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Determination of metals in biological and environmental samples
The Science of the Total Environment, 64 (1987) 1 12 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
1
D E T E R M I N A T I O N OF METALS IN BIOLOGICAL AND ENVIRONMENTAL SAMPLES
P. HOFFMANN and K.H. LIESER Technische Hochschule Darmstadt, Fachbereich Anorganische Chemie und Kernchemie, Hochschulstrafle 4, 6100 Darmstadt (Federal Republic of Germany)
ABSTRACT The determination of elements in biological and environmental samples such as wastewater, river water, rain water, birch leaves, grass and dust collected in the Federal Republic of Germany by neutron activation, X-ray fluorescence, atomic absorption spectrometry, inductively coupled nlasma atomic emission spectrometry, polarography and voltammetry is described. Some of these samples require enrichment or separation steps before they can be analyzed. The chemical forms of elements can be determined in liquid samples by ion chromatography, electrochemical methods, ion exchange and sorption techniques, optical spectrometry, coprecipitation and extraction. The speciation of toxic elements in solid samples has been performed by leaching experiments, IR-spectrometry, electron microscopy with a microprobe, light microscopy and by X-ray diffractometry. INTRODUCTION The d e t e r m i n a t i o n of t r a c e s of metals in v a r i o u s samples is very i m p o r t a n t for chemists, biologists, geologists, m e t e o r o l o g i s t s and e n v i r o n m e n t a l scientists. At the p r e s e n t time, n o t only is the c o n c e n t r a t i o n of a c e r t a i n element of interest, but also its c h e m i c a l form. F o r the d e t e r m i n a t i o n of the c o n c e n t r a t i o n of elements n u m e r o u s methods, such as n e u t r o n a c t i v a t i o n analysis (NAA), X-ray fluorescence (XRF), atomic a b s o r p t i o n s p e c t r o m e t r y (AAS), a t o m i c emission s p e c t r o m e t r y with an i n d u c t i v e l y coupled p l a s m a ( A E S - I C P ) and e l e c t r o c h e m i c a l m e t h o d s ( p o l a r o g r a p h y , v o l t a m m e t r y ) are available. Some of these m e t h o d s allow samples to be a n a l y z e d w i t h o u t p r e t r e a t m e n t . The choice of the m e t h o d is d e t e r m i n e d by - - the element to be d e t e r m i n e d - - the c o n c e n t r a t i o n of the element in the sample - - the c o m p o s i t i o n of the sample with respect to interferences and interelem e n t a l effects the a m o u n t of sample available for repetitive analyses - - the state of the sample or the state into w h i c h it c a n be t r a n s f o r m e d w i t h o u t c h a n g i n g the elemental composition, and - - the n u m b e r of elements to be determined. The sample must be collected in a m a n n e r t h a t avoids c o n t a m i n a t i o n and losses by absorption, and g u a r a n t e e s h o m o g e n e i t y . The samples must be p r o p e r l y stored and handled. Of p a r t i c u l a r i m p o r t a n c e are the c o n s t r u c t i o n -
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0048-9697/87/$03.50
© 1987 Elsevier Science Publishers B.V.
materials of the vessels with which the samples come into contact, the chemical parameters (pH, redox potential) of the samples, the temperature of the samples, and the biological activities in the samples (e.g., microorganisms), which may lead to precipitation, coprecipitation, adsorption, and loss by evaporation. In some cases samples must be processed or enriched so that the elements are in a suitable form for analysis. In these steps contamination of the sample by impurities from the chemicals added must be avoided. Also very important is the choice of a suitable standard material, which has to be as similar as possible in composition to the sample. Alkali metals, alkaline earth metals, d-transition elements, and non-metallic elements are involved in biological processes; d-transition elements and some main group elements (Si, Se, I) are important in animal nutrition. In the environment, d-transition elements and a number of main group elements are of great interest. Some of these elements are toxic [1, 2]. These elements have been determined in liquid samples such as wastewater [3, 4], seawater [5-7, 9, 10], river water [8], groundwater [9, 10], mineral water [9, 10], tap water [11], rain water and urine, and in solid samples such as sediments [8], sludges [3], soil [12], dust [13-16], and different plant materials [17, 18]. In this paper the determination of elements and their compounds in wastewater, river water, rain water, dust and plant materials [19] is discussed. WASTEWATER Chromium, nickel, copper, zinc, cadmium and lead, the elements identified in a 1982 "Sludge Regulation" of the FR of Germany as being of special importance, were determined daily during 1 week in samples of wastewater. The wastewater samples were inhomogeneous and contained the elements mentioned above in relatively high concentrations. Two-liter samples were collected from two wastewater canals in Darmstadt, West Germany, with a plastic dipper. After addition of 10 ml semiconcentrated nitric acid the samples were stored at 5°C for 4 weeks. The samples were digested by mixing 10ml 65% nitric acid and 10ml 30% hydrogen peroxide with each 11 wastewater and evaporating the mixture almost to dryness at 75°C. The residue was treated with 100ml 65% nitric acid and again evaporated nearly to dryness. The residue was treated with 50 ml 10% nitric acid and filtered. The material left on the filter contained negligible amounts of metals as ascertained by XRF analysis. Chromium, nickel, copper, zinc, cadmium and lead were determined by AES-ICP [20,21]. This method has detection limits of 2-10 pg 1 1for d-transition elements. Typical results are summarized in Fig. 1. The wastewater in the "south" canal comes from an industrial area, whereas the wastewater in the " n o r t h " canal is from a residential area. The "south" canal is more contaminated than the " n o r t h " canal. The concentrations of the elements vary between 1 pg l-1 for cadmium and 1 mg 1-1 for zinc. The concentrations in the "south" canal exhibit a pronounced minimum on Sunday, the day on which the industrial plants are
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27 Fr
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29 Su
1 Mo
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31 Tu
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May 1983
Fig. 1. Concentration of the elements measured during 1 week in the north canal and the south canal of the municipal sewage work in Darmstadt, West Germany (error bars - la).
not operating. The trends in the concentrations of Zn and Cd, Ni and Cu, and Pb and Cr are similar. WATER OF THE RHINE RIVER River water samples are inhomogeneous and contain elements at low, medium, and high concentrations. Samples of Rhine water were collected in 501 polyethylene tanks. Suspended matter was separated immediately from the sample by centrifuging at 10 000 r.p.m. (throughput 1.21 min-1). The suspended matter and the centrifugate were freeze-dried. The solid residues were placed in high-purity quartz ampoules. Rhine water contained ~ 100 mg suspended and 400 mg dissolved m a t t e r per liter. The simultaneous determination of 20 or more elements in a very broad concent r a ti on range is only possible by n e u t r o n activation analysis [22]. The sealed quartz ampoules were irradiated in a research r eact or for ~ 24 h at a n e u t r o n flux of ~ 1013 neutrons cm -2 s -1. After appropriate cooling times the samples were measured by y-spectrometry. The detection limits depend on the mass of the sample, the thermal neut ron crosssections of the elements, the neut r on flux, the irradiation time, the half-life of the product nuclei, the isotopic abundance of the nuclei, the cooling time, the
4 TABLE 1 Trace element content of suspended matter and in solution in Rhine water determined by NAA (mean values of three determinations) Element
Suspended matter (#gl -~) (ppb)
Water without suspended matter (,ugl ~) (ppb)
Ag As Au Ba Br Ca Ce Co Cr Cs Eu Fe Hg K La Na Rb Sb Sc Se Ta U Zn
6.3 14.7 0.20 480 18.0 65000 55.7 13.5 222 28.6 1.18 32000 0.55 30000 28.5 2900 165 2.6 10.3 1.1 0.8 3.7 612
0.014a 0.7 0.007 38.6 117 61000 0.33 0.36a 1.94 0.4 0.00F 295 1.36
_+ 0.3 _+ 1.3 ± 0.02 _+ 20 ± 5.0 i 5000 + 5.0 ± 0.6 ± 7.0 ± 1.0 ± 0.1 ± 800 + 0.1 + 13000 + 2.0 ± 500 i 10 + 0.1 + 0.3 ± 0.2 ± 0.13 ± 0.5 ± 80
0.26~ 46000 5.9~ 0.36 0.10 0.19a 0.00F 0.80 12.2
i ± ± i i +
0.1 0.001 5.0 4.0 6000 0.2
± 0.8 ± 0.03 ± 12 _+ 0.2
± 1500 ± 0.02 ± 0.01
i 0.4 ± 0.5
One determination. m e a s u r i n g t i m e , t h e d e t e c t o r efficiency, a n d t h e s p e c t r a l b a c k g r o u n d . T h e b a c k g r o u n d is a f u n c t i o n of t h e c o m p o s i t i o n of t h e s a m p l e . T h e c o n c e n t r a t i o n s of 23 e l e m e n t s i n t h e s u s p e n d e d a n d d i s s o l v e d m a t t e r a r e g i v e n i n T a b l e 1. A l k a l i , a l k a l i n e e a r t h , d - t r a n s i t i o n , f - t r a n s i t i o n , m e t a l l o i d a l , and non-metallic elements were found in concentrations spanning eight orders of m a g n i t u d e . O n l y a few e l e m e n t s (Br, Hg, N a ) a r e p r e s e n t i n t h e d i s s o l v e d matter at higher concentrations than in the suspended matter. The suspended m a t t e r c o n s i s t s m a i n l y of c l a y m i n e r a l s h a v i n g i o n e x c h a n g e p r o p e r t i e s a n d c o n t a i n i n g r e l a t i v e l y h i g h a m o u n t s of t h e h e a v i e r a l k a l i i o n s . D i v a l e n t c a t i o n s (Ba, Ca, UO2), w h i c h a r e n o t h y d r o l y z e d , a r e f o u n d i n a p p r e c i a b l e a m o u n t s i n t h e s o l u t i o n . T r i v a l e n t c a t i o n s (Ce, E u , Fe, La, Sc), w h i c h a r e r e a d i l y hydr o l y z e d , a r e s o r b e d i n t h e f o r m of h y d r o x o - c o m p l e x e s o n s o l i d p h a s e s . BIRCH LEAVES (BETULA PENDULA ROTH) I t w a s o f i n t e r e s t to i n v e s t i g a t e w h e t h e r o r n o t t h e l e a v e s o f b i r c h t r e e s c a n be u s e d as b i o i n d i c a t o r s for t h e t o x i c t r a c e e l e m e n t s Cr, Ni, Zn, Cd a n d Pb. I n
TABLE 2 Concentrations of cadmium, chromium, nickel, lead and zinc in birch leaves collected in residential areas of Darmstadt, F.R.G., and nearby forests Element
Concentration range (mgkg 1) (dry weight at 60°C)
Blank a (mgkg 1) (dry weight at 60°C)
Cr Ni Zn Cd Pb
0.2-1.3 0.3 2.1 45.7-863.3 0.03~).9 10.~26.3
0.054).5 < 3.0 < 100 < 0.1 < 10
aThe blank samples were birch leaves from unpolluted areas. October, at the end of the g r o w t h period, the leaves were collected by h a n d a l o n g a line s t r e t c h i n g 1 5 k m a c r o s s the city of D a r m s t a d t a n d stored in p o l y e t h y l e n e bags. T h e l e a v e s w e r e washed, dried and g r o u n d as described in the l i t e r a t u r e [23]. A p p r o x i m a t e l y 500mg of the dried, g r o u n d leaves w e r e h e a t e d a t 140°C w i t h 5 m l 65% nitric acid in a Teflon b e a k e r for 5h. W a t e r (10 ml) w a s t h e n added. T h e s o l u t i o n s w e r e a n a l y z e d by flameless a t o m i c abs o r p t i o n s p e c t r o m e t r y (AAS) w i t h a d e t e c t i o n limit of ~ 10 ng l- 1 for Cd, Cr, Ni, Pb a n d Zn [24]. T h e r e s u l t s are s u m m a r i z e d in T a b l e 2. T h e c o n c e n t r a t i o n s of c a d m i u m a n d zinc v a r i e d by m o r e t h a n one o r d e r of m a g n i t u d e a m o n g the v a r i o u s locations, the c o n c e n t r a t i o n s of c h r o m i u m a n d nickel by a f a c t o r of seven, a n d the c o n c e n t r a t i o n of lead by a f a c t o r of 2.5. A n a l y s i s of the g e o g r a p h i c s i t u a t i o n i n d i c a t e s t h a t r a i l w a y lines a p p e a r to be the s o u r c e s for c h r o m i u m a n d zinc, i n d u s t r i a l p l a n t s for zinc and c a d m i u m , and a u t o m o t i v e traffic for lead. GRASS In o r d e r to i n v e s t i g a t e the use of g r a s s as a bioindicator, the e l e m e n t a l c o m p o s i t i o n m u s t be known. T h e m a i n c o n s t i t u e n t s of g r a s s a r e o r g a n i c material (45%), silicon dioxide (45%) a n d c a l c i u m c a r b o n a t e (1-2%). T h e grass was cut w i t h scissors or a knife c o a t e d w i t h Teflon a n d stored in p o l y e t h y l e n e bags. E a c h s a m p l e was w a s h e d with 10ml of deionized w a t e r to r e m o v e dust a n d o t h e r a d s o r b e d m a t e r i a l s , dried to c o n s t a n t w e i g h t at 60°C, a n d g r o u n d to a p a r t i c l e size < 100 pm. T h e finely g r o u n d m a t e r i a l was a n a l y z e d w i t h a n e n e r g y dispersive T r a c o r N o r t h e r n S p e c t r a c e M o d e l 430 X-Ray F l u o r e s c e n c e I n s t r u m e n t u s i n g a n X-ray t u b e for e x c i t a t i o n [25, 26]. U s i n g p o w d e r e d s a m p l e s of ~ 5-6 g the d e t e c t i o n limits w e r e 2 10 mg k g - 1 dry weight. T h e r e f e r e n c e s a m p l e s m u s t h a v e a s i m i l a r c o m p o s i t i o n for a p p r o p r i a t e c o m p e n s a t i o n of m a t r i x effects. S t a n d a r d s w e r e p r e p a r e d by m i x i n g e q u a l a m o u n t s of cellulose a n d silicon dioxide a n d adding 4% c a l c i u m c a r b o n a t e a n d small a m o u n t s of m e t a l salts. T h e c o n c e n t r a t i o n s
6 TABLE 3 Concentrations of elements in grass determined by X-ray fluorescence spectrometry Element
Concentration (mgkg 1 dry weight)
Ca Mn Fe Ni Cu Zn Br Rb
6900 _+ 640 82 i 6 95 ± 8 10 ± 1 9±1 50 ± 4 16 ± 2 16 + 3
Sr
35 ± 3
found in the grass samples (Table 3) varied b e t w e e n 9 mg kg-1 for copper and ~ 7 0 0 0 m g k g 1 for calcium. E l e m e n t s of atomic n u m b e r s between 9 and 19 could be d e t e r m i n e d in a v a c u u m c h a m b e r in which the a b s o r p t i o n of the low e n e r g y X-rays by air is minimized. For work in a v a c u u m c h a m b e r the samples and the s t a n d a r d s must be mixed with a b i n d e r and pressed into pellets. The m e t h o d used for the grass samples is applicable to the analysis of dust, soil, sludge and o t h e r powdered materials. The i n s t r u m e n t can be t a k e n into the field and used for biological, e n v i r o n m e n t a l and geochemical analyses [27]. RAIN WATER Rain w a t e r c o n t a i n s v e r y small a m o u n t s of insoluble particles. Rain w a t e r samples were supplied by the K e r n f o r s c h u n g s a n l a g e Jiilich, w h e r e a system for the collection of r a i n and dust w i t h o u t cross c o n t a m i n a t i o n has been developed. The rain w a t e r was collected via a plastic funel in a p o l y e t h y l e n e bottle p r e v i o u s l y cleaned with nitric acid and water. The collected w a t e r was filtered t h r o u g h a 0.45 pm m e m b r a n e filter. The filtrate was analyzed for cadmium, copper, zinc and selenium by cathodic stripping v o l t a m m e t r y and for lead by anodic stripping v o l t a m m e t r y . Stripping v o l t a m m e t r y enriches an element on the c a t h o d e by e l e c t r o l y t i c deposition at a c o n s t a n t potential. Reversal of the c u r r e n t strips the deposited element from the cathode. This t e c h n i q u e has a d e t e c t i o n limit of 10ng1-1 [28, 29]. The results o b t a i n e d for r a i n w a t e r are listed in Table 4. The values are a v e r a g e s of five d e t e r m i n a t i o n s with r e l a t i v e s t a n d a r d deviations in the r a n g e 0.3-1%. The high c o n c e n t r a t i o n s of copper, lead and zinc are not surprising, because the rain w a t e r was collected n e a r the lead mines of Stolberg, F.R.G. DUST A i r b o r n e dust is a v e r y i n h o m o g e n e o u s m a t e r i a l c o n t a i n i n g organic and i n o r g a n i c c o m p o n e n t s and m a n y elements, the c o n c e n t r a t i o n s of which are
TABLE 4 Concentrations of elements in rainwater determined by stripping voltammetry Element
Concentration (#gl-:)
Cu Se Cd Zn Pb
15.2 0.32 0.39 19.5 24.1
d e t e r m i n e d by t h e o r i g i n of t h e p a r t i c l e s . D u s t m a y t r a n s p o r t e l e m e n t s to o t h e r r e g i o n s a n d d e p o s i t t h e m on soil a n d p l a n t s . V a r i o u s l a b o r a t o r i e s c o l l a b o r a t i n g in t h e " A r b e i t s g e m e i n s c h a f t z u r F S r d e r u n g d e r R a d i o n u k l i d t e c h n i k " [13-16] c a r r i e d o u t i n t e r l a b o r a t o r y a n a l y s e s of e l e m e n t s in dust. A v a r i e t y of a n a l y t i c a l m e t h o d s s u c h as n e u t r o n a c t i v a t i o n , p h o t o n - i n d u c e d a c t i v a t i o n , X-ray fluorescence, t o t a l r e f l e c t i o n X-ray f l u o r e s c e n c e , p r o t o n i n d u c e d X-ray e m i s s i o n , a t o m i c a b s o r p t i o n s p e c t r o m e t r y a n d i n d u c t i v e l y c o u p l e d p l a s m a a t o m i c emissi o n s p e c t r o m e t r y w e r e used. D u s t s a m p l e s w e r e c o l l e c t e d w e e k l y o v e r 1 y e a r a t v a r i o u s l o c a t i o n s in t h e F e d e r a l R e p u b l i c of G e r m a n y : D e u s e l b a c h ( u n p o l l u t e d air), H a m b u r g (residential area), K a r l s r u h e ( a g r i c u l t u r a l area), M a n n h e i m (industrialized region) and M f i n c h e n (traffic area). H i g h - v o l u m e s a m p l e r s w i t h m e m b r a n e filters of 26 cm d i a m e t e r w e r e used. R o u n d s e c t i o n s of 5 cm d i a m t e t e r w i t h ~ 0.5 mg d u s t p e r cm 2 s t o r e d in p o l y e t h y l e n e b a g s for X R F a n a l y s i s or in q u a r t z a m p o u l e s for TABLE5 Concentrations of elements in air-borne dust determined by instrumental neutron activation analysis and X-ray fluorescence spectrometry Element
As Br Co Cr Cu Hg Mn Ni Pb
Sb Se V Zn
Method
NAA NAA/XRF NAA NAA/XRF NAA/XRF NAA XRF XRF NAA/XRF NAA NAA NAA NAA/XRF
Concentration in air (ngm 3) at Deuselbach
Hamburg
Karlsruhe
Mannheim
Miinchen
1.7-4.5 1(~34 0.2 1.2 1.5-5.3 3 13 0.05~.5 10-55 2.34.5 50-200 0.8~8.0 0.7-5.0 5.4-8.5 27 170
5.6-34.6 2(~310 0.5-1.5 3.4-25 35-285 0.3-2.1 15-130 4-25 140-1650 4.6-11.1 1.~10.4 7.5-17.5 60~60
1.8-10.0 20~200 0.4-1.5 3.4~-30 10--50 0.1-0.5 13~95 4.7-67 100~750 1.9-9.0 0.9~5.0 9.5~12.4 70-500
3.0-20.0 25- 200 0.6-3 5-45 15-85 0.14).4 26-130 6.4-57 130-1050 2.5-15.0 1.1~.0 10.8-21.1 100-550
1.5-9.1 120400 0.6-2.0 1L 177 60-200 0.14).8 20-185 5.6-22 600-1600 20.2-40.0 0.5-2.0 3.5~.5 88-310
neutron activation analysis were distributed to the participating laboratories. Nine elements (Ca, Cr, Mn, Fe, Ni, Cu, Zn, Br, Pb) were determined by energydispersive X-ray fluorescence spectroscopy [15, 16] and 11 elements (Cr, Fe, Co, Cu, Zn, As, Se, Br, Cd, Sb, Hg) by instrumental neutron activation analysis. The results for each sampling area are summarized in Table 5. Some general trends are summarized here. The concentrations of the elements changed considerably during the 1-year period. The changes sometimes exceeded one order of magnitude and occurred very rapidly. During the winter the values are distinctly higher than during the summer. Sites with high lead concentrations also have high bromine concentrations, indicating that residential, industrial, high-traffic density regions, and agricultural regions are all polluted by exhaust gases from internal combustion engines. The concentrations of cobalt, nickel, selenium and zinc in dusts are especially high in the industrial regions, as expected. High concentrations of these elements were also found in the agricultural areas. Dust must have been transported by wind from the industrial to the agricultural regions. ENRICHMENT OF ELEMENTS Sometimes the detection limits of an analytical method are not sufficient for an analytical task. In these cases, the elements to be determined must be enriched. Highest enrichment factors were obtained by sorption or ion exchange procedures. Selective exchangers are known for certain elements or groups of elements [30, 31]. A review on the enrichment of elements is given in the literature [31]. SPECIATION IN LIQUID SAMPLES Environmental scientists are becoming increasingly interested in trace element speciation, because beneficial and harmful effects o f " t r a c e elements" are highly dependent on their chemical forms. In liquid samples cations and anions must electrically balance each other. Methods for the determination of cations have been described in the previous sections. The anions are generally separated and quantitatively determined by ion chromatography. Formation constants of complexes with a central metal atom can sometimes be determined by electrochemical methods by comparing the polarographic half-wave potential for the solution containing the complex data measured with or calculated for synthetic solutions. The charge of a complex can be determined from its behaviour on an ionexchange column. Rhine water was filtered through a 0.4#m polycarbonate filter and then passed through various columns. The percent retentions for cadmium, copper, lead and zinc are listed in Table 6 [32]. The copper species was completely retained on an anion exchange resin but not on a cation exchange resin. Therefore, the species should be anionic and is perhaps present as a negatively charged complex with humate ligands. The results for zinc indicate a cationic zinc species.
9 TABLE 6 Retention of cadmium, copper, lead and zinc present in filtered Rhine water on various column materials Type of column
Percent retained
Cation exchange (Lewatit S 1080) Chelating exchange (Hyphan) Anion exchange (Dowex 1 X 8) Charcoal
Cd
Cu
Pb
Zn
23
13
81
82
0
100
46
91
15
100
40
0
0
49
61
The valence states of the elements can be determined by methods such as optical spectrometry (UV-VIS-NIR), electrochemistry (voltammetry, polarography, electrophoresis), coprecipitation, extraction and ion chromatography. zoo
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ol I
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5O
Fig. 2. Powder diffractometry spectrum of air dust from Hamburg (A: ammonium sulfate, C: calcite, G: gypsum, K: koktaite, M: mohrite, Q: o-quartz).
10 DETERMINATION OF SPECIES IN SOLID SAMPLES [14, 33] The chemical behavior of toxic trace elements can be determined by leaching with various solutions. In this manner, the mobility of Cd, Cr, Cu, Mn, Ni and Pb was compared in airborne dust from Darmstadt and Hamburg. Extractants of pH 1 (aqueous acid), pH 4 (acid rain) and pH 6 (water) were used. In all cases the solubility of the elements increased with decreasing pH. Chromium, nickel and lead were leached to the same degree from the Darmstadt and Hamburg dusts. More copper and manganese were leached from the Darmstadt sample than from the Hamburg sample, whereas the Hamburg sample released more cadmium than the Darmstadt sample. IR-spectrometry of a solid sample containing 1 mg dust and 100mgKBr, which was ground, dried at 100°C to constant weight, evacuated and pressed to a pill, showed strong absorptions for NH4 ÷ and SO42- , weaker absorptions for SiO~ , HzO, carbohydrates and HSOi and absorptions of low intensity for PO] and C O ~ . A very useful method for the determination of species in air dust is electron microscopy with a microprobe (X-ray fluorescence analysis of single particles). In this way, a semiquantitative analysis of a chosen particle is obtained. Many minerals have been identified [14, 33]: a-quartz, potassium feldspar, coal light ash, Pb- and/or Ti-rich particles, concrete (fl-dicalcium silicate), calcite, calcium-sodium-feldspar (labradorite, plagioclase), clay minerals (kaolinite) and sodium chloride. In addition, particles of biological origin have been detected. The biological particles can best be identified by light microscopy, which can also be used to detect inorganic particles such as garnets, glass, asbestos, soot and coke. X-Ray powder patterns obtained by the Bragg Brentano method can identify chemical species in solid mixtures. A powder pattern for dust from Hamburg is reproduced in Fig. 2. By comparison with the patterns from pure compounds, ammonium sulfate, calcite gypsum, koktaite, mohrite and a-quartz were found to be present in the dust [33].
REFERENCES 1 D.R. Williams, The Metals of Life, Van Nostrand Reinhold Company, New York, 1971. 2 H.A.O.Hill (Senior Reporter), Inorganic Biochemistry,Vol. 3, The Royal Society of Chemistry, Burlington House, London WlV OBN, 1982. 3 P. Hoffmann, D. Holtz, K.H. Lieser, R. P~tzold and R. Speer, Multielementanalyse yon kommunalen Abw/issern mit Hilfe yon AES-ICP und der RFA, KorrespondenzAbwasser, 32 (1985) 80. 4 P. Hoffmann, K.H. Lieser, R. Speer and R. P~itzold, Multi-elementAnalysis of Waste Water Using AES-ICP and XRF Methods, in B. Sansoni (Ed.), Instrumentelle Multielementanalyse, Verlag Chemie, Weinheim, Deerfield Beach, Florida, 1985, p. 643. 5 K.H. Lieser, Chemic der Spurenelemente im Wasser, Jahrbuch 1982/83, Technische Hochschule Darmstadt, p. 132. 6 E. Heuss and K.H. Lieser, Versuche zur Abtrennung yon Spurenelementenaus Meerwasser
11 durch Extraktion und ihre Bestimmung durch Neutronenaktivierungsanalyse, J. Radioanal. Chem., 50 (1979) 277. E. Heuss und K.H. Lieser, Abtrennung von Spurenelementen aus Meerwasser durch Absorption und ihre Bestimmung durch Neutronenaktivierungsanalyse, J. Radioanal. Chem., 50
8 9
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19 20 21 22 23 24 25 26
27
(1979) 289. M. Calmano and K.H. Lieser, Trace element determination in suspended matter and in sediments by instrumental neutron activation analysis, J. Radioanal. Chem., 63 (1981) 335. P. Burba, B. Gleitsmann and K.H. Lieser, Abtrennung und Rontgenfluoreszenzanalyse von gel&tern Uran aus natiirlichem Wasser mittels chelatbildender Celluloseaustauscher, Fresenius Z. Anal. Chem., 289 (1978) 28. P. Burba, K.H. Lieser, V. Neitzert and H.-M. Rober, Preconcentration and determination of trace elements in freshwater and sea water, Fresenius Z. Anal. Chem., 291 (1978) 273. P. Burba, W. Dyck and K.H. Lieser, Abtrennung und energiedispersive RFA geloster Schwermetallspuren, speziell in Trinkwasser, mittels chelatbildender Celluloseaustauscher, Vom Wasser, 54 (1980) 227. RSpatz, Thesis, Anwendung der energiedispersiven Rontgenfluoreszenzanalyse als Multielementmethode fur die Spurenelementbestimmung in silikatischen Proben, TH Darmstadt, West Germany, 1978. R.Spatz and K.H.Lieser, Bestimmung von Spurenelementen in Staubproben durch RontgenAuoreszenzanalyse mit Radionuklidanregung unter besonderer Beriicksichtigung der Matrixeffekte, Z. Anal. Chem., 280 (1976) 197. R. Voigt, Thesis, Spurenelemente in Luftsaub Bestimmung mit Hilfe der Rontgenfluoreszenzanalyse und Versuche zur Identifizierung der chemischen Spezies, TH Darmstadt, West Germany, 1985. Arbeitsgemeinschaft zur Forderung der Radionuklidtechnik, Elementanalyse von Schwebstauben, Kernforschungszentrum Karlsruhe Postfach 3640, 7500 Karlsruhe, West Germany, KfK-AFR 006, 1983. Arbeitsgemeinschaft zur Forderung der Radionuklidtechnik, Elementanalyse von Schwebstauben, Kernforschungszentrum Karlsruhe Postfach 3640, 7500 Karlsruhe, West Germany, KfK-AFR 007, 1983. L. Schebeck, K.H. Lieser and M. Hollwarth, Die Birke (Betula pendula Roth) als Bioindikator fur Schwermetallimmissionen, Angew. Bot., 58 (1984) 475. M.E. Farago and P.J. Parsons, Determination and location of platinum metals in biological samples by neutron activation and microprobe analysis, in S.J. Lippard (Ed.), Platinum, Gold, and other Metal Chemotherapeutic Agents, Chemistry and Biochemistry, American Chemical Society Symposium Series, No. 209, 1983, p, 297. P. Hoffmann and K.H. Lieser, Analytical determination of metals in biological and environmental samples, Rev. Port. Quim., 27 (1985) 416. V.A. Fassel, Quantitative elemental analysis by plasma emission spectroscopy, Science, 202 (1978) 183. W. Schrader. Z. Grobenski and H. Schulze, Einfiihrung in die AES mit dem induktiv gekoppelten Plasma (ICP), Applied Atomic Spectroscopy, Perkin Elmer, 28 (1981) 1. K.H. Lieser, Einfiihrung in die Kernchemie, 2. Auflage, Verlag Chemie, Weinheim, 1980, p. 567. M. Stoeppler and F. Backhaus, Pretreatment studies with biological and environmental materials. I. System for preserved multisample decomposition, Z. Anal. Chem., 291 (1978) 116. B. Welz, Atomabsorptionsspektrometrie, 3. Auflage, Verlag Chemie, Weinheim, 1983. E.P. Bertin, Introduction to X-Ray Spectrometric Analysis, Plenum Press, New York, 1978. P. Hahn-Weinheimer, A. Hirner and K. Weber-Diefenbach, Grundlagen und praktische Anwendung der Rontgenfluoreszenzanalyse (RFA), Verlag F. Vieweg & Sohn, BraunschweigWiesbaden, 1984. P. Hoffmann, K.H. Lieser, T. Hofmann and R. Sommer, A mobile installation for energydispersive multielement X-ray fluorescence analysis for application in the field, X-Ray Spectrom.. 12 (1983) 175.
12 28 29
30 31
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M. Geissler, Polarographische Analyse, Verlag Chemie, Weinheim, 1981. H.W. Niirnberg, Differential-Pulspolarographie, Pulsvoltammetrie und Pulsinversvoltammetrie, in R. Bock, W. Fresenius, H. Giinzler, W. Huber and G. TSlg (Eds), AnalytikerTaschenbuch, Bd. 2, Springer Verlag, Berlin, 1981. K.H. Lieser, New ion exchangers, preparation, properties and application, Pure Appl. Chem., 51 (1979) 1503. K.H. Lieser, Spurenanalyse der Elemente: Anreicherung durch Austauscher und Sorbentium, in W. Fresenius, H. Giinzler, W. Huber, I. Liiderwald, G. TSlg and H. Wisser (Eds), AnalytikerTaschenbuch, Springer-Verlag, Berlin, 1986, p. 125. S. Sondermeyer-Knoop, Thesis, Chemie der Elemente Kupfer, Cadmium, Blei und Zink in natfirlichen Wiissern, TH Darmstadt, West Germany, 1984. R. Voigt, K.H. Lieser and B. Baumgartner, Identification of chemical species in air dust by powder diffractometry, Nature, 71 (1984) 377.
1
D E T E R M I N A T I O N OF METALS IN BIOLOGICAL AND ENVIRONMENTAL SAMPLES
P. HOFFMANN and K.H. LIESER Technische Hochschule Darmstadt, Fachbereich Anorganische Chemie und Kernchemie, Hochschulstrafle 4, 6100 Darmstadt (Federal Republic of Germany)
ABSTRACT The determination of elements in biological and environmental samples such as wastewater, river water, rain water, birch leaves, grass and dust collected in the Federal Republic of Germany by neutron activation, X-ray fluorescence, atomic absorption spectrometry, inductively coupled nlasma atomic emission spectrometry, polarography and voltammetry is described. Some of these samples require enrichment or separation steps before they can be analyzed. The chemical forms of elements can be determined in liquid samples by ion chromatography, electrochemical methods, ion exchange and sorption techniques, optical spectrometry, coprecipitation and extraction. The speciation of toxic elements in solid samples has been performed by leaching experiments, IR-spectrometry, electron microscopy with a microprobe, light microscopy and by X-ray diffractometry. INTRODUCTION The d e t e r m i n a t i o n of t r a c e s of metals in v a r i o u s samples is very i m p o r t a n t for chemists, biologists, geologists, m e t e o r o l o g i s t s and e n v i r o n m e n t a l scientists. At the p r e s e n t time, n o t only is the c o n c e n t r a t i o n of a c e r t a i n element of interest, but also its c h e m i c a l form. F o r the d e t e r m i n a t i o n of the c o n c e n t r a t i o n of elements n u m e r o u s methods, such as n e u t r o n a c t i v a t i o n analysis (NAA), X-ray fluorescence (XRF), atomic a b s o r p t i o n s p e c t r o m e t r y (AAS), a t o m i c emission s p e c t r o m e t r y with an i n d u c t i v e l y coupled p l a s m a ( A E S - I C P ) and e l e c t r o c h e m i c a l m e t h o d s ( p o l a r o g r a p h y , v o l t a m m e t r y ) are available. Some of these m e t h o d s allow samples to be a n a l y z e d w i t h o u t p r e t r e a t m e n t . The choice of the m e t h o d is d e t e r m i n e d by - - the element to be d e t e r m i n e d - - the c o n c e n t r a t i o n of the element in the sample - - the c o m p o s i t i o n of the sample with respect to interferences and interelem e n t a l effects the a m o u n t of sample available for repetitive analyses - - the state of the sample or the state into w h i c h it c a n be t r a n s f o r m e d w i t h o u t c h a n g i n g the elemental composition, and - - the n u m b e r of elements to be determined. The sample must be collected in a m a n n e r t h a t avoids c o n t a m i n a t i o n and losses by absorption, and g u a r a n t e e s h o m o g e n e i t y . The samples must be p r o p e r l y stored and handled. Of p a r t i c u l a r i m p o r t a n c e are the c o n s t r u c t i o n -
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0048-9697/87/$03.50
© 1987 Elsevier Science Publishers B.V.
materials of the vessels with which the samples come into contact, the chemical parameters (pH, redox potential) of the samples, the temperature of the samples, and the biological activities in the samples (e.g., microorganisms), which may lead to precipitation, coprecipitation, adsorption, and loss by evaporation. In some cases samples must be processed or enriched so that the elements are in a suitable form for analysis. In these steps contamination of the sample by impurities from the chemicals added must be avoided. Also very important is the choice of a suitable standard material, which has to be as similar as possible in composition to the sample. Alkali metals, alkaline earth metals, d-transition elements, and non-metallic elements are involved in biological processes; d-transition elements and some main group elements (Si, Se, I) are important in animal nutrition. In the environment, d-transition elements and a number of main group elements are of great interest. Some of these elements are toxic [1, 2]. These elements have been determined in liquid samples such as wastewater [3, 4], seawater [5-7, 9, 10], river water [8], groundwater [9, 10], mineral water [9, 10], tap water [11], rain water and urine, and in solid samples such as sediments [8], sludges [3], soil [12], dust [13-16], and different plant materials [17, 18]. In this paper the determination of elements and their compounds in wastewater, river water, rain water, dust and plant materials [19] is discussed. WASTEWATER Chromium, nickel, copper, zinc, cadmium and lead, the elements identified in a 1982 "Sludge Regulation" of the FR of Germany as being of special importance, were determined daily during 1 week in samples of wastewater. The wastewater samples were inhomogeneous and contained the elements mentioned above in relatively high concentrations. Two-liter samples were collected from two wastewater canals in Darmstadt, West Germany, with a plastic dipper. After addition of 10 ml semiconcentrated nitric acid the samples were stored at 5°C for 4 weeks. The samples were digested by mixing 10ml 65% nitric acid and 10ml 30% hydrogen peroxide with each 11 wastewater and evaporating the mixture almost to dryness at 75°C. The residue was treated with 100ml 65% nitric acid and again evaporated nearly to dryness. The residue was treated with 50 ml 10% nitric acid and filtered. The material left on the filter contained negligible amounts of metals as ascertained by XRF analysis. Chromium, nickel, copper, zinc, cadmium and lead were determined by AES-ICP [20,21]. This method has detection limits of 2-10 pg 1 1for d-transition elements. Typical results are summarized in Fig. 1. The wastewater in the "south" canal comes from an industrial area, whereas the wastewater in the " n o r t h " canal is from a residential area. The "south" canal is more contaminated than the " n o r t h " canal. The concentrations of the elements vary between 1 pg l-1 for cadmium and 1 mg 1-1 for zinc. The concentrations in the "south" canal exhibit a pronounced minimum on Sunday, the day on which the industrial plants are
1000
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North Canal
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Fig. 1. Concentration of the elements measured during 1 week in the north canal and the south canal of the municipal sewage work in Darmstadt, West Germany (error bars - la).
not operating. The trends in the concentrations of Zn and Cd, Ni and Cu, and Pb and Cr are similar. WATER OF THE RHINE RIVER River water samples are inhomogeneous and contain elements at low, medium, and high concentrations. Samples of Rhine water were collected in 501 polyethylene tanks. Suspended matter was separated immediately from the sample by centrifuging at 10 000 r.p.m. (throughput 1.21 min-1). The suspended matter and the centrifugate were freeze-dried. The solid residues were placed in high-purity quartz ampoules. Rhine water contained ~ 100 mg suspended and 400 mg dissolved m a t t e r per liter. The simultaneous determination of 20 or more elements in a very broad concent r a ti on range is only possible by n e u t r o n activation analysis [22]. The sealed quartz ampoules were irradiated in a research r eact or for ~ 24 h at a n e u t r o n flux of ~ 1013 neutrons cm -2 s -1. After appropriate cooling times the samples were measured by y-spectrometry. The detection limits depend on the mass of the sample, the thermal neut ron crosssections of the elements, the neut r on flux, the irradiation time, the half-life of the product nuclei, the isotopic abundance of the nuclei, the cooling time, the
4 TABLE 1 Trace element content of suspended matter and in solution in Rhine water determined by NAA (mean values of three determinations) Element
Suspended matter (#gl -~) (ppb)
Water without suspended matter (,ugl ~) (ppb)
Ag As Au Ba Br Ca Ce Co Cr Cs Eu Fe Hg K La Na Rb Sb Sc Se Ta U Zn
6.3 14.7 0.20 480 18.0 65000 55.7 13.5 222 28.6 1.18 32000 0.55 30000 28.5 2900 165 2.6 10.3 1.1 0.8 3.7 612
0.014a 0.7 0.007 38.6 117 61000 0.33 0.36a 1.94 0.4 0.00F 295 1.36
_+ 0.3 _+ 1.3 ± 0.02 _+ 20 ± 5.0 i 5000 + 5.0 ± 0.6 ± 7.0 ± 1.0 ± 0.1 ± 800 + 0.1 + 13000 + 2.0 ± 500 i 10 + 0.1 + 0.3 ± 0.2 ± 0.13 ± 0.5 ± 80
0.26~ 46000 5.9~ 0.36 0.10 0.19a 0.00F 0.80 12.2
i ± ± i i +
0.1 0.001 5.0 4.0 6000 0.2
± 0.8 ± 0.03 ± 12 _+ 0.2
± 1500 ± 0.02 ± 0.01
i 0.4 ± 0.5
One determination. m e a s u r i n g t i m e , t h e d e t e c t o r efficiency, a n d t h e s p e c t r a l b a c k g r o u n d . T h e b a c k g r o u n d is a f u n c t i o n of t h e c o m p o s i t i o n of t h e s a m p l e . T h e c o n c e n t r a t i o n s of 23 e l e m e n t s i n t h e s u s p e n d e d a n d d i s s o l v e d m a t t e r a r e g i v e n i n T a b l e 1. A l k a l i , a l k a l i n e e a r t h , d - t r a n s i t i o n , f - t r a n s i t i o n , m e t a l l o i d a l , and non-metallic elements were found in concentrations spanning eight orders of m a g n i t u d e . O n l y a few e l e m e n t s (Br, Hg, N a ) a r e p r e s e n t i n t h e d i s s o l v e d matter at higher concentrations than in the suspended matter. The suspended m a t t e r c o n s i s t s m a i n l y of c l a y m i n e r a l s h a v i n g i o n e x c h a n g e p r o p e r t i e s a n d c o n t a i n i n g r e l a t i v e l y h i g h a m o u n t s of t h e h e a v i e r a l k a l i i o n s . D i v a l e n t c a t i o n s (Ba, Ca, UO2), w h i c h a r e n o t h y d r o l y z e d , a r e f o u n d i n a p p r e c i a b l e a m o u n t s i n t h e s o l u t i o n . T r i v a l e n t c a t i o n s (Ce, E u , Fe, La, Sc), w h i c h a r e r e a d i l y hydr o l y z e d , a r e s o r b e d i n t h e f o r m of h y d r o x o - c o m p l e x e s o n s o l i d p h a s e s . BIRCH LEAVES (BETULA PENDULA ROTH) I t w a s o f i n t e r e s t to i n v e s t i g a t e w h e t h e r o r n o t t h e l e a v e s o f b i r c h t r e e s c a n be u s e d as b i o i n d i c a t o r s for t h e t o x i c t r a c e e l e m e n t s Cr, Ni, Zn, Cd a n d Pb. I n
TABLE 2 Concentrations of cadmium, chromium, nickel, lead and zinc in birch leaves collected in residential areas of Darmstadt, F.R.G., and nearby forests Element
Concentration range (mgkg 1) (dry weight at 60°C)
Blank a (mgkg 1) (dry weight at 60°C)
Cr Ni Zn Cd Pb
0.2-1.3 0.3 2.1 45.7-863.3 0.03~).9 10.~26.3
0.054).5 < 3.0 < 100 < 0.1 < 10
aThe blank samples were birch leaves from unpolluted areas. October, at the end of the g r o w t h period, the leaves were collected by h a n d a l o n g a line s t r e t c h i n g 1 5 k m a c r o s s the city of D a r m s t a d t a n d stored in p o l y e t h y l e n e bags. T h e l e a v e s w e r e washed, dried and g r o u n d as described in the l i t e r a t u r e [23]. A p p r o x i m a t e l y 500mg of the dried, g r o u n d leaves w e r e h e a t e d a t 140°C w i t h 5 m l 65% nitric acid in a Teflon b e a k e r for 5h. W a t e r (10 ml) w a s t h e n added. T h e s o l u t i o n s w e r e a n a l y z e d by flameless a t o m i c abs o r p t i o n s p e c t r o m e t r y (AAS) w i t h a d e t e c t i o n limit of ~ 10 ng l- 1 for Cd, Cr, Ni, Pb a n d Zn [24]. T h e r e s u l t s are s u m m a r i z e d in T a b l e 2. T h e c o n c e n t r a t i o n s of c a d m i u m a n d zinc v a r i e d by m o r e t h a n one o r d e r of m a g n i t u d e a m o n g the v a r i o u s locations, the c o n c e n t r a t i o n s of c h r o m i u m a n d nickel by a f a c t o r of seven, a n d the c o n c e n t r a t i o n of lead by a f a c t o r of 2.5. A n a l y s i s of the g e o g r a p h i c s i t u a t i o n i n d i c a t e s t h a t r a i l w a y lines a p p e a r to be the s o u r c e s for c h r o m i u m a n d zinc, i n d u s t r i a l p l a n t s for zinc and c a d m i u m , and a u t o m o t i v e traffic for lead. GRASS In o r d e r to i n v e s t i g a t e the use of g r a s s as a bioindicator, the e l e m e n t a l c o m p o s i t i o n m u s t be known. T h e m a i n c o n s t i t u e n t s of g r a s s a r e o r g a n i c material (45%), silicon dioxide (45%) a n d c a l c i u m c a r b o n a t e (1-2%). T h e grass was cut w i t h scissors or a knife c o a t e d w i t h Teflon a n d stored in p o l y e t h y l e n e bags. E a c h s a m p l e was w a s h e d with 10ml of deionized w a t e r to r e m o v e dust a n d o t h e r a d s o r b e d m a t e r i a l s , dried to c o n s t a n t w e i g h t at 60°C, a n d g r o u n d to a p a r t i c l e size < 100 pm. T h e finely g r o u n d m a t e r i a l was a n a l y z e d w i t h a n e n e r g y dispersive T r a c o r N o r t h e r n S p e c t r a c e M o d e l 430 X-Ray F l u o r e s c e n c e I n s t r u m e n t u s i n g a n X-ray t u b e for e x c i t a t i o n [25, 26]. U s i n g p o w d e r e d s a m p l e s of ~ 5-6 g the d e t e c t i o n limits w e r e 2 10 mg k g - 1 dry weight. T h e r e f e r e n c e s a m p l e s m u s t h a v e a s i m i l a r c o m p o s i t i o n for a p p r o p r i a t e c o m p e n s a t i o n of m a t r i x effects. S t a n d a r d s w e r e p r e p a r e d by m i x i n g e q u a l a m o u n t s of cellulose a n d silicon dioxide a n d adding 4% c a l c i u m c a r b o n a t e a n d small a m o u n t s of m e t a l salts. T h e c o n c e n t r a t i o n s
6 TABLE 3 Concentrations of elements in grass determined by X-ray fluorescence spectrometry Element
Concentration (mgkg 1 dry weight)
Ca Mn Fe Ni Cu Zn Br Rb
6900 _+ 640 82 i 6 95 ± 8 10 ± 1 9±1 50 ± 4 16 ± 2 16 + 3
Sr
35 ± 3
found in the grass samples (Table 3) varied b e t w e e n 9 mg kg-1 for copper and ~ 7 0 0 0 m g k g 1 for calcium. E l e m e n t s of atomic n u m b e r s between 9 and 19 could be d e t e r m i n e d in a v a c u u m c h a m b e r in which the a b s o r p t i o n of the low e n e r g y X-rays by air is minimized. For work in a v a c u u m c h a m b e r the samples and the s t a n d a r d s must be mixed with a b i n d e r and pressed into pellets. The m e t h o d used for the grass samples is applicable to the analysis of dust, soil, sludge and o t h e r powdered materials. The i n s t r u m e n t can be t a k e n into the field and used for biological, e n v i r o n m e n t a l and geochemical analyses [27]. RAIN WATER Rain w a t e r c o n t a i n s v e r y small a m o u n t s of insoluble particles. Rain w a t e r samples were supplied by the K e r n f o r s c h u n g s a n l a g e Jiilich, w h e r e a system for the collection of r a i n and dust w i t h o u t cross c o n t a m i n a t i o n has been developed. The rain w a t e r was collected via a plastic funel in a p o l y e t h y l e n e bottle p r e v i o u s l y cleaned with nitric acid and water. The collected w a t e r was filtered t h r o u g h a 0.45 pm m e m b r a n e filter. The filtrate was analyzed for cadmium, copper, zinc and selenium by cathodic stripping v o l t a m m e t r y and for lead by anodic stripping v o l t a m m e t r y . Stripping v o l t a m m e t r y enriches an element on the c a t h o d e by e l e c t r o l y t i c deposition at a c o n s t a n t potential. Reversal of the c u r r e n t strips the deposited element from the cathode. This t e c h n i q u e has a d e t e c t i o n limit of 10ng1-1 [28, 29]. The results o b t a i n e d for r a i n w a t e r are listed in Table 4. The values are a v e r a g e s of five d e t e r m i n a t i o n s with r e l a t i v e s t a n d a r d deviations in the r a n g e 0.3-1%. The high c o n c e n t r a t i o n s of copper, lead and zinc are not surprising, because the rain w a t e r was collected n e a r the lead mines of Stolberg, F.R.G. DUST A i r b o r n e dust is a v e r y i n h o m o g e n e o u s m a t e r i a l c o n t a i n i n g organic and i n o r g a n i c c o m p o n e n t s and m a n y elements, the c o n c e n t r a t i o n s of which are
TABLE 4 Concentrations of elements in rainwater determined by stripping voltammetry Element
Concentration (#gl-:)
Cu Se Cd Zn Pb
15.2 0.32 0.39 19.5 24.1
d e t e r m i n e d by t h e o r i g i n of t h e p a r t i c l e s . D u s t m a y t r a n s p o r t e l e m e n t s to o t h e r r e g i o n s a n d d e p o s i t t h e m on soil a n d p l a n t s . V a r i o u s l a b o r a t o r i e s c o l l a b o r a t i n g in t h e " A r b e i t s g e m e i n s c h a f t z u r F S r d e r u n g d e r R a d i o n u k l i d t e c h n i k " [13-16] c a r r i e d o u t i n t e r l a b o r a t o r y a n a l y s e s of e l e m e n t s in dust. A v a r i e t y of a n a l y t i c a l m e t h o d s s u c h as n e u t r o n a c t i v a t i o n , p h o t o n - i n d u c e d a c t i v a t i o n , X-ray fluorescence, t o t a l r e f l e c t i o n X-ray f l u o r e s c e n c e , p r o t o n i n d u c e d X-ray e m i s s i o n , a t o m i c a b s o r p t i o n s p e c t r o m e t r y a n d i n d u c t i v e l y c o u p l e d p l a s m a a t o m i c emissi o n s p e c t r o m e t r y w e r e used. D u s t s a m p l e s w e r e c o l l e c t e d w e e k l y o v e r 1 y e a r a t v a r i o u s l o c a t i o n s in t h e F e d e r a l R e p u b l i c of G e r m a n y : D e u s e l b a c h ( u n p o l l u t e d air), H a m b u r g (residential area), K a r l s r u h e ( a g r i c u l t u r a l area), M a n n h e i m (industrialized region) and M f i n c h e n (traffic area). H i g h - v o l u m e s a m p l e r s w i t h m e m b r a n e filters of 26 cm d i a m e t e r w e r e used. R o u n d s e c t i o n s of 5 cm d i a m t e t e r w i t h ~ 0.5 mg d u s t p e r cm 2 s t o r e d in p o l y e t h y l e n e b a g s for X R F a n a l y s i s or in q u a r t z a m p o u l e s for TABLE5 Concentrations of elements in air-borne dust determined by instrumental neutron activation analysis and X-ray fluorescence spectrometry Element
As Br Co Cr Cu Hg Mn Ni Pb
Sb Se V Zn
Method
NAA NAA/XRF NAA NAA/XRF NAA/XRF NAA XRF XRF NAA/XRF NAA NAA NAA NAA/XRF
Concentration in air (ngm 3) at Deuselbach
Hamburg
Karlsruhe
Mannheim
Miinchen
1.7-4.5 1(~34 0.2 1.2 1.5-5.3 3 13 0.05~.5 10-55 2.34.5 50-200 0.8~8.0 0.7-5.0 5.4-8.5 27 170
5.6-34.6 2(~310 0.5-1.5 3.4-25 35-285 0.3-2.1 15-130 4-25 140-1650 4.6-11.1 1.~10.4 7.5-17.5 60~60
1.8-10.0 20~200 0.4-1.5 3.4~-30 10--50 0.1-0.5 13~95 4.7-67 100~750 1.9-9.0 0.9~5.0 9.5~12.4 70-500
3.0-20.0 25- 200 0.6-3 5-45 15-85 0.14).4 26-130 6.4-57 130-1050 2.5-15.0 1.1~.0 10.8-21.1 100-550
1.5-9.1 120400 0.6-2.0 1L 177 60-200 0.14).8 20-185 5.6-22 600-1600 20.2-40.0 0.5-2.0 3.5~.5 88-310
neutron activation analysis were distributed to the participating laboratories. Nine elements (Ca, Cr, Mn, Fe, Ni, Cu, Zn, Br, Pb) were determined by energydispersive X-ray fluorescence spectroscopy [15, 16] and 11 elements (Cr, Fe, Co, Cu, Zn, As, Se, Br, Cd, Sb, Hg) by instrumental neutron activation analysis. The results for each sampling area are summarized in Table 5. Some general trends are summarized here. The concentrations of the elements changed considerably during the 1-year period. The changes sometimes exceeded one order of magnitude and occurred very rapidly. During the winter the values are distinctly higher than during the summer. Sites with high lead concentrations also have high bromine concentrations, indicating that residential, industrial, high-traffic density regions, and agricultural regions are all polluted by exhaust gases from internal combustion engines. The concentrations of cobalt, nickel, selenium and zinc in dusts are especially high in the industrial regions, as expected. High concentrations of these elements were also found in the agricultural areas. Dust must have been transported by wind from the industrial to the agricultural regions. ENRICHMENT OF ELEMENTS Sometimes the detection limits of an analytical method are not sufficient for an analytical task. In these cases, the elements to be determined must be enriched. Highest enrichment factors were obtained by sorption or ion exchange procedures. Selective exchangers are known for certain elements or groups of elements [30, 31]. A review on the enrichment of elements is given in the literature [31]. SPECIATION IN LIQUID SAMPLES Environmental scientists are becoming increasingly interested in trace element speciation, because beneficial and harmful effects o f " t r a c e elements" are highly dependent on their chemical forms. In liquid samples cations and anions must electrically balance each other. Methods for the determination of cations have been described in the previous sections. The anions are generally separated and quantitatively determined by ion chromatography. Formation constants of complexes with a central metal atom can sometimes be determined by electrochemical methods by comparing the polarographic half-wave potential for the solution containing the complex data measured with or calculated for synthetic solutions. The charge of a complex can be determined from its behaviour on an ionexchange column. Rhine water was filtered through a 0.4#m polycarbonate filter and then passed through various columns. The percent retentions for cadmium, copper, lead and zinc are listed in Table 6 [32]. The copper species was completely retained on an anion exchange resin but not on a cation exchange resin. Therefore, the species should be anionic and is perhaps present as a negatively charged complex with humate ligands. The results for zinc indicate a cationic zinc species.
9 TABLE 6 Retention of cadmium, copper, lead and zinc present in filtered Rhine water on various column materials Type of column
Percent retained
Cation exchange (Lewatit S 1080) Chelating exchange (Hyphan) Anion exchange (Dowex 1 X 8) Charcoal
Cd
Cu
Pb
Zn
23
13
81
82
0
100
46
91
15
100
40
0
0
49
61
The valence states of the elements can be determined by methods such as optical spectrometry (UV-VIS-NIR), electrochemistry (voltammetry, polarography, electrophoresis), coprecipitation, extraction and ion chromatography. zoo
I
I
Q
I
!
I
D
-
K
~1 M~G
~
K 50
G
K A
K
KKA
K*G AHS KA M K GG Q ~ - - C
ol I
Io
I
2o
I
30 Angle
I
40
I
5O
Fig. 2. Powder diffractometry spectrum of air dust from Hamburg (A: ammonium sulfate, C: calcite, G: gypsum, K: koktaite, M: mohrite, Q: o-quartz).
10 DETERMINATION OF SPECIES IN SOLID SAMPLES [14, 33] The chemical behavior of toxic trace elements can be determined by leaching with various solutions. In this manner, the mobility of Cd, Cr, Cu, Mn, Ni and Pb was compared in airborne dust from Darmstadt and Hamburg. Extractants of pH 1 (aqueous acid), pH 4 (acid rain) and pH 6 (water) were used. In all cases the solubility of the elements increased with decreasing pH. Chromium, nickel and lead were leached to the same degree from the Darmstadt and Hamburg dusts. More copper and manganese were leached from the Darmstadt sample than from the Hamburg sample, whereas the Hamburg sample released more cadmium than the Darmstadt sample. IR-spectrometry of a solid sample containing 1 mg dust and 100mgKBr, which was ground, dried at 100°C to constant weight, evacuated and pressed to a pill, showed strong absorptions for NH4 ÷ and SO42- , weaker absorptions for SiO~ , HzO, carbohydrates and HSOi and absorptions of low intensity for PO] and C O ~ . A very useful method for the determination of species in air dust is electron microscopy with a microprobe (X-ray fluorescence analysis of single particles). In this way, a semiquantitative analysis of a chosen particle is obtained. Many minerals have been identified [14, 33]: a-quartz, potassium feldspar, coal light ash, Pb- and/or Ti-rich particles, concrete (fl-dicalcium silicate), calcite, calcium-sodium-feldspar (labradorite, plagioclase), clay minerals (kaolinite) and sodium chloride. In addition, particles of biological origin have been detected. The biological particles can best be identified by light microscopy, which can also be used to detect inorganic particles such as garnets, glass, asbestos, soot and coke. X-Ray powder patterns obtained by the Bragg Brentano method can identify chemical species in solid mixtures. A powder pattern for dust from Hamburg is reproduced in Fig. 2. By comparison with the patterns from pure compounds, ammonium sulfate, calcite gypsum, koktaite, mohrite and a-quartz were found to be present in the dust [33].
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