A further discussion of the factors controlling the distribution of Pt, Pd, Rh and Au in road dust, gullies, road sweeper and gully flusher sediment in the city of Sheffield, UK

Biodynamics and Environmental Concentrations of the Platinum Group Elements in Freshwater Systems

Growing reliance on platinum group elements (PGEs) as critical minerals for emerging technologies raises concerns regarding their ecotoxicological behavior. We studied their environmental fate in various inorganic and biological matrices from Canada using ICP-MS/MS analysis. Our findings confirmed previously published rhodium, palladium, and platinum concentration gradients from road dust to sediments, soils, and water, but differed from the literature reporting high biological contamination, which was not observed in our study. We also conducted experiments using a predator-prey model by exposing Chaoborus americanus to PGE mixtures for 24 h and to contaminated prey (Daphnia magna) for 8 days, followed by a 3-day excretion period. We estimated water uptake rate constants (kuw = 1.6-3.5 mL g-1 d-1), assimilation efficiencies (AEs = 0.024-32.2%), and efflux rate constants (ke = 0.51-0.69 d-1) for four PGEs. Overall, Chaoborus showed poor bioaccumulation and low trophic transfer of the PGEs, which were rapidly excreted. Experimental results supported low detection of PGEs in wild organisms, underscoring the need for caution when interpreting studies reporting high PGE levels in biological matrices. Nonetheless, this study improves our understanding of the PGEs' environmental fate, revealing correlations with several quantitative ion character-activity relationships (QICARs) and highlighting chemical bond softness (σParr) as a predictor of biological assimilation and excretion.

Identification of the featured-element in fine road dust of cities with coal contamination by geochemical investigation and isotopic monitoring

The exploitation of coal releases large amounts of contaminants into the environment. However, the featured pollutants of coal utilization as well as the scope and degree of their impact remain to be revealed. To identify the featured-element of coal contamination in a complex environment, a typical coal resource city was selected, and the major elements, 18 trace elements, as well as δ¹³C, δ¹⁵N, and δ³⁴S in the fine road dust and certain source materials were analyzed. Through multiple analysis methods, the featured-element was determined step-by-step: firstly, elements with enrichment coefficients greater than two in road dust were focused: Zn, Hg, Pb, Cu, Cd, and Cr; secondly, difference analysis showed a significant difference (p < 0.05) of Hg and Cu concentration at different distance from the coal-fired power plant, making Hg and Cu the only candidates for the featured-element; finally, through coal-related source materials determination, Cu was not qualified as a featured-element. Therefore, Hg was the only left element to be considered as the featured-element. To be more convincing, more analyses were performed to support Hg as the featured-element: cluster analysis and isotope monitoring indicated Hg in road dust could originate from coal combustion; X-ray photoelectron spectroscopy was also conducted, where the forms of Hg in road dust with possible source materials were compared, and the presence of HgO and Hg only in the road dust near the power plant indicated the impact of the power plant on the surrounding dust. Through the health risk assessment, it was found that Hg in the road dust had no health risk, though the study area still had Pb, Cr, and As risks, which were not closely related to the pollutants released by coal-related sources.

Impact of urbanization and steel mill emissions on elemental composition of street dust and corresponding particle characterization

Street Dust (SD) acts as a sink and source of atmospheric particles containing Potentially Toxic Elements (PTEs) and can pose a possible pathway of PTEs to human bodies. Comprehensive SD study, where 249 samples were collected from rural, urban and industrialized areas aimed to increase the understanding between sedimentation of atmospheric dust derived from anthropogenic activities and elemental composition of SD. Elemental composition for 53 elements (ICP-MS, aqua regia digestion) was determined on fraction <0.063 mm. Significantly increased levels of Sn-Cu-Sb-Bi-Ag-Ba-Mo-Pt-Pb and other elements have been detected in urban environments, compared to the rural ones. SEM/EDS investigation identified that main carriers of Ba, Cu and Sn are most likely particles derived from non-exhaust traffic emissions. Areas around steel mills show a strong enrichment with Cr, Mo, Ni and W, which exponentially decreases with the increased distance from the plant, reaching corresponding urban background 15 and 20 km from the source. SEM/EDS inspection identified spherical and melted irregular particles as the main carriers of the above-mentioned elements. City managers shall adapt measures to reduce amount of vehicular traffic and quantity of deposited SD on the public surfaces and encourage green city planning, while industrial emitters are encouraged to reduce their dust emissions.

Influences of coal mines, metallurgical plants, urbanization and lithology on the elemental composition of street dust

Street dust (SD) acts as a sink and a source of atmospheric particulate matter, which is especially significant in urban environments. World studies of natural and anthropogenic impacts on the elemental composition of SD are generally limited to specific areas or case studies. The objectives of this study are to determine the impacts of different anthropogenic atmospheric dust emitters and natural factors on the chemical composition of SD, and to define sources of variance in elemental composition of SD, temporal variations and geochemical associations of elements on large number of samples, collected in different time periods, anthropogenic environments and geological settings. Nested ANOVA shows that the majority of the elemental-level variations were found to be regional ones. Increased variations on local scale were observed for Hg, Mo, Ni, Zn and Ag. Increased temporal variations were observed for Zn, As, Cd and Pb. Spatial variations within the same sampling location were increased for Hg and Ag. Three anthropogenic geochemical associations were detected: Coal mining and coal-fired power production enriched SD with Al, Co, Fe, La, Sc, Th, Ti, V, Zr and U, metallurgy with Cr, V, Ni and Mn, and urbanization with Ag, Bi, Ca, Cd, Mg, Mo, Pb and Zn.

Tracing Sources and Contamination Assessments of Heavy Metals in Road and Foliar Dusts in a Typical Mining City, China

Road and foliar dust samples from four land-use districts of Panzhihua City, a famous V-Ti magnetite production area of China, were collected to investigate the sources and distribution characteristics of 9 heavy metals (V, Pb, Cd, Cu, Zn, Ni, Cr, Fe, and Mn). The results suggest that foliar samples had smaller particle size and higher heavy metal contents than road dusts. The contamination assessments of heavy metals were as follows: Pb and V (significant enrichment) > Zn, Ni, Cr, Fe, and Mn (moderate enrichment) > Cd and Ni (minimal enrichment). Statistical analyses showed Pb, as the primary pollution element, originated from waste incineration and lead-fuel combustion. The sources of Zn, Ni, Cr, Fe, V, and Mn were fugitive dust and traffic activities. Potential origins of Cu were corrosion of alloys used in vehicle components, vehicle covers, or other metallic surfaces and materials. The sources of Cd were different from any other heavy metals. Traffic and industrial activities were the main anthropogenic origins of heavy metals in dusts of Panzhihua, and more attention should be paid to heavy metal pollution in agricultural area.

Spatial variation of contaminant elements of roadside dust samples from Budapest (Hungary) and Seoul (Republic of Korea), including Pt, Pd and Ir

Roadside dusts were studied to explain the spatial variation and present levels of contaminant elements including Pt, Pd and Ir in urban environment and around Budapest (Hungary) and Seoul (Republic of Korea). The samples were collected from six sites of high traffic volumes in Seoul metropolitan city and from two control sites within the suburbs of Seoul, for comparison. Similarly, road dust samples were obtained two times from traffic focal points in Budapest, from the large bridges across the River Danube, from Margitsziget (an island in the Danube in the northern part of Budapest, used for recreation) as well as from main roads (no highways) outside Budapest. The samples were analysed for contaminant elements by ICP-AES and for Pt, Pd and Ir by ICP-MS. The highest Pt, Pd and Ir levels in road dusts were found from major roads with high traffic volume, but correlations with other contaminant elements were low, however. This reflects automobile catalytic converter to be an important source. To interpret the obtained multi-element results in short, pollution index, contamination index and geo-accumulation index were calculated. Finally, the obtained data were compared with total concentrations encountered in dust samples from Madrid, Oslo, Tokyo and Muscat (Oman). Dust samples from Seoul reached top level concentrations for Cd-Zn-As-Co-Cr-Cu-Mo-Ni-Sn. Just Pb was rather low because unleaded gasoline was introduced as compulsory in 1993. Concentrations in Budapest dust samples were lower than from Seoul, except for Pb and Mg. Compared with Madrid as another continental site, Budapest was higher in Co-V-Zn. Dust from Oslo, which is not so large, contained more Mn-Na-Sr than dust from other towns, but less other metals.

IBIL analysis of road dust samples from San Bernardo tunnel

Road dust in urban or industrial sites is an important source of atmospheric particulate by re-suspension of finer particles that may contain potentially toxic pollutants. In this work Ion Beam Induced Luminescence (IBIL), Nuclear Magnetic Resonance and fluorescence spectroscopy analyses were used to characterize road dust samples with particle size lower than 250 μm collected on the walls and on the floor of the ventilation air shaft of "Traforo del San Bernardo" highway tunnel. Moreover, for comparison, IBIL analyses were performed both on some possible anthropic sources of particulate matter and on a road dust reference sample (BCR-723). IBIL spectra as a function of the fluence were analyzed with a multivariate approach in order to identify the spectral components evolving with different rate. Nuclear Magnetic Resonance and fluorescence spectroscopy analyses were performed on extracted samples of the road dust in order to study the contribution of organic compounds to the IBIL features. Results point out that IBIL, here performed for the first time for road dust analysis, can be applied for the identification of compounds by characterizing the sample origin.

First study on anthropogenic Pt, Pd, and Rh levels in soils from major avenues of São Paulo City, Brazil

Over the last years, investigations on the increase of platinum (Pt), palladium (Pd), and rhodium (Rh) levels in urban environments of big cities all over the world - especially to catalytic converters emissions - have been grown up enormously. São Paulo City is the 6th largest megacity in the world having about 20 million inhabitants and an ever increasing seven million motor vehicle fleet. In spite of this, there has never been an investigation regarding Pt, Pd, and Rh levels in the city. In the present study, Pt, Pd, and Rh concentrations were determined in soils adjacent to seven main high-density traffic avenues in the metropolitan region of São Paulo City. Inductively coupled plasma mass spectrometry was employed - after ultrasound-assisted aqua regia leaching - as analytical technigue. The results showed concentration levels up to 378 ng g(-1) for Pd, 208 ng g(-1) for Pt, and 0.2 to 45 ng g(-1) for Rh. These levels are much higher than those considered for the geochemical background of soils, indicating a catalytic converter source. Due to the different Pt/Pd/Rh ratio in Brazilian automobile catalytic converters, lower levels of Pt/Pd ratios compared with other similar studies were observed. The obtained results are the first data for monitoring Pt, Pd, and Rh pollution in São Paulo City soils.

Identification of platinum and palladium particles emitted from vehicles and dispersed into the surface environment

Platinum, palladium, and rhodium are emitted from vehicle catalytic converters. Until now, the form of precious metal particles in road dust and urban waste has not been identified. This study has located, imaged, and analyzed these particles in road dust and gully waste. Two fragments of catalytic converter have been observed in road dust. They are 40-80 μm in size and covered in many minute particles (<0.3 μm) of either platinum with minor rhodium or palladium. One fragment identified in gully sediment is smaller, 25 μm in diameter, hosting only one attached particle of palladium with minor rhodium. As fragments are washed off roads they begin to disintegrate and the precious metals become detached. Also precious metal-bearing particles have been located in incinerated sewage ash including a 20 μm diameter cluster of <3 μm sized platinum particles that may be the remains of a catalytic converter fragment that has survived incineration. The form of these precious metal-bearing particles described here reveals that as they are dispersed from roads they are likely to be present predominantly as two particle sizes. Either they are attached to larger fragments of catalytic converter or they are released as individual detached tiny <0.3 μm to nanoparticle sizes.

Dissolution kinetics of Pd and Pt from automobile catalysts by naturally occurring complexing agents

Powder samples prepared from gasoline (Pt, Pd, Rh, new GN/old GO) and diesel (Pt, new DN/old DO) catalysts and recycled catalyst NIST 2556 were tested using kinetic leaching experiments following 1, 12, 24, 48, 168, 360, 720 and 1440-h interactions with solutions of 20mM citric acid (CA), 20 mM Na(2)P(4)O(7) (NaPyr), 1 g L(-1) NaCl (NaCl), a fulvic acid solution (FA-DOC 50 mg L(-1)) and 20 mM CA at pH 3, 4, 5, 6, 7, 8 and 9. The mobilisation of platinum group elements (PGEs) was fastest in solutions of CA and NaPyr. In the other interactions (NaCl, FA), the release of PGEs was probably followed by immobilisation processes, and the interactions were not found to correspond to the simple release of PGEs into solution. Because of their low concentrations, the individual complexing agents did not have any effect on the speciation of Pd and Pt in the extracts; both metals are present in solution as the complexes Me(OH)(2), Me(OH)(+). Immobilisation can take place through the adsorption of the positively charged hydroxyl complexes or flocculation of fulvic acid, complexing the PGEs on the surface of the extracted catalysts. The calculated normalised bulk released NRi values are similar to the reaction rate highest in the solutions of CA and NaPyr.

Platinum-group elements in sewage sludge and incinerator ash in the United Kingdom: assessment of PGE sources and mobility in cities

Platinum-group element (PGE) concentrations in sewage sludge and incinerator ash compared with average PGE concentrations in road dust show a common pattern, characterized by a negative Rh anomaly. This similarity, found at 9 UK incinerators, suggests that there is a universal characteristic PGE pattern produced by common processes of dispersal of Pt, Pd and Rh derived from automobile catalytic converters. Ninety-one sewage sludge and incinerator ash samples from the sewage treatment facilities in Sheffield, Birmingham and 7 other UK cities were analyzed for PGE. The highest concentrations are 602ppb Pt and 710ppb Pd with lower maximum concentrations of 65ppb Rh, 100ppb Ru, 33ppb Ir and 12ppb Os. Ash from incinerated sewage was found to have higher PGE concentrations compared to the original sludge and the PGE ratios are preserved during incineration. Rh is more mobilized and dispersed than the other PGE as it is transported from roads into the drainage system and into sewage. Pt/Pd ratios of 1.0 in road dust and 0.9 in sewage and incinerator ash suggest that Pd is more mobile than Pt during dispersal. PGE abundances in stored incinerator ash of varying ages appear to have been affected by the variation in use of Pt, Pd and Rh in catalytic converters due to variation in their market prices. Concentrations of Os, Ir and Ru in ashes are greater in Sheffield and London than all the other city sites and may be derived from point industrial sources.