The environment may be affected: chemicals can pollute the air we breathe, the water we drink and the food we eat; they can also affect forests and lakes, destroying wildlife and degrading ecosystems.
Human exposure may occur directly through skin or eye contact, inhalation or ingestion of hazardous chemicals.
The harmful effects of chemical substances depend on the toxicity of the chemical and exposure to it. Toxicity is a property of the chemical substance, while exposure depends on the way the chemical is used. The level of exposure depends on the concentration of the hazardous chemical and the period of contact time. Many substances do not give any warning by odour, even though they may be present at dangerous concentrations in the air.
The effects of chemicals on humans may be acute: after brief exposure an immediate effect may be experienced. Chronic effects usually require repeated exposure and involve a delay between the first exposure and the appearance of adverse health effects. A substance may have both acute and chronic effects. Both acute and chronic conditions can result in permanent injury. Exposure to solvents may cause contact dermatitis, headache or nausea and these effects could be both acute and temporary.
Consequences of chemical accidents are not limited to direct human exposure, death or injury but also include environmental contamination requiring decontamination and recovery. In the case of severe accidents (like Bhopal in 1984, Enschede in 2000 or Toulouse in 2001) with thousands of victims, there are also psychological, economic and social consequences to be taken into account.