H. Th. Wolterbeek

Relationship between epiphytic lichens, trace elements and gaseous atmospheric pollutants

A study was conducted to determine the joint effect of gaseous atmospheric pollutants and trace elements on epiphytic lichens. We used our data to test the hypothesis that lichens are generally insensitive to toxic effects of trace elements, and can therefore be used as accumulator organisms to estimate concentrations of these elements in the environment. In a field study in The Netherlands the abundance of epiphytic lichen species was estimated, and their supporting bark was collected. Concentrations of a range of trace elements were determined in the bark, and concentrations of atmospheric trace gases were estimated at the sites of collection. Multivariate statistics were used to determine the relation between the abundance of the species and pollutant concentrations. Atmospheric SO2 and NO2 appeared to be the most important factors determining lichen biodiversity. Nearly all species were sensitive to these compounds. The effect of the other trace elements was very slight; only Sb had a significantly negative effect on the abundance of a few species. It is concluded that lichens can safely be used as accumulator organisms in pollution studies, provided that concentration in lichen thalli reflect atmospheric concentrations.

Distribution in Portugal of some pollutants in the lichen Parmelia sulcata

During the months of July and August 1993 a lichen (Parmelia sulcata Taylor) collection campaign was held in Portugal where samples were obtained from olive tree bark at 228 sites, following a grid of 10 x 10 km along the Atlantic coast and 50 x 50 km in the interior of the country. The samples were analysed by instrumental neutron activation analysis and proton induced X-ray emission techniques. Concentration data patterns for the pollutants As, Cr, Hg, Ni, Pb, S, Sb, Se, and V were obtained for the whole country surface by making use of an extinction rule of 1/r(3), preventing any cut-off distance from being artificially introduced. Some pollution sources were identified: (1) oil-powered plants on the Lisbon-Setúbal axis (V, Ni), (2) coal-power plants in Porto and Sines (S, Se), (3) traffic in the northern area and the Lisbon-Setúbal axis (Pb), (4) a chemical industry south of Porto (Hg, As), and (5) soil influence (Cr, Sb). Arsenic and chromium results largely exceed, in a few areas, the concentrations acceptable to plants, and in a few spots also Hg, Ni, and Pb data.

FACTOR ANALYSIS OF ATMOSPHERIC TRACE-ELEMENT DEPOSITION DATA IN THE NETHERLANDS OBTAINED BY MOSS MONITORING

Monte Carlo-Assisted Factor Analysis has been applied to a data set of trace element concentrations in samples of the moss species Pleurozium schreberi, collected in 1992 from 66 locations in the Netherlands. A Monte Carlo approach was used to give more insight in the uncertainties and significance levels of the factor analysis results. Using a selection of 23 elements, factor analysis enabled the identification of 8 significant pollution source types. Two source types were assumed to be related to the influence of foliar leaching from higher plants. The remaining source types were found to correspond with the major source types obtained in earlier biomonitoring surveys in the Netherlands using lichen and bark, i.e. crustal material, sea aerosol and various types of industrial pollution sources, associated with metallurgical industries, refuse incineration and oil combustion or processing of oil products. The contribution of the industrial pollution sources appeared to have decreased between 1987 and 1992.

Citric acid in tomato plant roots and its effect on cadmium uptake and distribution

Experiments were carried out to investigate the effects of root citric acid on uptake and initial distribution of cadmium (Cd) in tomato plants (Lycopersicon esculentum, cv. Tiny Tim). Cd was measured by γ-spectrometry, using 115Cd spikes. Citric acid was measured by UV-detection, and, after spiking with 14C-citric acid, by β-spectrometry. Cd was applied for 48 h periods, in control experiments, in the presence of citric acid, and after 24 h plant pre-incubation with citric acid.Pre-incubation resulted in two-fold increases in fast-exchangeable amounts of root citric acid, as measured by the presence of citric acid in xylem exudates of decapitated and pressurized roots.Simultaneous application of Cd and citric acid did not change Cd accumulation in total plants and in the roots, nor did any significant change occur with respect to Cd root-to-shoot transport, and Cd concentrations in shoot tissues and xylem fluid. After citric acid pre-incubation, total plant uptake of Cd increased twofold, without any significant change in Cd accumulation in the roots. Cd root-to-shoot transport was increased 5–6 fold, and Cd concentrations in shoot tissues and xylem fluid were increased 6–8 fold. Speciation calculations indicated that, under the conditions applied, xylem Cd may be, at least partly, complexed in citric acid. A C Borstlap Section editor

Factor analysis of trace-element data from tree-bark samples in The Netherlands

Monte Carlo-assisted factor analysis has been applied to a data set of 20 trace-element concentrations in tree-bark samples obtained from 123 locations in The Netherlands, with the aim to investigate the suitability of bark as a biomonitor for air pollution. A Monte Carlo approach was used to give more insight to the uncertainties and significance levels of the factor analysis results. Notwith-standing a rather strong influence of soil material on the concentration levels, factor analysis enabled the identification of five significant pollution source types, all of which corresponded with source types found in an earlier biomonitoring study in The Netherlands using epiphytic lichens. A more detailed comparison with the lichen results showed a remarkable difference in lead concentrations between bark and lichen. It was concluded that bark can be successfully employed as a biomonitor for air pollution. The power of factor analysis to adequately determine the soil contribution may render extensive sample washing procedures superfluous.

Bio-monitoring of trace-element air pollution in Portugal: Qualitative survey

During the months of July and August 1993 a lichen collection campaign was held in Portugal where about 250 samples were collected and analysed by thick target TIPIXE and INAA. Results for 44 different elements were obtained and a data base was built and subjected to Monte Carlo Aided Target Transform Factor Analysis (MCATTFA), a method developed at IRI (Delft). 10×10 km2 coast and 50×50 km2 far from coast sampling grids were used for collection. In this work we will present the results which were obtained based on a reduced data set of 36 elements measured by INAA. The results for 22 elements obtained by TTPIXE were published elsewhere. In this work we will also present the conclusions considering all the 44 elements determined by both techniques.

Lichens (Parmelia sulcata) time response model to environmental elemental availability

Parmelia sulcata transplants, collected in a non-polluted area, were exposed to new atmospheric conditions at six stations, of which five were located near power plants and one at an unpolluted area. Data were collected for a 1-year period, on rainfall, airborne particulates, elemental deposition and on lichen elemental composition. The study was carried out to quantify the relationships between elemental availability and elemental accumulation in lichens. A mathematical model was developed, involving a simple representation of the lichen, and a memory loss function which describes the time relations for the lichens progressive representation of its new ambient conditions. The collected data set was used to test the model. The results indicate that the environmental data on Na, Al and Pb could be reproduced and predicted by the model, including the variability patterns. Half-memory times were calculated for Na, Al and Pb as 200, 500 and 600 days, respectively, based on using all station data. However, further improvements are still needed, including the clarification of differences in model outcomes between stations. Copyright (C) 1998 Elsevier Science B.V.

Analysis of major tomato xylem organic acids and PITC-derivatives of amino acids by RP-HPLC and UV detection

Major amino acids and organic acids in xylem exudates of tomato plants were separated by reversed phase high performance liquid chromatography (RP-HPLC) and quantified by UV detection. Before separation, amino acids were converted into their phenylisothiocyanate (PITC) derivatives. In a single run, Asp, Glu, Ser, Gln, His, Thr, Ala, Tyr, Val, Met, Cys, Ile, Leu, Phe, and Lys could be separated and detected down to the pmol level. Unresolved peaks were obtained for Asn and Gly and for Arg and Pro. For organic acid analysis, exudates were pre-treated by perfusion over a prepacked Adsorbex SCX cation exchange column, to eliminate exudate amino acids. Elution recoveries for organic acids were close to 100%. The exudate organic acids were separated by ion suppression RP-HPLC chromatography, and peaks could be resolved for L-malic acid, malonic acid, maleic acid, citric acid and fumaric acid, down to the pmol level. UV signals for exudate ascorbic acid, and succinic acid were below the limits of detection. Determination of oxalic acid and tartaric acid was impossible, due to the presence of the exudate salt peak in the chromatogram. The results indicate the potential of the methods applied, and show the applicability of RP-HPLC analysis for the determination of both amino acids and organic acids in xylem exudates.

Transport rate of arsenic, cadmium, copper and zinc in Potamogeton pectinatus L.: radiotracer experiments with 76As,109,115Cd,64Cu and 65,69mZn.

The present study was aimed at obtaining an insight into possible experimental approaches for providing numerical data on both the accumulation of sediment As, Cd, Cu and Zn in the submerged water plant Potamogeton pectinatus L., and the possible corresponding metal flows into the water phase. A hydroculture two-compartment system was used as the experimental set-up, and the selected metals were followed by measurements of their radioisotopes 76As, 109Cd, 115Cd, 64Cu, 65Zn and 69mZn. All experiments were performed in single plant mode. The results stress the extreme importance of leakage tests, which were performed using 99mTcO4-, and which resulted in approximately 30% of all experiments being discarded. Metal flows were shown as very near the metal limits of detection or obscured by and/or numerically very near the occurring leakage phenomena. Bio-concentration factors BCF (fresh wt. fine root basis) were calculated as 100, 10, 10 and 100-500 l/kg for Cu, Zn, Cd and As, respectively. The mobility, expressed as the shoot/root concentration ratio, CR, was obtained as < 10(-4), < 10(-5), 10(-3) and 10(-3) - 10(-2) for Cu, As, Cd and Zn, respectively. Double-labeling experiments showed that the CR values were due to the exclusive root-mediated transport in radiotracer experiments: results for simultaneous applications of 109Cd and 115Cd or 65Zn and 69mZn showed field-simulated CR values of approximately 0.04 and 14, respectively. Single-tracer experiments, using liquid scintillation counting (LSC) with 109Cd and 65Zn, were shown to strongly improve the sensitivities of flow determinations. Under the applied conditions, metal flows could be determined as <5 x 10(-8), <5 X 10(-8), 3.5+/-1.8 x 10(-10) and <8 x 10(-9) mol/h per kg root fresh wt. for Cu, As, Cd and Zn, respectively. Upscaling calculations, assuming plant steady state behavior, indicate that the metal accumulation in the plants may comprise up to 1% of the sediment metal occurrence, that the major part of an accumulated metal is retained in the plant roots, and that plant-mediated metal flow into the water phase (< 0.01% for Cd, Cu and Zn, < 0.1% for As within a growing season) may be regarded as not significantly contributing to the overall process of metal mobilization. It should be noted, however, that the above conclusions should be drawn with care, due to the pilot nature and the short-term duration of the presented experiments.

The use of Monte Carlo methods in factor analysis

Abstract Monte Carlo techniques are introduced in target transformation factor analysis (TTFA), in combination with the concept of the principal factor model, in order to account for local variances in the data set and to estimate the uncertainties in the obtained source profiles. The new method is validated using several types of artificial data sets. It was found that application of the Monte Carlo method leads to a significant improvement of the accuracy of the derived source profiles in comparison with standard TTFA. From the introduction of (known) error sources to the artificial data sets it was found that the source-profile reproduction quality is optimal if the magnitudes of the Monte Carlo variations are chosen equal to the magnitudes of the introduced errors.