Pentachlorophenol is a toxic pesticide and wood preservative. It enters water from industrial runoff and treated wood products. Most uses were banned in 1987 due to health risks.

Pentachlorophenol (PCP) is a synthetic chemical widely used as a pesticide and wood preservative until 1987. It can contaminate water through industrial discharge and leaching from treated wood products. PCP is persistent in the environment and can accumulate in aquatic organisms. The EPA measures PCP in parts per billion (ppb) and has set a maximum contaminant level for drinking water. Despite its ban for most uses, PCP may still be present in older treated wood and contaminated sites.