Latency Period The period of time between an exposure and onset of toxicity. Lipid A large and diverse group of organic compounds that contain primarily carbon and hydrogen atoms with a lesser amount of oxygen.  Most lipids are insoluble in water but will readily dissolve in other lipids and in organic solvents. Lipid Soluble Capable of being dissolved in fat or in solvents that dissolve fat.  Usually non-ionized compounds. Lipophilic Having an affinity for fats or lipids.  A substance that is lipophilic has high lipid solubility and can penetrate cell membranes by passive diffusion. Lipophilicity A term used to describe the ability of a substance to dissolve in, or associate with, fat and therefore living tissue.  This usually applies to substances that are non-ionized or non-polar or have a non-polar portion.  High lipid solubility usually implies low water solubility.