Octanol/Water Partition Coefficient The ratio of the amount of a substance that will dissolve in octanol versus the amount that will dissolve in water.  The higher the octanol/water partition coefficient the greater the tendency of substance to be stored in fatty tissues. Odds Ratio (O/R) A statistical calculation in a case-control study involving the ratio of risk of an exposed group to that of an unexposed group.  An O/R=2 means that the exposed group has twice the risk of the non-exposed group. One Hit Model This is the most conservative quantitative cancer assessment model.  It assumes that a single molecular event can induce a cell transformation which leads to cancer. Organogenesis The period of fetal development when the embryo differentiates and specific organs develop. OSHA Occupational Safety and Health Administration.  The component of the Department of Labor responsible for assuring safe working conditions. Oxidation A change in a chemical characterized by the loss of electrons.