Abnormal Development - Heavy Metals
The industrialization of the modern world has led to the proliferation in our environment of many different metal compounds. Some metals, such as zinc and iron are required in trace amounts for many biological functions. Other metals such as lead and mercury have had significant toxic effects on development.
There are historic examples of large scale disasters, for example the mercury poisoning of waterways in Japan (More? Mercury) Mercury poisoning (by methyl mercury) or Minamata disease had substantial neurological effects similar to Hunter Russell syndrome.
In addition to their direct toxic effects, the potential reduction in fetal growth and long-term effects should also be considered. Much of the basic research relies on studies in various animal models of development and we should also consider the ongoing development of new industrial products in the environment with unknown or untested effects upon development.
The specific effects of some metals are detailed in Material Safety and Data Sheets (MSDS) available from an chemical index page that relate to developmental abnormalities. These sheets are now generally required to be supplied along with the chemical purchased from a supplier and give a standardised description of the chemical, its physical properties, handling and health effects/toxicity. There are also several internet sites that have searchable databases of MSDS information. Note that handling chemical saftey may vary from country to country.
Some Recent Findings
|Heavy Metals Toxicity (Table: U.S. GEOLOGICAL SURVEY CIRCULAR 1133, 1995)|
In another recent study using the sea urchin embryo, Japanese researchers have identified a hierarchy of toxic effects from different heavy metals.
"Interactive toxic effects between heavy metals were investigated using a sea urchin (Anthocidaris crassispina) bioassay. An effluent from an abandoned mine showed significant inhibitory effects on embryo development as well as producing specific malformations. The effects on the embryos were reproduced by synthetic polluted seawater consisting of eight metals (manganese, lead, cadmium, nickel, zinc, chromium, iron, and copper) at the concentrations detected in the mine effluent. This indicated that the heavy metals were responsible for the effects observed. Five heavy metals were ranked in decreasing order of toxicity as follows: Cu > Zn > Pb > Fe > Mn. Among these, zinc and manganese could cause malformation of the embryos. From bioassay results using 27 combinations of heavy metals, 16 combinations including zinc could produce specific malformations, such as radialized, exo-gastrulal, and spaceship Apollo-like gastrulal embryos. Zinc was one of the elements responsible for causing malformations and its effects were intensified by the presence of the other metals, such as manganese, lead, iron, and copper." Naomasa Kobayashia and Hideo Okamurab.
Metal in Water
A major dilemma is the biological difficulty of clearing heavy metals and the subsequent accumulation of these metals in the food chain mainly from the hydrologic environment.
Lead in the environment is postnatally toxic and prenatally teratogenic. Lead exposure can occur in industrial and mining and can also be derived from leaded petrol, old lead piping, historic paints, and other environmental sources).
For children aged less than 6 years of age the CDC (USA) has defined an elevated blood lead level (BLL) as >10 µg/dL, but also indicated that evidence exists for subtle effects at lower levels. (Links: CDC - Lead Poisoning Prevention Program | Blood Lead Levels in Young Children - United States and Selected States 1996-1999)
- Lead crosses the placental barrier readily.
- Fetal blood levels are directly proportional to maternal levels.
- Lead poisoning affects virtually every system in the body, and often occurs with no distinctive symptoms.
- Lead in our diet is mainly found in osseous (bone) structures.
- Lead can damage a child's central nervous system, kidneys, and reproductive system and, at higher levels, can cause coma, convulsions, and death.
- Even low levels of lead are harmful and are associated with decreased intelligence, impaired neurobehavioral development, decreased stature and growth, and impaired hearing acuity.
- CDC has established a national surveillance system for children with elevated blood lead levels.
- CDC helped to initiate federal activities to reduce lead in gasoline, which brought about declines in average blood lead levels in the U.S. population. Data from the most recent National Health and Nutrition Examination Survey (NHANES) show that the percentage of U.S. children with elevated blood lead levels has dropped from 88.2% in the late 1970s to 4.4% in the early 1990s. (NHANES Chart)
- Interrelations of lead levels in bone, venous blood, and umbilical cord blood with exogenous lead exposure through maternal plasma lead in peripartum women
- Effect of breast milk lead on infant blood lead levels at 1 month of age
Used traditionally in the felting of hats, hence "mad hatters", a more recent example of mercury's toxicity was shown in Japan.
|Japan Minamata disease map|
Japan had industrial mercury poisoning of waterways by methyl mercury causing Minamata disease, which had substantial neurological effects similar to Hunter Russell syndrome. For more information on mercury the chemical, see Mercury MSDS. There has also been a movie available "Medical Study of Minamata Disease".
Australia - Food Standards Australia New Zealand (FSANZ)
"FSANZ’s Chief Scientist, Dr Marion Healy, said ‘Our investigations show that the level of mercury in most fish caught and sold in Australia is low."
"The Australian Dietary Guidelines advise eating one or two fish meals per week for good health. The good news is that FSANZ has found it is safe for all population groups to eat 2-3 serves per week of most types of fish. There are only a few types of fish, which FSANZ recommends limiting in the diet – these are billfish (swordfish / broadbill and marlin ), shark/flake, orange roughy and catfish." FSANZ updates advice on mercury in fish (Australia only) 18 March 2004 see also 2 June 2011.
Hexavalent chromium (CrVI) is used in more than 50 industries and is an important heavy metal pollutant. A recent study (2005) in monkeys (Macaca radiata) has demonstrated an effect on testicular spermatogenesis, possibly by inducing free radical toxicity. If these effects also occur in humans, then spermatazoa development could also be affected, the study further suggested a supplementation of antioxidant vitamins may be beneficial to the affected subjects.
(More? Related References)
Lithium (Li, atomic number 3) is a soft alkali metal found in the natural environment, in industrial products (lithium batteries, some glass and ceramic products) and also is used to treat people with bipolar disorder. Lithium used as a drug, in a salt form, acts on the central nervous system as an antimanic agent to treat episodes of mania (frenzied, abnormally excited mood) associated with bipolar disorders. Lithium has been associated with fetal cardiac teratogenicity possibly by affecting Wnt/beta-catenin signaling.
- Links: Abnormal Development - Drugs | MedlinePlus - Lithium | MedlinePlus - Lithium Toxicity | OTIS - Lithium and Pregnancy PDF
A therapeutic radioactive form of yttrium used in microspheres for the internal treatment of various liver cancers. As such it would be unlikely to be found in a human development situation.
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June 2010 "Heavy Metal Teratogen" All (744) Review (72) Free Full Text (86)
Search Pubmed: Heavy Metal Teratogen
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- Center for Disease Control and Prevention Screening Young Children for Lead Poisoning: Guidance for State and Local Public Health Officials | CDC - Blood Lead Levels United States, 1999-2002
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Cite this page: Hill, M.A. (2019, December 5) Embryology Abnormal Development - Heavy Metals. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Abnormal_Development_-_Heavy_Metals
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