Impacts on human health
Hazardous chemicals enter our bodies via the air we breathe, through food and drinking water, or by direct contact with the skin.
Chemicals may cause acute poisoning or burns, chronic health problems, or have long-term effects such as cancer, fetal damage and reduced fertility. It is easiest to quantify acute effects, because the injury appears so rapidly after exposure. The products that cause most of the poisonings and chemical burns among ordinary consumers are household chemicals, tobacco and pesticides.
In general, people are more likely to be repeatedly affected by small doses of chemicals than to suffer acute injury. We know less about the damage caused by long-term exposure than we know about the acute effects of high single doses. This is because it is difficult to prove the connection between exposure and effects when the effects may take years to appear. The fact that everyone is exposed to a number of different substances, and that we know too little about their combined effects, complicate the picture further. So also do factors such as heredity and lifestyle.
Impacts on the environment
Chemicals can cause higher mortality, slow down growth or disturb reproductive processes in plants, animals and micro organisms. Many hazardous substances are persistent, meaning that they break down very slowly in the environment. They therefore enter food chains, being transferred from one species to another and becoming more concentrated in the process.
There is a serious risk that environmental concentrations of some pollutants may reach levels that make it difficult to repair the damage before their effects are detected. And the damage does not stop here. In mammals, hazardous chemicals are transferred from mother to offspring through the placenta, or to infants through the mother's milk. Future generations may suffer the impacts of pollution if chemicals damage the genetic material in sperm and egg cells.