A Pseudo - Problem of Pollution Trace Metals in the Environment , Volume 4 - Palladium & Osmium

Although there are numerous publications describing the toxicology and environmental impact of the better known metals such as lead, cadmium and mercury, information on the less common metals is not as readily available. The Mid-West Research Institute has therefore undertaken a programme initiated by the National Institute of Environmental Health Sciences to assemble information on the natural occurrence, processing, use, human and animal health effects, and environmental impacts of a series of selected trace elements. The fourth book of this series is concerned with palladium and osmium. A problem with books of this nature is that probably because of the paucity of information on environmental and health effects the supporting chapters tend to form a disproportionately large part of the book. The section on palladium contains only nine pages on losses to the environment and five on the physiological effects of palladium and its compounds, while there are thirty seven on occurrence, economics, processing and uses. These are supported by no fewer than sixty pages of appendices containing tables on sources, production figures, imports, exports, stocks, sales, principal uses and the firms involved, and sub-sections on the chemistry and analysis of palladium. One serious criticism is that with one exception the references only go up to 1973; thus by the time of publication the book was already five years out of date. Repeated mention is made in the text of increased losses of palladium to the environment resulting from greater use of the metal in automobile emission control devices, and recommendations are made regarding epidemiological, toxicological and other studies that should be undertaken to evaluate its effect on the environment. In fact many such studies have already been reported and “scare” reports dismissed. A sub-committee of the American National Research Council has made a study for the Environmental Protection Agency to establish a broad background of information on the medical, biological and environmental affects of selected pollutants, to evaluate that information and to recommend studies aimed at remedying information inadequacies or gaps. The conclusion they reached on this use of the platinum group metals is therefore worth quoting: “The newest and most extensive use of the platinum group metals is in catalysts for purifying exhaust from automobiles. Minute quantities of platinum or palladium (about 1-3pg:mile or 0.6-r.gpg;km) are emitted from the exhaust systems of automobiles equipped with catalytic converters; much of this material may accumulate alongside roadways. However, this material is in a chemical form that is physiologically innocuous (no detectable soluble salts) and it is concluded that such emission poses no threat to the environment. Because there is no evidence that platinum metal can be methylated by microorganisms and solubilised in the same way that mercury is methylated, this deposited material should not have an adverse effect on the cnvironment”(1). Although the authors are concerned that the loss of palladium(I1) compounds to waste water streams may be in sufficient concentrations to be toxic to aquatic organisms they offer little information on this. The chapters on sources, processing and uses are interesting but the lack of recent information does show through and there are some unfortunate omissions, particularly in discussing the primary sources of the platinum metals in South Africa. The section on osmium is significantly shorter than that on palladium, reflecting the relative occurrence and uses of the two metals. The major sources of osmium loss to the environment are thought to occur as the volatile tetroxide during pyrometallurgical