Cadmium (Cd)

Courtney GagnonBiol 464 PresentationMay 5, 2011

Discovered in 1817 in Germany as an impurity in zinc carbonate

Atomic number: 48 Melting point: 609.93° F Chemically similar to zinc and mercury Natural Abundances: Earth’s crust: 15x10-6 %

Oceans: 5x10-9 % Humans: 7x10-5 %

Structure and Properties

Semiconductor as cadmium sulfide that becomes more conductive when exposed to light

Classic paint pigment popularly used by impressionist painters like Monet

Anticorrosive plating (most popular use) Thin foil used in nuclear research facilities for use

as radiation shielding. Ni-Cd batteries and Li-Cd batteries Present in P fertilizers used for crop production Solar panels

Uses of Cadmium

Runoff during storm events◦ Rain is slightly acidic from dissolved CO2 and leeches

cadmium from metals◦ Washed from crops treated with Cd-P fertilizers

Release of wastewaters generated by anthropogenic sources

Settlement of air particles on water that are polluted by cigarette smoke, road dust, burning plastics and wood.

Accumulates in mud and microalgae

Mode of Entry into the Aquatic Environment

Cadmium does not react with water Instead, it accumulates over time in bottom

sediments Natural Radioisotopes

◦ 113Cd: Half life = 7.7x1015 years

◦ 116Cd: Half life = 2.9x1019 years

Cadmium and Water

Contamination starts at the level of microalgae , which bioaccumulates and biomagnifies at higher trophic levels

The surface of microalgal cells is negatively charged and provides binding sites for metal cations

Algae bioabsorb and bioconcentrate heavy metals from the aquatic environment:

Cd2+ > Hg2+ > Cr6+ > Pb2+ > As5+

Cd concentrations were shown to cause 90% cell inhibition of microalgae at 5 mg/L. Lower concentrations caused a slow decline in biomass

Cadmium concentration in fish (also meat and fruit): 0.005- 0.01 μg/g of dry weight. Shellfish contain higher concentrations.

Dissolution of Cd-P in fertilizers increases with decreasing soil pH

Toxicity to Aquatic Life

Half life in blood 75-128 days (fast component) to 7-16 years (slow component), in bone is 30 years, and in the kidney is 6-38 years.

Accumulates in humans by contaminated food, coffee, and water, inhalation of contaminated air and cigarette smoke (20 μg/pack)

The EPA calculated an inhalation unit risk estimate of 1.8x10-3 (μg/m3 )

The estimated lowest observed adverse effect level for a single oral dose is 19.5 μg/lb body weight

Cadmium, once in the body, stays, probably for life, in the kidneys, the liver, bone and the blood vessels.

As little as 2 μg daily absorbed and retained results in a body burden of 30 mg in 40 years

Chronic intake of Cd over a long period of time most commonly cause kidney damage and weak bones

Toxic effects noted

The lungs and gastrointestinal tract are the two main routes of Cd to cause toxicity. Skin does not easily absorb cadmium.

Cd is absorbed from the gastrointestinal tract by a transporter, DMT1 in the duodenum.

Cd absorbed into circulation is taken up by the liver and bound to metallothionein (MT) where it is filtered in the kidney and almost completely reabsorbed in renal tubules.

Only a small amount is absorbed into the body from the gut 10%, most of which is excreted in the urine.

About half of Cd inhaled is retained, which is absorbed from the lungs.

Mode of entry into organisms

The kidney is the main organ affected by chronic Cd exposure and toxicity

Cd2+ induces an increase in lipid peroxidation which can damage organs such as the liver, kidney, and testis.

Cd directly inhibits Na-K channels

Mechanisms of cadmium toxicity

Cd-MT is degraded in endosomes and lysosomes, which releases Cd2+

into the cytosol. Cd2+

accumulates in the mitochondria and inhibits the respiratory chain (by electron transfer).

Results in production of reactive oxygen species (ROS) and mitochondrial disruption with the release of cytochrome c, causing cell death by apoptosis and necrosis

Classified as a carcinogen, but it is hard to determine if due to high Cd concentrations, or from other toxins present in cigarettes

Toxic effects of Cd2+

Cd can induce autoantibodies to MT, which may interfere with Cd detoxification.

Plants and algaes use the phytohormone, gibberellic acid (GA3 ) to metabolize Cd; however, it does not withstand strong toxic dosage (10-4 M).

Exposure significantly decreases the cytochrome P450 side chain cleavage complex which catalyzes the biosynthesis of steroids

Cd2+ induces oxidative stress by binding to sulfyhydryl groups of proteins and by depleting glutathione.

Lipoic acid and selenium have been proven to reverse damage caused by Cd2+ on antioxidant defense mechanisms

Biochemical metabolism and breakdown

Cd exposure up-regulates MT production in the liver as a protective response, but once the MT-producing capacity is exhausted, tubular cells are damaged

Urinary cadmium excretion is slow; however, it constitutes the major mechanism of elimination

Hair has proven to be a vehicle of detoxification of substances from the human body because metal cations bind to the sulphur of keratin. Concentrations were up to 10 fold higher than levels found in blood and urine samples

Defense strategies available for detoxification

Process of Cd detoxification

Bharavi, K., Reddy, A.G., Rao, G.S., Kumar, P.R., Prasadini, P.P. 2011. Prevention of cadmium bioaccumulation by herbal adaptogens. Indian J. Pharmacol. 43: 45-49. Available from: http://www.ijp-online.com/text.asp?2011/43/1/45/75669

Falkowshka, M., Pietryczuk, A., Piotrowska, A., Bajguz, A., Grygoruk, A., Czerpak, R. 2011. The effect of gibberellic acid (GA3 ) on growth, metal biosorption and metabolism of the green algae Chlorella vulgaris (Chlorophyceae) Beijerinck exposed to cadmium and lead stress. Polish J. of Environ. Stud. 20(1): 53-59.

Gel, F., Hernandez, A.F., Marquez, C., Femia, P., Olmedo, P., Lopez-Guarnido, O., Pla, A. 2011. Biomonitorization of cadmium, chromium, manganese, nickel and lead in whole blood, urine, axillary hair and saliva in an occupationally exposed population. Science of the Total Environment 409: 1172-1180.

Johri, N., and Jacquillet, G., Heavy metal poisoning: the effects of cadmium on the kidney. Biometals 23: 783-792.

Monteiro, C.M., Fonseca, S.C., Castro, P.M.L., Melcata, F.X. 2011. Toxicity of cadmium and zinc on two microalgae, Scenedesmus obliquus and Desmodesmus pleiomorphus, from Northern Portugal. J. Appl. Phycol 23: 97-103.

Schroeder, M.D., Henry. 1974. The Poisons Around Us, Toxic metals in food, air and water. Found on: www.ithyroid.com

Illinois Dept. of Public Health www.idph.state.il.us/cancer/factsheets.cadmium.htm

References