Frontiers in Marine Science (Jun 2014)
Evidence of Increased Anthropogenic Emissions of Platinum in Coastal Systems from Time-Series Analysis of Mussels Samples (1991-2011)
Abstract
The Platinum Group Elements (PGEs), which include platinum (Pt), palladium (Pd), iridium (Ir), rhodium (Rh), osmium (Os) and ruthenium (Ru), are amongst the rarest trace elements in the Earth’s crust. They have similar physical and chemical properties, and tend to occur together in the same mineral deposits. Their properties are resistance to chemical corrosion over a wide temperature range, high melting point, high mechanical strength and good ductility, as well as outstanding catalytic properties, being therefore critical in many emerging technologies. Although natural environmental concentrations of PGEs are extremely low – generally at or below the ng/g –, levels of Pt, Pd and Rh are increasing, mainly because of their use in catalytic converters of motor vehicles (Zereini et al., 2007). The automobile catalysts converters use noble metals as active components, and were developed with the aim of reducing emissions of hydrocarbons, carbon monoxide and nitrogen oxides (Sures et al., 2005). Since the beginning of the 1980s, the PGEs represent a relatively new category of trace metals in the environment, especially in relation to automobile traffic (Haus et al., 2007). The PGEs of automobile catalytic converters are eroded from the surface of the catalyst and subsequently emitted in metallic form or as oxides (Turner and Price, 2008). The PGEs are subject to various physical and chemical transformations after deposition, and can potentially result in migration into environmental compartments (Moldovan et al., 2001; Vaughan and Florence, 1992). The concentration of PGEs has much increased in traffic exposed environmental samples (Lesniewska et al., 2004; Ely et al., 2001; Zereini et al., 2001; Schäfer et al., 1999; Fritsche and Meisel, 2004). However, what constituted a decrease in greenhouse gas emissions has resulted in increased levels of PGEs in the environment as shown in some studies in the dust of the road, roadsides, river sediments, sewage, soil and marine ecosystems (Ravindra et al., 2004). As a consequence of the growing use of PGEs, concentrations of these noble metals are rising clearly in different environmental matrices, mainly as road dusts, soils along heavily frequented roads, sewage sludge and sediments of urban rivers and harbour basins (Zimmermann and Sures, 2004). Currently, these emissions continue to grow. From the places near to the emission points, such as roads and other traffic routes PGEs are introduced into aquatic habitats where they accumulate in sediments and marine organisms. Despite this growing interest as emerging contaminants in recent decades, few studies in this field have been reported. This is due to the specific analysis methods and with a very high limit of detection for the determination of traces of PGEs at the ultra-trace level (Alsenz et al., 2009). The work here presented is focused on the assessment of changes in concentration of the PGEs, especially platinum, introduced by humans and the impact of its use in catalytic converters. To this aim, time-series analysis (1991-2011) of Pt were performed in mussel samples (Mytilus galloprovinciales) collected in the Vigo Ria (NW Iberian Peninsula) within the Instituto Español de Oceanografía (IEO) Marine Pollution Monitoring Program. Mussels are ideal organisms for use as bio-indicators of water pollution because as filtering organisms tend to accumulate dissolved substances in the environment. Mussels are abundant in the study environment and may constitute an important food source for fish and other predators, allowing platinum to enter food chains. The determination of platinum was carried out by catalytic adsorptive cathodic stripping voltammetry (Cobelo-García et al. 2014). The effects of PGE on the marine organisms have been investigated in several laboratory experiments but very limited field studies have been carried out. The uptake rate of the noble metals is dependent on various factors such as exposure concentration, exposure period, metal species and water chemistry (Zimmermann and Sures, 2004). The results of this work shows an increase of platinum concentrations in mussels in the recent year; accordingly, for the period between 1991 and 1999 the average concentration was 0.396 ± 0.103 ng/g, increasing to 0.501 ± 0.114 ng/g for mussels collected during the last decade (2000-2011), and were significantly different at the 95% level. On the other hand, the yearly trend observed for the increase in the concentrations of Pt in the mussels samples are in agreement with the Pt demand in Europe for their use in catalytic converters and with the number of vehicles sold in Spain during this period.
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