The lipophilic capacity of OS made it accessible to different tissues and organs. However, The main effect was seen related to nervous system. effects could be acute or chronic depending on period of exposure and the concentration of the compounds. The efects are ranged from acute (as a result of short-term exposure) or chronic as a result of long term exposure. The effect also depends on the airborne concentration in the workplaces.The main effects as seen in epidemiological studies are.