s o

Sp, Fra

uabytrocatarbronbys, Ba, Cr, Fe, Mn, Ni, Ta, V, and Zn were compared to the Mexican regulations and

lupe inon sincpid groect of i

[13]. The general public has great concerns about the environmental are no differences. In this way, to be considered as a pollutant, any po-

Microchemical Journal 103 (2012) 158164

Contents lists available at SciVerse ScienceDirect

Microchemic

e lsquality of the regions in which they are living and want to maintain ahealthy life style. The quality of the urban environment is of vital im-portance for the population because human health depends heavilyon the status of the soil [4,5].

The main anthropogenic sources of pollution in urban soil of Zaca-tecas and Guadalupe include mine tailings, vehicular trafc, and airpollution [4,68]. The most hazardous wastes include the mine tail-ings that can represent a risk to health, by their content of heavymetals such as Pb, Cd, As, Cu, Zn, Se, and Ni, among others. These el-ements tend to accumulate in the topsoils most accessible to the pop-

tentially harmful compound must satisfy simultaneously two criteria:(1) be present at increased concentrations near the urban soil surfaceand (2) exceed the legal limits. In the present work, the results arecompared to the limits of concentrations established by the MexicanOfcial Norm; and as well as to the concentration guidelines of theUnited States Environmental Protection Agency (US EPA) [12].

The high-precision, nuclear quantitative analytical technique ofinstrumental neutron activation analysis (INAA) was used in this in-vestigation of urban soils due to its very high sensitivity [13,14]. Inthe present work, this analytical technique was used to determineulation [2,3,9]. Measuring the concentraenvironmental samples (soil, water, sedimeof the most important steps in the process ofof pollution [5,10].

Corresponding author. Tel./fax: +52 492 922 7043E-mail address: fmireles@uaz.edu.mx (F. Mireles).

0026-265X/$ see front matter 2012 Elsevier B.V. Aldoi:10.1016/j.microc.2012.02.009ntroducing toxic metalses in mining areas placeso various heavy metals

2004. The expressed limits refer to soils and sediments used for agri-cultural, residential, commercial and industrial purposes [5,11]. Theyinclude both soils and sediments; but between these categories thereinto the urban soils. The location of these citithe population at higher risk of exposure tMine tailingsEnrichment factorINAA

1. Introduction

The cities of Zacatecas and GuadaMxico, have a strong mining traditi1546 by Spanish conquers, and the rathe last 30 years has had the side eff 2012 Elsevier B.V. All rights reserved.

the state of Zacatecas,e they were founded inwth of vehicle trafc in

Individual countries have issued regulations stating the limits ofconcentrations of heavy metals or other pollutants that can be consid-ered acceptable or dangerous. In Mxico, these limits have beenestablished by the Minister of the Environmental Protection and pub-lished in the Mexican Ofcial Norm NOM-147-SEMARNAT/SSA1-Urban soils the guidelines of United States Environmental Protection Agency. Enrichment factors for quantied elementsidentied high Cs, Zn, As, and Sb contents using Al as a crustal reference.Urban pollutionHeavy metals levels for elements such as AAssessing urban soil pollution in the citieinstrumental neutron activation analysis

F. Mireles a,, J.I. Davila a, J.L. Pinedo a, E. Reyes a, R.J.a Unidad Acadmica de Estudios Nucleares, Universidad Autnoma de Zacatecas, Ciprs 10b Center for Applied Isotope Studies, University of Georgia, Athens, GA, 30602, USAc Research Reactor Center, University of Missouri, Columbia, MO, 65211, USA

a b s t r a c ta r t i c l e i n f o

Article history:Received 8 February 2012Received in revised form 14 February 2012Accepted 14 February 2012Available online 18 February 2012

Keywords:

The cities of Zacatecas and Gthey were founded in 1546has had the side effect of inwere collected from eight lowere collected from two nelyzed by instrumental neutthe health risk to the public

j ourna l homepage: www.tions of elements innt, airborne, etc.) is onediagnosis and resolution

.

l rights reserved.f Zacatecas and Guadalupe, Mexico by

eakman b, M.D. Glascock c

c. La Peuela, Zacatecas, Zac., C.P. 98068, Mexico

dalupe in the state of Zacatecas, Mxico, have strong mining traditions sinceSpanish conquers, and the rapid growth of vehicle trafc in the last 30 yearsducing toxic metals into the urban soils. For this study, urban soil samplesions around the cities of Zacatecas and Guadalupe; and mine tailing samplesy tailing dams named Barones and Pedernalillo. The ten samples were ana-activation analysis for 33 major, trace, and rare earth elements to estimateurban soil contamination with heavy metals. The results of the contamination

al Journal

ev ie r .com/ locate /mic rocthe concentrations of major, trace, and rare-earth elements (REEs)in eight urban soil samples collected from locations around urbanareas of Zacatecas and Guadalupe and two samples collected fromnearby tailing dams at Barones and Pedernalillo [1518]. This studywas aimed at applying INAA for the analysis of eight urban soils andtwo mine tailing samples to uncover evidence of possible pollutionin urban areas of the two cities for the elements in question. UsingAl as a crustal reference, the enrichment factors (EF) values were

cate

159F. Mireles et al. / Microchemical Journal 103 (2012) 158164Fig. 1. Geographic location of the cities of Zacalculated by comparing the means of element concentrations foundin the eight urban soil samples with the continental crust average toconrm the existence of pollution in urban soils [1921].

2. Experimental

2.1. Description of eld area

The cities of Zacatecas and Guadalupe are located in the mountainsof the state of Zacatecas, Mexico. The climate is dry and temperate,with average annual rainfalls of 469 and 428 mm, temperatures of15.6 and 15.6 C, and altitudes of 2420 and 2280 masl, respectively.

Fig. 2. Site locations of urban so

Table 1Irradiation and counting conditions.

Elements and half-life Sample weight mg I

Short-lived elements:Al, Ba, Ca, Dy, K, Mn, Na, Ti, V

150 8

Medium-lived elements:As, La, Lu, Nd, Sm, U, Yb

200 5

Long-lived elements:Ce, Co, Cr, Cs, Eu, Fe, Hf, Ni, Rb, Sb, Sc, Sr, Ta, Tb, Th, Zn, Zr

200 5cas and Guadalupe. Major roads are shown.The extreme geographic coordinates of Zacatecas and Guadalupe are22 51 N and 22 37 S of North latitude, 102 32 E and 102 51W ofWest longitude; and 23 00 N and 22 32 S of North latitude; 10211 E and 102 39 W of West longitude, respectively [22]. Guadalupeis located about 6 km east of the city of Zacatecas. Fig. 1 shows the geo-graphic location of the state of Zacatecas on a map of Mxico, as well asthe locations of the cities of Zacatecas and Guadalupe [23].

2.2. Sampling and sample preparation

Soil samples were collected at eight sites, where ve cores of soilwere taken over an area of ~1000 m2 during the autumn season of

il and mine tailing samples.

rradiation ux (n cm2 s1) Irradiation time Decay time Counting time

1013 5 s 25 min 12 min

1013 24 h 7 days 2000 s

1013 24 h 28 days 3 h

2000. In the same way, two mine tailing samples were collected fromBarones and Pedernalillo. Each core was taken to a depth of 5 cm at arandomly chosen point within the site area. The only constraint wasthat no core should be taken near a eld boundary, tree, building, orother physical obstruction. In order to obtain a representative sample,the soil cores collected at each site were thoroughly mixed together,sieved to remove stones and pebbles, and crushed to pass through a2-mm mesh sieve. After homogenization, a sample of 3 L was air-dried for several days to remove water content [5,24]. Sampling was

Upon arrival at University of Missouri Research Reactor (MURR) of

The short-irradiation samples in polyvials were sequentially irra-diated in a thermal neutron ux of 8.01013 n cm2 s1 for 5 s,allowed to decay for 25 min so that radioactivity from short-lived ra-dioisotope 28Al (half-life of 2.24 min) could decrease to a level com-parable to the remaining radioisotopes. The samples were countedfor 12 min each on a high-purity intrinsic germanium (HP Ge) detec-tor with 25% relative efciency and FWHM resolution of 1.85 keV forthe 1332 keV gamma ray of 60Co [5,14]. Elements measured from theshort-irradiation samples were the following: Al, Ba, Ca, Dy, K, Mn,Na, Ti, and V (Table 2).

The long-irradiation samples in quartz vials were irradiated as asingle bundle using a thermal neutron ux of 5.01013 n cm2 s1

for a period of 24 h. Two counts were made on the samples afterthe long irradiation also using a HP Ge detector. The rst count for2000 s per sample was made after the samples decayed for 7 daysto permit the activity for 24Na (half-life of 15 h) to decay to a safehandling level. This count enabled successful measurement of the fol-lowing medium-lived elements: As, La, Lu, Nd, Sm, U, and Yb. A sec-ond count for 3 h per sample was made after the samples decayedfor an additional 21 days and enabled measurement of the followinglong-lived elements: Ce, Co, Cr, Cs, Eu, Fe, Hf, Ni, Rb, Sb, Sc, Sr, Ta,Tb, Th, Zn, and Zr. Concentrations in the unknown samples were de-termined relative to the National Institute of Standards and Technol-

tions for the hazardous elements such as As, Ba, Cr, Mn, Sb, V and Znwere 109 ppm, 487 ppm, 135 ppm, 878 ppm, 13.1 ppm, 144 ppm,

Table 2Estimated detection limits for INAA using decay gamma rays. Assuming irradiation in areactor thermal neutron ux of 11013 n cm2 s1.

Sensitivity (picograms) Elements

1 Dy, Eu110 In, Lu, Mn10100 Au, Ho, Ir, Re, Sm, W1001E3 Ag, Ar, As, Br, Cl, Co, Cs, Cu, Er, Ga, Hf, I,

La, Sb, Sc, Se, Ta, Tb, Th, Tm, U, V, Yb1E31E4 Al, Ba, Cd, Ce, Cr, Hg, Kr, Gd, Ge, Mo, Na,

Nd, Ni, Os, Pd, Rb, Rh, Ru, Sr, Te, Zn, Zr1E41E5 Bi, Ca, K, Mg, P, Pt, Si, Sn, Ti, Tl, Xe, Y1E51E6 F, Fe, Nb, Ne1E7 Pb, S

amp

5

.419

.4

.788

.564

.793

160 F. Mireles et al. / Microchemical Journal 103 (2012) 158164the University of MissouriColumbia, USA, the sample powders weretransferred to glass vials and dried for 24 h at 100 C. For INAA, twoaliquots of powdered soil and mine tailing samples weighing150 mg and 200 mg each were placed in separate clean high-density polyethylene vials and high-purity quartz vials used forshort and long irradiations, respectively. The irradiation and countingparameters utilized for the element analyses are reported in Table 1.

Table 3Concentrations of major and trace elements in eight urban soils and two mine tailing s

Element ZG-1 ZG-2 ZG-3 ZG-4 ZG-

Al (%) 7.030 6.432 7.660 7.858 6Ba 233.6 305 664.8 382.3 968Ca (%) 3.366 1.304 0.812 0.514 0Dy 3.289 3.937 3.311 3.391 7K (%) 1.354 1.682 3.101 1.748 2performed in such a way as to obtain, as far as possible, a uniformand representative distribution of the sampling sites for soil collec-tion throughout the urban regions of interest and from the mine tail-ing dams at Barones and Pedernalillo. These tailing dams are close tourban areas. The region was divided into NE, NW, SE, and SW areas,and two samples were collected from each. Fig. 2 shows the ten sam-pling sites [5,24].

2.3. Instrumental neutron activation analysisMn 815.8 1631 1417 996.9 348.2Na (%) 0.6172 0.4683 0.5034 0.4592 0.468Ti (%) 0.3259 0.4019 0.4550 0.4632 0.190V 188.9 156.1 195.7 198.6 51.76

Table 4Concentrations of major and trace elements in eight urban soils and two mine tailing samp

Element ZG-1 ZG-2 ZG-3 ZG-4 ZG-5

As 44.42 340.2 196.6 98.55 57.45La 12.86 15.93 10.14 13.92 34.15Lu 0.2773 0.3117 0.3347 0.3517 0.427Nd 15.34 13.14 11.96 14.79 31.41Sm 3.271 3.770 3.176 3.666 6.901U 1.267 1.887 0.7555 1.377 3.066Yb 2.128 2.525 2.478 2.540 3.490and 766 ppm, respectively. The relative errors (%) of most of the de-termined elements were within 5%.

INAA is also favorable for the determination of several rare earthelements (REE), such as, Ce, Eu, La, Lu, Nd, Sm, and Yb. Table 6

les for short-lived elements (in mg kg1).

ZG-6 ZG-7 ZG-8 JBA1 JPE1

5.602 8.092 5.162 3.981 6.173577.5 408.3 355.9 173 572.7

0.486 1.435 0.511 3.305 2.0933.424 3.932 3.562 2.099 3.6952.451 1.878 1.373 1.388 1.965

445.7 909.7 463.3 4378 12645 0.6045 1.598 0.5431 0.4080 0.86880 0.2404 0.5138 0.3205 0.1690 0.3731

87.5 202.4 73.36 132.8 184.5

les for medium-lived elements (in mg kg1).

ZG-6 ZG-7 ZG-8 JBA1 JPE1

38.35 56.58 40.27 511.5 150.617.70 12.83 17.15 3.923 14.18

0 0.2922 0.3118 0.3122 0.1604 0.312116.27 13.56 16.30 5.908 14.523.300 3.606 3.600 1.424 3.7412.550 1.202 2.287 0.0 1.1832.109 2.383 2.380 1.047 2.254ogy (NIST) certied standards SRM-1633a Coal Fly Ash and SRM-688Basalt Rock which were prepared and irradiated under identical con-ditions along with the urban soil and mine tailing samples. Measure-ment uncertainties for almost all of the elements are under 5% [5,14].

3. Results and discussion

The results for 33 elements from the eight soil and two mine tail-ing samples are presented in Tables 3, 4, and 5 according to their re-spective half-life: short, medium and long. The mean concentrationsof the major elements such as Al, Ca, Fe, K, Na, and Ti were 6.78%,1.15%, 4.61%, 2.05%, 0.658% and 0.364%, respectively. Mean concentra-

Table 5Concentrations of major and trace elements in eight urban soils and two mine tailing samples for large-lived elements (in mg kg1).

Element ZG-1 ZG-2 ZG-3 ZG-4 ZG-5 ZG-6 ZG-7 ZG-8 JBA1 JPE1

Ce 26.64 32.00 22.45 29.48 69.55 57.77 34.51 40.24 7.686 30.40Co 20.45 15.09 21.28 24.50 5.679 13.74 24.60 7.678 19.35 20.71Cr 203.6 125.3 130.8 233.3 44.29 59.89 183.3 99.13 148.3 164.9Cs 29.48 12.43 31.86 13.25 28.88 12.22 16.84 7.349 10.53 16.12Eu 0.7734 0.9242 0.8973 0.8916 0.7124 0.5773 0.9676 0.6683 0.9151 0.9273Fe (%) 4.781 6.077 6.422 6.378 1.937 2.479 5.325 3.469 7.527 5.091Hf 4.521 4.928 3.954 4.265 6.501 4.538 3.751 8.786 0.8986 3.562Ni 46.63 36.95 41.16 68.05 0.0 0.0 0.0 28.35 0.0 51.31Rb 100.5 120.0 235.7 130.2 203.1 115.9 183.1 89.69 70.38 98.47Sb 8.302 19.82 28.62 6.912 17.90 9.437 9.206 4.517 50.75 47.57Sc 19.86 14.51 25.05 23.33 7.848 7.087 21.50 7.863 16.28 20.33Sr 52.60 0.0 0.0 103.0 69.80 61.04 76.21 52.18 0.0 .00Ta 0.5943 0.7695 0.5854 0.6911 1.256 0.7979 0.5673 1.005 0.0 0.6092

.02 0.51 0.58 0.54 0.3 0.6

.54 5.66 3.6 6.3 0.41 3.61

.6 85.2 101.5 112 4345 2608

.1

s (in

G-5

9.550.714.150.421.416.903.49

161F. Mireles et al. / Microchemical Journal 103 (2012) 158164shows the mean concentration of the REEs in the eight urban soilsamples in ppm.

For an assessment of the contamination level of the urban soils of

Tb 0.5 0.62 0.5 0.58 1Th 3.52 4.13 2.7 3.91 11Zn 346 3951 1016 373.6 143Zr 167.3 139 87.6 103.3 174

Table 6Concentrations of rare-earth elements in eight urban soils and two mine tailing sample

Element ZG-1 ZG-2 ZG-3 ZG-4 Z

Ce 26.64 32.00 22.45 29.48 6Eu 0.7734 0.9242 0.8973 0.8916La 12.86 15.93 10.14 13.92 3Lu 0.2773 0.3117 0.3347 0.3517Nd 15.34 13.14 11.96 14.79 3Sm 3.271 3.770 3.176 3.666Yb 2.128 2.525 2.478 2.540the cities of Zacatecas and Guadalupe, the elemental concentrationsfor As, Ba, Cr, Fe, Mn, and Zn were compared with the guidelines ofthe US EPA [12] which are presented in Table 7. By this comparison,it can be concluded that As and Ba in ten samples, Cr and Fe in eightsamples, Mn in seven samples, and Zn in six samples were highly pol-luted in some of the sampling locations for urban soils and mine tail-ings in the cities of Zacatecas and Guadalupe. According to thePreliminary Remediation Goals (PRGs) from USEPA, As levels of4.5 ppm increase the risk of cancer to one per million through dermalabsorption [25]. Elements generally known to be associated with airpollution, such as As, showed heavily polluted levels [10,15,26]. Onthe other hand, for the assessment of the contamination levels inurban soils of Zacatecas and Guadalupe, the elemental concentrationsfor As, Ba, Cr, Ni, Ta, and V were compared with the guidelines ofMxico, NOM-147-SEMARNAT/SSA1-2004 which are presented inTable 8. By this comparison, it can be concluded that concentrationvalues of Ba, Cr Ni and Ta are below guidelines of Mxico. However,

Table 7Comparison of elemental contents with USEPA guidelines (mg kg1) [12].

Element USEPA guidelines for classication ofgreat lakes harbor sediments

Present work

Notpolluted

Moderatelypolluted

Heavilypolluted

In urban soils

Range Mean

As b3 38 >8 38.35340.2 109Ba b20 2060 >60 233.6968.4 487Cr b25 2575 >75 44.29233.3 134.9Fe b17,000 17,00025,000 >25,000 19,37264,217 46,084Mn b300 300500 >500 348.21631.3 878.5Zn b90 90200 >200 85.233951.4 766.1As in ten samples and V in eight samples are above guidelines of Mex-ico, by a factors of 5 and 2, respectively.

By comparing the elemental concentrations in urban soils and

127.9 132 224 0 118.5

mg kg1).

ZG-6 ZG-7 ZG-8 JBA1 JPE1

57.77 34.51 40.24 7.686 30.4024 0.5773 0.9676 0.6683 0.9151 0.9273

17.70 12.83 17.15 3.923 14.1870 0.2922 0.3118 0.3122 0.1604 0.3121

16.27 13.56 16.30 5.908 14.521 3.300 3.606 3.600 1.424 3.7410 2.109 2.383 2.380 1.047 2.254mine tailing samples with continental crust values, enrichment fac-tors (EF) have been calculated using following expression:

EFX X=Al urbansoilorminetailing= X=Al ContinentalCrust

where EFX stands for the enrichment factor of element X in urban soilor mine tailing samples, after having its concentration (X) in urbansoil or mine tailing samples is normalized to (Al) concentrations inurban soil and mine tailing samples or crust. A value of EF>1 greaterthan one for a particular element indicates the enrichment of that el-ement in urban soil and mine tailing samples [20,27,28]. The dataused to calculate enrichment factors of various elements in urbansoil and mine tailing samples, and the enrichment are shown inTable 9 and in Figs. 3 and 4, respectively. It is clear from these gures

Table 8Comparison of elemental contents with NOM-147-SEMARNAT/SSA1-2004 guidelinesof Mxico (mg kg1).

Element NOM-147-SEMARNAT/SSA1-2004 guidelines of Mxico

Present work

Commercial,agricultural,andresidentialuse

Industrialuse

In urban soils

Range Mean

As 22 260 38.35340.2 109Ba 5400 67,000 233.6968.4 487Cra 280 510 44.29233.3 134.9Ni 1600 20,000 0.068.5 27.64Ta 5.2 67 0.56731.256 0.7833V 78 1000 51.76202.43 144.3

a Hexavalent chromium

Table 9Enrichment factors of elements in urban soils, mine tailings of Barones and Pedernalillo relative to continental crust, taking Al as a crustal reference.

Element This workUrban soilsMean(mg kg1)

This workMine tailingBarones(mg kg1)

This workMine tailingPedernalillo(mg kg1)

Continental crust averagea

(mg kg1)Urban soilsEF

Mine tailingBaronesEF

Mine tailingPedernalilloEF

Al 67,817 39810.00 61731.00 82,300 1.0 1.0 1.0As 109.0 511.50 150.60 1.80 73.5 587.5 111.5Ba 487 173.00 572.70 425 1.4 0.8 1.8Ca 11,522 33047.00 20926.00 41,500 0.3 1.6 0.7Ce 39.08 7.69 30.40 60 0.8 0.3 0.7Co 16.63 19.35 20.71 25 0.8 1.6 1.1Cr 134.9 148.30 164.90 100 1.6 3.1 2.2Cs 19.04 10.53 16.12 3 7.7 7.3 7.2Dy 4.051 2.10 3.70 3 1.6 1.4 1.6Eu 0.8015 0.92 0.94 1.2 0.8 1.6 1.0

,300 1.0 2.8 1.23

,900300

950,6002875900

226

375209

7002

162 F. Mireles et al. / Microchemical Journal 103 (2012) 158164Fe 46,084 75274.00 50915.00 56Hf 5.156 0.90 3.56K 20,474 13878.00 19649.00 20La 16.83 3.92 14.18Lu 0.3273 0.16 0.31Mn 878.5 4378.00 1264.00Na 6578 4080.00 8688.00 23Nd 16.60 5.90 14.52Ni 27.64 0.00 51.31Rb 147.3 70.38 98.47Sb 13.09 50.75 47.57Sc 15.88 16.28 20.33Sm 3.912 1.42 3.74Sr 51.85 0.00 0.00Ta 0.7833 0.00 0.61Tb 0.6114 0.31 0.60Th 5.172 0.41 3.61Ti 3638 1690.00 3731.00 5U 1.799 0.00 1.18that the concentrations of several elements are slightly higher in theurban soil samples compared to the background continental crust.This indicates that there is some contamination and accumulation ofthese elements in the urban soils. While EF1 are usually regardedas nondescript for the elements, in increasing order Sr, Ca, Na, Ni,Ta, Th, La, Nd, Ti, Ce, Sm, Lu, Co, U, Eu, Tb, Sc, Fe, Al, and Yb. Elementswith EF values that are considerably higher than 1, EF>1, can be con-sidered not originated from the local soil background and may be at-tributed to anthropogenic sources such as trafc vehicles, minetailings and air pollutants [2628]. Those elements in increasingorder are Zr, Mn, K, V, Ba, Cr, Dy, Rb, Hf, Cs, Zn, As, and Sb in urbansoil samples. However, the elements Cs, Zn, As, and Sb showed high-est enrichment factors. The widely accepted threshold for substantialenrichment over the natural continental crustal background is EF10[5,21,27].

V 144.3 132.80 184.50 135Yb 2.504 1.05 2.25 3Zn 766.1 4345.00 2608.00 70Zr 144.4 0.00 118.50 165

a Taylor, S.R. 1964 [20].

0.00.20.40.60.81.01.21.41.61.8

Sr Ca Na Ni Ta Th La Nd Ti Ce Sm Lu Co U Eu Tb Sc

Enri

chm

ent F

acto

r

Elements

Urban Soils Mine Tailing of Barones Mine Tailing of Pedernalillo

Fig. 3. Enrichment factors (EF) for major, minor, and trace elements in urban soils withEFb1 and mine tailings.2.1 0.6 1.61.2 1.4 1.30.7 0.3 0.6

.5 0.8 0.7 0.81.1 9.5 1.80.3 0.4 0.50.7 0.4 0.70.4 0.0 0.92.0 1.6 1.5

.2 79.4 524.6 317.10.9 1.5 1.20.8 0.5 0.80.2 0.0 0.00.5 0.0 0.4

.9 0.8 0.7 0.9

.6 0.7 0.1 0.50.8 0.6 0.9

.7 0.8 0.0 0.6The result, when EF1 indicates that the element of study is notenriched by additional sources and its origin it is purely natural. Ifthe EF>1, the contribution of the element is probably of two kindsboth natural and anthropogenic. If the EF>10, the element is consid-ered to be highly enriched, and conrms that an anthropogenicsource has contributed to the metal concentration; see Table 10 [28].

For a better overview of the data, the metal concentration varia-tions in the urban soils were plotted. See Fig. 5. The As and Cr concen-trations were multiplied by 10, and the Sb concentration wasmultiplied by 100 to improve the visualization of the data. For a betteroverview of the data, the rare-earth element concentration variationsin the urban soils were also plotted. See Fig. 6. The Eu and Lu concen-trations were multiplied by 10, to improve the visualization of thedata [4,6].

1.3 2.0 1.81.0 0.7 1.0

13.3 128.3 49.71.1 0.0 1.0

0.02.04.06.08.0

10.012.014.0

Fe Al Yb Zr Mn K V Ba Cr Dy Rb Hf Cs Zn/10 As/100 Sb/100

Enri

chm

ent F

acto

r

Elements

Urban Soils Mine tailing of Barones Mine tailing of Pedernalillo

Fig. 4. Enrichment factors (EF) for major, minor, and trace elements in urban soils withEF1 and mine tailings.

Finally, the elements may be divided into the following threegroups according to their median values [5,29]:

(1) Major elements (110%): Al, Ca, Fe, K.(2) Minor elements (10 ppmb1%): As, Ba, Ce, Co, Cr, Cs, La, Mn,

Na, Nd, Ni, Rb, Sb, Sc, Sr, Ti, V, Zn, Zr.

age elemental concentrations in urban soil samples have more similarto the elemental concentrations of the mine tailings from

References

[1] S. Enciso-De-la-Vega, Crecimiento Urbano de la Ciudad de Zacatecas y sus Asen-tamientos Humanos en Zonas Mineralizadas Poli metlicas, Rev. Mex. Cienc.Geol. 11 (1994) 106111.

[2] I. Cano-Aguilera, B.E. Rubio-Campos, G. De-la-Rosa, A.F. Aguilera-Alvarado, Arse-nic mobility from mining tailings of Monte San Nicolas to Presa de Mata in Gua-najuato, Mexico, Int. J. Chem. Biomol. Eng. 1 (2008) 181184.

Table 10Enrichment factor and element origin for urban soils.

EF Elements Element origin

1 Sr, Ca, Na, Ni, Ta, Th, La, Nd, Ti, Ce, Sm,Lu, Co, U, Eu, Tb, Sc, Fe, Al, Yb

Natural origin

>1 Zr, Mn, K, V, Ba, Cr, Dy, Rb, Hf, Cs Natural origin with slightanthropogenic enrichment.

>10 Zn, As, Sb Element highly enriched by someanthropogenic sources.

163F. Mireles et al. / Microchemical Journal 103 (2012) 158164Pedernalillo.

5000

6000

/ kg

ZG03 ZG05 ZG08 ZG09 ZG13ZG15 ZG17 ZG19 JBA1 JPE1(3) Trace elements (b10 ppm): Dy, Eu, Hf, Lu, Sm, Ta, Tb, Th, U, Yb.

4. Conclusions

In this study, eight urban soil samples from the cities of Zacatecasand Guadalupe and two mine tailing samples from tailing dams ofBarones and Pedernalillo were analyzed by INAA and 33 elementswere determined, using short- and long-irradiation samples. Whenthe elemental contents for As, Ba, Cr, Fe, Mn, and Zn were comparedwith the guidelines of the US EPA, the urban soils turned out to beheavily polluted.

The differences in the elemental concentrations between guide-lines of US EPA and guidelines of Mxico are large. The results ofthis study indicated that urban soils from the cities of Zacatecas andGuadalupe present concentration levels of As, Ba, Cr, Fe, Mn, and Znhigher than the heavily polluted US EPA guidelines values. Concentra-tion levels for Ba, Cr, Ni, and Ta, are lower than residential MxicoGuideline values, but As and V are higher than residential MxicoGuideline values.

The results of the elemental concentrations of urban soils showthat Al, Dy, Eu, Fe, Hf, La, Lu, Na, Nd, Sm, Ta, Tb, Th, Ti, U, Yb and Znhave a more or less uniform distribution, otherwise As, Ba, Ca, Ce,Co, Cr, Cs, K, Mn, Ni, Rb, Sb, Sc, Sr, V, and Zr have a greater variationbetween samples. Comparing elemental concentrations of the urbansoil to mine tailing samples, we nd that the urban soil sampleshave a largest concentration of some elements, such as Al, Ce, Cs,Dy, Hf, K, La, Lu, Nd, Rb, Sm, Sr, Ta, Tb, Th, U, B, and Zr. Also, the aver-0

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As x10 Ba Cr x10 Sb x100 Zn

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tion,

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Fig. 5. Concentrations of metal elements in urban soils of the City of Zacatecas and Gua-dalupe, and mine tailings of Barones and Pedernalillo.The main lessons learned from the present study can be expressedas follows: (1) urban soils in the cities of Zacatecas and Guadalupe arepolluted with As, Ba, Cr, Fe, Mn, and Zn in all the eight urban soil sam-ples. The contamination is probably derived from air pollutants, vehi-cle trafc and mine tailing pollution. (2) In all cases, the urban soilconcentrations for As, Ba, Cr, Fe, Mn, and Zn exceed the heavily pollut-ed by factors of 14, 8, 2, 2, 2, and 4 according to US EPA legislation, re-spectively. (3) In eight cases for As and in six cases for V in urban soil,the concentrations exceed the minimum threshold of safety accord-ing to Mexican legislation, by a factors of 5 and 2, respectively. Theenrichment factors found through this study show that urban soilsare efcient accumulators of elements from the environment. TheCalculated EF for quantied elements identied Cs, Zn, As, and Sb aselements with very high EF values of 7.7, 13.3, 73.5, 79.4, respectively,suggest that these elements may be derived from vehicle trafc (Znand Sb), from mine tailing (As, Zn, and Sb), from air pollutants (As)that are anthropogenic sources.

Disclaimer

Any opinions, ndings, and conclusions or recommendationsexpressed in this material are those of the author(s) and do not nec-essarily reect the views of the Department of Energy.

Acknowledgments

The authors are grateful to Dr William H. Miller and operators ofthe University of Missouri Research Reactor for their valuable assis-tance in the INAA. This work was supported in part by the US Depart-ment of Energy grant DE-FG07-02ID14380.

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Ce Eu x10 La Lu x10 Nd Sm Yb

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ZG03 ZG05 ZG08 ZG09 ZG13ZG15 ZG17 ZG19 JBA1 JPE1

Fig. 6. Concentrations of rare-earth elements in urban soils of the City of Zacatecas andGuadalupe, and mine tailings of Barones and Pedernalillo.[3] L. Lizarraga, M.C. Durn, M.R. Gonzles, Environmental assessment of an activetailings pile in the State of Mexico (Central Mexico), Res. J. Environ. Sci. 2(2008) 197208.

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164 F. Mireles et al. / Microchemical Journal 103 (2012) 158164

Assessing urban soil pollution in the cities of Zacatecas and Guadalupe, Mexico by instrumental neutron activation analysis1. Introduction2. Experimental2.1. Description of field area2.2. Sampling and sample preparation2.3. Instrumental neutron activation analysis

3. Results and discussion4. ConclusionsDisclaimerAcknowledgmentsReferences