Bioaccumulation is the concentration of toxic substances by an organism over an extended period of time. This occurs in all species, and is magnified progressively up the food chain.
Toxic elements we consume in liquids and foods, breathe in from the air, or absorb through our skin are retained in the body for different durations, depending on their chemical properties. The amount of time it takes for the body to eliminate half of a specific substance is called its half-life.
Toxic heavy metals such as cadmium, mercury, and lead can accumulate over a lifetime and have long half-lives in different organs and tissues.
Cadmium is a toxic heavy metal that enters the body mostly through food consumption and tobacco smoke, as certain plants concentrate this heavy metal. Average cadmium absorption from food per day is around 1 µg, but those who smoke one pack of cigarettes per day (made from tobacco leaves) will take in an additional 1 to 3 µg. Although this amount may not seem like a lot, cadmium is slowly eliminated from the body with a blood half-life of 75-128 days and a body half-life of 7-16 years. Cadmium will primarily affect the kidneys, but also damages the nervous and cardiovascular systems, liver, lungs, pancreas, bones, and reproductive organs. High cadmium levels have been linked to cancers of the reproductive organs, including the breasts, prostate, and uterus.   Cadmium is believed to increase cancers of estrogen-sensitive tissues by acting as a metalloestrogen to activate estrogen-regulated genes.
Mercury is a well-known toxic heavy metal that is present in different forms including inorganic, organic, and elemental species. Inorganic mercury’s target organs are the gut and kidney, while elemental and organic mercury primarily accumulates in fatty tissue such as the brain. The half-life of elemental and inorganic mercury in blood is 40–60 days, while the half-life of organic mercury in blood is about 70 days.   Organic and elemental mercury can penetrate the blood-brain barrier and enter the brain where the elimination half-life of the heavy metal may exceed several years. Mercury’s toxicity is primarily through the creation of reactive oxygen species (ROS) which burn-down antioxidants such as glutathione, and react with selenium-containing enzymes involved in antioxidant actions (e.g., glutathione peroxidase) and thyroid hormone formation (thyroid deiodinases).
Lead is a neurotoxin that was present in paint and pipes until the 1970s and gas until the 1990s. Many houses built prior to the 1970s still have leaded paint and pipes, increasing exposure via food, water, and air in the home environment. Target organs of lead toxicity are the urinary, skeletal, immune, gastrointestinal, reproductive, cardiovascular, and nervous systems. The half-life of lead in blood is around 30 days, while in bones it is much longer at 20-30 years. Rapid breakdown of bone that occurs in some women at menopause can release a high level of lead that accumulated for years. 
What can you do to determine current heavy metal exposure?
ZRT now offers dried urine testing for three of the most prevalent toxic heavy metals (cadmium, mercury, and arsenic) in combination with the essential elements iodine and selenium. Currently we are developing a similar test for lead and other elements using whole blood, the best biomarker of lead exposure. Cadmium, mercury, and lead are three of the top ten most hazardous substances according to the Agency for Toxic Substances and Disease Registry’s (ATSDR) Priority List of Hazardous Substances, and along with arsenic make up the top four most hazardous heavy metals.
It is important to know if you have been bioaccumulating heavy metals, as this could help identify and eliminate their source and help curb current or future health problems associated with their bioaccumulation.
 Lewis GP, Coughlin LL, Jusko WJ, Hartz S. Contribution of cigarette smoking to cadmium accumulation in man. Lancet. 1972;1(7745):291-2.
 Järup L, Rogenfelt A, Elinder CG, Nogawa K, Kjellström T. Biological half-time of cadmium in the blood of workers after cessation of exposure. Scand J Work Environ Health. 1983;9(4):327-31.
 Nordberg GF. Historical perspectives on cadmium toxicology. Toxicol Appl Pharmacol. 2009;238(3):192-200.
 McElroy JA, Shafer MM, Trentham-Dietz A, Hampton JM, Newcomb PA. Cadmium exposure and breast cancer risk. J Natl Cancer Inst. 2006;98(12):869-73.
 Zeng X, Jin T, Jiang X, Kong Q, Ye T, Nordberg GF. Effects on the prostate of environmental cadmium exposure--a cross-sectional population study in China. Biometals. 2004;17(5):559-65.
 Akesson A, Julin B, Wolk A. Long-term dietary cadmium intake and postmenopausal endometrial cancer incidence: a population-based prospective cohort study. Cancer Res. 2008;68(15):6435-41.
 Kortenkamp A. Are cadmium and other heavy metal compounds acting as endocrine disrupters? Met Ions Life Sci. 2011;8:305-17.
 Park JD, Zheng W. Human exposure and health effects of inorganic and elemental mercury. J Prev Med Public Health. 2012;45(6):344-52.
 US Centers for Disease Control and Prevention (CDC). Third national report on human exposure to environmental chemicals. Atlanta: CDC; 2005. Available: www.cdc.gov/exposurereport/3rd/default.htm (accessed 2015 Aug 28).
 Agency for Toxic Substances and Disease Registry (ATSDR). Toxological profile for mercury. Washington (DC): ATSDR, Public Health Service, US Department of Health and Human Services; 1999. Available: www.atsdr.cdc.gov/toxprofiles/tp46.html (accessed 2014 Aug 28).
 Clarkson TW, Magos L, Myers GJ. The toxicology of mercury - current exposures and clinical manifestations. N Engl J Med 2003;349:1731-7.
 Petering HG, Tipper LB. Pharmacology and toxicology of heavy metals: mercury. Pharmacol Ther 1976;1:131–151.
 Cuvin-Aralar ML, Furness RW. Mercury and selenium interaction: a review. Ecotoxicol Environ Saf. 1991;21(3):348-64.
 ATSDR. 2007. Toxicological profile for lead. Atlanta, GA: US Department of Health and Human Services, Public Health Service, Agency for Toxic Substances and Disease Registry. p. 582.
 WHO. Lead. Environmental Health Criteria, vol. 165. Geneva: World Health Organization, 1995.
 Potula V, Kaye W. The impact of menopause and lifestyle factors on blood and bone lead levels among female former smelter workers: the Bunker Hill Study. Am J Ind Med. 2006;49(3):143-52.