Palladium is one of the platinum group elements (PGEs) and it is present on the earth crust at very low concentration levels. The members of PGEs occur in nature as various mineral species, chiefly as antimonides, arsenides, bismuthides, sulfides, tellurides and in the native state (Reddi and Rao, 1999). The precious metals have some unique geochemical characteristics: they are very refractory, having high boiling points and a strong affinity for iron (siderophile) and for sulfur (chalcophile) (Goldschmidt 1954, Rösler and Lange 1972). They are normally present in silicate rocks at very low levels, often forming discrete phases, such as alloys and therefore, unlike the rare-earth elements, they do not appear to partition themselves extensively between silicate phases. It is therefore a critical task to select a representative natural sample mass for analysis, since the presence or absence of one precious metal grain in the analyzed aliquot could have a significant effect on the analysis, particularly if small sample masses (<5 g) are chosen. This inhomogeneity that is overall typical for the rock samples, might be taken into consideration by the analyst that generally are use to operate with samples of small size. In fact the homogeneity and the representativeness of the sample is the dominant factor to validate the analytical data on the real Pd distribution in environmental matrices (Hall et al. 1990; Reddi and Rao, 1999). These considerations, together with the difficulties that arise applying analytical procedure owing to the very low Pd concentration in the environmental matrices, contrast with the large body of information concerning other metals of environmental significance such as Cd, Cr, Hg, Ni, Pb etc. A significant collection of data on the environmental distribution of Pd and the consequent evaluation of the risks for human health and the environment from exposure to palladium are the results of the great effort of the Task Group on Environmental Health Criteria for Palladium (WHO, 2002). Pd concentration in surface fresh water is generally detectable in the range from 0.4 to 22 ng L-1 in fresh water and from 19 to 70 pg L-1 in salty water. Drinking-water samples usually contain extremely low levels of pal ladium (few data always at a concentration level 24 ng L-1 are available in literature). A limited number of data are also available for Pd in tissues of small aquatic invertebrates, different types of meat, fish, bread and plants. Pd in soil range from < 0.7 to 47 μg kg-1 (WHO, 2002). Soil samples were mainly collected from areas near major roads resulting enriched in this element. Pd concentration in sewage sludge ranges from 18 to 260 μg kg-1, while a very high concentration (4700 μg kg-1) has been found in sludge samples contaminated by wastes discharged from the local jewellery industry (WHO, 2002). Population is primarily exposed to palladium through different pathways that have different relevance: dental alloys, jewellery and metal refineries, food and emission from automobile catalytic converters (this one especially in the last decade). It is noteworthy to stress that at this time, at the relatively low concentration levels, metallic form of Pd and PGEs are considered to be inert respect to biological reactions (Ravindra et al. 2004). The human average dietary intake of palladium has been calculated to be up to 2 μg/day. Ambient air levels of palladium below 100 pg m-3 can be expected in urban areas where palladium catalysts are used. Therefore, the inhalative palladium uptake rate is very low. In roadside dust, soil and grass samples a slight accumulation of palladium has been detected, correlating with traffic density and distance from the road (Zereini and Alt, 2000; Barefoot, 1999; WHO, 2002; Ravindra et al. 2004). Worldwide demand for palladium in automobile catalysts rose from 23.5 tonnes in 1993 to 76.4 tonnes in 1996 (Cowley, 1997) up to 167 tonnes in 1999 (Ravindra et al. 2004). About 60% of the European gasoline cars present on the market in 1997 were equipped with palladium-based catalysts while in 2002 about 84% of the total Pd demand by application in Europe was employed for autocatalyst. The introduction of palladium in automotive catalytic converters in Europe during the early 1990s and the new catalyst introduced to satisfy the request of European legislation (Euro III and IV) have caused a growing demand for Pd. The consequence will be an increasing release and accumulation of this metal in the environment, paralleled by a reduction of Pt and Rh (Helmers et al. 1998; Hees, et al.1998; Schafer et al. 1999; Ravindra et al. 2004). The production and recycling of Pd-containing materials, as well as the use of Pd as a constituent of dental restorative alloys, may be a source for toxic and allergic reactions for the organisms (Begerow et al. 1999; Begerow and Dunemann, 2000). A critical evaluation of possible risks for human health can only be given if reliable analytical data are available (Messerschmidt et al. 2000). In fact, according to Boch et al. (2002), studies over the past 10 years have shown that the allergenic potential of palladium has been probably underestimated. For this reasons it is important to develop analytical methods suitable for relatively easy determination of traces and ultra traces levels of Pd in the environment, as well as in body fluids of living species (Messerschmidt et al. 2000). Until now Pd has been preferentially determined in solid matrices as soils, sludge and dust, where is present at relatively higher concentration, while the paucity of data relatively for water system is related to the low levels and at the presence of salt that cause not easily resolved interferences. (Hall et al. 1990; Hall and Pelchat, 1993). Terada et al. (1983) suggest that owing to these low concentrations in water, a preconcentration step is necessary. As an example, water insoluble chelating material (p-dimethylaminobenzylidenerhodanine on silica gel, or Thionalide) has been used for preconcentration of trace of palladium with a slow flow rate (2.5 mL/min).This have permitted the complete retention of palladium on the column. (Terada et al. 1980; Terada et al. 1983).
All Science Journal Classification (ASJC) codes
- Environmental Science(all)
- Earth and Planetary Sciences(all)
Angelone, M., Nardi, E., Pinto, V., & Cremisini, C. (2006). Analytical methods to determine palladium in environmental matrices: A review. In Palladium Emissions in the Environment: Analytical Methods, Environmental Assessment and Health Effects Springer Berlin Heidelberg. https://doi.org/10.1007/3-540-29220-9_18