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This paper reviews the growing literature dealing with the antagonistic effect of selenium (Se) compounds on the toxicity of mercury (Hg) compounds in higher animals and organisms present in the aquatic environment. It covers both laboratory and field studies and summarizes the possible mechanisms that explain the protective action of Se compounds on mercuric mercury (Hg2+) and methylmercury (CH3Hg+) toxicity. The review is subdivided according to the molecular form of Hg and the organisms in which the antagonism has been studied. Many authors suggest that the protective effect of selenite on the toxicity of Hg2+in mammals is due mainly to the in vivo formation of mercuric selenide (HgSe), a stable and biologically inert complex. The detection of HgSe has been confirmed in several studies in support of this mechanism. Possible mechanisms that may be involved in the antagonism between Se compounds and CH3Hg+in mammals and aquatic organisms are also presented. The possibility of adding Se compounds to contaminated lakes and reservoirs as a remediation technique to limit the bioaccumulation of Hg2+and CH3Hg+is critically discussed.

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Environmental context. Antimony first attracted public attention in the mid-1990s amid claims that it was involved in Sudden Infant Death Syndrome. A substantial number of papers have now been published on the element and its behaviour in the natural environment. However, many key aspects of the environmental chemistry of antimony remain poorly understood. These include critical areas such as its ecotoxicology, its global cycling through different environmental compartments, and what chemical form it takes in different environments. More focussed research would help the situation. The present review highlights several areas of environmental antimony chemistry that urgently need to be addressed.Abstract. The objective of the present article is to present a critical overview of issues related to the current state of knowledge on the behaviour of antimony in the environment. It makes no attempt to systematically review all published data. However, it does provide a list of the main published reviews on antimony and identifies subjects where systematic reviews are needed. Areas where our knowledge is strong -and the corresponding gaps -in subjects ranging from total concentrations and speciation in the various environmental compartments, to ecotoxicity, to cycling between compartments, are discussed, along with the underlying research. Determining total antimony no longer poses a problem for most environmental samples but speciation measurements remain challenging throughout the process, from sampling to analysis. This means that the analytical tools still need to be improved but experience shows that, to be useful in practice, this should be directly driven by the requirements of laboratory and field measurements. Many different issues can be identified where further research is required, both in the laboratory and in the field, the most urgently needed studies probably being: (i) long-term spatial and temporal studies in the different environmental compartments in order to collect the data needed to establish a global biogeochemical cycle; (ii) laboratory studies of antimony interactions with potential natural binders; (iii) reliable ecotoxicological studies. Montserrat Filella is a chemist and teaches Environmental Chemistry at the University of Geneva, Switzerland. Her main research interests focus on the understanding of the physicochemical processes regulating the behaviour of chemical components in environmental and biological compartments, mainly by combining computer modelling with field and laboratory measurements. The three main axes of her research concern the study of: colloids in natural waters, natural organic matter (quantification and interaction with trace elements) and Group 15 elements. She is also interested in other topics

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