Health hazard prospecting by modeling wind transfer of metal-bearing dust from mining waste dumps: application to Jebel Ressas Pb-Zn-Cd abandoned ...
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Environ Geochem Health (2014) 36:935–951 DOI 10.1007/s10653-014-9610-y ORIGINAL PAPER Health hazard prospecting by modeling wind transfer of metal-bearing dust from mining waste dumps: application to Jebel Ressas Pb–Zn–Cd abandoned mining site (Tunisia) Manel Ghorbel • Marguerite Munoz • Fabien Solmon Received: 29 September 2013 / Accepted: 6 March 2014 / Published online: 24 April 2014 Springer Science+Business Media Dordrecht 2014 Abstract This work presents a modeling approach 5.74 and 0.0768 lg/m3 for measured wind speed to simulate spatial distribution of metal contamination values up to 22 m/s. Preferential areas of contamina- in aerosols with evaluation of health hazard. This tion were determined in agricultural lands to the NW approach offers the advantage to be non-intrusive, less from the source dump where Pb and Cd exceeded expensive than sampling and laboratory analyses. It guidelines up to a distance of 1,200 m. The secondary was applied to assess the impact of metal-bearing dust spreading directions were SW and E, toward the from mining wastes on air quality for a nearby village. Health hazard prospecting shown that a major community and agricultural lands in Jebel Ressas part of the village was exposed to contaminated dust (Tunisia) locality. Dust emission rates were calculated and that daily hazard quotient (HQ) values reached using existing parameterization adapted to the con- locally 118 and 158, respectively, for Pb and Cd tamination source composed of mining wastes. Metal during the study period. However, HQ variations concentrations were predicted using a Gaussian model in the village are high, both temporally and (fugitive dust model) with, as input: emission rates, geographically. dump physical parameters and meteorological data measured in situ for 30 days in summertime. Metal Keywords Dust Metals Mining wastes concentration maps were built from calculated PM10 Transfer modeling Air quality Health hazard particle concentrations. They evidence the areas where Pb and Cd concentrations exceeded WHO guidelines (0.5 and 0.005 lg/m3, respectively). Maximum con- centrations of Pb and Cd in PM10 are, respectively, of Introduction M. Ghorbel Laboratoire de Ressources Minérales Et Environnement Mining activities can generate high quantities of fine- (RME), Tunis El Manar University, 2020 Tunis, Tunisia grained wastes, which were abandoned in the past and left exposed to meteoric and wind erosion. M. Ghorbel (&) M. Munoz Laboratoire Géosciences Environnement Toulouse (GET), Some studies have addressed dust emission from UMR 5563, Toulouse, France active mining sites and quarries linked to crushing, e-mail: ghorbel@get.obs-mip.fr grinding or transport (Chaulya et al. 2003; Sinha and Banerjee 1997; Sinha 1995; Kakosimos et al. 2011). F. Solmon International Center for Theoretical Physics, Strada Such results are used to optimize the material process Costiera, 34151 Trieste, Italy in order to reduce the negative impact on the areas in 123
936 Environ Geochem Health (2014) 36:935–951 the neighborhood. But studies on dust emission and these elements, air quality guidelines of 5 ng/m3 and transfer from abandoned mining wastes are missing 0.5 lg/m3, respectively, for Cd and Pb were estab- except for recent monitoring study of suspending lished (WHO 2000; Baars et al. 2001). particulate matter (Cigagna et al. 2014), and contam- Dust aerosol is a very relevant factor in the ination wind dispersion is generally addressed with a Mediterranean climate and social environments. A descriptive approach of contamination impact on preliminary study on health hazard assessment of surrounding soils. Modeling approach for quantifica- direct dust ingestion has been addressed in Jebel tion of airborne metal concentration and spatial Ressas site as a representative site of Pb–Zn–Cd representation of contamination dispersion is still not mining sites from northern Tunisia (Ghorbel et al. well advanced, neither are addressed the parameters 2010). The results indicated that the population is which influence dust emission from mining wastes. In exposed to Pb and Cd through direct ingestion of fact, wind erosion of mining wastes may be addressed deposited dust in the village transferred from fine- as emission of fugitive dust which is defined as dust grained treatment wastes dumped close to the village that could not be conducted through a confined path. and farming lands. Concentrations of fugitive dust released from a surface For a more complete investigation of exposure to vary greatly depending on the nature and the area of metals around the mining site, air quality has been the sources and on other factors such as surface investigated over an area comprising the mining roughness and weather conditions (Trindade et al. site, the village and the farmlands. The dust 1981; Marticorena and Bergametti 1995; Alfaro and emissions and concentrations of airborne metals Gomes 2001). have been calculated for the PM10 (particulate In Tunisia, numerous Pb–Zn–Cd mining sites have matter of a grain size equal or less than 10 microns) been abandoned with large amounts of mining wastes fraction which is the inhalable particle size usually exposed to wind erosion. They are usually adjacent to taken into consideration by health and environment villages and farmlands. Mediterranean climate pro- organizations (WHO, USEPA). The evaluation was motes spreading of metallic contamination toward air, conducted on a 24-h average concentration basis for soil and habitations, so that population may be 1 month in summer season. In addition, maps of seriously exposed. metal concentrations in inhalable particulate matter Many studies have evidenced the relationship over the studied area were performed and compared between environmental metal contamination and to the air quality guidelines in order to determine people poisoning (Zhuang et al. 2009; Von Braun the location of population potentially at risk and et al. 2002; Malcoe et al. 2002; Lee et al. 2005). Metal- hazard quotients (HQs) have been estimated to contaminated dust can cause various diseases after evaluate the level of hazard for population health exposure of the population in the neighborhood to high over the village. levels of metals through inhalation, ingestion and skin contact. Knowledge about air quality and air pollution is Site presentation fundamental to prevent health risk (Zou et al. 2009). In humans, the pulmonary deposition and absorption of The Jebel Ressas mining site is located 30 km south of inhaled chemicals can have direct consequences for Tunis where Pb exploitation and Zn exploitation were health. But in the literature, health hazard has been conducted during almost 70 years. The Jebel Ressas mainly calculated from metal doses incorporated by village stands at the foot of the Jebel Ressas Mountain consumption of contaminated food crops, drinking where the Pb–Zn extraction zone was located. It is water or soil [lead and blood poisoning is now bordered southwards by the former ore processing established for children due to their hand-to-mouth plant and westwards by the treatment dumps (Fig. 1a). and pica behavior (Carrizales et al. 2006; Malcoe et al. Almost two millions of tons of gravimetry and 2002)]. flotation wastes were generated by the ore treatment Cadmium, lead and their compounds are classified and dumped in three flattop dumps, DI, DII and DIII carcinogens. In addition, various effects are evidenced (Fig. 1b). Next to the western side of the dumps are the for nervous, renal and cardiovascular systems. For farming lands. 123
Environ Geochem Health (2014) 36:935–951 937 Fig. 1 Jebel Ressas site location Table 1 Metals content in the mining waste dumps DI, DII, No specific management was conceived to prevent DIII and surface DIII and reference concentrations in soils for erosion and chemical alteration of mining waste comparison dumps, and no vegetation has grown on these dumps. Pb (wt%) Zn (wt%) Cd (mg/kg) The northern dump DIII is the largest one with a surface of 35,250 m2 and is exposed to the westerly DI 1.27 5.20 170 and northwesterly prevailing winds which favor DII 0.09 2.02 110 contaminated dust transfer toward the village. DIII 2.30 7.11 290 The study area was chosen to assess the dispersion of DIII surface 2.96 9.27 360 the contamination by wind process around the waste Reference 0.01 0.03 2.0 dumps. The total surface is of 3.9 9 5 km2. It includes concentrations in soils (Baize 1997) the western flank of Ressas Mountain, the waste dumps, Jebel Ressas village, farmlands and HMA stream. Methodology The waste materials have a weak cohesion and fine grain size dominated by silts and clay. Metal-bearing In this work, we considered only DIII dump (Fig. 1b) minerals consisted of carbonates (cerussite, smithson- as significant dust source in the model for the ite, hydrozincite), silicates (hemimorphite, willemite), following reasons: sulfides (sphalerite and galena) and iron oxyhydroxide enriched in Pb and Cd (Ghorbel et al. 2010; Ghorbel • its large surface and its high concentrations in Pb 2012). Pb, Zn and Cd concentrations in the waste and Zn and Cd compared to the other two dumps, dumps and on a representative sample of the surface of • simplification of the modeling operation by reduc- the dump DIII are given in Table 1. ing the number of sources and parameters. 123
938 Environ Geochem Health (2014) 36:935–951 Dust transfer modeling approach the time and the volume that are flagged on the counter of air volume were noted. Dust emission and aerosol concentration modeling Aerosols analysis An emission model adapted from a desert dust emission parameterization used in meteorological Pb and Cd in PM10 were analyzed after total acid and climate model (Marticorena and Bergametti digestion with HF and HNO3. The protocol was 1995; Alfaro et al. 1997) was adapted to the site conducted with four blank filters, one chemistry blank conditions and used to calculate dust emission rates of and one international standard of urban incinerator ash the source of contamination. The generated emission (SKO1). data were then included in a Gaussian dispersion The solutions were analyzed with an ICP-MS model to obtain estimations airborne dust concentra- Agilent 7500. Isobaric interferences have been cor- tions. Details about the modeling approach used are rected with automatic calculations and polyatomic given in the ‘‘Supplementary data’’ part. interference has been corrected by the operator of the machine. Spatial distribution of airborne metal concentrations Analysis of blanks shows that contamination from handling does not exceed 0.3 ppb for Pb while Cd Pb and Cd mean concentrations over the summer remains below the limit of detection of the machine (0, month are represented as contour maps to allow 01 ppb). visualization of the contamination extension and For Pb and Cd, standard analyses show that the intensity. For this purpose, we used Surfer software. protocol yields are between 92 and 125 %. Meteorological data Health hazard quotient evaluation Wind parameters were measured with an Oregon The modeling of air metallic concentrations allows us Scientific WMR200 weather station installed on the to address health hazard. roof terrace of the nearest house to DIII dump at a Calculation has been performed for PM10 which is height of 7.5 m of the ground surface. an inhalable fraction that may remain suspended in the The station is equipped with a wind vane anemom- atmosphere for weeks and can penetrate deeply in the eter which measures speeds and gusts of wind in m/s. lungs passages. The weather data were recorded every minute by a In order to estimate health hazard for Pb and Cd, the central unit for 30 days between July 13 and August HQ for human health is obtained by dividing metal 12, 2009. At the end of this period, these data were concentrations in airborne PM10 (lg/m3) by the air retrieved from the central unit to a computer via an quality guideline values for these elements (USEPA USB cable. 2011). If HQ [ 1, the exposure level is higher than the Analytical approach for modeling validation guideline value, then there is a potential risk for the receptor. Aerosol sampling An aerosol sampler was used to collect PM10 on the Results and discussion roof terrace of the nearest house to DIII dump behind the meteorological station, to measure the suspended Measured parameters particle concentrations. The sampler conducts a vol- ume of air through a particle size separator for PM10. Wind data These particles are collected on Zefluor Teflon filters. Filters were replaced every 24 h during the first During the measurement period, wind gusts ranged 7 days of the 1-month study period. During each from 0 to 22 m/s. The rose of hourly mean wind manipulation, the sampler was stopped, and the date, direction shows that the dominant wind is N (26 % of 123
Environ Geochem Health (2014) 36:935–951 939 Fig. 3 Grain size distribution of the mining waste on DIII dump surface the study period would be representative of the summer season. Temperature Fig. 2 Rose of hourly mean wind direction in Jebel Ressas site between July 13th and August 12th, 2009 and wind frequencies (%) Hourly mean temperatures were calculated from field measurements. Over the study period, they ranged between 20 and 47 C. Table 2 Wind frequencies percentage given by velocity intervals and directions Pasquill stability classes and mixing heights Hourly mean wind N NE E SE S SW W NW velocity intervals Information about Pasquill stability class and mixing V B 1 m/s 20 20 16 21 18 19 5 21 height must be given as input data in FDM model. We 1 \ V B 5 m/s 63 57 52 56 56 47 47 56 obtained them from the Web site of NOAA (2010) 5 \ V B 10 m/s 17 23 32 21 22 34 47 23 (Air Resource Laboratory). These data are specific for V [ 10 m/s 0 0 0 2 4 0 1 0 our period and locality. Pasquill stability classes are between A and F and are noted, respectively, from 1 to 6 with respect to the total observations) (Fig. 2). SE winds are the format of input files to FDM. second dominant direction with a frequency of 18 % Mixing height level ranges between 61 and of the total observations during this summertime. 3,320 m. Considering their high velocity occurrence (Table 2) with their high frequency, the SE winds were the most efficient winds for dust emission during this period. Grain size data Wind toward the village was less frequent and less violent. Grain size analysis of the surface sample of DIII dump Tunis-Carthage is the closest meteorological sta- shows that sand fraction (63–2,000 lm) is dominant tion to Jebel Ressas site. Meteorological statistics in (85 %). The sand fraction would be carried in saltation this station between October 2001 and August 2013 and would generate emission flux. PM10 is the particle show that mean wind speed in summer season fraction of a grain size equal or below 10 lm. It makes (August, July and June) is 5 m/s and dominant wind 3.5 % of the whole sample (Fig. 3). is NNE as it is mentioned in Windfinder Web site Emission model calculates emitted particle quanti- (2013). These results are concordant with our in situ ties for each diameter class previously defined in the measurements; thus, our derived modeling results over code. So that mean diameter of each class and the 123
940 Environ Geochem Health (2014) 36:935–951 Table 3 Grain size distribution of emitted PM10 from the Table 5 PM10 emission flux for the in situ measured wind surface of DIII dump speed interval and corresponding emission modes Diameter class [0.1; 1] [1; 2.5] [2.5; 5] [5; 10] Wind speed PM10 emission Emission mode intervals (lm) (m/s) flux (g/m2/s) Mean diameter (lm) 0.55 1.75 3.75 7.50 0 0.00 9 10?00 Aerodynamic Emitted fraction 0.17 0.19 0.19 0.45 entrainment 1 2.13 9 10-10 2 1.71 9 10-09 3 5.76 9 10-09 4 1.36 9 10-08 Table 4 Values of overall aerodynamic roughness (z0g) 5 2.66 9 10-08 rounded to the tenth for the dominant wind directions measured in Jebel Ressas site 6 4.61 9 10-08 7 7.31 9 10-08 Wind direction Overall aerodynamic 8 1.09 9 10-07 roughness z0g (lm) 9 1.55 9 10-07 SE 260 10 2.45 9 10-05 Saltation N 240 11 8.71 9 10-04 NW 340 12 5.68 9 10-03 13 5.96 9 10-03 14 4.15 9 10-02 associated emitted fraction were considered as grain 15 2.95 9 10-02 size data for FDM input (Table 3). 16 3.18 9 10-02 17 3.80 9 10-02 Roughness values (z0g) 18 4.69 9 10-02 19 6.03 9 10-02 Surface roughness values for the three directions are 20 2.49 9 10-01 given in Table 4. 21 1.49 9 10-01 For the period from July 13 to August 12, 2009, the 22 1.62 9 10-01 estimation of the emission flux was made with the roughness of 260 lm, corresponding to the most efficient wind measured during this period able to generate dust emission. The most elevated emission rates are noted for days 6, 11, 12, 28 and 30. For these days, wind gusts more Dust emission rate than 10 m/s were the most frequent over the measure- ment period. This high PM10 emission rate due to the PM10 emission flux was calculated for the wind speed fine grain size and weak cohesion of the mining wastes interval [0; 22 m/s] (Table 5) that was registered would be even higher with the violent winds which in situ. occur occasionally in this region. In those cases, the Wind speed and surface roughness are the two influence of the variation in the wind direction on the principle variables that control emission flux. For low surface roughness would necessary be addressed for wind speed (\10 m/s in our study case), the particles accurate emission estimation. are initially mobilized by aerodynamic entrainment. However, the values obtained in this study are For high wind speed (C10 m/s), saltation is imple- similar to those of Chane Kon et al. (2007), who mented and emission flux increases rapidly. calculated emission values that reach 3.5 9 10-3 g/ Then, mean daily dust emission rate from the m2/s on the flattop of a mining waste in Mantos source (dump DIII) was calculated to have a visibil- Blancos (Chile) and where the maximum speed of ity on daily variations. The flux interval obtained wind during the measurement period was 13 m/s. On is between 2.46 9 10-6 and 2.50 9 10-3 g/m2/s the other hand, emission rates calculated in this work (Fig. 4). are significantly lower than the values of Neumann 123
Environ Geochem Health (2014) 36:935–951 941 et al. (2009), who measured an interval between 1 and Table 6 Calculated Pb and Cd concentration range in airborne 4 g/m2/s of PM10 with simulations in tunnel of PM10 over Jebel Ressas study site emission from mining waste. Element (lg/m3) PM10 Pb Cd Pb and Cd concentrations in airborne PM10 particles Maximum 5.74 7.68 9 10-2 -13 Minimum 3.84 9 10 5.14 9 10-15 Calculated Pb and Cd concentrations in airborne PM10 Table 7 Daily metal concentrations in PM10 sampled in the Dust emission rates were integrated in FDM to village calculate PM10 airborne concentrations. Pb and Cd daily concentrations in airborne PM10 Day Pb (lg/m3) Cd (lg/m3) were calculated on a grid of 2,030 points covering the D1 0.03 0.0002 study area more than 30 days of modeling. Thereby, D2 0.03 0.0004 60,900 concentration values were obtained for each D3 0.012 \0.0002 metal. D4 0.12 0.0016 Then, we calculated the mean metal concentration D5 0.07 0.0008 in each point over the whole period to obtain D6 0.03 0.0004 representative values for summer month. Table 6 D7 0.01 0.0002 gives a summary of the mean metal concentrations intervals obtained for the considered set of points. Comparison between modeling and direct analysis results on the sampling point Measured Pb and Cd concentrations in airborne PM10 Pb and Cd calculated and analyzed concentrations were set up on the same figures (Fig. 5a, b). Concentrations of metals in collected airborne Both the shapes of the two curves for Pb and Cd and PM10 on the terrace roof in the Jebel Ressas the orders of magnitude of concentrations obtained village were converted in lg/m3 with respect to air through direct measurement and modeling are similar, volume (m3) corresponding to each aerosol sample so modeled values can be validated. Some discrepancy (Table 7). between the two kinds of values can be explained Pb concentrations ranged from 0.01 to 0.12 lg/m3, because the model considers that, for every 24 h, the and Cd concentrations were two orders of magnitude beginning aerosol concentration is zero, which means lower with a minimum below 0.0002 lg/m3. that the atmosphere is perfectly clean before each 24-h Fig. 4 Mean daily dust emission rate for PM10 (particulate matter B10 lm) from the surface of the waste dump DIII 123
942 Environ Geochem Health (2014) 36:935–951 Fig. 5 Calculated and analyzed a concentrations of Pb in the PM10 fraction in air, b concentrations of Cd in the PM10 fraction in air calculation. However, in reality, the atmosphere is above 10 m/s was higher and so their efficiency for never pure and there may be quantities of particles that dust emission and transfer. remain suspended in the air after a windy day for many Then, agricultural lands and farms are particularly hours before they eventually settle down. This fact exposed to contamination during the summer season. explains the underestimation of low concentrations by Maximum concentrations of Pb and Cd in PM10 are, FDM. Such an agreement between measured and respectively, of 5.74 and 0.0768 lg/m3 (Table 6) in a predicted FDM data was already shown for dust farm located at few hundreds of meter NW DIII dump concentrations in air generated by a cement plant and receiving SE wind with a speed up to 22 m/s. (Abdul-Wahab 2006). Due to the secondary NW winds, the village which is concentrated in the few tens of meters SE from DIII Spatial representation of calculated Pb and Cd waste dump is also under the heaviest metals contam- concentrations in airborne PM10 ination zone shown in Fig. 6. SW sector is the area likely to be less contaminated The maps of the spatial distribution of concentrations during the measurement period due to most frequent in the air were dressed (Fig. 6). This spatial distribu- wind speeds are below 5 m/s, which protect it from tion uses Pb and Cd monthly mean concentrations contaminated dust. obtained for the 2,030 receptor points. In fact, season variation in meteorological param- These maps highlight that metal distributions display eters especially wind direction and speed has an an eleven branches star centered on the source (DIII important control on air quality. Particularly, because waste dump) and concentrations decrease with distance the surface roughness value depends on wind direc- from the source area over several orders of magnitude tion, coupling both parameters in the emission model pending on the direction. On the study site, minimum Pb would improve the dust emission flux estimation. and Cd concentrations are in the order of 10-12 and 10-14 lg/m3, respectively, and they are considered as negligible below 10-4 and 10-6 lg/m3 (several thou- Health hazard prospecting sands of times lower than the recommended values). Wind transfer is most important toward NW and Spatial representation less important toward E and N. Although the prevail- ing winds are from the N and NW, the transport is In order to obtain an overall vision of the potential mainly by easterly winds because their frequency of health hazard area from the modeled data obtained on 123
Environ Geochem Health (2014) 36:935–951 943 Fig. 6 Spatial distribution of 1 month mean Pb concentrations and mean Cd concentrations in airborne PM10 metal-bearing PM10 in the area of Jebel Ressas for each of the 2,030 receptor points used in the modeling process, Pb and Cd mean concentrations calculated for the considered summer month and exceeding WHO (2000) air quality guidelines are displayed in Fig. 7. WHO air quality guidelines are 0.5 lg/m3 for Pb and 5 ng/m3 for Cd. In the side of agricultural land, a tenth of farms are concerned by the potential health hazard up to a distance of about 1,200 m from the mining waste dumps in the NW direction and of about 700 m toward W direction. In this area, several farms are concerned both for exposure of inhabitants to metals by inhalation and for possible contamination of locally grown agricultural products which may enter the food chain and increase the indirect exposure to metals. Although the village of Jebel Ressas is not in the main wind directions, it is also exposed to contamination by the yearly prevailing NW wind due to its location close to the waste dumps. Pb and Cd concentrations in PM10 can exceed guide- Fig. 7 Spatial representation of areas where Pb and Cd lines up to a distance of 500 m to the east of DIII concentrations in airborne PM10 exceeded WHO air quality dump, so that the major area of the village is guidelines concerned. 123
944 Environ Geochem Health (2014) 36:935–951 Table 8 Maximum, minimum and mean concentrations of Pb and Cd in airborne PM10 calculated on the basis of the 30 days study period individually for each point in the village Village points PM10 Pb (lg/m3) PM10 Cd (lg/m3) Max Min Mean Max Min Mean 1 5.82 3.12 9 10-05 5.02 9 10-01 7.79 9 10-02 4.17 9 10-07 6.71 9 10-03 -06 -01 -01 -08 2 8.54 3.11 9 10 9.36 9 10 1.14 9 10 4.17 9 10 1.25 9 10-02 -05 -01 -02 -07 3 1.70 2.28 9 10 2.75 9 10 2.28 9 10 3.05 9 10 3.68 9 10-03 -01 -02 4 4.65 0.00 2.42 9 10 6.22 9 10 0.00 3.24 9 10-03 -01 -02 5 2.91 0.00 1.33 9 10 3.89 9 10 0.00 1.78 9 10-03 6 6.82 9 10-01 0.00 3.19 9 10-02 9.13 9 10-03 0.00 4.27 9 10-04 -06 -01 -08 7 59.0 5.84 9 10 4.83 7.90 9 10 7.82 9 10 6.46 9 10-02 -01 -02 8 5.19 0.00 3.07 9 10 6.94 9 10 0.00 4.11 9 10-03 -01 -02 9 5.15 0.00 3.11 9 10 6.89 9 10 0.00 4.16 9 10-03 -05 -01 -02 -07 10 6.51 1.80 9 10 4.13 9 10 8.71 9 10 2.40 9 10 5.53 9 10-03 11 6.00 0.00 3.47 9 10-01 8.02 9 10-02 0.00 4.64 9 10-03 12 3.03 0.00 2.06 9 10-01 4.06 9 10-02 0.00 2.76 9 10-03 13 3.45 0.00 2.31 9 10-01 4.61 9 10-02 0.00 3.08 9 10-03 -01 -02 14 3.14 0.00 1.98 9 10 4.20 9 10 0.00 2.65 9 10-03 -01 -02 15 3.69 0.00 2.41 9 10 4.94 9 10 0.00 3.22 9 10-03 16 3.78 0.00 2.36 9 10-01 5.06 9 10-02 0.00 3.15 9 10-03 -08 -01 -02 -10 17 3.99 5.07 9 10 2.58 9 10 5.34 9 10 6.79 9 10 3.45 9 10-03 -01 18 37.1 0.00 3.53 4.97 9 10 0.00 4.73 9 10-02 -01 -02 19 2.20 0.00 1.43 9 10 2.95 9 10 0.00 1.91 9 10-03 -01 -02 20 1.75 0.00 1.03 9 10 2.34 9 10 0.00 1.38 9 10-03 -01 21 19.8 0.00 1.03 2.65 9 10 0.00 1.38 9 10-02 22 3.84 0.00 2.57 9 10-01 5.14 9 10-02 0.00 3.43 9 10-03 -01 -01 23 15.6 0.00 6.80 9 10 2.09 9 10 0.00 9.10 9 10-03 -01 -02 -03 24 7.35 9 10 0.00 2.62 9 10 9.84 9 10 0.00 3.50 9 10-04 -02 -04 -04 25 1.68 9 10 0.00 5.59 9 10 2.24 9 10 0.00 7.48 9 10-06 -05 -07 -07 26 1.58 9 10 0.00 6.76 9 10 2.12 9 10 0.00 9.04 9 10-09 27 3.11 9 10-04 0.00 1.04 9 10-05 4.16 9 10-06 0.00 1.39 9 10-07 28 4.60 9 10-03 0.00 1.54 9 10-04 6.16 9 10-05 0.00 2.05 9 10-06 -04 -06 -06 29 1.52 9 10 0.00 5.09 9 10 2.04 9 10 0.00 6.81 9 10-08 -06 -07 -07 30 8.53 9 10 0.00 2.85 9 10 1.14 9 10 0.00 3.81 9 10-09 Estimation of health hazard for the Jebel Ressas In order to prospect more in detail the potential village population health hazard in the village, we have considered modeling data for 30 points covering the housing area. Jebel Ressas village is of several hundreds of people We calculated Pb and Cd concentration in airborne living during the year in there. Thus, exposure to toxic PM10 in each point for the 30-day period. metals from mining waste may be qualified as chronic. Table 8 gives maximum, minimum and mean In this case, health issue in the village should be concentrations of Pb and Cd in airborne PM10 ideally treated at least, on the basis of 1-year data. In individually for each point in the village more than this modeling approach, we considered one summer the study 30-day period. For Pb, concentrations vary month to obtain data on the ‘‘worst case’’ knowing that between 0 and 59 lg/m3 with a global mean value of summer is the driest season with frequent strong wind 0.51 lg/m3. For Cd, concentrations vary between 0 which promotes contaminated dust emission. and 0.79 lg/m3 with a global mean value of 123
Environ Geochem Health (2014) 36:935–951 945 Table 9 Maximum, minimum and median values of health HQ related to Pb and Cd in Jebel Ressas village and calculated for each day on the basis of the whole set of points in the village Day Health HQ for Pb Health HQ for Cd Max Min Median Max Min Median D1 0.22 \10-6 7 9 10-3 0.3 \10-6 9 9 10-3 -6 -6 D2 3.64 \10 0.12 4.88 \10 0.16 D3 0.18 \10-6 1.1 9 10-4 0.23 \10-6 1 9 10-4 -6 -6 -6 D4 0.04 \10 7 9 10 0.05 \10 9 9 10-5 -6 -5 -6 D5 19.74 \10 2.3 9 10 26.42 \10 3 9 10-5 D6 57.91 \10-6 \10-6 77.5 \10-6 \10-6 -6 -6 D7 3.44 \10 0.06 4.6 \10 0.08 D8 2.32 \10-6 7 9 10-3 3.1 \10-6 9 9 10-3 -6 -6 D9 0.13 \10 0.0002 0.17 \10 2 9 10-4 -6 -5 -6 D10 0.38 \10 9 9 10 0.51 \10 1.2 9 10-4 D11 13.3 \10-6 6 9 10-6 17.8 \10-6 8 9 10-6 D12 65.62 \10-6 \10-6 87.82 \10-6 \10-6 D13 0.07 \10-6 0.012 0.1 \10-6 0.016 -6 -5 D14 0.005 \10 7 9 10 0.006 \10-6 9 9 10-5 -6 -5 -6 D15 0.37 \10 2 9 10 0.5 \10 2.2 9 10-5 D16 1.79 \10-6 2 9 10-5 2.39 \10-6 2.4 9 10-5 -6 -6 D17 4.15 \10 1.36 5.55 \10 1.82 D18 3.66 \10-6 1.2 9 10-4 4.89 \10-6 1.6 9 10-4 -6 -5 -6 D19 1.84 \10 3 9 10 2.46 \10 4 9 10-5 -6 -6 -6 D20 3.42 \10 2 9 10 4.57 \10 3 9 10-6 -4 -6 -5 -4 -6 D21 6 9 10 \10 8 9 10 8 9 10 \10 1.1 9 10-4 D22 1.02 \10-6 0.55 1.37 \10-6 0.74 -6 D23 13.02 \10 2.43 17.42 \10-6 3.25 D24 2.85 \10-6 0.22 3.82 \10-6 0.29 D25 1.27 \10-6 0.0021 1.7 \10-6 3 9 10-3 -6 -5 -6 D26 3.4 \10 2 9 10 4.56 \10 3 9 10-5 D27 39.6 \10-6 6 9 10-5 53 \10-6 8 9 10-5 D28 118 \10-6 \10-6 158 \10-6 \10-6 -6 -3 -6 D29 0.09 \10 3 9 10 0.12 \10 4 9 10-3 -6 -6 -6 D30 19.72 \10 \10 26.39 \10 \10-6 HQ values below 0.000001 are designed by \10-6 0.0069 lg/m3. Regarding reference metal concentra- Finally, daily metal concentrations in each point in tions, both mean values slightly exceed WHO the village could make a very large interval, but a guidelines. punctual mean value over a given study period gives a Moreover, in 24 points of the village, Pb and Cd more correct idea on the real concentrations taking maximum concentrations exceed WHO guidelines. into account the air mixing effect. If we consider the global air quality during the To prospect the population exposure to contamina- month through mean metal concentrations in each tion during the study period, a HQ has been calculated point, six points in the village show mean Pb and Cd for each day for the whole set of points in the village. concentrations above the guidelines. The HQ defined as the ratio of the potential exposure 123
946 Environ Geochem Health (2014) 36:935–951 Fig. 8 Maximum and median values of health HQ due to Pb air contamination (all minimum values are\10-6 and only median values [10-6 are represented) to the substance and the level at which no adverse However, median HQ values are low for most of the effects are expected. If the HQ is calculated to be equal days. Only 5-day display values above 0.1 and only for or less than 1, then no adverse health effects are the 17th and the 23rd days, HQ exceeds 1 in more than expected as a result of exposure. If the HQ is greater the half of the considered points. than 1, then adverse health effects are possible Extremely elevated health HQ is located in points (USEPA 2011). very close to DIII and exposed to W wind which was So that HQs related to Pb and Cd are, respectively, the third most efficient wind for contamination given by: transfer over the study period. It appears that despite the smallness of the village, HQðPbÞ there are large variations of the HQ related to the Calculated Pb concentration in airborne PM10 distance from the source due to the W wind particles ¼ 0:5lg=m3 transport capacity. Contamination of the media generally diminishes HQðCdÞ with the distance from the contamination source Calculated Cd concentration in airborne PM10 (Zhuang et al. 2009; Cangialosi et al. 2008), so that ¼ related health risk should also decrease. It is clear that 0:005lg=m3 distance from the source can be a useful, simple proxy Table 9 gives maximum, minimum and median for assessing exposure and assigning health effects. health HQ for each of the 30 days of modeling for the But in several papers, the results were opposite to whole set of points in the village. Only HQ values above the basic assumption of closer proximity equals 10-6 have been reported, considering it as a limit of greater concentration and exposure (Cordier et al. negligible HQ. Minimum HQ values are all below 10-6. 2004). Our study evidences that although the proxim- A diagram has been provided for Pb HQ values only ity rule applies, air contamination is mainly related to because Cd HQ values would have plot almost wind directions and velocities, hence to location identical although they are slightly higher. relative to the source. Table 9 and Fig. 8 show large variations in HQs in This study also evidences the variability of health the village for each day. This fact is mainly related to hazard variable more than 1 month. A more detailed the daily variation of wind directions which controls study along 1 year on the most exposed locations in PM10 concentrations. So that, when contamination is the village would be necessary to address the chronic highly transferred toward a given direction, in other exposure of the population under these conditions. directions, metal concentrations could be almost zero. In addition, reliable exposure estimation would Among the 30, 18-day display HQ above 1 require detailed human activity data in order to (HQ [ 1) in at least two points in the village. establish contact rates previously to any epidemiolog- Maximum HQ values reach 118 for Pb and 158 for Cd. ical study. Hence, human inhalation models quantify 123
Environ Geochem Health (2014) 36:935–951 947 human chemical inhalation from contact with the Finally, modeling allows quantitative prediction relevant air pollutants (Fryer et al. 2006). and spatial distribution of metal contamination with evaluation of health hazard. This approach offers the advantage of being non-intrusive for population and Conclusion also less time and money consuming than in situ sampling followed by laboratory analyses. It allows to This study allowed assessing wind erosion of Jebel target on areas of potential higher hazard. Ressas wastes dump and then determine the residential However, in order to improve the quality of the and agricultural areas potentially impacted by mining modeling, it will be necessary to use yearly weather waste and where health hazard could occur, using an data to obtain more realistic prediction of metals emission model coupled to a transfer model (FDM). transfer and more precise health hazard prediction. In Wind transfer of metallic contamination was stud- addition, it will be necessary to carry out a calibration ied during 1 month in summer season when wind pattern of dust emission and transport in realizing: erosion is likely most effective. • Measures of the emission rates on the ground to The concentrations in the air of PM10 were calcu- calibrate key parameters, lated, using meteorological data measured in situ, on a • Sampling of aerosols with collection duration short set of receiving points, around the mining waste dump enough to fit with variability of wind speed and DIII, corresponding to an area of 19.5 km2. direction and improve the accuracy of the calculation. During the study, maximum wind speed is 22 m/s and the daily mean dust flux reaches 2.50 9 10-3 g/ A difficulty to be overcome will be to develop an m2/s. This high PM10 emission rate due to the fine aerosol sampling device able to collect a sufficient grain size and weak cohesion of the mining wastes amount for analysis. would be even higher with the violent winds which occur occasionally in this region. Acknowledgments We are grateful for the support provided by the IRD Ph.D grant and the CMCU program (N09G 1003). Thus, the comparison with the few existing in the We are indebted to Christiane Cavaré for the quality of her literature for emission from mining waste does not graphics. lead to a generalization in particular due to the diversity of both meteorological and surface physical Supplementary data: methodology of dust emission parameters from a site to another. and aerosol concentration modeling For the considered period, spatial representation of PM10 metal concentration results shows the prevail- Dust emission calculation ing migration of contamination mostly toward agri- cultural lands and farms located in the NW of DIII The dust emission rate is the sum of the direct soil dump. The secondary spreading directions are SW and particle aerodynamic entrainment [f (lg/m2/s)] and of E, in particular toward the village of Jebel Ressas. the vertical flux [F (lg/m2/s)] resulting from saltation Moreover, Pb and Cd would exceed air quality and sand-blasting processes. guidelines in agricultural land and farms, up to a The aerodynamic entrainment function (f) gives the distance of 1,200 m and in the village up to a distance emission rate of mobilized particles on the source of 500 m. surface in the absence of saltation at low wind speed Modeling and cartography results allow concluding (Loosmore and Hunt 2000 in Shao 2008). that health hazard should be expected after inhalation of Pb and Cd bearing PM10 especially in the village f ¼ 3:6U 3 where the population is concentrated but also in farms on the main wind direction. where U (m/s) is the friction velocity Daily and overall HQs are variable but frequently KUðzÞ very elevated (up to 158 for Cd and up to 118 for Pb) U ¼ ln zz0 which imposes a deeper investigation of the health situation particularly on some locations close to the K: von Karman’s constant, z: height above the surface, waste dump. m, z0: roughness height, m, U: wind speed, m/s, F is 123
948 Environ Geochem Health (2014) 36:935–951 the emission flux generated by saltation when wind speed is high enough. The vertical flux F of particles emitted is first based on the calculation of the horizontal flux of soil saltating particles G (g/m2/s) according to Marticorena and Bergametti (1995): Z " 2 # q Ut Ut G ¼ EC a U 3 1þ 1 dSrel ðdpÞddp g U U dp Fig. 9 Schematic drawing of a surface waste ripple exposed to wind from different directions with parameters of shape used for E: ratio of erodible to total surface (taken to 1 here), C: aerodynamic roughness calculation constant of proportionality with a value of 2.61 determined from wind tunnel experiments (White • Plants and stones that are consistently exposed to 1979), qa: air density, g: gravity acceleration (m/s2), the wind. The roughness caused by these elements dp: soil particles diameter (lm), Srel: relative surface is uniform for all wind directions. Then, it is called occupied by a soil aggregate bin of diameter dp (m2), isotropic roughness. U : friction velocity of wind (m/s). It depends on wind • Ripples with curvilinear forms have different velocity and on aerodynamic roughness z0 of the fronts of exposure to wind according to their eroded surface. Ut : threshold friction velocity of wind directions (Fig. 9). Thus, the number of fronts (m/s): minimal wind friction velocity able to mobilize (n) in front of the wind as well as their height sand particles by saltation (cf Marticorena and (h) and their widths (b) are variable depending on Bergametti 1995 for more details). the direction of the wind. The effect of such Initially, this parameterization is designed for desert anisotropic roughness varies with the orientation dust emissions, and the soil aggregate distribution is of the ripple with respect to the direction of the related to a given textural class using standard distri- wind. Therefore, wind erosion will not be homo- bution (e.g., Zakey et al. 2006). Here, the soil aggregate geneous and amounts of emitted dust will vary distribution has been defined directly from in situ with wind direction. This effect of anisotropic measurements according to the following method. roughness has been studied to assess the conse- Samples from DIII surface have been taken in 5 quences of the presence of grooves of labor in the different points by scraping off the surface on 1–2 cm agricultural land on wind erosion (Saleh et al. over several hundreds of cm2. The samples were 1997; Armbrust et al. 1964). homogenized to make one representative sample from On DIII, surface rough elements are spread in a which 500 g were quartered, got rid of the fraction heterogeneous way. We distinguished between four more than 2 mm and then analyzed for grain size. different parcels in their aspects of surface roughness First, dry grain size separation was performed with which was measured for three wind directions: an AFNOR column: 1,600, 1,250, 630, 400, 355, 250, 200, 150, 125, 80 and 63 lm. • in the N direction which is the dominant wind Then, grain size distribution of fraction below direction measured in situ during the period 63 lm was determined using a Coulter LS 200 laser between July 13th and August 12th, 2009. granulometer with a small water volume. Measure- • in the SE direction which is the second dominant ment range is between 0.393 and 905 lm. direction and for which strong winds were com- In the G formulation, the roughness length z0 (lm) mon during the period between July 13th and is a very sensitive parameter. We have thus deter- August 12th, 2009. mined the roughness from direct measurement of the • in the NW direction which is the annual prevailing surface of DIII mining waste dump. direction known for the region. The surface of dump DIII contains erodible and We performed measurements of roughness on non-erodible or rough elements. There are two types of representative surfaces between 0.25 and 4 m2 accord- rough elements: ing to the dimensions of the rough elements. 123
Environ Geochem Health (2014) 36:935–951 949 For each parcel, we proceeded as follows: Calculation of airborne dust concentrations 1. We determined the number of isotropic ele- PM10 concentrations (lg/m3) have been calculated ments (plants, rocks), their widths and their with the fugitive dust model (FDM, Winges 1992). heights. FDM is a Gaussian plume model designed for 2. For each wind direction, we determined the computing particle concentrations and deposition number of ripple-fronts exposed to the wind, the rates from fugitive dust emissions. The model is well width (b) and the height (h) of each front. k accepted by USEPA for this purpose. It incorporates represents the totality (n) of fronts (bh) exposed to transport, dispersion and deposition of pollutants in the wind on a surface (s) with k = nbh/s. the atmosphere, using input data for particulate matter Pending on the k value, z0 can be calculated (particle diameter, density) and air parameters (wind using one of the following equations (Marshall velocity, wind direction, temperature) measured in the 1971; Jarvis et al. 1976; Garrat 1977; Raupach et al. site together with flux of emitted PM10 from the 1980; Raupach 1991) where n, b and h are, emission model. For the 30 days, 720 data for hourly respectively, the number, width and the height of mean emission rate of PM10 were integrated on FDM. the rough element and s is the measurement surface. Pb and Cd concentrations in PM10 were calculated So that, z0 = 0.005 h, if k \ 0.1 and z0 = (0.479 using metal content of dump DIII surface. k - 0.001)h, if k [ 0.1. The aerodynamic roughness was calculated for the Source and receptors other wind directions in the same way. An overall roughness z0g which takes into account The source, DIII waste dump, is assimilated to a the different types of surfaces was calculated by rectangle of 235 m 9 150 m. summing the different roughness observed on the We considered 2,000 receptor points obtained with dump and weighted by the fractions of surface they a 100 9 100 m gridding over a surface of 20 km2. We occupy. also added 30 points over the village. From the saltation flux, the aerosol vertical emis- sion flux is finally calculated according to Alfaro et al. (1997) approach as: References p di3 F ¼ G qp bpidp 6 ei Abdul-Wahab, S. A. (2006). Impact of fugitive dust emissions from cement plants on nearby communities. Ecological where i represents three modes of a predefined log- Modelling, 195(3), 338–348. normal emission distribution. G: the saltation flux (lg/ Alfaro, S. C., Gaudichet, A., Gomes, L., & Maillé, M. (1997). m2/s), qp: density of particles, b: proportionality Modeling the size distribution of a soil aerosol produced by sandblasting. Journal of Geophysical Research, 102(10), constant, pidp : fraction of kinetic energy of particles 11239–11249. of each diameter class dp able to generate aerosols of Alfaro, S. C., & Gomes, L. (2001). Modeling mineral aerosol mode i, di: mass of aerosols of mode i (g), ei: kinetic production by wind erosion: Emission intensities and aer- energy of aerosols of mode i (g cm2/s2). osol size distributions in source areas. Journal of Geo- physical Research, 106(16), 18075–18084. The total vertical flux is obtained by integrating all Armbrust, D. V., Chepil, W. S., & Siddoway, F. H. (1964). flux resulting from each diameter class of surface Effects of ridges on erosion of soil by wind. Soil Science. particles and then by summing the quantities of Society of America, Proceedings, 28, 557–560. emitted aerosol. Baars, A. J., Theelen, R. M. C., Janssen, P. J. C. M., Hesse, J. M., van Apeldoorn, M. E., Meijerink, M. C. M., Verdam, L., & The model we use did not consider the local Zeilmaker, M. J. (2001). Re-evaluation of human toxico- turbulence related to the topography of the site. We logical maximum permissible risk levels. RIVM report alleviate this point by calculating emission rate with 711701025, Bilthoven, the Netherlands. http://www.rivm. wind gusts measured every minute. Also, the surface nl/bibliotheek/rapporten/711701025.pdf. Accessed Febru- ary 1, 2014. moisture was not considered as we worked in summer Baize, D. (1997). Teneurs totales en éléments traces métalliques season. dans les sols (France). INRA Editions, Paris. 123
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