Bioaccumulation is the steady accumulation of substances, such as pesticides or other chemicals, in an organism. Bioaccumulation occurs when an organism intakes a substance at a faster rate than that at which the substance is removed from body through catabolism and excretion. Thus, the longer the biological half-life of a toxin, the greater the risk of chronic poisoning, even if environmental levels of the toxin are not very high. Biotransformation can greatly modify bioaccumulation of chemicals in an organism. Bioaccumulation refers to uptake from all sources combined (e.g. water, food, air, etc.), while bioconcentration refers to uptake and accumulation of a substance from water alone