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Health risks of the occupational exposure to microbiological and chemical pollutants in a municipal waste organic fraction treatment plant
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Int. J. Hyg. Environ. Health 212 (2009) 661–669 www.elsevier.de/ijheh
Health risks of the occupational exposure to microbiological and chemical pollutants in a municipal waste organic fraction treatment plant Martı´ Nadala, Isabel Inzab, Marta Schuhmachera,c, Marı´a J. Figuerasb, Jose´ L. Domingoa, a
Laboratory of Toxicology and Environmental Health, School of Medicine, IISPV, ‘‘Rovira i Virgili’’ University, Sant Llorenc¸ 21, 43201 Reus, Catalonia, Spain b Unit of Microbiology, School of Medicine, IISPV, ‘‘Rovira i Virgili’’ University, Sant Llorenc¸ 21, 43201 Reus, Catalonia, Spain c Environmental Engineering Laboratory, ETSEQ, ‘‘Rovira i Virgili’’ University, Av. Paı¨sos Catalans 26, 43007 Tarragona, Catalonia, Spain Received 25 March 2009; received in revised form 6 June 2009; accepted 15 June 2009
Abstract Composting is a good alternative for the treatment of organic waste. However, an important amount of hazardous agents such as bioaerosols and volatile organic compounds may be released during the process. Therefore, the presence of microbiological and chemical pollutants emitted to air may mean a risk for the health of composting plants workers. We here report the results of an investigation aimed at evaluating the occupational exposure to chemical and biological agents for workers of an organic waste treatment facility (Montcada i Reixac, Catalonia, Spain). Total concentrations of bacteria and fungi (at 25 1C and 37 1C), including Aspergillus fumigatus, were determined on a 3-month basis in 4 areas of the composting plant (reception, sorting, composting and cogeneration halls). Non-cancer and cancer risks were assessed. Workers in the sorting cabins seemed to be the most exposed to pollutants. Consequently, the use of preventive measures, such as integrated P3 filter masks and gloves are highly recommended. On the other hand, the emission and dispersion of bioaerosols and particles should be minimized during the process through the application of additional measures, such as the humectation of waste and the installation of biofilters. The results of this study can be useful to elaborate occupational risk prevention programs for workers in composting plants. r 2009 Elsevier GmbH. All rights reserved. Keywords: Health risk; Organic waste treatment plant; Workers; Volatile organic compounds (VOCs); Bioaerosols; Montcada i Reixac (Catalonia, Spain)
Introduction As a consequence of the 3-R (Reduction, Reuse, and Recycling) paradigm, in recent years the public Corresponding author. Tel.: +34 977 759 380; fax: +34 977 759 322. E-mail address: [email protected] (J.L. Domingo).
1438-4639/$ - see front matter r 2009 Elsevier GmbH. All rights reserved. doi:10.1016/j.ijheh.2009.06.002
administrations are encouraging the development of integral treatments for the management of municipal solid waste (MSW). With respect to the treatment of organic waste, sorting-composting has been increasing importance as one of the most viable alternatives (Gajalakshmi and Abbasi, 2008). This approach presents many advantages in comparison to other waste management options. However, an important amount
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of hazardous agents may be released during the waste sorting, composting, and compost refining (Harrison, 2007; Kummer and Thiel, 2008). Among these contaminants, bioaerosols, such as bacteria and fungi, and volatile organic compounds (VOCs), such as benzene, styrene, etc., have been pointed out as agents of special concern (De´portes et al., 1995; Herr et al., 2003; Albrecht et al., 2008). The presence of these microbiological and chemical pollutants emitted to air may mean a risk for the health of workers in composting plants (Fischer et al., 2000; Domingo and Nadal, 2009), making evident the necessity to control their levels to prevent adverse health effects (Byeon et al., 2008). In fact, emissions from waste facilities are an issue from both occupational health and safety as well as environmental hygiene aspects (Kummer and Thiel, 2008). In order to fulfill the EU Landfill Directive aimed at reducing the amount of the biodegradable municipal waste sent to landfill, the Autonomous Government of Catalonia is currently implementing new methodologies to reduce the percentage of MSW deposited on landfills. In the metropolitan area of Barcelona, various MSW management facilities (known as Ecoparcs) are being built. Three facilities are currently already operative. Ecoparcs are set up to get a valorization of energy and materials through two operation lines to treat the MSW organic fraction, and the remaining fraction. In addition to accomplish with the EU legislation, Ecoparcs are intended to reduce the amount of refuse and improve its characteristics. Unfortunately, guidelines for preventing risks of occupational exposure to toxic agents have only been defined for a few chemical contaminants (INSHT, 2008). Threshold values for bioaerosols in workplaces have not been established yet. Moreover, it must be taken into account that the potential exposure to pollutants in MSW management plants may be quite important, and a specific regulation is clearly necessary. The purpose of the present investigation was to assess the occupational exposure to chemical and biological agents for workers at an organic waste treatment facility located in Montcada i Reixac (Catalonia, Spain), as well as to determine seasonal trends. Risk characterization for workers of the composting plant was carried out to facilitate the elaboration of occupational risk prevention programs for composting plants workers and to help the regulatory bodies.
Materials and methods Sampling areas The Ecoparc-2 is located in Montcada i Reixac (Barcelona, Catalonia, Spain). Its construction was started in 2001, and it has been operating since 2004.
The input material includes the organic fraction of the MSW, as well as vegetal residues from parks and gardens of a number of municipalities of the metropolitan area of Barcelona. The total capacity for the integral treatment of the MSW is 240,000 tons/year (Ponsa´ et al., 2008). During the process, 23,000 tons/year of materials and 38,000 tons/year of quality compost are recovered, while 12.6 million of m3 of biogas (electric production: 16,000 MWh per year) are generated. Between March 2007 and June 2008, six 3-month samples of indoor air were collected within the premises of Ecoparc-2. Selected sampling points corresponded to those areas where a potentially higher occupational exposure was expected. Samples were taken at the following 4 zones: A) sorting cabins, B) reception, C) anaerobic digestion, and D) composting tunnels. Two reference air samples were collected outside the treatment plant at 50 m upwind and downwind (E and F, respectively). The distribution of the different sampling points is depicted in Fig. 1.
Sampling and analysis Microbiological pollutants Because of the expected high variability in the microbial concentrations, to determine the levels of bioaerosols 5 replicate air samples were collected at each sampling point. A Sampl’Air MK2 (AES Laboratoire, Bruz, France) with a double header was used. The flow rate was set at 80 and 100 L/min for bacteria and fungi, respectively. Time of sampling varied from 30 s (indoor) to 1 min (outdoor). As culture media, Triptyc Soy Agar (TSA), MacConkey and Potato Dextrose Agar (PDA) were used to determine total bacteria, Gram-negative bacteria, and fungi, respectively. Samples were incubated for 48 h at 37 1C for the analyses of total bacteria, and 24 h for the determination of Gram-negative bacteria. To determine fungi, PDA was incubated at 25 1C and 37 1C for 5-7 days. In 2 of the 5 fungi samples, the presence of Aspergillus fumigatus (A. fumigatus), an allergenic, toxigenic, and opportunistic mould (Albrecht et al., 2008), was evaluated. The counting, in colonyforming units per cubic meter of air (CFU/m3), was based on the ISO 8199:2005 general guideline on the enumeration of microorganisms by culture. Volatile organic compounds (VOCs) The levels of the following VOCs were determined: benzene, toluene, m,p-xylene and o-xylene, styrene, naphthalene, methylene chloride, 1,2-dichloroethane, chloroform, trichloroethylene, tetrachloroethylene, 1,3-butadiene, 1,3,5-trimethylbenzene, 1,2,4-trimethylbenzene, ethylbenzene, p-isopropyltoluene, n-propylbenzene, isopropylbenzene and formaldehyde. Sampling and analysis of most VOCs were carried out according
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663
D
E C
A
F B
Fig. 1. Sampling points in Ecoparc-2 (A) Sorting cabins; (B) Reception; (C) Anaerobic digestion; (D) Composting tunnels; (E) Downwind outdoor; (F) Upwind outdoor.
to the NIOSH 1501 guide, with the exception of formaldehyde, whose determination was in compliance to NIOSH 2016 norm. A personal Gilian LFS-113 air sampling pump (Sensidyne, Clearwater, FL, USA) with a double header was used. Samples were collected by passing air through Anasorb 747 activated carbon tubes (SKC Ltd., Dorset, UK) and 2,4-dinitrophenylhydrazine (2,4-DNPH) coated silica gel tubes (SKC Ltd., Dorset, UK), where VOCs and formaldehyde, respectively, were retained. The pump flow rate was previously set at 0.2 and 0.5 L/min, respectively. The time of sampling lasted an entire working day (8 h). Tubes were rapidly transferred to the lab and stored at 4 1C. VOCs contained in the activated carbon tubes were extracted by liquid desorption with 1-3 mL of carbon sulphide for 60 min. Analysis was done by gas chromatography-mass spectrometry (GC-MS), with an Rtx-1 fused-silica capillary column (30 m 0.32 mm 1.5 mm). The experimental conditions were the following: oven temperature started at 40 1C and kept 1 min, was increased to 220 1C at 14.9 1C/min up to 220 1C, and finally was raised to 320 1C at 40 1C/min. Helium was used as carrier gas. In turn, the extraction of formaldehyde in the 2,4-DNPH coated silica gel tubes was based on an ultrasonic bath for 30 min with 2 mL of acetonitrile. Analysis was done by high pressure liquid chromatography with UV
detection (HPLC-UV), using a C-18 column (5 mm, 200 cm 4.6 mm). The initial mobile phase was acetonitrile:water (50:50). The gradient program for acetonitrile, given as time-concentration percentage, was the following: min. 0.1 – 50%, min. 5 – 50%, min. 20 – 80%, min. 25 – 100%, min. 48 – 50%, min. 52 – stop. The quality control/quality assurance was checked by analyzing blank and replicate samples. Calibration was done by using standard solutions of the target compounds in CS2 and DNPH derivatives of aliphatic aldehydes in acetonitrile for the determination of VOCs and formaldehyde, respectively. Detection limits differed according to each specific VOC, ranging from 0.1 to 40 mg/m3.
Statistics Data analysis was performed with the SPSS 15.0 statistical software package. The significance of the differences was firstly evaluated by applying the Levene test in order to determine the variance equality. ANOVA (analysis-of-variance) or Kruskal-Wallis K-test were subsequently executed depending on whether data followed a normal distribution or not, respectively. A probability lower than 0.05 (po0.05) was considered as statistically significant. For calculations,
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a concentration of zero was assumed for non-detected pollutants (ND ¼ 0).
Results and discussion Indoor concentrations of bioaerosols The mean levels of the different microbiological pollutants assessed in each sampling area are summarized in Table 1. In general terms, and as expected, a high variability was observed. The sorting cabin presented the highest concentrations of all the microorganisms, with the exception of total bacteria and A. fumigatus at 37 1C, whose maximum levels were observed in the organic matter receiving area. The minimum concentration was detected in the biomethanization control room, as well as in the blank samples. In fact, the values in the 2 reference areas (E and F) were very similar, independently on their situation (upwind and downwind, respectively). Because the air of the facility halls, especially in control rooms, polluted by odors and dust, is purified by a double system of chemical washers and biological filtration, lower levels might be there expected. The differences of the bacterial concentrations in the sorting cabins were especially significant to those of the outdoor and biomethanization areas. In turn, significantly lower levels of fungi were noted in the anaerobic digestion control room. The temporal trend of the air levels of studied bioaerosols is depicted in Fig. 2. The concentrations were remarkably variable depending on the sampling period and the kind of microorganism. The microbial growth, derived from the increase in the temperature during the Summer, has been suggested to cause seasonal differences in outdoor concentrations of microbiological pollutants (Zucker and Mu¨ller, 2004). In spite of the small number of sampling points, a relative increase of the levels could be observed in June of 2008. In fact, the highest concentrations of total bacteria, mainly in the receiving and composting areas, were noted in summer.
Table 1. Median concentrations of microbiological pollutants (in CFU/m3) at different working areas of Ecoparc-2 (Montcada i Reixac, Barcelona, Spain). A
B
C
D
Gram-negative bacteria 1743a 155b 1c 123ab a a Total bacteria 1463 2025 76c 1663ab Fungi-25 1C 2294a 598a 69c 592ac A. fumigatus-25 1C 60ab 35ab o2a 60b a a c Fungi-37 1C 488 130 7 178a ab ab a A. fumigatus-37 1C 5 7 o2 40b
E
F
26c 543b 383ac o2a 102a o2ab
13c 374b 605ac o2a 160a 2a
For each parameter, different superscripts (a,b,c) indicate significant differences at po0.05. The sampling areas (A, B, C, D, E, F) are described in the ‘‘Materials and methods’’ section.
Workers in organic waste treatment plants may be exposed to a considerable variety of biological agents, which mean a potential threat for infections, such as bacteria and/or bacteria and/or endotoxins produced by them, allergenic fungi, and parasitic protozoa (Tolvanen et al., 2005; Tolvanen and Ha¨nninen, 2006; Domingo and Nadal, 2009). However, the specific occupational characteristics may be very different according to parameters such as typology of the input materials, operational treatment processes, and the meteorological conditions of the zone. Among them, the kind of organic residue and the used technology seem to be the two fundamental factors in the generation of A. fumigatus and mesophilic bacteria during the handling of organic waste (Sa´nchez-Monedero et al., 2006). Consequently, the pollution levels in different investigations have been enormously variable, being hardly to compare each other. Anyhow, some previous studies have suggested discrete values of microbiological contamination inside/outside composting plants (Fischer et al., 2008). In an occupational study, Lavoie et al. (2006) reported median concentrations of up to 50,300 and 101,700 CFU/m3 of bacteria and fungi in different working scenarios in Quebec (Canada). In turn, in a one-year monitoring study undertaken in a typical composting plant treating green wastes by windrowing in the open, located in the North of England, Sa´nchezMonedero et al. (2005) found that background air concentrations of A. fumigatus and mesophilic bacteria fell within the range of o102-103 CFU/m3 in background sites, being very similar to those levels detected at potentially impacted locations when not a vigorous activity took place. In Spain, the number of occupational health investigations in composting and biogas plants is very scarce. Recently, Solans et al. (2007) carried out a wide study to characterize the exposure to bioaerosols in a sorting source-separated packages household waste plant. The highest concentrations of fungi and gram-negative bacteria were found in the sorting area (412,000 and 5,280 CFU/m3, respectively), while the minimum levels were found at the surroundings of the facility (750 and 85 CFU/m3, respectively). In a subsequent study of the same research group, it was reported that the fungi environmental concentration in a coffee-processing plant ranged between 220 and 412,000 CFU/m3 (Alonso et al., 2008). These levels are slightly higher than those observed in the current investigation, both inside and outside the Ecoparc-2.
Volatile organic compounds (VOCs) The individual concentrations and the sum of the 19 VOCs analyzed, according to the sampling area, are summarized in Table 2. The accumulated levels of
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B
C
D
5000
4000
4000
3000
3000
CFU/m3
CFU/m3
Gram(-) bacteria 5000
2000
F
Total bacteria
2000 1000
1000 0
E
665
mar-07
jun-07
oct-07
jan-08
mar-08
0
jun-08
Fungi - 25°C
mar-07
oct-07
jan-08
mar-08
jun-08
mar-08
jun-08
mar-08
jun-08
mar-08
jun-08
A. fumigatus - 25°C
600
5000
jun-07
CFU/m3
CFU/m3
4000 3000 2000
400
200
1000 0
mar-07
jun-07
oct-07
jan-08
mar-08
0
jun-08
Fungi - 37°C
5000
3000 2000
1000
mar-07
jun-07
oct-07
jan-08
mar-08
0
jun-08
mar-07
jun-07
VOCs 60
50
50
40
40
30
20
10
10 jun-07
oct-07
jan-08
jan-08
30
20
mar-07
oct-07
BTEX
60
mg/m3
mg/m3
jan-08
500
1000
0
oct-07
1500 CFU/m3
CFU/m3
jun-07
A. fumigatus - 37°C
2000
4000
0
mar-07
mar-08
jun-08
0
mar-07
jun-07
oct-07
jan-08
Fig. 2. Temporal trends of VOCs and microbiological pollutants at different workplaces of Ecoparc-2.
BTEX (benzene, toluene, ethylbenzene, m,p-xylene, and o-xylene) are also shown. In general terms and with a few exceptions, the highest concentrations of most VOCs were observed in the sorting cabins, where the highest values of the sum of VOCs and BTEX (14.4
and 8.41 mg/m3, respectively) were also found. When studying the temporal trend of the chemical pollution, a notable changing pattern can be observed (Fig. 2), being the maximum and minimum mean VOC levels found in June 2007 and March 2007, respectively. Although an
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Table 2.
M. Nadal et al. / Int. J. Hyg. Environ. Health 212 (2009) 661–669
Median VOC concentrations (in mg/m3) at different working areas of Ecoparc-2 (Montcada i Reixac, Barcelona, Spain).
Benzene Toluene Ethylbenzene m,p-Xylene o-Xylene Styrene Naphthalene Methylene chloride 1,2-Dichloroethane Chloroform Trichloroethylene Tetrachloroethylene 1,3-Butadiene 1,3,5-Trimethylbenzene 1,2,4-Trimethylbenzene p-Isopropyltoluene n-Propylbenzene Isopropylbenzene Formaldehyde Total VOCs (mg/m3) BTEX (mg/m3)
A
B
C
D
VLA-ED*
11.5a 4775.0a 780.0a 2497.5a 350.0a 64.5a 1.8 15.0 o2.0 21.0a 66.0a 1335.0a o40.0 152.5a 440.0a 635.0 56.5a 20.5a 8.2 14.4a 8.41a
12.0ab 845.0b 172.5b 660.0b 104.5b 21.5a 1.2 27.5 2.5 19.0a 28.5a 118.5b o40.0 36.5b 140.0b 1272.5 16.0b 4.9b 4.6 4.61b 1.80b
2.4b 50.5c 5.8c 11.ca 3.1c o0.2c 0.2 o20.0 o2.0 1.9b 4.6c o10.0c o40.0 2.4c 9.7c 735.0 1.4c 0.5c 10.3 1.06c 0.12c
13.5ab 467.5b 106.0b 430.0b 61.0b 9.3b 1.3 10.5 9.5 15.5a 27.5b 96.0b o40.0 26.0b 89.0b 1435.0 14.5b 4.0b 5.2 2.91b 1.08b
3250 192,000 441,000 221,000 221,000 86,000 53,000 177,000 20,000 10,000 273,000 n.a. 4500 100,000 100,000 n.a. n.a. n.a. n.a. n.a. n.a.
n.a.: not available. For each parameter, different superscripts (a,b,c) indicate significant differences at po0.05. *VLA-ED are environmental limit values for daily exposure to chemical pollutants developed by the Spanish National Institute of Safety and Hygiene at Work (INSHT, 2008). The sampling areas (A, B, C, D) are described in the ‘‘Materials and methods’’ section.
increase in the air concentrations of VOCs could be expected in summer, as a result of the environmental temperature raise (20.6 and 21.5 1C in June 2007 and June 2008, respectively), no seasonal influence was observed in any sampling area. As for bioaerosols, the current knowledge regarding to the VOC levels in organic waste composting plants is very scarce (Pagans et al., 2006). The first study giving specific data on VOCs in composting plants was done by Eitzer (1995), who identified the emitted VOCs and the approximate air concentrations during the composting process inside 8 facilities in the USA. With the exception of benzene, the indoor levels of VOCs in the Ecoparc-2 are generally very similar to those reported by Eitzer (1995). Currently, the MSW of Barcelona is mainly treated in three Ecoparcs, while the construction of a fourth facility is ongoing. In 2003, the air quality of the Ecoparc-1, located in Zona Franca (Barcelona, Spain), was assessed by determining the concentration of a series of chemical parameters, including BTEX, styrene, NH3, CH4, CO2, and O2 (Leguizamo´n, 2003). Indoor air in composting tunnels technologically similar to those in the Ecoparc-2 was evaluated. The concentrations of benzene, toluene, ethylbenzene, m,p-xylene, o-xylene, and styrene were 15.3, 567, 61.3, 245, 46, and 15.3 mg/m3, respectively, being very similar to those currently found in the Ecoparc-2 (13.5, 468, 106, 430, 61, and 9.3 mg/m3, respectively). BTEX and styrene have
been remarked as the dominant aromatics in gas released during the decomposition of MSW (Staley et al., 2006). However, Kiviranta et al. (1999) found VOC concentrations of up to 2850 mg/m3 in a waste processing room at a Finnish resource recovery plant, where very high values of bioaerosols had also been observed (median levels of 150,000 and 65,000 CFU/m3 of total and gram-negative bacteria, respectively). Recently, outdoor concentrations of VOCs were found to range between 0.9 and 121.2 mg/m3 in the vicinity of another MSW management facility in Catalonia (Vilavert et al., 2009). Automobile exhausts have been considered as the main source of mono-aromatic hydrocarbons such as BTEX (Dutta et al., 2009). Therefore, ambient air levels of VOCs may highly differ, being more abundant in urban sites (Ras-Mallorquı´ et al., 2007). Complementarily to the present investigation, an odor exposure study, using field panel observations was carried out around the Ecoparc-2, according to the German standard EN3940 (Feliubadalo´ et al., 2008). Although the results in the industrial complex exceeded the German criteria for industrial areas (15% odor hours), those found in the most immediate urban zone were below the criteria for residential areas (10% odor hours). In addition, a dispersion model of the odor impact was also obtained by applying ESCT and CALPUFF models.
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Human health risks A first evaluation of the chemical risks was carried out by comparing the median VOC concentrations and the Daily Exposure Values established by the Spanish National Institute of Safety and Hygiene at Work (Table 2). The current exposure level to VOCs would be clearly lower than the maximum recommended threshold, indicating that indoor VOC concentrations would not be of concern for the health of workers. Subsequently, a more accurate and specific risk assessment approach was executed. The occupational exposure to the target compounds was subsequently assessed by applying the standard methodology developed by the US EPA. Since all the studied contaminants are volatile, inhalation was considered to be the main exposure route to VOCs. Exposure concentration through inhalation was calculated with the following equation: EC ¼
C air EF ED ET AT
where EC is the exposure concentration (in mg/m3), Cair is the air median concentration of each pollutant (in mg/m3), EF is the exposure frequency (250 days/year), ED is the exposure duration (25 years), ET is the daily exposure time (8/24 h), and AT is the average time (365 days/year ED). The health risks for the workers, differentiating between non-carcinogenic and carcino-
Table 3.
667
genic risks, were characterized. For each chemical contaminant, non-cancer risk (Hazard Quotient) was estimated by comparing the exposure concentration and the inhalation reference concentration (RfCi). On the other hand, the carcinogenic risk was calculated by multiplying the exposure by the US EPA Inhalation Unit Risk (IUR). For cancer risks calculations, ED was 25 years, while AT was 70 years. The estimated noncarcinogenic and carcinogenic risks due to the exposure to each VOC are summarized in Table 3. The sorting cabins (A) and the receiving hall (B) were the only areas where the Hazard Index, calculated as the sum of the Hazard Quotients, was estimated to be above the unity (6.19 and 1.15, respectively). This would be consequence of the especially high concentrations of toluene registered in both areas. In turn, the cancer risk was estimated in 8.73 104, 1.55 104, 1.83 105 and 1.39 104 in the sampling zones A, B, C and D, respectively, assuming that the carcinogenic risk of different pollutants is cumulative. Because risk estimates for various chemicals are presented as values on the same numeric scale, total cancer risks are often calculated as the sum of risks (US EPA, 2003). For the general population, the maximum acceptable risk threshold ranges between 106 and 104. However, some authors consider that levels of up to 103 might be accepted in case of occupationally exposed populations (Tran et al., 2000). Anyhow, and individually studying
Non-carcinogenic and carcinogenic risks (unitless) of exposure to VOCs in different workplaces in Ecoparc-2. Non-carcinogenic risk
Benzene Toluene Ethylbenzene m,p-Xylene o-Xylene Styrene Naphthalene Methylene chloride 1,2-Dichloroethane Chloroform Trichloroethylene Tetrachloroethylene 1,3-Butadiene 1,3,5-Trimethylbenzene 1,2,4-Trimethylbenzene p-Isopropyltoluene n-Propylbenzene Isopropylbenzene Formaldehyde Total risk
Carcinogenic risk
A
B
C
D
A
B
C
D
7.84E05 5.45 1.78E01 3.99E01 5.59E02 1.47E02 1.20E06 3.77E03 – 4.70E04 – 8.23E02 – 2.09E04 7.03E04 – – – 1.83E05 6.19
8.22E05 9.65E01 3.94E02 1.05E01 1.67E02 4.91E03 7.88E07 6.91E03 1.37E03 4.25E04 – 7.30E03 – 5.00E05 2.24E04 – – – 1.03E05 1.15
1.64E05 5.76E02 1.31E03 1.84E03 4.87E04 1.03E07 – – 4.25E05 – – – 3.29E06 1.54E05 – – – 2.30E05 6.14E02
9.25E05 5.34E01 2.42E02 6.87E02 9.75E03 2.12E03 8.90E07 2.64E03 5.18E03 3.47E04 – 5.92E03 – 3.56E05 1.42E04 – – – 1.16E05 6.53E01
7.28E06 – 1.59E04 – – – 4.85E06 5.75E07 – 3.94E05 1.08E05 6.42E04 – – – – – – 8.69E06 8.73E04
7.63E06 – 3.52E05 – – – 3.19E06 1.05E06 5.30E06 3.56E05 4.65E06 5.70E05 – – – – – – 4.88E06 1.55E04
1.53E06 – 1.17E06 – – – 4.16E07 – – 3.56E06 7.42E07 – – – – – – – 1.09E05 1.83E05
8.59E06 – 2.16E05 – – – 3.60E06 4.02E07 2.00E05 2.91E05 4.48E06 4.62E05 – – – – – – 5.51E06 1.39E04
The sampling areas (A, B, C, D) are described in the ‘‘Materials and methods’’ section. Total non-carcinogenic risk (Hazard Index) and carcinogenic risk were calculated as the sum of risks due to individual compounds.
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each one of the analyzed VOCs, a cancer risk index of 104 would be only exceeded in the sorting cabins, being exclusively due to exposure to ethylbenzene and tetrachloroethylene (1.59 104 and 6.42 104, respectively). With respect to the health risks derived from exposure to bioaerosols, currently, there are no standards set by the National Institute of Occupational Safety and Health (NIOSH) and the American Conference of Governmental Industrial Hygienists (ACGIH) concerning the allowable amount of microbiological agents at the workplace (Vilavert et al., 2009). However, some recommendations have been published by both institutions (guidelines of 100-1000 and 1000 CFU/m3 for total fungi and total number of bioaerosols particles, respectively). In addition, some investigators have suggested a limit value of 10,000 CFU/m3 for total bacteria, and 1,000 CFU/m3 for gram-negative bacteria (Marchand et al., 1995; Kiviranta et al., 1999). In comparison to those levels, the current bacterial concentrations would exceed the proposed limits in the sorting cabins for exposure to gram-negative bacteria. In fact, the relationship between the occupational levels in the zone A and the reference concentrations, considered as estimative method to obtain a measure of the exposure degree (Domingo and Nadal, 2009), would be up to 80. The above results indicate that workers in the sorting cabins seem to be the most exposed to chemical and microbiological pollutants during the treatment of the organic fraction of MSW. Protective equipment is already recommended for plant operators of waste handling facilities. Workers should be subjected to preventive measures such as the use of integrated P3 filter masks to avoid exposure to gases, vapors and particles. Gloves should be also used. Moreover, because of the relatively higher levels of pollution detected in the reception and composting areas, workers in the remaining zones, where a direct contact to organic waste exists (B and D), should strongly be advised to wear the same protection equipment. On the other hand, as previously suggested (Sa´nchez-Monedero and Stentiford, 2003), the emission and dispersion of bioaerosols and particles should be minimized during the process through the application of additional measures, such as the humectation of waste and the installation of extractor hoods in zones with a high potential risk. Thus, biofiltration seems to be a promising method to reduce not only odors, but also the release of both microbiological and chemical agents. In a comprehensive study at nine different composting plants and in their surrounding, an odor reduction was observed at facilities equipped with a biofilter (Fischer et al., 2008). In turn, removal efficiencies of 97% and 90% for VOCs and A. fumigatus, respectively, have been achieved after installing biofilters in composting sites (Sa´nchez-Monedero et al., 2003; Pagans et al., 2006).
The current strategy of the local authorities in Barcelona is enforced to achieve an integral treatment of the MSW, including its organic fraction. The construction of several Ecoparcs of similar characteristics to that evaluated here is already planned. However, in spite of the singular importance that these facilities will/should perform in the near future, until now, there has been a complete gap with respect to the health risks for the workers of those plants. The screening results here presented mean a first attempt to cover that gap.
Acknowledgments This study was financially supported by the Spanish National Institute of Safety and Hygiene at Work, through the project 06-03-FORSU-URV-302. The authors thank Joan Feliubadalo´ and Javier Cerezo for their collaboration through the investigation. We also thank Jessica Jime´nez and Albert Rallo for their valuable technical assistance during the sampling. Finally, Jordi Borra`s and Catalina Ubiedo are acknowledged for their teaching of the sampling devices.
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Int. J. Hyg. Environ. Health 212 (2009) 661–669 www.elsevier.de/ijheh
Health risks of the occupational exposure to microbiological and chemical pollutants in a municipal waste organic fraction treatment plant Martı´ Nadala, Isabel Inzab, Marta Schuhmachera,c, Marı´a J. Figuerasb, Jose´ L. Domingoa, a
Laboratory of Toxicology and Environmental Health, School of Medicine, IISPV, ‘‘Rovira i Virgili’’ University, Sant Llorenc¸ 21, 43201 Reus, Catalonia, Spain b Unit of Microbiology, School of Medicine, IISPV, ‘‘Rovira i Virgili’’ University, Sant Llorenc¸ 21, 43201 Reus, Catalonia, Spain c Environmental Engineering Laboratory, ETSEQ, ‘‘Rovira i Virgili’’ University, Av. Paı¨sos Catalans 26, 43007 Tarragona, Catalonia, Spain Received 25 March 2009; received in revised form 6 June 2009; accepted 15 June 2009
Abstract Composting is a good alternative for the treatment of organic waste. However, an important amount of hazardous agents such as bioaerosols and volatile organic compounds may be released during the process. Therefore, the presence of microbiological and chemical pollutants emitted to air may mean a risk for the health of composting plants workers. We here report the results of an investigation aimed at evaluating the occupational exposure to chemical and biological agents for workers of an organic waste treatment facility (Montcada i Reixac, Catalonia, Spain). Total concentrations of bacteria and fungi (at 25 1C and 37 1C), including Aspergillus fumigatus, were determined on a 3-month basis in 4 areas of the composting plant (reception, sorting, composting and cogeneration halls). Non-cancer and cancer risks were assessed. Workers in the sorting cabins seemed to be the most exposed to pollutants. Consequently, the use of preventive measures, such as integrated P3 filter masks and gloves are highly recommended. On the other hand, the emission and dispersion of bioaerosols and particles should be minimized during the process through the application of additional measures, such as the humectation of waste and the installation of biofilters. The results of this study can be useful to elaborate occupational risk prevention programs for workers in composting plants. r 2009 Elsevier GmbH. All rights reserved. Keywords: Health risk; Organic waste treatment plant; Workers; Volatile organic compounds (VOCs); Bioaerosols; Montcada i Reixac (Catalonia, Spain)
Introduction As a consequence of the 3-R (Reduction, Reuse, and Recycling) paradigm, in recent years the public Corresponding author. Tel.: +34 977 759 380; fax: +34 977 759 322. E-mail address: [email protected] (J.L. Domingo).
1438-4639/$ - see front matter r 2009 Elsevier GmbH. All rights reserved. doi:10.1016/j.ijheh.2009.06.002
administrations are encouraging the development of integral treatments for the management of municipal solid waste (MSW). With respect to the treatment of organic waste, sorting-composting has been increasing importance as one of the most viable alternatives (Gajalakshmi and Abbasi, 2008). This approach presents many advantages in comparison to other waste management options. However, an important amount
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of hazardous agents may be released during the waste sorting, composting, and compost refining (Harrison, 2007; Kummer and Thiel, 2008). Among these contaminants, bioaerosols, such as bacteria and fungi, and volatile organic compounds (VOCs), such as benzene, styrene, etc., have been pointed out as agents of special concern (De´portes et al., 1995; Herr et al., 2003; Albrecht et al., 2008). The presence of these microbiological and chemical pollutants emitted to air may mean a risk for the health of workers in composting plants (Fischer et al., 2000; Domingo and Nadal, 2009), making evident the necessity to control their levels to prevent adverse health effects (Byeon et al., 2008). In fact, emissions from waste facilities are an issue from both occupational health and safety as well as environmental hygiene aspects (Kummer and Thiel, 2008). In order to fulfill the EU Landfill Directive aimed at reducing the amount of the biodegradable municipal waste sent to landfill, the Autonomous Government of Catalonia is currently implementing new methodologies to reduce the percentage of MSW deposited on landfills. In the metropolitan area of Barcelona, various MSW management facilities (known as Ecoparcs) are being built. Three facilities are currently already operative. Ecoparcs are set up to get a valorization of energy and materials through two operation lines to treat the MSW organic fraction, and the remaining fraction. In addition to accomplish with the EU legislation, Ecoparcs are intended to reduce the amount of refuse and improve its characteristics. Unfortunately, guidelines for preventing risks of occupational exposure to toxic agents have only been defined for a few chemical contaminants (INSHT, 2008). Threshold values for bioaerosols in workplaces have not been established yet. Moreover, it must be taken into account that the potential exposure to pollutants in MSW management plants may be quite important, and a specific regulation is clearly necessary. The purpose of the present investigation was to assess the occupational exposure to chemical and biological agents for workers at an organic waste treatment facility located in Montcada i Reixac (Catalonia, Spain), as well as to determine seasonal trends. Risk characterization for workers of the composting plant was carried out to facilitate the elaboration of occupational risk prevention programs for composting plants workers and to help the regulatory bodies.
Materials and methods Sampling areas The Ecoparc-2 is located in Montcada i Reixac (Barcelona, Catalonia, Spain). Its construction was started in 2001, and it has been operating since 2004.
The input material includes the organic fraction of the MSW, as well as vegetal residues from parks and gardens of a number of municipalities of the metropolitan area of Barcelona. The total capacity for the integral treatment of the MSW is 240,000 tons/year (Ponsa´ et al., 2008). During the process, 23,000 tons/year of materials and 38,000 tons/year of quality compost are recovered, while 12.6 million of m3 of biogas (electric production: 16,000 MWh per year) are generated. Between March 2007 and June 2008, six 3-month samples of indoor air were collected within the premises of Ecoparc-2. Selected sampling points corresponded to those areas where a potentially higher occupational exposure was expected. Samples were taken at the following 4 zones: A) sorting cabins, B) reception, C) anaerobic digestion, and D) composting tunnels. Two reference air samples were collected outside the treatment plant at 50 m upwind and downwind (E and F, respectively). The distribution of the different sampling points is depicted in Fig. 1.
Sampling and analysis Microbiological pollutants Because of the expected high variability in the microbial concentrations, to determine the levels of bioaerosols 5 replicate air samples were collected at each sampling point. A Sampl’Air MK2 (AES Laboratoire, Bruz, France) with a double header was used. The flow rate was set at 80 and 100 L/min for bacteria and fungi, respectively. Time of sampling varied from 30 s (indoor) to 1 min (outdoor). As culture media, Triptyc Soy Agar (TSA), MacConkey and Potato Dextrose Agar (PDA) were used to determine total bacteria, Gram-negative bacteria, and fungi, respectively. Samples were incubated for 48 h at 37 1C for the analyses of total bacteria, and 24 h for the determination of Gram-negative bacteria. To determine fungi, PDA was incubated at 25 1C and 37 1C for 5-7 days. In 2 of the 5 fungi samples, the presence of Aspergillus fumigatus (A. fumigatus), an allergenic, toxigenic, and opportunistic mould (Albrecht et al., 2008), was evaluated. The counting, in colonyforming units per cubic meter of air (CFU/m3), was based on the ISO 8199:2005 general guideline on the enumeration of microorganisms by culture. Volatile organic compounds (VOCs) The levels of the following VOCs were determined: benzene, toluene, m,p-xylene and o-xylene, styrene, naphthalene, methylene chloride, 1,2-dichloroethane, chloroform, trichloroethylene, tetrachloroethylene, 1,3-butadiene, 1,3,5-trimethylbenzene, 1,2,4-trimethylbenzene, ethylbenzene, p-isopropyltoluene, n-propylbenzene, isopropylbenzene and formaldehyde. Sampling and analysis of most VOCs were carried out according
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D
E C
A
F B
Fig. 1. Sampling points in Ecoparc-2 (A) Sorting cabins; (B) Reception; (C) Anaerobic digestion; (D) Composting tunnels; (E) Downwind outdoor; (F) Upwind outdoor.
to the NIOSH 1501 guide, with the exception of formaldehyde, whose determination was in compliance to NIOSH 2016 norm. A personal Gilian LFS-113 air sampling pump (Sensidyne, Clearwater, FL, USA) with a double header was used. Samples were collected by passing air through Anasorb 747 activated carbon tubes (SKC Ltd., Dorset, UK) and 2,4-dinitrophenylhydrazine (2,4-DNPH) coated silica gel tubes (SKC Ltd., Dorset, UK), where VOCs and formaldehyde, respectively, were retained. The pump flow rate was previously set at 0.2 and 0.5 L/min, respectively. The time of sampling lasted an entire working day (8 h). Tubes were rapidly transferred to the lab and stored at 4 1C. VOCs contained in the activated carbon tubes were extracted by liquid desorption with 1-3 mL of carbon sulphide for 60 min. Analysis was done by gas chromatography-mass spectrometry (GC-MS), with an Rtx-1 fused-silica capillary column (30 m 0.32 mm 1.5 mm). The experimental conditions were the following: oven temperature started at 40 1C and kept 1 min, was increased to 220 1C at 14.9 1C/min up to 220 1C, and finally was raised to 320 1C at 40 1C/min. Helium was used as carrier gas. In turn, the extraction of formaldehyde in the 2,4-DNPH coated silica gel tubes was based on an ultrasonic bath for 30 min with 2 mL of acetonitrile. Analysis was done by high pressure liquid chromatography with UV
detection (HPLC-UV), using a C-18 column (5 mm, 200 cm 4.6 mm). The initial mobile phase was acetonitrile:water (50:50). The gradient program for acetonitrile, given as time-concentration percentage, was the following: min. 0.1 – 50%, min. 5 – 50%, min. 20 – 80%, min. 25 – 100%, min. 48 – 50%, min. 52 – stop. The quality control/quality assurance was checked by analyzing blank and replicate samples. Calibration was done by using standard solutions of the target compounds in CS2 and DNPH derivatives of aliphatic aldehydes in acetonitrile for the determination of VOCs and formaldehyde, respectively. Detection limits differed according to each specific VOC, ranging from 0.1 to 40 mg/m3.
Statistics Data analysis was performed with the SPSS 15.0 statistical software package. The significance of the differences was firstly evaluated by applying the Levene test in order to determine the variance equality. ANOVA (analysis-of-variance) or Kruskal-Wallis K-test were subsequently executed depending on whether data followed a normal distribution or not, respectively. A probability lower than 0.05 (po0.05) was considered as statistically significant. For calculations,
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a concentration of zero was assumed for non-detected pollutants (ND ¼ 0).
Results and discussion Indoor concentrations of bioaerosols The mean levels of the different microbiological pollutants assessed in each sampling area are summarized in Table 1. In general terms, and as expected, a high variability was observed. The sorting cabin presented the highest concentrations of all the microorganisms, with the exception of total bacteria and A. fumigatus at 37 1C, whose maximum levels were observed in the organic matter receiving area. The minimum concentration was detected in the biomethanization control room, as well as in the blank samples. In fact, the values in the 2 reference areas (E and F) were very similar, independently on their situation (upwind and downwind, respectively). Because the air of the facility halls, especially in control rooms, polluted by odors and dust, is purified by a double system of chemical washers and biological filtration, lower levels might be there expected. The differences of the bacterial concentrations in the sorting cabins were especially significant to those of the outdoor and biomethanization areas. In turn, significantly lower levels of fungi were noted in the anaerobic digestion control room. The temporal trend of the air levels of studied bioaerosols is depicted in Fig. 2. The concentrations were remarkably variable depending on the sampling period and the kind of microorganism. The microbial growth, derived from the increase in the temperature during the Summer, has been suggested to cause seasonal differences in outdoor concentrations of microbiological pollutants (Zucker and Mu¨ller, 2004). In spite of the small number of sampling points, a relative increase of the levels could be observed in June of 2008. In fact, the highest concentrations of total bacteria, mainly in the receiving and composting areas, were noted in summer.
Table 1. Median concentrations of microbiological pollutants (in CFU/m3) at different working areas of Ecoparc-2 (Montcada i Reixac, Barcelona, Spain). A
B
C
D
Gram-negative bacteria 1743a 155b 1c 123ab a a Total bacteria 1463 2025 76c 1663ab Fungi-25 1C 2294a 598a 69c 592ac A. fumigatus-25 1C 60ab 35ab o2a 60b a a c Fungi-37 1C 488 130 7 178a ab ab a A. fumigatus-37 1C 5 7 o2 40b
E
F
26c 543b 383ac o2a 102a o2ab
13c 374b 605ac o2a 160a 2a
For each parameter, different superscripts (a,b,c) indicate significant differences at po0.05. The sampling areas (A, B, C, D, E, F) are described in the ‘‘Materials and methods’’ section.
Workers in organic waste treatment plants may be exposed to a considerable variety of biological agents, which mean a potential threat for infections, such as bacteria and/or bacteria and/or endotoxins produced by them, allergenic fungi, and parasitic protozoa (Tolvanen et al., 2005; Tolvanen and Ha¨nninen, 2006; Domingo and Nadal, 2009). However, the specific occupational characteristics may be very different according to parameters such as typology of the input materials, operational treatment processes, and the meteorological conditions of the zone. Among them, the kind of organic residue and the used technology seem to be the two fundamental factors in the generation of A. fumigatus and mesophilic bacteria during the handling of organic waste (Sa´nchez-Monedero et al., 2006). Consequently, the pollution levels in different investigations have been enormously variable, being hardly to compare each other. Anyhow, some previous studies have suggested discrete values of microbiological contamination inside/outside composting plants (Fischer et al., 2008). In an occupational study, Lavoie et al. (2006) reported median concentrations of up to 50,300 and 101,700 CFU/m3 of bacteria and fungi in different working scenarios in Quebec (Canada). In turn, in a one-year monitoring study undertaken in a typical composting plant treating green wastes by windrowing in the open, located in the North of England, Sa´nchezMonedero et al. (2005) found that background air concentrations of A. fumigatus and mesophilic bacteria fell within the range of o102-103 CFU/m3 in background sites, being very similar to those levels detected at potentially impacted locations when not a vigorous activity took place. In Spain, the number of occupational health investigations in composting and biogas plants is very scarce. Recently, Solans et al. (2007) carried out a wide study to characterize the exposure to bioaerosols in a sorting source-separated packages household waste plant. The highest concentrations of fungi and gram-negative bacteria were found in the sorting area (412,000 and 5,280 CFU/m3, respectively), while the minimum levels were found at the surroundings of the facility (750 and 85 CFU/m3, respectively). In a subsequent study of the same research group, it was reported that the fungi environmental concentration in a coffee-processing plant ranged between 220 and 412,000 CFU/m3 (Alonso et al., 2008). These levels are slightly higher than those observed in the current investigation, both inside and outside the Ecoparc-2.
Volatile organic compounds (VOCs) The individual concentrations and the sum of the 19 VOCs analyzed, according to the sampling area, are summarized in Table 2. The accumulated levels of
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B
C
D
5000
4000
4000
3000
3000
CFU/m3
CFU/m3
Gram(-) bacteria 5000
2000
F
Total bacteria
2000 1000
1000 0
E
665
mar-07
jun-07
oct-07
jan-08
mar-08
0
jun-08
Fungi - 25°C
mar-07
oct-07
jan-08
mar-08
jun-08
mar-08
jun-08
mar-08
jun-08
mar-08
jun-08
A. fumigatus - 25°C
600
5000
jun-07
CFU/m3
CFU/m3
4000 3000 2000
400
200
1000 0
mar-07
jun-07
oct-07
jan-08
mar-08
0
jun-08
Fungi - 37°C
5000
3000 2000
1000
mar-07
jun-07
oct-07
jan-08
mar-08
0
jun-08
mar-07
jun-07
VOCs 60
50
50
40
40
30
20
10
10 jun-07
oct-07
jan-08
jan-08
30
20
mar-07
oct-07
BTEX
60
mg/m3
mg/m3
jan-08
500
1000
0
oct-07
1500 CFU/m3
CFU/m3
jun-07
A. fumigatus - 37°C
2000
4000
0
mar-07
mar-08
jun-08
0
mar-07
jun-07
oct-07
jan-08
Fig. 2. Temporal trends of VOCs and microbiological pollutants at different workplaces of Ecoparc-2.
BTEX (benzene, toluene, ethylbenzene, m,p-xylene, and o-xylene) are also shown. In general terms and with a few exceptions, the highest concentrations of most VOCs were observed in the sorting cabins, where the highest values of the sum of VOCs and BTEX (14.4
and 8.41 mg/m3, respectively) were also found. When studying the temporal trend of the chemical pollution, a notable changing pattern can be observed (Fig. 2), being the maximum and minimum mean VOC levels found in June 2007 and March 2007, respectively. Although an
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Table 2.
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Median VOC concentrations (in mg/m3) at different working areas of Ecoparc-2 (Montcada i Reixac, Barcelona, Spain).
Benzene Toluene Ethylbenzene m,p-Xylene o-Xylene Styrene Naphthalene Methylene chloride 1,2-Dichloroethane Chloroform Trichloroethylene Tetrachloroethylene 1,3-Butadiene 1,3,5-Trimethylbenzene 1,2,4-Trimethylbenzene p-Isopropyltoluene n-Propylbenzene Isopropylbenzene Formaldehyde Total VOCs (mg/m3) BTEX (mg/m3)
A
B
C
D
VLA-ED*
11.5a 4775.0a 780.0a 2497.5a 350.0a 64.5a 1.8 15.0 o2.0 21.0a 66.0a 1335.0a o40.0 152.5a 440.0a 635.0 56.5a 20.5a 8.2 14.4a 8.41a
12.0ab 845.0b 172.5b 660.0b 104.5b 21.5a 1.2 27.5 2.5 19.0a 28.5a 118.5b o40.0 36.5b 140.0b 1272.5 16.0b 4.9b 4.6 4.61b 1.80b
2.4b 50.5c 5.8c 11.ca 3.1c o0.2c 0.2 o20.0 o2.0 1.9b 4.6c o10.0c o40.0 2.4c 9.7c 735.0 1.4c 0.5c 10.3 1.06c 0.12c
13.5ab 467.5b 106.0b 430.0b 61.0b 9.3b 1.3 10.5 9.5 15.5a 27.5b 96.0b o40.0 26.0b 89.0b 1435.0 14.5b 4.0b 5.2 2.91b 1.08b
3250 192,000 441,000 221,000 221,000 86,000 53,000 177,000 20,000 10,000 273,000 n.a. 4500 100,000 100,000 n.a. n.a. n.a. n.a. n.a. n.a.
n.a.: not available. For each parameter, different superscripts (a,b,c) indicate significant differences at po0.05. *VLA-ED are environmental limit values for daily exposure to chemical pollutants developed by the Spanish National Institute of Safety and Hygiene at Work (INSHT, 2008). The sampling areas (A, B, C, D) are described in the ‘‘Materials and methods’’ section.
increase in the air concentrations of VOCs could be expected in summer, as a result of the environmental temperature raise (20.6 and 21.5 1C in June 2007 and June 2008, respectively), no seasonal influence was observed in any sampling area. As for bioaerosols, the current knowledge regarding to the VOC levels in organic waste composting plants is very scarce (Pagans et al., 2006). The first study giving specific data on VOCs in composting plants was done by Eitzer (1995), who identified the emitted VOCs and the approximate air concentrations during the composting process inside 8 facilities in the USA. With the exception of benzene, the indoor levels of VOCs in the Ecoparc-2 are generally very similar to those reported by Eitzer (1995). Currently, the MSW of Barcelona is mainly treated in three Ecoparcs, while the construction of a fourth facility is ongoing. In 2003, the air quality of the Ecoparc-1, located in Zona Franca (Barcelona, Spain), was assessed by determining the concentration of a series of chemical parameters, including BTEX, styrene, NH3, CH4, CO2, and O2 (Leguizamo´n, 2003). Indoor air in composting tunnels technologically similar to those in the Ecoparc-2 was evaluated. The concentrations of benzene, toluene, ethylbenzene, m,p-xylene, o-xylene, and styrene were 15.3, 567, 61.3, 245, 46, and 15.3 mg/m3, respectively, being very similar to those currently found in the Ecoparc-2 (13.5, 468, 106, 430, 61, and 9.3 mg/m3, respectively). BTEX and styrene have
been remarked as the dominant aromatics in gas released during the decomposition of MSW (Staley et al., 2006). However, Kiviranta et al. (1999) found VOC concentrations of up to 2850 mg/m3 in a waste processing room at a Finnish resource recovery plant, where very high values of bioaerosols had also been observed (median levels of 150,000 and 65,000 CFU/m3 of total and gram-negative bacteria, respectively). Recently, outdoor concentrations of VOCs were found to range between 0.9 and 121.2 mg/m3 in the vicinity of another MSW management facility in Catalonia (Vilavert et al., 2009). Automobile exhausts have been considered as the main source of mono-aromatic hydrocarbons such as BTEX (Dutta et al., 2009). Therefore, ambient air levels of VOCs may highly differ, being more abundant in urban sites (Ras-Mallorquı´ et al., 2007). Complementarily to the present investigation, an odor exposure study, using field panel observations was carried out around the Ecoparc-2, according to the German standard EN3940 (Feliubadalo´ et al., 2008). Although the results in the industrial complex exceeded the German criteria for industrial areas (15% odor hours), those found in the most immediate urban zone were below the criteria for residential areas (10% odor hours). In addition, a dispersion model of the odor impact was also obtained by applying ESCT and CALPUFF models.
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Human health risks A first evaluation of the chemical risks was carried out by comparing the median VOC concentrations and the Daily Exposure Values established by the Spanish National Institute of Safety and Hygiene at Work (Table 2). The current exposure level to VOCs would be clearly lower than the maximum recommended threshold, indicating that indoor VOC concentrations would not be of concern for the health of workers. Subsequently, a more accurate and specific risk assessment approach was executed. The occupational exposure to the target compounds was subsequently assessed by applying the standard methodology developed by the US EPA. Since all the studied contaminants are volatile, inhalation was considered to be the main exposure route to VOCs. Exposure concentration through inhalation was calculated with the following equation: EC ¼
C air EF ED ET AT
where EC is the exposure concentration (in mg/m3), Cair is the air median concentration of each pollutant (in mg/m3), EF is the exposure frequency (250 days/year), ED is the exposure duration (25 years), ET is the daily exposure time (8/24 h), and AT is the average time (365 days/year ED). The health risks for the workers, differentiating between non-carcinogenic and carcino-
Table 3.
667
genic risks, were characterized. For each chemical contaminant, non-cancer risk (Hazard Quotient) was estimated by comparing the exposure concentration and the inhalation reference concentration (RfCi). On the other hand, the carcinogenic risk was calculated by multiplying the exposure by the US EPA Inhalation Unit Risk (IUR). For cancer risks calculations, ED was 25 years, while AT was 70 years. The estimated noncarcinogenic and carcinogenic risks due to the exposure to each VOC are summarized in Table 3. The sorting cabins (A) and the receiving hall (B) were the only areas where the Hazard Index, calculated as the sum of the Hazard Quotients, was estimated to be above the unity (6.19 and 1.15, respectively). This would be consequence of the especially high concentrations of toluene registered in both areas. In turn, the cancer risk was estimated in 8.73 104, 1.55 104, 1.83 105 and 1.39 104 in the sampling zones A, B, C and D, respectively, assuming that the carcinogenic risk of different pollutants is cumulative. Because risk estimates for various chemicals are presented as values on the same numeric scale, total cancer risks are often calculated as the sum of risks (US EPA, 2003). For the general population, the maximum acceptable risk threshold ranges between 106 and 104. However, some authors consider that levels of up to 103 might be accepted in case of occupationally exposed populations (Tran et al., 2000). Anyhow, and individually studying
Non-carcinogenic and carcinogenic risks (unitless) of exposure to VOCs in different workplaces in Ecoparc-2. Non-carcinogenic risk
Benzene Toluene Ethylbenzene m,p-Xylene o-Xylene Styrene Naphthalene Methylene chloride 1,2-Dichloroethane Chloroform Trichloroethylene Tetrachloroethylene 1,3-Butadiene 1,3,5-Trimethylbenzene 1,2,4-Trimethylbenzene p-Isopropyltoluene n-Propylbenzene Isopropylbenzene Formaldehyde Total risk
Carcinogenic risk
A
B
C
D
A
B
C
D
7.84E05 5.45 1.78E01 3.99E01 5.59E02 1.47E02 1.20E06 3.77E03 – 4.70E04 – 8.23E02 – 2.09E04 7.03E04 – – – 1.83E05 6.19
8.22E05 9.65E01 3.94E02 1.05E01 1.67E02 4.91E03 7.88E07 6.91E03 1.37E03 4.25E04 – 7.30E03 – 5.00E05 2.24E04 – – – 1.03E05 1.15
1.64E05 5.76E02 1.31E03 1.84E03 4.87E04 1.03E07 – – 4.25E05 – – – 3.29E06 1.54E05 – – – 2.30E05 6.14E02
9.25E05 5.34E01 2.42E02 6.87E02 9.75E03 2.12E03 8.90E07 2.64E03 5.18E03 3.47E04 – 5.92E03 – 3.56E05 1.42E04 – – – 1.16E05 6.53E01
7.28E06 – 1.59E04 – – – 4.85E06 5.75E07 – 3.94E05 1.08E05 6.42E04 – – – – – – 8.69E06 8.73E04
7.63E06 – 3.52E05 – – – 3.19E06 1.05E06 5.30E06 3.56E05 4.65E06 5.70E05 – – – – – – 4.88E06 1.55E04
1.53E06 – 1.17E06 – – – 4.16E07 – – 3.56E06 7.42E07 – – – – – – – 1.09E05 1.83E05
8.59E06 – 2.16E05 – – – 3.60E06 4.02E07 2.00E05 2.91E05 4.48E06 4.62E05 – – – – – – 5.51E06 1.39E04
The sampling areas (A, B, C, D) are described in the ‘‘Materials and methods’’ section. Total non-carcinogenic risk (Hazard Index) and carcinogenic risk were calculated as the sum of risks due to individual compounds.
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each one of the analyzed VOCs, a cancer risk index of 104 would be only exceeded in the sorting cabins, being exclusively due to exposure to ethylbenzene and tetrachloroethylene (1.59 104 and 6.42 104, respectively). With respect to the health risks derived from exposure to bioaerosols, currently, there are no standards set by the National Institute of Occupational Safety and Health (NIOSH) and the American Conference of Governmental Industrial Hygienists (ACGIH) concerning the allowable amount of microbiological agents at the workplace (Vilavert et al., 2009). However, some recommendations have been published by both institutions (guidelines of 100-1000 and 1000 CFU/m3 for total fungi and total number of bioaerosols particles, respectively). In addition, some investigators have suggested a limit value of 10,000 CFU/m3 for total bacteria, and 1,000 CFU/m3 for gram-negative bacteria (Marchand et al., 1995; Kiviranta et al., 1999). In comparison to those levels, the current bacterial concentrations would exceed the proposed limits in the sorting cabins for exposure to gram-negative bacteria. In fact, the relationship between the occupational levels in the zone A and the reference concentrations, considered as estimative method to obtain a measure of the exposure degree (Domingo and Nadal, 2009), would be up to 80. The above results indicate that workers in the sorting cabins seem to be the most exposed to chemical and microbiological pollutants during the treatment of the organic fraction of MSW. Protective equipment is already recommended for plant operators of waste handling facilities. Workers should be subjected to preventive measures such as the use of integrated P3 filter masks to avoid exposure to gases, vapors and particles. Gloves should be also used. Moreover, because of the relatively higher levels of pollution detected in the reception and composting areas, workers in the remaining zones, where a direct contact to organic waste exists (B and D), should strongly be advised to wear the same protection equipment. On the other hand, as previously suggested (Sa´nchez-Monedero and Stentiford, 2003), the emission and dispersion of bioaerosols and particles should be minimized during the process through the application of additional measures, such as the humectation of waste and the installation of extractor hoods in zones with a high potential risk. Thus, biofiltration seems to be a promising method to reduce not only odors, but also the release of both microbiological and chemical agents. In a comprehensive study at nine different composting plants and in their surrounding, an odor reduction was observed at facilities equipped with a biofilter (Fischer et al., 2008). In turn, removal efficiencies of 97% and 90% for VOCs and A. fumigatus, respectively, have been achieved after installing biofilters in composting sites (Sa´nchez-Monedero et al., 2003; Pagans et al., 2006).
The current strategy of the local authorities in Barcelona is enforced to achieve an integral treatment of the MSW, including its organic fraction. The construction of several Ecoparcs of similar characteristics to that evaluated here is already planned. However, in spite of the singular importance that these facilities will/should perform in the near future, until now, there has been a complete gap with respect to the health risks for the workers of those plants. The screening results here presented mean a first attempt to cover that gap.
Acknowledgments This study was financially supported by the Spanish National Institute of Safety and Hygiene at Work, through the project 06-03-FORSU-URV-302. The authors thank Joan Feliubadalo´ and Javier Cerezo for their collaboration through the investigation. We also thank Jessica Jime´nez and Albert Rallo for their valuable technical assistance during the sampling. Finally, Jordi Borra`s and Catalina Ubiedo are acknowledged for their teaching of the sampling devices.
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