 Biorecumulation, biorecumulation is the accumulation of substances, such as pesticides, or other chemicals in an organism. Biorecumulation occurs when an organism absorbs a substance at a rate faster than that at which the substance is lost by catabolism and excretion. Thus, the longer the biological half-life of a toxic substance, the greater the risk of chronic poisoning, even if environmental levels of the toxin are not very high. Biorecumulation, for example in fish, can be predicted by models. Hypotheses for molecular size cut-off criteria for use as biorecumulation potential indicators are not supported by data. Biotransformation can strongly modify biorecumulation of chemicals in an organism. Bioconcentration is a related but more specific term, referring to uptake and accumulation of a substance from water alone. By contrast, biorecumulation refers to uptake from all sources combined e.g. water, food, air, etc.