Milagros Gómez

Environmental risk of particulate and soluble platinum group elements released from gasoline and diesel engine catalytic converters

A comparison of platinum-group element (PGE) emission between gasoline and diesel engine catalytic converters is reported within this work. Whole raw exhaust fumes from four catalysts of three different types were examined during their useful lifetime, from fresh to 80,000 km. Two were gasoline engine catalysts (Pt-Pd-Rh and Pd-Rh), while the other two were diesel engine catalysts (Pt). Samples were collected following the 91441 EUDC driving cycle for light-duty vehicle testing, and the sample collection device used allowed differentiation between the particulate and soluble fractions, the latter being the most relevant from an environmental point of view. Analyses were performed by inductively coupled plasma-mass spectrometry (ICP-MS) (quadrupole and high resolution), and special attention was paid to the control of spectral interference, especially in the case of Pd and Rh. The results obtained show that, for fresh catalysts, the release of particulate PGE through car exhaust fumes does not follow any particular trend, with a wide range (one-two orders of magnitude) for the content of noble metals emitted. The samples collected from 30,000-80,000 km present a more homogeneous PGE release for all catalysts studied. A decrease of approximately one order of magnitude is observed with respect to the release from fresh catalysts, except in the case of the diesel engine catalyst, for which PGE emission continued to be higher than in the case of gasoline engines. The fraction of soluble PGE was found to represent less than 10% of the total amount released from fresh catalysts. For aged catalysts, the figures are significantly higher, especially for Pd and Rh. Particulate PGE can be considered as virtually biologically inert, while soluble PGE forms can represent an environmental risk due to their bioavailability, which leads them to accumulate in the environment.

Levels and risk assessment for humans and ecosystems of platinum-group elements in the airborne particles and road dust of some European cities

Traffic is the main source of platinum-group element (PGE) contamination in populated urban areas. There is increasing concern about the hazardous effects of these new pollutants for people and for other living organisms in these areas. Airborne and road dusts, as well as tree bark and grass samples were collected at locations in the European cities of Göteborg (Sweden), Madrid (Spain), Rome (Italy), Munich (Germany), Sheffield and London (UK). Today, in spite of the large number of parameters that can influence the airborne PGE content, the results obtained so far indicate significantly higher PGE levels at traffic sites compared with the rural or non-polluted zones that have been investigated (background levels). The average Pt content in airborne particles found in downtown Madrid, Göteborg and Rome is in the range 7.3-13.1 pg m(-3). The ring roads of these cities have values in the range 4.1-17.7 pg m(-3). In Munich, a lower Pt content was found in airborne particles (4.1 pg m(-3)). The same tendency has been noted for downtown Rh, with contents in the range 2.2-2.8 pg m(-3), and in the range 0.8-3.0 and 0.3 pg m(-3) for motorway margins in Munich. The combined results obtained using a wide-range airborne classifier (WRAC) collector and a PM-10 or virtual impactor show that Pt is associated with particles for a wide range of diameters. The smaller the particle size, the lower the Pt concentration. However, in particles <PM-10, some of the highest values correspond to the fraction <0.39 microm. Considering an average Pt content in all particles of approximately 15 pg m(-3), which is representative for all countries and environmental conditions, the tracheobronchial fraction represents approximately 10% and the alveolar fraction approximately 8% of the total particles suspended in air. However, from the environmental risk point of view, an exposure to PGEs in traffic-related ambient air is at least three orders of magnitude below the levels for which adverse health effects might theoretically occur (of approx. 100 ng m(-3)). Therefore, today inhalation exposure to PGEs from automotive catalysts does not seem to pose a direct health risk to the general population. Even though the data available today indicate no obvious health effects, there are still a number of aspects related to PGEs and catalysts that justify further research. First, continual monitoring of changes in PGE levels in air and road dust is warranted, to make sure that there is no dramatic increase from todays levels. Secondly, more detailed information on the chemical composition of the PGE-containing substances or complexes leaving the catalyst surface and the size distribution of the PGE-containing particles released during driving will facilitate a more in-depth human risk assessment.

Platinum-group elements: quantification in collected exhaust fumes and studies of catalyst surfaces

Automotive catalytic converters, in which Pt, Pd and Rh (platinum-group elements; PGEs) are the active components for eliminating several noxious components from exhaust fumes, have become the main source of environmental urban pollution by PGEs. This work reports on the catalyst morphology through changes in catalyst surface by scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX) and laser-induced breakdown spectrometry (LIBS) from fresh to aged catalytic converters. The distribution of these elements in the fresh catalysts analysed (Pt-Pd-Rh gasoline catalyst) is not uniform and occurs mainly in a longitudinal direction. This heterogeneity seems to be greater for Pt and Pd. PGEs released by the catalysts, fresh and aged 30,000 km, were studied in parallel. Whole raw exhaust fumes from four catalysts of three different types were also examined. Two of these were gasoline catalysts (Pt-Pd Rh and Pd-Rh) and the other two were diesel catalysts (Pt). Samples were collected following the 91,441 EUDC driving cycle for light-duty vehicle testing. The results show that at 0 km the samples collected first have the highest content of particulate PGEs and although the general tendency is for the release to decrease with increasing number of samples taken, exceptions are frequent. At 30,000 km the released PGEs in gasoline and diesel catalysts decreased significantly. For fresh gasoline catalysts the mean of the total amount released was approximately 100, 250 and 50 ng km(-1) for Pt, Pd and Rh, respectively. In diesel catalysts the Pt release varied in the range 400-800 ng km-1. After ageing the catalysts up to 30,000 km, the gasoline catalysts released amounts of Pt between 6 and 8 ng km(-1), Pd between 12 and 16 ng km(-1) and Rh between 3 and 12 ng km(-1). In diesel catalysts the Pt release varied in the range 108-150 ng km(-1). The soluble portion of PGEs in the HNO3 collector solution represented less than 5% of the total amount for fresh catalysts. For 30,000 km the total amount of soluble PGEs released was similar or slightly higher than for 0 km.

Bioaccumulation of palladium, platinum and rhodium from urban particulates and sediments by the freshwater isopod Asellus aquaticus

The three-way catalytic converters introduced to oxidize and reduce gaseous automobile emissions represent a source of platinum group elements (PGEs), in particular platinum, palladium and rhodium, to the urban environment. Abrasion of automobile exhausts leads to an increase of the concentration of PGEs in environmental matrices such as vegetation, soil and water bodies. The bioaccumulation of Pd, Pt and Rh by the freshwater isopod Asellus aquaticus was studied in natural ecosystems and under laboratory conditions. Owing to the low concentration level (ng g(-1)) of PGEs in the animals studied. analyses were performed with a quadrupole inductively coupled plasma mass spectrometry (ICP-MS) and hafnium, copper, yttrium, rubidium, strontium and lead were monitored for spectral interference correction. Asellus aquaticus collected in an urban river showed a content (mean +/- s) of 155.4 +/- 73.4, 38.0 +/- 34.6, and 17.9 +/- 12.2 ng g(-1) (dry weight) for Pd, Pt and Rh, respectively. The exposure of Asellus aquaticus to PGE standard solutions for a period of 24h give bioaccumulation factors of Bf: 150, 85, and 7 for Pd, Pt and Rh, respectively. Exposure of Asellus aquaticus to environmental samples for different exposure periods demonstrated that PGE bioaccumulation is time dependent. and shows a higher accumulation for the materials with a higher PGE content. While all three elements have the same uptake rate for exposure to catalyst materials, for exposure to environmental materials they havc a different uptake rate which can be attributed to transformations of the PGE species in the environment.

Platinum and rhodium distribution in airborne particulate matter and road dust

In this work the platinum and rhodium content in the atmosphere of Madrid was monitored for 1 year at seven different sites. Samples were taken with medium volume PM-10 collectors (< 10 microm) for 48 h and analysed by ICP-MS. The Pt and Rh content was dependent on the sampling site, ranging from < 0.1 to 57.1 and < 0.2 to 12.2 pg m(-3) with a medium value of 12.8 and 3.3 pg m(-3), respectively. These results show that the Pt and Rh content in airborne samples depends on the traffic density per day and also on medium driving speed. Road dust < 63 microm was analysed at the same time and at the same location. The Pt and Rh content at the six sites analysed was in the 31-2252 and 11-182 ng g(-1) range with an average of 317 and 74 ng g(-1), respectively. The average Pt/Rh ratio obtained was 4.3. similar to that obtained for airborne particles (4.0), and agrees with that of the more commonly used gasoline car catalyst [J.J. Mooney, Encyclopaedia of Chemical Technology (1996) 982]. Platinum distribution as a function of particle size in airborne particulate matter was also studied, by sampling with two high-volume sample collectors, a five-stage WRAC (from 10 to 65.3 microm and total) and a seven-stages PM-10) cascade impactor (from 9 to < 0.39 microm). Platinum is associated with a wide range of particle diameters. Due to the ultratrace level of Pt in airborne samples, its distribution in the atmosphere could not be considered as homogeneous. No trend could be established in Pt distribution in the different fractions, except that in most cases the highest value of Pt was obtained in the < 0.39-microm fraction. The Pt content was usually high in airborne samples when the Pb, Ce, Zr and Hf content was also high, thus confirming that the source of these pollutants is from traffic.

Determination of platinum, rhodium and palladium in exhaust fumes

With the introduction of catalytic converters for reducing emissions of CO, NO x and HC, a higher concentration of Pt, Pd and Rh is being observed in environmental samples. These platinum group elements (PGE) are the main active components of catalytic converters and they are mainly released as a result of surface abrasion of the catalyst during car operation. The present work reports the procedure employed for sampling, mineralization and determination of PGE by quadrupole ICP-MS in three different types of catalysts. Whole raw exhaust fumes were collected directly from the end of the exhaust pipe following the 91441 extra urban drive cycle (EUDC) using a newly developed sampling device. The sampling procedure allows the further differentiation between a soluble and particulate (insoluble) sample fraction. The release of pollutants such as Hf, Cu, Y, Rb, Sr and Pb present in the catalyst washcoat or in the fuel was also monitored since these elements cause spectral interferences in the determination of PGE. These spectral interferences, 179 Hf 16 O + on 195 Pt, 40 Ar 65 Cu + and 89 Y 16 O + on 105 Pd and 40 Ar 63 Cu + , 87 Rb 16 O + , 87 Sr 16 O + and 206 Pb 2+ on 103 Rh, were considered and mathematically corrected. The sampling procedure was applied to quantify the PGE released from two different types of fresh gasoline catalyst (Pt/Pd/Rh and Pd/Rh), a diesel catalyst (Pt only) and a 18 000 km aged Pt/Pd/Rh gasoline catalyst. Most of the released PGE is in particulate form (Pt >95%, Pd >85% and Rh >90%). Release was found to vary from catalyst to catalyst and between samples of the same catalyst. The determination of PGE in the exhaust fumes shows that they are released at the ng km –1 level.

ICP-MS determination of Pt, Pd and Rh in airborne and road dust after tellurium coprecipitation

A method has been developed for the simultaneous determination of Pd, Pt and Rh (PGE) in environmental airborne and road dust samples by tellurium coprecipitation and ICP-MS. The Te coprecipitation was applied after digestion of the sample with aqua regia–HF in a microwave oven. This separation method removes more than 95% of the elements producing mass interference in PGE determination by ICP-MS. The methodology was validated with reference road dust samples CW7 and CW8. The detection limits are 0.3, 0.6 and 0.8 pg m−3 for Pt, Pd and Rh in airborne particulate matter, and 1, 1 and 0.4 ng g−1 for Pt, Pd and Rh in road dust. Application of the isotopic dilution method for Pt and Pd after their coprecipitation improves the results obtained for road dust samples. Rh (monoisotopic element) analysis was carried out by external calibration after Te coprecipitation.

Assessment of environmental contamination risk by Pt, Rh and Pd from automobile catalyst

The main active components of present-day car catalysts are the noble metals Pt, Pd and Rh, belonging to the platinum group elements (PGEs). It is recognized that these elements are being spread into the environment to an as-yet incompletely known extent, mainly due to surface abrasion of the catalyst during car operation. These new pollutants have motivated extensive research on PGE determination. Our work is planned to ascertain the health and ecosystem risks of these PGEs emitted through a series of interrelated objectives that address the pathway of these elements from the catalyst to the different environmental compartments. Combined studies of catalyst surface abrasion and exhaust fumes analysis, the monitoring of Pt, Pd and Rh in airborne particles and road dust sediments and bioaccumulation studies in aquatic organisms, plants and urine enable a realistic assessment of the risk that this release represents for man and environment. In this work some previous results are presented.

On-line preconcentration and determination of trace platinum by flow-injection atomic absorption spectrometry

The analytical performance of a platinum preconcentration method using a 0.01 M HNO3 carrier solution and an alumina microcolumn is discussed. On-line preconcentration is followed by flame atomic absorption spectrometry (FAAS), and off-line preconcentration by graphite furnace atomic absorption spectrometry (GFAAS). The preconcentration factors were 600 for FAAS (25 μl elution volume) and 30 for GFAAS (500 μl elution volume), both with a 15-ml sampling volume. The detection limits in these conditions were 0.02 mg l−1, and relative standard deviation (R.S.D.) of 9% (0.1 mg l−1 solution, n = 5) for FAAS and 0.33 μg l−1, and a R.S.D. of 7% (5 μg l−1 solution n = 5) for GFAAS. The proposed method is suitable for platinum determination in natural water samples.

Stability studies of arsenate, monomethylarsonate, dimethylarsinate, arsenobetaine and arsenocholine in deionized water, urine and clean-up dry residue from urine samples and determination by liquid chromatography with microwave-assisted oxidation-hydride generation atomic absorption spectrometric detection

Abstract The stability of arsenate, monomethylarsonate, dimethylarsinate (DMA), arsenobetaine (AsB) and arsenocholine (AsC) at a concentration of 200 μg l −1 in deionized water, urine and dry clean-up residue of urine, stored in dark at −20 °C, 4 °C and ambient temperature, without the addition of any stabilizer reagent was evaluated. The five species were determined independently by liquid chromatography with microwave-assisted oxidation-hydride generation atomic absorption spectrometric detection. At −20 °C, all species were stable in water and untreated urine; at 4 °C and ambient temperature, they were stable during the 67 days of testing in the urine dry residue after the clean-up procedure. In untreated urine samples at 4 °C and ambient temperature, AsC is unstable and easily transformed to the more oxidized species, AsB. In deionized water, AsB and AsC are transformed to other species such as DMA. The dry urine residue may be a good matrix as a reference material for As species.