Heavy metal poisoning happens when your body's soft tissues absorb an excessive amount of a certain metal. Mercury and lead are the most frequent metals that the human body may absorb in hazardous proportions. Lead. Lead is a heavy metal that can be found in many things including old paint and soil. Lead enters the body through ingestion (eating) of contaminated food, water, or inhalation of lead dust. In adults, the main target for lead is the brain and kidneys. Children are also at risk because their bodies are still developing and they use up lead faster than others. The only way to know for sure if you have been exposed to lead is with blood tests. Heavy metals such as mercury and lead can stay in the body for a long time before any symptoms appear. However, if you are able to identify the source of your exposure, then you can take action to protect yourself by removing yourself from that situation. Mercury. Like lead, mercury is a heavy metal that can be found in many things including old thermometers and dental fillings. If you eat fish regularly, you may be getting some mercury into your body. That's because fish is one of the only sources of protein that contains enough mercury to be harmful. Even though small amounts of mercury are needed by our bodies, too much can be bad for you. People who work with mercury on a regular basis are at increased risk for developing problems themselves.