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Journal of Hazardous Materials 229– 230 (2012) 192– 200

Contents lists available at SciVerse ScienceDirect

Journal of Hazardous Materials

j our na l ho me p age: www.elsev ier .com/ locate / jhazmat

nvironmental hazard of oil shale combustion fly ash

rina Blinovaa,∗ , Liidia Bityukovab, Kaja Kasemetsa, Angela Ivaska, Aleksandr Käkinena,c , Imbi Kurveta ,lesja Bondarenkoa,d, Liina Kanarbika,c, Mariliis Sihtmäea, Villem Aruojaa, Hedi Schvedeb, Anne Kahrua

Laboratory of Molecular Genetics, National Institute of Chemical Physics and Biophysics, Akadeemia tee 23, Tallinn 12618, EstoniaInstitute of Geology at Tallinn University of Technology, Ehitajate tee 5, 19086, EstoniaDepartment of Chemical and Materials Technology, Tallinn University of Technology, Ehitajate tee 5, Tallinn 19086, EstoniaDepartment of Gene Technology, Tallinn University of Technology, Akadeemia tee 15, Tallinn 12618, Estonia

i g h l i g h t s

Water eluates of oil-shale fly ash are toxic due to high alkalinity.Toxicity of oil-shale fly ash depends on combustion technology.Fly ash emissions have not lead to apparent soil contamination by trace elements.

r t i c l e i n f o

rticle history:eceived 26 January 2012eceived in revised form 25 May 2012ccepted 26 May 2012vailable online 2 June 2012

a b s t r a c t

The combined chemical and ecotoxicological characterization of oil shale combustion fly ash was per-formed. Ash was sampled from the most distant point of the ash-separation systems of the Balti andEesti Thermal Power Plants in North-Eastern Estonia. The fly ash proved potentially hazardous for testedaquatic organisms and high alkalinity of the leachates (pH > 10) is apparently the key factor determiningits toxicity. The leachates were not genotoxic in the Ames assay. Also, the analysis showed that despite

eywords:il shale combustionly ashoxicityeavy metalsoil pollution

long-term intensive oil-shale combustion accompanied by considerable fly ash emissions has not led tosignificant soil contamination by hazardous trace elements in North-Eastern Estonia. Comparative studyof the fly ash originating from the ‘new’ circulating fluidized bed (CFB) combustion technology and the‘old’ pulverized-fired (PF) one showed that CFB fly ash was less toxic than PF fly ash. Thus, completetransfer to the ‘new’ technology will reduce (i) atmospheric emission of hazardous trace elements and(ii) fly ash toxicity to aquatic organisms as compared with the ‘old’ technology.

. Introduction

Increase in the price of oil stimulates interest to use oil-shale fornergy production [1,2]. Estonia is the leading producer of oil-shalen the world: since 1916 over one billion tons have been extracted3]. Nearly 90% of this amount has been used for electricity produc-ion and the rest for heat generation and production of syntheticrude oil. Oil shale combustion at two of the world’s largest oil-hale-fired Thermal Power Plants (Balti and Eesti TPPs) startedn 1959 and 1969, respectively. Until 2005, only pulverized-firedPF) combustion technology was used. To improve the operational

fficiency and to decrease the hazardous emissions, a new circulat-ng fluidized bed combustion (CFB) technology was introduced in005. Currently, 20 PF boilers and 4 CFB boilers operate at both of

∗ Corresponding author. Tel.: +372 6 398 361; fax: +372 6 398 382.E-mail address: irina.blinova@kbfi.ee (I. Blinova).

304-3894/$ – see front matter © 2012 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.jhazmat.2012.05.095

© 2012 Elsevier B.V. All rights reserved.

the above-mentioned TPPs [4]. Oil-shale combustion entails pol-lution of the surrounding environment: considerable amount ofsolid waste (ash) is generated in addition to gases (CO2, NOx, SOx)and fly ash emissions to the atmosphere. Long-term oil shale com-bustion has led to the generation of approximately 300 milliontons of ash deposited in gigantic ash fields near TPPs, coveringaltogether about 20 km2 [5]. The largest part of this solid wasteis furnace ash. The finer and lighter ash particles (fly ash) col-lected in cyclones and electrostatic precipitators are also depositedin the ash fields. In the Estonian registry of waste, the above-described ashes are registered as ‘hazardous waste’ due to thehigh alkalinity of their leachates. As the filters do not capture allash particles formed during oil shale combustion, TPPs are consid-ered the main source of air pollution in the region: approximately

1–2% of produced ash has been shown to be emitted into theatmosphere [6]. The sum of annual atmospheric emission of 9 heavymetals (As, Cd, Cr, Cu, Hg, Ni, Pb, Zn and V) from both TPPs wasapproximately 130 t in 1992 [7] and 94 t in 2002 [8], the total

ous Materials 229– 230 (2012) 192– 200 193

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I. Blinova et al. / Journal of Hazard

nnual emissions of polyaromatic hydrocarbons (PAHs) in 2001ere 67.8 kg [8]. Renovation of the power units and installation ofew efficient electrostatic precipitators has led to significant reduc-ion in the emission of exhaust gases and fly ash particles [9], buthe total amount of fly ash emission is still remarkable (about 6000 tf solid particles [3]).

The earlier investigations in environmental problems related toil shale combustion have been mainly focused on chemical com-osition of the ashes, leaching of the pollutants from ash dumpsnd quantitative assessment of atmospheric emissions. It has beenhown that ash deposits have negative impact on the nearby envi-onment. The very alkaline leachates formed as a result of waterltration through the ash plateaus account for the contaminationf environment around the ash fields [5,10]. A slight increase ofeavy metal concentrations in the soils and vegetation were regis-ered near and to the north of Balti PP [11]. However, the possiblempact of the fly ash emission on the contamination of surroundingoils and surface waters has not been studied systematically.

The current investigation aimed to fill the knowledge gaps con-erning the potential environmental hazard of oil shale combustiony ash. For that we used a combined approach involving chemicalnd ecotoxicological methods. As the ‘old’ PF technology is beingeplaced by the ‘new’ CFB technology, PF- and CFB-fly ash sam-les were studied in parallel. As Kuusik et al. [12] have shown thatFB and PF fly ash have different physicochemical properties, wetudied how these different properties translate into toxicity of theeachates of these ashes, i.e., whether the ‘new’ CFB technology is

ore environmentally friendly than the ‘old’ (PF) one.

. Experimental

.1. Sampling

Four fly ash samples from the last filter (i.e., closest to thexhaust) of the ash-separation system of TPPs were collected in009. Two samples (PF-E and CFB-E) originated from the electro-tatic precipitator at Eesti TPP (the 3rd and 4th filters, respectively)nd two (PF-B and CFB-B) from the 4th filter of electrostatic precip-tator at Balti TPP. The ash samples were not sieved before analysiss the fly ashes from electrostatic precipitators were very fine andomogeneous; the particles did not exceed 100 �m [4,12]. 24 top-oil samples (0–20 cm) were collected in 2008 in the prevailingownwind direction from of Balti and Eesti TPPs (Fig. 1). Soil sam-les were air-dried at room temperature and sieved using a 2 mmesh screen. The sieved fractions were pulverized to a grain size

0.063 mm.

.2. Preparation of the eluates

The preparation of fly ash water eluates (leaching procedure atig. S1, Supplementary material) with different solid-to-liquid ratioSLR) was performed according to the existing standards:

European standard EN 14735:2005 on Characterization of waste:Preparation of waste samples for ecotoxicity tests [13]; SLR(1:10); 100 g of dry fly ash per 1 L of MilliQ water;OECD Test Guideline No. 23 on Aquatic toxicity testing of diffi-cult substances: Water-Accommodated Fraction (WAF) [14]; SLR(1:10,000), 100 mg of dry fly ash per 1 L of MilliQ water.

fter shaking during 24 h at 23 ◦C suspensions of SLR 1:10 were

ettled for 1 h, decanted, filtered (nylon filter, pore size of 0.45 �m,upelco) and the eluates used for testing. Suspensions of SLR:10,000 were settled for 24 h, upper layers decanted and usedor testing. For tests with crustaceans and algae the respective

Fig. 1. The sampling map of the topsoils.

test media were used for the leaching (1:10,000) instead of MilliQ.Water extracts of soils (1:10) were prepared according to [15].

2.3. Physicochemical analysis

The elemental composition of solid samples and respective elu-ates was analyzed by the ICP-MS method in the Certified ACMEanalytical laboratories Ltd. (Vancouver, Canada). Prior to the chemi-cal elements measurements in the solid samples a strong multi-acid(HNO3–HClO4–HF–HCl) digestion was applied for the treatment ofsolid samples. Conductivity of the eluates was measured by con-ductivity meter Ecosan CON 5, pH by pH-meters Orion 2star andJenway 3310.

The organic matter content (loss-on-ignition, LOI) in soils wasdetermined according to [16] and total dissolved solid (TDS) and pHof the soils water extracts according to [17] using the Hach HQ40dmulti Portable Meter. The size and shape of the fly ash particleswas studied with scanning electron microscope (SEM). Specific sur-face area (SSA) was measured by Brunauer–Emmett–Teller (BET)method.

2.4. Ecotoxicological evaluation

Vibrio fischeri luminescence inhibition assay is an acute toxicitytest based on decrease of the natural luminescence of test bacteriaupon exposure to toxicants [18]. In our studies, toxicity of fly ashwater-eluates was analyzed using V. fischeri (strain NRRL B-11177)reconstituted from the freeze-dried bacterial reagent (Aboatox,Finland). The test follows ISO standard 11348-3:2007 (exposuretime 30 min, 15 ◦C, 3,5-dichlorophenol as a positive control) [19].Luminescence was measured on Thermo Labsystems 1253 lumi-nometer (Finland). The eluates were tested at original (pH 10–12)and adjusted pH (pH 7–8 by 0.1 M HCl).

Toxicity of the fly ash water eluates to crustaceans and algae wasstudied according to standard test procedures: immobilization testwith crustacean Daphnia magna (OECD 202) [20] and growth inhi-

bition test with algae Pseudokirchneriella subcapitata (OECD 201)[21]. In both assays respective test media were used as a controland for the dilution of the investigated 1:10 eluates of ashes. In thecase of 1:10,000 eluates, only full-strength samples were analyzed.

194 I. Blinova et al. / Journal of Hazardous Materials 229– 230 (2012) 192– 200

Table 1Physicochemical characterization of fly ash samples.

Parameter Unit Eesti TPP Balti TPP

PFb-E CFBc-E PFb-B CFBc-B

SSAa m2/g 2.12 8.45 2.05 23.9Ca wt, % 18.52 20.20 23.44 21.21Fe wt, % 2.73 3.40 3.92 3.73Mg wt, % 1.97 3.10 2.44 2.98K wt, % 2.50 2.29 2.37 2.24Na wt, % 0.130 0.075 0.091 0.093P wt, % 0.100 0.095 0.077 0.106S wt, % 3.80 2.42 2.60 2.61As mg/kg 48.9 25.8 28.2 17.2Cd mg/kg 0.94 0.13 0.26 0.17Cr mg/kg 51 48 42 49Cu mg/kg 20.18 18.56 12.37 15.29Pb mg/kg 193.79 67.23 112.62 75.49Zn mg/kg 179.1 50.6 45.9 61.7

a SSA, specific surface area.b

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PF, pulverized firing.c CFB, circulating fluidized bed.

In seed germination and growth inhibition test with higherlants sorghum Sorghum saccharatum and mustard Sinapis alba (ISO1269-1:1993) [22] natural soil was spiked with water eluates (full-trength 1:10,000 and 10% concentration of 1:10 eluates) and flysh was mixed with soil (3%, w/w, dry weight). Seeds were exposeduring 72 h in the dark.

For the interpretation of the toxicity results the adverse effectrigger values proposed by Römbke et al. [23] were used: 20% foracterial or algal tests, 30% for the plant tests and 10% for theaphnia test. Accordingly, when growth inhibition/mortality didot exceed the respective trigger value in full-strength eluates, theisk for the adverse biological effects was considered low.

The bacterial biosensors have been successfully used forhe determination of bioavailable toxic elements in both solidnd liquid samples [24,25]. In the current study, bioavailabil-ty of heavy metals in the fly ash (1:10 and 1:10,000) and soil

ater eluates and suspensions (1:10) was evaluated using metal-pecific recombinant luminescent sensor-bacteria: (i) Arsene –scherichia coli MC1061 (parsluxCDABE), (ii) Cd, Zn, Hg, Pb –seudomonas fluorescens OS8::KncadRPcadAlux, (iii) Cu – P. fluo-escens OS8::KncueRPcopAlux and Cr – Ralstonia eutropha AE104pchrBPchrAlux). Respective test procedures are described in26,27].

Mutagenicity of the fly ash eluates was studied by Ames testOECD 471) [28] using Salmonella typhimurium strains TA98 andA100. Water- and methanol eluates (1:10) of fly ash were ana-yzed in parallel. Methanol was used as an extractant to predicthe potential hazard/mutagenicity of less soluble and fly ash-boundollutants. Methanol is widely used as a solvent of relatively lowoxicity compared to other solvents for increasing the solubilityf hydrophobic compounds. Methanol allows desorption of lessoluble/particle-bound pollutants and thus can help to discriminateoxicity/hazard due to soluble and less soluble pollutants [29]. Allhe extracts were analyzed with (+S9) and without (−S9) metabolicctivation supplementation and the direct plating test protocol wassed [30].

The toxic effect of fly ash eluates was evaluated on the basisf results of 2 different water/methanol eluates, 2–3 independentxperiments and each experiment was run in two replicates.

. Results and discussion

In the current study the hazardous properties of fly ash fromhe most distant filters of electrostatic precipitators at the Balti

and Eesti TPPs were evaluated. It has been shown [5,7,12] that thecontent of hazardous trace elements in fly ash (per mass) gradu-ally increases along the ash separation process (cyclone–filters ofelectrostatic precipitator–emission into atmosphere). According to[7,31] content of metals in fly ash emitted into the atmosphereincreases 1.1- to 2.5-fold as compared with ash from the most dis-tant filters of electrostatic precipitators, however, high variationsof the results [31] make the accurate prediction of trace metalemission difficult. Thus, it could be assumed that results of tox-icity evaluation of fly ash from these pre-exhaust filters may beextrapolated to the ash emitted into the atmosphere.

3.1. Physicochemical characterization of PF and CFB fly ashes

The fly ash properties such as particle size and chemical com-position determine the fate and recovery (leachability, mobilityand bioavailability) of the fly-ash emission-related toxic elementsin the environment. The size, shape and, as a result, specificsurface area (SSA) of the studied fly ash particles (Table 1,Fig. 2) noticeably differed and depended on the combustiontechnology, especially on temperature in boilers [12]. The anal-ysis of size distribution of fly ash particles from pre-exhaustfilter [12] and from emissions [32] showed that average parti-cle size of fly ash from CFB boilers was smaller than from PFones.

The content of the major- and trace elements in the fly ashes(Table 1) was comparable with the earlier data on PF ashes [5,7]indicating reliability of our data.

The content of trace elements in PF fly ash from Eesti TPP washigher than that from the Balti TPP, but chemical composition ofCFB fly ashes from both TPPs was very similar. Therefore, reductionof the content of some trace elements in fly ash (Table 1) as a resultof replacement of the ‘old’ PF combustion technology by ‘new’ CFBis more evident at the Eesti TPP. It is significant that content of verytoxic trace elements such as As, Cd and Pb was remarkably lowerin CFB ashes from both TPPs. Thus, the analysis of the chemicalcomposition of fly ashes reveals that application of the ‘new’ CFBcombustion technology reduces the total atmospheric emission oftoxic trace elements.

Chemical analysis (Table 1) showed that content of Cd, Cr, Pb andZn in the oil-shale fly ashes was 5–10 times lower than it has beenshown for municipal waste incineration fly ashes [23] and lower orcomparable with average values for coal fly ash [33–35].

I. Blinova et al. / Journal of Hazardous Materials 229– 230 (2012) 192– 200 195

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.2. Water eluates of the fly ashes

Leaching of compounds from the solid samples depends onhe extraction procedure whereas the solid/liquid ratio (SLR) isne of the most important factors [33,36]. Moreover, release ofontaminants from the solid waste in laboratory leaching testsnd the leaching behaviour of trace metals in natural conditionsay noticeably differ [34,37]. However, standardized leaching

rocedures still remain as the main cost-effective approach forharacterization of potential environmental hazard of solid wastesllowing to obtain reproducible and comparable results. In the cur-ent study, two SLR were used (see Section 2). The SLR 1:10 issually applied for the characterization of hazardous solid wastes38,39] and the SLR 1:10,000 is used in aquatic toxicity testing ofoorly water-soluble substances. From our point of view the latter

s more environmentally relevant approach for the risk assessmentf the emitted fly ash which is distributed over a large area andubjected to precipitation.

Table 2 shows that all fly ash water eluates were highly alkalinepH 10.5–12.8), especially the leachates prepared from PF ashes.imilarly, conductivity in 1:10 leachates from PF fly ashes was 2–3imes higher than that of the CFB ashes reflecting the differencen the concentration of soluble salts in the eluates. There was a

eak correlation between concentrations of trace elements in flysh and their respective water eluates as well as between 1:10 and:10,000 eluates. For example, Pb content in CFB ashes was 1.5- to-fold lower than in PF ashes and the similar ratio was detected

n 1:10,000 eluates, but concentration of Pb in CFB 1:10 eluatesas 280- to 370-fold lower than in PF eluates. The comparison of

he chemical composition of water eluates revealed that concen-rations of most trace elements (Table 2) in 1:10,000 eluates were

ower or largely comparable with 1:10 ones. Only Zn concentrationsn 1:10,000 eluates were accordingly 2-fold and 10-fold higher.hat shows that leachability of trace elements from the ashes isore efficient when SLR 1:10,000 is used.

opy (SEM) of the fly ashes.

3.3. Biotesting of eluates

Currently, the standard approach for waste ecotoxicity assess-ment includes both chemical and biological methods. Biologicaltests evaluate the integrated effect of all waste components toliving organisms which cannot be predicted on the basis of chem-ical analysis. As all species do not respond identically to thesame pollution stress, the test battery of several species rep-resenting different trophic levels should be applied for wasteecotoxicity assessment. The test battery involves, as a rule, bothaquatic and terrestrial species representing different trophic levels[10,23,40].

In the current study the toxicity of fly ash to three aquatic species(bacterium V. fischeri, crustacean D. magna and microalga P. subcap-itata) and two terrestrial plant species (sorghum S. saccharatum andmustard S. alba) was evaluated. As all fly ash eluates were highlyalkaline (Table 2), their toxicity to crustaceans and bacteria wasevaluated at initial (alkaline) and adjusted pH 7.5–8.5 to reveal theimpact of pH on the test results.

Expectedly, the more concentrated 1:10 eluates were notice-ably more toxic than 1:10,000 eluates to all test species(Tables 3 and 4). Therefore, the calculation of EC50 values on thebasis of dose–response curves (Table 3) was possible only for1:10 eluates. In the case of 1:10,000 eluates, the inhibitory effectsexceeding 50% were obtained only for full-strength samples (i.e.,undiluted eluates −100% for algae and crustaceans, 80% (v/v) forbacteria) and, thus, only inhibition % caused by full-strength eluatesis presented in Table 4.

The testing revealed that 1:10 eluates of PF-E and PF-B asheswere significantly more toxic to aquatic species than CFB-E andCFB-B ashes. In the case of 1:10,000 eluates, the same tendency

was observed but difference in toxicity of PF and CFB eluates wasnot so remarkable. Comparison of the toxicity of eluates with ini-tial and adjusted to neutral pH (Tables 3 and 4) demonstratedthat high alkalinity seems to be the key factor of their toxicity.

196 I. Blinova et al. / Journal of Hazardous Materials 229– 230 (2012) 192– 200

Table 2Chemical composition of fly ash water eluates.

Parameter Unit Eluates (1:10) Eluates (1:10,000)

PF-E CFB-E PF-B CFB-B PF-E CFB-E PF-B CFB-B

Ca ppm 50 1792 958 1765 1214 16.5 13.6 17.0 12.3K ppm 50 812 115 660 166 1.06 0.34 0.77 0.43S ppm 1 635 506 541 564 4.0 2.0 2.0 2.0Fe ppb 10 351 <10 369 27.0 84.0 67.0 57.0 107Mg ppb 50 <50 665 <50 563 307 817 347 938Na ppb 50 5503 2817 7335 3676 73.0 <50 94.0 <50As ppb 0.5 4.0 3.7 2.4 5.6 5.1 1.8 1.3 1.2Cd ppb 0.05 0.11 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05Cr ppb 0.5 569 549 95.0 537 4.0 2.2 1.0 2.1Cu ppb 0.1 7.2 4.0 6.6 5.2 0.60 0.40 0.40 0.30Pb ppb 0.1 73.9 0.20 113 0.40 1 0.30 0.90 0.40Zn ppb 0.5 10.3 4.1 16.3 4.9 104 100 93.7 98.2pH 12.8 11.4 12.8 11.1 10.8 10.6 11.0 10.5Cond.a �S/cm 12,290 3630 12,660 4450 114.3 85.9 128.6 79.2

a Cond., conductivity.

Table 3Ecotoxicological characterization of fly ash water eluates (SLR 1:10).

Fly ash water eluates Toxicity (EC50, %, v/v)

Crustacean Daphnia magna Alga Pseudokirchneriella subcapitata Bacterium Vibrio fischeri48-h, 20 ◦C 72-h, 24 ◦C 30-min, 15 ◦C

PF-EInitial pH (12.8) 2.7 ± 0.5 ndc 0.29 ± 0.04Adjusted pHa 16.3 ± 11.0 67.3 ± 7.5 Not toxicb

PF-BInitial pH (12.8) 1.8 ± 0.4 ndc 0.22 ± 0.01Adjusted pHa 31.5 ± 2.1 27.5 ± 2.8 Not toxicb

CFB-EInitial pH (11.4) 55.0 ± 9.9 ndc 14 ± 7Adjusted pHa 69.0 ± 1.4 Not toxic Not toxicb

CFB-BInitial pH (11.1) 46.5 ± 13.4 ndc 42 ± 27Adjusted pHa 55.0 ± 9.9 Not toxic Not toxicb

by the 50%

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a Adjusted pH, initial pH of the eluates were adjusted near to neutral (pH 7–7.6)

b Not toxic, inhibition of luminescence of undiluted (full-strength) samples was <c nd, not determined.

owever, tests with crustaceans and algae showed toxicity alsoor neutralized eluates (both 1:10 and 1:10,000). One of the expla-ations for the observed toxic effects of neutralized eluates may behe synergistic effect of all components (including macroelements).he concentrations and ratio of the macroelements essential for

ife such as Ca, Mg, Na, S in natural aquatic ecosystems vary

ithin certain limits (adaptation range) and their deficit/excessn the samples can also lead to weakening (or even mortality)f exposed test organisms that in turn may cause their elevated

able 4oxicity (inhibition %) of full-strength (100%) fly ash eluates (SLR 1:10,000).

Fly ash water eluates Daphnia magna

48-h, 20 ◦C

PF-EInitial pH (10.8) 51.7 ± 15.3

Adjusted pH 57.5 ± 3.5

PF-BInitial pH (11.0) 58.3 ± 2.9

Adjusted pH 65.0 ± 7.1

CFB-EInitial pH (10.6) 20.0 ± 13.2

Adjusted pH 10.0 ± 1.1

CFB-BInitial pH (10.5) 11.7 ± 10.4

Adjusted pH 15.0 ± 7.1

a Inhibition of luminescence of Vibrio fischeri by 80% fly ash water-eluates (highest conb nd, not determined.c Stim, stimulation of luminescence of Vibrio fischeri by the 80% fly ash water-eluates c

0.1 M HCl.

sensitivity to toxic substances. The unnatural ratio of macroele-ments in fly ash water eluates may partly explain the toxicity ofneutralized 1:10,000 eluates to D. magna and P. subcapitata. Indeed,concentrations of toxic trace elements in 1:10,000 eluates wereone order lower than corresponding LC50 values for Zn and 2–3

orders lower for other elements [41,42]. Analysis of bioavailablemetals in 1:10,000 eluates with recombinant heavy metal sensorbacteria showed that bioavailable Cr, Cu, Cd, Zn, Pb, Hg was notdetected in any of the eluates and bioavailable As was present

Pseudokirchneriella subcapitata Vibrio fischeria

72-h, 24 ◦C 30-min, 15 ◦C

ndb 79 ± 1361.4 ± 10.4 Stimc

ndb 59 ± 3425.6 ± 0.9 Stimc

ndb 26 ± 855.0 ± 5.3 1 ± 1

ndb Stimc

32.7 ± 0.5 Stimc

centration that can be tested in this test format).

ompared to the control (2% NaCl).

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I. Blinova et al. / Journal of Hazard

nly in the eluates of ‘old’ PF technology ashes. Therefore, it coulde assumed that bioavailable As is among the factors explainingigher toxicity of PF-ashes 1:10,000 eluates compared to CFB elu-tes (Tables 3 and 4). In 1:10 eluates there was no bioavailable Cund As but Cr-biosensor showed the presence of bioavailable Cr inll 4 tested eluates. Cd/Zn/Pb/Hg sensors showed the presence ofome of these bioavailable metals in both PF 1:10 eluates. As Pboncentrations in PF 1:10 eluates were comparable with LC50 val-es for crustaceans and algae [41], it could be supposed that justigh concentrations of Pb along with higher than optimal concen-rations of macroelements (reflected by high conductivity; Table 2)aused higher toxicity of PF 1:10 eluates compared with CFB onesTable 3).

In total, toxicity testing of water eluates revealed that investi-ated fly ashes were potentially hazardous to aquatic organisms.owever, as very different results were obtained with two differ-nt leaching ratios (SLR 1:10 and 1:10,000), this once more raiseshe question on further interpretation of the results obtained. Fromur point of view, the choice of leaching procedure should dependn the aim of the investigation. Indeed, the results of chemicalnd ecotoxicological assessment of the 1:10 fly ash eluates showhe potential hazard of concentrated leachates from ash dumps toeighbouring environment (ground and surface water, soils). Highoxicity of investigated eluates (especially of PF fly ashes) indicateshe necessity of adequate waste disposal techniques to prevent theontamination by leaching of contaminants from the disposed ash.t the same time, the concentrations of As, Cd, Cu, Pb, and Zn in ally ash 1:10 eluates were below the Estonian permitted limit valuesPLVs) for groundwater (Table 5). Only the concentration of Cr inhe PF-E, CFB-E and CFB-B 1:10 eluates exceeded these PLV values.

The results of chemical and ecotoxicological study of the:10,000 fly ash eluates may be used for environmental risk assess-ent of oil shale fly ashes emitted into the atmosphere and/or used

n other industrial sectors (such as production of cement and otheruilding materials, glass ceramic, soil improvement, and road con-truction [1,45–47]). In the latter case it is important to note that theirect contact of fly ash with soils matrix may considerably decreasehe bioavailability of trace metals [48]. Indeed, our test results alsohowed that even short-term contact of PF-E 1:10 eluates with soilignificantly reduced its toxicity to D. magna (data not shown). Tox-city test with terrestrial plants S. saccharatum and S. alba showedhat eluates of all tested fly ashes (full-strength 1:10,000 eluatesnd 10% (v/v) concentration of 1:10 eluates) had no influence on theeed germination, and growth inhibition of roots and shoots did notxceed 30%. Moreover, in some cases the eluates even stimulatedhe growth of plants compared to the control. The direct additionf fly ash into the soil (3%, w/w, dry weight) did not inhibit theeed germination and even slightly stimulated the growth of theoots and shoots (data not shown). In this respect there was no dif-erence between fly ashes from PF and CFB technologies. Based onhe results on the toxicity of the 1:10,000 eluates to aquatic organ-sms and plants it could be concluded that environmental risks ofy ash application in agriculture are minor. Moreover, content ofeavy metals in fly ash samples (Table 1) was much lower thanermitted limit values for water treatment sludge used in agricul-ure (Table 5). However, although the content of As, Cu, Cd, Cr,b and Zn in ashes did not exceed the Estonian permitted limitPLVs) for soils for residential area (with exceptions of As in PF-), the content of As and Pb exceeded the respective target valuesTable 5). The concentrations of trace elements in 1:10,000 eluatesf all tested fly ash samples were significantly below Estonian PLVsor groundwater, the concentrations of some hazardous elements

Zn, As and Pb) exceeded the maximum concentrations observedn the Estonian rivers during past 10 years (Table 5). Thus, applica-ion of large amounts of oil shale fly ash may potentially lead to soilontamination by As and Pb.

aterials 229– 230 (2012) 192– 200 197

As some compounds in the fly ash such as heavy metals andPAHs are known mutagens, the genotoxicity of fly ashes was eval-uated by the Ames test [30]. The results showed that the tested 1:10water-eluates of ashes (at concentration of 250, 500 and 1000 �l perplate) and also 1:10 methanol-eluates (100 �l per plate) were notmutagenic both in the absence and in the presence of metabolicactivation (S9). Thus, the relatively low concentrations of heavymetals (Table 1) and PAHs [49] in fly ashes cause no apparent hazardfor organisms from the point of view of mutagenicity.

3.4. Content of hazardous trace elements in the soils

Taking into account that fly ash emitted into the atmospherebecomes distributed over a wide area, the total input into thesoils via atmospheric depositions cannot be very high. To evaluatethe influence of atmospheric emissions from long-term intensiveoil-shale combustion (since 1960s) on the soil contamination byhazardous elements, 24 topsoil samples (Fig. 1) were analyzed. Thesampling set is characterized by different mineral compositions andcontents of organic matter and reflect the soil diversity in the region(see Supplementary material).

Chemical analysis of the soil samples revealed that average con-tent of Cu, Cd and Zn in the studied fly ashes (Table 1) and soils(Table 6) were comparable, but fly ashes contained noticeably moreAs, Cr and Pb. However, the content of toxic elements such as As,Cr, Cu, Cd, Zn and Pb in all topsoil samples was below Estonian per-mitted limit values (PLV) for residential area soils (Tables 5 and 6).Content of As, Cr and Zn in the soil samples was comparable witharable and residual topsoils in Northern Estonia (Table 7), but aver-age concentration of Pb was higher. Nevertheless, investigated soilscontained less Pb than soils in the Tallinn region (Table 7) as wellas soils from urban parks (66.2 mg/kg) in Beijing [53] or pollutedsoils (50.9 mg/kg) in Poland [54].

The risk of toxic compounds present in the soils for biotadepends on their mobility and bioavailability [25]. Mobility ofheavy metals in soils is usually predicted by water extraction tests[55,56]. In the current study SLR 1:10 was used in the leaching pro-cedure for soils. The chemical analysis showed that during 24 h onlya small amount of toxic elements was released to the water: up to0.2% of As, 0.23% of Cd, 0.14% of Cr, 0.41% of Cu and 0.17% of Zn.The leaching of Pb was the lowest (0.01% of total Pb). There was nocorrelation between total content of As, Cd, Pb and Zn in the soilsand in their corresponding aqueous extracts (Table 6), for Cu andCr the slight positive correlation was observed. The concentrationsof trace elements (Table 6) in the soil water extracts did not exceedthe permitted limit values (PLV) for groundwater in Estonia, but insome eluates the concentrations exceeded long-term average valuefor Estonian rivers (Table 5).

The bioavailability of toxic elements may be evaluated onlyby biological methods. The metal specific recombinant bacterialbiosensors showed the presence of As in 13 soils and Pb/Zn/Cd/Hgin 20 soils (Table 8). It is important to stress that these biosensorswill be ‘activated’ already by subtoxic concentrations of respectivemetals [27] i.e., their results may be interpreted as ‘biomarkers’ thatcan be considered early-warning signals. As a rule, these sensorsare not strictly specific, i.e., they may be ‘activated’ simultaneouslyby several metals. However, based on the chemical analysis of soilsand their respective extracts it may be concluded that the inductionof Pb/Zn/Cd/Hg biosensor was caused by Pb and Zn. The bioavail-able fractions of As, Pb and Zn in the soils were not correlated withthe soil organic matter content nor with the total content of theseelements in the soils (data not shown).

The underlying parent rocks and anthropogenic pollution arethe main sources of trace elements in the soils. In the investigatedregion (Fig. 1) soils formed on Palaeozoic silicaclastic and carbon-ate bedrocks covered by Quaternary deposits which are unevenly

198 I. Blinova et al. / Journal of Hazardous Materials 229– 230 (2012) 192– 200

Table 5Estonian environmental standards.

PLVa, mg/kg PLVb, mg/kg PLVc, �g/L Riversd, �g/L

As 30 (20) – 100 (5) 1.1Cd 5 (1) 20 10 (1) 0.07Cr 300 (100) 1000 200 (10) 1.4Cu 150 (100) 1000 1000 (15) 2.5Pb 300 (50) 750 200 (10) 0.5Zn 500 (200) 2500 5000 (50) 7

a Permitted limit (target) values for soils for residential area [43].b Permitted limit values for water treatment sludge used in agriculture [44].c Permitted limit values for groundwater (Estonia) [43].d Highest concentrations in Estonian rivers (1995–2005).

Table 6Concentration of the selected elements in soil samples (Fig. 1) and 1:10 soil eluates.

Sample Soils, mg/kg Eluates, �g/L

As Cd Cr Cu Pb Zn As Cd Cr Cu Pb Zn

E-1 15.1 0.57 29 14.17 62.86 51.4 8 1.28 1.5 12.7 1.6 34.7E-2 3.8 0.37 35 10.86 31.43 75.4 2.8 0.15 0.8 4.7 0.6 38.1E-3 3.8 0.35 47 8.21 32.59 68.1 5.2 0.82 2.9 8 0.3 14.6E-4 6.5 0.44 49 10.68 35.70 83.4 1.7 <0.05 1.7 4.7 <0.1 5.6E-5 4.9 0.34 47 18.44 23.26 60.5 3.1 0.55 1.8 11.4 1 21.1E-6 4.4 0.33 50 19.78 49.18 81.7 4.9 0.76 3.5 21 1.3 29.3E-7 2.4 0.22 3.0 2.09 12.38 12.8 2.3 <0.05 1.9 8.5 0.7 7.0E-8 8.6 0.50 40 16.11 28.66 72.9 5.7 0.09 2.6 16.8 0.9 15.3E-9 6.8 0.44 13 7.03 34.99 25.7 1.8 0.19 18.5 11.6 0.2 19.4E-10 2.9 0.38 26 15.84 63.47 124.2 5.9 0.18 5 6.2 0.5 21.5E-11 2.0 0.07 2.0 1.62 16.29 13.3 2.3 <0.05 0.6 1 0.2 7.6E-12 2.2 0.12 3.0 2.35 21.80 17.3 1.1 <0.05 0.8 1.4 0.1 39.3W-1 4.1 0.55 35 23.76 176.63 68.1 1.5 <0.05 1.7 8 <0.1 9.3W-2 3.9 0.30 21 11.22 22.57 92.9 2.2 0.08 1 14.5 <0.1 10.5W-3 3.7 0.25 16 8.35 24.83 42.5 2.3 <0.05 0.8 12.5 <0.1 6W-4 4.8 0.22 67 24.83 23.25 75.3 0.8 0.16 1.7 9 0.4 17.1W-5 2.5 0.21 13 11.08 22.08 33.9 2.3 0.41 0.9 16.3 0.2 21.8W-6 4.8 0.24 13 40.66 50.23 72.6 1.8 0.21 0.9 12.4 0.5 23.8W-7 6.4 0.41 24 13.26 28.63 60.6 4.7 0.81 1.3 13.9 0.5 20.8W-8 23.6 0.92 48 14.92 58.82 114 1.6 0.1 1.4 7.7 <0.1 8W-9 11.0 0.57 36 10.97 38.46 98.6 1.9 0.16 1 8.4 0.5 14.7

539570

dugbWcr

TC

W-10 9.4 0.42 38 8.30 30.66

W-11 6.7 0.66 66 10.41 41.63

W-12 9.3 0.41 50 12.06 36.82

istributed over the studied area. In some cases the impact ofnderlying rocks on the content of trace elements in the investi-ated soils can be clearly observed. The soils developed on blackish

rown graptolite argillite showed higher content of As (W-8, W-10,-11, W-12) that is in agreement with [57,58] who showed high

ontent of As in argillite compared with other rocks in the studyegion. Soils formed on Holocene sands or dunes formed by the

able 7ontent of selected trace elements (mean/min–max) in soil samples from different region

Selected topsoils,Narva regiona

Agricultural soils, Northernand North-Eastern Estoniab

As6.4 5

2–23.6 4–7

Cd0.390.07–0.92 nd

Cr32 23

2–67 17–31

Cu13.21 ≤10

1.62–40.66 <10–20

Pb40.30 17

12.38–176.63 13–19

Zn65.2 57

12.8–124.2 40–88

a Data from Table 6.b Ref. [50].c Ref. [51].d Ref. [52].

.3 2 0.18 1.1 10.1 0.5 42.5

.2 1.6 0.05 1.8 4.6 <0.1 6.9

.5 1.8 0.3 18 41.2 0.1 7.0

well-sorted Aeolian sand are characterized by low concentrationsof trace elements (E-7, E-13, E-14). However, in the case of slightlypolluted soils, often the determination of the exact origin of toxic

elements in the soils is not possible as their mobility/accumulationdepends on many factors (e.g., soil matrix, climatic condition,biological processes). The main anthropogenic sources of trace ele-ments in the soils at the investigated territory are waste disposal

s.

Topsoils, Tallinnregionc

Residual topsoils, Northern andNorth-Eastern Estoniad

7 9<1–184 5–14

nd nd26 41<1–475 31–5225 ≤10<1–604 <10–1144 172–468 11–25107 562–1463 33–83

I. Blinova et al. / Journal of Hazardous Materials 229– 230 (2012) 192– 200 199

Table 8Biosensor analysis of bioavailable metals in soil suspensions.

Sensor bacteria strain Metal inducing thesensor

MDLa for metals(mg/kg soil)

Soil samples (Fig. 1) that induced the respective sensorstrains (indicating the presence of bioavailable metal)

Escherichia coli MC1061 (parsluxCDABE) As As – 0.04 E-1, E-5, E-6, E-7, E-8, E-12, W-1, W-2, W-3, W-4, W-5,W-8, W-9

Pseudomonas fluorescens OS8::KncadRPcadAlux Cd, Zn, Pb, Hg Cd – 0.68Zn – 1.30Pb – 1.74Hg – 0.04

E-2, E-3, E-4, E-5, E-7, E-8, E-10, E-11, W-1, W-2, W-3,W-4, W-5, W-6, W-7, W-8, W-10, W-11

Pseudomonas fluorescens OS8::KNcueRPcopAlux Cu Cu – 1.28 NoneRalstonia eutropha AE104 (pchrBPchrAlux) Cr Cr – 0.044 None

sfbadli

fiAtesatAsb

4

tfirgdsscssaibAooipt

A

eaSD

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a MDL, method detection limit.

ites, transport exhaust emissions and use of the coal/wood/peator domestic heating. The impact of the waste dumps was avoidedy planning of the soil sampling. The long-term combustion of coalnd/or peat as well as the lead emission from transport sectionuring several decades undoubtedly has contributed to the soil pol-

ution by toxic trace elements, but quantitative estimation of thempact of these sources is impossible.

In general, it may be concluded that long-term fly ash emissionrom oil-shale combustion has not led to significant soil contam-nation by hazardous trace elements in the Northeast of Estonia.pparently, fly ash precipitated from atmosphere has contributed

o soil pollution by As, Pb and in lesser degree by Cr, but there is novidence that this input was more remarkable than that from otherources (e.g., natural for As, or traffic exhaust for Pb). As the studiedrea shows high variability in composition of the parent material,he role of natural sources of trace elements might be significant.nalogously, Punning et al. [59] have shown that the role of emis-ions from oil-shale combustion in environmental contaminationy previous investigations has been overestimated.

. Conclusions

The combined chemical and ecotoxicological characterization ofhe oil shale fly ash sampled from the most distant (pre-exhaust)lters of the ash-separation system at the Balti and Eesti TPPsevealed that oil-shale combustion fly ash may be potentially dan-erous for the environment. The analysis showed that the key factoretermining the toxicity of aqueous eluates of fly ash to aquaticpecies is high alkalinity but the toxic impact of trace elementsuch as As and Pb cannot be excluded. The comparison of chemicalomposition of fly ash and content of the hazardous elements in theoils revealed that the impact of long-term TTPs emissions on theoil contamination by As, Cd, Cu, Pb and Zn is not evident. However,s hazardous trace elements can accumulate in soils and soil organ-sms the application of fly ash in agriculture must be accompaniedy monitoring of their content (especially As and Pb) in the topsoils.pplication of the ‘new’ circulating fluidized bed (CFB) technologyf oil shale combustion noticeably reduces atmospheric emissionf hazardous trace elements and fly ash toxicity to aquatic organ-sms as compared with ‘old’ pulverized-fired technology (PF). Thus,hasing-out the ‘old’ oil shale combustion technology will reducehe negative impact of oil shale combustion on the environment.

cknowledgements

This work was supported by the Estonian-Norwegian knowl-

dge exchange Grant EMP45, Estonian Ministry of Sciencend Education (targeted funding projects SF0690063s08 andF0140016s09) and by the European Union European Regionalevelopment Fund Project ‘OxyFuel’.

[

Appendix A. Supplementary data

Supplementary data associated with this article can befound, in the online version, at http://dx.doi.org/10.1016/j.jhazmat.2012.05.095.

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