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Microsampling technique and determination of blood lead by zeeman atomic absorption spectrophotometry
The Science of the Total Environment, 71 (1988) 37-43 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
37
MICROSAMPLING TECHNIQUE A N D D E T E R M I N A T I O N OF BLOOD L E A D BY ZEEMAN ATOMIC A B S O R P T I O N SPECTROPHOTOMETRY*
S.T. WANG, S. PIZZOLATO and F. PETER*
Biochemistry Laboratory, Laboratory Services Branch, Ontario Ministry of Health, Toronto, Ontario M9W 5K9 (Canada) (Received October 7th, 1986; accepted February l l t h 1987)
ABSTRACT Quality control materials and participation in proficiency testing programmes were used for assessing the long-term performance of our blood lead analysis. The accuracy and precision of the blood controls, Metals I and 2 from the Behring Institute, were evaluated over a 1-year period. The accuracy of the method was also monitored by the Centers for Disease Control (CDC) Blood Lead Proficiency Testing Programme over a 3-year period. Nearly 85% (28 out of 33 samples) of our results were within _+5% of the CDC reference values. There were excellent correlations between our results and the target values of several proficiency testing samples, with correlation coefficient values of 0.9959-0.9970. The method was used for the screening of blood lead in children in conjunction with microsampling techniques.
INTRODUCTION
In recent years, graphite furnace atomic absorption spectrophotometry (GFAAS) is being widely used in clinical laboratories for the determination of trace elements in biological fluids [1-3]. Recently, we developed a direct method with simple dilution for the determination of blood lead in our laboratory [4] using a Hitachi Zeeman atomic absorption spectrophotometer equipped with an automatic sampling system. The method was designed to take full advantage of modern GFAAS technology based on microprocessor control of the function and sequence of the analysis and on the Zeeman background correction technique. This method has been routinely used in our laboratory for the past 3 years and has proved very reliable based on the results obtained from the CDC Blood Lead Proficiency Testing Programme. The method has been successfully used to screen blood lead in Ontario children in conjunction with a microsampling technique. This report describes our experience with the determination of lead in blood with respect to precision and accuracy by evaluating long-term results of * Dedicated to the memory of Professor J o h n Michael Ottaway. *To whom all correspondence should be addressed.
0048-9697/88/$03.50
© 1988 Elsevier Science Publishers B.V.
38
quality control specimens, several proficiency programmes and blood lead surveys. EXPERIMENTAL METHODS
Apparatus and instrument setting A Zeeman graphite furnace atomic absorption spectrophotometer (ZGFAAS, Hitachi Model 180-80) equipped with a data processing unit (Model 180-0205), an automatic sampler (Model 180-0127) and a temperature control unit (Model 180-0451) was used. A pyrolytic graphite cup-type cuvette from RingsdorffWerke, Germany, was employed. The instrumental parameter setting is shown in Table 1. The Eppendorf pipet system and pipet tips were used to pipet reagents and specimens.
Chemicals, reagents and quality control materials The chemicals and reagents used for the blood lead analysis have been described in previous publications [4, 5]. Quality Control blood standards were M1 and M2 from the Behring Institute, West Germany. Standard Blood lead reference materials (SRM) from the National Bureau of Standards (NBS), U.S.A., were used to monitor the accuracy of the method. Blood lead proficiency testing specimens from CDC, Atlanta; Ontario Ministry of Labour, Toronto; West Allis Memorial, Wisconsin; and the Quebec Centre of Toxicology, were employed to verify the analytical performance. All the glassware used was acid-washed and cleaned with high purity distilled-deionized water. Venous whole blood specimens were normally collected in Becton-Dickinson vacutainers with sodium heparin as anticoagulant TABLE 1 Instrument setting for the blood lead determination Wavelength Lamp current Slit Analytical mode Measurement mode Equation type Background corrector Carrier gas Furnace programme
Temperature control unit
283.3 nm 7.5 mA 1.3 nm Concentration Peak area Linear fit Zeeman Argon, 200 ml min- 1 Drying: 40-100°C, 60 s Ashing: 500°C, 30 s Atomization: 1600°C, 7 s Cleaning: 2100°C, 3 s Cooling: 25°C, 5 s Control level, 860 Temperature setting, 860 (high)
39 (B-D No. 6480; with green stopper) or with di-sodium EDTA as a n t i c o a g u l a n t (B-D No. 6451; with lavender stopper). Each specimen was gently mixed for at least 5min on a single-speed orbital mixer (Adams, Nutator, New Jersey) to ensure homogeneity before pipetting. For the children's blood lead screening programme, finger-pricked blood specimens were collected in B-D microtainers with ammonium heparin anticoagulant (No. 5963). The children's fingers were t h o r o u g h l y washed with soap and warm water to ensure t h a t t her e was no lead contamination. A sharp disposable microlancet was used to make a swift pin-prick incision and a few drops of blood were allowed to r un into the collector-top of the microtainer. At least 100-pl samples of finger-pricked blood were collected to minimize external contamination. The microtainers were t hen labelled, capped, inverted several times to ensure t h o r o u g h mixing with the anticoagulant, packed and transported to our l a b o r a t o r y for analysis. To check the lead c ont e nt of the B-D microtainers, a m i crot ai ner from each package was randomly selected and tested for lead. Each m i crot ai ner was filled with 100 #l of saline solution and shaken for 24 h before analysis. In all, 80 microtainers were tested; no detectable amount of lead was found. The detection limit of the method was 1.5 #g 1-1, as described elsewhere [5].
Analytical procedures The procedures used for blood lead determination are described in previous publications [4, 5]. A 50-pl aliquot of the blood specimen was pipetted into a small polypropylene tube (Sarstedt brand), t oget her with 450#1 of 12.5gl 1 (NH4)2HPO 4 and 5g1-1 Triton-X-100 solution. The tube was swirled for 30s and transferred to a 2 ml polystyrene sample cup placed in the autosampler. A 10-#l aliquot of the diluted sample was transferred by the autosampler probe to a pyrolytic graphite cup-type cuvette. The blood lead was then analyzed under the optimized furnace programme as shown in Table 1. The c o n c e n t r a t i o n of Pb in the blood specimen was calculated from an aqueous standard curve containing the matrix-modifiers. The quality control and proficiency testing specimens were assayed the same way as the blood specimens. RESULTS AND DISCUSSION A typical internal monthly quality control chart of the M1 and M2 Quality Control specimens is shown in Fig. 1. The monthly mean value and standard deviation of M1 and M2 were 402.0 + 16.6#gl 1 with a % coefficient of variation (%CV) of 4.1 (N = 35) and 748.0 _+ 24.9#gl 1 with a %CV of 3.3 (N = 35), respectively. The target values of M1 and M2 were 410.3 #g l- ~(range 368.8-451.7) and 733.5#g1-1 (range 679.6-787.4). The quality control chart of M1 and M2 specimens in 1985 is shown in Fig. 2. The mean values of M1 and M2 over the 12-month period were 406.2#gl -1 (CV = 2.3%) and 741.8~g1-1 (CV = 1.6%). The precision of the blood lead determination over the years is
40
i i l l ] l l l l
452
MI
~
I I I l l l l l l i l l l l l l l l l l l
431
ISD
410
Mean
389
- 1SD O
Qe
368
-2SD
I
M2
~o-
2SD
O
e
788
2SD
761
1SD
Q_
734
~
~lean
7O7
-1SD
68O
-2SD
Day
Fig. 1. A monthly quality control chart of M1 and M2. The concentration range of M1 and M2 is 368.8-451.7 and 679.~787.4 t~g 1 ~, respectively. (~---O) Individual values; ( O - ~ ) mean daily value.
very consistent, all w i t h i n 5% of the CV. The accuracy of the M1 and M2 specimens is very close to the target values set by the company. The accuracy of the method was also checked periodically using the N B S standard reference materials. The results are s h o w n in Table 2. The accuracy of the m e t h o d was w i t h i n 5% of the N B S certified value, with the actual bias r a n g i n g from + 1.8% to - 4.3% for c o n c e n t r a t i o n s of blood lead between 57 and 732pg 1 1. We monitored the long-term performance of our method by participating in the CDC proficiency testing programme. Figure 3 shows our results with respect to the CDC reference values for the period 1984-86. N o t e from Fig. 3 that our values for 28 out of 33 samples were w i t h i n +_5% of the CDC reference value; the results for the remaining five samples ranged from _+ 5 to + 10%. The linear regression e q u a t i o n for our results (Y) with the CDC reference values (X) was Y = 0.98X + 1 0 . 4 p g l - ' . The correlation coefficient was 0.9970 ( N = 33) over the wide c o n c e n t r a t i o n range of 62.21153.0pgl -], with a mean + SD (pgl 1) for the CDC reference values of 445.5 + 265.2 and 443.4 +_ 259.0 for our results. In addition to the CDC blood proficiency testing programme, we participated in the Ontario Ministry of Labour Blood Lead Comparison Program, the West Allis Memorial Hospital, W i s c o n s i n Blood Lead Reference Program and the Quebec Interlaboratory Comparison Program. The results for the past 3 years
41
800
J
6oo
"0 _I "0 II)
400
M1
I 1
I 2
I 3
I 4
I 5
l 6
I 7
! 8
I 9
I 10
I 11
I 12
Month
Fig. 2. The mean monthly blood lead concentration in 1985. The target value of M1 and M2 is 410.3 and 733.5pg 1 1, respectively. TABLE 2 National Bureau of Standards Standard Reference Material 955: Lead in Blood Code
Certified value mean + 2SD (pgl 1)
Our result mean + 2SD (#g1-1)
Bias (%)
A B C D
57 305 494 732
58 292 491 717
+1.8 -4.3 -0.1 -2.0
+ 5 i 3 _+ 8 + 7
+_ 8 + 12 + 23 + 15
h a v e all b e e n w i t h i n the a c c e p t a b l e ranges. The l i n e a r r e g r e s s i o n line a n a l y s i s of o u r r e s u l t s (Y) v e r s u s t h e t a r g e t v a l u e s (X) o f t h e p r o f i c i e n c y p r o g r a m m e s i n 1985 a r e s h o w n i n T a b l e 3. I t s h o w s t h a t t h e c o r r e l a t i o n b e t w e e n o u r r e s u l t s a n d t h e t a r g e t v a l u e s is e x c e l l e n t o v e r a w i d e r a n g e o f c o n c e n t r a t i o n s ; t h e c o r r e l a t i o n c o e f f i c i e n t s w e r e c o n s i s t e n t l y b e t w e e n 0.9959 a n d 0.9968. T h i s shows t h a t our a n a l y s i s of blood lead has b e e n very c o n s i s t e n t over the years. W e f o u n d t h a t t h e p r o f i c i e n c y p r o g r a m m e s w e r e v e r y u s e f u l for m o n i t o r i n g t h e a n a l y t i c a l p e r f o r m a n c e , p a r t i c u l a r l y t h e C D C p r o g r a m i n w h i c h m o r e t h a n 260 l a b o r a t o r i e s p a r t i c i p a t e d u s i n g d i f f e r e n t m e t h o d o l o g i e s . T h e a c c u r a c y of a n
42
E10%
T 1
-~o%
-lo% Fig. 3. The bias between our results and the CDC reference values presented as a percentage in 3 years from 1984 to 1986. The percent deviation from the CDC reference value is obtained by calculating the difference between our results and the CDC value and then dividing the difference by the CDC value as a percentage. I-IV represent different quarters of the year. ( ~ - - ~ ) 1984; (A--A) 1985; (l~--$) 1986. TABLE 3 The regression line analysis of blood lead results in 1985 Blood lead programme
N
Regression line a
CDC Quebec Ontario Ministry of Labour Wisconsin
12 21 30 6
Y Y Y Y
= = = =
0.95X 1.00X 1.02X 0.96X
+ + +
14.0 1.3 3.5 2.7
Concentration range ~ g l 1)
r (correlation coefficient)
63-1153 130~25 115-742 108-703
0.9968 0.9959 0.9968 0.9965
a y = Our result; X = target value. analytical determination, therefore, is e a s i l y e s t a b l i s h e d through this programme. O u r m e t h o d w a s u s e d t o s c r e e n b l o o d l e a d i n 1269 O n t a r i o c h i l d r e n [6]. T h e d i s t r i b u t i o n o f b l o o d l e a d b y r e s i d e n c e is s h o w n i n T a b l e 4; u r b a n c h i l d r e n h a d t h e h i g h e s t l e v e l s . T h e o v e r a l l m e a n v a l u e f o r 1269 O n t a r i o c h i l d r e n w a s 103.6 # g l - ] , w h i c h is s i m i l a r t o t h e a v e r a g e b l o o d l e a d c o n c e n t r a t i o n f o u n d i n t h e U n i t e d S t a t e s p o p u l a t i o n i n 1980 [7]. O n l y 18 o f t h e 1269 c h i l d r e n h a d b l o o d lead > 250gg1-1. Repeat sampling and analysis confirmed these high lead
43 TABLE 4 Blood lead survey in Ontario, 1984 Residence
Blood lead concentration mean _+ SD (~gl 1)
No. of children tested
No. of children with blood lead > 250 pg 1-1
Urban Suburban Rural Total
120.2 99.5 89.1 103.6
392 507 370 1269
7 (1.8%) 8 (1.6%) 3 (0.8%) 18 (1.4%)
_+ 43.5 _+ 35.2 +_ 39.3 _+ 41.4
r e s u l t s . A r e p e a t t e s t of h i g h b l o o d l e a d l e v e l s is n e c e s s a r y i n t h e s c r e e n i n g p r o g r a m m e s i n c e i t h a s b e e n r e p o r t e d t h a t t h e c o n t a m i n a t i o n of c a p i l l a r y b l o o d s a m p l e s f r o m s k i n is a s e r i o u s p r o b l e m [8-10]. W i t h c a r e f u l w a s h i n g of t h e s k i n a n d a v o i d i n g direct c o n t a c t of the s k i n d u r i n g s a m p l i n g , the m i c r o t a i n e r finger-prick blood method in conjunction with the ZGFAAS technique gives a s u f f i c i e n t l y a c c u r a t e r e s u l t for b l o o d l e a d s c r e e n i n g i n c h i l d r e n . REFERENCES 1 2 3 4 5 6
7 8 9 10
E.J. Hiderbeger, M.L. Kaiser and S.R. Koirtyohann, At. Spectrosc., 2 (1981) 1. J.M. Ottaway, At. Spectrosc., 3 (1982) 89. C. Veillon, Anal. Chem., 58 (1986) 851A. S.T.Wang, G. Strunc and F. Peter, in S.S. Brown and J. Savory (Eds), Chemical Toxicology and Clinical Chemistry of Metals, Academic Press, New York, 1983, pp. 57-60. S.T. Wang and F. Peter, J. Anal. Toxicol., 9 (1985) 85. C. Duncan, R.A. Kusiak, H. O'Heany, L.F. Smith, L. Spielberg and J. Smith, Blood Lead and Associated Risk Factors in Ontario Children, December, 1985. Ontario Government, Toronto, Ontario. Centers for Disease Control, Morbidity Mortality Weekly Report, 31 (1982) 132. R.E. Cooke, K.L. Glynn, W.W. Ullmann, N. Lurie and M. Lepow, Clin. Chem., 20 (1974) 582. D.G. Mitchell, K.M. Aldous and F.J. Ryan, N.Y. State J. Med., 74 (1974) 1599. M.P. Bratzel Jr. and A.J. Reed, Clin. Chem., 20 (1974) 217.
37
MICROSAMPLING TECHNIQUE A N D D E T E R M I N A T I O N OF BLOOD L E A D BY ZEEMAN ATOMIC A B S O R P T I O N SPECTROPHOTOMETRY*
S.T. WANG, S. PIZZOLATO and F. PETER*
Biochemistry Laboratory, Laboratory Services Branch, Ontario Ministry of Health, Toronto, Ontario M9W 5K9 (Canada) (Received October 7th, 1986; accepted February l l t h 1987)
ABSTRACT Quality control materials and participation in proficiency testing programmes were used for assessing the long-term performance of our blood lead analysis. The accuracy and precision of the blood controls, Metals I and 2 from the Behring Institute, were evaluated over a 1-year period. The accuracy of the method was also monitored by the Centers for Disease Control (CDC) Blood Lead Proficiency Testing Programme over a 3-year period. Nearly 85% (28 out of 33 samples) of our results were within _+5% of the CDC reference values. There were excellent correlations between our results and the target values of several proficiency testing samples, with correlation coefficient values of 0.9959-0.9970. The method was used for the screening of blood lead in children in conjunction with microsampling techniques.
INTRODUCTION
In recent years, graphite furnace atomic absorption spectrophotometry (GFAAS) is being widely used in clinical laboratories for the determination of trace elements in biological fluids [1-3]. Recently, we developed a direct method with simple dilution for the determination of blood lead in our laboratory [4] using a Hitachi Zeeman atomic absorption spectrophotometer equipped with an automatic sampling system. The method was designed to take full advantage of modern GFAAS technology based on microprocessor control of the function and sequence of the analysis and on the Zeeman background correction technique. This method has been routinely used in our laboratory for the past 3 years and has proved very reliable based on the results obtained from the CDC Blood Lead Proficiency Testing Programme. The method has been successfully used to screen blood lead in Ontario children in conjunction with a microsampling technique. This report describes our experience with the determination of lead in blood with respect to precision and accuracy by evaluating long-term results of * Dedicated to the memory of Professor J o h n Michael Ottaway. *To whom all correspondence should be addressed.
0048-9697/88/$03.50
© 1988 Elsevier Science Publishers B.V.
38
quality control specimens, several proficiency programmes and blood lead surveys. EXPERIMENTAL METHODS
Apparatus and instrument setting A Zeeman graphite furnace atomic absorption spectrophotometer (ZGFAAS, Hitachi Model 180-80) equipped with a data processing unit (Model 180-0205), an automatic sampler (Model 180-0127) and a temperature control unit (Model 180-0451) was used. A pyrolytic graphite cup-type cuvette from RingsdorffWerke, Germany, was employed. The instrumental parameter setting is shown in Table 1. The Eppendorf pipet system and pipet tips were used to pipet reagents and specimens.
Chemicals, reagents and quality control materials The chemicals and reagents used for the blood lead analysis have been described in previous publications [4, 5]. Quality Control blood standards were M1 and M2 from the Behring Institute, West Germany. Standard Blood lead reference materials (SRM) from the National Bureau of Standards (NBS), U.S.A., were used to monitor the accuracy of the method. Blood lead proficiency testing specimens from CDC, Atlanta; Ontario Ministry of Labour, Toronto; West Allis Memorial, Wisconsin; and the Quebec Centre of Toxicology, were employed to verify the analytical performance. All the glassware used was acid-washed and cleaned with high purity distilled-deionized water. Venous whole blood specimens were normally collected in Becton-Dickinson vacutainers with sodium heparin as anticoagulant TABLE 1 Instrument setting for the blood lead determination Wavelength Lamp current Slit Analytical mode Measurement mode Equation type Background corrector Carrier gas Furnace programme
Temperature control unit
283.3 nm 7.5 mA 1.3 nm Concentration Peak area Linear fit Zeeman Argon, 200 ml min- 1 Drying: 40-100°C, 60 s Ashing: 500°C, 30 s Atomization: 1600°C, 7 s Cleaning: 2100°C, 3 s Cooling: 25°C, 5 s Control level, 860 Temperature setting, 860 (high)
39 (B-D No. 6480; with green stopper) or with di-sodium EDTA as a n t i c o a g u l a n t (B-D No. 6451; with lavender stopper). Each specimen was gently mixed for at least 5min on a single-speed orbital mixer (Adams, Nutator, New Jersey) to ensure homogeneity before pipetting. For the children's blood lead screening programme, finger-pricked blood specimens were collected in B-D microtainers with ammonium heparin anticoagulant (No. 5963). The children's fingers were t h o r o u g h l y washed with soap and warm water to ensure t h a t t her e was no lead contamination. A sharp disposable microlancet was used to make a swift pin-prick incision and a few drops of blood were allowed to r un into the collector-top of the microtainer. At least 100-pl samples of finger-pricked blood were collected to minimize external contamination. The microtainers were t hen labelled, capped, inverted several times to ensure t h o r o u g h mixing with the anticoagulant, packed and transported to our l a b o r a t o r y for analysis. To check the lead c ont e nt of the B-D microtainers, a m i crot ai ner from each package was randomly selected and tested for lead. Each m i crot ai ner was filled with 100 #l of saline solution and shaken for 24 h before analysis. In all, 80 microtainers were tested; no detectable amount of lead was found. The detection limit of the method was 1.5 #g 1-1, as described elsewhere [5].
Analytical procedures The procedures used for blood lead determination are described in previous publications [4, 5]. A 50-pl aliquot of the blood specimen was pipetted into a small polypropylene tube (Sarstedt brand), t oget her with 450#1 of 12.5gl 1 (NH4)2HPO 4 and 5g1-1 Triton-X-100 solution. The tube was swirled for 30s and transferred to a 2 ml polystyrene sample cup placed in the autosampler. A 10-#l aliquot of the diluted sample was transferred by the autosampler probe to a pyrolytic graphite cup-type cuvette. The blood lead was then analyzed under the optimized furnace programme as shown in Table 1. The c o n c e n t r a t i o n of Pb in the blood specimen was calculated from an aqueous standard curve containing the matrix-modifiers. The quality control and proficiency testing specimens were assayed the same way as the blood specimens. RESULTS AND DISCUSSION A typical internal monthly quality control chart of the M1 and M2 Quality Control specimens is shown in Fig. 1. The monthly mean value and standard deviation of M1 and M2 were 402.0 + 16.6#gl 1 with a % coefficient of variation (%CV) of 4.1 (N = 35) and 748.0 _+ 24.9#gl 1 with a %CV of 3.3 (N = 35), respectively. The target values of M1 and M2 were 410.3 #g l- ~(range 368.8-451.7) and 733.5#g1-1 (range 679.6-787.4). The quality control chart of M1 and M2 specimens in 1985 is shown in Fig. 2. The mean values of M1 and M2 over the 12-month period were 406.2#gl -1 (CV = 2.3%) and 741.8~g1-1 (CV = 1.6%). The precision of the blood lead determination over the years is
40
i i l l ] l l l l
452
MI
~
I I I l l l l l l i l l l l l l l l l l l
431
ISD
410
Mean
389
- 1SD O
Qe
368
-2SD
I
M2
~o-
2SD
O
e
788
2SD
761
1SD
Q_
734
~
~lean
7O7
-1SD
68O
-2SD
Day
Fig. 1. A monthly quality control chart of M1 and M2. The concentration range of M1 and M2 is 368.8-451.7 and 679.~787.4 t~g 1 ~, respectively. (~---O) Individual values; ( O - ~ ) mean daily value.
very consistent, all w i t h i n 5% of the CV. The accuracy of the M1 and M2 specimens is very close to the target values set by the company. The accuracy of the method was also checked periodically using the N B S standard reference materials. The results are s h o w n in Table 2. The accuracy of the m e t h o d was w i t h i n 5% of the N B S certified value, with the actual bias r a n g i n g from + 1.8% to - 4.3% for c o n c e n t r a t i o n s of blood lead between 57 and 732pg 1 1. We monitored the long-term performance of our method by participating in the CDC proficiency testing programme. Figure 3 shows our results with respect to the CDC reference values for the period 1984-86. N o t e from Fig. 3 that our values for 28 out of 33 samples were w i t h i n +_5% of the CDC reference value; the results for the remaining five samples ranged from _+ 5 to + 10%. The linear regression e q u a t i o n for our results (Y) with the CDC reference values (X) was Y = 0.98X + 1 0 . 4 p g l - ' . The correlation coefficient was 0.9970 ( N = 33) over the wide c o n c e n t r a t i o n range of 62.21153.0pgl -], with a mean + SD (pgl 1) for the CDC reference values of 445.5 + 265.2 and 443.4 +_ 259.0 for our results. In addition to the CDC blood proficiency testing programme, we participated in the Ontario Ministry of Labour Blood Lead Comparison Program, the West Allis Memorial Hospital, W i s c o n s i n Blood Lead Reference Program and the Quebec Interlaboratory Comparison Program. The results for the past 3 years
41
800
J
6oo
"0 _I "0 II)
400
M1
I 1
I 2
I 3
I 4
I 5
l 6
I 7
! 8
I 9
I 10
I 11
I 12
Month
Fig. 2. The mean monthly blood lead concentration in 1985. The target value of M1 and M2 is 410.3 and 733.5pg 1 1, respectively. TABLE 2 National Bureau of Standards Standard Reference Material 955: Lead in Blood Code
Certified value mean + 2SD (pgl 1)
Our result mean + 2SD (#g1-1)
Bias (%)
A B C D
57 305 494 732
58 292 491 717
+1.8 -4.3 -0.1 -2.0
+ 5 i 3 _+ 8 + 7
+_ 8 + 12 + 23 + 15
h a v e all b e e n w i t h i n the a c c e p t a b l e ranges. The l i n e a r r e g r e s s i o n line a n a l y s i s of o u r r e s u l t s (Y) v e r s u s t h e t a r g e t v a l u e s (X) o f t h e p r o f i c i e n c y p r o g r a m m e s i n 1985 a r e s h o w n i n T a b l e 3. I t s h o w s t h a t t h e c o r r e l a t i o n b e t w e e n o u r r e s u l t s a n d t h e t a r g e t v a l u e s is e x c e l l e n t o v e r a w i d e r a n g e o f c o n c e n t r a t i o n s ; t h e c o r r e l a t i o n c o e f f i c i e n t s w e r e c o n s i s t e n t l y b e t w e e n 0.9959 a n d 0.9968. T h i s shows t h a t our a n a l y s i s of blood lead has b e e n very c o n s i s t e n t over the years. W e f o u n d t h a t t h e p r o f i c i e n c y p r o g r a m m e s w e r e v e r y u s e f u l for m o n i t o r i n g t h e a n a l y t i c a l p e r f o r m a n c e , p a r t i c u l a r l y t h e C D C p r o g r a m i n w h i c h m o r e t h a n 260 l a b o r a t o r i e s p a r t i c i p a t e d u s i n g d i f f e r e n t m e t h o d o l o g i e s . T h e a c c u r a c y of a n
42
E10%
T 1
-~o%
-lo% Fig. 3. The bias between our results and the CDC reference values presented as a percentage in 3 years from 1984 to 1986. The percent deviation from the CDC reference value is obtained by calculating the difference between our results and the CDC value and then dividing the difference by the CDC value as a percentage. I-IV represent different quarters of the year. ( ~ - - ~ ) 1984; (A--A) 1985; (l~--$) 1986. TABLE 3 The regression line analysis of blood lead results in 1985 Blood lead programme
N
Regression line a
CDC Quebec Ontario Ministry of Labour Wisconsin
12 21 30 6
Y Y Y Y
= = = =
0.95X 1.00X 1.02X 0.96X
+ + +
14.0 1.3 3.5 2.7
Concentration range ~ g l 1)
r (correlation coefficient)
63-1153 130~25 115-742 108-703
0.9968 0.9959 0.9968 0.9965
a y = Our result; X = target value. analytical determination, therefore, is e a s i l y e s t a b l i s h e d through this programme. O u r m e t h o d w a s u s e d t o s c r e e n b l o o d l e a d i n 1269 O n t a r i o c h i l d r e n [6]. T h e d i s t r i b u t i o n o f b l o o d l e a d b y r e s i d e n c e is s h o w n i n T a b l e 4; u r b a n c h i l d r e n h a d t h e h i g h e s t l e v e l s . T h e o v e r a l l m e a n v a l u e f o r 1269 O n t a r i o c h i l d r e n w a s 103.6 # g l - ] , w h i c h is s i m i l a r t o t h e a v e r a g e b l o o d l e a d c o n c e n t r a t i o n f o u n d i n t h e U n i t e d S t a t e s p o p u l a t i o n i n 1980 [7]. O n l y 18 o f t h e 1269 c h i l d r e n h a d b l o o d lead > 250gg1-1. Repeat sampling and analysis confirmed these high lead
43 TABLE 4 Blood lead survey in Ontario, 1984 Residence
Blood lead concentration mean _+ SD (~gl 1)
No. of children tested
No. of children with blood lead > 250 pg 1-1
Urban Suburban Rural Total
120.2 99.5 89.1 103.6
392 507 370 1269
7 (1.8%) 8 (1.6%) 3 (0.8%) 18 (1.4%)
_+ 43.5 _+ 35.2 +_ 39.3 _+ 41.4
r e s u l t s . A r e p e a t t e s t of h i g h b l o o d l e a d l e v e l s is n e c e s s a r y i n t h e s c r e e n i n g p r o g r a m m e s i n c e i t h a s b e e n r e p o r t e d t h a t t h e c o n t a m i n a t i o n of c a p i l l a r y b l o o d s a m p l e s f r o m s k i n is a s e r i o u s p r o b l e m [8-10]. W i t h c a r e f u l w a s h i n g of t h e s k i n a n d a v o i d i n g direct c o n t a c t of the s k i n d u r i n g s a m p l i n g , the m i c r o t a i n e r finger-prick blood method in conjunction with the ZGFAAS technique gives a s u f f i c i e n t l y a c c u r a t e r e s u l t for b l o o d l e a d s c r e e n i n g i n c h i l d r e n . REFERENCES 1 2 3 4 5 6
7 8 9 10
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