Metal levels in indoor and outdoor dust in Riyadh, Saudi Arabia

PII SMO-4120(96)tW17-7

METAL LEVELS IN INDOOR AND OUTDOOR DUST IN RtYADH, SAUDI ARABIA MA. Al-Rajhl and MRD. Department

of Environmental

Seaward sckrw,

Uniwni

c4 Bradfwd,

Bndfwd

607 IDF. UK

A.$. Al-Aamer Medical phyaio

Departmsni,

Univemily

ECswthompton,

Soulhamp4m1 SOB 2’TU, UK

Cancanbations of Cd, Cr, Cu, Li, Ni, Pb, and ZII of outdoor and indDM dusts in Riydh. Saudi Arabia, have been invest@& in relation to plytielc siaw 0.04-0.08 mm using Atomic Absorptb Spcc~~swpy (AAS). Although the muIts ~howcd rcl&W~ ICW contcmlncdon in gateml, the old industrial llrca hnd apPr&bly hfgh levels of toxic m&Is and ulcer wtec rclr(ively high Pb levels mu motorw&ys. Mwr dc#u of oufdoorduala fw Cd, Cr, Cu, Ll, Ni, Pb, and Zn wao 2.5 * 0.3,JS.l f 2.7.93.9 E!C41.9,4.6 * 0.3,43.9 * S.6, 1762 FIZ593, and 443 + 223 w.g’, reapcabty, and mean concenbathns of indoor dusts were 2.0 k 1.1,69.2 + 16,5,271 * 140,63 * O.S,S2.9 f 17.7,639 + 279, and 547 f 197 p&g’, ny#ctively. The main sourceof& he8vymet& In both autdoar and indoor dusts, was tim autamobils at&ions. The rcltioaship bchwn &door and indoor dusk was investigated. tn vlcw of the high levels of same of thede toxic met&, these caa bc considered a significant hand-to-mouth soux of exposure, especially for childma,

INTRODUCTlON There is strong evidence that dust is an imporknt pathway in the exposure of people, cspceialiy children, to toxic metals (Jensen and Laxen 1985; Duggan et al. 1985). Several studies in Bump and the USA, for exampie, have stressed the possibility that contaminated soil or dust, ingested either directly or indirectly as a result of hand-togmouth activity, may rcpresent a significant pathway of lead intake during early childhood (Galiaeher et al. 1984; Angle ct al. 1974, 1984). In addition, indoor dust is a source of toxic metals and, therefore, has health implicationa where most people spend much of their time indoors (Sexton et al. 1984). Indoor pollutants may cmanato from many sources, including infiltration of outdoor pollutants, such as dust, soil, and fuel consumption products, and intcr315

nally hm amokin& inccnss burn& Wdiig md fumitum materials, and consumer @WC@ (Madany et al. 1994). Metal pollution in outdoor dust, in putioulnr kd, hasbeeuinv&igaWbynumcroua workeraindif%wt countrio (Irvine et al. 19eP; kgusson Md Kim 1991; Feng and Bunts 1994, Akhtcr and Mrdirny 1993; Madany et a!. 1994). TherefoR, altcmpts have bssn made to quantify exposure route3 leading to mo&8@ clevctions in chikkcn’s blood kad by spccitkally codttg cm the unintentional in* of outdoor and indoor dusts, contaminated by industrial tivity, taken into the body via &qucnt hand-to-mouth activity, or on toys, contaminated with soil ff duet, whlchcutkplroedLthbm~.Y~~chiidrralivinS nearasmeittr~echigberritof~sxpawna~

M.A. Al-Rajhi et al.

316

adults~ivinginthesame~(Rohertsetal. 1974;Yankel etaI. 1977).Analysas ofcontaminated soil and dust on the hands of children led to the concIusion that lead transfer from hand-to-mouth may have increased their observed blood lead levels, However, more studies are required to substantiate these interpretations, especially in the case of older children. To ident@ metal pollutant sources accurately, some workers have fractionated dust samples according to particle size (Krivan 1989). It has been found that the concentrations of certain elements increase with a decrease in dust particle size (Fergusson and Ryan 1984; Beckwith et al. 3985; Hopke et al. 1980; AlRajhi et al. 1996). The rapid growth of Riyadh, the capital city of Saudi Arabia, has created numerous environmental problems common to most cities worldwide; however, climatic conditions and mobile sands create particular problems for Riyadh in respect to dust, a common pollutant that represents an impmtant source of toxic metals. Riyadh suffers from heavy dustfall, with an average of about 2 Mg kmT2 d-’ and suspended particles of about 500 pg.mJ (El-Shobokshy 1985). Dust composition and accumulation vary according to many factors, including weather, traffic density, industry, and proximity of mobile soil. This is attributed to the geographical nature of Riyadh, which is surrounded by vast desert areas and to the major constructional activities in many and widespread areas ofthe city. ElShobokshy reported the average deposition of heavy met& over the city to be 0.37 Mg km-* d-l. There have been several studies on metals and the inhalable particles in the ambient atmosphere of Riyadh(ECShohokshy 1984,1985; El-Shohokshydal. 1990; Rowe et al. I!%). However, there has been no study of the metal pollution burdetl of the indoor and outdoor swept dusts of Riyadh, based on a single range of particle sizes. This procedure enables investigators to explain more accurately the sources and effects of metals in the environment, and to obtain more accurate comparisons between different locations. This study, which forms part of a major investigation into the metal burden of Riyadh. including cadmium, chromium, copper, nickel, lead, and zinc, pays particular attention to the spatial distribution of selected metals in the environment, based on particle size. It also evaluates the metal contents of dusts in order to demonstrate the correlation between outdoor and indoor dust.

MATERIALS Study

AND

METHODS

am3

Riyadh is located in the centre of Saudi Arabia, at an altitude of 600 III, being about 1000 km from the Red Sea to the west and about 400 km from the Arabian Gulfto the ectst. It is a rapidly growing city, extending over 1600 k~$, with a present population estimated at over 1.5 million, compared with about 100 000 in 1950. The city is surrounded by sandy hilts, sand dunes, and desert, which cIause it serious dust COP taminstion problems, The climate in Riyadh is mostly warm and dry, with temperatures reaching 38-45”C during summer, but it is often cold during winter with temperatures reaching as low as 7’C. Two large industrial sites have been established for light industries. The first one, developed in 1969, is located near the city centre, with a total area of 45 I 000 m2 and 59 factories. The second, established in 1978, is 17.5 km southeast oftbe city centre, with a total area of I2 000 000 m2 and 497 factories. Etnissions from these, plus those of densely distributed motor vehicles, a petroleum refinery, and a cement factory, coupled with hightemperaturesandliickofrein, lead to the accumulation of air pollutants overthe city. Thesituation isexacerbatedbyduststorms, whichblow mainly during springandautumn, and low wind speeds. Samples co//ecfion and data ana/@ Dust samples were collected from various urban, suburban, rural, motorway, and thetwo industrial sites in Riyadh, to represent their different activities and features. Outdoor dust samples were collected from 23 I sites (Fig. I), to include a wide range of rural, suburban, urban, industrial. and motorway environments. All samples were obtained from pnvemcnts (or surfaces equivalent to pavements) by means of a brush and plastic dustpan. indoor dusr samples were collected from 20 public community centres, using a vacuum cleaner. Clean self-sealing polyethylene bags with a distinctive label were used for all samples. Samples were oven-dried overnight at 105”C, and then sieved to subsamples using stainless steel sieves with a range of aperture sizes (2.0-1.0, 1.0-0.5, OS0.3, 0.3X1.2, 0.2.0.14, 0.14-0.08, 0.08-0.04, and 0.04. 0.02 mm). lndoot dust samples were fractionated as above into 0.14-0.08, 0.08~0,04, and 0.04-0.02 mm; greater particle size could not be obtained in sufficient quantity for analysis. Each sample was stored separately in a clean setf-sealing bag with rl distino-

hlclal tevets in indoor and outdoor dua in Riyadh, Swdi Ambta

tive label.Beforeany ilrther work, the weight of each subsample was measurad. Subsatupks of 0.5 g were weighed in previously weighed Pyrex tubes and then ashed at 500°C in a muffle furnace for 6 h. ARer re-weighing, the samples were extracted by adding 5 mL of aqua regia (3HCI:IHNO~, both AR grade). Samples were then transferred to R previously programmedheating block for 9 h to aid digestion. Samples were then centrifuged and transferred to volumetric tubes and made up to 20 mL volume with double-distilled water. Metal analyses were carried out by using an atomic absorption spectromater (Perkin-Elmer model 1100, microcomputer, controlled with integratedCRT screenand keyboard function). House dust and soil reference materials (Buffalo River Sediment SRM 2704) were usedto checkthe precisionof the instrument,andabout 20% ofthe sampleswere duplicated in every batchto checkthe accuracyof the meastirements.

317

RESULTSAN0 DlSCUSSiON The concentmtion of metalsvariedwith particle size. To investigate the pattern of metal concenhation distribution on particle size, the concentration of varlatlon vs. partick size may be plotted,However, such gmphical intqnWatio48 will not necesskly huly refiect

the distribution pattern with the presenceof trouble shooting samples,which is a common f&ure in dust analyses,especiallyfor the HI.5 mm particle size,since they my contain fine metal fmgruents. To overcome the problem of troubleshootingsamples,a plot of the ratio

betweenthe concentrationofspecific rangeof partick

size I0 the sum of conoentration of all Sizepa&es asn &Won of particle sizeis recommended(Fig. 2) (AlRajhi et al. 19%). Small-size particlesof indoordust (Fig. 21) had high

metal kvels, which decreasedwith an incrensein particle size. Pb and Cu dii not show this ~attsmof

M.A. Al-Rajhi

318

ctal.

0835

0.3 .e 3 0.25

1

0.2

0.15

0.t

Rb5

a

D

am

P.b6

0.04

0.03

0.1

D.12

Par(lcle size Cm) 0.30

(b) outdoor

dust

0.25

0.20

U.10

0

0.2

0.4

0.a

0.6 Pa&k

Fig. 2. Variation

I

1.2

1.4

1.6

she [mm)

in average ratio of wtcentration of pa&k size (Ai] IO the rum of concen~ions puticle si.w (i) in indoor (a) and ouldoor (II) dusts,

of dl particks

ha

@I) aa L fun&on

of

Metal kvcls in indoor and outdoor dust in RiyA,

Suburban

Rural

Old indusbinl

Mii. MVL Avapge Medii Min. Mm. AWtSg~ Mediin Min. Max. Avenpc MAim

Min. MW.

Average M5W

iaduatrial

MOtorwSy

Averape

Median Min. MWL Avenge Mcdilm Min. MSX. Average Medii

Cd 1.8 2.8 29 2.4

1.6

Satdi Ambii

319

Cr

cu

Li

Ni

226 s92 35.2 31.6

16.4 180.0 61.7

3.4 6.0 5.1

3x2 69.6 4s.o

51.1 IO.8 83.2 29.2 24.0 18.8

5.2

43.9

Pb 104

za aa 900

2134

338 258 28 608 137 116 52 176

2.8

14.6

7-4 4.6

4f.2 37.1

67.8

4.6 4.4 8.0’

38.2 38.2 47.0

40.2 37.1 88.8

5.5 is 3.0

41.1 39.6 47.8

692.3 301.3 212.0 37.4

6.4 4.5 4.3 3.0

85.4 69.5 72.5 3.6

12B.O

4.0

67.2 53n6 10.6 94a.o 63.8

3.3 3.2 1.8 7.2 4.8

39.0 2B.8 32.2 27.4 127.8 41.9

1040 60 4548 832 348 Isa 460 276 228 SW 3928 2001 1742 488 1676 WI 1010 100 24180 4345

2.4 2.3

18.8 47.2 28.5 26.9

1.6 2.6 1.9

28.0 30.0 29.3

2.4 2.8 4.2

29.6 35.4

3.8 3.9 1.6

44.9 42.4 18.4

3.0

23 6.7 33

45.0 31.9 32.0 196 96.8 41.0

2.1 2.5

37.2

39-4

4.8

40.8

2!s8

216

35.1

93.9

4.6

43.9

1762

443

56

15

1.5

59.5

concentration distribution; this could be due to their sources,which give rise to vsriabloske particles.In outdoor dusts,them was a wider rangeof particle size (Fig. 2b). Small-size particles showed high metal concentration, which decnased with an increasein particlesize.Graphically,metal concentrationreached a virtual plateau with particlesof sixe HI.4 mm. Cd showedan incrensein concentratioubeyond 0.4 uuu particles,which was due to tbe presenceof tiny fragmeritsof automobile tire. Whenmetalconcentrationdccrusts with an increase in particle size,pollutantSi+ragenerallyof Wnakdw particles,suchas soot and smoke.On the other hand, when metal concentrationincreaseswith an increasein particlerixe, then thu pollutmt~ arceither of relatively large-sizeparticlts or smallparticlesattachedto large particles, us observedundor a microscope. Somedust samplesmay contain high proportionsof smallparticlesixeand low proportionsof largeparticle size loading to a high concentrationof the an&& metal, and other dust samplesmay contain low small particle sixeand high large particlt sizepercentages, which will give a law concentrationof the amdysed, metal, Those particle sizesWithii the range of O&l-

101 8s 760 246¶ IS41 1472 IS2 nlo

303 2% 34 1044 236

0.08 mm were selectedfor this study sincethey were availablein botb outdoor and indoor dusts,and, more iutercstingly,gave relativelyhigh metal levels. cwtmorlnetl9llwds The werage and median levelsof sevenmetals in outdoordustsamplss~~RiyadhircshominT~le1 and Fig. 3. Lead,whichhadtbehighestkvelsamongthemetals, is a universalpolkant in urban euviroumentadue to automobib emissions.This in patticularly the CLD~in Riyadbdueto the useof k&d fuel, with Iaveb being espeeiallyhighnearmoMvayaasaresultofhightrafk den&y. Similarly, high tmfflc density was tht main SQlUteof Ieadin the viciiity of lhe city’s oId industri8l m As expected, outdoor Iesd levtlr decmasein suburbauand rural areaswhere automobile etniwioma weremuchlesstbaninurbauareas.Lbedlevelsintk seconduewerindustrialrrrtrwereaboutss%Icl!latban inurbanateqandStI%lessthantbeoklindustMcity, emphasizing that the maiu sources of lead are automobilesratherthan industries.

320

M.A. Al-Rqihi et al.

Metal levels in indoor and outdoor dust in Riyadh, swdi

321

Arabia

Lead levels in the dust of Riyadh are comparable with those of some cities in other countries (Hopke et al. 1980; Jensen and Laxen 1985; Fergusson et al. 1983; Fergusson and Ryan 1984; Ramlan and Badri 1989; Ward 1990). The cadmium levels were high for particles of size OS-2 mm, indicating that it had arisen from automobile tires and/or soot attached to thest particles, and high for particles of size ~0.04 mm, indicative of automobile oil. The cadmium levels were highest in motorways and in the old industrial area due to the presence of many tire service garages, besides the high density of traffic, Compared to cities in other countries, cadmium level was low (Ha&on 1979; Fergusson and Ryan 1984; Blake et al. 1987; Culbard et al. 1988; Ramlan and Badri 1989; Fergusson and Kim 1991). Chromium, copper, nickel, and zinc levels in Riyadh were generally lower than, or comparable with, cities in other countries (Harrison 1979; Fergusson and Ryan 1984; Hopke et al. 1980, Blake et al. 1987; Culbard et al. 1988; Fergusson and Kim 1991). There was a strong correlation between the concentration patterns of chromium and nickel. The sources of chromium and nickel were via attrition of chromium and nickel plating and alloys in automobiles, and of yellow paint on mads (Madany et al. 1994). Chromium levels were highest from near motorways and the old industrial city, while levels in suburban and rural areas were low. Copper originated from copper smelters in the old industrial area and from attrition of automobiles. The higher copper levels in the urban area were due to copper pollutants transfused from the old industrial area by wind, Zinc was attributable to automobile tires and oil, and factories using zinc in their products. The old industrial area had high levels of copper, nickel, and zinc. Lithium levels were similar in all areas studied since it was not related to pollution euurces; however, due to its ubiquitous presence in sands, it was investigated for other aspects of this research pmgramme in terms of evaluating metal ratios to determine natural and unnatural sources. In order to establish intra-metal nlationships in the sampfes, the correlation coefficients of metals were calculated for all areas studied, urban and motorways. In general, there were reasonably good correlations (0.60 - 0.80) between all metals studied except fix lead, which is dependent on traffic density, and varied widely in the 231 dust samples collected. However, there was a fairly good correlation between lead and

chromium. In urban stws, there were stmng carrelations between copper, nickel, md zinc, and between chromium and lead. In motorway areas, there were gcmd correlations between chromium, colsper, nickel, lead, and zinc, which show their relationship with automobile emissions. The we& correlation of cadmium indicates the presence of another source besides automobile emissions. hldoor melal levels The average and median levels of metals evaluated from the indoor dust samples of Riyadh are shown in Table 2 and Fig. 3. The presence of many car service garages, welding and lathe workshops, and the lack of anti-pollution management in the old industrial site resulted in high lead levels indoom (SO?? of total indoor lead Ievels~ in contrast to the second industrial site (1 I%), where industries were designed to modem standards, which gave due consideration to pollution control. Automobile emissions added much more to the indoor lead levels in urban areas compared to the rural and suburban areas. L&l mean levels in indoor dust of urban area represent about 29% of the total lead level, and 43% less than lead levels in outdoor dusts. Lead mean levels in rural and suburban areas H~CIFvery low, comprising only about 44% of the total levels. However, all indoor lead levels are lower than, or comparable to, cities in other countries (Fergusson and Ryan 1984,199l; Cultutrd et al. 1988; Fergussoe and Kim 1991). Cadmium arose from outdoor dust, paint, and smoking, It was low in all areas except the old industrial area, where it reached 6.5 pg.g“, equivalent to 64% of the total Ievel in Riyadh, due to the same reasons mentioned above. Cadmium levels were lower in comparison with other cities (Solomon and Hardixd 1977; Culbard et al. 1988). The sources of chromium and nickel were outdoor dusts and the use of chromium and nickel-plated household products; cupper and zinc originated fhxn outdoor dust. All areas showed similar levels, except the old industrial area where chromium levels were about 60% higher. Due to the presence of copper smelters, the old industrial area had high levels of copper, nickel, and zinc. Despite this, chromium, copper, and nickel levels in Riyadh m generally lower than, or comparable with, cities in other countries (Harrison 1979; Fergusson and Ryan 1984. 19% Hopke et al. 1980; Blake et al. 1987; Culbard et

M.A. At-Rajhi et at.

322

Table 2. The concentration(ug.&) of sevenmetalsin indoor dustfor particlesize 0.04 - 0.08 mm. Area Urben

Min. Max. Average

Suburban

Rural

Old industrial

Min. Max. Madian Min.

MiX. Aversge Median Min. MaX. Average Median Mill. MaX. Average Median

Average

Cd b

Cr 29.1

2.7

70.6 52.5

1.1 0.9 0 2.2 1.1 0.6 0.4 1.7 0.9 0.8 3.4 8.1 6.5 7.2 0.4 2.1 0.6 0.2 2.0

55.1 21.8 66.3 51.2 58.3 20.0 72.2 553 64.6 43.2 289.1 135.0 103.9 28.6 87.6 52.0 45.9 69.2

al. 1988;FergussonandKim1991).Lithiumwassimilar in all areas,indicating widespreadcontamination by wind-blowndustsderivedfromdresurroundingde~~s. Reiafitmsb@ Mwe8n

indoorend outdoor met& level

In general,therewas a positiverelationshipbetween metals in outdoor and indoor dusts, indicating that there were common sources, namely automobile emissionsand attritions. The overall mean ratios of metal levels in indoor to outdoor dust are shown in Table3. The correlationsbetweenoutdoor and indoor heavymetal levelsin all areaswere 93% f 4%, which showsthe significant contribution of outdoor dust to indoor dust.The levelsofkul and cadmiumin outdoor dusts were higher than those in indoor dusts, while other metal levelsin indoor dustswere higher than in outdoor dusts, particularly copper and chromium, which could be either due to the contribution of an internal source(s)in additionto outdoor sources,or due to their accumulation in the indoors. Indoor copper levels in the old industrial area were about I3 times higher than outdoor dusts,but in the secondindustrial area, copper levelswere one-third of levelsoutdoors. This was dueto the useof outdatedmethodsof copper smeltingin the old industrialarea, which are absentin the mend industrial area. In general, significantly

CU 48.8 302.3 134.8 94.1 $6.9 371.1 187.6 161.3 39.7 213.9 125.1 123.4 262.6 t240.8 828.0 904.3 20.8 179.3 80.0 60 271.1

Li

Pb

Zn

4.3 7.7 6.6 7.1 5.0 6.3 5.6 5.5 3.9 5.9 5.0 5.1 7.4 8.2 7.8 7.9 4.7 6.8 6.2 6.6 6.2

357

218

56.7 36.9 34.4 18,4 52.4 34.5 33.6 119 47.1 34.6

39.6 61.8 188.4 123.6 122.1

15.6 54.5 35.0 3s 52.9

2003 921 662 185 372 206 164 41 179 122 I35 781 31Sl 1606 1245 190

641 340 264 639.1

526 39s 419

207 617 426 440

I60 533 284 221 899 1740 1330 1340

I50 574 300 238 547.1

higher indoor metal levelsthan outdoor wete found in the old industrialarea. In general, an accumulation of indoor metals may result from different factors: I) indoor pollutant source(s);2) settlement of infiltrating outdoor dust; and 3) absorption of metals due to indoor humidity. However, more studiesare required to investigatethe effect of thesefactors. There was a strong correlation between the distribution pattern of metal concentrationsvs. particle size in the outdoor and indoor dusts (Table 4). This correlation was applied to three ranges of smaller particle size, namely 0.02-0.04, 0.04-0.08, and 0.08. 0.14 mm, but for larger particle sizes,there may or may not be a similarcorrelation;however,this requires farther investigation.Using the averageconcentration as a function of particle size may not show the hue correlation between outdoor and indoor dust; for example,copper in outdoor and indoor dust showeda negative correlation (-990/9xwhich is unrealistic,but using the averageratio of concentrationof one-size particle to the sum of concentrationsof all particle sizesof indoor and outdoor dust showed a positive correlation (69%). Similarly, chromium and zinc showeda higher correlation. There was no correlation between lead in the outdoor and indoor dust, its presencebeing relatedto d&rent sources.

Metal kvcls

in indoor and

wtdoordust

Table 3. Correlation Slk UlbMl Suburban Rtlml Old industrial New industrial Avenrge of Indwr/Outdwr 1nrklor/outdwr

mm 0.02 - 0.04

in Riydh,

Saudi Amtin

323

between indoor and outdoor dusts of Riisdh,

l

cu

LI

NI

w

zn

0.48 0.48 0.39 1.69 020 0.71

I.49 I,79 1.89 3.01 1.63 1.97

2.19 6.42 3.11 2.75 1.19 2.t9

1.28 I22 0.91 1.73 1.86 1.35

0.82 0.93 0.84 I*73 122 1.21

0.43 035 0.44 0.80 0.35 0.36

1.17 3,12 2,&! 0.86 0.99 1.23

89

92

97

-29

93

87

98

cd

Correlation 0.02 -001 O.M-00s O.Ob-0.14 Comhtian

64.29 36.39 22.59 65%

68.24 73.57 39.98

0.02 - 0.04 0.04 * 0.08 0.01-0.14 Correlation

66.30 59.41 35.94 -99%

177.82 190.29 295.69

0.02 - 0.01 0.04 - 0.01 0.08.0.14 Correlation

6.13 4.57 2.45 75%

6.59 8.06 2.93

0.02 - 0.04 0.04 - 0.01

46.22 47.10 36.93

Correlation

57.05 41.72 23.10 85%

0.02 - 0.04 0.04 - 0.01 O.OB-0.14 Correhtion

4165.69 336191 l84I.15 -68%

470.69 665.04 639.23

297.89 265.06 154.22

457.77 570.50 376.08

0.17 0.14 0.09 99%

0.42 0.37 0.21

0.23 0.19 0.11 99%

0.42 0.36 0.22

0.25 0.21 0.11 69%

0.33 0.35 0.32

0.27 0.21 0.11 96%

0.43 0.39 0.19

0.25 0.19 0.10 9m

0.40 0.36 0.25

0.24 0.21 0.11 -89%

0.33 0.32 0.36

0.23 0.20 0.11

0.36 0.35 029

Cr

CU

Li

Ni

O.OE-0.14

Pb

al 0.02 - 0.04 0.04 - 0.011 O,OP-0.14

048 mm.

Cr

1.63 1.42 1.15

0.08 - 0.14

size O.!M

Cd

3.33 2.85 I.94 100%

o.cM - 0.08

for prtick

324

CONCLUSIONS The actual distribution pattern of metal concentration, based on particle size, can be studied by plotting the ratio between the concentration of one or one-range pwficle size to the sum of concentration of all size particles as a function of particle sizz. Studying tr& concentration in dust samples, using a specified range of particle size, provides results which can be more realistically compared with samples from different environments. The levels of metals in outdoor and indoor dusts of Riyadh were generally lower or comparable with those of cities in other countries. Homer, the present work has clarly shown that lead contamination is widespread in and around Riyadh motorways. The levels of chromium, copper, nickel, and zinc indoors may create health problems, especially in children. Metat levels in the old industrial area were one of two major sources of environmental pollution in Riyadh. Anti-pollution procedures should, therefore, be applied in this area. The other major source of metal pollution was automobile emissions and attritions, but, in this case, high levels resulted in both outdoor and indoor dusts. Achde~ennr-We ace most grateful to tie Saudi Governmen For financial support of ibis research programme and 10 Dr. H.G.M. Edwards (Chemiilry B Chemical Teebr&gy,Universi~y of Bradford) for his helpful criticism ofa dral manuscript of lhis paper.

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al.

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