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The Elements in the Second Rank 3 Elements in the Second Rank - an OverviewIn this chapter the most important information on the 11 elements is summarized, while Appendix A contains more detailed data sheets for each element. 3.1 Uses and amountsThe metals are used in a wide spectrum of products, where the content can be as small as a few percent or less. Table 3.1 gives an overview of the main fields of use and the estimated yearly consumption of the metals in Denmark. The consumption estimates were in general calculated by multiplying the Danish population figure with the per capita consumption in USA. The expected consumption trend is reported as unknown, decreasing, constant or increasing. More information on the consumption can be found in the data sheets (Appendix A). The data on use and consumption were obtained from a literature screening. The different usages are not prioritised with respect to the amount used. For some of the metals, the content in fossil fuels is very high compared to the other uses. Since the use of fossil fuels is not related with the content of trace metals, the amounts of the elements in the second rank resulting from energy production based on fossil fuels are given separately. Table 3.1
*only the consumption as bleaching agent The majority of the metals are used in small or large scale in the metal industry in e.g. alloys. Many of the metals are used in electronics. As seen from Table 3.2, a relatively large part of the total amount of especially gallium, lithium and vanadium is found in coal. The Table shows minimum and maximum values for the content of the metals calculated from a yearly consumption of coal of 6.7 × 106 tonnes (Danmarks Statistik 2001). No data was found for ordinary heating oil. Table 3.2
Antimony is used mainly as flame retardant, in lead alloys in batteries and infrared detectors. The consumption of antimony for lead alloys is decreasing due to their replacement with alloys that have a lower impact on the environment. Antimony is used along with e.g. polybrominated diphenyl ethers as flame retardant. Substitution of brominated flame retardants due to their adverse health and environmental effects will possibly result in decreased consumption of antimony. However, this drop in consumption will probably be counterbalanced by increasing use in the production of infrared detectors. Boron is used for many purposes. The quantitatively most important use is in the form of sodium borate, which has the function of bleaching agent in detergents. Boron compounds are also used as e.g. flame retardant, biocide, dietary supplement and in the production of pyrex glass. The consumption is expected to be constant. Molybdenum is used for alloys of steel - mainly specialty steel and stainless steel. Molybdenum is used as catalyst in the chemical and petrochemical industris, in colour pigments, as flame retardant and as dietary supplement. The consumption is expected to be relatively constant. Vanadium is used mainly in the metal industry. It is used in titanium alloys, hard steel, and trade steel. Furthermore it is used as catalyst, pigments and dietary supplement. The consumption is expected to be constant. 3.2 Dispersal to and levels in the environmentWhen the metals are found in chemical combinations, e.g. as oxides or halides, the physico-chemical properties are significantly different from those of the pure metals. This applies for e.g. the aqueous solubility, which for most halides is very high. The character and extent of dispersal of an element into the environment varies according to the consumption, the specific chemical form and its physico-chemical properties. Table 3.3 reports the most important ways of dispersal of the metals to the environment with the different emissions and waste streams (as a sum of all metal compounds). The number of "x"s indicate the relative importance of the ways of dispersal for the individual metal. Thus, the number can not be compared within each way of dispersal. Table 3.3
Due to sparse literature data regarding the presence and concentration of the metals in the major waste streams in the Danish society, chemical analyses of a number of selected emission sources and waste products were included in this study. Seven types of waste streams and waste products from which the metals can be dispersed into the environment were chosen: treated municipal waste water, sewage sludge, sediment from road runoff basins, compost from garden waste and municipal solid waste (MSW), leachate from controlled landfills, leachate from disposal sites containing residuals from waste incineration plants with semi-dry and wet gas cleaning technology, respectively, and cleaned stack gas from the same plants. From each waste type, a representative sample was taken from two plants, except for garden compost, MSW compost, leachate from residuals from semidry and wet waste gas treatment, respectively. An overview of the results is given in Table 3.4, and more detailed results can be found in the data sheets. Table 3.4. Data from Swedish measurements of the concentration in sewage sludge, sediment from road runoff basins and leachate is in general in the same range as the data presented in Table 3.4. However, there is tendency of the measured Danish concentrations to be somewhat higher, especially for palladium where the level is approximately a factor of 10 higher. Considering the amounts consumed, it was not unexpected to find the highest concentrations in most waste types among antimony, boron, lithium, molybdenum and vanadium. It was, however, unexpected to find high concentration of gallium and palladium in e.g. sewage sludge and compost. 3.3 Health effectsThe toxicological properties of the metals and their individual inorganic compounds vary greatly. An oxide of a metal can for example be more toxic than its chloride. It order to compare the toxicity of the metals, Table 3.5 gives a short summary of the information regarding the most toxic metal compounds. It is underlined that the search and evaluation of data on environmental effects did focus on exposure of low concentration from ingestion or from exposure in the environment for prolonged periods of time. In other words, the focus was on the assessment of the possible impact on the general population more than assessment of the risk from exposure to high concentrations in the working environment. Table 3.5
Antimony as antimony trioxide exhibit acute and local effects, and in experiments with animals, sensitization, reprotoxicity, and teratogenicity have been observed. According to IARC, beryllium is regarded as carcinogenic. The critical exposures are mainly observed in the working environment. The divalent beryllium-ion can substitute Mg2+ in enzymes, and thereby inactivate them. At high doses, lung cancer has been observed. Bismuth and bismuth compounds have resulted in adverse effects on humans from medical treatment more frequently than from exposure in the working environment [9]. Chronic exposure can result in poisoning symptoms which resemble the symptoms from lead and mercury exposure: Hyper salivation, stomatitis and greyish colouring of the gums. From prolonged exposure symptoms of damage on the central nervous system can be observed. Exposure to boron, boric acid, and boron derivatives is related with exposure in the working and indoor environment. Ingestion, uptake from skin or mucous membrane result in loss of appetite, loss of weight, vomiting, mild diarrhea, skin eruption and anaemia. Lithium is used therapeutically in treatment of manic-depression. It was shown that LiCl is moderately toxic in rats. Lithium resembles sodium chemically, but is more toxic: 5 g LiCl can result in mortal poisoning in humans. Brain weight of male offspring of rat was shown to decrease as a result of chronic exposure. Molybdenum is a constituent of many enzymes and is regarded as an essential metal. No chronic effects seem to arise from exposure to low molybdenum concentrations. Palladium has not been identified as acutely toxic or to cause CMR effects. Contact dermatitis has been reported from exposure to metallic palladium and palladium alloys. Platinum in its metallic form is relatively harmless, but allergic dermatitis from especially complex salts is known. Platinum is, as the other noble metals, relatively toxic or ion form on soluble form. The metallic form of vanadium does not seem to pose any essential risk to the human health. However, selected vanadium compounds are toxic with mutagenic and reprotoxic effects. 3.4 Environmental propertiesCertain metal ions are essential micronutrients for both plants and animals and are assimilated by cells in trace concentrations. The metal ions are used in cell metabolism in e.g. redox reactions and many enzymatically catalyzed reactions. In high concentrations, the ions will have adverse effects on the cells. Some metal ions can be assimilated instead of the essential metal ions and thereby decrease or stop parts of the cell metabolism. This is the case for e.g. beryllium, which on ion form can be assimilated in cells instead of Mg2+ and replaces magnesium in certain magnesium-containing enzymes. Thereby, the reactions which are catalysed by these enzymes are deactivated. Metals in the aquatic environment can, depending to their environmental behaviour and extent of assimilation in organisms be classified as either nutrient type, conservative or particle bound (Zenk, 1996 and Nozaki, 1997). Metals of the nutrient type are essential for growth. They are assimilated naturally by e.g. algae and their function is related to for instance enzymatic processes. They are released into the environment with the eventual degradation of organic matter. The metals do not necessarily have a biological function. This applies to Be, B, Ga, In, Pd, Pt and V. Conservative metals are not influenced by biologic assimilation or sorption and they have normally long retention times in aquatic environments. The consequence of a release of such a metal would be a long lasting presence in the environment. This is especially the case for alkali metals. Of the metals included in this study, lithium is the only conservative metal. Metals strongly influenced by sorption will bind to particulate matter. This applies to a various degree to Sb, Bi, Ga, In, Mo, Pd and V. 3.4.1 Environmental chemistryThe environmental properties of the metals depend among others on their form (speciation), redox state and distribution into highly and low soluble compounds. In aquatic ecosystems, the metals are found as ions, as halogenated compounds and as oxo- and hydroxylated compounds. 3.4.1.1 Ion form Beryllium and lithium are found as ions. Their concentration is regulated by the solubility of their salts, which depends on e.g. pH. The concentration of beryllium ions is normally low in aquatic ecosystems because of the low solubility of the salts at the pH-values typically found in these environments. 3.4.1.2 Halogenated compounds Most of the metals in the second rank can be found as halogenated compounds. In the aquatic environment it is primarily palladium and platinum that are found in this form. In sea water, PdCl42- and PtCl42- are the most common forms of these two elements. 3.4.1.3 Oxo compounds Nearly all elements form compounds with oxygen. Molybdenum and vanadium are in the aquatic environment found as MoO42-and HVO4-2. In oxygen limited environments, molybdenum is reduced and forms low-soluble compounds with e.g. iron monosulfides, which subsequently precipitate. 3.4.1.4 Hydroxylated compounds Many of the metals in the second rank form hydroxylated compounds, and in the aquatic environment the following compounds are found: BeOH+, Bi(OH)2+, B(OH)4-, Ga(OH)4-, In(OH)2+, In(OH)30, Pd(OH)20, Pd(OH)20, Sb(OH)3 and Sb(OH)6-. Their chemistry varies a lot and the pH has for example very different effect on the solubility. Some metals also form complexes with other metal ions. 3.4.1.5 Persistency Metals and other elements are conservative. Some elements are changed by radioactive decay, but none of the metals included in this study do so. The metals can form numerous inorganic compounds and certain among them can also be methylated. The latter is, however, a phenomenon that is relatively poorly investigated among the second rank metals. 3.4.2 Aquatic toxicityThe aquatic toxicity of the metals depends greatly on which metal compound is used for the toxicity testing. This is partly due to the different solubility of the inorganic compounds, but also the susceptibility for formation of complexes is important. In Table 3.6, the highest aquatic toxicity reported of the metals (the specific compounds are shown in the table) is given. It can be seen that antimony, beryllium, bismuth, palladium and platinum are very toxic to aquatic organisms. 3.4.3 BioaccumulationSome metals can accumulate in organisms because of their lipophilic character, and biomagnification can be observed in the food web. The ion forms of the metals are non-lipophilic, but organo-metallic forms can often bioaccumulate. In Table 3.6, bioconcentration factors (BCF) or expected ability to bioaccumulate are shown. The biochemical regulation of certain metals in cells depends on proteins, which are induced by the presence of certain metals. Induction depends upon the metal - the classic heavy metals have highest effect - but also indium, bismuth and gallium have this property. Table 3.6
3.5 Existing regulationThere are only few limit values and quality criteria for the metals in the second rank in air, soil and water. This is possibly a result of the general lack of information on their effects on health and environment and their lower priority compared to the traditional heavy metals. There are limit values in drinking water for boron, lithium and molybdenum. Limit values exist for antimony, beryllium, boron, lithium, molybdenum, palladium, platinum and vanadium on national or EU-level, see Table 3.7. Table 3.7
* temporary value.
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