Liquid paints have solvents that contain pollutants called volatile organic compounds(VOCs).  VOCs easily evaporate into a form of invisible vapor that can be inhaled by humans.  VOCs can cause healths problems from throat irritation, headaches, and dizziness all the way to increased chance of cancer, liver damage, and central nervous system damage.  These compounds not only pose a health risk to people but are also a danger to the environment.  It contaminates the water and is toxic to lifeforms in the ecosystem, and polutes the atmosphere and is a contributing factor to the greenhouse effect.