Extraction behaviour of polycyclic aromatic hydrocarbons adsorbed on waste incineration fly ash

Chemosphere, Vol. 29, No. 2, pp. 311-317, 1994 Copyright O 1994 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0045-6535/94 $7.00+0.00

Pergamon 0045-6535(94)00158-8

EXTRACTION BEHAVIOUR OF POLYCYCLIC AROMATIC HYDROCARBONS ADSORBED ON WASTE INCINERATOR FLY ASH

R. Fischer, R. Kreuzig, M. Bahadir *

Institute of Ecologicai Chemistry and Waste Analysis Technical University of Braunschweig I-lagenring 30, D-38106 Braunschweig

(Received in Germany 27 December 1993; accepted 29 April 1994)

Abstract

Fortification experiments were performed with waste incineration fly ash samples. The extraction recovery of PAIl was found to be influenced by spiking method, PAH concentration, molecular size, storage time, and carbon content of the matrix. Applying 14C-labelled PAH the extracts were found to exhibit only slight alterations in composition compared to the reference substances.

Introduction

Analyzing organic residues in complex solid sample matrices, exhaustive extraction of the analytes is required in order to give accurate information about the extent of sample contamination. However, extraction efficiency may be impaired by strong adsorption on activated surfaces of the matrix, and by the formation of non-extractable residues. Further, the adsorbate may undergo chemical reactions as it is well known for PAH adsorbed on silica gel TLC plates (1). The extraction of coal combustion fly ash samples was investigated under various aspects, e.g. the influence of extraction method and solvent on the recovery of spiked PAH (2, 3) and PCDD (4). Increased recoveries of organic substances from fly ash by pretreatment with hydrofluoric or hydrochloric acid were reported (5), but the recovery rates of spiked pyrene were not found to increase with such treatment (6). Experiments with radiolabelled substances showed different results for naphthalene and benzo(a)pyrene where the latter was extracted in much smaller amounts (7). Carbon-enriched fly ash fi'actions showed higher sorptivity and a larger specific surface suggesting that carbonaceous matrix components influenced the extractability of PAH. Normal-phase HPLC indicated that more polar products were detected along with the PAH in the extract (8).

311

312 The extraction of contaminants is an essential step during the analysis of solid samples and may be affected by several parameters, among them the variability of the matrix. Consequently, the results of experiments with coal combustion fly ash should not indiscriminately be transferred to waste incinerator fly ash. In this work PAH fortification experiments were performed in order to evaluate the influence on recovery rate of spiking method, extraction method, concentration and kind of PAH, and carbon content of the matrix. Besides the formation of non-extractable residues, a decrease of extraction efficiency may be caused by chemical reactions of the adsorbate. Thus, the extracts of radiotracer-spiked fly ash samples were also analyzed for more polar products by thin layer chromatography.

Experimental Samples: 1. ESP fly ash from municipal waste incinerator. 2. Fly ash from a large scale chemical plant. 3. Flue dust, industrial waste incineration. 4. Flue dust, municipal waste incineration. Chemicals: Four PAH with increasing ring number were chosen in order to evaluate the influence of molecular size. Phenanthrene (phe), pyrene (py), benzo(a)pyrene (bap) were purchased from Supelco, benzo(ghi)perylene (bper) from Promochem. Radiolabelled PAIl were purchased from Sigma Chemie (3-14C-fluoranthene (fla), 2035 MBq/mmol; 7,1014C-benzo(a)pyrene, 599.4 MBq/mmol) and Amersham Buchler (4,5,9,10-14C-pyrene, 2070 MBq/mmol). Solvents from Baker were ~-IPLC grade' and 'for organic residue analysis', respectively. Evaluating the spiking method: 0.5 g of fly ash 1 was spiked by adding 200 pJ of a PAIl standard solution and mixed well. After one hour, ultrasonic extraction (Bandelin TK52, 60/120 W) for 15 min with 10 ml toluene were performed two times, followed by ¢entrifugation (5 rain/3000 rpm). The extracts were combined and rotary-evaporated nearly to dryness. The residue was dissolved in acetonitrile:water 7:3 and the solution analyzed by HPLC (HewlettPackard HP Series 1050 HPLC pump, HP 1046 A programmable fluorescence detector, and HP 3396 A integrator; column: Macherey-Nagel ET 150/8/4 Nucleosil 5 C18 PAH, eluent flow 1 ml/min, column temperature 23 °C, gradient elution 70 % to 100 % acetonitrile within 18 min, constant 100 % acetonitfile for 12 rain; excitation/emission wavelengths were programmed to 250/360 nm, after 8 min 240/390 nm and after 12 rain 295/440 nm. Radiotracer experiments: The radiolabelled compounds were dissolved in hexane. Standard solutions were prepared by diluting the specific activity so that 15 kBq (py, fla) and 10 kBq (bap) were added to the respective samples (5 g of fly ash, spiked concentration 1 mg/kg, solvent 200 ~1 hexane). The samples were mixed well by vigorous shaking for one hour. Two extraction techniques were applied successively: 1. Shaking for 8 hours after ultrasonic treatment (50 mi toluene). 2. Soxhlet extraction for 16 hours (180 ml toluene). The extracts were concentrated

313 and the radioactivity of an aliquot was determined by liquid scintillation counting (Tri Carb Liquid Scintillation Analyzer Model 2500 TIL Packard Instrument Company, LSC-cocktall Opti-Fluor O, Canberra-Packard). The residual radioactivity of the sample matrix atter extraction was determined by combustion and absorption of the 14CO2 (Biological Material Oxidizer OX-500, Harvey Instrument Corporation, LSC-cocktail Oxysolve C400, Zinsser Analytic), followed by liquid scintillation counting. TLC was performed using HPTLC plates RP 18 with concentration zone (Merck) and a mixture of acetonitrile:water 19:1 as eluent. The radioactivity on the plates was scanned using a Tracemaster 20 Automatic TLC-Linear Analyzer (Berthold) followed by integration of the peak activities.

Results and discussion

Influence of svikin~ method The results in Table 1 show the recoveries obtained using different solvents for spiking. Spiking in a less polar solvent led to higher recoveries. Except pyrene, the lowest extraction recovery was obtained with acetonitrile, the most polar solvent tested. The greater recoveries of PAIl added in a less polar solvent could be explained by supposing a decreased adsorption of the PAH due to competitive adsorption of the solvent at non-polar sites on the matrix. In order to evaluate this question, samples were pretreated with the same volume ofhexane as that used for spiking. Then they were spiked with PAH standard solutions in acetonitrile. Recoveries increased to 70 % (phe), 72 % (py), 42 % (bap), and 38 % (bper), but did not reach the recoveries of the experiments with hexane as the spiking solvent. Table 1. Influence of solvent used for PAH addition on extraction recovery of the PAIl at 1 mg/kg concentration level [%]

spiking solvent

phe

py

bap

bper

hexane

91

94

50

52

acetone

46

52

49

41

acetonitrile

41

58

37

24

Table 2. Influence of PAH concentration on extraction recovery (spiking solution in hexane) [%].

concentration [mg/kg]

phe

py

bap

bper

1

91

94

50

52

0.2

71

79

56

25

0.1

46

59

52

22

0.05

48

68

44

20

314 Fortification experiments with PAH in concentrations down to 0.05 mg/kg fly ash showed decreasing recoveries due to decreasing concentration levels (Table 2). Further, these results were directly dependent on the molecular size of discrete PAIl compounds so that high-molecular weight PAH were extracted with more difficulty than lowmolecular weight PAH. Extraction method and composition of extracts In radiotracer experiments, extraction efficiency was investigated by carrying out a sequential extraction procedure. First, the spiked samples were extracted with toluene by shaking (sh), followed by soxhlet extraction (sux). Then, residual radioactivity was determined after combustion of the sample (res). Detailed radioactivity balances showed that adsorption of PAIl and formation of non-extractable residues were dependent on molecular size and concentration of the PAH spiked (Figure 1). In case of pyrene, most of the amount spiked was extracted in the first step by vigorous shaking. The soxhlet extraction procedure improved the low extraction efficiency and bound residues were of little significance at each concentration level. However, particularly at lower concentration levels, stronger adsorbed and non-extractable residues of benzo(a)pyrene predominated the ones which could be easily extracted by shaking with toluene. Different fly ash samples from municipal and industrial waste incineration were spiked with pyrene. In spite of the different inorganic sample compositions, the recoveries (Table 3) did not vary much.

% radioactivity recovery 100 80

• k\\\\\\\~

.

.

.

.

.

.

.

.

.

.

.

fraction .. ~

60

[]sh [ ] sox

N

40

•

res

20

1

0.1

0.01

1

0.1

0.01

concentration [mg/kg] spiked PAH:

py

bap

Figure 1. Distribution of radioactivity [%] depending on PAH species and concentration level.

315 In order to evaluate the influence of the sample carbon content sample 1 was made carbon-free by oxidation and 5 % activated charcoal was added to the matrix. The results are listed in Table 4. It can be seen that a higher carbon content of the sample matrix led to appreciably lower extraction recoveries. A similar effect on the extraction of spiked PCDD from fly ash has been reported (4). Table 3. Extraction efficiency of pyrene with different samples [%].

sample

sh

sox

res

i

95 98 94 85

7 2 4 12

1 1 1 5

Table 4. Influence of sample carbon content on extraction efficiency of pyrene [%].

sample

sh

sox

res

1 oxidized 1 1 oxidized + 5 % C

94 50 0.4

4 43

2 8 94

9

% radioactivity recovery 120 100 fraction

80

[]sh 60

[ ] SOX

• res

40 20

lh

spiked PAH:

lm2m py

lh

lm fla

2m

lh

lm

2m

bap

Figure 2. Influence of storage time (1 hour, 1 month, and 2 months) on extraction efficiency [%].

316 If the spiked samples were stored before extraction for one or two months in the dark, adsorption was stronger, which emphasized the necessity of soxhlet extraction. As shown in Figure 2 both pyrene and fluoranthene were recovered in similar amounts whereas benzo(a)pyrene was extracted less easily. The results indicate a slight increase of non-extractable residual radioactivity on the sample matrix during storage, but the amount of these bound residues were only significant with spiking of benzo(a)pyrene. In additional experiments we found that soxhlet extraction in a single step yielded recoveries similar to the sum of the two successive extraction steps mentioned above. Especially in the case of activated surfaces of fly ashes, chemical reactions can contribute to poor recoveries of PAH. In order to obtain qualitative information about the radioactive substances extracted from the samples, the extracts were investigated by reversed-phase TLC. The partitioning of radioactivity among PAH as well as more or less polar substances was compared to that of the applied reference substance (ref) whose radiochemical purity was 94 % (py) to 98 % (fla). The occurrence of (presumably more polar) radioactive components could be ascribed to transformation reactions of the adsorbed analyte. However, it was not possible to examine the nature of the non-extractable residue which was quantified by combustion. The distribution of radioactivity in the solutions obtained by sequential extractions varied very litte regardless of the solvent used, storage time, and PAH examined. As an example, in Figure 3 the extraction recoveries and the composition of the extracts compared to those of the applied reference substances are presented. These samples had been stored for 1 month before extraction. The largest fraction of polar products found was 7 % (calculated as a sum of the two successive extractions of benzo(a)pyrene one hour after spiking) which is less than 17.3 % of polar products reported for benzo(a)pyrene extraction from coal combustion fly ash (8).

% radioactivity recovery 100 ~x

80

~x

fraction •

~x

60

residue

[ ] more polar

,::<

i PAH 40

~x

[ ] less polar

~x

20

0

PAH:

<×

ref sh sox res ref sh sox res ref sh sox res py

fla

bap

Figure 3. Efficiency of sequential extractions after storage for 1 month and composition of extracts.

317 Conclusions Real sample conditions are reflected only approximately by fortification experiments. These investigations on the extraction behaviour of PAH spiked on waste incinerator fly ash indicate that the extraction recoveries were appreciably affected by the concentration and the molecular size of the analytes as well as the carbon content of the matrix. Additionally, the use of different solvents for spiking and the extraction method can influence the results. However, working with artificially contaminated samples belong to the basic research techniques in order to optimize and to validate analytical methods.

Acknowledgement We gratefully acknowledge financial support and providing with samples by GSF - Forschungszentrum ~ r Umwelt und Gesundheit, MOnchen - Braunschweig.

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