bioaerosols and particle release during composting of contaminated sawmill soil

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Bioaerosols and Particle Release During Composting ofContaminated Sawmill SoilM. Minna Laine a c , Kirsten S. Jørgensen a , Hannu Kiviranta b , Terttu Vartiainen b , Jouni K.Jokela c , Abiodun Adibi c & Mirja Salkinoja-Salonen ca Finnish Environment Institute, Research Laboratory, Finlandb National Institute of Public Health, Department of Environmental Hygiene and Toxicology,Finlandc Department of Applied Chemistry and Microbiology, University of Helsinki, FinlandPublished online: 03 Jun 2010.

To cite this article: M. Minna Laine , Kirsten S. Jørgensen , Hannu Kiviranta , Terttu Vartiainen , Jouni K. Jokela , AbiodunAdibi & Mirja Salkinoja-Salonen (1999) Bioaerosols and Particle Release During Composting of Contaminated Sawmill Soil,Bioremediation Journal, 3:1, 47-58, DOI: 10.1080/10889869991219190

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47

Bioaerosols and Particle Release During Composting

of Contaminated Sawmill Soil

M. Minna Laine,

1,3

* Kirsten S. Jørgensen,

1

Hannu Kiviranta,

2

Terttu Vartiainen,

2

Jouni K. Jokela,

3

Abiodun Adibi,

3

and Mirja Salkinoja-Salonen

3

1

Finnish Environment Institute, Research Laboratory, Finland;

2

National Institute of Public Health,Department of Environmental Hygiene and Toxicology, Finland;

3

Department of Applied Chemistry andMicrobiology, University of Helsinki, Finland

Abstract:

Compost windrows for bioremediation of soil were built at a wood-preserving site contaminated withchlorophenols, polychlorinated dibenzo-

p

-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs). Samplingof airborne particles during the mixing of the compost windrows found concentrations of PCDDs and PCDFs in dif-ferent particle sizes. The congener distribution of PCDDs and PCDFs in the collected air particle fractions was sim-ilar to that in the compost windrows, and the level of PCDDs and PCDFs was 1000-fold higher than the atmosphericbackground values reported previously. Viable particle-sizing samplers and several selective growth media wereused to enumerate bacteria and fungi in the airborne particles. From the collected air samples, 40 bacteria were iso-lated and identified. Among the isolated bacteria, 80% were Gram-positive and spore-forming. Two of the identifiedairborne bacteria,

Pseudomonas aeruginosa

and

Bacillus cereus

, may cause human disease and are classified in bi-ological agent hazard group 2. The amounts of airborne fungi, molds, and yeasts were 1000 to 2000 colony-formingunits (CFUs) per m

3

. The number of actinomycetes was up to 6-fold, and the number of bacteria was 2- to 20-foldcompared to background values. The overall level of airborne bacteria (200 to 3500 CFUs per m

3

) was low comparedto the level of bacteria (10

5

to 10

8

CFUs per m

3

) found when composting municipal waste.

Keywords:

airborne microorganisms, bioremediation, composting, particle sizes, polychlorinated dibenzo-

p

-dioxin (PCDD),

polychlorinated dibenzofuran (PCDF), polychlorinated phenol.

Introduction

The soil of nearly 800 former and present sawmill sitesin Finland is contaminated with chlorophenols,PCDDs, PCDFs, polychlorinated phenoxyphenols,polychlorinated diphenyl ethers, and polychlorinatedbiphenyls (PCBs) originating from the commercialchlorophenol mixture sold under the trade name Ky-5(Humppi, 1985; Valo et al., 1984) that was used until

1988 to preserve wood. PCDDs and PCDFs are rankedas the most toxic human-engineered compounds in theworld (Webster and Commoner, 1994). The toxicmechanism of PCDDs, PCDFs, and related compoundsis based on their binding to an Ah-receptor found inhigher organisms. The Ah-receptor-mediated mecha-nism of action, however, is only one of several suggest-ed as the toxic mechanism of PCDDs and PCDFs(Webster and Commoner, 1994).

* Lead author address: Finnish Environment Institute, Research Laboratory, Hakuninmaantie 4-6 B, FIN-00430 Helsinki, Finland;Phone: (358) 9 40300884, Fax: (358) 9 40300880; Electronic mail address: [email protected]. A preliminary draft of this articlewas published as a part of the lead author’s dissertation at the University of Helsinki.

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Researchers’ current opinions differ as to howharmful PCDD and PCDF compounds really are, whattheir effects are in humans, and the actual threshold val-ue of their effective dose. Recent studies indicate thatchlorophenols rather than the PCDDs and PCDFs arethe main cause for detrimental health effects to humanin contaminated sawmill areas (Vartiainen et al.,1995a). Chlorophenols are relatively polar and mayleach into the groundwater and thus cause a threat tohumans and to the environment. Removing the chlo-rophenols from the contaminated sawmill soil by, forexample, composting was shown to reduce the risk forsubstantial spreading of the chlorophenol pollution(Laine et al., 1997a,b). PCDDs and PCDFs are less mo-bile than chlorophenols because they are not soluble inwater and they adsorb more strongly to the organicmatter in soil (Adriaens et al., 1995). However, theymay spread from the soil via air particles.

Large, airborne particles remain in the upper respi-ratory tract, nose, and nasopharynx (Zeterberg, 1973).Particles smaller than 6

µ

m in diameter may be trans-ported to the lungs, but the greatest retention in the al-veoli is of 1- to 2-

µ

m particles (Salem and Gardner,1994). Thus, the smallest particles (approximately0.65

µ

m in diameter or smaller) are the most harmfuland may cause detrimental health effects.

Bioaerosols are a heterogeneous group of airbornebiological particles of different sizes ranging from0.5 to 30

µ

m in diameter (Lighthart, 1994). Inhalationis the predominant route of entry into individuals, re-sulting in adverse health effects after exposure to air-borne microorganisms (Stetzenbach, 1997). Bacteriaand fungi adhering to soil particles may be inhaled byworkers at the bioremediation site.

Particles may be released during outdoor compost-ing when the compost windrows are constructed(Figure 1) and when they are turned. During othertimes, the release of microbial or chemical componentsto the air can be prevented by covering the windrowswith tarps or similar materials.

Composting of municipal waste has been shown toemit airborne pathogenic microbes, endotoxins, andfungi that may cause lung disease or allergic reactions(Weber et al., 1993). Two types of respiratory disor-ders, hypersensitivity pneumonitis and organic dusttoxic syndrome, may occur after exposure to organicdust containing fungal spores and endotoxins (Weber etal., 1993). Bacteria may cause hypersensitivity pneu-monitis, infections, or mucous membrane irritations(Stetzenbach, 1997). Gram-negative bacteria maycause headache and diarrhea to compost workers han-dling household refuse (Lundholm and Rylander,1980). The Gram-negative bacterial cell wall containsendotoxins, i.e., lipopolysaccharides, that may causecoughing, headaches, fever, loss of balance, muscle

aches, nausea, and respiratory distress to human(Stetzenbach, 1997).

Actinomycetes, especially thermophilic actinomy-cetes having an optimum growth temperature of 40°C,may cause allergic reactions. Two respiratory diseases,farmer’s lung and mushroom worker’s lung, are causedby actinomycete spores from heated compost (Lacey,1974; Pepys et al., 1963).

Mycobacterium tuberculosis

and nontuberculous mycobacteria have been associatedwith respiratory illness (Kirschner et al., 1992).

Fungi may cause allergic reactions, asthma, der-mal irritation, or infections (Stetzenbach, 1997). Fungialso may contain mycotoxins, which cause symptomsas serious as those of bacterial endotoxins. These in-clude headache, muscle problems, neurologic disor-ders, respiratory distress, and toxicosis (Stetzenbach,1997). However, the study of Déportes et al. (1997)suggested no formation of aflatoxins in municipal solidwaste composts.

The aim of this study has been to quantitate the mi-crobial and particle-bound dioxin release to the airduring mixing of compost windrows. This informationwill be used to evaluate potential health effects duringbioremediation of chlorophenol-contaminated soil.

Materials and Methods

Full-Scale Composting of Contaminated Sawmill Soil

The construction of the compost windrows and the pa-rameters followed during the composting were de-scribed in detail by Laine et al. (1997b). Full-scale

Figure 1.

Construction of the stacked contaminated soil wind-row produced large amounts of dust

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composting took place during three summer seasonsfrom 1995 through 1997. Three windrows were builtwith a total volume of 520 m

3

. The windrows were con-structed on plastic beds, each inclined toward a sepa-rate underdrainage system. Each bed was covered witha 0.5-m insulation layer of bark.

The pH was adjusted to near neutral with fine gran-ular lime (dolomite, 5 kg m

–3

), and nutrients (1 kg m

–3

)were added in a form of a commercial fertilizer. Thecommercial fertilizer contained 26% N (14% ammoni-um-N and 12% nitrate-N), 3% P (2.1% water-soluble P), 3% K, 1.5% S, 0.5% Mg, 0.03% B, and0.0006% Se.

All three compost windrows contained contaminat-ed sawmill soil, nutrients, and lime, but they differed inamendments and soil types. Windrows 1 and 2 con-tained soil from the same batch of contaminated soilcomprising sandy soil and partially degraded sawdust.The initial concentrations of chlorophenols in windrows1 and 2 were 960 and 740 mg (kg dry wt)

–1

, respectively.The soil in windrow 3 was clay, and its initial chloro-phenol concentration was 30 mg (kg dry wt)

–1

. Wind-row 1 was amended with bark chips (pine and spruce) asthe bulking agent. To improve chlorophenol degrada-tion, decomposing straw compost was added as a bulk-ing agent to windrows 2 and 3. The fresh straw compost(25,000 kg) was partially decomposed for chlorophenoldegradation by pre-incubating it for 5 weeks with7000 kg of composted chlorophenol-contaminated soilobtained from the pilot-scale test (Pile 2, see Laine andJørgensen, 1997) before adding it to the compost wind-rows. The ratio of the materials was 2 parts of contami-nated soil to 1 part of bulking agent by volume.

All of the materials in the windrows were mixed byturning and were covered with tarps. The windrowswere mixed every third week in 1995 and once a monthin 1996 and 1997. An excavator was used to turn thewindrows by moving the compost soil 5 m along thewindrow length.

Measurement of Soil Gas-Components and Temperature

Before each mixing, the soil-gas composition in thecompost windrows was measured in perforated gascollection tubes installed inside the windrows. The O

2

and CO

2

concentrations were measured using aMultiwarn II (Dräger, Germany) gas meter. Additionalgas detector tubes (Dräger, Germany) were used forCO

2

and humidity measurements. The temperature in-side the windrows was measured using a 2-m-longtemperature probe. The temperature gradient was mea-

sured at 0.25-m-depth intervals, and the average tem-perature was calculated.

Air Sampling During the Mixing of Compost Windrows

Airborne particles were sampled during the mixing ofthe compost windrows using an Andersen (GrasebyAndersen, Atlanta, GA, USA) nonviable ambient parti-cle-sizing sampler with capacity of 1 actual cubic footper minute (ACFM), and the airborne microbes weresampled using an Andersen viable particle-sizing sam-pler. During the airborne particle sampling, each parti-cle-size level of the Andersen nonviable sampler wasloaded with a thin plate of 0.5% agar in water (approx-imately 6 to 7 g) on aluminum foil. PCDDs and PCDFswere extracted from the agar-water plates, and theirconcentrations were measured.

A one-stage Andersen PM10 sampler was used tomeasure particle mass, because it was not possible toweigh the water-agar plates. Each of two PM10 airsamplers collected 1.64 m

3

of air during the October 29,1996 mixing of the compost windrows. Air was collect-ed to pretreated and preweighed glass fiber filters thatwere weighed after air collection to measure particlemass.

Sampling Conditions

The sampling times varied from 8 to 30 min with an av-erage flow of 28 mL min

–1

. The air volume was mea-sured for each viable and nonviable sampler before andafter air collection. The samplers were situated on theground approximately 5 m from the windrows, with thewind direction mainly toward the samplers. To imitateexcavation and the worst-case scenario, a pile ofstacked contaminated soil was “artificially” mixed witha shovel at a distance of 1 m from the sampler. Thewind direction was variable during samplings becausethe compost windrows and the sawmill were situatedon a cape where the wind speed and direction changedrapidly. Air sampling was performed after removal ofthe tarps from the compost windrows (before mixing)as background measurements, and during the mixing inspring of 1996 and autumn of 1996. During the thirdparticle sampling in spring of 1997, background mea-surements were taken, both before the tarps were re-moved and after mixing of the windrows, on thelakeshore approximately 2 km away, opposite the capewhere the sawmill was located. Another set of back-ground samples was taken outside the laboratory inHelsinki before and after samplings at the sawmill area.

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Sampling equipment was rinsed with ethanol and driedbetween the samplings.

Table 1 shows the temperatures, gas conditions,and relative humidities in windrows and compost soilpores during the air sampling of particle-bound PCDDsand PCDFs. The water content of the windows rangedfrom 16 to 27%, the average temperatures in windrowsranged from 12 to 33°C, and the relative humidities inthe compost pores ranged from 35 to 74%.

Growth Media

The following selective growth media were used to enu-merate bacteria and fungi in airborne particles:

1

/

5

tryptone-glucose-yeast extract (TGY) medium and

1

/

2

tryptonesoy agar (TSA) with 0.005% of cycloheximide for enu-meration of bacteria, and R8 medium with 50

µ

g mL

–1

of cycloheximide for enumeration of actinomycetes;potato dextrose agar (PDA), pH 3.5 with tartaric acid,for enumeration of molds and yeasts; along with maltextract agar (MEA, Biokar, Beauvaise, France) andcornmeal agar (CMA), both containing 50

µ

g mL

–1

ofpenicillin and 50

µ

g mL

–1

of streptomycin, for enumer-ation of fungi. TGY, TSA, and R8 plates were incubat-ed at 28°C, whereas PDA, MEA, and CMA plates were

incubated at room temperature for 24 hours, 48 hours,or 5 days before counting.

Isolation and Identification of Airborne Microbes

From the collected air samples, 40 bacteria were iso-lated by repetitive plating and were identified using theBiolog

™

microbial identification system and by ana-lyzing the whole-cell fatty acid composition. Identifi-cation of the isolated strains was performed usingBiolog GN and GP MicroPlates

™

according to themanufacturer’s instructions (Biolog, 1993). The bacte-ria were pregrown overnight at 30°C on TSA (BectonDickinson, USA) or Biolog Universal Growth Medi-um (BUGM, Biolog Inc., USA). Biolog GN and GPMicroPlates

™

were incubated at 30°C for 4 and24 hours, and the absorbance was measured thereafterat 590 nm using a Biolog MicroPlate Reader. Thewhole-cell fatty acid composition was analyzed as de-scribed by Väisänen et al. (1994) using the MicrobialIdentification System (MIDI Inc. Newark, DE, USA).The isolates were pre-grown on Trypticase® soy brothagar (TSBA, Becton Dickinson, USA) medium at28°C for 24 hours before the cells were harvested and

Table 1.

Humidity, gas, and temperature measurements (as average ± SD) from compost windrows, soil pores, and

ambient air at time points for determining airborne PCDDs and PCDFs.

(a)

Windrow Soil

Compost Soil Pores

Ambient Air

Date andWindrow

Dry wt. inCompost

(%)

Aver.Temp.

(°C)H

2

O(mg/L)

RelativeHumidit

y(%)

O

2

(vol-%)CO

2

(vol-%)

Ambient

Temp.(°C)

Ambient

H

2

O(mg/L)

RelativeHumidity

(%)

5-31-96 23.1 nm

(b)

nmWindrow 1 75 ± 1.9 23 ± 1.7 9.5 ± 0.5 49 13.9 ± 0.9 7.5 ± 0.6Windrow 2 75.2 22 ± 0.3 10.5 ± 0.5 57 7.8 ± 2.2 13.5 ± 4.4Windrow 3 80 ± 4.4 18 ± 0.6 8.5 ± 0.5 59 14.6 ± 1.8 7.6 ± 1.5

8-27-96 22.5 10 50Windrow 1 77 ± 3 33 ± 1.2 14.5 ± 2.5 42 5.4 ± 0.2 16 ± 3.5Windrow 2 74 ± 0.9 28 ± 0.2 20 74 5.5 ± 0.4 17 ± 3.6Windrow 3 82 ± 0.6 24 ± 1 16 ± 1 74 14.4 ± 1.1 7.2 ± 1.5

10-29-96 11.1 nm nmWindrow 1 75 ± 3.2 17 ± 1.3 5.0 35 15.2 ± 0.7 7.4 ± 0.8Windrow 2 73 ± 0.6 14 ± 1.2 6.0 50 14.3 ± 1.3 7.5 ± 1Windrow 3 82 ± 1 12 ± 0.3 5.0 47 18.1 ± 0.3 3.2 ± 0.5

5-29-97

(c)

Windrow 1 76 ± 4 12.7 ± 0.6 nm nm nm nm 8.9 2.5 29Windrow 2 76 ± 0.3 nm nm nm nm nm 13.1 3 26Windrow 3 84.4 nm nm nm nm nm 18.5 2.5 16

(a)

The dates refer to the following terms in Table 3: May 31, 1996 = spring 1996; August 27, 1996 = autumn 1996, October 29,1996 = particle mass determined using PM10 samplers (see Materials and Methods section); May 29, 1997 = spring 1997.

(b)

nm = not measured.

(c)

Gas collection tubes were not installed because the sampling took place during the first mixing of compost windrows after winter.Ambient temperatures and humidities were measured three times: before, during, and after mixing of the windrows.

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the fatty acids were saponified, methylated, extracted,and finally analyzed using a gas chromatograph.

Determination of PCDDs and PCDFs

Abbreviations.

T = tetra-, Pe = penta-, Hx = hexa-,Hp = hepta-, and O = octachlorinated dibenzo-

p

-dioxin(CDD) and dibenzofuran (CDF).

Analytical Procedure.

An agar sample was spikedwith internal

13

C-labeled PCDD and PCDF standards(115 pg per sample, 16 congeners of 2,3,7,8-chlorinat-ed PCDD and PCDF). The agar sample was extractedwith toluene, the solvent was exchanged to hexane withnonane as a keeper, and the sample was dried overnightwith Na

2

SO

4

(Vartiainen et al., 1997). The sample wasdefatted in a silica gel column (MN-Kieselgel 60, 70, to230 mesh), and separation of PCDDs and PCDFs fromPCBs was performed on an activated carbon column(Carbopack C, 60/80 mesh) containing Celite (Merck2693). The sample was further purified with an activat-ed alumina column (Merck 1097, standardized, activitylevel II to III). Next,

13

C-labeled 1,2,3,4-TCDD and1,2,3,7,8,9-HxCDD were added to the sample as recov-ery standards and the solvent was exchanged to nonane.

The sample was analyzed with a high-resolutionmass spectrometer (VG 70-250 SE) equipped with afused silica capillary column (DB-Dioxin, 60 m,0.25 mm, 0.15

µ

m). The quantitation of PCDDs and

PCDFs was performed by selective ion recording usinga resolution of 10,000. Blank agar, laboratory reagent,and equipment blank samples were treated and ana-lyzed by the same method as the experimental samples,with one blank for five samples. Recoveries for internalstandards were more than 60% for all congeners.

Results

Microbial Release During Composting

The amounts of airborne actinomycetes were between100 and 600 compared to the background value of100 CFU m

–3

(Figure 2). The number of airborne bacteriadetected for windrows 1 and 2 ranged from 200 to1000 CFU m

–3

compared to the background value of200 CFU m

–3

(Figure 2); 4 to 20 times more airborne bac-teria, 3500 CFU m

–3

, were detected for windrow 3. In thecompost windrow soils, the average number of bacteriagrowing on TGY plates was 10

8

CFU (kg dry wt)

–1

. Ofthe 40 isolated airborne bacteria, 32 were Gram-positive,and many of them were spore-forming bacilli (Table 2).

PCDDs and PCDFs in Compost Soils

The concentrations of PCDDs and PCDFs were mea-sured in compost soils during the composting period in1995. High concentrations up to 1 mg (kg dry wt)

–1

oftotal PCDDs and PCDFs were measured (Figure 3).

Figure 2.

Amounts of culturable airborne microbes collected during mixing of the compost windrows. TSA = tryptone soy agar;TGY = tryptone-glucose-yeast extract, R8 = R8 medium (Amner et al., 1989); MEA = malt extract agar; CMA = cornmeal agar; andPDA = potato dextrose agar.

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The concentrations of PCDDs and PCDFs did notchange during the composting. The isomer distributionwas typical for a sawmill site contaminated with thewood preservative Ky-5: OCDFs and HpCDFs werethe predominating isomers; the next most abundantPCDD/PCDF isomer was the HxCDFs (Laine et al.,1997a; Vartiainen et al., 1995b). Ky-5 contained thesedioxin isomers as impurities. The results suggest thatPCDDs and PCDFs were neither formed nor biode-graded during the composting of contaminated sawmillsoil.

PCDDs and PCDFs in Airborne Particles

Airborne particles were collected three times duringmixing of the compost windrows for dioxin analysis: inspring and autumn 1995, and in spring 1996. The rela-tive concentrations of different PCDD and PCDF iso-mers in each particle-size fraction were calculated fromthe measured values (Figure 4). The isomer distribu-tions of PCDDs and PCDFs were similar in differentparticle-size fractions, although the amounts of PCDDsand PCDFs were different in the different size classes.The results show that the isomer distribution of PCDDsand PCDFs in collected airborne particle fractions wassimilar to the distribution in the compost windrows,suggesting that the source of PCDDs and PCDFs wasthe contaminated soil being remediated. However, it

Table 2.

Isolated and identified bacterial species collected from different particle-size fractions during mixing of the compost windrows. Number of isolates, if more than one, identified as the same species is given

in parentheses.

Level[particle size]

Bacterial Species Identified

Windrow 1 Windrow 2 Windrow 3

Level 1[

≥

7

µ

m]

Curtobacterium flaccumfaciensRhodococcus erythropolis

Bacillus sphaericusPseudomonas stutzeri

No identification (id)

Bacillus sphaericusArthrobacter viscosusSphingobacterium multivorumCellulomonas flavigenaMicrococcus agilis

No id (2)Level 2

[4.7 to 7

µ

m]

Rahnella aquatilis

Level 3[3.3 to 4.7

µ

m]

Clavibacter michiganenseArthrobacter pascens

Pseudomonas putida

biotype B

Rhodococcus erythropolis

(2)

Bacillus mycoidesBacillus badiusRhodococcus erythropolis

(2)Level 4

[2.1 to 3.3

µ

m]

Rhodococcus erythropolis Pseudomonas aeruginosa

Level 5[1.1 to 2.1

µ

m]

Pseudomonas syringaeStreptoverticillium reticulum

Bacillus thuringiensis/cereusBacillus sphaericus

Level 6[0.65 to 1.1

µ

m]

Bacillus megaterium

Figure 3.

Distribution of PCDDs and PCDFs in compost wind-row 2 at different time points during composting in 1995. Thesamples were analyzed to the congener level. The results areshown as sums of isomers.

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Fig

ure

4.

Rel

ativ

e is

omer

dis

trib

utio

n (a

s %

) of

PC

DD

s an

d P

CD

Fs

in e

ach

airb

orne

par

ticle

siz

e cl

ass

colle

cted

dur

ing

mix

ing

of th

e co

mpo

st w

indr

ows.

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seemed that slightly lower proportions of OCDFs werefound in the airborne particles than in the soil (Figure 4).

The concentrations of particle-bound PCDDs andPCDFs in air were between 200 pg m

–3

for the back-ground and 19,000 pg m

–3

during shovel-mixing of thestacked contaminated soil (Table 3). The latter simulat-ed excavation conditions when a large amount of dustis released (Figure 1), and thus can be regarded as theworst-case situation when handling contaminated saw-mill soil.

Blank agar plates, where no air was collected, wereanalyzed for their PCDD/PCDF content. In spring of1996, three blank agar plates were equivalent to 1920pg m

–3

of the PCDDs and PCDFs, assuming that0.29 m

3

of clean air had passed through eight plates(Table 3). In spring of 1997, blank agar plates (16 total)with aluminum foil and two samples of agar (6 to 7 geach) were analyzed. The average sum of the PCDDsand PCDFs was 5 pg in each plate, equivalent to160 pg m

–3

of the PCDDs and PCDFs, based on similarassumptions. The detection limits were 0.5 pg forOCDD and OCDF and 0.05 pg for the other PCDDsand PCDFs. Thus, the theoretical detection limit wasbetween 1.4 and 14 pg m

–3

with a sampling volume of0.29 m

3

.

A one-stage Andersen PM10 sampler was used todetermine particle mass, because it was not possible toweigh the water-agar plates. Two parallel samplerswere used to collect 1.64 m

3

of air. The average particlemass was 32 µg m–3. The concentrations of PCDDs andPCDFs were 5.42 and 12.3 pg m–3, respectively.

Discussion

Bioaerosols During Bioremediation

Andersen nonviable and viable samplers used for thecollection of airborne particles are designed to simulatethe human respiratory system. The samplers have 6 or8 levels, which collect different size fractions of air-borne particles with diameters from 0.43 µm to 10 µm.

Mixing of different kinds of composting materialsinvolves a release of bioaerosols. Airborne dust fromgarden compost during shoveling released 106 to 108

CFUs of fungi per m3 and 105 to 108 CFUs of bacteriaper m3, most of them being Gram-negative, endotoxin-producing bacteria (Weber et al., 1993). At a municipalcompost plant site, 30,000 CFUs of airborne Gram-negative bacteria per m3 were reported (Lundholmand Rylander, 1980). Turning the active windrows ofthe leaf and yard material released between 700 and140,000 CFUs of airborne bacteria and fungi per m3

(van der Werf, 1996). In comparison, the overall levelsof airborne bacteria during bioremediation in our study(200 to 3500 CFUs per m3) were low. Usually at indus-trial sites and wood-preserving facilities, the amountsof fungi are higher than at our sawmill site duringbioremediation (Simeray et al., 1997; Stetzenbach,1997). The reason for this could be that the compostingwas performed at neutral pH to select for bacterial deg-radation instead of fungal activities.

The straw compost used in our study as the inocu-lum was rich in actinomycetes, which may indicate ahealth hazard. Thermophilic actinomycetes, generally

Table 3. PCDDs and PCDFs in airborne particles collected at three different time points of composting.

SamplingTime

Polychlorinated PCDDs and PCDFs

At Sawmillbefore→after

mixingAt Sawmill

during mixing

Near Sawmillbefore→after

mixing

Helsinki Areabefore→after

samplingBlank AgarSamples(a)

total concentration as pg/m3

Spring 1996 14,000→nm(b) 630 to 19,000 nm nm 1920Autumn 1996 4400→nm 8500 to 12,000 nm nm nmSpring 1997 200→240 270 to 870 220→300 200→320 160

pg I-TEQ/m3 (c)

Spring 1996 84→nm 3.7 to 100 nm nm nmAutumn 1996 20→nm 31 to 50 nm nm nmSpring 1997 2.7→3.6 2.9 to 5.8 1.7→4.8 2.0→4.4 nm

(a) The blank agar plate values were calculated from the average sum of the PCDDs and PCDFs inthe blank agar plates as if 0.29 m3 of clean air would have been passed through eight plates.

(b) nm = not measured.(c) International 2,3,7,8-TCDD toxic equivalent (Safe, 1992).

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considered the most harmful, were scarce because thetemperature in the contaminated soil windrows rarelyexceeded 35°C.

In our study, most of the isolated airborne bacteriawere Gram-positive and spore-forming, although themajority of bacteria (70 out of 100 isolated ones) in thecontaminated soil (Laine, 1998) were Gram-negative.This difference is expected because Gram-positive bac-teria tolerate stress during air transport better than doother bacteria (Stetzenbach, 1997). However, we didnot place emphasis on selectively collecting Gram-neg-ative bacteria from air.

Airborne microorganisms are stressed duringtransport and collection and may not respond to incuba-tion conditions in the laboratory (Kingston, 1971). Fun-gal and bacterial spores, enteric viruses, and amoebiccysts are somewhat resistant to environmental stressesencountered during transport through the air. Bacteriaand algae are more susceptible, although bacterial en-dospores (e.g., Bacillus spp.) are quite resistant (Knud-sen and Spurr, 1987). Gram-positive cocci and Bacillusspp. are common airborne organisms that do not causeadverse health effects (Stetzenbach, 1997). In summa-ry, bacterial airborne pathogens usually are Gram-neg-ative, endotoxin-producing organisms found inmunicipal waste treatments but not in contaminatedsoil.

Two of the identified airborne bacteria, Pseudomo-nas aeruginosa and Bacillus cereus, may cause humandisease and are classified in hazard group 2 by the Ad-visory Committee on Dangerous Pathogens (Depart-ment of Health, United Kingdom, 1995). Otheridentified bacteria were not known to demonstratepathogenic potential.

Airborne PCDDs and PCDFs During Bioremediation

The levels of particle-bound PCDDs and PCDFs in air atthe composting site ranged from 200 to 19,000 pg m–3

(Table 3), which was 1000-fold higher than the atmo-spheric background values reported previously (Table 4).

Our studies support previous findings that the mosttoxic dioxin isomer, 2,3,7,8-TCDD, is not recovered inambient air (Christmann et al., 1989; Edgerton et al.,1989; Hunt and Maisel, 1990; Rappe et al., 1989). Oth-er researchers have used high-volume air samplers thatcollect hundreds or thousands of cubic meters of air toquartz microfiber filters (particulates) and polyure-thane foam (PUF, vapor phase) (Table 4).

It was shown by Kurokawa et al. (1996a,b) and Na-kano et al. (1990) that most of the airborne PCDDs andPCDFs are found in the particulate phase. However,Bidleman (1988) stated that the fraction of particulate-

Table 4. Comparison of the total concentrations of PCDDs and PCDFs in air particles in ambient air in different industrial and rural areas.

Sampling Volume and Apparatus Air Collection Site

Total PCDDs and PCDFsin Air Particulates,

pg m–3 Ref.

High-volume air sampler, 24 h on quartz microfiber filter

Urban air in Japan PCDDs < 0.1 to 28.2(mean 4.8, N = 24) PCDFs < 0.1 to 22.4 (mean 2.8, N = 24)

Nakano et al., 1990

Glass fiber filters with high volume (1500 m3) air sampler

Urban air in Göteborg, Sweden

2.43 to 13.39 (mean 6.09, N = 3)

Rappe et al., 1989

Rural area in Rörvik, Sweden

0.24 to 4.49 (mean 1.53, N = 6)

Medium low-volume sampler (0.2 m3 min–1) with quartz fiber filter and PUF plug, long collection time (3 to 7 d), volume of the collected air 860 to 2020 m3

Industrial and urban sites in Ohio, USA

1.9 to 9.9 Edgerton et al., 1989

Rural area in Waldo, Ohio, USA

3.6

Low-volume sampling (0.05 m3 min–1) for prolonged time of 10 to 14 days, volume of the collected air 700 to 1000 m3, with PUF

Near a copper smelter in Austria

Both particulate and vapor phase 72.8 to 128 (mean 98, N = 4)

Christmann et al., 1989

Ambient air in Berlin, Germany

Both particulate and vapor phase 9.5 to 22 (N = 15)

High-volume air sampler, 1600 to 2500 m3 of air collected on quartz fiber filter, fractionation to five particle sizes

Urban, industrial, and rural areas in Japan

14.6 to 24.6 (mean 18, N = 3)

Kurokawa et al., 1996b

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bound organochlorines from high-volume experimentsis lower than predicted. Moreover, Fairless et al. (1987)noticed that an increasing sample volume (samplingtime) moved spiked TCDD and TCDF from the quartzfilter to the PUF, thus causing blow-off losses. Wateragar may have properties that trap more particles thando dry samplers; it has been shown that wet surfacescollect 1.5 to 3 times more organochlorine depositionthan do dry surfaces of the same geometry (Christensenet al., 1979).

The heights at which samples were collected mayhave affected the number of particles collected. Wesampled at ground level, except that collection of parti-cles using an Andersen PM10 one-stage sampler wasperformed at standardized conditions: 5 m from thewindrows at 1.5 m height. The concentrations ofPCDDs and PCDFs were 1000-fold lower than thoseobtained with an Andersen multistage sampler; thus,these concentrations were on the same level as previ-ously reported high-volume samples from ambient air(Table 4). One reason for the high concentrations andhigh variation could be that large quantities of particlesare produced during mixing of the compost windrows.

According to studies of Kurokawa et al. (1996b),particles of diameter less than 1.1 µm accounted formore than 50% of the total amount of PCDDs andPCDFs. In our study, the amounts of PCDDs andPCDFs varied randomly among different size fractions,but most of the PCDDs and PCDFs were recovered infractions larger than 1.1 µm (Laine, 1998).

The concentrations of PCDDs and PCDFs in air-borne particles during the mixing of compost windrowsvaried largely among the different samplings. It is dif-ficult to evaluate whether the differences were due to atrue variation in the environmental conditions, back-ground contamination, or analytical/methodologicalproblems. This is a trace analysis, and low air-volumemeasurements manifold the error. The present casestudy included only three sampling times during themixing of the compost windrows. Even though no rep-licate samples were taken, more than 150 air samplerplates were analyzed.

Evaluation of Health Effects During the Composting

The average human inhales approximately 10 m3 of airper day (Lynch and Poole, 1979). Composts usuallywere turned six times during the summer period. Everymixing lasted approximately 2 hours, but a working dayat a sawmill lasts for 8 hours. Thus, workers in the saw-mill area inhaled approximately 48 m3 of air during thattime. A cumulative dose of particles containing PCDDsand PCDFs as calculated per average daily intake was

between 0.1 and 4.8 ng of PCDDs and PCDFs as inter-national 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) toxic equivalent (I-TEQ) during mixing of thecompost windrows in one summer season. That doseequals the amount of PCDDs and PCDFs taken in byeating 1 kg of Finnish lake fish, pike, which contains0.2 to 0.5 ng of PCDDs and PCDFs as I-TEQ per kg, orby eating 100 g of Baltic salmon (Vartiainen et al.,1995b). For a 70-kg person, the daily intake will be be-tween 1.4 and 69 pg I-TEQ/kg/day. This maximum val-ue in the summer season is about 20 times highercompared to the acceptable daily intake (ADI) given bythe Nordic countries, i.e., 35 pg I-TEQ/kg/week (Nord-isk Ministerråd, 1988). However, the ADI value is giv-en for the lifetime exposure and not just for theoccupational exposure.

Acknowledgments

We thank Kirsi Sirkiä at the Finnish Environment Insti-tute, as well as Riitta Boeck and Heidi Pelkonen at theUniversity of Helsinki, for skillful laboratory assis-tance, and we thank Teija Strandman at the NationalInstitute of Public Health for calculating the concentra-tions of dioxin congeners. We also appreciate the coop-eration with Juha Hiltunen at the Vääksy sawmill. Thiswork was supported by the Academy of Finland(Restore2000 program).

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bioaerosols and particle release during composting of contaminated sawmill soil

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