Antimony in the environment: a review focused on natural waters: I. Occurrence
Introduction
A good deal of research on geochemical and biogeochemical processes in natural waters has been, and continues to be, devoted to trace elements, particularly transition metals. Rather less attention has been focused on the so-called metalloid elements. Among them, antimony is the one that has received the scantiest attention.
Antimony is a naturally occurring element. It belongs to the group 15 of the Periodic Table of the Elements. Antimony can exist in a variety of oxidation states (−III, 0, III, V) but it is mainly found in two oxidation states (III and V) in environmental, biological and geochemical samples. The relative abundance of antimony in different terrestrial systems is given in Table 1.
According to the classical classification of Goldschmidt, antimony is a strong chalcophile element and as such mainly occurs in nature as Sb2S3 (stibnite, antimonite) and Sb2O3 (valentinite), which is a transformation product of stibnite. These compounds of antimony are commonly found in ores of copper, silver, and lead. Antimony is also a common component of coal and petroleum.
Little information is available on the transformation and transport of antimony in the different environmental compartments. Even information on antimony speciation and total content in the various media is scarce and often contradictory. This lack of understanding of antimony behaviour and fate in the environment hinders further research. In this series of papers, we have launched an exhaustive review of the scientific literature in order to identify and evaluate all sources of information related to antimony. In this first paper, we have attempted to include all studies devoted to freshwaters, marine waters, and estuaries. To illustrate key aspects of antimony occurrence in nature, some selected information on sediments and soils is also included. Values quoted come from the original sources. Multireferencing has been avoided. In the very few cases where it has been used, the origin of the reference is given. A total of 420 papers have been reviewed. Other studies on subjects such as relevant aquatic chemistry, antimony in biota, etc., will follow.
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Uses
Antimony was already known to the ancients. Since it can dissolve many other metals including gold, this property was used for purifying gold from copper and silver up to the 18th century. A peat core from an ombrotrophic Swiss bog revealed significant enrichments of antimony extending back to Roman times, indicating that the anthropogenic fluxes of this metal have exceeded natural ones for more than 2000 years. The present day enrichment factor (relative to the element/Sc ratios of typical
Toxicity
Antimony and its compounds were considered as pollutants of priority interest by the Environmental Protection Agency of the United States (USEPA, 1979) and the European Union (Council of the European Communities, 1976). The USEPA drinking water standards are: maximum contaminant level goal (MCLG) and maximum contaminant level (MCL), both 6 μg/l (USEPA, 1999). The European Union established a maximum admissible concentration of antimony in drinking water of 5 μg/l (Council of the European Union,
Occurrence in natural waters
Antimony is present in the aquatic environment as a result of rock weathering, soil runoff and anthropogenic activities. Typical concentrations of dissolved antimony in unpolluted waters are less than 1 μg/l. However, in the proximity of anthropogenic sources, concentrations can reach up to 100 times natural levels.
Antimony is present in substantial concentrations in precipitates from hot springs and boreholes and in geothermal waters. Concentrations ranging from 500 mg/l up to 10 wt.% have
Occurrence in sediments and soils
Antimony concentrations in sediments and soils are of the order of a few μg/g Table 6, Table 7. Higher concentrations are directly related to anthropogenic sources, mainly proximity to smelting plants O'Toole et al., 1971, Crecelius et al., 1974, Cawse et al., 1975, Ragaini et al., 1977, Ainsworth et al., 1990a, Asami et al., 1992. Elevated concentrations in sediments near the outfalls of sewage and fertiliser facilities have also been reported Papakostidis et al., 1975, Grimanis et al., 1977.
Reference materials
In comparison with other trace elements, reference materials (RM) with certified antimony contents are scarce. The most often used and easily available environmental reference materials containing antimony are given in Table 8. Data quoted in Table 3, Table 4, Table 5, Table 6, Table 7 do not contain any published result for this type of samples. However, the reader can find complementary information on the use of these reference materials in the following selection of recent papers where these
Occurrence in biota
There is no evidence of bioconcentration of antimony in aquatic algae Bonotto et al., 1983, Mann and Fyfe, 1988, Mann et al., 1988. Reported concentrations for antimony in freshwater and marine algae are 0.1–0.2 μg/g dry weight (range from 0.02 to 1 μg/g dry weight) Leatherland and Burton, 1974, Strohal et al., 1975, Payer et al., 1976, Bowen, 1979, Abu-Hilal and Riley, 1981, Kantin, 1983, Andreae and Froelich, 1984, Maher, 1986, Djingova et al., 1987, Mann and Fyfe, 1988, Mann et al., 1988,
Speciation in natural waters
It is nowadays well recognised that the understanding of biogeochemical processes depends upon the knowledge of the chemical forms, or species, that are present in the natural environment. Despite this well-known requirement, the speciation of many elements in the natural environments is not adequately known. Antimony is not an exception.
Antimony occurs in two oxidation states in natural waters and, thus, its behaviour can be affected by changes in the redox status of the aquatic environment.
Importance of atmospheric input
Airborne supply to aquatic and terrestrial systems is important for the environmental fate of some elements. Although existing data are sparse, this seems to be the case for antimony in systems far from direct pollution sources Payer et al., 1976, Andreae and Froelich, 1984, Austin and Millward, 1986, Van der Weijden et al., 1990, Cutter, 1993, Guieu et al., 1993, Cutter et al., 2001.
Atmospheric emission values for antimony, as estimated by Nriagu and Pacyna (1988) and Nriagu, 1989, Nriagu, 1990
Conclusions
This extensive review on the occurrence of antimony in the environment presents most of the information available on the distribution and speciation of antimony in aquatic systems in a condensed format. More importantly, it has identified several important biogeochemical aspects of the element for which further research is still needed, namely:
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speciation of antimony in natural waters and its partition among dissolved and solid phases in both oxic and anoxic systems,
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kinetics of oxidation for
Acknowledgements
The support from the Agence Universitaire de la Francophonie (Programme d'invitation de professeur/chercheur) is acknowledged by one of the authors (MF). This work was also supported by the Natural Sciences and Engineering Research Council of Canada and the Elliot Lake Research Field Station of Laurentian University.
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