Chemosphere 104 (2014) 25–31

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Chemosphere

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Occupational exposure to solid chemical agents in biomass-fired powerplants and associated health effects

0045-6535/$ - see front matter � 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.chemosphere.2013.10.025

⇑ Corresponding author. Tel.: +358 30 474 7242; fax: +358 30 474 7474.E-mail address: mika.jumpponen@ttl.fi (M. Jumpponen).

M. Jumpponen a,⇑, H. Rönkkömäki b, P. Pasanen c, J. Laitinen a

a Finnish Institute of Occupational Health, Neulaniementie 4, FI-70101 Kuopio, Finlandb Finnish Institute of Occupational Health, Topeliuksenkatu 41 a A, FI-00250 Helsinki, Finlandc University of Eastern Finland, Department of Environmental Sciences, Yliopistoranta 1, FI-70211 Kuopio, Finland

h i g h l i g h t s

�Multiple exposures to metals were inevitable among workers.� Heavy metals can affect the CNS and RS, and increase risks for cancer.� Compressed air breathing apparatus is the best form of protection.

a r t i c l e i n f o

Article history:Received 12 February 2013Received in revised form 18 September 2013Accepted 8 October 2013Available online 27 November 2013

Keywords:Biomass-fired power plantOccupational exposureInhalable dustMultiple metal exposureCrystalline silica

a b s t r a c t

Occupational exposure to aluminium, arsenic, lead, cadmium, and manganese can increase the risk ofnumerous neurophysiological changes in workers, and may lead to conditions resembling Parkinson’sand Alzheimer’s disease. However, although the health hazard aspect of these agents has been examined,biomass-fired power plant workers’ exposure to them remains a neglected issue. The purpose of thisstudy was to measure maintenance and ash removal workers’ multiple exposures to inhalable dust, met-als, and crystalline silica during their work tasks in biomass-fired power plants. Maintenance and ashremoval workers were exposed to high inhalable dust concentrations inside biomass-fired boilers. Themedian air inhalable dust concentration in workers’ breathing zones were 33 mg m�3 and 120 mg m�3

in ash removal and maintenance tasks, respectively. The median concentration of manganese(0.31 mg m�3) exceeded the occupational exposure limit in worker’s breathing zone samples in mainte-nance tasks. The most evident exposure-associated health risk from multiple exposures to metals wasthat of cancer, followed by central nervous system disorders, lower respiratory tract irritation, and finallyupper respiratory tract irritation. To avoid the above mentioned health effects, powered air respiratorswith ABEK + P3 cartridges and carbon monoxide gas detectors are recommended as the minimumrequirement for these work tasks. A compressed air breathing apparatus is the best form of protectionfor the most demanding work phases inside boilers in biomass-fired power plants.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

Maintenance and ash removal work is usually performed indemanding work postures inside boilers. During these work tasks,workers are exposed to power plant ashes and various dusts, gases,volatile organic compounds (VOCs) and polycyclic aromatic hydro-carbons (PAHs) (Heating and Boiler Plant Equipment Mechanic,5309., 1992; Hicks and Yager, 2006; Mani et al., 2007; Khanet al., 2009; Jumpponen et al., 2013). Power plant ash is reportedto contain both the major (Al, Ca, Fe, K, Mg, Na, P, Si, Ti) and minor(As, Ba, Cd, Co, Cr, Cu, Hg, Mn, Mo, Ni, Pb, Sb, TI, V, Zn) elementsthat are formed from solid biomass, together with Cl and S

(Obernberger et al., 2006; Khan et al., 2009). Formed ash has beenreported to contain toxic heavy metals as well as carcinogeniccrystalline silica (Shukla and singhal, 1984; Celik et al., 2007;Garcon et al., 2007; Mani et al., 2007; Halatek et al., 2009; Walton2011). More precise examination of metals has shown that expo-sure to aluminium (Al) can cause neurological and respiratory dis-eases. Chronic routine exposure to low-dose levels of aluminiummay be a causative factor in Parkinson’s and Alzheimer’s disease(Walton, 2011). Arsenic (As) and its inorganic compounds affectnumerous systemic functions and organs, such as the nervousand haematopoietic systems, the liver, kidneys, and the skin. Theeffects of nervous system exposure to As may cause impaired con-duction velocity in the peripheral motor or sensory nerves. Thesymptoms are paresis or numbness, or numerous neurophysiologicchanges (Halatek et al., 2009). Chronic occupational exposure to

26 M. Jumpponen et al. / Chemosphere 104 (2014) 25–31

inorganic forms of lead (Pb) and/or cadmium (Cd) can causenephropathy, which usually starts insidiously (Garcon et al.,2007). Chronic, low-level occupational manganese (Mn) exposureis also prevalent among smelters and welders, and can lead toirreversible damage to neurological structures. The neurologicalsigns and symptoms of manganism are similar to those of idio-pathic Parkinson’s disease (Cowan et al., 2009). Crystalline silicawhen inhaled is carcinogenic to humans (Group 1) (WHO, 1997).Coal fly ash in particular has been reported to contain significantamounts of crystalline silica (Van Maanen et al., 1999). Silicaoccurs in both crystalline and amorphous forms. Of the severalcrystalline polymorphs of silica found in nature, crystalline silicais by far the most common, being abundant in most rock types,sands and soils (WHO, 1997).

Although it seems obvious that the most detected heavy metalsand crystalline silica have additive or even synergistic healtheffects, multiple exposures to Al, As, Pb, Cd, and Mn have not con-sistently been taken into account in exposure assessments. Thepurpose of this study was to measure workers’ multiple exposureto inhalable dust, metals, and crystalline silica during maintenanceand ash removal tasks in eight biomass-fired power plants, and toevaluate the possible exposure-associated additive and synergistichealth effects of the exposing agents.

2. Materials and methods

2.1. Biomass-fired power plants

Eight biomass-fired power plants were sampled during this sur-vey in Finland. Plants that were willing to participate in the studywere randomly selected from a list. We also randomly selectedworkers with different work tasks at the power plants. The capac-ity of biomass-fired power plants ranged from small, 0.3 MW, tolarge, 110 MW. Pellets were the main fuel in two of the plants(total thermal input 0.3–0.7 MW), wood in three (total thermalinput 17–40 MW), and peat in another two (total thermal input4.5–110 MW). Recycled fuels were used in one biomass-firedpower plant, although peat remained its main fuel.

2.2. Test group

We visited each biomass-fired power plant twice in the summerof 2010, and measured the exposure of 35 male workers (with anaverage age of 37 and standard deviation of 11 years) both insideand outside the biomass-fired power plant boilers. We first mea-sured the ash removal workers’ occupational exposure (n = 18) toinhalable dusts, metals (Al, As, Pb, Cd, Mn, Se, Be, and Th), andrespirable crystalline silica inside the boilers. We then did thesame for maintenance workers (n = 5) during their tasks insidethe boilers. The work tasks performed were recorded during directobservation of the workers’ activities.

2.3. Sampling methods and quality of sampling

We measured the concentrations of inhalable dusts (n = 64);metals Al (n = 32), As (n = 32), Pb (n = 31), Cd (n = 32), Mn(n = 32), Se (n = 31), Be (n = 32), and Th (n = 32); and respirablecrystalline silica (n = 15) in the air of the biomass-fired powerplants. The sampling pumps were calibrated before sample taking.Air samples were collected from the breathing zones of workers orfrom stationary sampling points during the ash removal and main-tenance tasks. The sampling periods varied from 53 min to464 min, because some of the work tasks were carried out in veryshort period of time (partial shifts) whereas others constituted fullshifts. When all dust samples were taken into account, the average

sampling period was 3 h and 17 min. The stationary samplingpoints for each task were located next to the workers. The inhala-ble dusts and metals were collected in an IOM sampler ((Millipore-filter, 25 mm AAWP, pore size 0.8 lm), and respirable crystallinesilica in an IOM foam sampler (Millipore-filter, 25 mm AAWP, poresize 0.8 lm, foam (MultiDust Foam Discs for Respirable Sampling,SKC Inc.)) at a calibrated flow rate of 2.0 L min�1. After sample col-lection, we gravimetrically analysed the filters of all IOM samples.The metal and crystalline silica analysis of the samples used theICP/MS technique (NIOSH 7303, 2003) and FT-IR technique (NIOSH7602, 1994), respectively.

The Client Services of the Finnish Institute of OccupationalHealth, T013, is an accredited test laboratory that specializes inchemical exposures and aerosol specification in work environ-ments/indoor air. The sample collection and laboratory analysismethod of inhalable dust, metals, and respirable crystalline silicamentioned in this article falls under the purview of accreditation.

2.4. Mixie computer-based tool for evaluating the risks of multipleexposures to metals

The American Conference of Industrial Hygienists (ACGIH�) rec-

ommends that the presence of all contaminants that have similareffects on the same organs or systems of the human body shouldbe taken into account in exposure assessment. These exposuresshould be added together rather than considered individually.The MIXIE programme for evaluating multiple exposures can beused to determine additive interactions of exposures. If interac-tions are found, this programme can add these exposures together(Vyskocil and Droled, 2010). In our study, we used this computer-based tool for evaluating the risks posed to the workers by themetals. We used the average concentrations of the metals to obtaininformation on the worst-case exposure in the different work tasksin biomass-fired power plants, as advised in standard SFS-EN 689(1996). The measured metals (Al, As, Pb, Cd, Mn, Se, Be) and theirconcentrations were fed into the MIXIE programme. The first levelof the secondary literature analysis of the MIXIE results revealedfour different combined effects of the analysed metals (cancer, cen-tral nervous system disorders, and irritation of the upper and lowerrespiratory tract), and the metals that were responsible for theseeffects. The second level of the analysis of the MIXIE primary liter-ature results provided information regarding the interactions(additive and supra-additive effects) of the analysed metals.

2.5. Statistical analysis of data

For statistical analysis, we determined the exposure-associatedneurological effects of metals Al, As, Pb, Cd, Mn, Se and Be amongthe workers in ash removal and maintenance tasks. We used theaverage values of each metal that was responsible for exposure-associated health risks in the biomass-fired power plants, and con-verted the values (mg m�3) to percentage values using the FinnishOEL of the metals. Our statistical analyses used SAS for Windows9.2, and we used one-way ANOVA to analyse the differences be-tween the means of groups (biomass-fired power plants), accord-ing to the generalized linear model (GLM) procedure. Weseparately analysed the data of the acute health hazards (cancer,central nervous system disorders, and upper and lower respiratorytract irritation) of the metals in the biomass-fired power plants.We used Tukey’s multiple comparison method to determine anysignificant differences (p < 0.05 (�)) between the acute health haz-ards of different biomass-fired power plants, classified by hazardand type of biomass-fired power plant.

M. Jumpponen et al. / Chemosphere 104 (2014) 25–31 27

3. Results and discussion

3.1. Concentrations of inhalable dust and crystalline silica

We measured the inhalable dust in the workers’ breathingzones during ash removal and maintenance tasks. The median con-centration of inhalable dust was 33 mg m�3 in ash removal tasks,and 120 mg m�3 in maintenance tasks. These concentrations were330% and 1200% of the Finnish OEL (10 mg m�3) of inorganic dustduring these tasks, respectively. The concentrations of inhalabledust ranged from 1.3 mg m�3 to 290 mg m�3 during ash removaltasks and from 20 to 260 mg m�3 during maintenance tasks. Work-ers’ exposure to inhalable dust exceeded the OEL of inorganic dustin 83% of the air samples in ash removal tasks and in 100% of the airsamples in maintenance tasks (Table 1). Wojtczak et al. (1989)studied workers’ exposure to dust in power plants and thermoelec-tric power stations, and found that the mean concentration ofrespirable dust exceeded its hygienic standard value in 64% ofpower plants.

We also measured inhalable dust at stationary sampling pointsinside boilers’ and superheaters’ air, as well as outside the boilers.The highest median air concentration of inhalable dust at station-ary sampling points was measured during ash removal tasks insidethe boilers (boilers’ air and superheaters’ air), where the medianconcentration of inhalable dust was 20 mg m�3. During mainte-nance tasks inside the boilers, the median concentration of inhala-ble dust was 4.8 mg m�3. Outside the boilers, the median airconcentration of inhalable dust was 0.5 mg m�3 and 2 mg m�3 dur-ing ash removal and maintenance tasks, respectively. At stationarysampling points, air concentrations of inhalable dust exceeded theOEL of inorganic dust in 80%, 25%, 10% and 0% of the air samples inash removal tasks inside the boilers, during maintenance tasks in-side the boilers, during maintenance tasks outside the boilers, and

Table 1Summary of concentrations of inhalable dust (mg m�3) and crystalline silica (mg m�3) in

Agent and sampling location No. of samples Median

Dust (mg m�3)Ash removal tasksPersonal samples 18 33Stationary samples inside boilers 10 20Stationary samples outside boilers 17 0.5

Maintenance tasksPersonal samples 5 120Stationary samples inside boilers 4 4.8Stationary samples outside boilers 10 2.0

Wood-fired power plants (S)Ash removal inside boilers 7 130Ash removal outside boilers 6 0.5Maintenance outside boilers 2 2.9

Peat-fired power plants (S)Ash removal inside boilers 9 16Ash removal outside boilers 4 0.9Maintenance inside boilers 4 9.4Maintenance outside boilers 2 1.4

Recycled fuel-fired power plants (S)Ash removal inside boilers 4 34Ash removal outside boilers 6 0.5Maintenance inside boilers 1Maintenance outside boilers 2 0.9

Pellet-fired power plants (S)Ash removal inside boilers 2 22Ash removal outside boilers 5 3.4

Respirable crystalline silica (mg m�3)Respirable crystalline silica a 15 0.07

S = Stationary sample.a Total amount of silica (includes amorphous and crystalline silica).

during ash removal tasks outside the boilers, respectively. Inhala-ble dust concentrations varied between different types of bio-mass-fired power plants. The median concentrations of inhalabledust were 130 mg m�3, 16 mg m�3, 34 mg m�3, and 22 mg m�3 inthe wood-fired power plants, peat-fired power plants, the recycledfuel-fired power plant, and the pellet-fired power plants, respec-tively. At these stationary sampling sites, air concentrations ofinhalable dust exceeded the OEL of inorganic dust in 100%, 100%,100% and 78% of the air samples in the wood-fired power plants,the recycled fuel-fired power plant, the pellet-fired power plants,and the peat-fired power plants, respectively. In the maintenancetasks inside the boilers the highest median air concentrations ofinhalable dust was 9.4 mg m�3 in the peat-fired power plants(Table 1). The inhalable dust concentrations were smaller outsidethe boilers. During ash removal tasks outside the boilers, the med-ian air concentrations of inhalable dust were 0.5 mg m�3,0.9 mg m�3, 0.5 mg m�3, and 3.4 mg m�3 in the wood-fired powerplants, peat-fired power plants, the recycled fuel-fired power plant,and the pellet-fired power plants, respectively. All measured con-centrations, except one sample in the pellet fired power plant(17 mg m�3), were below the OEL of inorganic dust. The medianair concentrations of inhalable dust during maintenance tasks out-side the boilers were 2.9 mg m�3, 1.4 mg m�3, and 0.9 mg m�3 inthe wood-fired power plants, peat-fired power plants, and therecycled fuel-fired power plant, respectively, and did not exceedthe OEL of inorganic dust. Bird et al. (2004) found that 0.3% of airsamples exceeded the permitted occupational exposure value dur-ing routine workers’ activities in coal-fuelled power plants. In ourstudy, only one inhalable dust sample exceeded the OEL of inor-ganic dust outside the boilers during work tasks (Table 1).

An analysis of crystalline silica revealed that amorphous silicawas a disturbing factor when the concentration of the respirabledust was over 5.3 mg m�3. Due to analytical problems with the

biomass-fired power plants.

Range Mean ± SD Prevalence of agents over OEL (%)

1.3–290 93 ± 104 830.8–120 46 ± 47 800.2–9.1 1 ± 2 0

20–260 122 ± 105 1000.5–14 6 ± 6 250.2–53 7 ± 16 10

14–290 175 ± 106 1000.2–1.5 1 ± 1 02.1–36 3 ± 1 0

1.0–200 63 ± 71 780.5–3.0 1 ± 1 04.7–20 11 ± 8 500.8–2.0 1 ± 1 0

15–120 53 ± 43 1000.2–9.1 2 ± 4 09.0 00.4–1.4 1 ± 1 0

11–32 22 ± 15 1000.4–17 5 ± 7 20

<0.2–0.5 0.2 ± 0.2

Table 2Summary of concentrations of metals (mg m�3) in breathing zone samples of workers in biomass-fired power plants.

Agent and sampling location No. of samples Median Range Mean ± SD Prevalence of agents over OEL (%)

Ash removal tasksAluminium 16 1.35 0.013–5.3 2.0 ± 2.0 38Manganese 16 0.185 0.008–3.1 0.7 ± 1.1 50Lead 15 0.018 0.0002–0.53 0.07 ± 0.2 13Cadmium 16 0.0004 <0.0001–0.03 0.003 ± 0.007 6Arsenic 16 0.0007 <0.0001–0.08 0.007 ± 0.02 0Selene 16 0.0004 <0.0001–0.01 0.002 ± 0.003 0Beryllium 16 0.0001 <0.0001–0.0002 0.0001 ± 0.00003 0Thorium 16 0.0005 <0.0001–0.002 0.0006 ± 0.0005

Maintenance tasksAluminium 5 0.42 0.12–4.5 1.9 ± 2.2 40Manganese 5 0.31 0.08–0.8 0.4 ± 0.3 80Lead 5 0.0053 0.002–0.05 0.02 ± 0.02 0Cadmium 5 0.0002 0.001–0.002 0.0007 ± 0.0009 0Arsenic 5 0.003 0.001–0.005 0.003 ± 0.001 0Selene 5 0.0001 <0.0001–0.0001 0.0001 ± 0 0Beryllium 5 0.0001 <0.0001–0.0001 0.0001 ± 0 0Thorium 5 0.0013 <0.0001–0.003 0.001 ± 0.001

28 M. Jumpponen et al. / Chemosphere 104 (2014) 25–31

FT-IR technique, we only obtained the sum results of amorphousand crystalline silica. The average sum concentration of crystallineand amorphous silica was 0.2 mg m�3 (Table 1.).

3.2. Prevalence and concentrations of metals

The most commonly found metals whose air concentrations ex-ceeded the OELs of metals (prevalence) in workers’ breathing zonesamples were Al and Mn. Their median concentrations were

Table 3Summary of concentrations of metals (mg m�3) in stationary samples in biomass-fired po

Agent and sampling location No. of samples Median Range

Ash removal inside boilersAluminium 4 1.08 0.01–Manganese 4 0.275 0.002Lead 4 1.0035 0.000Arsenic 4 0.0097 <0.00Cadmium 4 0.0015 <0.00Selene 4 0.0001 <0.00Beryllium 4 0.0001 <0.00Thorium 4 0.0001 <0.00

Ash removal outside boilersAluminium 1 0.01Manganese 1 0.007Lead 1 0.000Arsenic 1 <0.00Cadmium 1 <0.00Selene 1 <0.00Beryllium 1 <0.00Thorium 1 <0.00

Maintenance inside boilersAluminium 3 0.12 0.03–Manganese 3 0.024 0.018Lead 3 0.003 0.003Arsenic 3 0.0002 0.000Cadmium 3 0.0001 <0.00Selene 3 0.0001 <0.00Beryllium 3 0.0001 <0.00Thorium 3 0.0001 <0.00

Maintenance outside boilersAluminium 3 0.13 0.1–0Manganese 3 0.026 0.02–Lead 3 0.0003 0.000Arsenic 3 0.0001 <0.00Cadmium 3 0.0001 <0.00Selene 3 0.0001 <0.00Beryllium 3 0.0001 <0.00Thorium 3 0.0001 <0.00

0.42–1.35 mg m�3 and 0.19–0.31 mg m�3, respectively. These con-centrations of Al and Mn were 68% and 95% of their Finnish OEL forash removal tasks, and 21% and 155% of the OEL for maintenancetasks, respectively (Table 2). The OELs of Al and Mn were exceededin 38–50% of the ash removal task samples and in 40–80% of themaintenance task samples, respectively. Liu et al. (2005) studiedboilermakers’ exposure to Mn during the overhaul of an oil boiler,and found that manganese concentrations in personal sampleswere 4.6 lg m�3. The median air concentrations of Mn in our study

wer plants.

Mean ± SD Prevalence of agents over OEL (%)

6.9 2.3 ± 3.2 25–0.55 0.3 ± 0.2 751–4.5 1.6 ± 2.1 5001–0.05 0.02 ± 0.02 5001–0.01 0.003 ± 0.005 001–0.0032 0.0009 ± 0.002 001–0.0001 0.0001 ± 0 001–0.0001 0.0001 ± 0

00

2 001 001 001 001 001

0.5 0.2 ± 0.2 0–0.14 0.06 ± 0.07 0–0.003 0.003 ± 0.0004 01–0.0007 0.0003 ± 0.0003 001–0.0001 0.0001 ± 0 001–0.0001 0.0001 ± 0 001–0.0001 0.0001 ± 0 001–0.0001 0.0001 ± 0

.17 0.14 ± 0.03 00.04 0.03 ± 0.01 03–0.002 0.0009 ± 0.001 001–0.0002 0.0001 ± 0.00006 001–0.0001 0.0001 ± 0 001–0.0001 0.0001 ± 0 001–0.0001 0.0001 ± 0 001–0.0001 0.0001 ± 0

Table 4Multiple exposures to metals in biomass-fired power plants.

Power plants Tasks Exposure to metals (mean ± SD.%) P-values

CancerRecycled fuel-fireda Ash removal 2100 ± 1800Peat-fired power plant Ash removal 230 ± 330 0.0308Wood-fired power plant Ash removal 56 ± 48 0.0011Peat-fired power plant Maintenance 21 ± 5 0.0008Recycled fuel-fired Maintenance 15 ± 0.1 0.0007Wood-fired power plant Maintenance 50 ± 37 0.0006Pellet-fired power plant Ash removal 16 ± 5 <0.0001 (�)

Central nervous system disordersRecycled fuel-firedc Ash removal 2000 ± 1800Wood-fired power plant Ash removal 630 ± 630 0.5414Wood-fired power plant Maintenance 180 ± 180 0.4178Pellet-fired power plant Ash removal 110 ± 93 0.2945Peat-fired power plant Ash removal 73 ± 57 0.8885Peat-fired power plant Maintenance 69 ± 43 0.4214Recycled fuel-fired Maintenance 14 ± 1 0.3413

Lower respiratory tract irritationWood-fired power plantd Ash removal 660 ± 660Wood-fired power plant Maintenance 180 ± 170 0.9687Recycled fuel-fired Ash removal 150 ± 110 1.0000Pellet-fired power plant Ash removal 120 ± 94 0.9942Peat-fired power plant Maintenance 76 ± 42 0.8207Peat-fired power plant Ash removal 69 ± 45 1.0000Recycled fuel-fired Maintenance 22 ± 2 0.7209

Upper respiratory tract irritationPeat-fired power plant b Ash removal 320 ± 360Recycled fuel-fired Ash removal 320 ± 280 1.0000Wood-fired power plant Ash removal 120 ± 110 0.4005Wood-fired power plant Maintenance 99 ± 110 0.5990Peat-fired power plant Maintenance 24 ± 8 0.4173Pellet-fired power plant Ash removal 6 ± 4 0.0429 (�)Recycled fuel-fired Maintenance 5 ± 3 0.1470

a Results of recycled fuel-fired power plant (n = 24) versus results of other power plants for cancer (peat (n = 32), wood (n = 55), and pellet (n = 16)). Total number ofsamples nTOT = 127.

b Results of peat-fired power plant (n = 24) versus results of other power plants for upper respiratory tract irritation (recycled fuel-fired (n = 18), wood (n = 41), and pellet(n = 12)). Total number of samples nTOT = 95.

c Results of recycled fuel-fired power plant (n = 18) versus results of other power plants for central nervous system disorders (peat (n = 24), wood (n = 40), and pellet(n = 12)). Total number of samples nTOT = 94.

d Wood-fired power plant (n = 55) versus results of other power plants for lower respiratory tract irritation (recycled fuel (n = 24), pellet (n = 16), and peat (n = 32)). Totalnumber of samples nTOT = 127.

M. Jumpponen et al. / Chemosphere 104 (2014) 25–31 29

were much higher than this. The second most commonly foundmetals whose air concentrations exceeded the OELs of metals(prevalence) in workers’ breathing zone samples were Cd and Pb.The median concentrations of these metals were 0.0002–0.0004 mg m�3 and 0.0053–0.018 mg m�3, respectively. Their OELswere exceeded in 6–13% of samples in ash removal tasks only; theOELs of these metals were not exceeded in maintenance task sam-ples (Table 2). The median concentrations of cadmium and leadwere 2% and 18% of the Finnish OEL of these metals in ash removaltasks, and 1% and 5% of the OEL in maintenance tasks, respectively.The third most commonly found metals in workers’ breathing zonesamples were As, Be, Se, and Th. Their median concentrations were0.0007–0.003 mg m�3, 0.0001 mg m�3, 0.0001–0.0004 mg m�3,and 0.0005–0.0013 mg m�3, respectively, and the OELs of thesemetals were not exceeded during the work tasks. However, themedian concentrations of As were 7% and 30% of the Finnish OELin maintenance and ash removal tasks, respectively. The medianconcentrations of Be and Se were small (Table 2). At stationarysampling sites, Mn, Pb, As, and Al air concentrations exceeded theirOELs during the ash removal tasks inside the boilers in 75%, 50%,50%, and 25% of the samples, respectively. During the maintenancetasks inside the boilers, the OELs of these metals were not ex-ceeded, and their median concentrations were only 12%, 3%, 2%,and 6% of the Finnish OELs. The median concentrations of Cd, Beand Se were less than 8% of their Finnish OEL in the ash removaland maintenance tasks inside the boilers. The median concentra-tions of Mn, Pb, As, Al, Cd, Be and Se were less than 13% of their

Finnish OELs in the ash removal and maintenance tasks outsidethe boilers (Table 3).

3.3. Multiple exposures to metals and exposure-associated health risks

Ash removal workers and maintenance workers are simulta-neously exposed to more than one metal during their work in bio-mass-fired power plants. According to the results of the Mixieprogramme, these multiple exposures are associated with an in-creased risk of cancer, central nervous system disorders, and upperand lower respiratory track irritation. The increased cancer risk canbe explained by the combined effects of As, Be, Cd, and Pb; centralnervous system disorders by the combined effects of Mn, Pb andSe; irritation of the upper respiratory tract by the combined effectsof Al, As and Se; and irritation of the lower respiratory tract by thecombined effects of Be, Cd, Mn, and Se. In addition, according to theMixie programme, exposure to a mixture of As and Cd may have asupra-additive effect on the kidneys. Simultaneous exposure to Mnand Pb may cause a supra-additive effect on the blood-forming sys-tem and the liver. Simultaneous exposure to As and Se also have asupra-additive effect that may lead to mammary cancer.

The most evident exposure-associated health risk of multipleexposures to metals was that of cancer. The average combinedmetal concentrations causing cancer among workers were signifi-cantly (p < .005) higher during ash removal in the recycledfuel-fired power plant than in the other measured power plants(Table 4). The average combined metal concentrations that could

30 M. Jumpponen et al. / Chemosphere 104 (2014) 25–31

cause cancer were higher than the combined OEL values for metalsin the recycled fuel-fired power plant and in the pellet-fired powerplants during ash removal. The measured combined concentrationswere 21 and 2.3 times higher than the combined OEL of the metalsof each plant, respectively (Table 4). The second most significantexposure-associated health risk was that of central nervous systemdisorders. The average concentrations of metals causing this didnot differ statistically (p > 0.05) among the biomass-fired powerplants. The explanation for this is the very high variation of results,which caused a high standard deviation and led to a lack of statis-tical power. The average combined metal concentrations causingcentral nervous system disorders were higher than the combinedOEL values for the metals in the recycled fuel-fired power plantduring ash removal, in the wood-fired power plants during ash re-moval and maintenance, and also in the pellet-fired power plantsduring ash removal. The respective measured combined concentra-tions were 20, 6.3, 1.8 and 1.1 times higher than the combined OELof the measured metals (Table 4). The third most significant expo-sure-associated health risk was lower respiratory tract irritation.The average concentrations of the metals did not vary statisticallysignificantly (p > 0.05) among the biomass-fired power plants(Table 4). The explanation for this was the very high variation ofresults, which caused high standard deviation and led to a lack ofstatistical power. The average combined metal concentrationscausing lower respiratory tract irritation were higher than thecombined OEL values of the metals in the wood-fired power plantsduring ash removal and maintenance, in the recycled fuel-firedpower plant during ash removal, and also in the pellet-fired powerplants during ash removal. The respective measured combinedconcentrations were 6.6, 1.8, 1.5 and 1.2 times higher than thecombined OEL of the measured metals (Table 4). Finally, the fourthhealth effect caused by metals was upper respiratory tract irrita-tion, which was significantly higher (p < 0.0429) during ash re-moval in the peat-fired power plants than during that in thepellet-fired power plants (Table 4). The average combined metalconcentrations causing upper respiratory tract irritation werehigher than the combined OEL values for the metals in the peat-fired power plants during ash removal, in the recycled fuel-firedpower plant during ash removal, and in the wood-fired powerplants during ash removal. The respective measured combinedconcentrations were 3.2, 3.2 and 1.2 times higher than the com-bined OEL of the measured metals (Table 4).

4. Conclusions

Ash removal workers and maintenance workers are simulta-neously exposed to many metals during their work in biomass-fired power plants. According to the measured concentrationsand the results of the Mixie programme, the most evident expo-sure-associated health risk was that of cancer, followed by centralnervous system disorders, lower respiratory tract irritation, and fi-nally upper respiratory tract irritation. Significant differences wereseen between biomass-fired power plants in the risks of cancer andupper respiratory tract irritation. The highest combined risk fordifferent health effects was recorded during ash removal in therecycled fuel-fired power plants. Due to findings of suspected su-pra-additivity of combined metal concentrations (supra-additivityof As and Cd, Mn and Pb, and As and Se), our results may underes-timate the additive risks of cancer, central nervous systemdisorders, and upper respiratory tract irritation.

In the breathing zone samples, the maintenance and ash re-moval workers’ exposure to inhalable dust exceeded the OEL ofinorganic dust in 83% of all air samples in ash removal tasks andin 100% of all air samples in maintenance tasks. At the stationarysampling sites, the inhalable dust concentrations were exceeded

during work tasks inside the boilers but not in work tasks outsidethe boilers, and inhalable dust concentrations were mainly belowthe OEL for inorganic dust. Maintenance and ash removal workerswere exposed to Al and Mn, the concentrations of which exceededthe OELs by 38–80% in the workers’ breathing zone samples. Pband Cd concentrations exceeded the OELs in 6–13% of samples,but only in ash removal tasks. Median concentrations of As were7% and 30% of the Finnish OEL in maintenance and ash removaltasks in the workers’ breathing zone samples, respectively, andmedian concentrations of Be and Se were less than 11% of theirOELs, or even lower. At stationary sampling sites, Mn, Pb, As, andAl concentrations exceeded their OELs only during ash removaltasks inside the boilers in 75%, 50%, 50%, and 25% of the samples,respectively. During maintenance tasks inside the boilers, the med-ian concentrations of these metals were 2–12% of their FinnishOELs. The median concentrations of Cd, Be and Se were less than11% of their Finnish OELs in ash removal and maintenance tasksat all stationary sampling sites. The average air concentration ofthe sum of crystalline and amorphous silica was four times higherthan the OEL of respirable crystalline silica during ash removaltasks. As amorphous silica was a disturbing factor in our analysisof crystalline silica, the results are semiquantitative. The highestsum concentrations were measured during ash removal tasks in-side the boilers and superheaters of the biomass-fired powerplants.

We recommend powered air respirators with ABEK + P3 car-tridges and carbon monoxide gas detectors as the minimumrequirement for people who have to work inside biomass-firedpower plant boilers. The worker should also use a gas detector be-cause carbon monoxide can pass through ABEK + P3 cartridges.Compressed air breathing apparatus is the best form of protectionfor the most demanding work phases inside boilers in biomass-fired power plants. Gases such as carbon monoxide are mentionedin this article, because gases (VOCs, and PAHs) and their exposure-associated health risks are also present inside boilers, and workersneed to protect themselves against these. The exposure-associatedhealth risks of gases, VOCs, and PAHs are presented in our previousarticle (Jumpponen et al., 2013).

Acknowledgements

This project (109140) was funded by The Finnish Work Environ-ment Fund, the Finnish Institute of Occupational Health, and a bio-mass-fired power plant. We thank the biomass-fired power plantpersonnel and the subcontractors of the power plants for their ac-tive participation in this project. We thank Maria Hirvonen for herhelp with the statistical analyses. We also thank Alice Lehtinen forrevising the English language.

References

Bird, J.M., MacIntosh, D.l., Williams, P.L., 2004. Occupational exposures duringroutine activities in coal-fueled power plants. Journal of Occupational andEnvironmental Hygiene 1, 403–413.

Celik, M., Donbak, L., Unal, F., Yüzbasioglu, D., Aksoy, H., Yilmaz, S., 2007. Cytogenicdamage in workers from a coal-fired power plant. Mutation Research 627, 158–163.

Cowan, D.M., Zheng, W., Zou, Y., Shi, X., Chen, J., Rosenthel, F.S., Fan, Q., 2009.Manganese exposure among smelting workers: relationship between bloodmanganese-iron ratio and early onset neurobehavioral alterations.NeuroToxicology 30, 1214–1222.

Garcon, G., Leleu, B., Marez, T., Zerimech, F., Haguenoer, J.M., Furon, D., Shirali, P.,2007. Biomonitoring of the adverse effects induced by the chronic exposure tolead and cadmium on kidney function: usefulness of alpha-glutathione S-transferase. Science of Total Environmental 377, 165–172.

Halatek, T., Sinczuk-Walczak, H., Rabieh, S., Wasowicz, W., 2009. Associationbetween occupational exposure to arsenic and neurological, respiratory andrenal effects. Toxicology and Applied Pharmacology 239, 193–199.

M. Jumpponen et al. / Chemosphere 104 (2014) 25–31 31

Heating and Boiler Plant Equipment Mechanic, 5309. 1992. Federal Wage SystemJob Grading Standard for Heating and Boiler Plant Equipment Mechanic, 5309.U.S. Office of Personnel Management.

Hicks, J., Yager, J., 2006. Airborne crystalline silica concentrations at coal-firedpower plants associated with coal fly ash. Journal of Occupational andEnvironmental Hygiene 3, 448–455.

Jumpponen, M., Rönkkömäki, H., Pasanen, P., Laitinen, J., 2013. Occupational exposureto gases, polycyclic aromatic hydrocarbons and volatile organic compounds inbiomass-fired power plants. Chemosphere 90 (2013), 1289–1293.

Khan, A.A., de Jong, W., Jansens, P.J., Spliethoff, H., 2009. Biomass combustion influidized bed boilers: potential problems and remedies. Fuel processingtechnology 90, 21–50.

Liu, Y., Woodin, M.A., Smith, T.J., Herrick, R.F., Williams, P.L., Hauser, R., Christiani,D.C., 2005. Exposure to fuel-oil ash and welding emissions during the overhaulof an oil-fired boiler. Journal of Occupational and Environmental Hygiene 2,435–443.

Mani, U., Prasad, A.K., Kumar, V.S., Lal, K., Kanojia, R.K., Chaudhari, B.P., Murthy, R.C.,2007. Effect of the ash inhalation on biochemical and histomorphologicalchanges in rat liver. Ecotoxicology and Environmental Safety 68, 126–133.

NIOSH 7303, 2003. ELEMENTS by ICP (Hot Block/HCl/HNO3 Ashing): METHOD7303. NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 3/1/03.

NIOSH 7602, 1994. SILICA, CRYSTALLINE by IR: METHOD 7602. NIOSH Manual ofAnalytical Methods (NMAM), fourth ed., 8/15/94.

Obernberger, I., Brunner, T., Bärnthaler, G., 2006. Chemical properties of solidbiofuels-significance and impact. Biomass and Bioenergy 30, 973–982.

SFS-EN 689, 1996. Workplace atmospheres. Guidance for the assessment ofexposure by inhalation to chemical agents for comparison with limit valuesand measure strategy. Chemical Industry Federation of Finland.

Shukla, G.S., Singhal, R.L., 1984. The present status of biological effect of toxicmetals in the environment: lead, cadmium, and manganese. Canadian Journal ofPhysiology and Pharmacology Aug 62 (8), 1015–1031.

Van Maanen, J.M.S., Borm, P.J.A., Knaapen, A., Van Herwijnen, M., Schilderman,P.A.E.L., Smith, K.R., Aust, E.A., Tomatis, M., Fubini, B., 1999. In vitro effects ofcoal fly ash: hydroxyl radical generation, iron release, and DNA damage andtoxicity in rat lung epithelial cells. Inhalation Toxicology 11, 1123–1141.

Vyskocil, A., Droled, D., 2010. Mixie: Mixtures of Substances in the Workplace:Computer-Based tool for Evaluating the Chemical Risk (Calculation of the Rm).IRSST.

Walton, J.R., 2011. Bioavailable aluminum: its effects on human health.Encyclopedia of Environmental Health, 331–342.

Wojtczak, J., Bielichowska, G., Stroszejn-Mrowca, G., Tenerowicz, B., 1989. Fly ashand its biological effect. 3. Exposure to dust of workers in the energy-generatingindustry (power plants and thermoelectric power stations). Medycyny Pracy 40(5), 294–301.

World Health Organization, 1997. IARC Monographs on Evaluation of CarcinogenicRisks to Humans, vol. 68. Silica.