Environmental contaminants are chemicals that enter the environment through natural processes or human activities. Some are man-made and very stable, so they persist without breaking down and can build up in the food chain. Others occur naturally but may circulate at higher levels due to industrial activity. Contaminants found in food include metals, ionic compounds (like perchlorate), and persistent organic pollutants (POPs), which remain in the environment for long periods. Banned substances like PCBs still linger, while newer ones such as brominated flame retardants are also being detected.