Sources of Platinum Group Elements in the Environment

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.

Contrasting platinum trajectories in three major French rivers using dated sediment cores (1910-2021): From geochemical baseline to emerging source signals

Platinum (Pt) is a Technology Critical Element (TCE) which, since the 1990s, has been mainly used in the industry in catalytic converters for automobile emission control. Previous studies have shown Pt contamination of road-side sediments and surface sediments in urban rivers and lakes but few of them have addressed temporal variations. The present work presents historical Pt concentration trends in 137Cs-dated sediment cores from floodplains or secondary channels at the outlets of three major French watersheds (Loire, Rhone, and Seine Rivers) covering the past ∼110 years, i.e., from the 1910s to 2021. Platinum baseline levels in the sediment were estimated for the Loire River (0.76 ± 0.22 μg kg-1 for the period ∼1910-∼1955) and the Rhone River (1.64 ± 0.41 μg kg-1), and historical Pt variations seem to reflect variations in hydrodynamics and grain size composition. Since the early 2000s, Pt concentrations in the Loire and the Rhone River sediments tend to increase (>2.5 μg kg-1) and were attributed to the use of car catalytic converters, an emerging technology since the 1990s using >50 % of European Pt demand. High and variable historical Pt concentrations (up to 14.6 μg kg-1) in the Seine River sediments may reflect legacy Pt sources due to former anthropogenic activities in this watershed, such as the use of Pt-based catalysts for petroleum refinery since the end of the 1940s, coal handling and precious metals refining, probably concealing the likely presence of an emerging traffic-related Pt signal. This first comparison of historical Pt concentration trends in sediments from contrasting watersheds allows to distinguish signals originating from different natural and anthropogenic sources (background level, historical sources, road traffic).

Platinum Group Element distribution in water and marine biota from two impacted estuarine environments (Douro and Ave estuaries, Portugal)

Platinum Group Elements (PGEs) are contaminants of emerging environmental concern considering their continuous increasing use and subsequent release in the environment. While recent field studies provided PGE levels in seawater, scarce knowledge still exists regarding PGE contamination in marine organisms, especially for rhodium (Rh). Water, macroalgae and mussels were sampled along two representative urbanized estuarine systems and adjacent coastal areas (Douro and Ave estuaries, Portugal). Rhodium and platinum (Pt) concentrations were quantified through both stripping voltammetry and mass spectrometry in collected samples. Spatial mapping of PGE contamination was, to a certain extent, correlated with proxies of urban effluents. The use of Pt/Rh ratios reflected the dominant influence of PGE traffic emissions along the Douro and inputs from various sources (including industries) on the Ave Estuary. Macroalgae and mussels PGE concentrations reflected urban pressure, amplifying environmental signals, and supporting their relevant use as bioindicators of PGE contamination in estuarine/coastal systems.

Mercury, Platinum, Antimony and Other Trace Elements in the Atmospheric Environment of the Urban Area of Mexico City: Use of Ficus benjamina as Biomonitor

The application of Sb, Pt and Hg in the development of new strategic technologies has increased significantly in recent years. This study evaluates the impact of vehicular traffic on the rise in emission of Sb, Pt and Hg in the atmospheric environmen of Mexico City and their correlation to Co, Cr, Cu, Ni, Pb, V and Zn. Ficus benjamina leaves were collected as biomonitor of atmospheric metals deposited in areas exposed to heavy vehicular traffic. High enrichment factor values (metal(loid) concentration/background values) were calculated: 146 (Sb), 52.8 (Pb), 29.7 (Pt) and 25.1 (Cr). Enrichment factors of Ni, Zn, Co, V, Cu and Hg decrease in that order and are < 10. Principal component analysis allows recognize that most of the analyzed metal(loids) are related to traffic sources; Ni and Cr are also attributable to an additional anthropogenic source. No relationship was found relating Pb to vehicular sources.

Drivers of Rh and Pt variability in the water column of a hydrodynamic estuary: Effects of contrasting environments

Rhodium and platinum are amongst the less studied elements in estuarine waters and the understanding of their speciation analysis and environmental fate remains limited. In this study, we address the occurrence and discrimination of soluble/insoluble Rh and Pt species in aquatic systems, as well as their potential transport. Particulate and dissolved (< 0.45 μm) rhodium (Rh_P and Rh_D) and platinum (Pt_P and Pt_D), respectively, were determined in the water column of contrasting environments during neap (NT) and spring (ST) tide semi-diurnal cycles: in the upper Tagus estuary (VFX) and near the mouth, close to a wastewater treatment plant outfall (ALC). Both elements were analyzed by AdCSV and ICP-MS, as well ancillary parameters were determined. Concentrations of Rh and Pt followed the tidal regime, presenting higher concentrations during low tide. Concentrations of Rh_P (0.1-5.1 ng g^-1) and Rh_D (0.03-0.12 ng L^-1) were lower than Pt_P (1.0-25.6 ng g^-1) and Pt_D (0.1-11.7 ng L^-1), respectively. Concentrations found in ALC were higher than VFX, except for Rh_D, mirroring anthropogenic inputs attributed to automotive catalytic converters and an additional Pt source originated in Pt-based compounds. Distribution coefficients (K_D) of 10⁴ were computed and were independent of the salinity gradient. The speciation analysis done at VFX during NT showed that truly dissolved forms measured by AdCSV represented 39 ± 9% of total Pt in the water column, while total filter-passing species measured by ICP-MS were higher, 65 ± 14%. Pt speciation was controlled by its dissolved forms, whereas particulate Rh forms represented the bulk value (> 65%). The potential transport evaluated at downstream station indicated recirculation within the estuary and export towards the Atlantic Ocean, with higher concentrations associated with the ebb opposing to the flood. These results show estuaries as important pathways to introduce PGE in coastal regions, transferring them towards the ocean.

Platinum group elements in atmospheric PM10 particles and dry deposition in France

Platinum group elements (PGEs, i.e. platinum, Pt; palladium, Pd; and rhodium, Rh) catalyse over 90% of carbon monoxide, nitrogen oxides and hydrocarbons from combustion residues into water vapour, carbon dioxide and nitrogen in the vehicle's catalytic converter. But there is a major concern over these metals in the scientific world, since they are emitted by catalytic converters and accumulating in the environment. The distribution of PGEs in PM10 fraction was studied in an open urban site (Nantes, France) and in a tunnel (Paris, France) using low- and high-volume air samplers. PGEs were also investigated in dry deposition particles and deposited dust sampled in the tunnel. Pd occurred at the highest levels in both PM10 and dry deposition samples, followed by Rh and Pt. Maximum concentrations in PM10 fraction were 114 pg m-3 for Pd, 14.3 pg m-3 for Rh and 3.3 pg m-3 for Pt in the urban site (Nantes) and 91 pg m-3 for Pd and 16 pg m-3 for Rh in the tunnel (Paris). The concentrations for dry depositions in the tunnel were 261 μg kg-1 for Pt, 431 μg kg-1 for Pd and 85 μg kg-1 for Rh. The results on PGEs levels in atmospheric particles and dry depositions are the first data of their kind in France and will provide new insights into the contribution of catalytic converters to the environment. We also observed Pd and Rh being 2 times higher PM10 particles compared to dry depositions, leading us to suggest that particles rich in Pd and Rh are smaller than 10 μm. An overall concentration trend of Pd > Rh > Pt was observed in all samples, showing the replacement of Pt by Pd and Rh in newer catalytic converters.

Platinum and rhodium in Tagus estuary, SW Europe: sources and spatial distribution

The spatial distribution of Pt and Rh was assessed in Tagus estuary and their sources discussed. Both elements were analysed in superficial sediment samples (n = 72) by adsorptive cathodic stripping voltammetry. Concentrations varied within the following ranges: 0.18-5.1 ng Pt g^-1 and 0.02-1.5 ng Rh g^-1. Four distinct areas were established: "reference"; waste- and pluvial water discharge; motorway bridges and industrialised areas. The calculated reference median concentrations were 0.55 ng Pt g^-1 and 0.27 ng Rh g^-1. Linear relationships were found between Pt and Al, Fe and LOI, whereas Rh depicted scattered patterns. The highest concentrations were found nearby industrialised areas and a motorway bridge, corresponding to the enrichment of 10 and 6 times the background of Pt and Rh, respectively. The main sources of contamination to the Tagus estuary derived from historical and present industrial activities and from automotive catalytic converters. Large variations of Pt/Rh ratio (0.48-39) point to different sources, reactivity and dilution effects.

Bioaccumulation and metal-associated biomarker responses in a freshwater mussel, Dreissena polymorpha, following short-term platinum exposure

Due to the increasing presence of platinum (Pt) in the environment, the caveat arises to identify its toxic potential in species at risk of being exposed - especially those found in aquatic environments where pollutants tend to accumulate. Comprehensive characterisation of possible adverse effects following exposure of aquatic organisms to Pt remains elusive. To address this, Zebra mussels (Dreissena polymorpha) were exposed to a range of Pt(IV) concentrations (0.1, 1, 10, 100 and 1000 μg/L) for one and four days, respectively, after which bioaccumulation was quantified and compared to alterations in biomarker profiles relevant to metal toxicity i.e. glutathione-S-transferase (GST) and catalase (CAT) activity, lipid peroxidation and metallothionein (MT) induction. Despite pre-conditioning of the tanks, Pt recovery in the exposure media was found to be 36% (0.1 μg/L), 42% (1 μg/L), 47% (10 μg/L), 68% (100 μg/L) and 111% (1000 μg/L) due to biological and non-biological processes. Pt concentrations in dried mussel soft tissue increased with exposure concentrations and were 20-153 times higher compared to quantified Pt concentrations in the exposure media. CAT activity was significantly increased in the tissue of mussels exposed to 0.1-100 μg/L Pt after Day 1 while the lowest effect concentration (LOC) for this response on both Day 1 and Day 4 was 0.1 μg/L. The effect on the GST activity was less pronounced but demonstrated a similar trend. However, enhanced lipid peroxidation was measured in the tissue of mussels exposed to ≥0.1 μg/L on Day 4. Bioaccumulation of Pt was also associated with a concentration-dependent increase in Pt-MT. Although these effects occurred at Pt levels higher than those present in the environment, it indicates that Pt has the ability to cause aberrancies in metal-associated biomarker profiles.

Platinum in sediments and mussels from the northwestern Mediterranean coast: Temporal and spatial aspects

Platinum (Pt) is considered a Technology Critical Element (TCE) and an emerging metallic contaminant with increasing release into the environment. Gaps in knowledge and understanding of environmental levels, fate and effects of Pt still exist, especially in the marine environment. This work presents Pt concentrations in the northwestern Mediterranean coast including: (i) temporal variability from sediment cores and farmed mussels in the Toulon Bay (historically affected by intense human activities) and (ii) spatial distribution from recent wild mussels collected along ∼ 700 km coastline with contrasting ecosystems (including natural reserves), quantified using voltammetry and inductively coupled plasma-mass spectrometry. The historical (>100 years) record of Pt in sediments from the Toulon Bay suggests the existence of non-negligible Pt sources older than those related to vehicle emission devices, such as petrol industry and coal-fired activities. A strong Pt increase in more recent sediments (from ∼12 to 16 ng g^-1) and mussels (8-fold increase from ∼0.12 to 0.80 ng g^-1) covering the past 25 years reflect the overall evolution of Pt demand in Europe (∼20-fold increase for vehicle catalysts in 20 years). Spatial biomonitoring of Pt in mussels along the northwestern Mediterranean coast is assumed to reflect inter-site differences of Pt exposure (0.09-0.66 ng g^-1) despite seasonal effect on tissue development. This study highlights the need for thorough and regular monitoring of Pt levels in sediments and biota from urbanized coastal areas in order to better assess the environmental impact of this TCE, including potential risks for marine organisms.

Improved voltammetric method for simultaneous determination of Pt and Rh using second derivative signal transformation - application to environmental samples

The determination of Platinum-group elements (PGE) in relevant environmental matrices is a challenging task. Sensitive and accurate analytical procedures for simultaneous determination of Pt and Rh are still needed. In this study, we report for the first time on the use of second derivative signal transformation to the ultra-trace simultaneous determination of Pt and Rh by Adsorptive Cathodic Stripping Voltammetry (AdCSV). With that step, the ill-defined peaks typically observed in the original voltammograms are transformed into well-shaped peaks, resulting in accurate detection. The experimental conditions were investigated and optimised: a suitable electrolyte for both elements, with less reagents consumption, (0.25M H₂SO₄, 0.05M HCl, 0.01M FA and 0.5mM HZ), deposition time (t_d) and deposition potential (E_d). For t_d = 120s and E_d = -0.75V, linear relationships r > 0.999 were obtained in the concentration range up to 5.8ngL^-1 (27 pM) for Pt and up to 3.4ngL^-1 (34 pM) for Rh. Limits of detection were 0.2ngL^-1 for Pt and 0.08ngL^-1 for Rh. Lower values can be achieved by increasing the deposition time. Limits of quantification, LOQ, calculated as 3 times LOD, were 0.5ngL^-1 for Pt and 0.2ngL^-1 for Rh. The sensitivity of Pt was affected by elevated Zn concentrations, whereas a minor effect was observed for Rh. However, Pt and Rh determinations were not influenced using the standard addition method. Precision as intermediate precision and expressed as relative standard deviation, based on Pt and Rh spiked solutions and digested road dust CRM BCR-723 was 17% and 20% for Pt and Rh, respectively. Recoveries of CRM were around 90% for both elements. The method was successfully applied in the simultaneous determination of Pt and Rh in sediments from Tagus estuary and, for the first time, dissolved Rh was determined in water samples of a waste water treatment plant. Application of this technique in a multidisciplinary approach will be a relevant contribution to the current understanding of PGE cycle and fate in the environment.

Assessing the potential of inorganic anions (Cl-, NO3-, SO42- and PO43-) to increase the bioaccessibility of emitted palladium in the environment: Experimental studies with soils and a Pd model substance

Palladium (Pd) emitted from vehicles equipped with exhaust catalytic converters has been accumulating at a greater rate relative to other platinum group elements (PGE) in the last 10-20 years. Little is known, however, regarding the various environmental factors and conditions which are likely to modulate the chemical behavior and bioaccessibility of this element post-emission. To meet data needs, soils and a Pd model substance were treated with solutions containing common anions (Cl^-, NO₃^-, SO₄^2- und PO₄^3-) to shed light on the geochemical behavior of emitted Pd under ambient conditions. As part of this, the particle surface chemistry of treated residues (insoluble phase) and solutions (soluble phase) was examined using XPS to assess the chemical transformation of Pd in the presence of inorganic anions. The results show that Pd is the most soluble in the presence of anionic species, followed by rhodium (Rh) and platinum (Pt). Pd in field-collected samples was found to be considerably more soluble than the metallic Pd in the model substance, Pd black, when treated with anionic species. The results also demonstrate that the solubility of Pd black is strongly dependent on solution pH, concentration and the duration of reaction. The outer 3-4 atomic layers of metallic Pd was determined via XPS to be partially oxidized when treated with anion solutions, with the degree being dependent on anion type. The concentration of dissolved O₂ in solution was found to have little impact on the transformation of metallic Pd. Given the ubiquitous nature of the anions examined, we can expect that Pd will become more bioaccessible post-emission.

Anthropogenic platinum group element (Pt, Pd, Rh) concentrations in PM10 and PM2.5 from Kolkata, India

This study investigates platinum group elements (PGEs) in the breathable (PM10) and respirable (PM2.5) fractions of air particulates from a heavily polluted Indian metro city. The samples were collected from traffic junctions at the heart of the city and industrial sites in the suburbs during winter and monsoon seasons of 2013-2014. PGE concentrations were determined by inductively coupled plasma-mass spectrometry (ICP-MS). The PGE concentrations in the samples from traffic junctions are within the range of 2.7-111 ng/m(3) for Pd, 0.86-12.3 ng/m(3) for Pt and 0.09-3.13 ng/m(3) for Rh, and from industrial sites are within the range of 3.12-32.3 ng/m(3) for Pd, 0.73-7.39 ng/m(3) for Pt and 0.1-0.69 ng/m(3) for Rh. Pt concentrations were lower in the monsoon compared to winter while Pd concentrations increased during monsoon and Rh stayed relatively unaffected across seasons. For all seasons and locations, concentrations of Pd > Pt > Rh, indicating dominance of Pd-containing exhaust converters. Most of the PGEs were concentrated in the PM2.5 fraction. A strong correlation (R ≥ 0.62) between the PGEs from traffic junction indicates a common emission source viz. catalytic converters, whereas a moderate to weak correlation (R ≤ 0.5) from the industrial sites indicate mixing of different sources like coal, raw materials used in the factories and automobile. A wider range of Pt/Pd, Pt/Rh and Pd/Rh ratios measured in the traffic junction possibly hint towards varying proportions of PGEs used for catalyst productions in numerous rising and established car brands.

Active biomonitoring of palladium, platinum, and rhodium emissions from road traffic using transplanted moss

The use of transplanted moss (Pleurozium schreberi) in active biomonitoring of traffic-related emissions of Pd, Pt, and Rh was studied. Moss mats were transplanted to three locations along highway E75 (in Oulu, Finland) at three different distances from the highway. Five samples were collected from a background site after the same exposure period. Mass fractions of Pd, Pt, and Rh as well as mass fractions of 18 other elements were determined in these samples. The results indicated that P. schreberi is well suited for active biomonitoring of Pd, Pt, and Rh. Mass fractions above the background values were observed in the samples exposed to traffic-related emissions. When the results were compared with those of the other elements, high correlations of Pd, Pt, and Rh with commonly traffic-related elements (e.g., Cu, Ni, Sb, Zn, etc.) were found. It was also found that the amounts of Pd, Pt, and Rh in moss samples decreased when the distance to the highway increased. This trend gives evidence for the suitability of P. schreberi for active biomonitoring of Pd, Pt, and Rh. Furthermore, it can be concluded that the mass fractions determined in this study provide valuable evidence about the current state of Pd, Pt, and Rh emissions in Oulu, Finland.