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The Elements in the Second Rank

1 Antimony

1.1 Identity

Table 1.1
CAS No., EINECS No and molecular weight for antimony

1.2 Physico-chemical properties

Antimony is a metalloid from the same group in the periodical table as arsenic and phosphorus (group VB). Normally it has the valences +3 (Sb(III)) and +5 (Sb(V)). Metallic antimony has a crystalline structure with a bluish white color and has a metallic lustre. Antimony is not attached with diluted acid or base.

Typical compounds of antimony are sulfides, hydroxides, and oxides [1, 2]. Metallic antimony is insoluble in water, whereas the oxides Sb₂O₅ and Sb₂O₃ and sulfides of antimony are slightly soluble in water. Table 1.2 shows selected physico-chemical data for metallic antimony (data from [3]).

Table 1.2
Physico-chemical data for metallic antimony

1.3 Uses and consumption

1.3.1 Uses

Antimony is used for:

	Production of high alloy steel
	Lead alloy in batteries
	Flame retardant in textiles, plastic and electronic components
	Yellow pigments (Sb2S3)
	Ceramics, enamel and glassware
	Infrared detectors
	Plastic/rubber (as stabilizer)
	Lubricant
	Certain medical/pharmaceutical products
	Cosmetics

Antimony is used as metallic antimony in alloys and as salts. Within the EU, antimony is used in the following high volume compounds: diantimony trioxide (CAS No. 1309-64-4), antimony trisulfide (CAS No. 1345-04-6) and sodium hexahydroxoantimonate (CAS No. 33908-66-6) [4]. Antimony is also found in cosmetics [7, 13, 17].

1.3.2 Consumption

The global production of antimony has been approximately 150,000 tons/year and. It has increased in the last years. China accounts for approximately 70 % of the production. Based on the per capita-consumption in USA, the consumption in Denmark is estimated be to approximately 840 tons per year in 1995/1996 [9].

The price fluctuates with the supply form China [14]. The major producing countries are China (100,000 t/year), South Africa (6,000 t/year), Bolivia (5,000 t/year), and Russia (3,000 t/year). Major antimony reserves are found in the countries mentioned above and in the USA and Kyrgyzstan.

As seen in Table 1.3, the consumption is expected to decrease in a few of the use categories. However, the overall consumption is expected to increase.

Table 1.3
Expected trend in the Danish consumption of antimony within different use categories [9]

In Table 1.4, the estimated Danish consumption of approximately 840 tons/year is divided into five categories based on the distribution in USA in 1996 [9].

Table 1.4
The relative distribution of the consumption in USA and the estimated Danish use of antimony in 1996 based on [9]

1.4 Emissions to and occurrence in the environment

Antimony is found in trace concentrations in coal and oil. Consequently, it is emitted to the environment from combustion of fossil fuels. Emission from industry and combustion of fossil fuels has resulted in significant increase in the total emission of antimony through the last 50 years [9].

Antimony is found in solid waste due to the use of antimony oxide as flame retardant in e.g. plastics, textiles and electronic equipment. It is estimated that both combustion and land filling of solid waste will result in emission of antimony. A Swedish study showed that antimony in cinder, fly ash and stack gas condensate from waste incineration is 526 µg/kg dw, 425 µg/kg dw and approximately 1 mg/L, respectively [9]. 0.1-1 % of the antimony in the waste is emitted to the atmosphere by incineration, depending on the type of waste gas cleaning applied.

Swedish experience shows that the level of antimony in arable land increases significantly by sludge amendment.

The concentration of antimony in fresh and sea water (primarily as Sb(OH)₆^-) is low, see Table 1.5. The data are literature values, which do not necessarily reflect the background concentration in Denmark. 25-75 ng/L of antimony has been found in the Baltic Sea. Antimony can be associated with particulate matter. In the environment, a considerable amount of antimony is found as methylated antimony [9].

Table 1.5
Typical background concentration of antimony in the environment. Data from [9, 12, 16]

A limited investigation of the levels of antimony (and the other elements covered by this study) in the major emissions and waste streams in society was conducted in the autumn of 2001, see Table 1.6.

In the waste streams antimony was found primarily in sewage sludge and sediment from road runoff retention basins. The concentration of antimony was relatively high in leachate compared to the other metals measured as part of this study. The concentration was low in stack gas.

Table 1.6
Levels of antimony in selected emissions and waste products from measurements conducted as part of this study in the autumn of 2001.

1.5 Danger classification

Antimony compounds are found on the Danish list of dangerous compounds. Antimony tetra oxide (Sb₂O₄), antimony pentoxide (Sb₂O₅), antimony trisulfide (Sb₂S₃), antimony pentasulfide (Sb₂S₅) are classified as harmful with risk phrase R20/22 (harmful by inhalation and if swallowed) and dangerous for environment with risk phrase R51/53 (toxic to aquatic organisms, may cause long-term adverse effects in the aquatic environment) [8].

Within the EU, antimony trioxide is classified as carcinogenic (category Carc3) with R-phrase R40 (possible risk of irreversible effects) [8]. EU is currently evaluating the compound in order to assess its environmental classification and risk phrases.

Antimony chlorides are classified as corrosive and dangerous for environment and antimony trifluoride is classified as toxic and dangerous for environment [8].

Table 1.7
EU-classification of antimony and antimony compounds [8]

- not classified

1.6 Toxicology

Epidemiological investigations have shown that antimony in the form of antimony trioxide can result in dermatitis and possibly it has adverse effects on female reproduction. Studies with rats have shown that inhalation of antimony trioxide can result in teratogenic effects. Neither IARC nor EPA has evaluated the carcinogenic characteristics of antimony, but antimony trioxide is classified as carcinogenic in category 3 within the EU (carcinogenic in experimental animals). Effects at low concentration are observed by exposure by inhalation, and lung neoplasms have been observed in experimental animals; apparently female animals are more sensitive than males [9].

Increased concentrations can be found in selected working environments and in the air close to e.g. metallurgical industry, coal fired power plants and incinerators. Metallic antimony and certain trivalent antimony compounds have highest potential for exposure while pentavalent compounds are less problematic [15].

1.7 Environmental properties

1.7.1 Environmental chemistry

Salts of antimony form hydrated antimony compounds in aqueous environments. Sb(III) is found as Sb(OH)₃ in most aquatic environments while the dominating species of Sb(V) in aqueous environments is Sb(OH)₆^- (pH > 3) [2]. Formation of complexes with organic matter is not important for the overall antimony flux. The mobility of antimony in soil and sediment is controlled of binding to clay and minerals, and precipitation with oxides of Fe, Al and Mn [2].

Biomethylation of antimony is observed in the environment as for tin, arsenic and other related metals. Apparently, methylated antimony compounds do not have any significant adverse environmental effect [2], but other references report that methylated antimony is very toxic [7].

1.7.2 Environmental toxicology

Antimony trioxide showed 50% inhibition of growth (EC₅₀) on the fresh water alga Selenastrum capricornutum at 0.7 mg/L, while the no observed effect concentration was 0.2 mg/L. [5]. Therefore, the compound is classified as very toxic to algae. The EC₅₀ on Daphnia magna (measured as immobilisation) of the compound antimony trioxide was 423-555 mg/L. Antimony trichloride had a LC₅₀-value of 12.1 mg/L on Daphnia magna. The LC₅₀ of antimony trichloride on rainbow trout in a long term test (28 days) was 0.66 mg/L.

Antimony chloroxide had a no observed effect concentration of 0.03 mg/L on the fresh water alga Chlorella vulgaris after three months' exposure.

Table 1.8
Selected test results for environmental toxicity of antimony (mg/L). Data from [5]

1.7.3 Bioaccumulation

The available information on bioaccumulation of antimony does not give reason to view antimony as bioaccumulating. The highest concentrations are observed for macro algae with a bioconcentration faction (BCF) of 7 to 17. Certain plants do, however, accumulate considerably more antimony. Values for bivalves, crustacean, and fish are lower [5].

1.8 Conclusions

Increased industrial use and combustion of fossil fuels have resulted in increased emission to the atmosphere. This has enhanced the dry and wet deposition. Antimony compounds are generally harmful, but selected compounds have other effects. Antimony trioxide is on the list of dangerous compounds and classified as carcinogenic in category Carc3. Antimony trifluoride is toxic to humans and aquatic organisms.

1.9 References

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