Document Neaa53d69Kgy7E13KLgYK1jYV

0007-SWP-000118164 4 / '* V* / >* I tic i/cieriiiiu:iiim <n i-cau in t'uint l'llina with a Portable Imo Io j ic Fluorescence Analyser by 0. lUstreor,* Cl.l UMHiiiu , ml N. J. P. Kiu u l a . I'nlninr flail Si. Varyi Hmfiftl MrJirml &Ih I Ltmiltm. KmftmnJ Although tktr* ere numerous anvlrtraniitil Murcia of laid of ai(Hiriemea for children (i) the major load haaard in aaoat urban papulations is doaisatic paint (>) Conventional land eerseniag programs have previously baan focuaaad an tha child rathar than hia anwiraamant and aa datact only tboaa childran who hava accumulated a aufficiant body burden af land to render tha taata positive. Although auch pragrana have shewn an annual poiaoning rata af O.J)l among children at riak (3) they fail to identify thoae dwellings that are potential hazards for childran not yet enpoaad. Chemical anal ysis af paint from surfaces accessible to children have shown that a wide range of load contents may bo present in boats of varying age tout aocia> status It), Paint sampling in this way has disadvantages in that tha aubsaquant analysis la relatively time consuming and costly and that the painted surface oust be dam aged so that a representative full-thickness sample awy be obtained.. Tha portable leotope fluoreecdnce analyser hes long been used bjr geologists far the determination of the mineral'content of oraa but has not previously found application in this field. Tha apparatus la based on tha principle of x-ray fluorescence and has ths advantages that it is portable and that it can ba applied repeatedly to any surface without damage. Pre liminary studios have suggested that tha device might rind application in tha determination of lead in dom estic paint films in situ. Zn this paper tha apparatus and its application to the analysis af paint films both in the laboratory end in, the domestic environment arc described. ' Apparatus The device employed wee the Portable Isotope Fluorescence Analyser manufactured by Rank Precision Instruments Ltd., London, England. Zt comprises a portable battery-powered rotameter which is eonn- acted 6y means af a flexible for application to tha teat s weight af tha assembly is 7-5 contains a radioactive source mCl) scaled In an aluminium c shielded when not in uao by m shutter which ia displaced on being applied to the toot sur sinultonaausly operated! Tha the Instrument whan not in us ared/h and thus prassnts no h Tha radiations emanating Aram xcita a fluorescent x-radiat tha teat material, are uranium kaY, which penetrate to an af an ite composition, but seldom Tha fluaraacant amission aris enters tha probe unit through aperture eurrounding ths sour through one of a pair af bala ected and measured by means o sodium iodide crystal and phs , housed in tha probe. The bala gallium or goruonlieo end or# cut off emissions above end b lead emission at i.179 A. - Gi tha effeetive load content e'f determined Aram the differenc rates obtained when tha filte utively. Standardisation The observed difference given element will vary accor which Che cleeMnt la disperse roading can be obtained with element of sufficient thickne with lesser concentrations w ternal absorption of tha oxc tions. ldaaily a sariae af s ical composition would have t Cast situation eo that a stan in count rates ogainat lead c While this is inpaaeible for it ie simply achieved for a g additions of a load compound sample .from which uniform film driad to give a standard seri * Wellcome Senior Research Fellow in Clinics! Science, v Zn this study a commerci undercoat doaieatle paint cont lK lead was used so tha stand 00 or Uie point! increasing weights of load oxide (Pb.O, ) er added and thurouglily (iixed mutf that a rim uf paint filaia of lead content in the renge ]-))S wuro obtained. Subtraction of the reading due to tha loud'content of the beae .paint allowed the conetruetion of u calibration curve for tha range 0-)0K, the naxinun reading waa obtained by substitution of load foil for point V give lOOK lead (fig. i). Tha raadinge ebtainad allowed darda (6.5 {) into Potri dialiee of AmU'arai e area (Ch cm1) aupportad on a top-loddlng bala Tlia paint waa allowed te cover the whole of t aurfaco auch that a relatively thick filn of depth waa obtained. The ntandarda were dried oughly and raweighad before uae in order te d the lead content par gran of dried paint filn W0W-W0M0C8WBITY , w Mon-hoaegenelfey of the teat paint filn n Introduce difficultlee in intarpracntlbn of t readinga ebtainad and in aoaia caaaa render it ibla ta obtain a representative figure. .In n situations thia result* '.from the succeeeiv* a ation *f filne of different lead or natrix co to n given eurface. In ita elnpleat fern thi prises a double layered filn but in neny field etlons nere conplex fllna with nultiple layer ancountsrad. A double'layered riln nay produ enenaleua reeulta in two ways depending on wh layer is superficial with regard to the analy probe. A eurface layer of high lead content ' thus register a falsely high lead eontent for whela filn, conversely if the lead containing is deap, the overlying filn of lav lead conte inpelr the efficiency #f dotecclan. Tha usua situation in the field involves the second of two situations in which the deepest layar of hna tho highest lend content. , Figure 1. Count rate dlffereheea for painte of varying lead content a) laboratory praparad etan- . darda (open elrclea and curve) and b) doneotic paint filiea In altu (cloaed clrclea). In order to eiieaa the effect of overlyin a aerie* of standard paint filne waa prepared Petri diehee as described above te contain After drying each filn was covered with secon filne of increasing thickness of tho base poi low lead coatout (l.0)( load) ouch that each f weighed 8og/cn* When dry. Successive observa shewed a progressive decrease in the apparent concantratlon until thia approachsd sare with covering paint filn *f 77g/pqulvalent te thinly brushed layera (Fig. 2). KELP TESTING determination of tho lead content of o given filn in the range 0-5# to an accuracy batter than 0.2Ji. It woa found thot folia of 0.002* thickneea gov# raadinge'that did not differ fron thoee obtained from Che ourface of a lead brick, ao that tha eff ective thickness for the pure elenont wee probably laaa than thia. Standard palpt filne ware obtained k touring equal welghte of the prepared paint etat Thirty-four hones inhabited by ftailiea children in the 1-5 age group ware salactad group of raalllea previously studied (1). T ection waa arranged sueh that there wee a wid acattar of lead concentrations In tha doaeat to which tha children had access. In each ho reading waa ebtainad fron a palntad surface rooa usually aeeuplad by tha children, in r thia waa a window till or door fraaa. Tha CRAMS s u r f a c e p a in t / d is h FINDINGS In general there vis good correlation the oheoiieal and x-ray methods and the in results are given in Figure 1. which also part of the standard curvs derived in the Curva fitting of the data from the domes together with statistical analysis was un by moans of a least squares program with 1950E computer and tho derived curve toge 95# confidence limits are reproduced (Fig is evident that tha scatter of results vas an apparent zero lead content could be ob the analyser in a paint film with an actu tent of 5# and that convarsoly a Count rat as 2.5X10) cps could bo obtained with very concentrations. Similarly the wide separ tho 9$# confidence limits require that a c of 3.0 XlO3 epa before it could bo inferre that degree of certainty that tha load con the paint filss exceeded 1#, conversely suc e#. .rata could equally indicate a lead conten Figure 2. Graph shoving the decrease in count rate difference for a paint containing 31 g# lead with successive applications of a aocond paint of lov lead content (l.O g#) in a dish of Ck cm. The interr upted line indicates the Value, obtained vith the 1.0# lead containing paint alone. P fluorescence analyser vas standardised In each home by means of a standard paint film previously prepared in the laboratory but in practice no appreciable change in machine performance occurrod betveen home visits. Several readings were obtained from oech surface to onsurs that local variations in paint film thickness or lead content did not- bies the results.. After each aarios of readings a full thickness specimen of the paint film weighing about 50-100 rag * was obtained from the surface with the ' aid of a atainleea etoel scalpel blade. Chemical analysis of each paint specimen was made after wet digestion by means of a aeraiautomated alkaline dithizone method (6) and tha results compared with the analyser readings. ' LEAD GRAMS%PAIN Figure 3. Best fit curve and 95# cc^ifidenc for domestic paint film data with lead c the range 0-15#. In its present form it- is unlikely thSt this type of apparatus could find applicstion (in lead screening programs since it is incapable >of discrinunoting between lead contents of domestic paint films in the 0-6S range. These findings are in marked contrast to the laboratory results for a scries of standard paints and almost certainly result from the non-homogeneity end the variable thickness of paint.films encountered in tbe field. SUMMARY The application of x-ray fluoreacanee to the determination of the leed content of peint films was evaluated using a portable isotope fluorescence anal yser. Accurote determinations were achieved in the laboratory using prepared films in which the lead was dispersed through matrices of constant composition in a single layer. The presence of lead could be masked by overlying paint films of low leed content and was almost obscured by an overlying peint film of 77 mg/cm2. The results for domestic peint films correlated with chemical analyses but the confidence limlta were too widely separated to allow appli cation of thia technique to lead screening programs. The field results'probably reflect non-homogeneity of domestic point films. . Acknowledgements Vs are Indebted to Hr. G.A. Cooper of the Computer Centre, Queen Mary College, University of London, for analysis of soma of the data. Befercncca 1- Baritrop, D* Postgrad. Med. J. 45f 129 fi969). 2. Chisolm, J.J.Jr. And Harrison. H.E* 18* 9*0 (1956). * Pediatrics * 3* Sacha, K.K., Blanksma, L.A., Murray, E.F* and 0'Connsll, H.J. Pediatrics 389 (2970). ` k. Berltrop, D. and Sillala, N.J.P. Childh. 44, 476 (1969). 'Arch. Dis. 5. Barltrop, D. Arhiv. Hig. Rad. Tolcsikol. 21. No. 3 (1970). - * 6. Browett, E.V. and Hosa, R. Analyst. Lond. 90. iM 0007-SWP