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Pollutants emitted by a cement plant: health risks for the population living in the neighborhood
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Environmental Research 95 (2004) 198–206
Pollutants emitted by a cement plant: health risks for the population living in the neighborhood Marta Schuhmacher,a,b Jose L. Domingo,a, and Josepa Garretaa a
Laboratory of Toxicology and Environmental Health, School of Medicine, ‘‘Rovira i Virgili’’ University, San Lorenzo 21, 43201 Reus, Spain b Environmental Engineering Laboratory, Department of Chemical Engineering, ‘‘Rovira i Virgili’’ University, Sescelades Campus, 43007 Tarragona, Spain Received 26 March 2003; received in revised form 7 July 2003; accepted 12 August 2003
Abstract The aim of this study was to investigate the health risks due to combustor emissions in the manufacturing of Portland cement for the population living in the neighborhood of a cement kiln in Catalonia, Spain. Pollutants emitted to the atmosphere in the course of cement production were modeled. The ISC3-ST model was applied to estimate air dispersion of the contaminants emitted by the cement plant. Air concentrations of NO2, SO2, PM10, metals, and polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/ Fs), as well as the potential exposure in the vicinity of the facility, were assessed via models based on US EPA guidance documents. PCDD/F and metal concentrations were also modeled for soil and vegetation. Based on these concentrations, the levels of human exposure were calculated. Individual cancer and noncancer risks for the emissions of the cement kiln were assessed. Health effects due to NO2, SO2, and PM10 emissions were also evaluated. Risk assessment was performed as a deterministic analysis. The main individual risk in the population was evaluated in a central-tendency and a high-end approach. The results show that the incremental individual risk due to emissions of the cement plant is very low not only with regard to health effects, but also in relation to toxicological and cancer risks produced by pollutants such as metals and PCDD/Fs emitted by the cement kiln. r 2003 Elsevier Inc. All rights reserved. Keywords: Cement plant; Atmospheric emissions; Criteria and noncriteria pollutants; Human health; Risk assessment
1. Introduction Studies on the potential impact on public health associated with stack emissions from combustion of fuels have mainly focused on two classes of compounds: (1) criterion pollutants such as carbon monoxide (CO), nitrogen, and sulfur oxides (NOx and SOx), particulate matter (PM), and hydrocarbons (HC), and (2) noncriterion pollutants such as arsenic, cadmium, chromium, lead, zinc, dioxins, and furans (PCDD/Fs), polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), benzene, and other organic compounds. In recent years, quantitative risk assessment tools have been used to evaluate stack emissions from different combustion sources (Rice et al., 1999; Ziqiang et al., 1996). Environmental Risk Assessment (ERA) is a
Corresponding author. Fax: +34-977-759322. E-mail address: [email protected] (J.L. Domingo).
0013-9351/$ - see front matter r 2003 Elsevier Inc. All rights reserved. doi:10.1016/j.envres.2003.08.011
procedure for evaluating the probability that adverse effects on the environment and/or the human health occur (or may occur) as a consequence of the exposure to one or more physical, chemical or biological agents. The evaluation of the environmental risk requires the knowledge of the adverse effects that may be caused by exposure to chemical substances or materials (Fan et al., 1995). The intensity and duration to produce adverse effects on the environment and the population are also required. Knowledge of the intrinsic physical–chemical properties of the pollutants, their biodegradability, the potential for bioaccumulation, and the potential adverse effects of the chemical substances is necessary for evaluation of environmental risks. Moreover, it is also necessary to carry out a detailed evaluation of the emission sources and the fate and distribution in the different media. For it, the analysis of environmental samples concurrently with the application of mathematical models is essential.
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Chemicals emitted from a source into the atmosphere are directly transmitted to humans through air inhalation. However, these chemicals can also cross-environmental media boundaries, becoming distributed in soils, vegetation, water, biota, etc. Consequently, human health can be also indirectly affected through different pathways such as drinking water or groundwater, skin absorption of the chemicals present in water, intake of contaminated foodstuffs, and oral and skin absorption of chemicals from soils. Therefore, for an accurate health risk estimation, the chemical concentrations in each of these environmental media must be determined (Nessel et al., 1991; Zemba et al., 1996). The knowledge of pollutant fate and transport is essential to assess the potential environmental impact. Compartment multimedia models have become useful screening tools to determine multimedia pollutant exposure and for risk assessment. Portland cement results from the grinding of a clinker. The clinker is produced by burning a mixture of limestone, clay, and gypsum at high temperatures (1450–1600 C for the materials, and approximately 2000 C for the combustion fumes). Cement is manufactured in three basic steps: extraction and preparation of raw materials, calcining, and finally grinding of the clinker (Suess et al., 1985). Atmospheric emissions include particles, NOx, SO2, CO2 and lower amounts of CO, organic compounds such as PCDD/Fs and PAHs, metals (mainly adhered to particles), as well as other minor pollutants (Alcock et al., 1999; Brzuzy and Hites, 1996; Isikli et al., 2003; Kalafatoglu et al., 2001; Sidhu et al., 2001). Portland cement dust is a gray powder with an aerodynamic diameter ranging from 0.05 to 5 mm. This size is within the range of sizes of respirable particles. Therefore, exposure to Portland cement dust has been long associated with respiratory symptoms (Kalacic, 1973). To date, data on environmental levels and health risks for populations living near cement plants are very scarce (Brockhaus et al., 1981; Ginns and Gatrell, 1996; Legator et al., 1998; Yang et al., 2003). Moreover, studies simultaneously assessing health risks due to emissions from criteria pollutants and toxicants are also scarce. The main goal of the present study was to evaluate the environmental impact caused by air emissions from a cement plant located in a residential area with no other industrial air emission sources in the area. Specifically, the study was focused on the long-term aspect of air pollution (acute and chronic) and human health risks associated with emissions of criterion and noncriterion pollutants. For it, pollutant concentrations in air, soil, and vegetation were determined through computational models. Although air emissions from a cement plant can generate local and long-range impacts, in the present study only local impacts (about 50 km) were considered.
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2. Materials and methods 2.1. Description of the plant The cement plant began operating in 1902 and has a production capacity of 1,500,000 tons of clinker per year. The facility consists of two kilns and two clinker cooling units. However, since one of the cooling units incorporates the gases inside the kiln, only three stacks have air emissions. A cyclone system, together with an electrostatic precipitator, is used to retain the particle emissions to air. 2.2. Pollution transport To evaluate pollutant air concentrations in the vicinity of the cement plant, the ISC3-ST model (Gaussian dispersion model from US EPA) was run for the different contaminants emitted by the facility. This is a short-term model whose use is not recommended beyond 50 km due to uniform vertical mixing a long range and meteorological variability. Although the ISC3-ST can model gas and particle emissions, secondary pollutants such as O3 or sulfates cannot be modeled. Annual average air concentrations and wet and dry deposition were available. Site-specific information such as stack emission rates, meteorological data, stack parameters, and cartographic data, were input into the model. On the other hand, when the dispersion model was applied the buildings that could cause a disturbance of the air flow were taken into account. A meteorological station located at the same plant provides hourly meteorological data (wind speed, ambient temperature, cloudiness, direction of the wind, and sun radiation). The primary wind direction was ENE, with a frequency of 19.01% (annual average), while the secondary wind direction was NE, with a frequency of 18.52%. The percentage of calms was more or less constant throughout the year (around 4.8%). The plant is located near a residential area with an important vineyard crop. No other industrial activities are operating in that area. Therefore, to assess health risks for the population living in the neighborhood of the facility, no other emission sources were considered. In the present study, 16 sensitive receptors were selected. These receptors corresponded to zones of a high density of population or protected areas. The study area has a population of 80,976 inhabitants with a density of 136.7 inhabitants/km2. The receptor with the highest impact from the plant (Santa Margarida i Els Monjos) is placed at a distance of only a few hundred meters from the plant, which has a population of 5042 inhabitants. Fig. 1 shows the location of the receptors plotted in a Geographic Information System (GIS).
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M. Schuhmacher et al. / Environmental Research 95 (2004) 198–206 Table 1 Mean pollutant emissions ðn ¼ 4Þ from the cement plant Pollutant
Emissions from each cement kilna (g/s)
Emissions from the cooling unitb (g/s)
As Cd Cr Hg Ni Pb Zn Particulate matter NOx SO2 HCl TOC PCDD/Fs
5.53 104 1.11 103 1.47 103 3.68 104 2.39 103 1.22 102 7.18 103 9.21 125 1.71 2.69 4.75 8.84 109
9.19 105 4.78 104 5.88 104 4.96 104 1.84 104 2.52 103 4.04 104 9.17 101 — — — — —
a b
Fig. 1. Location of sampling points.
2.3. Rate of pollutant emissions Metals are present at small concentrations in the raw material and fuel used for cement clinker production. The behavior of metals in the burning process is dependent on their volatility. Elements such as lead or cadmium are semivolatile under the temperature conditions in the kiln. They are partly taken into the gas phase at sintering temperatures to condense on the raw material in cooler parts of the kiln system. This leads to a cyclic effect within the kiln system, which builds up the point where equilibrium is established and maintained between input and output via the cement clinker. On the other hand, volatile metals like mercury condense on raw material particles at lower temperatures. Therefore, mercury can be caught to an extent proportional to the degree of its absorption by the dust particles within the air pollution control device. Pollutants such as PCDD/ Fs are byproducts formed in the combustion kiln. With respect to gases such as SO2, HCl, and HF, the material leaving the calcination stage of a kiln process has a high content of calcium oxide, with a high absorptive capacity for acid species (Sidhu et al., 2001). In turn, SO2 can be converted to calcium sulfate into the calcining zone, leaving the kiln with the clinker. Table 1 shows the measured emissions (n ¼ 4) for the cement plant (kilns and cooling units). In contrast to the cement kilns, the clinker-cooling unit emits mainly PM and metals. Therefore, other pollutants were not considered. Mercury, sulfur dioxide (SO2), hydrogen chloride (HCl), nitrogen oxides (NOx), and PCDD/Fs were
Emission rate: 425,000 N m3/h for each kiln stack. Emission rate: 70,000 N m3/h.
simulated as the gas phase, while arsenic (As), cadmium (Cd), chromium (Cr), lead (Pb), nickel (Ni), zinc (Zn), and particles were simulated as the particulate phase. Air concentrations were calculated at the ground level. 2.4. Estimation of metal and PCDD/F concentrations in soil and vegetation Metal and PCDD/F concentrations in soil and vegetation were determined for each of the 16 receptors in the study area. Average results were calculated as estimates of the mean heavy metal and PCDD/F concentrations. Moreover, the highest deposition fluxes of the region were used in order to estimate the maximum concentrations in soil and vegetation resulting from the stack emissions of the cement kiln. In contrast to air dispersion, no fully developed models could be applied to calculate metal and PCDD/F concentrations in soil and vegetation. Consequently, it was necessary to establish equations, which might give a realistic description of the accumulation and loss of contaminants in the environmental media (Meneses et al., 2002; US EPA, 1996, 1998, 1999). 2.4.1. Soils The accumulation of pollutants in soils is the result of particle deposition, vapor diffusion, and the loss of contaminants through various processes such as leaching or volatilization. Distribution and mobility of contaminants are affected by soil conditions such as pH, structure and characteristics, and water content. In a first step, cumulative soil concentrations were calculated. These estimates accounted for the quantities of all metals and PCDD/Fs in soils that resulted from the stack emissions of the cement kiln only. The obtained cumulative concentrations were used for the calculation of pollutant levels in vegetation due to root uptake. To
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evaluate the impact produced by the facility, natural background concentrations of the area and potential influences of other human activities in the zone were not considered. The following equation was used to calculate cumulative soil concentrations of each metal. It contains the deposition fluxes, the period in that deposition occurs, as well as site-specific terms Cs ¼
ðDp þ DvÞ ð1 expð ks TD ÞÞ; ks BD Zs
ð1Þ
where Cs is concentration in soil (mg/g), Dp is particle deposition flux (g/m2 yr), Dv is vapor deposition flux (g/m2 yr), ks is soil loss constant (yr1), BD is bulk density of the soil (g/cm3), Zs is soil mixing depth (cm), and TD is time period of deposition (yr). As the particle-bound metals do not underlie vapor diffusion, only particle deposition was considered in the model. In contrast, Hg was assumed to exist only in vapor form. Although Hg is the object of various transformation processes in soil, it was assumed to accumulate primarily as Hg2+. With respect to PCDD/ Fs, depending on their vapor pressure the different PCDD/Fs congeners can be joined to the vapor or particulate phase. In the present study, it has been assumed that all PCDD/Fs had the same behavior as that of TCDD. Therefore, only vapor deposition would contribute to the concentration of PCDD/Fs in soils.
ith plant group (yr), and Ypi is yield or standing crop biomass of the ith plant group (kg dw/m2). Plant concentration due to vapor deposition. Only PCDD/Fs and Hg were considered to occur in vapor form. Dry diffusion and wet deposition contributed to accumulation of these pollutants in vegetation. Calculation of vapor deposition on the plants was essentially the same as for particle deposition, Cvdi ¼
1000ðDdv þ Fw Dwv ÞRpi Tpi ; Ypi
Cpdi ¼
1000ðDdP þFw DwP Þ kp Ypi Rpi ð1 expð kp Tpi ÞÞ;
ð2Þ
where Cpdi is concentration in the ith plant group due to particle deposition (mg/g dw), DdP is dry particulate deposition flux (g/m2 yr), DwP is wet particulate deposition flux (g/m2 yr), Fw is fraction of wet deposition that adheres to plant surfaces, kp is plant surface loss coefficient (yr1), Rpi is interception fraction of edible portion of plant tissue for the ith plant group, Tpi is time of plant’s exposure to deposition per harvest for the
ð3Þ
where Cvdi is concentration in the ith plant group due to deposition (mg/g dw), Ddv is dry deposition flux (g/ m2 yr), Dwv wet deposition flux (g/m2 yr), Rpi is interception fraction of the edible portion of plant tissue for the ith plant group, Tpi is time of the plant’s exposure to deposition per harvest for the ith plant group (yr), Ypi is the yield or standing crop biomass of the ith plant group (kg dw/m2). Plant concentration due to root uptake. Above-ground, plants take up soil contaminants through the roots. The contaminants accumulate in the below-ground parts or are moved to the above-ground shoots of the plant. The levels of contaminants in plants were determined from the concentration of the contaminant in soil and a chemical-specific bioconcentration factor (Br), Cpri ¼ Cs Bri ;
2.4.2. Vegetation In vegetation, the principal routes of chemical accumulation are particle and vapor deposition and root uptake. Plant concentration due to particle deposition. The particulate air concentrations of contaminants lead to levels in vegetation through dry and wet deposition on plant surfaces. The algorithm for vegetation concentrations includes the deposition fluxes and several plantspecific parameters. In this study, deposition fluxes of metals were obtained from the air dispersion model. Dry deposition was assumed to remain on the plant surface until weathering occurs. However, only a fraction of wet deposition remains on the plant and the rest is assumed to wash down immediately,
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ð4Þ
where Cpri is the concentration in the ith plant group due to root uptake (mg/g dw), Cs is the soil concentration (mg/g soil), Bri is the soil-to-plant bioconcentration factor ([mg/g dw plant]/[mg/g soil]). The calculation of concentrations in roots varies depending on the characteristics of the contaminant. For organic substances such as PCDD/Fs, the calculation is a function of the root concentration factor (RCF). However, the calculation of metals in the belowground parts is the same as for root uptake in aboveground plants (Fries, 1995). The above models were recently used and validated (Meneses et al., 2002). 2.5. Human health risk assessment Human health risks posed by contaminated air, soil, and vegetation in a residential area depend on the potential extent of exposure, as well as the toxic properties of the pollutants. In the current study, the concentrations of As, Cd, Cr, Hg, Ni, Pb, Zn, and PCDD/Fs in soil and vegetation in the area under evaluation were calculated according to the models presented above. For soil deposition, a period of 70 years of emission (mean life of a person) was assumed. Risk assessment has been defined as a process having four steps (NAS, 1983):
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2.5.1. Hazard identification Among the pollutants emitted by the cement kiln, PM10, NO2, SO2, metals (As, Cd, Cr, Hg, Ni, Pb, Zn) and PCDD/Fs were considered. Due to a lack of information from emissions or from the dispersion model approach, other primary (CO or PAH) or secondary (O3, sulfates, and nitrates) contaminants were not taken into account. 2.5.2. Dose– (or concentration–) response (effects) assessment An association between daily concentrations of pollutants in air with daily morbidity and mortality has been reported (Levy et al., 1999; Schwartz et al., 2001). For carcinogenic effects the US EPA has developed cancer slope factors (CSFs), while oral reference doses (RfDs) or inhalation reference concentrations (RfCs) have been developed for noncarcinogenic effects. 2.5.3. Exposure assessment The present study was simplified by analyzing the exposure of common people living in the study area, but not working in the cement plant. They were considered to be representative of the population of the area. Only adults were included. No distinctions by sex were made. Human exposure to metals was modeled based on the concentrations of these elements in air, soil, and vegetation of the area. Central-tendency estimates of human exposure were calculated with the mean concentrations of metals in the study area. In the high-end approach, the maximum concentrations were used. Human exposure was considered for inhalation and oral pathways, including air inhalation and inhalation of resuspended particles, as well as the ingestion of soil and vegetation. Dermal absorption of metals by skin contact with contaminated soil was also considered. It was ascribed to oral exposure as recommended by the US EPA (1998). The relevant algorithms for each exposure pathway were previously detailed (Schuhmacher et al., 2001). 2.5.4. Risk characterization Human health effects were divided into (1) health damage (caused by criteria contaminants as PM10, NO2, and SO2) that can produce morbidity or mortality effects on human populations, (2) carcinogenic effects (produced by PCDD/Fs and some metals), and (3) noncarcinogenic effects (due to oral or inhalation exposure to various pollutants). 2.6. Health risks caused by criteria contaminants Taking into account the results of recent epidemiological studies showing mortality and morbidity impacts associated with concentration changes in air criteria
pollutants (Brauer et al., 2001; Goldberg et al., 2003; Levy et al., 1999; Schwartz et al., 2001; Tenias et al., 2002), the rates of increased number of outcomes per exposed individual and per unit of pollution were used for respiratory effects. The model elaborated by Levy et al. (1999) was applied. In this model, epidemiological studies were updated and a quantitative methodology was used to pool epidemiological findings and account for co-pollutant confounding. The estimated pooled effect, as well as the percentage change in outcome per increased unit of ambient pollution were also calculated. These effects are given per 10 mg/m3 increase in 24-h average ambient pollution concentrations. A detailed description of the model structure, its findings and uncertainties were previously reported (Levy, 1999). 2.6.1. Acute mortality According to Levy et al. (1999), the following acute mortality rates were used: For PM10, with all other pollutant concentrations unchanging, acute mortality rates increased by 0.6% for every 10 mg/m3 increase in concentrations. This implies that acute mortality rates increased by 0.6% for every 10 mg/m3 increase in PM10 concentrations. PM health effects were presented as function of PM10 and convert other measures using default values of 0.55 for PM10/ TSP (US EPA, 1982). Although none of the studies evaluating SO2 in a multipollutant model found statistical significance (Levy et al., 1999), all central estimates were positive, indicating the potential for a weak independent effect. In the current study, as proposed by Levy et al. (1999), the acute mortality rates increased by 0.04% for every 10 mg/m3 increase in concentrations. For NO2, the pooled single-pollutant estimate is highly insignificant. Consequently, NO2 was not considered as a causal predictor of mortality. To calculate the expected change in the number of deaths per exposed individual per mg/m3 of pollution, a daily nonaccidental death rate of 2.3 105 (SCS, 1996) was used. 2.6.2. Chronic mortality Two recent investigations have found evidences of chronic mortality by exposure to PM10 (Pope et al., 1995; Schwartz et al., 2001). From these data, a chronic mortality rate of 4% for a 10 mg/m3 increase in PM10 concentration was here considered. 2.6.3. Morbidity Impacts of criteria pollutants on a number of morbidity outcomes such as chronic bronchitis, respiratory and cardiovascular admissions, emergency room visits, asthma attacks, and other respiratory symptoms can be enhanced by increasing air contamination caused by cement kiln emissions (Samet et al., 2000).
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The enhanced rate considered in the present study was 0.3% increase in admissions for lung obstructive disease for SO2, and 0.2% increase in asthma visits for NO2 (Cox, 1999). For particles, rates of 8.2 during summer and 2.3 during winter were previously reported (Castellsague et al., 1995). According to this, an incremental rate of 5.3% was considered. For the evaluation of morbidity outcomes, daily local respiratory outcomes were taken into account. In the current study, daily asthma admissions of 0.96, and 4.1 daily emergencies by chronic lung obstruction were considered (SCS, 1996). 2.7. Noncarcinogenic risks Depending on the exposure level, adverse health effects other than cancer can be associated with all chemical substances. Therefore, a noncancer risk characterization is always a dose–response analysis, which compares whether the actual human exposure exceeds a defined exposure level. This critical exposure level represents a threshold below which adverse effects are assumed to be unlikely. For a noncarcinogenic evaluation, the daily intake is compared with the reference dose for chronic exposure (RfD) in order to determine if the contaminant poses a human health risk. RfD is an estimate of daily exposure to a human population (Smith, 1996). Noncancer risks are expressed by the hazard quotient HQ, which relates the exposure to the RfD/RfC (Han et al., 1998). HQ refers only to the potential to which some individuals may be affected, and cannot address the absolute risk level. If HQ is higher than 1, this does not necessarily indicate a potential health risk.
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2.8. Carcinogenic risks Cancer risk expresses the likelihood of occurring cancer due to a definite daily intake of a pollutant. In the current study, inhalation and oral exposure were considered separately. Therefore, different human health benchmarks were required. Oral cancer risk was assessed using an oral CSF, while for inhalation of carcinogens the inhalation unit risk factor was used. CSFs do not represent a safe exposure level, but relate the exposure to the probability of causing carcinogenic effects (Gold et al., 1995). The carcinogenic risk was calculated by multiplying the estimated dose by the cancer potency factor. A total pathway risk was calculated by summing the cancer risk estimates of the chemical to each pathway. Since cancer risks describe the probability of developing cancer over a lifetime, the entire duration of exposure must be considered for risk assessment. In this study, 70 yr was assumed to be the average lifetime for the population of the area. During this period, individuals would be exposed to the emissions of the cement kiln. Reference doses and CSFs for the main pollutants emitted by the cement plant are summarized in Table 2.
3. Results and discussion 3.1. Evaluation of the contamination in different media Table 3 shows the simulated concentrations in air, soil, and vegetation of the pollutants emitted by the cement plant for the 16 receptors. Although it is well known that particles are among the most important pollutants emitted by cement plants, the use of air
Table 2 Calculated concentrations of the pollutants emitted by the cement planta Pollutant As Cd Cr Hg Ni Pb Zn PCDD/F (I-TEQ)
Air (ng/m3) 0.08 (0.21) 0.45 (1.16) 0.17 (0.43) 0.10 (0.26) 0.69 (1.79) 1.19 (3.10) 6.40 (16.50) 2.60 109 (9.27 109) (mg/m3)
Particles (TSP) TOC NOx SO2 HCl a
2.5 (8.4) 1.5 (4.9) 38.2 (128.0) 0.53 (1.78) 0.83 (2.78)
Mean values for the 16 receptors (maximum values in parentheses).
Soil (mg/kg dry weight)
Vegetation (mg/kg wet weight)
0.001 (0.002) 0.004 (0.012) 0.001 (0.004) 0.0003 (0.001) 0.026 (0.088) 0.007 (0.028) 0.051 (0.173) 1.39 108 (5.42 108)
0.00002 (0.0001) 0.001 (0.009) 0.00005 (0.006) 0.00006 (0.0025) 0.005 (0.012) 0.0001 (0.0008) 0.009 (0.017) 7.25 1010 (2.83 109)
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emission cleaning devices reduces these emissions in a remarkable quantity. The particles emitted by other processes in the facility such as mineral extraction or storage of raw materials were not considered. It must be taken into account that particle matter can also proceed from other anthropogenic (vehicles, agricultural activities, etc.) and natural (soil, particles from air coming from deserts, etc.) sources. PCDD/F concentrations in soil and vegetation were previously measured in the study area (Schuhmacher et al., 2002). Mean concentrations were 0.37 ng I-TEQ/ kg (dry weight) and 0.16 ng I-TEQ/kg (dry weight) for soil and herbage, respectively. The comparison of these results with those obtained by modeling show that the contributions of the cement plant to total I-TEQ in the area under evaluation were 3.8% and 3.0% for soil and vegetation, respectively. For metals, the comparison between the simulated data and recent experimental results in soils collected in Table 3 Reference doses and cancer factors of the principal pollutants emitted by the cement kilna Pollutant
As Cd Cr Hg Ni Pb Zn TCDD a
Reference Doses (mg/day kg) 4
3.0 10 5.0 104 1.0 3.0 104 2.0 102 6.0 103 0.30 4.0 109
Carcinogenic Factor (kg day/mg) Oral
Inhalation
1.75
50 6.3 42 1.2
1.6 105
1.2 105
Data from Smith (1996).
the area under study (Schuhmacher et al., 2002) shows that the lowest and highest contribution of the cement plant correspond to As and Cd, with percentages of 0.02% and 1.33%, respectively. In turn, the comparison of the modeling data with the analytical results in vegetation (Schuhmacher et al., 2002) indicates that the lowest and highest contribution of the cement plant correspond to Pb and Cd, respectively, with percentages of 0.1% and 33%. Taken these results into account, it can be concluded that a number of anthropogenic sources/human activities play an essential role in the environmental levels of most contaminants here assessed.
3.2. Human health risks Table 4 summarizes the results of the respiratory effects (acute and chronic mortality and morbidity increase) produced by the emissions of the cement kiln. In turn, Table 5 presents the incremental carcinogenic (inhalation and oral) and noncarcinogenic risks for the population living in the vicinity of the plant. The current results show that the incremental risk of mortality/morbidity produced by PM, and SO2 and NO2, does not mean any important additional health risk for the population living in the area under evaluation. The highest annual incremental risk corresponded to particles, with mean concentrations of 4.6 105 and 3.8 104 for chronic mortality and morbidity, respectively (1.6 104 and 1.3 103, for the maximum emissions). For a population of 80,976 inhabitants in the area of study, an annual increment of 37 subjects have been estimated to show health effects due to emissions from the plant. In turn, 8 individuals
Table 4 Adverse human health effects produced by pollutants emitted by the cement kiln Air immission concentrations due to the cement kiln (mg/m3)
Incremental annual risk for the population of the area
Incremental annual health effects due to emissions from the plant
Mean conc.
Mean conc.
Maximum conc.
Mean conc.a
Maximum conc.
Maximum conc.b
Acute mortality increase PM10c 1.4 SO2 0.5
4.6 1.8
6.9 106 1.7 107
2.3 105 6.0 107
0.56 0.01
0.12 0.00
Chronic mortality increase PM10c 1.4
4.6
4.6 105
1.6 104
3.72
0.81
4.6 1.8 51.2
3.8 104 3.9 106 1.9 105
1.3 103 1.4 105 6.2 105
30.77 0.32 1.54 36.92
6.55 0.07 0.31 7.86
Morbidity increase PM10c SO2 NO2d Total a
1.4 0.5 15.6
Population in the area of study: 80,976 inhabitants. Population living in the highest polluted area: 5042 inhabitants. c PM10=0.55 TPS. d NO2=40% NOx. b
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Table 5 Human health risk due to emissions from the cement kiln Noncarcinogenic risk (hazardous quotient)
Oral carcinogenic risk
Inhalation carcinogenic risk
Number of subjects developing cancer in their lifetime
Pollutant
Mean conc.
Maximum conc.
Mean conc.
Maximum conc.
Mean conc.
Maximum conc.
Mean conc.a
Maximum conc.b
As Cd Cr Hg Ni Pb Zn PCDD/F Total
5.7 105 4.7 104 3.7 108
1.7 104 3.2 103 1.0 106
6.9 109
2.9 108
6.6 107 4.7 107 1.2 106
1.7 106 1.2 106 3.0 106
0.05 0.04 0.10
0.01 0.01 0.02
4.6 105 3.6 105 8.4 106 2.9 105
1.1 104 1.3 104 1.8 105 1.2 104
1.8 108
7.6 108
5.0 1011
2.0 1010
1.5 103 0.19
3.8 104 0.03
a b
Population in the area of study: 80,976 inhabitants. Population living in the highest polluted area: 5042 inhabitants.
would be subjected to the maximum concentrations (5042 inhabitants) (Table 4). With respect to the incremental human health risk, the hazardous quotient (HQ) was clearly under 1 for all contaminants. On the other hand, the inhalation carcinogenic risk due to metals emitted by the plant ranged between a mean concentration of 1.2 106 for Cr to 4.7 107 for Cd (3.0 106 and 1.2 106, respectively, for the maximum concentrations). It must be taken into account that all emitted Cr has been considered to be present as Cr+6, which is the carcinogenic species of this element. In relation to PCDD/Fs, the inhalation cancer risks were 5.0 1011 and 2.0 1010 for the mean and maximum emissions, respectively. In turn, the oral carcinogenic risk was 1.8 108 and 7.6 108 for the mean and maximum concentrations, respectively. The incremental lifetime cancer risk for the population living in the vicinity of the plant would be of 0.2 for the total population of the area, 80,976 inhabitants. This risk would be of 0.03 for those living in the village most affected by the emissions (5042 inhabitants) (Table 5). Although some uncertainties in the results come from the use of fixed physicochemical properties of the contaminants, or are due to the use of some special considerations in the air, soil, and vegetation models, it is known that the highest uncertainty comes from the uncertainties in the general extrapolation to toxicity information (Asante-Duah, 2002). A probabilistic analysis (Monte Carlo simulation) was previously performed in order to regard the quantifiable uncertainty and variability of input in the calculation of human exposure and health risks (Schuhmacher et al., 2001). In general terms, it can be concluded that the incremental risk due to the emissions of the cement plant is comparatively very small, not only with respect to human health effects due to emission of criteria
contaminants, but also in relation to toxicological and cancer risks produced by exposure to pollutants such as metals and PCDD/Fs emitted by the facility. However, because risk assessment is subject to a great variability, the current results cannot be extrapolated to other cement kilns with different cleaning air pollution devices, different meteorology, or different operating conditions. This study must be considered as a preliminary evaluation of health risks derived from a concurrent exposure to criteria and noncriteria contaminants. Further investigations should also include long-range transport and secondary pollutants.
Acknowledgments This study is supported by the ‘‘Rovira i Virgili’’ Foundation, Tarragona, Spain.
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Pollutants emitted by a cement plant: health risks for the population living in the neighborhood Marta Schuhmacher,a,b Jose L. Domingo,a, and Josepa Garretaa a
Laboratory of Toxicology and Environmental Health, School of Medicine, ‘‘Rovira i Virgili’’ University, San Lorenzo 21, 43201 Reus, Spain b Environmental Engineering Laboratory, Department of Chemical Engineering, ‘‘Rovira i Virgili’’ University, Sescelades Campus, 43007 Tarragona, Spain Received 26 March 2003; received in revised form 7 July 2003; accepted 12 August 2003
Abstract The aim of this study was to investigate the health risks due to combustor emissions in the manufacturing of Portland cement for the population living in the neighborhood of a cement kiln in Catalonia, Spain. Pollutants emitted to the atmosphere in the course of cement production were modeled. The ISC3-ST model was applied to estimate air dispersion of the contaminants emitted by the cement plant. Air concentrations of NO2, SO2, PM10, metals, and polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/ Fs), as well as the potential exposure in the vicinity of the facility, were assessed via models based on US EPA guidance documents. PCDD/F and metal concentrations were also modeled for soil and vegetation. Based on these concentrations, the levels of human exposure were calculated. Individual cancer and noncancer risks for the emissions of the cement kiln were assessed. Health effects due to NO2, SO2, and PM10 emissions were also evaluated. Risk assessment was performed as a deterministic analysis. The main individual risk in the population was evaluated in a central-tendency and a high-end approach. The results show that the incremental individual risk due to emissions of the cement plant is very low not only with regard to health effects, but also in relation to toxicological and cancer risks produced by pollutants such as metals and PCDD/Fs emitted by the cement kiln. r 2003 Elsevier Inc. All rights reserved. Keywords: Cement plant; Atmospheric emissions; Criteria and noncriteria pollutants; Human health; Risk assessment
1. Introduction Studies on the potential impact on public health associated with stack emissions from combustion of fuels have mainly focused on two classes of compounds: (1) criterion pollutants such as carbon monoxide (CO), nitrogen, and sulfur oxides (NOx and SOx), particulate matter (PM), and hydrocarbons (HC), and (2) noncriterion pollutants such as arsenic, cadmium, chromium, lead, zinc, dioxins, and furans (PCDD/Fs), polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), benzene, and other organic compounds. In recent years, quantitative risk assessment tools have been used to evaluate stack emissions from different combustion sources (Rice et al., 1999; Ziqiang et al., 1996). Environmental Risk Assessment (ERA) is a
Corresponding author. Fax: +34-977-759322. E-mail address: [email protected] (J.L. Domingo).
0013-9351/$ - see front matter r 2003 Elsevier Inc. All rights reserved. doi:10.1016/j.envres.2003.08.011
procedure for evaluating the probability that adverse effects on the environment and/or the human health occur (or may occur) as a consequence of the exposure to one or more physical, chemical or biological agents. The evaluation of the environmental risk requires the knowledge of the adverse effects that may be caused by exposure to chemical substances or materials (Fan et al., 1995). The intensity and duration to produce adverse effects on the environment and the population are also required. Knowledge of the intrinsic physical–chemical properties of the pollutants, their biodegradability, the potential for bioaccumulation, and the potential adverse effects of the chemical substances is necessary for evaluation of environmental risks. Moreover, it is also necessary to carry out a detailed evaluation of the emission sources and the fate and distribution in the different media. For it, the analysis of environmental samples concurrently with the application of mathematical models is essential.
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Chemicals emitted from a source into the atmosphere are directly transmitted to humans through air inhalation. However, these chemicals can also cross-environmental media boundaries, becoming distributed in soils, vegetation, water, biota, etc. Consequently, human health can be also indirectly affected through different pathways such as drinking water or groundwater, skin absorption of the chemicals present in water, intake of contaminated foodstuffs, and oral and skin absorption of chemicals from soils. Therefore, for an accurate health risk estimation, the chemical concentrations in each of these environmental media must be determined (Nessel et al., 1991; Zemba et al., 1996). The knowledge of pollutant fate and transport is essential to assess the potential environmental impact. Compartment multimedia models have become useful screening tools to determine multimedia pollutant exposure and for risk assessment. Portland cement results from the grinding of a clinker. The clinker is produced by burning a mixture of limestone, clay, and gypsum at high temperatures (1450–1600 C for the materials, and approximately 2000 C for the combustion fumes). Cement is manufactured in three basic steps: extraction and preparation of raw materials, calcining, and finally grinding of the clinker (Suess et al., 1985). Atmospheric emissions include particles, NOx, SO2, CO2 and lower amounts of CO, organic compounds such as PCDD/Fs and PAHs, metals (mainly adhered to particles), as well as other minor pollutants (Alcock et al., 1999; Brzuzy and Hites, 1996; Isikli et al., 2003; Kalafatoglu et al., 2001; Sidhu et al., 2001). Portland cement dust is a gray powder with an aerodynamic diameter ranging from 0.05 to 5 mm. This size is within the range of sizes of respirable particles. Therefore, exposure to Portland cement dust has been long associated with respiratory symptoms (Kalacic, 1973). To date, data on environmental levels and health risks for populations living near cement plants are very scarce (Brockhaus et al., 1981; Ginns and Gatrell, 1996; Legator et al., 1998; Yang et al., 2003). Moreover, studies simultaneously assessing health risks due to emissions from criteria pollutants and toxicants are also scarce. The main goal of the present study was to evaluate the environmental impact caused by air emissions from a cement plant located in a residential area with no other industrial air emission sources in the area. Specifically, the study was focused on the long-term aspect of air pollution (acute and chronic) and human health risks associated with emissions of criterion and noncriterion pollutants. For it, pollutant concentrations in air, soil, and vegetation were determined through computational models. Although air emissions from a cement plant can generate local and long-range impacts, in the present study only local impacts (about 50 km) were considered.
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2. Materials and methods 2.1. Description of the plant The cement plant began operating in 1902 and has a production capacity of 1,500,000 tons of clinker per year. The facility consists of two kilns and two clinker cooling units. However, since one of the cooling units incorporates the gases inside the kiln, only three stacks have air emissions. A cyclone system, together with an electrostatic precipitator, is used to retain the particle emissions to air. 2.2. Pollution transport To evaluate pollutant air concentrations in the vicinity of the cement plant, the ISC3-ST model (Gaussian dispersion model from US EPA) was run for the different contaminants emitted by the facility. This is a short-term model whose use is not recommended beyond 50 km due to uniform vertical mixing a long range and meteorological variability. Although the ISC3-ST can model gas and particle emissions, secondary pollutants such as O3 or sulfates cannot be modeled. Annual average air concentrations and wet and dry deposition were available. Site-specific information such as stack emission rates, meteorological data, stack parameters, and cartographic data, were input into the model. On the other hand, when the dispersion model was applied the buildings that could cause a disturbance of the air flow were taken into account. A meteorological station located at the same plant provides hourly meteorological data (wind speed, ambient temperature, cloudiness, direction of the wind, and sun radiation). The primary wind direction was ENE, with a frequency of 19.01% (annual average), while the secondary wind direction was NE, with a frequency of 18.52%. The percentage of calms was more or less constant throughout the year (around 4.8%). The plant is located near a residential area with an important vineyard crop. No other industrial activities are operating in that area. Therefore, to assess health risks for the population living in the neighborhood of the facility, no other emission sources were considered. In the present study, 16 sensitive receptors were selected. These receptors corresponded to zones of a high density of population or protected areas. The study area has a population of 80,976 inhabitants with a density of 136.7 inhabitants/km2. The receptor with the highest impact from the plant (Santa Margarida i Els Monjos) is placed at a distance of only a few hundred meters from the plant, which has a population of 5042 inhabitants. Fig. 1 shows the location of the receptors plotted in a Geographic Information System (GIS).
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M. Schuhmacher et al. / Environmental Research 95 (2004) 198–206 Table 1 Mean pollutant emissions ðn ¼ 4Þ from the cement plant Pollutant
Emissions from each cement kilna (g/s)
Emissions from the cooling unitb (g/s)
As Cd Cr Hg Ni Pb Zn Particulate matter NOx SO2 HCl TOC PCDD/Fs
5.53 104 1.11 103 1.47 103 3.68 104 2.39 103 1.22 102 7.18 103 9.21 125 1.71 2.69 4.75 8.84 109
9.19 105 4.78 104 5.88 104 4.96 104 1.84 104 2.52 103 4.04 104 9.17 101 — — — — —
a b
Fig. 1. Location of sampling points.
2.3. Rate of pollutant emissions Metals are present at small concentrations in the raw material and fuel used for cement clinker production. The behavior of metals in the burning process is dependent on their volatility. Elements such as lead or cadmium are semivolatile under the temperature conditions in the kiln. They are partly taken into the gas phase at sintering temperatures to condense on the raw material in cooler parts of the kiln system. This leads to a cyclic effect within the kiln system, which builds up the point where equilibrium is established and maintained between input and output via the cement clinker. On the other hand, volatile metals like mercury condense on raw material particles at lower temperatures. Therefore, mercury can be caught to an extent proportional to the degree of its absorption by the dust particles within the air pollution control device. Pollutants such as PCDD/ Fs are byproducts formed in the combustion kiln. With respect to gases such as SO2, HCl, and HF, the material leaving the calcination stage of a kiln process has a high content of calcium oxide, with a high absorptive capacity for acid species (Sidhu et al., 2001). In turn, SO2 can be converted to calcium sulfate into the calcining zone, leaving the kiln with the clinker. Table 1 shows the measured emissions (n ¼ 4) for the cement plant (kilns and cooling units). In contrast to the cement kilns, the clinker-cooling unit emits mainly PM and metals. Therefore, other pollutants were not considered. Mercury, sulfur dioxide (SO2), hydrogen chloride (HCl), nitrogen oxides (NOx), and PCDD/Fs were
Emission rate: 425,000 N m3/h for each kiln stack. Emission rate: 70,000 N m3/h.
simulated as the gas phase, while arsenic (As), cadmium (Cd), chromium (Cr), lead (Pb), nickel (Ni), zinc (Zn), and particles were simulated as the particulate phase. Air concentrations were calculated at the ground level. 2.4. Estimation of metal and PCDD/F concentrations in soil and vegetation Metal and PCDD/F concentrations in soil and vegetation were determined for each of the 16 receptors in the study area. Average results were calculated as estimates of the mean heavy metal and PCDD/F concentrations. Moreover, the highest deposition fluxes of the region were used in order to estimate the maximum concentrations in soil and vegetation resulting from the stack emissions of the cement kiln. In contrast to air dispersion, no fully developed models could be applied to calculate metal and PCDD/F concentrations in soil and vegetation. Consequently, it was necessary to establish equations, which might give a realistic description of the accumulation and loss of contaminants in the environmental media (Meneses et al., 2002; US EPA, 1996, 1998, 1999). 2.4.1. Soils The accumulation of pollutants in soils is the result of particle deposition, vapor diffusion, and the loss of contaminants through various processes such as leaching or volatilization. Distribution and mobility of contaminants are affected by soil conditions such as pH, structure and characteristics, and water content. In a first step, cumulative soil concentrations were calculated. These estimates accounted for the quantities of all metals and PCDD/Fs in soils that resulted from the stack emissions of the cement kiln only. The obtained cumulative concentrations were used for the calculation of pollutant levels in vegetation due to root uptake. To
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evaluate the impact produced by the facility, natural background concentrations of the area and potential influences of other human activities in the zone were not considered. The following equation was used to calculate cumulative soil concentrations of each metal. It contains the deposition fluxes, the period in that deposition occurs, as well as site-specific terms Cs ¼
ðDp þ DvÞ ð1 expð ks TD ÞÞ; ks BD Zs
ð1Þ
where Cs is concentration in soil (mg/g), Dp is particle deposition flux (g/m2 yr), Dv is vapor deposition flux (g/m2 yr), ks is soil loss constant (yr1), BD is bulk density of the soil (g/cm3), Zs is soil mixing depth (cm), and TD is time period of deposition (yr). As the particle-bound metals do not underlie vapor diffusion, only particle deposition was considered in the model. In contrast, Hg was assumed to exist only in vapor form. Although Hg is the object of various transformation processes in soil, it was assumed to accumulate primarily as Hg2+. With respect to PCDD/ Fs, depending on their vapor pressure the different PCDD/Fs congeners can be joined to the vapor or particulate phase. In the present study, it has been assumed that all PCDD/Fs had the same behavior as that of TCDD. Therefore, only vapor deposition would contribute to the concentration of PCDD/Fs in soils.
ith plant group (yr), and Ypi is yield or standing crop biomass of the ith plant group (kg dw/m2). Plant concentration due to vapor deposition. Only PCDD/Fs and Hg were considered to occur in vapor form. Dry diffusion and wet deposition contributed to accumulation of these pollutants in vegetation. Calculation of vapor deposition on the plants was essentially the same as for particle deposition, Cvdi ¼
1000ðDdv þ Fw Dwv ÞRpi Tpi ; Ypi
Cpdi ¼
1000ðDdP þFw DwP Þ kp Ypi Rpi ð1 expð kp Tpi ÞÞ;
ð2Þ
where Cpdi is concentration in the ith plant group due to particle deposition (mg/g dw), DdP is dry particulate deposition flux (g/m2 yr), DwP is wet particulate deposition flux (g/m2 yr), Fw is fraction of wet deposition that adheres to plant surfaces, kp is plant surface loss coefficient (yr1), Rpi is interception fraction of edible portion of plant tissue for the ith plant group, Tpi is time of plant’s exposure to deposition per harvest for the
ð3Þ
where Cvdi is concentration in the ith plant group due to deposition (mg/g dw), Ddv is dry deposition flux (g/ m2 yr), Dwv wet deposition flux (g/m2 yr), Rpi is interception fraction of the edible portion of plant tissue for the ith plant group, Tpi is time of the plant’s exposure to deposition per harvest for the ith plant group (yr), Ypi is the yield or standing crop biomass of the ith plant group (kg dw/m2). Plant concentration due to root uptake. Above-ground, plants take up soil contaminants through the roots. The contaminants accumulate in the below-ground parts or are moved to the above-ground shoots of the plant. The levels of contaminants in plants were determined from the concentration of the contaminant in soil and a chemical-specific bioconcentration factor (Br), Cpri ¼ Cs Bri ;
2.4.2. Vegetation In vegetation, the principal routes of chemical accumulation are particle and vapor deposition and root uptake. Plant concentration due to particle deposition. The particulate air concentrations of contaminants lead to levels in vegetation through dry and wet deposition on plant surfaces. The algorithm for vegetation concentrations includes the deposition fluxes and several plantspecific parameters. In this study, deposition fluxes of metals were obtained from the air dispersion model. Dry deposition was assumed to remain on the plant surface until weathering occurs. However, only a fraction of wet deposition remains on the plant and the rest is assumed to wash down immediately,
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ð4Þ
where Cpri is the concentration in the ith plant group due to root uptake (mg/g dw), Cs is the soil concentration (mg/g soil), Bri is the soil-to-plant bioconcentration factor ([mg/g dw plant]/[mg/g soil]). The calculation of concentrations in roots varies depending on the characteristics of the contaminant. For organic substances such as PCDD/Fs, the calculation is a function of the root concentration factor (RCF). However, the calculation of metals in the belowground parts is the same as for root uptake in aboveground plants (Fries, 1995). The above models were recently used and validated (Meneses et al., 2002). 2.5. Human health risk assessment Human health risks posed by contaminated air, soil, and vegetation in a residential area depend on the potential extent of exposure, as well as the toxic properties of the pollutants. In the current study, the concentrations of As, Cd, Cr, Hg, Ni, Pb, Zn, and PCDD/Fs in soil and vegetation in the area under evaluation were calculated according to the models presented above. For soil deposition, a period of 70 years of emission (mean life of a person) was assumed. Risk assessment has been defined as a process having four steps (NAS, 1983):
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2.5.1. Hazard identification Among the pollutants emitted by the cement kiln, PM10, NO2, SO2, metals (As, Cd, Cr, Hg, Ni, Pb, Zn) and PCDD/Fs were considered. Due to a lack of information from emissions or from the dispersion model approach, other primary (CO or PAH) or secondary (O3, sulfates, and nitrates) contaminants were not taken into account. 2.5.2. Dose– (or concentration–) response (effects) assessment An association between daily concentrations of pollutants in air with daily morbidity and mortality has been reported (Levy et al., 1999; Schwartz et al., 2001). For carcinogenic effects the US EPA has developed cancer slope factors (CSFs), while oral reference doses (RfDs) or inhalation reference concentrations (RfCs) have been developed for noncarcinogenic effects. 2.5.3. Exposure assessment The present study was simplified by analyzing the exposure of common people living in the study area, but not working in the cement plant. They were considered to be representative of the population of the area. Only adults were included. No distinctions by sex were made. Human exposure to metals was modeled based on the concentrations of these elements in air, soil, and vegetation of the area. Central-tendency estimates of human exposure were calculated with the mean concentrations of metals in the study area. In the high-end approach, the maximum concentrations were used. Human exposure was considered for inhalation and oral pathways, including air inhalation and inhalation of resuspended particles, as well as the ingestion of soil and vegetation. Dermal absorption of metals by skin contact with contaminated soil was also considered. It was ascribed to oral exposure as recommended by the US EPA (1998). The relevant algorithms for each exposure pathway were previously detailed (Schuhmacher et al., 2001). 2.5.4. Risk characterization Human health effects were divided into (1) health damage (caused by criteria contaminants as PM10, NO2, and SO2) that can produce morbidity or mortality effects on human populations, (2) carcinogenic effects (produced by PCDD/Fs and some metals), and (3) noncarcinogenic effects (due to oral or inhalation exposure to various pollutants). 2.6. Health risks caused by criteria contaminants Taking into account the results of recent epidemiological studies showing mortality and morbidity impacts associated with concentration changes in air criteria
pollutants (Brauer et al., 2001; Goldberg et al., 2003; Levy et al., 1999; Schwartz et al., 2001; Tenias et al., 2002), the rates of increased number of outcomes per exposed individual and per unit of pollution were used for respiratory effects. The model elaborated by Levy et al. (1999) was applied. In this model, epidemiological studies were updated and a quantitative methodology was used to pool epidemiological findings and account for co-pollutant confounding. The estimated pooled effect, as well as the percentage change in outcome per increased unit of ambient pollution were also calculated. These effects are given per 10 mg/m3 increase in 24-h average ambient pollution concentrations. A detailed description of the model structure, its findings and uncertainties were previously reported (Levy, 1999). 2.6.1. Acute mortality According to Levy et al. (1999), the following acute mortality rates were used: For PM10, with all other pollutant concentrations unchanging, acute mortality rates increased by 0.6% for every 10 mg/m3 increase in concentrations. This implies that acute mortality rates increased by 0.6% for every 10 mg/m3 increase in PM10 concentrations. PM health effects were presented as function of PM10 and convert other measures using default values of 0.55 for PM10/ TSP (US EPA, 1982). Although none of the studies evaluating SO2 in a multipollutant model found statistical significance (Levy et al., 1999), all central estimates were positive, indicating the potential for a weak independent effect. In the current study, as proposed by Levy et al. (1999), the acute mortality rates increased by 0.04% for every 10 mg/m3 increase in concentrations. For NO2, the pooled single-pollutant estimate is highly insignificant. Consequently, NO2 was not considered as a causal predictor of mortality. To calculate the expected change in the number of deaths per exposed individual per mg/m3 of pollution, a daily nonaccidental death rate of 2.3 105 (SCS, 1996) was used. 2.6.2. Chronic mortality Two recent investigations have found evidences of chronic mortality by exposure to PM10 (Pope et al., 1995; Schwartz et al., 2001). From these data, a chronic mortality rate of 4% for a 10 mg/m3 increase in PM10 concentration was here considered. 2.6.3. Morbidity Impacts of criteria pollutants on a number of morbidity outcomes such as chronic bronchitis, respiratory and cardiovascular admissions, emergency room visits, asthma attacks, and other respiratory symptoms can be enhanced by increasing air contamination caused by cement kiln emissions (Samet et al., 2000).
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The enhanced rate considered in the present study was 0.3% increase in admissions for lung obstructive disease for SO2, and 0.2% increase in asthma visits for NO2 (Cox, 1999). For particles, rates of 8.2 during summer and 2.3 during winter were previously reported (Castellsague et al., 1995). According to this, an incremental rate of 5.3% was considered. For the evaluation of morbidity outcomes, daily local respiratory outcomes were taken into account. In the current study, daily asthma admissions of 0.96, and 4.1 daily emergencies by chronic lung obstruction were considered (SCS, 1996). 2.7. Noncarcinogenic risks Depending on the exposure level, adverse health effects other than cancer can be associated with all chemical substances. Therefore, a noncancer risk characterization is always a dose–response analysis, which compares whether the actual human exposure exceeds a defined exposure level. This critical exposure level represents a threshold below which adverse effects are assumed to be unlikely. For a noncarcinogenic evaluation, the daily intake is compared with the reference dose for chronic exposure (RfD) in order to determine if the contaminant poses a human health risk. RfD is an estimate of daily exposure to a human population (Smith, 1996). Noncancer risks are expressed by the hazard quotient HQ, which relates the exposure to the RfD/RfC (Han et al., 1998). HQ refers only to the potential to which some individuals may be affected, and cannot address the absolute risk level. If HQ is higher than 1, this does not necessarily indicate a potential health risk.
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2.8. Carcinogenic risks Cancer risk expresses the likelihood of occurring cancer due to a definite daily intake of a pollutant. In the current study, inhalation and oral exposure were considered separately. Therefore, different human health benchmarks were required. Oral cancer risk was assessed using an oral CSF, while for inhalation of carcinogens the inhalation unit risk factor was used. CSFs do not represent a safe exposure level, but relate the exposure to the probability of causing carcinogenic effects (Gold et al., 1995). The carcinogenic risk was calculated by multiplying the estimated dose by the cancer potency factor. A total pathway risk was calculated by summing the cancer risk estimates of the chemical to each pathway. Since cancer risks describe the probability of developing cancer over a lifetime, the entire duration of exposure must be considered for risk assessment. In this study, 70 yr was assumed to be the average lifetime for the population of the area. During this period, individuals would be exposed to the emissions of the cement kiln. Reference doses and CSFs for the main pollutants emitted by the cement plant are summarized in Table 2.
3. Results and discussion 3.1. Evaluation of the contamination in different media Table 3 shows the simulated concentrations in air, soil, and vegetation of the pollutants emitted by the cement plant for the 16 receptors. Although it is well known that particles are among the most important pollutants emitted by cement plants, the use of air
Table 2 Calculated concentrations of the pollutants emitted by the cement planta Pollutant As Cd Cr Hg Ni Pb Zn PCDD/F (I-TEQ)
Air (ng/m3) 0.08 (0.21) 0.45 (1.16) 0.17 (0.43) 0.10 (0.26) 0.69 (1.79) 1.19 (3.10) 6.40 (16.50) 2.60 109 (9.27 109) (mg/m3)
Particles (TSP) TOC NOx SO2 HCl a
2.5 (8.4) 1.5 (4.9) 38.2 (128.0) 0.53 (1.78) 0.83 (2.78)
Mean values for the 16 receptors (maximum values in parentheses).
Soil (mg/kg dry weight)
Vegetation (mg/kg wet weight)
0.001 (0.002) 0.004 (0.012) 0.001 (0.004) 0.0003 (0.001) 0.026 (0.088) 0.007 (0.028) 0.051 (0.173) 1.39 108 (5.42 108)
0.00002 (0.0001) 0.001 (0.009) 0.00005 (0.006) 0.00006 (0.0025) 0.005 (0.012) 0.0001 (0.0008) 0.009 (0.017) 7.25 1010 (2.83 109)
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emission cleaning devices reduces these emissions in a remarkable quantity. The particles emitted by other processes in the facility such as mineral extraction or storage of raw materials were not considered. It must be taken into account that particle matter can also proceed from other anthropogenic (vehicles, agricultural activities, etc.) and natural (soil, particles from air coming from deserts, etc.) sources. PCDD/F concentrations in soil and vegetation were previously measured in the study area (Schuhmacher et al., 2002). Mean concentrations were 0.37 ng I-TEQ/ kg (dry weight) and 0.16 ng I-TEQ/kg (dry weight) for soil and herbage, respectively. The comparison of these results with those obtained by modeling show that the contributions of the cement plant to total I-TEQ in the area under evaluation were 3.8% and 3.0% for soil and vegetation, respectively. For metals, the comparison between the simulated data and recent experimental results in soils collected in Table 3 Reference doses and cancer factors of the principal pollutants emitted by the cement kilna Pollutant
As Cd Cr Hg Ni Pb Zn TCDD a
Reference Doses (mg/day kg) 4
3.0 10 5.0 104 1.0 3.0 104 2.0 102 6.0 103 0.30 4.0 109
Carcinogenic Factor (kg day/mg) Oral
Inhalation
1.75
50 6.3 42 1.2
1.6 105
1.2 105
Data from Smith (1996).
the area under study (Schuhmacher et al., 2002) shows that the lowest and highest contribution of the cement plant correspond to As and Cd, with percentages of 0.02% and 1.33%, respectively. In turn, the comparison of the modeling data with the analytical results in vegetation (Schuhmacher et al., 2002) indicates that the lowest and highest contribution of the cement plant correspond to Pb and Cd, respectively, with percentages of 0.1% and 33%. Taken these results into account, it can be concluded that a number of anthropogenic sources/human activities play an essential role in the environmental levels of most contaminants here assessed.
3.2. Human health risks Table 4 summarizes the results of the respiratory effects (acute and chronic mortality and morbidity increase) produced by the emissions of the cement kiln. In turn, Table 5 presents the incremental carcinogenic (inhalation and oral) and noncarcinogenic risks for the population living in the vicinity of the plant. The current results show that the incremental risk of mortality/morbidity produced by PM, and SO2 and NO2, does not mean any important additional health risk for the population living in the area under evaluation. The highest annual incremental risk corresponded to particles, with mean concentrations of 4.6 105 and 3.8 104 for chronic mortality and morbidity, respectively (1.6 104 and 1.3 103, for the maximum emissions). For a population of 80,976 inhabitants in the area of study, an annual increment of 37 subjects have been estimated to show health effects due to emissions from the plant. In turn, 8 individuals
Table 4 Adverse human health effects produced by pollutants emitted by the cement kiln Air immission concentrations due to the cement kiln (mg/m3)
Incremental annual risk for the population of the area
Incremental annual health effects due to emissions from the plant
Mean conc.
Mean conc.
Maximum conc.
Mean conc.a
Maximum conc.
Maximum conc.b
Acute mortality increase PM10c 1.4 SO2 0.5
4.6 1.8
6.9 106 1.7 107
2.3 105 6.0 107
0.56 0.01
0.12 0.00
Chronic mortality increase PM10c 1.4
4.6
4.6 105
1.6 104
3.72
0.81
4.6 1.8 51.2
3.8 104 3.9 106 1.9 105
1.3 103 1.4 105 6.2 105
30.77 0.32 1.54 36.92
6.55 0.07 0.31 7.86
Morbidity increase PM10c SO2 NO2d Total a
1.4 0.5 15.6
Population in the area of study: 80,976 inhabitants. Population living in the highest polluted area: 5042 inhabitants. c PM10=0.55 TPS. d NO2=40% NOx. b
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Table 5 Human health risk due to emissions from the cement kiln Noncarcinogenic risk (hazardous quotient)
Oral carcinogenic risk
Inhalation carcinogenic risk
Number of subjects developing cancer in their lifetime
Pollutant
Mean conc.
Maximum conc.
Mean conc.
Maximum conc.
Mean conc.
Maximum conc.
Mean conc.a
Maximum conc.b
As Cd Cr Hg Ni Pb Zn PCDD/F Total
5.7 105 4.7 104 3.7 108
1.7 104 3.2 103 1.0 106
6.9 109
2.9 108
6.6 107 4.7 107 1.2 106
1.7 106 1.2 106 3.0 106
0.05 0.04 0.10
0.01 0.01 0.02
4.6 105 3.6 105 8.4 106 2.9 105
1.1 104 1.3 104 1.8 105 1.2 104
1.8 108
7.6 108
5.0 1011
2.0 1010
1.5 103 0.19
3.8 104 0.03
a b
Population in the area of study: 80,976 inhabitants. Population living in the highest polluted area: 5042 inhabitants.
would be subjected to the maximum concentrations (5042 inhabitants) (Table 4). With respect to the incremental human health risk, the hazardous quotient (HQ) was clearly under 1 for all contaminants. On the other hand, the inhalation carcinogenic risk due to metals emitted by the plant ranged between a mean concentration of 1.2 106 for Cr to 4.7 107 for Cd (3.0 106 and 1.2 106, respectively, for the maximum concentrations). It must be taken into account that all emitted Cr has been considered to be present as Cr+6, which is the carcinogenic species of this element. In relation to PCDD/Fs, the inhalation cancer risks were 5.0 1011 and 2.0 1010 for the mean and maximum emissions, respectively. In turn, the oral carcinogenic risk was 1.8 108 and 7.6 108 for the mean and maximum concentrations, respectively. The incremental lifetime cancer risk for the population living in the vicinity of the plant would be of 0.2 for the total population of the area, 80,976 inhabitants. This risk would be of 0.03 for those living in the village most affected by the emissions (5042 inhabitants) (Table 5). Although some uncertainties in the results come from the use of fixed physicochemical properties of the contaminants, or are due to the use of some special considerations in the air, soil, and vegetation models, it is known that the highest uncertainty comes from the uncertainties in the general extrapolation to toxicity information (Asante-Duah, 2002). A probabilistic analysis (Monte Carlo simulation) was previously performed in order to regard the quantifiable uncertainty and variability of input in the calculation of human exposure and health risks (Schuhmacher et al., 2001). In general terms, it can be concluded that the incremental risk due to the emissions of the cement plant is comparatively very small, not only with respect to human health effects due to emission of criteria
contaminants, but also in relation to toxicological and cancer risks produced by exposure to pollutants such as metals and PCDD/Fs emitted by the facility. However, because risk assessment is subject to a great variability, the current results cannot be extrapolated to other cement kilns with different cleaning air pollution devices, different meteorology, or different operating conditions. This study must be considered as a preliminary evaluation of health risks derived from a concurrent exposure to criteria and noncriteria contaminants. Further investigations should also include long-range transport and secondary pollutants.
Acknowledgments This study is supported by the ‘‘Rovira i Virgili’’ Foundation, Tarragona, Spain.
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