'\ ,

Chemistry 1 Applications,

Toxicity 1 and Po·llution

Potential of Thallium

by v. Zitko

FISHERIES AND MARINE SERVICE SER V ICE DES PECHES ET DES SCIENCES DE LA MER TECHNfCAl REPORT No. RAPPORT TECHNIQUE N° 518

197 5 Environment Ehviro nnement + Canada Canada Fisheries Service des peches and Marine et des sciences Service de la mer Technical Reports

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Research and Development Directorate Direction de la Recherche et Developpement

TECHNICAL REPORT No. 518 RAPPORT TECHNIQUE N° 518

(Numbers 1-456 in this series were issued (Les numeros 1-4';6 dans cette serie furent

as Technical Reports of the Fisheries utilises comme Ra]Jports Techniques dE:, l' office

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name was changed with report number 457) Le nom de la serie fut change avec le

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Chemistry, applications, toxicity, and

pollution potential of thallium

By V. ZITKO

This is the seventy-eighth Ceci est le soixante-dix-huitieme

Technical Report from the Rapport Technique de la Direction de la

Research and Development Directorate Recherche et Developpement

Biological Station Station Biologique

St. Andrews, New Brunswick St-Andrews, N.-B.

1975 Zitko, V. 1975. Chemistry, applications, toxicity, and pollution potential of thallium. Fish. Mar. Servo Res. Dev. Tech. Rep. 518: 41 p.

ABSTRACT

The occurrence, production, properties, applications, determination, toxicity, and pollution potential of thallium are reviewed. Thallium is present at low levels in many rocks and ores and is recovered industrially from base-metal sulfide ores. Most thallium compounds are highly soluble in water and have little tendency to f orm complexes. Thallium is used in alloys, electronic devices, special glass, and catalysts f o r organic reactions. Many methods are available for the determination of traces o f thallium. Thallium is slightly more acutely toxic than mercury to mammals and as acutely toxic as copper to fish. Little is known about its chronic effects. The present industrial uses of thallium are too limited to generate pollution problems, but pollution may exist in the vicinity of mines and ore-processing plants. Thallium was detected in base-metal mining effluents. The conventional removal of heavy metals from waste water has little effect on thallium.

~ ~ RESUME

Nous revoyons ici les caracteres suiva nts du thallium: incidence, production, proprietes, applications, dosage, toxicite et pouvoir polluant. On rencontre le thallium en faible concentration dans plusieurs types de roches et de minerais et, sa recuperation industrielle se fait a partir de minerais de metaux communs sulfures. La plupart des composes du thallium sont tres solubles dans l'eau et ne se complexent que tres rarement. On utilise le thallium dans les alliages, les dispositifs electroniques, les verres speciaux et dans les catalyseurs de reactions organiques. On dispose de plusieurs methodes de dosage du thallium a l'etat de traces. La toxicite du thallium pour les mammiferes est legerement plus prononcee que celle du mercure et sensiblement la meme que celle du cuivre, pour les poissons. Ses effets chroniques nous sont presque completement inconnus. A l'heure actuelle, l'utilisation industrielle du thallium est encore trop restreinte pour entrainer des problemes de pollution sauf, peut-etre, a proximite des mines et des usines de traitement du minerai. On a decele la presence de thallium dans les effluents produits par l'extraction miniere des metaux ordinaires. L'elimination classique des metaux lourds des eaux usees a peu d'effets sur le thallium. 2. INTRODUCTION

Thallium is a metal not receiving much attention and relatively obscure for the non-specialist. The main reason for this is probably its limited use. Thallium is usually recovered as a byproduct of sulfide ore processing, however, due to the small demand many smelters, producing thallium, operate below capacity. Frequently thallium is not recovered and little is known about its fate in the waste products.

Thallium is very toxic and has a history of human and animal poisonings. Consequently, it would be desirable to know more about its environmental levels and chronic toxicity. Thallium was recently detected in effluents from base-metal mines and may also be present in wastes from the processing of other minerals. Judging from the patent literature, the number of potential thallium applications is increasing and may lead to a wider dissemination nf thallium in the environment.

This review summarizes chemical and toxicological properties and uses of thallium in order to stimulate further research of its environmental occurrence and possible pollution problems.

OCCURRENCE

The average concentration of thallium and several other metals in the lithosphere and in sea water is presented in Table 1. According to other estimates (Hampel 1968), the concentration of thallium in the earth crust may be up to 10 times higher than given in Table 1 which would make thallium more abundant than some other industrially important metals, such as mercury, antimony, bismuth, cadmium, and silver.

TABLE 1. Average concentration of metals in lithosphere and in seawater.

Lithosphere, \1g/g, Seawater (Lange and Forker, 1967) (Gaskell, 1971) 1-1etal \1g/~ t 9 Copper 70 3 5 x 10 9 Zinc 1 10 16 x 10 6 Cadmium 0.15 0.1 150 x 10 6 Mercury 0.5 0.003 46 x 10 6 Thallium 0.1 0.01 15 x 10 6 Lead 16 0.03 46 x 10 Thallium 0.0187* 0.0094-0.0166** *Matthews and Riley, 1969; **Matthews and Riley, 1970 3 • • Thallium ores, c ~ o~ ks it e, lo ~ an d i t e , and h utchinsoni t e are extremely rare. Thallium i s generaJly present in sulfide ores, such as galena (PbS), chalc opyrite (CuFeS ), sphalerite 2 (ZnS), and pyrite (FeS ). The average concentration of 2 thallium in ores and rocks is pre sented in Table 2. In

TABLE 2. Thallium concentration in ores and rocks.

C~ncentr a tion Material ~g/g Reference Galena 1.4-20 Kogan, 1970 Sphalerite 8-45 Kogan, 1970 Pyrite 5-23 Kogan, 1970 Calcareous-alkaline rocks 1.85-2.54 Dupuy et al., 1973 Granitic rocks 0.68-1.3 Mogarovskii et al., 1972 Sedimentary rocks 2.5 Nuriev and Dzhabbarova, 1973 Marine sediments 0.17-5.7 Matthews and Riley, 1970 Manganese nodules 1.85-199.8 Glasby, 1973 Mid-Atlantic Ridge basalts 0.20 DeAlbuquerque et al., 1972a Coal 0.05-10 Bowen, 1966 Limestone 0.5 Voskresenskaya, 1968 Silica-carbonate soil 2.7 Kothny, 1969

colloform varieties of sulfide ores the concentration of thallium may be as high as 10 mg/g (Robinson, 1973), and the occurrence of thallium in sulfide ores was extensively studied (Kiyoshi, 1966; Ivanov et al., 1967; Vershkovskaya et al., 1970; Ivanovet al., 1972). Thallium is also present in alkali-rich silicates such as alkali feldspars and micas. Sedimentary minerals such as manganese nodules contain relatively high levels of thallium and so do shales, in which thallium was probably deposited as a result of bacterial reduction (Voskresenskaya, 1972). Mathis and Kevern (1973) reported an average thallium conc entration of 8.1 ~g/g (range 2.1-23.1) in sediments of Wintergreen Lake, Michigan, and suggested that aerial fallout may be the primary source of thallium in this lake.

Not much information is available on the levels of thallium in biological material (Table 3). As the data indicate, thallium is generally present only in extremely low concentra­ tions. 4 .

TABLE 3. Tha ilium conten t of bie·logical material.

Sample Concentration Reference

Mammalian tissues 0.2-0.5 ).lg/g dry weight B.Jwe~l., 1966 Blood < 0.02 mg/Q, Bowen, 1966 Human body 0.1-0.6 ).lg/kg Goenechea and Sellier, 1967 Linaria triphylla 3800 ).lg/g ash Zyka, 1970 (Alsar, Yugoslavia) Kale 0.14 ).lg/g dry weight Kothny, 1969

PRODUC'TION

The current world production of thallium is 10-12 t/year, of which Bt are produced in West Germany and 2-3t in the United States. In Canada, 60 kg of thallium per year was produced at Flin Flon, Manitoba, in 1944-1946, and 125 kg in 1955. More recent production data are not availaLle (Kogan, 1970). The world production capacity is estimated at 25t/year. The amount of potentially recoverable thallium is much higher but the recovery is not economical because of the low demand for thallium. The U.S. yearly consumption of thallium is about 3t (Robinson, 1973).

Thallium is mainly recovered as a byproduct in the smelting of base-metal ores (Petrick et al., 1973), and from dust in the lithopone production (Kogan, 1970). Recovery is based on leaching with water or on distillation of the volatile chloride (Angelova et al., 1966; Angelova and Petkova, 1967), cementation and refining of thallium (Kogan, 1970; Petrova and Gladyshev, 1972; Ozols­ Kalnins and Purin, 1972; Oka et al., 1973). Thallium, containing only 0.3-5.5 ).lg/g of impurities, may be prepared (Wojtaszek and Lehman, 1973).

The U.S. thallium reserves are estimate d at 240t in sulfide ores and 10B,000t in coal ash. The world rese rves of thallium in these sources are 1260 and 650,000t, respectively (Robinson, 1973) The growth rate of thallium consumption projected to year 2000 is 1% per year (Petrick et al., 1973).

In Canada, about 48t of thallium per year (in New Brunswick 7t) could occur in zinc byproducts. This estimate is based on the annual zinc production (Financial Post, 1971), assuming an average zinc concentration of 5% in the ore, and an average thallium concentration of 2.2 g/ton (Robinson, 1973).

INORGANIC CHE~lISTRY

Thallium is the heaviest element of the IlIa subgrotip of the periodic system (boron, aluminum, gallium, indium, thallium). 5.

Its horizontal neighbours are me rcury and lea d. Elemental thallium is a soft metal (melting point 302°C, boiling point 1450°C). In its compounds, thallium is either mono (I, thallous) or trivalent (III, thallic). Thallium(I) compounds are easily oxidized by bromine, chlorine, hydrogen peroxide, or nitrous acid. Thallium(11I) compounds are reduced to thallium(I) compounds, for examp le by s ulfurous acid. Thallium (I) compounds are more stable.

Thallium is not a transition metal and thallium(I) compounds resemble quite closely the compounds of alkali metals and are soluble in water (Table 4). Thallium(I) hydroxide is a strong base.

TABLE 4. Solubility of thallium(I) compounds.

Compound Solubili t~> g/£ Thallium(I) alurr.inum sulfate 117.8 " carbonate 40.3 chloride 2.9 cyanide 168 ferrocyanide 3.7 fluoride 786 formate 5,000 hydroxide 259 iodide 0.006 " nitrate 95.5 " nitrite 321 " oxalate 14. 8 " orthophospha te 5 " pyrophosphate 400 " sulfate 48.7 " sulfide 0.2 " dithionate 418

Similarly to alkali metals, thallium(I) for ms relatively weak complexes with most ligands . A large number of stability constants may be found in a handbook (Sillen and Martell, 1964), and the coordination chemistry o f thallium(I) was recently reviewed (Lee, 1972). Of the l i gands important in water chemistry, equilibrium constants of the thallium-carbonate system have not been reported, a nd the structure of thallium carbonate is not known. Some s t ability constants of thallium and, for comparison, of other heavy metal complexes are summarized in Table 5. It can be seen that thallium and lead form relatively insoluble chlorides as compared to the soluble chlorides of the other metals. On the other hand, thallium(I) sulfide is comparatively soluble and, depending on pH and total sulfide concentration, the solub ility of thallium(I) ranges 8 from 10- to 10-5M (Gubeil and Retel, 1972). The logarithms of thallium(I) complex formation constants with most organic 6. ligands are in the range of 0.5-2.0, and relatively week complexes are formed even with complexing atfents such as EDTA and NTA. Thallium(I) is not complexed by humic acid (O'Shea, 1972). This is of interest from the point of view of thallium toxicity to fish. Humic acid decreases the toxicity of copper because of complex formation (Zitko et al., 1973). Due to the lack of complexing, it is likely that humic acid will not affect the toxicity of thallium to fish.

TABLE 5. Stability constants of heavy metal complexes.

Metal ion T13+ Pb2+

Ligand

C£ 3.76* 7.54 4.79* s2- 35.2* 21.6* 27.8* 52.4* ~0.3* 27.9* OH 6.5 4.4 2.3 10.3 0.49 12.9** 6.2 SO 2- 2.4 2.3 2.3 2.4 2.41 1.95 26.6* 4 PO 2- 3.2 2.4 32.6* 14.5* 1.33 42.1* 4 EDTA 18.8 16.5 16.5 21.8 4.42 25.0 18.0 NTA 12.7 10.5 10.1 12.7 6.55 18 11.8

* pK (K solubility product) s s = ** pK 43 s =

Thallium(III) forms much stronger cOIT21exes than thallium (I). The complexes are generally of the type TIX - or TIX 3-. 4 6 It is interesting to note that thallium(III) hydroxide is insoluble in water. Thallium(III) halogenid~s are on the other hand well soluble in ether.

The complexes of thallium(I) and (III) with a number of complexons were recently studied (Gorelov and Kolosova, 1973a,b).

ORGANIC CHEMISTRY

Monovalent ~Tl) and three types of trivalent organic thallium compounds (RTIX , R TIX, and R Tl) ~re known. At the 2 2 3 last survey in 1969 (Okavara, 1972), 26 of t.'le former and 452 of the latter were counted. Of the trivalent organothallium compounds, the R TIX compounds are the most stable ones. In 2 7 . + aqueous solutions most of them dissociate into R2Tl and X the hydroxides are stronc. bases, and dimethyl thallium hydroxide is dimerizee] in aqueous ~.olution. X may also be halogen, sulfate, nitrate, acetatE, etc. Water solubility is a function of R and X, and very likEly decreases with increasing hydro­ phobicity of R. Acid sulfides (X = SH) are generally insoluble in water. Quantitative ~olubility data are lacking. Abbott (1943) gives some values, mostly for substituted diarylthallium compounds. The solubility of dimethyl thallium saccharide was higher than 10 g/~. The stability of organothallium complexes was recently reviewed (Bcletskaya et al., 1973). Dialkyl thallium complexes are g( ~ nerally less stable than alkyl mercury complexes. A detailed review of synthesis and properties of organothallium compounds is presented by Nesmeyanov and Sokolik (1967).

Thallium compounds have a wide application in synti etic organic chemistry. A recent review by Taylor and McKillop (1970) is available. Thallium(I) salts of a-dicarbonyl compounds can be selectively and quantitatively C-alkylated and C- or O-acylated. Thallium(I) salts of phenols are readily alkylated, acylated, aroylated or tosylated, and unsymmetrical anhydrides may be prepared from thallium carboxylates with acid halides. Thallium(I) carboxylates are excellent intermediates in the preparation of alkyl bromides, and thallium(I) bromide is a very good reagent for the preparation of diaryls from aromatic Grignard compounds.

Thallium(I) acetate catalyzes the bromination of aromatics to single monobromo isomers and is a useful Friedel­ Crafts catalyst. Thallium(I) trifluoroacetate is a good reagent for thallation of aromatic compounds (ArTIX ), yielding 2 versatile intermediates.

As in the case of mercury, organocobalt complexes catalyze the alkylation and aryl at ion of thallium(III) compounds (Abley et al., 1973).

Thallium(III) salts may be used to oxidize organic compounds. Oxidative clearage of glycols was described by McKillop and Raphael (1972), the kinetics of oxidation of alcohols and ketones by Meenakshi and Santappa (1973), and Tl(II) ions were postulated as intermediates in the oxidation of oxalic acid (Srinivasan and Vankatasubramanian, 1973). Thallium(III) ions catalyze the electrochemical oxidation of alkenes (Favier et al., 1971).

Aromatic hydrocarbons are simultaneously chlorinated and carboxylated by thallium(III) chloride (Uemura et al., 1972), and the formation of carbamates from isonitriles is catalyzed by thallium(III) nitrate (Kienzle, 1972).

Pentafluorophenyl thallium complexes may be used to 8. oxidize other organometallic (tin, platinum, r iLOdium) compounds (Royo, 1972).

INORGANIC USES

Thallium is mainly used in alloys, electronic devices, and special glass.

Thallium and lead alloys have a good hardness and corrosion resistance and up to 7% thallium may be used in lead anodes in chromium plating from chromic acid baths (Krysztofowicz, 1973). Thallium-copper alloys have an improved heat resistance and conductance, thallium-aJ uminum and thallium­ zinc alloys have an excellent abrasion resi ~ tance and may be used for unlubricated bearincrs. Micro-occlusions of thallill i1l improve the machinability of stainless steel (Robinson, 1973). Thallium-aluminum alloys may be used in batteries (King, 1972) I selenium-thallium alloys in rectifiers. Solders for ceramics and semi-conductors often contain thallium in addition to indium, mercury, and gold.

An improved durability of furnace linings in aluminum smelters is achieved by the addition of the'llium, and thallium salts improve copper and nicLel plating on alumina (Foster and Kariapper, 1973).

The electronic applicC\tions of thallium include infrared photocells, scintillation spE'ctrometer detectors, tungsten filaments, and mercury-vapour lamps, where the addition of thallium doubles the light output (Robinsor I 1973).

In glass thallium increases the refractive index.

Thallium oxide is used to glaze electronic devices. Patents describe the use of thallium(I) chloride in batteries (Athearn and Liang, 1973), thallium borates in metal-polishing abrasives (Bither, 1973), and thallium alleys in abrasive tools (Drui et al., 1973). Thallium-containing ccltalyst for the oxidation of hydrogen chloride was described (Wolf et a]., 1973).

ORGANIC APPLICATION~

Thallium-containing catalysts have teen patented mainly for various oxidations, but also for reforn.ing, polyesterifica­ tion, and hydrogenation.

A catalyst containing antimony and thallium oxide can be used to prepare ethylene oxide from ethylene (Ichikawa et ale 1972), and thallium oxide catalyzed the formation of propylene oxide from propylene (Honda et al., 1972). In aqueous solutions, thallium(III) ions oxidize olefins to carbonyl compounds and glycols. The mechanism probably involves oxy 9. metallation adducts (Henry, 1968), and this step is rate­ determining (Henry, 1973).

Thallium is a comfonent of cataly sts for ammoxidation of propylene to acrylonitrile (Shiraishi et al., 1973a), for the oxidation of acrolein and methacrolein to acrylic and me~hacrylic acid, respectively (Niina et al., 1973), for the preparation of methacrolein from isobutylene(Shiraishi et al., 1973b), acrolein from propylene (Shiraishi et al., 1973c), and methacrylic acid from methacryl aldehyde (Akiyama and Niina, 1972).

A mixture of ferric bromide and thallium benzoate catalyzed the oxidation of alkylbenzenes to the corresponding aromatic acids (Massie, 1973). Thallium catalysts were used to prepare anthraquinone from anthracene (Nanba et al., 1973) and from I-methyl-3-phenyl indan (Wistuha et al., 1973).

Molten thallium catalyzed the ox ~ dation of methanol (Saito et al., 1971) and the conversion of amines into nitriles (Ogino et al., 1973).

Molybdenum-thallium catalysts di ;proportionated ole fins (Koblinski and Swift, 1971), and thalli'lm was the component of a reforming catalyst (Duhaut and Miquel . 1973).

Thallium chloride catalyzed the )olycondensation of methyl p-B-hydroxyethylbenzoate (Matsuklra et al., 1972), and thallium compounds accelerated the polyesterification of terephthalic acid with ethylene glycol (Chimura et al., 1972).

A hydrogenation with thall ium ca~alysts has been patented for the preparation of y-butyrolacton from succinic or maleic anhydride (Kanetaka et al., In73).

Some organothallium compounds ar(~ useful as catalysts in polymerization reactions and a patent describes their manufacture (Kurosawa and Yasuda, 1972) "

ANALYTICAL CHJ:MISTRY

Very extensive literature deals \ Ti th the analytical chemistry of thallium and a monograph 0 1 \ this subject is also available (Korenman, 1963). This revie' l covers only the determination of thallium at trace leve: s. In this case thallium must be precoz:.centrated and separated from other elements.

Chromatography

Chromatography on cation or anio l exchange resins is frequently used to separate thallium frl )ffi many other metals. 10.

Cation exchange resins are used for thallium(I). Gupta and Tandon (1972) determined the distribution coeffic­ ients (concentration in resin/concentration in solution) of thallium(I) and (III), zinc, cadmium, mercury(II) , and gold on Amberlite IR-120 in hydrochloric acid media. In O.lM hydrochloric acid the coefficients were 347, 925, and 295 for thallium (I) , zinc, and cadmium, respectively, as compared to 0.2, 0.1, and 3.5 for gold, mercury, and thallium(III). The presence of organic solvents such as methanol, acetone, and tetrahydrofuran affected the distribution coefficients and conditions could be selected for various separations. Strelow and Victor (1972) separated trivalent aluminum, gallium, indium, and thallium on an AG50W-XS (BioRad Laboratories) cation exchange resin by using a gradient of hydrochloric acid in aqueous acetone. Thallium was eluted with O.lM, irtdium with 0.5M hydrochloric acid~ both in 50% acetone, followed by gallium (2.0M hydrochloric acid, 70% acetone), and aluminum (3.0M hydrochloric acid). For samples containing a high concentration of thallium, the authors recommended the elution of thallium with O.lM aqueous hydrobromic acid, containing some free bromine, to avoid the reduction of thallium(III) and precipitation of thallium(I) chloride. Pakholkov and Ganyaev (1972) separated thallium(I) from the above metals, chromium (III), and uranium(VI) on a cation exchange resin using 0.05M ammonium fluoride as the eluant. Zukriegelova et ale (1972) described the separation of indium and thallium(I) on Dowex 50WX-S in sodium cycle.

Lepri and Desideri (1973) studied the thin-layer chromatography of a number of metals, including thallium on carboxymethyl cellulose and Dowex 50-X4, both in sodium form. Acetate, gluconate, and lactate buffers (acid:salt 1:2) were used as solvents and the ionic strength was adjusted by sodium perchlorate to ~ = 0.05-0.5 mole/~. Carboxymethyl cellulose was an excellent support for the chromatography of thallium and the R values were practically unaffected by buffer f variations. The best separation of thallium(I) from lead, mercury (I) , and silver was achieved in an 0.03M gluconate buffer.

The separation of thallium from other metals on inorganic cation exchangers was described. Qureshi et ale (1970) used titanium molybdate, Gill and Tandon (1972) ceric antimonate.

Anion exchange resins were used to separate or concentrate thallium(III). Trivalent thallium forms with halogens an anionic complex T1X - which has a high distribution 4 coefficient (Gupta and Tandon, 1972) on anion exchange resins. Matrix effects playa role, at least in the case of T1Br4-, which is also strongly adsorbed by macroporous resins, not containing cationic groups (Pfrepper, 1973). 11.

The separation of the IlIa group elements in the form of fluoride complexes on several anion exchange resins was described (Pakholkov et al., 1972).

Seymour and Fritz (1973) used liquid chromatography on Amberlite A-26, eluted with hydrochloric and perchloric acid, to separate a number of metals including thallium(III). UV absorbance of the chloride complexes was used to detect the eluted metals. An ion exchange procedure for concentration of thallium from sea water was described (Matthews and Riley, 1969). Thallium(III) was adsorbed on a strongly basic anion exchange resin, Deacidite FF, and eluted with a saturated solution of sulfur dioxide. The eluate contained also iron, gallium, antimony, and zinc.

Anion exchange resins in carbonate form were used to separate thallium(I) from many other metals (Eristavi and Mgagobishvili, 1973). Thallium(I) carbonate is highly soluble in water, whereas many other metals form insoluble in water carbonates or basic carbonate complexes. In addition anions such as molybdate, tungstate, and vanadate are adsorbed by anion exchange. Thus thallium(I) can be separated from iron, zinc, gallium, cadmium, copper, nickel, and lead (basic carbonates), aluminum, chromium(III), titanium(IV) , and managanese (II) (hydroxides).

Aluminum, gallium, indium, and thallium, all in the trivalent form, were separated on aminoethylcellulose in ethanolic hydrochloric acid (Fisel and Bilba, 1971).

Paper chromatography may be used to separate thallium(I) from many metals (Block et al., 1958). A semi-quantitative determination of thallium in minerals by paper chromatography was described (Agrinier, 1971). Thallium(III) was chromato­ graphed in methyl propyl ketone and detected by 1-(2-pyridylazo)- 2-naphthol. The detection limit was 4 ~g/g for thallium isolated from sulfide, sulfate, and silicate minerals and manganese oxides. From biological material, thallium(I) was extracted with dithizone in chloroform at pH 11.5 and chromatographed in methanol-water-25% sulfuric acid (7:4:1). Saturated dithizone in ethanol was used for detection (Boenig and Heigener, 1973).

The separation of thallium by thin layer chromatography is described in the literature (Kirchner, 1967). Wysocka and Bronisz (1967) chromatographed thallium(I) on silica gel G using methanol-water-25% sulfuric acid (7:7:4) as the developing solvent. Thallium was detected by potassium iodide.

EDTA complexes of many metals were separated from thallium by paper electrophoresis in an O.005M EDTA solution (Mukherjee and Nag, 1973). Isotachophoresis was used to separate thallium(I), silver, mercury (I) , and lead (Taglia, 1973). 12.

Attempts to determine thallium by gas chromatography of diphenyl thallium were unsuccessful (Schwedt and Russel, 1973) .

Solvent extraction

Thallium may be separated from ma ny metals by solvent extraction. Thallium(III) chloride is extractable from hydro­ chloric acid solutions with diethyl ethe r. Many other trivalent metals (iron, gold, gallium, indium, antimony, arsenic) are also extracted under these conditions, and their extractability generally increases with increasing concentration of hydrochloric acid in the aqueous phase. By extraction from 2M hydrochloric acid, thallium(III) may be separated from iron, gallium, and indium (Korenman, 1963). Hydrobromic acid is generally a better medium for the extraction of thallium(III) with ether, and the extraction from 1M hydrobromic acid is quantitative. Gold is co-extracted, but only lS% of indium, and 1.S% of each gallium and iron are extracted under these condi­ tions (Korenman, 1963). Thallium(I) is only slightly extractable from both hydrochloric and hydrobromiclcid.

Dean and Eskew (1971) extracted thallium(III) from 2M hydrobromic acid into methyl isobutyl ketone (MIBK) which was then washed with 1.SM hydrobromic acid in formamide. Thallium remained in the MIBK phase, whereas, tin(II,IV), gallium, indium, and iron were removed in the formamide phase.

Varentsova et ale (1973) developed an extraction of thallium(I) from 0.OS-0.2SM sulfuric acid into an O.SM solution of di-(2-ethylhexyl)dithiophosphoric acid in 2-ethylhexanol, and described the removal of co-extracted metals, which separated thallium(I) from all metals except copper.

Gupta and Mukerjee (1967) desc ribed the separation of thallium(III) from lanthanum(III) , zirconium(IV) , thorium (IV) , and uranyl ions by extraction with 10% phenol in petroleum ethe r from aqueous glycine. Thallium(III) was extracted by dibutyl butylphosponate or butyl dibutylphosphinate from aqueous solutions containing sodium chloride and sulfuric acid (Chuchalin et al., 1972).

Other methods of solvent extraction of thallium, assisted by ligands, are described under spectrophotometric methods.

Spectrophotometric methods

Most spectrophotometric methods for the determination of thallium are based on the extraction of ion-association complexes formed between thallium(III) and a basic dye by an organic solvent, and the measurement of absorbance of the complex. Tri­ phenylmethane (I, Fig. 1) and xanthene (II, Fig. 1) dyes are usually used. Of the triphenylmethane dyes, Brilliant green, Methyl violet, Malachite green, and Crystal violet are used most 13.

IT I

Figure 1. Triphenylmethane (I) and xanthene (II) dyes. I. Brillian green (C.I.42040, Basic green 1) R =R =C H , R3= phenyl l 2 2 5 Malachite green (C.I.42000, Basic green 4) R -R -CH , R - phenyl I 2 3 3 Methyl violet (C.I.42535, Basic violet 1) R =R =CH and H, R3 = p-methyl and p-dimethylaminophenyl l 2 3 Crystal violet (C.I.42555, Basic violet 3) R =R =CH , R3= p-d~methylaminophenyl l 2 3

Victoria blue R =R =CH , R3= N-ethyl or N-phenylnaphthylaminyl l 2 3

Phenylpyrazolone green R =R =CH , R3= x l 2 3

II. Basic violet 10 (C.I.45l70, Rhodamine B, in Russian papers S or C) R =R =C H , R =H, R =COOH l 2 2 5 3 4 14. frequently, but the application of fuchsine, Victoria blue, and pyrazolone dyes was also described. A characteristic representative of the xanthene dyes is Basic violet 10.

The above-mentioned dyes are not specific for thallium and form ion-association complexes with a number of other metals such as antimony, gallium, indium, mercury, gold, silver, etc., so that a pre-separation of thallium is required. This is usually achieved by solvent extraction, but chromatographic techniques could also be used. Thallium must be present in the trivalent form, and thallium(I) is oxidized by reagents such as bromine, ceric sulfate, hydrogen peroxide, or nitrous acid. The ion-association complex is extracted from aqueous hydro­ chloric or hydrobromic acid with t o luene, ethyl acetate, isopropyl ether, benzene, etc. The molar absorptivities of the 4 5 lon-assoclatlon. ., comp 1 exes are 10 - 10 Nmon 1 e -1 cm -1 T h e commercially available dyes may have to be purified before use. Extraction with an appropriate solvent such as acetone,in a Soxhlet extractor may be the most convenient way to do this.

Older methods (up until 1969) of the determination of thallium with triphenylmethane and xanthene dyes were reviewed by Fogg et al. (1971). Kothny (1969) studied the determination of thallium with Crystal violet in organic and inorganic samples and in water. The ion-association complex was extracted with toluene from aqueous hydrobromic acid. Molybdenum (100 mg/Q,) and tungsten (10 mg/Q,) precipitated during the extraction and interfered by adsorbing thallium. Insufficient data on the interference by other metals were presented. Chainani et al. (1971) studied the determination of thallium in zinc and zinc alloys. Crystal violet and Basic violet 10 were more sensitive than Methyl violet and Malachite green, and the sensitivity was further increased by using isopropyl ether instead of benzene as the extraction solvent. On the other hand, Levitman and Korol (1972) reported that Malachite green and Crystal violet were more sensitive than other dyes in the determination of thallium. The sensitivity of the deterPlination with Brilliant green was improved by extracting the chJ.oro- rather than the bromo-complex (Fogg et al., 1973). The molar absorptivity of the ion-association complex was 10.3 x 105 Q,mole-lcm-l , when the extraction was carried out immediately after the addition of Brilliant green so that the dye could not become fully protonated. The protonation equilibria of triphenylmethane dyes and their effect on the extraction of thallium were studied by Vdovenko et al. (1972).

Ferric ions, chloride, and phosphate interfere with the determination of thallium with Methyl violet and the calibration curve should be obtained on standard solutions, containing these ions in concentrations identical to those in the sample (Suvorovskaya et al., 1969).

Crystal violet was used to determine thallium in urine 15.

(Wawschinek et al., 1968). Acker mann and Anger mann (1970) determined thallium with Basic violet 10 in metals and alloys. Thallium(I) was extr acted with dithizone in carbon tetra­ chloride from an alkaline medium , back-extracted together with cadmium into diluted acetic a cid, and cadmium was separated by a dithizone extraction at pH = 5-6. Thallium was then oxidized with bromine, the bromo-complex wa s extracted with isopropyl ether, and equilibrat ed with a sol ution of Basic violet 10 to extract the ion-association complex.

It should be noted that for the dithizone separation thallium must be present in the monovalent form since only then is it extracted by dithi zone from an alkaline medium. A selective determination of thallium, based on this extraction, was also described (Stary, 1964). This method is, however, relatively insensitive.

Basic violet 10 was also used to determine thallium in zinc concentrates and tailings (Alexandrov and Dimitrov, 1972).

The less frequently used triphenylmethane dyes include fuchsine (Tarayan, 1969), Victoria blue (Serbanescu, 1973a), and pyrazolone dyes (Zhivopistsev and Lipchina, 1969,1971).

Cyanine dyes are used occasionally to determine thallium. Astrazon pink FG (Popa et al., 1971, 1972), Astrazon blue B 5GL (Constantinescu, 1972), Astrazon blue B (Serbanescu, 1973b), and Solochrome violet RS (Popa and Croitoru, 1971) were used. Molar absorptivities of the ion-association complexes are again 4 5 -1-1 in the 10 -10 tmole cm range and the interference by other metals is similar to that encoun t ered in the case of the triphenylmethane dyes.

The determination of thallium with Basic red (C.I.50040, Neutral red), a phenazine dye, was described (Serbanescu, 1971).

Several azo dyes have been used for the determination of thallium. Busev et al. (1972a) studied 1-(2-thiazolylazo)-2- naphthol-3,6-disulfonic acid, which forms an 1:2 complex with thallium(III) at pH = 2.3-2.8 in an aqueous medium. This dye is quite specific for gallium, indium, and thallium, and the absorption maxima of the complexes are 530, 570; 540, 570, and 550, 580 nm, respectively. This dye may also be used as a complexometric indicator. The reaction of thallium(III) with a closely related compouns, 1-(2-thiazolylazo)-2-naphthol-3- carboxylic acid, was described (Busev et al., 1972b).

Rodina et al. (1973) determined thallium(III) in the organic phase with 1-(2-pyridylazo)-2-naphthol. Thallium(III) was extracted with di-(2-ethylhexyl)phosphoric acid in heptane. Many co-extracted metals were removed by washing the organic phase with 0.25M sulfuric acid. Gallium and iron(III) remained in the organic phase but did not interfere, unless present in a 100-fold excess. An isomeric compound, 16.

2-(2-pyridylazo)-1-naphthol was used as a complexometric indicator in the determination of thallium (Gusev and Kurepa, 1972a).

Another azo dye, used for the determination of thallium, is 2-(4-antipyrylazo)-5-diethyl-m-aminophenol (Gusev and Kurepa, 1972b), and mixed ligand complexes of thallium with 4-(2-pyridylazo)-resorcinol and antipyrine were described (Biryuk and Ravitskaya, 1973). Stilbene-4,4'-bis (8-hydroxy-5-sulfoquinolinylazo)-2,2'-disulfonic acid was used to determine thallium in an aqueous solution (Raguzina, 1971). The usual groups of metals interfered.

Thallium(III) was selectively determined as its diethyl dithiocarbamate complex in carbon tetrachloride and the sensitivity was increased by converting this into the corre­ sponding copper complex (Keil, 1972).

Halogen complexes of thallium(I) have an absorption maximum at 245 nm in 10M hydrochloric acid, those of thallium (III) between 240 and 260 nm (Korenman, 1963). The UV absorption of thallium can be used for its quantitative determination, provided thallium is separated from interfering ions such as bismuth, mercury, lead, cadmium, and silver. The determination of thallium(I) may be carried out in the presence of lead and bismuth and a method for the spectrophotometric determination of bismuth, lead, and thallium was described (Merritt et al., 1953). In 6M hydrochloric acid the absorption maxima were at 244, 231, 270, 327, and 254 nm for thallium(I), mercury, lead, bismuth, and copper(I), respectively.

Spectrofluorimetric methods

Xanthene dyes-thallium(III) complexes, described in the previous section, are fluorescent and can be determined spectro­ fluorimetrically. The determination is seldom used since the dyes are fluorescent themselves, which leads to high blanks and not much increase in sensitivity.

Grigoryan et ale (1973) reviewed some of the older spectrofluorimetric methods, and described a method using acridine orange. Thallium(I) in 3M hydrochloric acid was oxidized by sodium nitrite, and thallium(III) was extracted by butyl acetate. The extract was washed by a small amount of 3M hydrochloric acid to remove some co-extracted interfering metals, and equilibrated with an aqueous solution of acridine orange. Fluorescence of the organic phase was excited at 495 nm and the emission measured at 520 nm and the sensitivity was approximately 10 ng/g. Mercury, gold, and antimony interfere and must be removed, for example, by cementation on a copper wire.

The blue fluorescence of thallium(I) in the presence of chloride ions has been known for a long time and formed a base of a qualitative test for thallium (Sill and Peterson, 1949). 17.

Bock and Zimmer (1963) developed it into a quantitative method and measured the fluorescence of thallium(I) in an almost saturated sodium chloride solution (excitation 240, emission 420 nm).

The method was further improved by Kirkbright et al., (1965). Thallium was separated from most interfering metals by the extraction of thallium(III) with ether, reduced, and the fluorescence of the chloro-complex was measured in 3.3M hydrochloric acid and 0.8M potassium chloride (excitation 250, emission 430 nm). A large excess of gold, bismuth, platinum, and antimony interfered. Sulfate ions had no effect, but nitrate ions interfered.

Koning et al. (1971) described a titration of thallium (III) by tin (II) with a spectrofluorimetric determination of the end-point. The reduction of thallium(III) gave a sharper end-point than the oxidation of thallium(I).

Polarographic methods

Polarographic determination of thallium was frequently reported and more than 300 papers on the determination and polarographic behaviour of thallium were published between 1922 and 1967 (Sargent-Welch, 1969). Thallium gives a well­ defined wave at approximately -0.45V (vs saturated calomel electrode) in most supporting electrolytes (Kolthoff and Lingane, 1965). Lead is the most commonly encountered interfering ion. Its interference is usually eliminated by a suitable electrolyte, or by complexing with EDTA. The sensitivity of the determination of thallium by classical polarography is about 10 ~g which corresponds to a concentration of approximately 500 ~g/ £ , assuming that 20 m£ of sample solution is used, and the method is not sensitive enough for the analysis of water samples. A modification of the equipment is claimed to increase the sensitivity by one order of magnitude (Bonastre et al., 1973). Petri and Lipiec (1959) determined thallium by polarography at pH = 9, thus eliminating the interference of lead. Landry (1960) analyzed solutions contain­ ing 1-50~g/m £ of thallium in the presence of up to 20 ~g/m£ of lead, after adding EDTA to the supporting electrolyte (2.7M calcium chloride, pH = 7.3). Lead interfered with the determin­ ation of thallium in O.lM succinic acid (Deshmukh and Naik, 1972), but the determination of both lead and thallium in their mixtures was possible in 1M ethanolamine, containing 3% mannitol at pH = 10.5. The addition of mannitol prevented the hydrolysis and precipitation of lead (Deshmukh and Naik, 1973). Lead and thallium could also be determined simultaneously in 0.5M monoethanolamine and O.lM sodium hydroxide (Rao and Puri, 1972). A simultaneous determination of indium and thallium was achieved in an electrolyte consisting of 0.5M ethylenediamine, 0.25M ammonium hydroxide, and 0.05M potassium chloride (Babich et al., 1971). Gladyshev et al. (1970) eliminated the interference of 18. copper, cadmium, and antimony by using a 10-3M solution of tetrabutyl ammonium sulfate in sulfuric acid, and the interference of bismuth and lead by the addition of tetra­ butyl ammonium sulfate to a sodium hydroxide medium.

All the above methods dealt with thallium(I). Thallium(III) was determined in 1M potassium nitrate, contain­ ing 3-50 mM EDTA at pH 11-12.3 (Kitagawa and Maruyama, 1970).

Lead and thallium were also determined in their mixtures by second harmonic AC polarography (Devay et al., 1973) .

Anodic stripping voltammetry (ASV) is approximately three orders of magnitude more sensitive than the classical polarography and is able t o determine thallium in the ng range. The increased sensitivity of ASV is due to the preconcentratio ' by electrolysis of the determined metals on the electrode. The electrolysis potential for thallium is usually -1.1 - -0.9V (vs saturated calomel electrode). Both hanging mercury drop electrode and amalgamated inert electrodes were used. As in classical polarography, several metals, particularly lead and cadmium may interfere. The interference may be eliminated in several ways such as preliminary separation, complexing, etc., reviewed briefly by Zieglerova et al. (1971). The most often used technique is complexing, but a separation method described by Morsches and Tolg (1970) deserves mentioning.

Morsches and Tolg separated thallium(III) by extraction with ether from arsenic, beryllium, cadmium, cobalt, chromium, copper, iron, mercury, manganese, molybdenum, nickel, lead, tin, vanadium, and zinc. Thallium was then determined by ASV in 0.02M EDTA on an amalgamated platinum electrode and the sensitivity was approximately 5 ng.

Zieglerova et al. (1971) used DCTA (diaminocyclohexane­ N,N,N' ,N'-tetraacetic acid) as a masking agent and determined traces of thallium in cadmium. The supporting electrolyte was O.OlM DCTA in an acetate buffer pH = 4.6, ~ = 0.1 mole/~. Cadmium was not reducible under these conditions.

Sinko and Gomiscek (1972) described an ASV determination of lead, cadmium, copper, thallium, bismuth and zinc in blood serum. The determination of thallium was carried out in an 0.2M acetate buffer pH = 6.4, containing 0.02M EDTA, and the sensitivity was 0.01 ~g/m~.

Paolaggi et al. (1972) compared the determination of thallium by ASV in digested and not digested samples of urine, tissues and feces. The supporting electrolysis was a Britton­ Robinson buffer pH = 3.2 and O.OlM EDTA. A good agreement between digested and not digested samples was obtained. Levit (1973) determined thallium in urine acidified by perchloric acid by AC ASV. Lead did not interfere and the sensitivity was 19.

50 ~g/~.

ASV of thallium was also studied on amalgamated graphite electrodes (Nagarev et al., 197 0; Moskovskikh et al., 1973; Neiman and Brainina, 1973). Seitz et ale (1973) described a tubular me r cury-graphite electrode, suitable for continuous monitoring of thallium concentration.

ASV was used to study the complexing of thallium by humic acid (O'Shea, 1972) .

The determination of thallium by cathodic stripping voltammetry was described (Dolezal and Hrabankova, 1971). Thallium was electrolytically deposited at pH = 10-12 Gnd +0.7V as thallic oxide on a platinum electrode, and then anodically redissolved. This method is somewhat less sensitive than ASV. Many metals do not interfere, however, lead must be absent.

Little attention was paid to the polarographic behaviour of organothallium compounds . Costa (1950) investigated diethyl-, dipropyl-, and dibutylthallium bromides by classical polarography. One electron reduction to R2TlTlR2 and a complete reduction were observed in the case of dipropyl- and dibutyl­ thallium whereas diethylthallium was reduced completely. The supporting electrolyte was 70% O.sM potassium chloride and 30% propyl alcohol. The half-wave potentials were -1.000, -0.922, and -0.89sV in order of increasing alkyl chain length, respectively. DiGregorio (1969) studied the reduction of dimethyl-, diethyl-, dipropyl-, and diphenylthallium in phosphate buffers pH 2.5-11.0. A single-wave reduction of the dialkyl compounds was observed and the half-wave potentials at pH = 6.2 were -1.00, -0.97, and -0.95, respectively. Diphenyl­ thallium was reduced in 3 waves corresponding to the adsorption of diphenythallium(II) , phenylthallium(I) , and to the reduction of phenylthallium(I), respectively.

Atomic absorption methods

Thallium hallow-cathode lamps are commercially available and thallium may be conveniently determined by atomic absorption spectrophotometry. The sensitivity of thallium detection with direct aspiration of aqueous solutions into an air-acetylene flame is 0.03-0.07 mg/~ (Perkin-Elmer, 1973). The sensitivity may be increased to 0.01 and 0.001 mg/ ~ by using the cup or boat microsampling technique, respectively (Perkin-Elmer, 1973), and to 0.4 ~g/~ by using the carbon rod atomizer (Parker, 1972). .

Curry et ale (1969) digested biological samples with a mixture of concentrated sulfuric and nitric acid and extracted thallium(III) with MIBK, which was ther aspirated into the flame. Alternatively, thallium was complexed with sodium diethyl dithiocarbamate at pH = 5.6, a ~ d extracted with MIBK. 20.

This extraction is not specific for thallium but may be used because of the specificity of atomic absorption. Using a tantalum boat, urine samples could be analyzed directly, whereas blood samples were pre-ashed with concentrated nitric acid. The detection limits were 0.2 and 0.04 mg/£ for water and MIBK aspiration, respectively, and less than 2 and 1 ng in the boat technique applied to water and urine. Berman (1967) also used the diethyl dithiocarbamate extraction to determine thallium by atomic absorption in tissues, blood, and urine.

Torres (1969) complexed thallium in urine with dithizone, extracted with MIBK and analyzed the extract by the boat technique. Machata and Binder (1973), and Kubasik and Volosin (1973) determined thallium in blood and urine using the graphite atomizer. Thallium was complexed with sodium diethyl dithiocarbamate and extracted with MIBK. Cadmium and lead could be determined simultaneously. The sensitivity for thallium was 5 ~g/£.

Shkolnik and Bevill (1973) determined thallium in 10 ~£ samples of plasma and urine using the cup technique. Urine samples required no pretreatment, plasma was partially oxidized by 30% hydrogen peroxide. The Deuterium Background Corrector was required to eliminate interferences.

Sighinolfi (1973) used the graphite atomizer to determine thallium in geochemical reference samples. The samples were digested with hydrofluoric and perchloric acid and thallium was extracted as bromide with isopropyl ether. A similar determination of thallium in carbonate and silicate rocks was reported (Heinrichs and Lange, 1973).

Pchelintsev et al. (1971) described the determination of thallium by atomic fluorescence.

Spectrographic methods

Numerous methods of the spectrographic determination of thallium are described. These methods are usually not used in routine analyses and will be mentioned only briefly. Their major advantage is the possibility of determining many elements simultaneously. Bykhovskaya and Babina (1956) determined thallium in standards with a sensitivity of 10 ~g, Mihalka and Ghelberg (1967) in the residue after the evaporation of water, with a sensitivity of approximately 1 ~g/g residue. Spectrography was used to determine thallium in alkali and alkaline earth metal salts (Pevtsov et al., 1967; Pevtsovand Manova, 1968; Belchev and Prodanova, 1969), and in organic solvents (Khorkina et al., 1969).

Busev et al. (1972) described a preconcentration procedure based on the extraction of thallium(III) from a hydrochloric acid medium with chloroform containing hexyl­ diantipyryl methane, which separated from chloroform after the 21. .. addition of petroleum ether, concentrating 93-98% of t he extracted thallium, and was applied to the spectrograph electrodes. This preconcentration technique could be useful in the boat, cup or graphite atomizer system of atomic absorption spectrophotometers.

A spectrographic method for the determination of 10 elements including thallium in mineral waters was described (Khitrov and Belousov, 1972).

Thallium in silicate rocks was determined spectro­ graphically after oxidation to thallium(III), adsorption on a Dowex l-X8 anion exchange resin from 1M hydrochloric acid and elution with 0.25M nitric acid, containing 1% hydrogen peroxide. The sensitivity was 0.03 ~g (DuAlbuquerque and Muysson, 1972b).

Chalkov et ale (1973) incr eased the sensitivity of the spectrographic determination of thallium to approximately 0.5-2 ~g/g by chlorination with lead chloride directly in the carbon electrode crater.

Other methods

The determination of thallium by neutron activation was described (Jaffrezic et al., 1972; Nadkarni and Haldar, 1972). In the latter work thallium was extracted with thionalide (thioglycol-2-naphthyl amide) in chloroform from aqueous alkali. Trimethylphenylammonium bromide was reported to quantitatively precipitate thallium(III) and gold (White, 1972). Thallium(I) was quantitatively precipitated by 6-phnnyl-2,3-dihydro-asym­ triazine-3-thione at ph 9-13, and, in t he presence of cyanide, the precipitation was specific f o r thallium (Edrissi et al., 1972).

Phenylthallium was determined by titration with EDTA (pepe et al., 1968).

TOXICITY

rrhallium and its compounds are highly toxic. Human toxicity of thallium was recently reviewed by Oehme (1972). Thallium is absorbed through skin and mucous membranes, is widely distributed throughout the body and accumulates in bones, renal medulla and, eventually, in the c e ntral nervous system. Thallium passes through the placenta and also occurs in milk. The biological half-life of thallium is 3-8 day s. Thallium is excreted mainly in the urine.

Toxic doses or concentrations of thallium, and for comparison, of some other metals are summarized in Tables 6 and 7. It can be seen that in mammals t hallium is slightly more acutely toxic than mercury and its toxicity is exceeded only by methyl mercury. To fish thallium is as acutely toxic 22 .

Table 6. Toxic dose or concentrations of thallium.

Effective dose Species or concentration Effect Reference

House 24-27 mg/kg LDSO Christensen,1972 " 16-19 mg/kg LDSO Tikhonova,1967 " O.S-l mg/kg IS days,measur­ able effects Tikhonova,1967 Rat 13-19 mg/kg LD50 Christense n,1972 II 6.S mg/kg 6 times in 14 days,measurable effects Malachovski~',1968 Dog IS mg/kg Lethal Christensen,1972 R.abbit 0.2 mg/kg 3-6 months,measur- able effects Tikhonova,1967 Atlantic salmon 0.03 mg/Q, LD50 Zitko et al.,1975 Rainbow trout 10-lS mg/Q, Lethal Nehring,1962 ?erch 60 mg/Q, " " " Roach 40-60 mg/Q, II " " Tadpoles 0.4 mg/Q, " Dilling and Healey, 1926 Daphnia 2-4 mg/Q, " Nehring,1962 Gammarus 4 mg/Q, " " " Azotobacter 20 mg/Q, Growth inhibi­ DeJong and Roman, tion 1971 Proteus mirabilis 390 mg/Q, Growth inhibi­ watanabe et al., tion 1971 Aspergillus niger 200 mg/Q, Growth inhibi­ tion Scharrer,1955 •

Table 7. Toxic doses or concentrations of some heavy metals.

Metal (chloride or acetate Species mg/kg m mole/kg Reference

Mercury Rat 27 0.13 Christensen, 1972 Methylmercury Mouse 13 0.06 " " Cadmium Rat 54 0.48 " " Lead " 150 0.46 " " Copper " 445 7 " " Zinc " 875 13.4 " "

mg/£ m mole/£

Mercury Stickleback 0.2 0.001 McKee and Wolf,1963 Ethylmercury Rainbow trout 0.09 0.0005 Amend et al., 1969 Cadmium Fathead minnow 1. 4-19 0.012-0.17 Pickering and Gast, 1972 Lead Rainbow trout 0.8-1.3 0.005-0.006 Lloyd and Herbert, 1962 Copper Minnow, salmon 0.05-0.5 0.0008-0.008 Sprague, 1964; Mount, 1968 Zinc " " 0.6-10 0.009-0.15 Sprague,1964; Brungs, 1969

N LV as copper on a weight basis, and 3-4 times more toxic than copper on a molar basis. Thallium kills fish quite slowly (Zitko et al., 1975) and this may explain the muc h higher toxic concentrations reported by Nehring (1962). Species differences, however, cannot be excluded. Hardness, which affects strongly the toxicity of metals to fish (see for example, Lloyd and Herbert, 1962), may not have much effect on the toxicity of thallium because of its low complexing ability. For the same reason, humic acid probably does not affect the toxicity of thallium. The acute toxicities of copper and thallium, and of zinc and thallium to fish are not additive (Zitko et al., 1974).

Hypertension is one of the symptoms of thallium poisoning in humans (Merguet et al., 1968, 1969) and in fish (Nehring, 1962). Burger and Starke (1969) suggest that this effect may be caused by the oxidation of thallium(I) to thallium(III) which inhibits the ATPase of amine-storing granules, thus causing alterations in the catecholamine metabolism. The uptake of thallium by yeast mitochondria (Lindgren, 1971) and the formation of thallium(III) oxide in these (Lindgren and Lindgren, 1973) confirms that oxidation of thallium in vivo takes place. It is not known to what extent this process is responsible for thallium toxicity. Thallium(III) catalyzed in v it~o the iodination of cytidine residues in a transfer RNA (Schmidt et al., 1973), but it is not clear whether a similar reaction could also occur i n vi vo .

Thallium(I) is able to s ubstitute monovalent cations, particularly potassium, in enzymatic reactions. Thallium is isomorphic with potassium, but has approximately 10 times high affinity than potassium for the enzymes. The increased affinity may cause the toxic effects.

The thallium activation was demonstrated in the case of several enzymes. Britten and Blank (1968), Inturrisi (1969a,b), Robinson (1970), Maslova et ale (1971), Nazarenko et ale (1972), Skul'skii et al. (1973), and Lishko et al. (1973) studied the effect of thallium on various sodium-potassium-sensitive ATPases, Manners et ale (1970) on a vitamin B12-dependent diol dehydratase, Kayne (1971) on pyruvate kinase, homoserine dehydrogenase, and AMP deaminase, and Antia et ale (1972) on L-threonine dehydratase.

In frog skin, thallium was tightly bound in the membrane and could not substitute potassium in the sodium-potassium pump system (Natochin and Skul'skuu, 1972). The relative rate of uptake of monovalent cations by goldfish intestinal mucosa decreased in the order thallium>potassium>rubidium>cesium> sodium>lithium (Ellory et al., 1973), and thallium restarted the activity of an isolated frog heart (Rusznyak et al., 1968). In chick embryos thallium induced achondroplasia (Hall, 1972), 25.

which was potentiated by cortisone acetate and prevented by vitamin C. Enlarged mitochondia were observed after exposure to thallium in the a xons of peripheral nerve fibers in mice • (Spencer et al., 1973) . Thallium inhibited the development of Pa r acen t r o tu8 lividus eggs (Lallier, 1968).

Thallium is toxic to bacteria, but quite high levels are generally required for measurable effects. Thallium inhibited t he nitrification by Nitr oba cte r agi lis (Tandon and Mishra, 1969). Staphy lococcu8 a ureus was approximately 15 times more resistant than S. epider mis (Kunze and Pramberger, 1972a) and, in general, Mycoplasmataceae were more resistant than Acholeplasmataceae (Kunze and Pramberger, 1972b).

Thallium is toxic to plants and inhibits chlorophyl l formation and seed germination (Scharrer, 1955). In Ch lor e l l a fU8ca the uptake of thallium was increased by illumination, and additional light-independent absorption of thallium was also observed (Solt et al., 1971). Similar results were obtained with Ul v a lactuc a (Skul'skii et al., 1972a). In contrast to potassium metabolism, sodium fluoride inhibited the uptake of thallium (I) (Skul t skii et al., 197 2b). On the other hand, the uptake of thallium(III) was independent of temperature, light or sodium fluoride (Polikarpov, 1970). The accumulation coefficients of thallium(I) and (III) were approximately 20 and 50, respectively, and an equilibrium was reached within 20 h (Polikarpov, 1970). Thallium was not adsorbed by alginic acid (Lazorenko and Polikarpov, 1972).

Little is known about the toxicity of organothallium compounds. Diphenyl thallium chloride and cyanate were toxic to a number of pathogenic fungi (Srivastava et al., 1973).

Antidotes against acute thallium poisoning were reviewed by Munch (1968) and included activated charcoal, BAL, calcium salts, cystine, dithiocarb, dithizone, histamine, theophylline, potassium chloride, and thiosulfate. Prussian blue and other hexacyanoferrates(II) were recently recommended as antidotes (Dvorak, 1969; Kamerbeek et al., 1971). A 2 % colloidal solution of ferrihexacyanoferrate(II) increased the urinary excretion of thallium by a factor of 2.8, but only if administered during the first 24 h (Guenther, 1971). The excretion of thallium was also increased by D-penicillamine (Slepicka et al., 1969), and a chronic thallium intoxication was somewhat alleviated by vitamin B12 (Malachovskis, 1968).

Data on the concentration of thallium in tissues and organs of acutely poisoned humans and animals were reviewed by Munch (1968). In the majority of human cases, the amount of thallium taken was not known. The concentration of thallium in kidney and liver was 2.7-42 and 10-34 ~g/g, respectively. Three subjects died as a result of thallium acetate poisoning 26.

(6.9 mg/kg, as thallium), and the concentration of thallium in kidney and liver was 60-79 and 482-862 ~g/g. Berman (1967) found a thallium concentration of 300 ~g/~ in blood, and 30-1240 ~g/~ in urine of subjects acutely poisoned by thallium. In cases of animal poisoning, the thallium concentrations were 12-135, 7-140, 3-103, and 3-120 ~g/g in kidney, liver, muscle, and spleen, respectively (Munch, 196 8) .

The concentration of thallium in urine, hair, and toenails is a useful indicator of sublethal thallium poisoning. Toenails are preferred to hair because they contain thallium in high concentration (Henke and Bohn, 1969).

Little is known about the chronic toxicity of thallium and the tissue levels of thallium, resulting from a chronic exposure. In fish exposed to metals in the laboratory, the accumualation factors of thallium are somewhat higher than those of other metals (Table 8). It can be seen that with the exception of methylmercury the accumulation factors are relatively low. No data are available on the accumulation of thallium in shellfish, which are known to accumulate some heavy metals to a high degree.

POLLUTION POTENTIAL

Bowen (1966) lists thallium together with silver, gold, cadmium, chromium, copper, mercury, lead, antimony, tin, and zinc as metals with a very high pollution potential. The rating is based on the ratio between the amount mined and the amount ~ost from the ocean per year. For all the above metals with the exception of tin this ratio is higher than 10. In the case of thallium it is 6,000 because of the very long residence time of thallium in the ocean (2.6 x 109 years).

As in the case of other metals, human activity cannot change the concentration of thallium on the global scale, but localized pollution incidents, in which thallium contaminates the environment either intentionally or unintentionally, are possible.

The intentional contamination includes the use of thallium compounds as rodenticides, which dates back to about 1920 (Munch, 1968). The high toxicity of these compounds resulted in the cancellation of their use against mammalian predators in the U.S.A. (Federal Register, 1972). Many countries, however, still use thallium compounds for this purpose. Saito and Masaharu (1972) reported that broadcast application of thallium sulfate did not cause water pollution. The rodenticidal application of thallium compounds may lead to accidental poisonings but is not likely to cause a major pollution problem and, in any case, will probably be phased out.

The present industrial uses of thallium are limited and almost certainly do not generate pollution problems. This situation, however, could change, were the applications of •

Table 8. Accumulation of some metals in fish during laboratory exposure.

Accumulation Metal Species Tissue coefficient* Reference

Thallium Atlantic salmon Muscle 130 Zitko et al., 1975 Liver 170 II II II Gills 480 It II "

Methylmercury Pike Kidney 9,000 Giblin and Massaro, 1973

Cadmium Bluegill Gills 5-8 Mount and Stephan, 1967

Copper Carp Whole fish 19-65 Kariya et al., 1967 Brown bullhead Gills 17 Brungs et al., 1973 Liver 65 II It "

Zinc Bluegill Muscle 2 Mount, 1964 Gut,gill 13 n II Muscle 8 Lebedeva and Kuznetsova, 1969 Gut,gill 100 n .. tI n Whole fi sh 10 Hoss, 1964

* Accumulation coefficient = tissue concentration ~g/g wet weight/water concentration ~g/m2.

tv -....J 28.

thallium expanded.

Thallium pollution may be a problem in the mining industry. As mentioned earlier, thallium is usually not recovered because of the limited market. In addition, the currently used wastewater treatment in the mining industry, aimed at the removal of heavy metals such as copper and zinc, and based on liming, would not remove thallium(I).

Hawley (1972) suggested that metals such as gold, silver, selenium, thallium, indium, gallium, antimony, and arsenic may be present in efflue nts from base-metal mining operations. Zitko et ale (1975) reported thallium concentra­ tions of 1-80 ~g/~ in two rivers draining base-metal mining properties in New Brunswick, Canada. Algae and moss from these rivers contained thallium in concentrations ranging from 9.5 to 162 ~g/g dry weight.

Thallium pollution may also be generated in the vicinity of smelters, particularly when thallium is not recovered. Mining of minerals other than sulfides, for example potash and silicates, may also release thallium into the environment.

ACKNOWLEDGMENTS

I thank Mrs. Madelyn M. Irwin for the efficient assistance in literature documentation, Miss M. Beryl Stinson and Mrs. Linda Morris for skillful librarian help. Mrs. Madelyn M. Irwin typed the manuscript, and Messrs. P.W.G. McMullon and F.B. Cunningham prepared the figure. 29. REFERENCES

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