning use of 1,4-DCB in mothballs and air fresheners because of its potential to cause cancer. Similar regulation in the US could protect more people from the health risks of 1,4-DCB exposure.

Barium is a silver-colored metal which is found in the earth in compounds with other elements. Many barium compounds have industrial uses: barium sulfate is used as a drilling lubricant by the oil and gas industries to facilitate drilling through rock; barium carbonate is a rat poison; and barium oxide is used in the production of electronics and glass. Barium can enter the air through the production of barium-containing compounds and the improper disposal of barium-containing waste. It can then enter the soil and water. Barium compounds that do not dissolve in water can persist in the soil and water for a long time.

People are most likely to be exposed to barium by drinking contaminated water. Barium compounds that do not dissolve in water – like barium sulfate and barium carbonate – are not known to be harmful to human health. However, barium compounds that do dissolve in water – like barium chloride and barium hydroxide – can harm human health because they release barium ions into the body. Barium ions interfere with the normal electrical impulses generated in the brain, muscles, and heart. Exposure can cause gastrointestinal dysfunction such as vomiting, diarrhea, and abdominal cramps. It can also cause anxiety, disorientation, difficulty breathing, decreased blood pressure, numbness, muscle weakness, and paralysis. The eyes, immune system, respiratory system, and skin can also be damaged by barium exposure. The Environmental Protection Agency (EPA) has set a limit on how much barium can safely be in drinking water, but almost 800 Superfund sites are known to have barium contamination, suggesting that there may be potential for barium exposure in some communities.