Thallium (Tl) Biol 564 Marine Toxicology Chia Lin
Physical and Chemical Properties l l l l Atomic number 81 MW = 204. 383 g/mol Hexagonal crystal structure 2 oxidation states, Tl+ (forms most stable compounds) and Tl 3+ (resembles Al 3+, high oxidizing property) 25 isotopes (179 -210 amu) Poor metal l Relatively lower BP and MP than transitional metals l Higher electronegativity l Softer/malleable Exhibits silver/gray in air Soon develops to blue-gray (resembles Pb) when left in air l Oxides build up http: //images. google. com/imgres? imgurl=http: //z. about. com/d/chemistry/1/0/k/Q/thallium. jpg&imgrefurl=http: //chemistry. about. com/od/periodictableelements/ ig/Element-Photo-Gallery. -98/Thallium. htm&h=222&w=197&sz=7&hl=en&start=10&um=1&tbnid=z. Kgn. NAy. LRq. Cgt. M: &tbnh=107&tbnw=95&prev=/images%3 Fq%3 Dthallium%26 ndsp% 3 D 20%26 um%3 D 1%26 hl%3 Den%26 client%3 Dfirefox-a%26 rls%3 Dorg. mozilla: en-US: official%26 sa%3 DN
Use, Application & Prod History l l l first isolated by Crookes in 1861 Occurs naturally in the minerals crookesite, lorandite, hutchinsonite and pyrites (Fe. S 2) obtained as a by-product in the production of H 2 SO 4 l l l Tl (or thallous salts) is used: l l l by roasting of pyrite by smelting of Pb and Zn ores in the electronics & pharmaceutical industries; in optical lenses manufacturing; in infrared detectors; in roden poisons & insecticides Elemental Tl not toxic Univalent, Tl (l) and trivalent, Tl (III) salts highly toxic l l Greater toxicity than Pb, Cd, Cu, Hg, Zn in mammals Prohibited in 1975 in the U. S. and many countries
Mode of Entry to Aquatic Env l A natural constituent in the Earth’s crust (0. 7 mg/kg) l l l rare, but widely distributed; present nearly in all environmental media Associates with K minerals in clays, soils and granites (not commercially recoverable) Major commercial Tl found in Cu, Zn, Pb & sulfide ores Low concentration in seawater (constant, 10 -15 ng/L), in unpolluted (5 -10 ng/L) and in polluted freshwater (20 -50 ng/L) Present in soils l l Sludge from waste water treatment K fertilizers
Reactivity with H 2 O Speciation & Half-life l l l l l Forms thallium hydroxide in the present of H 2 O Soluble enough to be toxic to organisms Stable isotopes: 203 Tl (29. 524 %) and 205 Tl (70. 476 %) Most stable radioisotope: 204 Tl l Half life = 3. 78 years Biological half-life = 3 -8 days Tl(I) forms compounds with halogen, oxygen, and sulfur ligands l similar chemical properties to those of the alkali metal cations Tl(III) more toxic than Tl(I) The 48 -h LC 50 values (Daphnia magna) l Tl(III)NO 3 - = 24 μg/L l Tl(III)Cl = 61 μg/L l Tl(III)CH 3 COO = 203 μg/L aquatic toxicity not affected by water hardness or humic acid concentration
Toxicity to aquatic life l l l High contents of Tl in surface water Known to kill fish slowly at 1 -60 ppm Lethal to aquatic insects and invertebrates at 2 -4 ppm Lethal to tadpoles at 0. 4 ppm Affect algae at 0. 1 ppm In aquatic environments, Tl 3+ : l l ~50, 000 fold more toxic than Tl+ to the unicellular chlorophyte ~34, 000 fold more toxic than Cd ions in aquatic environments
Toxic effects l l Affects sexual behaviors and reproductive organs in mammals Causes damage and changes in the mitochondrial system in neurons in animals Suspected human carcinogen Major symptoms from acute (ingest large amounts over a short time) Tl poisoning include: l l Vomiting, diarrhea, hair loss (temporary) Nervous system, lungs, heart, liver, kidneys death Major symptoms from chronic Tl poisoning include: l l Anorexia, headache, pains in abdomen, upper arms, thighs and in all over the body Blindness and death in extreme cases
Mode of entry into organisms l l Water, air (inhalation) but low conc. Ingestion (major; assimilation by crops) l l High solubility of Tl(I) compounds l l l Bioaccumulation and biomagnification in aquatic food webs Absorbed through skin and mucous membranes Widely distributed throughout the body Accumulates in bones, renal medulla and CNS
Molecular mode of toxic interactions l l The exact mechanism of toxicity of Tl not clear Possible toxic mechanisms: l Disrupt/bind to sulfhydril groups of proteins (ligand formation) & mitochondrial membranes inhibiting cellular respiration l Inhibiting enzymatic reactions and leading to “poisoning” l Interfere with the function of Na-K ATPase (univalent ions; similar ionic radii with K+) l Tl has a 10 x higher affinity than K l l Interfere in riboflavin homeostasis Forming insoluble complexes l intracellular sequestration of riboflavin l l Interfere calcium distribution
Biochemical Metabolism & Breakdown l Toxicokinetics of Tl in humans l l l Excreted mainly in the urine Increased excretion via the kidney due to l l l First phase: intravascular distribution (last 4 hrs) Second phase: distributed into the CNS (4 -48 hrs) Third phase: elimination (starts after 24 hrs of ingestion) KCl Diuretics antidotes include (acute Tl poisoning): l Activated charcoal, British antilewsite (BAL), calcium salts, cystine, dithiocarb, dithizone, histamine, theophyline, Prussian Blue (PB, Iron (III) ferrocyanide, ≈10 g)
Defense strategies / Detoxification l l Chemical ion-exchange, physical adsorption & ion trapping Ion-exchange: l l l In the gut, PB binds to unabsorbed Tl via: l l Tl exchanges with hydrogen from water bound in PB With monovalent cations such as Na+, K+, NH 4+ Adsorption of ions onto PB Trapping within PB Interfering with Tl’s enterohepatic circulation, resulting a reduction in tissue stores Binding of Tl to PB in vivo can be influenced by: l l l particle size Moisture content p. H
References l l l Hoffman RS. 2003. Thallium toxicity and the role of Prussian Blue in therapy. Toxicol Rev 22: 29 -40. http: //www. speclab. com/elements/thallium. htm http: //en. wikipedia. org/wiki/Isotopes_of_thallium http: //en. wikipedia. org/wiki/Thallium Hwieh CY, Tsai MH, Ryan DK, Pancorbo OC. 2004. Toxicity of the 13 priority pollutant metals to Vibrio fisheri in the Microtox® chronic toxicity test. The Science of the Total Environment 320: 37 -50. Lan C and Lin T. 2005. Acute toxicity of trivalent thallium compounds to Daphnia magna. Ecotoxicology and Environmental Safety 64: 432 -435. Moore D, House I, Dixon A, Williams G, Volans G, Henry J, Hughes RAC, Cochrane GM, Atkinson PL. 1993. Thallium poisoning. British Medical Journal 306: 1527 -1529. Peter ALJ and Viraraghavan T. 2005. Thallium: a review of public health and environmental concenrs. Environmental International 31: 493 -501. Vink BW. 1993. The behavior of thallium in the (sub) surface environment in terms of Eh and p. H. Chem Geol 109: 119 -123. Xiao T, Guha J, Boyle D, Liu C, Zheng B, Wilson GC, Rouleau A, Chen J. 2004. Naturally occurring thallium: a hidden geoenvironmental health hazard? Environment Internation 30: 501 -507. Yang Y, Faustino PJ, Progar JJ, Brownell CR, sadrieh N, May JC, Leutzinger E, Place DA, Duffy EP, Yu LX, Khan MA, Lyon RC. 2008. Quantitative determination of thallium binding to ferric hexacyanoferrate: Prussian blue. International Journal of Pharmaceutics 353: 187 -194.
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