Hendrik Emons

A peat bog record of natural, pre-anthropogenic enrichments of trace elements in atmospheric aerosols since 12 370 14C yr BP, and their variation with Holocene climate change

Abstract A peat bog in the Jura Mountains, Switzerland, provides a continuous record of peat accumulation since 12u2008370 14 C yr BP. Periods of enhanced soil dust deposition (10u2008590 14 C yr BP, 8230 14 C yr BP, and after 5320 14 C yr BP) are characterized by strongly elevated Ti/Sc and Zr/Sc ratios which imply an increase in the abundance (both relative and absolute) of heavy minerals such as ilmenite and zircon. With respect to trace elements such as Cu, Zn, As, Cd, Sb and Au, the M/Sc ratios are at their lowest, and often approach crustal values, during periods of enhanced soil dust deposition. The lowest rates of atmospheric deposition of soil dust date from 8030 to 5320 14 C yr BP, corresponding to the Holocene climate optimum, but here many trace elements exhibit their greatest natural enrichments: the average enrichment factor (calculated using Sc as the reference element, and normalizing to crustal abundance) was Zn 4.1±1.4, Sb 4.8±1.4, Cu 8.8±3.3, As 14.9±3.2, Au 53.9±25.1, and Cd 357.4±53.8. These enrichments cannot be explained by chemical diagenesis within the deeper sections of the peat profile during or subsequent to peat formation, but rather reflect the chemical composition of airborne material supplied to the surface layers of the bog at the time of deposition. The enrichments of trace metals in ancient peats, relative to crustal abundance, most likely reflects the natural enrichment of these elements in the fine fraction of soils during rock weathering. Periods of enhanced soil dust deposition such as the Younger Dryas cold climate phase (10u2008590 14 C yr BP) are characterized by reduced vegetation cover, greater exposed soil surface, and higher wind strengths; these conditions promote the transport of locally derived soil materials of greater particle size, lower concentration of trace metals, and M/Sc ratios approaching crustal values. During the Holocene climate optimum, vegetation cover was extensive, and with lower wind strengths and a reduction in erodible soil materials, long range transport of soil dust became relatively more important to the soil dust inventory of the bog; soil dust particles in this size class are characterized by strong enrichments of a wide range of trace elements. At the end of the Holocene optimum, dust fluxes increased once again, due mainly to soil erosion resulting from the combined effects of human activities (tillage) and the climatic deterioration at the beginning of the Neoglaciation Period; this promoted the supply of local, more coarse soil particles with M/Sc ratios approaching those of crustal rocks. While biological cycling and volcanic emissions probably also contributed to the atmospheric supply of many of these elements in the pre-anthropogenic past, these contributions appear to be less important than the chemical weathering, physical fractionation, and atmospheric transport of soil dust particles.

Analytical procedures for the determination of selected trace elements in peat and plant samples by inductively coupled plasma mass spectrometry

A simple, robust and reliable analytical procedure for the determination of 15 elements, namely Ca, V, Cr, Mn, Co, Ni, Cu, Zn, Rb, Ag, Cd, Ba, Tl, Th and U in peat and plant materials by inductively coupled plasma-quadrupole mass spectrometry (ICP-QMS) was developed. Powdered sample aliquots of approximately 220 mg were dissolved with various acid mixtures in a microwave heated high-pressure autoclave capable to digest 40 samples simultaneously. The selection of appropriate amounts of digestion acids (nitric acid, hydrofluoric acid or tetrafluoroboric acid) was crucial to obtain accurate results. The optimized acid mixture for digestion of plant and peat samples consisted of 3 ml HNO3 and 0.1 ml HBF4. An ultrasonic nebulizer with an additional membrane desolvation unit was found beneficial for the determination of Co, Ni, Ag, Tl, Th and U, allowing to aspirate a dry sample aerosol into the ICP-QMS. A pneumatic cross flow nebulizer served as sample introduction device for the other elements. Internal standardization was achieved with 103Rh for all elements, except for Th whose ICP-QMS signals were corrected by 103Rh and 185Re. Quality control was ascertained by analysis of the certified plant reference material GBW 07602 Bush Branches and Leaves. In almost all cases HNO3 alone could not fully liberate the analytes of interest from the peat or plant matrix, probably because of the silicates present. After adding small amounts (0.05–0.1 ml) of either HF or HBF4 to the digestion mixture, concentrations quantified by ICP-QMS generally increased significantly, in the case of Rb up to 80%. Further increasing the volumes of HF or HBF4 in turn, resulted in a loss of recoveries of almost all elements, some of which amounted to approximately 60%. The successful analytical procedures were applied to the determination of two bulk peat materials. In general, good agreement between the found concentrations and results from an inter-laboratory trial or from instrumental neutron activation data were obtained, underpinning the suitability of the developed analytical approach.

Sequential extraction studies on homogenized forest soil samples

Abstract Sequential extraction studies on two forest soil samples from the German Environmental Specimen Bank are presented. The reagents used in the five-step extraction scheme are: dilute ammonium acetate; 0.1 M acetic acid; 0.1 M hydroxylamine hydroehloride in 25% acetic acid; hydrogen peroxide; and hot concentrated nitric acid. Several elements in the extracts have been determined by JCP-MS and ICP-AES. The extraction behaviour of Mg, Ca, Mn, Fe, Co, Ni, Cu, Zn, As and Pb in this procedure is discussed with respect to the quantities extracted and the properties of these reagents in releasing the elements from the various solid phases usually considered in the literature. The studies indicate that reducible oxides and organics retain the major mobile fraction of the elements investigated. It has been found that the extraction time can be considerably reduced without compromising the chemical information for soil characterization.

Influence of digestion procedures on the determination of rare earth elements in peat and plant samples by USN-ICP-MS

Analytical procedures for the determination of rare earth elements (REE) in 250 mg aliquots of difficult-to-digest peat and plant matrices by ICP-MS were developed. Three different pressurised digestion approaches were tested for this purpose, namely (i) closed vessel acid digestion on a hot-plate at 180 °C, (ii) digestion in a microwave high pressure autoclave at a temperature of 240 °C and (iii) high pressure ashing (HPA) at a temperature of 320 °C. Acid mixtures for digestion contained concentrated nitric acid (3–5 ml) alone or additions of hydrofluoric acid (HF) or tetrafluoroboric acid (HBF4) at volumes of 0.05–1.0 ml. The selection of appropriate volumes of HF or HBF4 was identified as a critical step in obtaining accurate results. For several reasons, HBF4 is preferred in comparison with the normally used addition of HF for the destruction nof siliceous matter in the samples investigated. The optimum acid mixture consisted of 3 ml of HNO3 and 0.1 ml of HBF4. High sample throughput (40 samples simultaneously in about 2 h) favours the microwave autoclave over the other two digestion systems. An ultrasonic nebuliser (USN) with membrane desolvation used for sample introduction reduced the spectral interferences originating from oxide formation of lighter REE and Ba to a negligible extent. Internal standardisation with Rh and Re proved to be essential for obtaining correct results. In this way, all REE could be reliably quantified by USN-ICP-MS without applying any mathematical correction equations. The accuracy of the optimised procedures was assessed by the determination of REE in digests of the certified reference material GBW 07602 Bush Branches and Leaves and of the candidate reference material CRM 670 Aquatic Plant. The developed analytical procedures were applied to the determination nof REE in two different peat matrices. Results for these peat samples obtained by USN-ICP-MS showed good agreement with INAA values. Strong fractionation of REE caused by the addition of HF or HBF4 in excess, known as lanthanide contraction, could be experimentally established, except for europium, which revealed a different behaviour.

Urinary antimony speciation by HPLC-ICP-MS

This is the first study to report on the determination of Sb species in urine. To this end, HPLC was coupled online to an ICP-MS instrument using ultrasonic nebulization (USN) or hydride generation (HG) for sample introduction into the ICP-MS. The high chloride concentration in urine seriously hampered the chromatographic separation of Sb(V) and Sb(III) on the Dionex AS14 anion exchange column. Distinct signal suppression, shifting of retention times and severe peak broadening did not allow the application to urine samples. Progress to avoid these problems in HPLC-USN-ICP-MS could be made by employing a Hamilton PRP-X100 anion-exchange column. However, Na eluting in the void volume of the column gave rise to a Na-induced peak overlapping with the Sb(V) signal when USN was used to aspirate the HPLC eluents into the plasma. Therefore, a HG system was placed between the HPLC and ICP-MS instrumentation to overcome this dilemma. Thus, Sb(V) and Sb(III) were separated in urine with the PRP-X100 column using 20xa0mM EDTA at pHxa04.7 as the mobile phase. Similarly, an ION-120 anion-exchange column was employed to separate trimethylantimony dichloride (TMSbCl2) and Sb(V) with a mobile phase containing 2xa0mM NH4HCO3 and 1xa0mM tartaric acid at pHxa08.5. Detection limits of 20xa0ngxa0l−1, 12xa0ngxa0l−1 and 8xa0ngxa0l−1 for Sb(V), TMSbCl2 and Sb(III), respectively, could be established in a 1 + 2 diluted urine matrix. The developed HPLC-HG-ICP-MS method was applied to the speciation of Sb in the urine of occupationally exposed and non-exposed subjects. Additionally, two lyophilised urine reference materials were investigated. Sb(V) was by far the predominant Sb species, followed by TMSbCl2. Only ultratraces of Sb(III), if any detectable, could be found. The sum of the concentrations of Sb(V), Sb(III) and TMSbCl2 in urine samples ranged between 51 and 78% of their total Sb concentrations.

Simultaneous ultratrace determination of platinum and rhodium by cathodic stripping voltammetry

Abstract A highly sensitive, catalytic adsorptive stripping voltammetric procedure at the hanging mercury drop electrode for the simultaneous determination of ultratraces of platinum and rhodium in electrolyte solutions has been evaluated. Optimal conditions were found to be: first accumulation potential 0xa0V (vs. Ag/AgCl), second accumulation potential −0.8xa0V, first preconcentration time 90xa0s, second preconcentration time 120xa0s, scan rate 20xa0mVxa0s−1. The response of the system was found to be linear in a range of platinum concentrations up to 6xa0ngxa0l−1 and for rhodium up to 0.5xa0ngxa0l−1. The detection limit was 21xa0pgxa0l−1 for platinum and 5.6xa0pgxa0l−1 for rhodium. The effect of various possible interferences from other metal ions was also studied. With the exception of zinc (whose influence was studied in more detail), no significant interferences were observed. The method was successfully applied to the determination of traces of Pt and Rh in real environmental samples (spruce shoots) after high pressure digestion.

Statistical evaluation of ecosystem properties influencing the uptake of As, Cd, Co, Cu, Hg, Mn, Ni, Pb and Zn in seaweed (Fucus vesiculosus) and common mussel (Mytilus edulis)

In order to evaluate the influence of geographically varying marine ecosystem properties on the uptake of trace elements in bioindicators, samples were taken of seaweed (Fucus vesiculosus) and common mussel (Mytilus edulis) along the North Sea and Baltic Sea coast. Seasonal variations of the bioindicator status were minimized by sampling within 1 month. Ecosystem properties considered were the geographical position, the salinity and the concentrations of the macroelements Ca, Fe, K, Mg, Na, P and S in the bioindicators. Trace elements studied were As, Cd, Co, Cu, Hg, Mn, Ni, Pb and Zn. Factor analysis of the concentration patterns in the bioindicators and of salinity as a function of location confirmed the influence of the geographically varying salinity on the biological uptake of macroelements and trace elements. This influence of salinity was higher in the case of seaweed than in the case of mussel. Comparison of the geographical courses of the macroelement and trace-element concentrations by cluster analysis revealed corresponding courses for As and Hg in both bioindicators. All other elements showed different courses in seaweed and mussel. Subsequent cluster analysis comparing locations with respect to the macroelement or trace-element concentration patterns in the bioindicators, indicated a clear separation of North and Baltic Sea locations. However, the trace-element concentration patterns provided a regionally less distinctive ecosystem arrangement than those of the macroelement ones. The results of the cluster analysis were verified by discriminant analysis forming groups of locations with respect to geographical position and salinity. Results of discriminant analysis demonstrated, both for seaweed and for mussel as bioindicators, that the location groups formed according to the macroelement concentration patterns corresponded well with the geographical regions in the order of salinity. On the other hand, location groups based on the trace-element concentration patterns again showed a modified less distinctive ecosystem arrangement than the location groups based on macroelement concentration patterns. This confirms modified conditions for the uptake of trace elements in seaweed or mussel in comparison to the uptake of macroelements.

Speciation analysis of antimony by high-performance liquid chromatography inductively coupled plasma mass spectrometry using ultrasonic nebulization

Abstract The two inorganic Sb species Sb(III) and Sb(V) as well as trimethlyantimony dichloride (TMSbCl 2 ) were separated by anion exchange chromatography. HPLC eluents were directly aspirated into the plasma of an ICP-MS using ultrasonic nebulization (USN) with membrane desolvation. Leaching of Sb from glass bottles, especially pronounced under alkaline conditions, distinctly increased background 121 Sb signals. The use of conventional HPLC syringes made of glass resulted in non reproducible blank signals for Sb(V). To overcome these problems, polyethylene bottles for the storage of mobile phases and plastic syringes for the injection of Sb compounds onto the analytical columns were employed. The analysis of Sb(III) standard solutions in the sub μgxa0l −1 range prepared by dilution of stock standard solutions with high-purity water revealed that Sb(III) is easily oxidized to Sb(V) within a few hours. Deoxygenating the water for dilution of standards by flashing working standard solution with helium or using 1.25xa0mM EDTA — which served as mobile phase for the chromatographic separation — for the dilution of standards, no oxidation of Sb(III) was observed, at least for 8xa0h. USN parameters, such as the temperature of the heating area and of the desolvation area as well as the sweep gas flow rate were systematically optimized. Decreasing the USN heating temperature from the conventional settings of 140–80°C enhanced signal intensities by ∼25% and caused no condensation of the aspirated mobile phase. After optimization detection limits for all three Sb species in the low ngxa0l −1 range could be established, namely 14xa0ngxa0l −1 for Sb(III), 12xa0ngxa0l −1 for Sb(V) and 9xa0ngxa0l −1 for TMSbCl 2 .

Environmental specimen banking in Germany — present state and further challenges

The program of the German Environmental Specimen Bank has been expanded recently and its current status is briefly described. Selected results which have been obtained during the long term permanent operation of this project since 1985 are presented. Moreover, further aspects of environmental data evaluation and assessment are discussed.

Mussels and algae as bioindicators for long-term tendencies of element pollution in marine ecosystems

Results of more than ten years of experience in the determination of metals in mussels and algae collected in the North Sea and the Baltic Sea are presented. The various elements determined here are Hg, As, Se, Cd, Pb, Cu, Na, K, S, P, Zn, Mn, Fe, Sr, Ca, Ba, Mg, Tl, Ni, Co using techniques such as cold vapor AAS, INAA, hydride generation AAS, electrothermal AAS, ICP-AES, IDMS and stripping voltammetry. The results indicate the occurrence of three groups of elements with respect to long-term tendencies of their concentrations. In the first group, the concentrations in both mussels and algae varied in the same manner; in the second group no change was observed in either matrix while in the third group, the concentrations of elements changed in an opposite manner.