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The Elements in the Second Rank

3 Bismuth

3.1 Identity

Table 3.1
CAS No., EINECS No and molecular weight for bismuth

Bismuth is a rare metal, which typically is produced as a by-product during the refining of other metals [1].

3.2 Physico-chemical properties

Bismuth is found in group VB in the periodic table and it has the valences +3 (Bi(III)) and +5 (Bi(V)). Bismuth has a density of 9.80 g/cm³. It belongs to class B of the heavy metals, where the very toxic metals such as lead, thallium and mercury are found also [6]. Bioavailable bismuth is found as e.g. BiO⁺ or Bi(OH)₂⁺.

Table 3.2
Physico-chemical data for metallic bismuth. Data from [2, 8]

3.3 Uses and consumption

3.3.1 Uses

Bismuth has a wide range of uses and is often used as substitute for other metals, especially lead [13]. Below the most common uses are mentioned.

Antimony and bismuth can replace each other in several products [10]. Often bismuth, gallium and indium are used together in e.g. semi conductors [14]. Bismuth is used alone in metal alloys where a low melting point is required, in the petrochemical industry, ceramics, glass, pigments, electronics, plastic, fuses and optical instruments.

Bismuth is used to decrease the melting point of alloys when added in low concentrations. Good examples are Woods and Roses metals, which both contain bismuth, lead, and tin. These are used in thermal fuses in automatic fire protection installations [10].

An expanding area where bismuth is used (as a bismuth-molybdenum compound), is as a catalyst in the production of acrylonitrile and polyurethane foams [12].

The salts of bismuth have a low toxicity and they are therefore widely used in the pharmaceutical and cosmetic industry [6].

Additional areas where bismuth is used are in pigments/paint (often as a substitute for Cd-, Pb- and Cr-pigments), catalysts, super conducting materials, ceramic coloring, lubricants, flame retardants, glassware, ammunition, fluorescent lamps, prevention of tin-pest, and batteries [11, 12].

Substitution of organotin compounds in agricultural pesticides and marine antifoulants with organobismuth compounds decrease the marine-life toxicity problems. [12].

3.3.2 Consumption

The global production of bismuth (often as a by-product in mining of lead, tin, cobber, wolfram, silver, and gold) was 4,000 tons in 1996. The consumption in USA was approximately 1700 tons.

Assuming that the per capita consumption in Denmark and USA are identical, the Danish consumption is about 36 tons per year based on 1996 figures [6]. In Table 3.3 the distribution of the use in the USA is shown. From this distribution the yearly consumption in Denmark is calculated. The recycling percentage of bismuth is low.

Table 3.3
The relative distribution of USA's and Denmark’s consumption of bismuth in 1997 [6]

3.4 Emissions to and occurrence in the environment

Metallic bismuth is found in nature, but the background concentration in the aquatic and terrestrial environment is low, see Table 3.4.

Table 3.4
Typical background concentration of bismuth in the environment. Data from [8]

Bismuth is found in concentrations of up to 2.3 mg/kg in waste products from incineration of coal [6]. In oil the concentrations of bismuth can be as high as 0.4 mg/kg. Combustion of fossil fuels is assumed to account for a significant part of the total emission in Denmark. Use of bismuth in e.g. cosmetics, chemicals and other consumer products brings bismuth into solid waste and municipal waste water. This was confirmed by a Danish study, in which bismuth was found in waste water and in sludge from waste water treatment plants [3]. It is assumed that bismuth is emitted from incinerators as BiCl₃ [6]. The major part of the emission comes from incineration of municipal solid waste. Cinders and fly ash from coal fired power stations contain 2.6-8 and 9.4-14 mg/kg Bi, respectively [6].

In the analysis of emissions and waste carried out as part of this study, bismuth was identified primarily in sewage sludge and sludge from runoff retention basins, see Table 3.5. In stack gas, treated municipal waste water, and leachate from landfills, the concentration of bismuth is close to the detection limit.

Table 3.5
Levels of bismuth in selected emissions and waste products from measurements conducted as part of this study in the autumn of 2001.

3.5 Danger classification

Bismuth or inorganic bismuth compounds are not on the Danish list of dangerous compounds [7].

3.6 Toxicology

Adverse effects of bismuth and bismuth compounds in humans have been observed from medical treatment rather than exposure from the working environment [9]. In past days, therapeutic treatment with bismuth was often prolonged, and this chronic exposure resulted in symptoms of poisoning. The symptoms resemble those of lead and mercury: hyper salivation, stomatitis, and greyish pale colour of the gums. From prolonged exposure damages on the central nervous system are observed, e.g. absent-mindedness and amnesia, insomnia and encephalitis [15].

Some investigations show that bismuth can be transformed from compounds with low toxicity to compounds with higher toxicity by intestinal bacteria.

Organic Bi(CH₃)₃ has a relatively high vapor pressure and can irritate the respiratory tract and the eyes conjunctiva [9].

There is no evidence of carcinogenicity, mutagenicity, or teratogenicity from exposure to bismuth compounds [9].

3.7 Environmental properties

Bismuth is often marketed as an environmentally friendly alternative to the traditional, more toxic heavy metals. Under the present level of exposure and emission to the environment, no adverse effects of bismuth have been observed on humans and animals [6]. According to a Swedish study, no biological functions of bismuth are known. Furthermore, negative effects in the environment are not likely unless the emission increases significantly compared to the present level [6].

3.7.1 Environmental chemistry

Bismuth occurs in fresh and sea water as hydroxides (Bi(OH)₂⁺ and Bi(OH)₃⁰). In the aquatic environment bismuth is associated with particulate matter with a high retention time in the aquatic environment. Bismuth can be methylated in the environment. In this form, bismuth has high lipophilicity and it can bioaccumulate in lipid-rich environments. If plants take up the metal, it can be partly or completely deactivated by complexation with phytochelatin. Deactivation of enzymes, which are affected by metals, is thereby avoided. The fact that this mechanism of defence is active with bismuth (and other metals, e.g. Cd²⁺ and Pb²⁺) indicates that the metal can affect biological functions. The metal has high affinity to particles (comparable with leads metal affinity) [6].

3.7.2 Environmental toxicology

Only limited information regarding the environmental toxicology of bismuth and bismuth compounds is available. Bismuth nitrate has high acute toxicity in the aquatic environment and EC₅₀ has been determined to 0.66 mg/L in a four day test using Tubifex tubifex as test organism. According to this result, the compound should be classified as very toxic to aquatic organisms.

Table 3.6
Test results for environmental toxicity. Data from [4]

3.7.3 Bioaccumulation

The available data on environmental fate of bismuth is not sufficient to conclude on its ability to bioaccumulate. In the marine environment, bismuth is typically associated with particulate matter.

3.8 Conclusions

The physical properties of bismuth make it a good substitute for certain heavy metals. The metal is used in e.g. cosmetics where it shows no adverse effects in low concentrations. Bismuth is dispersed from diffuse sources and the concentration of bismuth in the environment is generally low. High concentrations of bismuth in sewage sludge and in ash from waste incineration were observed. The environmental toxicity of bismuth is generally low compared to other heavy metals.

3.9 References

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