Measurements of Some Trace Elements in Street Dust in Zilfi Province at Saudi Arabia Using Inductively Coupled Plasma-Mass Spectrometer

Dust has frequently been used as a material fo r monitoring trace elements polution . The wind may take the trace elements to the f arms. And we know that there are many farms around Zilfi Province., at Saudi Arab ia . So in this study the concentrations of some trace elements(As,Cd,Cr, ,Pb, and ,Zn) , in streets dust in major streets and inner ones in Hai Elsdeeg and Smnan at Zilfi Province have been studied for comparison, using Inductively Coupled Plasma-Mass Spectrometer (ICP-MS), after siev ing and digestion using HNO3 , HCL and HF . Concentrations of most elements have been found less than allowed concentrations in literature , but the concentration of arsenic is found higher than the limit allowed specially in some samples . . The concentrations of , Cd , , Pb, Cr , and Zn , are high nearby car repair workshop and also at main streets especially in Hai Elsdeeg compared to Hai Smnan .


Introduction
Zilfi Province is Located on Riyadh, capital of Saudi Arabia approximately 260 km North . Dust has frequently been used as a material for monitoring trace elements pollution. In some instances dust may present significant pollution source when rain falls and washes the road surfaces and storms so causes increased metals input to rivers and sewage [1] .Young children have been identified as the group that is at highest risk. A lso vegetables and fruits may be contaminated with superficial of dust [2]. The ma jor source of trace elements for human is the food of plant and anima l origin. Drin king water covers a few percent of the elements needed . Breathing and using dirty hands are other sources [3]. The damage that results fro m inhalation of elements is much more serve than that produced by swallowing. For these reasons; the study will measure the concentrations of some trace elements in streets dust in ma jor streets and inner ones fro m Hai Elsdeeg and Smnan at Zilfi Province for co mparison, using Inductively Coupled Plas ma-Mass Spectrometer(ICP-MS). The wind may take the trace elements to the farms. And we know that there are many farms around Zilfi Province.
There are four ma in sources of trace elements in the street d ust wh ich are road t raffic ,industrial act iv ity, weathered material and specific intermittent episode [4]. Ele ments identified as originating fro m auto mobiles are Pb , Cd , Cu , Zn , Fe , Cr and Ni . The mo rphology and chemical co mposition of heavy metal particles embedded in tire dust and traffic -related materials have been characterized [5] .Simultaneous elemental analysis in dust of the city of Riyadh ,Saudi Arabia by (ICP-MS) [ 6] , also this technique have been used in microwave d igestion method of soil samples for to xic elements analysis [7] . The concentrations of 23 chemical elements have been determined using energy dispersive X-ray fluorescence (EDXRF) [8] . the elemental concentrations of heavy metal pollutants that may be present in street dust samples in Mubi, Adama wa state, Nigeria, were measured [9]. A few heavy metal contamination related studies in several cities fro m China over the past 10 years was reviewed [ 10] . The concentrations of Fe, Cu, Cd, Pb, Zn and Ni in the dusts were determined by atomic absorption spectrophotometer in Amman, Jo rdan [11] , and in (Turkey) [12] . So il samples fro m different roads in Jeddah city were co llected and analyzed for their elemental co mposition [13] .

Instrumentation
The analytical determination of As,Cd,Cr, ,Pb, and ,Zn, was carried out by ICP-M S(Inductively Coupled Plas ma-M ass Spectrometer ):ELAN 9000 (Perkin Elmer Sciex Instrumento , Concord ,Ontario ,Canada).The Table(1) highlights the operating conditions of the instruments used in this study .

Reagents
Nitric acid (69 % v/v ) ,super purity grade fro m Ro mil , England . hydrochloric acid (37% v/v) and hydrofluoric acid (40% v/v) were suprapure from Merck Germany .High purity water obtained fro m Millipore Milli-Q water purification system was used throughout the work .

Calibration
The ICP-MS calib ration was carried out by external calibrat ion with the blank solution and three working standard solutions (20,40 and 60 pp m ),starting fro m a 1000mg/l single standard solutions for ICP-MS (A ristar grade , BDH laboratory supplies ,England for the elements: As ,Cr ,Cd ,Pb , and Zn .

Sample Collection and Preparation
The area o f study (Hai Elsdeeg and Smnan in Zilfi Province ) was surveyed during October 2011 collecting (14 ) samp les fro m d ifferent streets by gently sweeping along the edge of the road , then they were transferred to plastics bags ,and sieved through 200 mm thieve . Sa mples were prepared by accurately weighing a round 200 mg of dust samples into a dry and clean Teflon digestion beaker ,6 ml of HNO 3 ,2 ml HCl and 2 ml HF were added to the Teflon beaker .Sa mp les were digested on the hot plate at 120-150˚C for appro ximately 40 minutes .The resulting digest was not clear ,so it was filtered through whatman filtered paper no.42.The filtered d igest was transferred to a 50 ml plastic volu metric flask and made up to mark using deionized water .A blank d igest was carried out in the sa me way .

Results and Discussion
All calibration graphs are linear in the selected range of each element .The square of the correlation (r2) ranges from 0.9985-0.099999 for most of the elements in this investigati on .Good precision values were obtained .The results have been reviewed in tables (2-7) and figures (1)(2)(3)(4)(5)(6) .Street dust shows considerable metallic contamination deposits of vehicle -derived metals and to reduction of meta l deposited on the road surface. The concentrations of ind ividual trace elements in street dust correlate with traffic density. Distance fro m the roads, urban and suburban differences and the mode of traffic density.     The concentrations of most elements have been found less than allowable concentrations in literature, but arsenic is found in concentrations higher than the limit allowed specially in the samp les (1, 2, 3 and 10). These high levels of As may due to human activates(table (7)and fig.( 6) .
The high concentrations of Zn, Cd , Pb, and Cr are found in the crossroads , nearby car repair workshop and also at the intersection of roads or area on main streets . Zn may have its origin fro m auto motive sources i.e. wear and tear of vulcanized rubber tires, lubricating oils and corrosion of galvanized vehicular parts. Study conducted in differing urban areas indicate that the most important source of anthropogenic Pb to street dust is from vehicular lead emissions. Throughout the literature, the source of Cu in the street dust was due to corrosion of metallic parts of cars derived fro m engine wear, thrust bearing, brushing, bearing meta ls and brake dust The Cd concentration in the street dust is likely to be associated to combustion product in the accumulators of motor vehicles or in carburetor [5,7,9,11]. Higher contamination was found in Hai Elsdeeg ( Table (7) as it contains the ma ximu m values of ,Pb, Cd, Zn,and As compared to Hai Smnan . A further study can be made of the causes of increased concentration of arsenic allowab le limits for large to xic for this element. These ite ms can also be measured in the rest of the revival of the study of Zulfi parts .As the concentrations of trace elements are very important for plant growth, so an study can be done in the future to see some trace elements concentrations in the territory of some fa rms in Zilfy or other places in Saudi Arabia .

Conclusions
Concentrations of most elements have been found less than allowable concentrations in literature ,but arsenic is found in concentrations higher than the limit allowed specially in the samp les (1, 2, 3 and 10).. The high concentrations of Zn, Cd, , Pb, and Cr, are found in the crossroads , nearby car repair workshop and also at the intersection of roads or area on main streets which lies in Hai Elsdeeg ,i.e. Hai Elsdeeg was found to be mo re contaminated compared to Hai Smnan