The product from the burning of a combination of carbonaceous materials.

Exposure related observations in humans: other data

Administrative data

Endpoint:

exposure-related observations in humans: other data

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Non-GLP compliant, non-guideline experimental and computational investigation. Study published in scientific, peer reviewed journal.

Data source

Reference

Reference Type:

publication

Title:

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

Author:

Jumpponen, M. et al.

Year:

2014

Bibliographic source:

Chemosphere 104, 25-31

Materials and methods

Type of study / information:

Analytical data and computer-based assessment of exposure.

Endpoint addressed:

not applicable

Principles of method if other than guideline:

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 respirable crystalline silica (n = 15) were measured in workers’ breathing zones and in stationary sampling points during maintenance and ash removal tasks. These measurements were carried out twice on the plants including inside and outside boilers with participation of 35 male workers.

GLP compliance:

no

Test material

Test material information

Constituent 1

Reference substance name:

Biomass ash

IUPAC Name:

Biomass ash

Test material form:

solid: particulate/powder

Remarks:

powder

Details on test material:

- Name of test material (as cited in study report): Ash
- Substance type: UVCB
- Physical state: Dust
- Other: The capacity of biomass-fired power plants ranged from small, 0.3 MW, to large, 110 MW. Pellets were the main fuel in two of the plants (total thermal input 0.3–0.7 MW), wood in three (total thermal input 17–40 MW), and peat in another two (total thermal input 4.5–110 MW). Recycled fuels were used in one biomass-fired power plant, although peat remained its main fuel.

Method

Details on study design:

Air samples were collected from the breathing zones of workers or from stationary sampling points during the ash removal and maintenance tasks. The sampling periods varied from 53 to 464 min. The inhalable dusts and metals were collected in an IOM sampler ((Millipore-filter, 25 mm AAWP, pore size 0.8µm), and respirable crystalline silica in an IOM foam sampler (Millipore-filter, 25 mm AAWP, pore size 0.8 µm, foam (MultiDust Foam Discs for Respirable Sampling, SKC Inc.)) at a calibrated flow rate of 2.0 L min-1. FIlters were analysed gravimetrically. The metal and crystalline silica analysis of the samples used the ICP/MS technique (NIOSH 7303, 2003) and FT-IR technique (NIOSH 7602, 1994), respectively.

Computer-equipped with MIXIE-programme (The American Conference of Industrial Hygienists (ACGIH)) for evaluating the health risks posed to the workers by the metals was applied. Such programme allows determining additive interactions of many exposures by taking into account all contaminants having similar effects on the same organs or systems of human body.

The average values (mg/m3) of each metal were converted to percentage values using the Finnish OEL of the metals. Statistical analyses were made using SAS for Windows 9.2. The differences between the means of groups (biomass-fired power plants) were analysed using one-way ANOVA according to the generalized linear model (GLM) procedure. The data of the acute health hazards (cancer, central nervous system disorders, and upper and lower respiratory tract irritation) of the metals in the biomass-fired power plants was analysed separately. Tukey’s multiple comparison method was used to determine any significant differences (p < 0.05 (*)) between the acute health hazards of different biomass-fired power plants, classified by hazard and type of biomass-fired power plant.

Exposure assessment:

measured

Results and discussion

Results:

Workers were exposed to high inhalable dust concentrations inside biomass-fired boilers. The median concentrations of inhalable dust were 33 mg m-3 (ranged from 1.3 to 290 mg m-3) during ash removal and 120 mg m-3 (from 20 to 260mg m-3) during maintenance tasks. These values were of 330% and 1200% of the Finnish OEL (10 mg m-3) of inorganic dust. Exposures exceeded the OEL of inorganic dust in 83% of air samples in ash removal tasks and in 100% of air samples in maintenance. In most of the samples taken outside the boiler did not exceed the Finnish OEL limit value. At stationary sampling points, air concentrations of inhalable dust exceeded the OEL of inorganic dust in 80%, 25%, and 10% and 0% of the air samples in ash removal tasks inside the boilers, during maintenance tasks inside the boilers, during maintenance tasks outside the boilers, and during ash removal tasks outside the boilers, respectively. The median concentration of inhalable dust was highest in the wood-fired power plants (130 mg m-3) and lowest in the pellet-fired power plants (22 mg m-3).

In workers’ breathing zone the air concentrations with Al (0.42 - 1.35 mg m-3) and Mn (0.19 - 0.31 mg m-3) exceeded the OELs metals on 68-95% for Al and on 21-155% for Mn. The air concentrations for Cd (0.0002 - 0.0004 mg m-3) and Pb (0.0053-0.018 mg m-3) also exceeded the OELs of metals. That is 2% and 18% of the Finnish OEL of these metals in ash removal and 1% and 5% in maintenance tasks. At stationary sampling sites, Mn, Pb, As, and Al air concentrations exceeded their OELs during the ash removal tasks inside the boilers in 75%, 50%, 50%, and 25% of the samples, respectively. During the maintenance tasks the OEL values were not exceeded.

Multiple exposures to many metals at the same time increased risk of cancer (by combined effects of As, Be, Cd, and Pb) with subsequent disorders of the central nervous system (by combined effects of Mn, Pb, and Se), irritation of the lower respiratory tract by Be, Cd, Mn, and Se, and irritation of the upper respiratory tract by Al, As, and Se. Additionally, exposure to a mixture of As and Cd may have a supra-additive effect on the kidneys, exposure to Mn and Pb may cause a supra-additive effect on the blood-forming system and the liver, and simultaneous exposure to As and Se also have a supra-additive effect that may lead to mammary cancer.

The average sum concentration of crystalline and amorphous silica was 0.2 mg m-3. It exceeded the OEL of respirable crystalline silica during the ash removal tasks.

The most evident exposure-associated health risk of multiple exposures to metals was that of cancer. The average combined metal concentrations causing cancer among workers were significantly (p < 0.005) higher during ash removal in the recycled fuel-fired power plant than in the other measured power plants. During ash removal in the peat-fired power plants the upper respiratory tract irritation was higher (p<0.0429) than in pellet-fired plants.

Applicant's summary and conclusion

Conclusions:

The concentrations of inhalable dust and metals, in workers' breathing zone inside biomass-fired boilers exceeded partly the Finnish OEL values.

Multiple exposures to many metals at the same time potentially increased risk of cancer (by combined effects of As, Be, Cd, and Pb) with subsequent disorders of the central nervous system (by combined effects of Mn, Pb, and Se), irritation of the lower respiratory tract by Be, Cd, Mn, and Se, and irritation of the upper respiratory tract by Al, As, and Se.

Executive summary:

Eight biomass-fired power plants of Finland were randomly selected for this study. As fuel, these plants used pellets (total thermal input 0.3 - 0.7 MW), three wood (17 - 40 MW), peat (4.5 - 110 MW), and recycled wood (70 MW). Power plant boilers are routinely shut down at about one-year intervals for ash removal and maintenance operations. Ash removal workers start their work in the boilers after a two-day cooling down period.

 

Exposure to inhalable dust, metals, and crystalline silica of workers during maintenance and ash removal works were examined by measurements of air concentrations in different work places. These measurements were carried out twice on the plants including inside and outside boilers with participation of 35 male workers.

 

Computer equipped with the MIXIE-programme for evaluating the health risks posed to the workers by the metals was applied. Such programme allows determining additive interactions of many exposures by taking into account all contaminants having similar effects on the same organs or systems of human body.

 

The inhalable dusts and metals were collected in an IOM sampler and respirable crystalline silica in an IOM foam sampler. Metals were analysed with ICP-MS.

 

Typically, the Finnish OEL values of inorganic dust and metals were exceeded in ash removal and maintenance tasks inside the boilers. The median concentration of inhalable dust was highest in the wood-fired power plants (130 mg m-3) and lowest in the pellet-fired power plants (22 mg m-3). The most commonly found metals which air concentrations exceeded the OELs of metals (prevalence) in workers’ breathing zone samples were Al and Mn.

 

According to the MIXIE-programme, the most evident potential health risk of multiple exposures to metals was that of cancer. The average combined metal concentrations causing cancer among workers were significantly (p < 0.005) higher during ash removal in the recycled fuel-fired power plant than in the other measured power plants. Multiple exposures to many metals at the same time increased risk of cancer (by combined effects of As, Be, Cd, and Pb) with subsequent disorders of the central nervous system (by combined effects of Mn, Pb, and Se), irritation of the lower respiratory tract by Be, Cd, Mn, and Se, and irritation of the upper respiratory tract by Al, As, and Se. During ash removal in the peat-fired power plants the upper respiratory tract irritation was higher (p<0.0429) than in pellet-fired plants. 

 

Due to analytical problems the concentration of crystalline and amorphous silica was reported as an average sum concentration (0.2 mg m-3). It exceeded the OEL of respirable crystalline silica during the ash removal tasks.

 

To avoid these health risks the use of respirators, preferably a compressed air breathing apparatus with ABEK+P3 cartridges and carbon monoxide detector were recommended. Compressed air breathing apparatus is the best form of protection for the most demanding work phases inside boilers in biomass fired power plants.