Vehicle Exhaust Catalysts Research Articles

Occurrence of palladium and platinum in human scalp hair of adolescents living in urban and industrial sites

Platinum group elements (PGEs) can be naturally found at very low concentrations in the Earth's crust. However, the increasing uses of PGEs in vehicle exhaust catalysts, in addition to some other applications (industry, jewelry, anticancer drugs) cause their anthropogenic emission and dispersion in the environment. The use of human hair samples analysis is considered a suitable biological indicator to assess human occupational and environmental exposure. It is an easily accessible material for individuals or population groups of non-invasive sampling. The aim of this study is a comparative analysis to investigate human hair content of Pd and Pt in adolescents, of both genders, residing near petrochemical plants of Augusta and Gela, in urban area of Palermo, and Lentini as control site (Sicily, Italy). A total of 108 samples were taken from school students (11–14 years old). Hair samples were cleaned, mineralized, and processed for analyses by inductively coupled plasma–mass spectrometry (ICP-MS).The samples from the industrial sites of Gela and Augusta do not have statistically significant differences between them for either Pd for Pt; however, they differ from the samples relating to the city of Palermo. Median Pd concentrations are higher than Pt in industrial sites and control site. In urban site the levels of both metals were comparable. The study does not reveal any statistically significant difference between Pd and Pt concentrations in female and male samples. The data confirm that the study areas are heavily affected by industrial and urban emissions of Pd and Pt, representing a potential hazard to the local population.

Platinum Nanoparticle Extraction, Quantification, and Characterization in Sediments by Single-Particle Inductively Coupled Plasma Time-of-Flight Mass Spectrometry.

Particulate emissions from vehicle exhaust catalysts are the primary contributors to platinum group elements (PGEs) being released into roadside environments, especially platinum (Pt) particles. With increasing traffic density, it is essential to quantify the emission, accumulation, and potential health effects of traffic-emitted Pt particles. In this study, three procedures were investigated to extract Pt nanoparticles (NPs) from sediments and characterize them by single-particle inductively coupled plasma time-of-flight mass spectrometry (spICP-TOF-MS). For this purpose, a reference sediment sample was spiked with manufactured Pt NPs. Pt NPs’ extraction recoveries reached from 50% up to 102%, depending on the extraction procedure and whether the particle mass or number was used as the metric. Between 17% and 35% of the Pt NPs were found as unassociated Pt NPs and between 31% and 78% as Pt NPs hetero-aggregated with other sediment particles. Multi-elemental analysis of Pt-containing NPs in the pristine sediment revealed frequently co-occurring elements such as Au, Bi, and Ir, which can be used to determine a natural background baseline. Our results demonstrated that spICP-TOF-MS elemental characterization allows for distinguishing anthropogenic Pt NPs from the natural background. In the future, this could enable the sensitive monitoring of PGE release from anthropogenic sources such as vehicle exhausts.

Professor Geoffrey Bond: ‘Mr Gold’ International Expert in Gold Catalysis 1927–2022

Professor Geoffrey C. Bond, PhD, DSc, FRSC, passed away after a short illness, peacefully in his sleep, on 9th January 2022 at Watford General Hospital, UK, close to his home in Rickmansworth. He was an international authority in the field of heterogeneous catalysis: the science that underpins almost all major industrial chemical processes. He specialised in catalysis by metals, which was the title of his first book published in 1962. Throughout his life he was in the vanguard of those extending the boundaries of his subject. Early work at the University of Hull, UK, featured the use of deuterium as an isotopic tracer to determine the detailed mechanisms of catalytic reactions. Next, at Johnson Matthey, UK, as Head of the Catalyst Research group he contributed to the development of vehicle exhaust catalysts. Then, at Brunel University, UK, he initiated a wide range of projects, culminating in his demonstration of the catalytic activity of gold: a metal which, until that time, ‘conventional wisdom’ had relegated to a class of inactive metals.

ZrO2 and MxOy (M= La, Ce, and Nb) synergistically reinforced porous cordierite ceramics synthesized via a facile solid-state reaction

In an attempt to enhance the sintering and mechanical performance of porous cordierite ceramics (Mg2Al4Si5O18) as support materials for vehicle exhaust catalysts, ZrO2 and MxOy (M = La, Ce, and Nb) were simultaneously introduced into cordierite sintered at 1350 °C for 4 h. Then, the reinforced function of ZrO2 and MxOy on the properties of porous cordierite ceramics was systematically evaluated, especially for the sample co-doped with ZrO2 and La2O3. The results displayed a distinct enhancement in mechanical and thermal performance, and the cold compressive strength increased from 72.74 to 158.59 MPa as well as thermal conductivity ranged from 1.66 to 2.01 W m−1 K−1, respectively. It is found that ZrO2 facilitated activation sintering introduced via lattice distortion in cordierite and La2O3 accelerated the formation of cordierite and ZrSiO4 microcrystalline through the low-temperature liquid phase. The synergic effect between ZrO2 and La2O3, therefore, had a significant role in the reinforced mechanical and thermal performance of porous cordierite ceramics. This work not only offers a feasible strengthening strategy, but also expands the possibilities for building high-performance structural and functional ceramics.

An automatic on-line sorptive extraction platform for palladium determination in automobile exhaust catalysts based on a PTFE-turnings packed column, flow injection analysis and flame atomic absorption spectrometry

ABSTRACT A novel simple sensitive and effective on-line flow injection column preconcentration platform using poly-tetrafluoroethylene turnings as sorbent was developed prior to flame atomic absorption spectrometric (FAAS) determination of palladium in vehicle exhaust catalysts, hydrogenation catalysts and environmental water samples. The method is based on the sorption of palladium(II)-diethyldithiophosphate, which was found to be more effective than dithiocarbamate ones. Methyl isobutyl ketone (MIBK) was used as eluent prior atomisation and quantification. All parameters like pH, DDPA concentration, flow rates, preconcentration time that affect the sensitivity of the method as well as interferences of other metals were investigated in detail. The enhancement factor calculated as 114 for 60 s preconcentration time while the sampling frequency as 40 h−1. The detection limit was 0.9 μg L−1 and the relative standard deviation (RSD) was 2.8% at 20.0 μg L−1 concentration level. The accuracy of the proposed method was estimated by analysing certified reference material and spiked environmental samples. The analytical features of the method were compared with other on-line column preconcentration methods reported in the literature.

Variation in palladium and water quality parameters and their relationship in the urban water environment.

Palladium (Pd) is widely used in vehicle exhaust catalysts (VECs) to reduce toxic emissions from motor vehicles. The study aimed to quantitatively determine Pd content and water quality parameters, to analyze the variation differences and to explore the effect of water quality parameters on Pd content in the urban water environment system (wet deposition-rainfall runoff-receiving water body-estuary) of the city of Haikou, Hainan Island, China. The method used in this study included microwave digestion under high pressure and temperature, analysis by inductively coupled plasma mass spectrometry, quality control of the experimental procedure and guaranteed recovery (85% -125%). The results showed that the dissolved Pd average content in the urban water environment system was the highest in rainfall runoff (4.93 ng/L), followed by that in the receiving water body (4.56 ng/L), and it was the lowest in wet deposition (0.1 ng/L). The suspended Pd average content was the highest in the estuary (2.83 ng/L), followed by that in rainfall runoff (1.26 ng/L), and it was the lowest in wet deposition (6 × 10-4 ng/L). The particle-water partition ratio of the estuary Pd was the highest (1.26), followed by that of Pd in rainfall runoff (0.26). The particle-water partition ratio of the wet deposition Pd was the lowest (6 × 10-3). The dissolved Pd was correlated with the pH, Cl-, and total suspended solids (TSS) (correlation coefficient = 0.52, -0.68, 0.39, p < 0.05; regression coefficient = 1.27, -1.39, 0.01). The suspended Pd was only correlated with Cl- and TSS (correlation coefficient = -0.36, 0.76, p < 0.05; regression coefficient = -1.45, 0.01). Cl- and TSS were the most closely related to Pd in the water environment system. Although individual factors such as pH, Cl-, and TSS had certain migration and transformation effects on Pd in the wet deposition-rainfall runoff-receiving water body-estuary system, the probability of strong correlations was not high. In particular, Eh was not related to the dissolved nor suspended Pd content (correlation coefficient = 0.14, 0.13), which may be due to the synergistic effect of the multiple physical factors on Pd. This study was helpful to better understand the environmental behavior of Pd and provided important theoretical support for the prevention and protection against urban water environmental pollution.

Comparative study of cytotoxicity by platinum nanoparticles and ions in vitro systems based on fish cell lines

Emission of platinum nanoparticles (Pt NPs) especially from vehicle exhaust catalysts and pharmaceutics cause an increase in concentrations of this metal in aquatic environments. In this study, small (4‐9 nm) uncoated and polyvinylpyrrolidone (PVP) coated Pt NPs were synthetized and their dispersion in different exposure media were evaluated. Pt NP uptake in two established fish cell lines were investigated and comparative in vitro cytotoxicity of Pt NPs and ions were assessed.The coated and uncoated Pt NPs dispersions in minimum essential medium (MEM) with fetal bovine serum (FBS) displayed high colloidal stability. Transmission electron microscopy (TEM) and high-resolution scanning electron microscope equipped with an energy-dispersive X-ray spectrometer (STEM/EDX) indicated no detectable cellular uptake of Pt NPs in both cell line monolayers. But with ICP-MS analysis, trace amount of Pt content was determined in all digested monolayer cell samples.The cytotoxicity of both Pt NPs and Pt ions on both fish cell lines after 48 h exposure was investigated through three assays to monitor different endpoints of cytotoxicity. In all studied concentrations (0.325–200 mg/L) no significant cytotoxicity (p > .5) compared to controls were observed in the cells exposed to coated Pt NPs. Uncoated Pt NP and ion exposed cells indicated similar concentration dependent cytotoxicity on both cell lines.

Dissolved palladium in heavy traffic location runoff: dynamic variation and influencing factors

ABSTRACTPalladium (Pd) is widely used in vehicle exhaust catalysts (VECs) and rapidly increasing in urban environments worldwide. This research collected runoff samples in a typical heavy traffic location and analysed the concentrations of dissolved palladium by inductively coupled plasma-mass spectrometry (ICP-MS). For most precipitation events, the maximum Pd concentration level occurred at the beginning of the runoff period and then decreased in subsequent runoff. The results showed that the Pd concentration in runoff was lower in the wet season when compared with the dry season. The wet season had fewer clear days to accumulate pollutants on the impervious surface and had a higher precipitation intensity to dilute dissolved Pd in runoff. Our experimental results also proved that the migration and transformation of palladium in urban environments are affected by runoff water quality parameters. Lower pH, higher Eh and higher concentrations led to a higher dissolved Pd concentration.

Size-dependent genotoxicity of silver, gold and platinum nanoparticles studied using the mini-gel comet assay and micronucleus scoring with flow cytometry.

Metallic nanoparticles (NPs) are promising nanomaterials used in different technological solutions as well as in consumer products. Silver (Ag), gold (Au) and platinum (Pt) represent three metallic NPs with current or suggested use in different applications. Pt is also used as vehicle exhaust catalyst leading to a possible exposure via inhalation. Despite their use, there is limited data on their genotoxic potential and possible size-dependent effects, particularly for Pt NPs. The aim of this study was to explore size-dependent genotoxicity of these NPs (5 and 50 nm) following exposure of human bronchial epithelial cells. We characterised the NPs and assessed the viability (Alamar blue assay), formation of DNA strand breaks (mini-gel comet assay) and induction of micronucleus (MN) analysed using flow cytometry (in vitro microflow kit). The results confirmed the primary size (5 and 50 nm) but showed agglomeration of all NPs in the serum free medium used. Slight reduced cell viability (tested up to 50 µg/ml) was observed following exposure to the Ag NPs of both particle sizes as well as to the smallest (5 nm) Au NPs. Similarly, at non-cytotoxic concentrations, both 5 and 50 nm-sized Ag NPs, as well as 5 nm-sized Au NPs, increased DNA strand breaks whereas for Pt NPs only the 50 nm size caused a slight increase in DNA damage. No clear induction of MN was observed in any of the doses tested (up to 20 µg/ml). Taken together, by using the comet assay our study shows DNA strand breaks induced by Ag NPs, without any obvious differences in size, whereas effects from Au and Pt NPs were size-dependent in the sense that the 5 nm-sized Au NPs and 50 nm-sized Pt NPs particles were active. No clear induction of MN was observed for the NPs.

The catalytic behavior of precisely synthesized Pt–Pd bimetallic catalysts for use as diesel oxidation catalysts

The demands of stricter diesel engine emission regulations have created challenges for current exhaust systems. With advances in low-temperature internal combustion engines and their operations, advances must also be made in vehicle exhaust catalysts. Most current diesel oxidation catalysts use heavy amounts of precious group metals (PGMs) for hydrocarbon (HC), CO, and NO oxidation. These catalysts are expensive and are most often synthesized with poor bimetallic interaction and dispersion. The goal of this work was to study the effect of aging on diesel emission abatement of Pt–Pd bimetallic nanoparticles precisely prepared with different morphologies: well dispersed core–shell vs. well dispersed homogeneously alloyed vs. poorly dispersed, poorly alloyed particles. Alumina and silica supports were studied. Particle morphology and dispersion were analyzed before and after hydrothermal treatments by XRD, EDX, and STEM. Reactivity as a function of aging was measured in simulated diesel engine exhaust.While carefully controlled bimetallic catalyst nanoparticle structure has a profound influence on initial or low temperature catalytic activity, the differences in behavior disappear with higher temperature aging as thermodynamic equilibrium is achieved. The metallic character of Pt-rich alumina-supported catalysts is such that behavior rather closely follows the Pt–Pd metal phase diagram. Nanoparticles disparately composed as well-dispersed core–shell (via seq-SEA), well-dispersed homogeneously alloyed (via co-SEA), and poorly dispersed, poorly alloyed (via co-DI) end up as well alloyed, large particles of almost the same size and activity. With Pd-rich systems, the oxidation of Pd also figures into the equilibrium, such that Pd-rich oxide phases appear in the high temperature forms along with alloyed metal cores. The small differences in activity after high temperature aging can be attributed to the synthesis methods, sequential SEA and co-DI which give rise, after aging, to a bimetallic surface enriched in Pd.

Platinum group elements in the precipitation of the dry region of Xinjiang and factors affecting their deposition to land: the case of Changii City, China

Platinum group elements and their compounds are a class of incident allergens and some platinum group element compounds also have carcinogenic effects. They accumulate in city environment as a result of emissions from catalysts used for vehicle exhausts. In this study, sixteen precipitation samples were collected on the north campus of Changji University located in the center of Changji. They were analyzed for palladium (Pd), platinum (Pt), and rhodium (Rh) by inductively coupled plasma–mass spectrometry. The average concentrations of Pd, Pt, and Rh were found to be 26.73ng L-1 (range: 3.18–84.25ng L-1), 1.71ng L-1 (range: below the detection limit to 6.38ng L-1), and 1.49ng L-1 (range: below the detection limit to 3.53ng L-1), respectively. Pd deposition was most pronounced for single precipitation events, reaching 35.47ng m-2 (range: 1.27–101.10ng m-2), followed by Rh (max. 4.96ng m-2, range: 0–14.85ng m-2) and Pt (max. 1.38ng m-2, range: 0-7.66ng m-2). Both Pd and Pt were higher in winter than in other seasons in terms of their wet deposition amounts and their concentrations in precipitation, whereas Rh was lower in winter. Moreover, the results indicated that discharge from coal combustion in winter, the amount of precipitation, and the number of dry days before rainfall events all significantly affected the wet deposition amount and precipitation concentration of platinum group elements. Pd deposition flux was highest (reaching 5.47×103 ng m-2) corresponding to 18 and 16 times the Rh and Pt fluxes, respectively. Finally, vehicle exhaust catalyst emissions from motor vehicles were not the only source of atmospheric platinum group metals in the city environment; in fact, combustion of coal in winter was found to be the dominant contributor of Pt and Pd in the atmosphere.

Effects triggered by platinum nanoparticles on primary keratinocytes

The platinum (Pt)-group elements (PGEs) represent a new kind of environmental pollutant and a new hazard for human health. Since their introduction as vehicle-exhaust catalysts, their emissions into the environment have grown considerably compared with their low natural concentration in the earth crust. PGE emissions from vehicle catalysts can be also in the form of nanometer-sized particles (Pt nanoparticles [PtNPs]). These elements, both in their metallic form or as ions solubilized in biological media, are now recognized as potent allergens and sensitizers. Human skin is always exposed to toxic particles; therefore, in the present study we addressed the question of whether polyvinylpyrrolidone-coated PtNPs may have any negative effects on skin cells, including predominantly epidermal keratinocytes. In this study, PtNPs of two sizes were used: 5.8 nm and 57 nm, in concentrations of 6.25, 12.5, and 25 μg/mL. Both types of NPs were protected with polyvinylpyrrolidone. Primary keratinocytes were treated for 24 and 48 hours, then cytotoxicity, genotoxicity, morphology, metabolic activity, and changes in the activation of signaling pathways were investigated in PtNP-treated cells. We found that PtNPs trigger toxic effects on primary keratinocytes, decreasing cell metabolism, but these changes have no effects on cell viability or migration. Moreover, smaller NPs exhibited more deleterious effect on DNA stability than the big ones. Analyzing activation of caspases, we found changes in activity of caspase 9 and caspase 3/7 triggered mainly by smaller NPs. Changes were not so significant in the case of larger nanoparticles. Importantly, we found that PtNPs have antibacterial properties, as is the case with silver NPs (AgNPs). In comparison to our previous study regarding the effects of AgNPs on cell biology, we found that PtNPs do not exhibit such deleterious effects on primary keratinocytes as AgNPs and that they also can be used as potential antibacterial agents, especially in the treatment of Escherichia coli, representing a group of Gram-negative species.

Pt and Pd in sediments from the Pearl River Estuary, South China: background levels, distribution, and source

This study assessed the concentrations of platinum (Pt) and palladium (Pd) in surface sediments and sedimentary cores collected from the Pearl River Estuary with a view of evaluating the distribution, background levels, possible sources, and contamination level of anthropogenic Pt and Pd. Thirty-six samples of surface sediments and 12 samples from sedimentary cores were collected. Al(2)O(3) was analyzed on fused glass disks by X-ray fluorescence spectrometer. Heavy metal elements were measured by inductively coupled plasma-mass spectrometry. Pt and Pd were separated from the sample matrix by anion exchange chromatography and subsequent solvent extraction after samples had been digested in Carius tubes using aqua regia. The analysis of Pt and Pd was performed by isotopic dilution-inductively coupled plasma-mass spectrometry. Pt and Pd concentrations in surface sediments were 0.28-2.11 and 0.39-38.30 ng/g, respectively, and Pt and Pd concentrations in sedimentary cores were 0.19-1.18 and 0.15-1.76 ng/g, respectively. Background values of Pt and Pd were 0.20-1.17 and 0.10-1.34 ng/g, respectively. The spatial distribution of the enrichment factor differed between Pt and Pd in surface sediments. Down-core variations in Pt, Pd, and other heavy metal elements were similar in all cases and were related to sediment type. Some of the Pt and Pt in surface samples were derived from anthropogenic emissions. Pt and Pd were delivered to the sediment by fluvial input. In addition to vehicle exhaust catalysts, Pt and Pd were derived from other sources (e.g., industrial process). An important post-burial remobilization process of Pt and Pd is likely to be particle mixing by billows caused by typhoon.

Fractionation of traffic-emitted Ce, La and Zr in road dusts

The introduction of catalytic converters has led to a new environmental problem since catalysts emit platinum group elements (PGEs) which are among the least distributed elements in nature. Along with PGEs the vehicle exhaust catalysts contain also a number of stabilizers, commonly oxides of rare earth elements and alkaline earth elements such as Ce, La and Zr. Since vehicular emission of these elements has received little attention so far this work attempts to offer insight into their distribution and fate in the environment by measuring their speciation in road dust samples collected along several highways in Germany and a city centre (Saarbrücken). Speciation of the elements (fractionation into associated mineralogical phases) was carried out via a conventional sequential extraction protocol and the complexing abilities of humic substances in the organic matter were investigated by selective extraction methods in combination with size segregation. For evaluation purposes soil samples spiked with catalytic converter material were analyzed, showing a much lower fraction of Ce, La and Zr mobilized in comparison to the road dust samples. It was found that the elements were effectively bound to humic substances in road dust with a preference for complexation with low molecular weight compounds (<1600 Da).

Effects of platinum from vehicle exhaust catalyst on carbon and nitrogen mineralization in soils

There is strong evidence of continuously increasing contamination of soils with platinum group elements (PGE), in particular with platinum (Pt) from vehicle exhaust catalysts in roadside soils. However, knowledge about the effects of Pt contamination on soil processes is very limited. The objective of this study was to investigate whether the contamination of soils with Pt at realistic environmental levels leads to observable adverse effects on selected indicator parameters of the carbon and nitrogen turnover in soils. Incubation experiments with artificially contaminated soils and solutions containing dissolved organic matter (DOM) were carried out by the use of milled material from a Pt-containing vehicle exhaust catalyst. Interaction of the catalyst material with the soil resulted in a mobilization of Pt into the dissolved phase reaching up to 0.1% of the added Pt. The amount of Pt mobilization seemed to be mainly driven by the pH of the soil. Mineralization of carbon and nitrogen did not reveal any significant adverse effect of the Pt addition as compared to the control samples. Future studies dealing with Pt effects on soil processes should focus on environmental conditions favoring Pt mobilization, e.g. such as very low pH values or large concentrations of DOM.

Platinum, palladium and rhodium release from vehicle exhaust catalysts and road dust exposed to simulated lung fluids

The risk associated with the inhalation of platinum group element (PGE) emissions from vehicle exhaust catalysts (VECs) has been investigated by extracting road dust and milled auto catalyst with simulated lung fluids. Gamble's solution (representative of the interstitial fluid of the deep lung) and artificial lysosomal fluid (ALF) (representative of the more acidic environment within the lung) were employed as extraction fluids. The highest PGE release was observed in ALF, implying that inhaled particles would have to be phagocytized before significant amounts of PGEs dissolve. The greatest percentage (up to 88%) of PGEs was released from road dust, possibly due to the presence of mobile PGE species formed in the roadside environment. Pt showed the highest absolute bioavailability, due to its greater concentration in the environmental samples. Pd and Rh had higher percentage of release, however, because of their more soluble nature. From the toxicological perspective, the results demonstrate potential health risks due to the likely formation of PGE-chloride complexes in the respiratory tract, such species having well-known toxic and allergenic effects on human beings and living organisms.

Complexation of platinum, palladium and rhodium with inorganic ligands in the environment

Platinum (Pt), palladium (Pd) and rhodium (Rh) are emitted by vehicle exhaust catalysts (VECs) and their concentrations have increased significantly in various environmental compartments, including airborne particulate matter, soil, roadside dust, vegetation, rivers and oceanic environments, over the last two decades as the use of VECs has increased. However, data on the chemical speciation of the platinum-group elements (PGEs) and their bioavailabilities are limited. In this paper, the thermodynamic computer model, HSC, has been used to predict the interactions of Pt, Pd and Rh with different inorganic ligands and to estimate the thermodynamic stability of these species in the environment. Eh–pH diagrams for the PGEs in aqueous systems under ambient conditions (25°C and 1 bar) in the presence of Cl, N and S species have been prepared. The results indicate that Pt, Pd and Rh can form complexes with all of the inorganic ions studied, suggesting that they are capable of mobilizing the PGEs as aqueous complexes that can be transported easily in environmental and biological systems and that are able to enter the food chain. Hydroxide species can contribute to the transport of PGEs in oxidizing environments such as road-runoff waters, freshwater, seawater and soil solutions, whereas bisulphide complexes could transport Pt and Pd in reducing environments. Ammonia species appear to be significant under near-neutral to basic oxidizing conditions. Chloride species are likely to be important under oxidizing, acidic and saline environments such as seawater and road-runoff waters in snowmelt conditions. Mixed ammonia–chloride species may also contribute to the transport of Pt and Pd in highly saline solutions.

Environmental exposure to platinum group elements released by automotive catalytic converters: the risk for children

The increasing use of Platinum Group Elements (PGEs) in vehicle exhaust catalysts causes their anthropogenic emission and spread all over the environment. The PGEs contamination initially occurs in airborne particulate matter, roadside dust, soil, sludge and water, and afterwards results in bioaccumulation in living organisms through diverse pathways. Several studies have reported enhanced PGE levels in human body fluids and tissues exposed to environmental PGEs. These elements are potent allergens and sensitisers, and have also been associated with asthma, nausea, increased hair loss, increased spontaneous abortion, dermatitis and other serious health problems in humans. Considering all the above points, the present paper reviews the literature on the topic related to PGEs environmental contamination, bioavailability and bioaccumulation, and possible health risk, with particular regard to more susceptible population groups such as children.

The estimation of the bioavailabilities of platinum, palladium and rhodium in vehicle exhaust catalysts and road dusts using a physiologically based extraction test

Platinum group element (PGE) levels in the environment have increased following the introduction of vehicle exhaust catalysts (VECs). In order to evaluate the potential pathways of PGEs from VECs into humans, a physiologically based extraction test (PBET) was used to study the uptake of PGEs by the human digestive tract. The PBET assay was implemented in two phases, to first simulate the passage of ingested soil through the acid conditions of the stomach before it enters the near neutral conditions of the small intestine. The results showed that Pt, Pd and Rh did not undergo precipitation reaction when passing from the acid environment of the stomach to the neutral environment of the small intestine. The greatest fractions of bioavailable PGEs (up to 68%) were observed in road dust samples, possibly due to the presence of mobile PGE species formed in the roadside environment. Higher percentages of Pd and Rh were bioavailable than Pt, probably due to the differences in their mobilities and tendencies to form soluble complexes. Pt showed the highest absolute bioavailability however, due to its greater concentration in environmental samples. The solubilization of PGEs in the human digestive tract could involve the formation of PGE-chloride complexes, with perhaps increased health-hazard issues because of the known toxic and allergenic effects of these species.

Observed trends in ambient concentrations of C 2–C 8 hydrocarbons in the United Kingdom over the period from 1993 to 2004

Hourly measurements of up to 26 C 2–C 8 hydrocarbons have been made at eight urban background sites, three urban-industrial sites, a kerbside and a rural site in the UK from 1993 onwards up until the end of December 2004. Average annual mean benzene and 1,3-butadiene concentrations at urban background locations have declined at about −20% per year and the observed declines have exactly mimicked the inferred declines in benzene and 1,3-butadiene emissions over the same period. Ninety-day rolling mean concentrations of ethylene, propylene, n- and i-butane, n- and i-pentane, isoprene and propane at urban and rural sites have also declined steadily by between −10% and −30% per year. Rolling mean concentrations of acetylene, 2- and 3-methylpentane, n-hexane, n-heptane, cis- and trans-but-2-ene, cis- and trans-pent-2-ene, toluene, ethylbenzene and o-, m- and p-xylene at a roadside location in London have all declined at between −14% and −21% per year. These declines demonstrate that motor vehicle exhaust catalysts and evaporative canisters have effectively and efficiently controlled vehicular emissions of hydrocarbons in the UK. Urban ethane concentrations arising largely from natural gas leakage have remained largely unchanged over this same period.