1492
Anal. Chem. 1904, 56, 1492-1496
Therefore, this quantity is not normally distributed and so exact confidence limits cannot be found in terms of Student’s t distribution. On the other hand, first-order propagation of variance applied to AX is feasible and this procedure leads to a standard error expression for AX analogous to eq 9b for a single end point. In the following equations, subscripts 1 and 2 refer to the end points between branches A, B and B, C, respectively. The end point difference
A X = -Aae/Ab2
+ Aal/Abl
(15)
is a random variable depending explicitly on four random variables, the Aa’s and Ab’s as shown. Because all four of these variables depend on the data points which lie along branch B, nonzero covariances exist between all four. Therefore, the variance of AX is the sum of variances of X 1 and Xzas expressed separately by eq 9a plus the four covariances
cov(Aal,Aa2)= 2(var j i + ~ 2~~var bg)/AblAb2
(16a)
cov (Aal,Ab2) = -22BX2 var bB/Ab,Ab2
(16b)
cov (Aa2,Abl) = -2iBx1 var bB/Ab,Ab2
(16c)
cov (Abl,Ab2)= 2 X 1 X 2 var b ~ / A b ~ A b(16d) ~ The standard error estimate is su
= (var X 1 + var X 2 + C~COV)’/’
(17)
where C~COV is the sum of eq 16a-d. We now apply these equations to the analysis of the complete titration curve of the illustrative example seeking to find an optimal set of data points for the acetic acid assay. Again following the logic of part 11, we include and exclude data points falling near both end points in a search for the minimum uncertainty in AX. Because we cannot calculate exact confidence limits in this case, we use the small-variance confidence interval 2 t 2 a instead. The results of this search
appear in Table IV. We start with the optimal data set for X , , which is five points xAi = 4-12 mL and six points xBi = 22-32 mL, and find that six points 3cci = 35-44 mL, yields a provisional minimum confidence interval of 0.424 mL. Then with this set of six points fixed on branch C, we add one point at a time to branches A or B as shown in the table. The final optimal set yields a minimum CI of 0.356 mL. Some of the details of this optimal calculation are also shown in Table IV. A AX value of 17.887 mL leads to an acetic acid assay of 1.789 mmol which has 95% confidence limits of 1.806 and 1.771 mmol. It is interesting to note that the optimal 95% confidence interval for AX (0.356 mL) appears to be almost the same as that for XI alone (0.353 mL). These two intervals are based on different variance V estimates, however. A better comparison can be made when we put both intervals on the same basis by replacing V = 1.670 X (df = 7, t , = 2.365) with V = 0.9453 X (df = 13, t , = 2.160) in the X1 statistics. When this is done, the 95% confidence interval for X , reduces to 0.243 mL. The variance of AX is less than the sum of the variances of XI and X 2 in this example because the net effect of the covariance terms is subtractive. This fact cannot be expected to be true in general, however.
LITERATURE CITED ( 1 ) Berkson, J. J. Am. Stat. Assoc. 1950,4 5 , 164-180. (2) Acton, F. S.“Analysis of Straight-Line Data”; Dover Publications: New York, 1966; pp 50-53. (3) Brownlee, K. A. “Statistical Theory and Methodology in Science and Engineering”, 1st ed.; Wlley: New York, 1960. (4) Kendall, M.; Stuart, A. “The Advanced Theory of Statistics”, 4th ed.; Macmlllan: New York, 1977; Volume 1, Section 10.6. (5) Schwartz, L. M. Anal. Chem. 1977, 4 9 , 2062-2068. (6) Schwartz, L. M. Anal. Chem. 1979,57,723-727.
RECEIVED for review February 3, 1984. Accepted March 23, 1984.
Analysis of Skin Lipids for Halogenated Hydrocarbons Mary
S. Wolff
Environmental Sciences Laboratory, Mount Sinai School of Medicine of The City University of New York, 1 Gustave L. Levy Place, New York, New York 10029
Utilization of skln lipid anaiysls has been investigated as a nonlnterventlve aiternatlve to blood or adipose for estimation of human body burden of perslstent halogenated hydrocarbons. For p ,p ’-DDE (2,2-bis(4-chiorophenyl)-l,l-dlchloroethene), which was determined In 110 paired skin ilpid and blood serum samples and in 29 concomitant adipose samples, the skln llpld analysls provlded an acceptable aiternatlve to adlpose or serum. The method was less satisfactory for other residues, whlch were observed at lower concentratlons than p ,p ‘-DDE, lncludlng hexachlorobenzene, trans-nonachlor, and polychlorlnated biphenyls (PCBs). However, the results suggested that wlth sufflclently long sample collection time, the method would be useful. The amount of skln llplds collected was greater wlth longer Sampllng time, as was the amount of halogenated hydrocarbon resldue.
Human exposure to chemicals may be derived from the workplace or from other environmental sources. Estimation 0003-2700/84/0356-1492$01.50/0
of chemicals in the body, based on pharmacological considerations, provides an important biological marker in clinical evaluation or in epidemiologic studies which establish population norms of human exposure. Chemicals or their metabolites are usually determined as concentrationsin blood, urine, maternal milk, or adipose tissue. Adipose tissue has been of particular importance since lipophilic pesticide residues, which are poorly metabolized, are largely sequestered in lipid, with partition via blood to other tissues. Partition of such chemicals to milk occurs during lactation, facilitated by the fat content of milk and by efficient blood flow to mammary tissue (1). Utilization of noninvasive techniques to estimate chemicals in the body has been of interest to us as a means of evaluating human exposure. We have investigated skin lipids as an accessible source of determining chemical body burden. The skin is rich in lipids and is a major storage site of halogenated hydrocarbons in animals (2). Excretion of skin oil (or sebum) has been reported as a quantitative phenomenon, in the context of dermatological pathogenesis (3, 4). Matthews and co-workers have reported the analysis of halogenated hydrocarbons in lipids from human hair (5). We 0 1984 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 56, NO. 8, JULY 1984
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Table I. Average Weights of Lipid Collected from the Foreheada average weight for time of collection period, mg study group fire fighters Canadian Indians New Jersey waste removers New Jersey, misc. (1st sample) New Jersey waste removers chemical workers capacitor manufacturers
sex
10 min
30 min
M F M M M M M F M
0.59 f 0.45 (19) 0.83 i: 0.66 ( 5 ) 1.1(1)
1.34 f 0.70 (20) 0.72 i: 0.68 (5) 1.47 f 0.51 ( 4 ) 1.77 f 0.41 ( 5 ) 1.47 i. 0.91 (20)
all samples a
180 rnin
60 min
1.64 f 0.73 (20) 3.96 f 1.63 (23) 2.61 i: 1.65 (8) 4.44 t 2.17 (12)
0.36 r 0.19 (8) 0.53 i: 0.21 (11) 0.57
f
0.41 (44)
1.38 i. 0.77 (54)
1.64 i. 0.73 (20)
3.84 i. 1.87 (43)
Mean c standard deviation ( N ) ;weight represents half the sample, or 18 cmz area of forehead.
Table 11. Replicate Weight and Residue Determinations of a Standard Solutionu experiment 1 oil weight, mg (without procedure)
actual value (recovery) mean range
i:
std dev
1.072 i: 0.008 (1.06-1.09)
experiment 2 oil weight, mg (analytical procedure) DDE (ppm) Aroclor 1260 (ppm)
1.049 (102%) actual value (recovery)
mean range mean range mean range
f
std dev
f
std dev
f
std dev
1.154 f 0.23 (1.126-1.190) 1.81 i. 0.13 (1.53-1.95) 2.31 i. 0.41 (1.92-2.89)
1.049 (110%) 2.24 (81%)b 2.28 (101%)
Each experiment included seven determinations, from a solution of DDE and Aroclor 1260 in corn oil. procedure provides 8 0 4 5 % recovery of DDE, due to Florisil retention, have studied various chemicals in skin oil from the forehead, which we considered to be the most convenient and reproducible source of skin lipids. EXPERIMENTAL SECTION Human Subjects. During the course of six clinical field evaluations,nonpolar halogenated hydrocarbons were determined in blood serum, and in adipose tissue for a smaller number. A subsample of 5-20 persons in each study was asked to provide skin oil samples for analysis. Clinical and chemical investigations were performed under guidelines of informed consent, administered by Mount Sinai School of Medicine. Collection of Skin Oil. The technique followed that of S t r a w and Pochi (4). Several types of absorbent papers were tested for presence of potential interfering residues. Half-extra size Bambu cigarette paper was found to be the most suitable. The gummed margin was trimmed, and the papers were washed with ether and hexane and then air-dried. Sterile gauze (4 X 9 cm) was washed in the same manner. The paper, prepared in packets of 3 papers and 1gauze strip, was stored in precleaned aluminum foil. The packet (gauze side out) was applied to the forehead with forceps and was secured loosely with an elasticized fabric headband. The procedure of collection was to obtain one 10-min sample (discarded), a second 10-min sample (retained), and a third 30180-min sample. The innermost two papers were stored in prewashed scintillation vials, and were kept at -20 "C until analyzed. Analysis of Skin Oil Samples. The papers were transferred to glass tubes (16 X 100 mm) with Teflon-lined screw caps and were extracted three times with 5 mL of 1:l ether-hexane. The combined extracts were evaporated under a gentle stream of dry nitrogen to about 0.2 mL. The residue was taken to 1.0 mL with hexane. Half was transferred to a tared Teflon cup (2 mL capacity). The hexane was allowed to evaporate in the hood, and the residue was weighed. Weighings were performed with a Cahn 16 microbalance, accurate to hO.1 pg. The remaining extract (0.5 mL) was chromatographed on Florisil(l.8 g in a disposable 5-mL pipette, topped with 0.5 cm of sodium sulfate, activated overnight at 130 "C). A hexane fraction (13 mL) was collected, evaporated under reduced pressure on a rotary evaporator, adjusted to 0.5 mL, and placed in vials for gas chromatography (GC) analysis.
Preparative
Each lot of Florisil was checked to verify quantitative recovery of PCBs and hexachlorobenzene: 8045% recovery of 2,2-bis(4-chlorophenyl)-l,l-dichloroethylene (DDE);and less than 15% recovery of l,l-bis(4-chlorophenyl)-2,2,2-trichloroethane(DDT). Appropriate blanks and recoveries were analyzed with each batch of samples. Some blanks had detectable levels of PCBs (0.44-1.5 ng). Samples with total PCB residues less than twice those of the blanks were not used for statistical analyses. Analysis of Blood Serum. Serum samples were prepared and analyzed by using a technique comparable to that above, which has been previously described. The method for adipose analysis has also been described (6, 7). GC Analysis. GC was performed, with an electron capture (EC) detector, using a Perkin-Elmer Sigma 1 GC data system, and AS-100 autosampler. The column was a 2 m X 3 mm glass tube packed with 4% SE 3C-60% OV210 on Supelcoport 80/100 operated at 180 "C (so that DDE eluted at 7 rnin). Calibration was achieved with external standards, and PCBs were calculated as Aroclor 1254 or 1260 using the method of Webb and McCall (8). Statistical computations were performed at the City University of New York Computer Center with the Statistical Analysis System (SAS, Inc., Raleigh, NC). RESULTS AND DISCUSSION Lipid Weights. From previous reports, lipid weight could be expected to vary with collection time ( 3 , 4 ) . Initially, a 3-h collection period was chosen, but other times were investigated in an effort to evaluate more convenient procedures for use in the clinical setting. The 10-min collection, which was analyzed for a few cases, was intended as a control for exogenous chemicals. The 30-min collection was investigated because of the convenient sampling time and because the sample size (1 mg range) was judged to be sufficient for accurate weighing. Lipid weights are reported in Table I. The amounts conformed approximately to those previously reported, 1-2 Mg cm-' min-' ( 3 , 4 ) . Excretion in males was higher than in females, as reported (9). The reproducibility of weighing and
ANALYTICAL CHEMISTRY, VOL. 58, NO. 8, JULY 1984
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Table 111. Analysis of Two Sequential 30-Minute Skin Oil Samplesa analy te
n
trans-nonachlor (ng/mg) P,P’-DDE (ng/mg) PCBs (ng/mg) P146 lipid wt (mg)
11
17 10 9 17
regression analysis r2 intercept 0.94 0.62 0.60 0.89 0.47
0.007 0.19 0.35 0.12 0.34
slope
mean 1st sample
0.88 0.98 0.66 0.96 0.53
0.21 i 2.16 f: 1.02 t 0.31 i 1.69 i
f
std dev 2nd sample
0.27 0.91 1.26 0.21 0.80
0.20 r 2.32 f: 1.02 r 0.20 f: 1.23 f
0.25 1.14 1.06 0.21 0.61
a All samples had 0.5 mg or more lipid weight. PCBs were corrected for blanks (see Methods). P146 denotes PCB peak (corrected for blank) with Webb and McCall retention time 146 (8). This peak is mainly 2,4,5,2’,4’,5’-hexachlorobiphenyl. Linear regression was done €or second sample (y ) vs. first ( x ) . Coefficients of variation (average)were 26 (trans-nonachlor), 14 (DDE), 52 (PCB), 39 (P146), and 33 (lipid weight), where CV = ( ix - y I)/ ( x t y ) X 2”* X 100.
Table IV. Comparison of “Microscale” Adipose Tissue Analysis (Using Skin Oil Technique) with Original Analysis n
P,P’-DDE (ng/mg) PCBs (ng/mg) lipid wt (mg)
20 20
regression analysis ra intercept 0.81
0.62
0.46 0.60
mean “microscale”
slope 0.73 0.84
i
std dev original
2.21 r 1.07 1.86 i 0.97 3.46 * 1.81
2.40 t 1.32 1.49 t 0.91 58.1 i 11.8
a Linear regression was done for “microscale” vs. original. PCBs were determined as Aroclor 1260 peaks with retention times later than p,p’-DDE. Similar statistics were obtained for those “microsamples” with less than 4 mg of lipid. Coefficient of variation (average) was 12.8 for DDE and 21.5 for PCB. CV = ( / x , - x , l ) / ( x , + x , ) x 2*’*x 100.
Lipid W r i ht,
DDE i n sample ng
mg(d 4
m
3
m
DDE Adiporr concentration conc. ng/mg l i p i d n g h g
b
!
.W
2
0
0
I
-
I Z t
:I
.. . .
0
0
4
o
m
.
0
10 30 60 180
10 30 60 180
10 30 60 180 (30)
COLLECTION TIME, min
f
0
I-
,
1
Flgure 1. Skin lipM analysis for persons with midrange p p ’ D D E serum concentrations (7- 15 ng/mL), in order to standardize body burden, accordlng to collection time.
of analyzing residues of 2 ppm in oil was demonstrated for the 1 mg range (Table 11). Two sequential 30-min samples were obtained for 17 persons in one group. The means of residue concentrations were similar for the two collections, and linear regression showed similar values for first and second concentrations (Table 111). The second collection had a lower lipid weight than the first. This corroborateda previous report for successive 3-h samples, where, for 29 samples, a slope of 0.76 was observed with r2 0.88 (3). To further establish reproducibility of analytic data, 20 adipose samples were reanalyzed on a microscale, using the preparative technique for skin oil (Table IV). The Coefficients of variation for PCBs and DDE represent the normal range observed in other studies in this laboratory. Relation of Sampling Time to Skin Oil Residues. The amount of skin oil was related to collection time. The relation of lipid weight to total time of collection has been reported to be linear (4), and total lipid residues in Table 1reflect that trend. To examine the relation of DDE residues with lipid weight, DDE residue concentration and total residues were compared for persons with a restricted range of serum concentrations, regardless of collection time (Figure 1). The midrange of serum DDE values was chosen (7-15 ng/mL), in order to standardize body burden. Both the totalchemical residue and lipid collected were correlated with collection time, but the strongest relationship was that between total residue and lipid
0
2
1
3
1
4
5
Weight o f s k i n i i p i d i n s a m p l e , m g
Flgure 2. Relation of total p ,p’-DDE residue to amount of skin lipid, regardless of collection time (10-180 min), for persons with midrange p,p’-DDE serum concentrations (7-15 ng/mL): r = 0.85, n = 59. 12
c
0
”
0
2
4
6
Cumulative skin l i p i d w e i g h t (mg)
Figure 3. Relation of cumulative p ,p’-DDE residue to cumulative skin lipid weight in sequential samples from a single individual during approximately 400 min: r = 0.992, n = 10.
collected (Figure 2). The trend was clearer in sequential samples from a single individual (Figure 3). Here, lipid weight, collection time, and total p,p-DDE residue were strongly associated, with correlation coefficients of 0.99. Concentration of residues in skin oil (ng of residues/lipid weight) showed a nonlinear trend of decreasing with collection time. Skin Oil Residue Concentration as a Reflection of Body Burden. From several studies of halogenated hydrocarbons, it has become evident that blood concentration is an
ANALYTICAL CHEMISTRY, VOL. 56, NO. 8, JULY 1984
.
0 '
5
IO Serum
m
I
20
15
25
DDE, n g / m L
Figure 4. Comparison of adipose (0)and skin lipid (0)concentration (30-min collection) of p,p'-DDE with that in serum for 29 persons: adipose-serum, r = 0.79; skln lipid-serum, r = 0.60; adipose-skin iipld, r = 0.73. r-
I
180 m i n u t e
0
IO
20
30
40
Serum D D E , n g / m L
Figure 5. Relation of p ,p'-DDE concentration in skin lipid, for 180-min collection time, with that in serum: r = 0.87, n = 41. Resuits were similar for a 30-min collection time, where lipid weight was greater than 0.5 mg, r = 0.70, n = 49, and for a 60-min collection tlme, r = 0.90, n = 20.
adequate estimate of body burden as measured in adipose tissue (6, 7,10,11). Therefore, the relation of skin oil residues with serum concentration was examined to evaluate whether this method can be useful in assessment of chemical body burden. In addition, adipose tissue was also analyzed for 29 persons who had 30-min skin oil collections with 0.5 mg or more lipid. The correlation coefficient (r) for adipose DDE concentration (ng/mg or ppm) was 0.73 with skin oil concentration (ng/mg), 0.72 with total DDE in the skin sample (ng), and 0.79 with serum DDE (ng/mL). The correlation of serum DDE concentration (ng/mL) was 0.60 with skin oil DDE concentration and 0.53 with total DDE in the skin sample. For comparison, adipose and skin oil concentrations are plotted against serum concentrations in Figure 4. The concentration of DDE in skin oil was correlated with that in serum for 30-, 60-, and 180-min collection times (Figure 5). For 110 samples, where the skin sample had at least 0.5 mg of lipid, the concentrationof DDE was correlated with that in serum, regardless of collection time (r = 0.80, slope = 0.10). The slopes of the linear regression for the three collection times were not individually different from that for the combined data, when the highest values (serum DDE 2 40 ng/mL) were excluded (variance ratio F = 0.92 with 4, 102 degrees of freedom). PCB skin oil residues were evaluated separately for PCBexposed workers and for the remaining groups. The capacitor workers had been exposed to Aroclor 1254 prior to 1971 and to Aroclor 1016 until 1977 (7). However, ambient air analyses for Aroclor 1016 in the capacitor plant showed levels of approximately 60 pg/m3 in 1978 and 30 pg/m3 in 1980 (12).
1495
Twenty workers were examined in 1979, as part of a larger study. The PCBs in the skin oil samples represented both kinds of exposure. Aroclor 1016 was present, as a pattern practically indistinguishable from the standard, in marked contrast to blood serum, where two to four major peaks were observed (13). In 180-min samples, 69-670 ng (Aroclor 1016) were seen (mean 269, standard deviation 184, representing 18 cm2 of skin area, 3.93 f 2.03 mg of lipid). In 10-min collections, 12-349 ng were found (18 samples, 90 f 77 ng, 0.48 f 0.10 mg). The total residue (ng) and the concentrations (ng/mg lipid) were significantly correlated for the 10-min vs. 180-min collections (r = 0.75 and 0.95, respectively). The correlations of PCB concentration in skin oil (ng/mg) or total skin residue (ng)with serum PCB (Aroclor 1016)residues were poor (r = 0.35, p > 0.05 and 0.44, p < 0.025, respectively). The Aroclor 1016 residues probably represent lipid dissolution of topically retained PCBs. Investigations by other laboratories have found 0.1-7 pg/cm2 as Aroclor 1242 on the hands and face, where workplace air was 81 pg/m3 (14) and 2-28 pg/cm2 (hands) where air levels were 48-275 pg/m3 (15). In the present study, samples were collected away from the workplace, after the usual personal hygiene. The pattern of Aroclor 1254 gas chromatographic peaks in skin oil of exposed workers was similar to that in serum. Although the scatter was wide, there was a clear association of skin oil concentrations of Aroclor 1254 with that in serum. The correlation coefficients ( r ) were 0.34 (linear, skin concentrations vs. serum, p > 0.1),0.59 (both log,,, p = 0.006), 0.53 (linear, total PCB in skin sample vs. serum, p = 0.02), and 0.68 (both loglo, p = 0.001), for 20 cases. For the same cases, a single PCB peak (corresponding to 2,4,5,2',4',5'hexachlorobiphenyl) was used to calculate concentration, in order to determine whether the analytical variance could be reduced. For this peak, the correlation (skin vs. serum) was 0.53 (linear, skin concentration, p = 0.021, 0.72 (log,,, p < 0.001), 0.72 (linear, total skin, p < 0.001), and 0.79 (log,, total, p < 0.001). These correlations for skin oil PCB concentration (but not total PCB residue) with serum were considerably improved when one outlier was excluded, with an increase in r2 of 0.15-0.23. For persons with no occupational exposure to PCBs, skin PCB content was not significantly correlated with that in serum for 30- and 60-min collections. For 31 samples, the adipose-serum correlation ( r ) was 0.83 for PCBs as Aroclor 1260 and 0.88 for 2,4,5,2',4',5'-hexachlorobiphenyl. For 180min samples (n = 23), the correlation of skin lipid with serum concentration was not significant for PCBs (p = 0.14) but was significant for 2,4,5,2',4',5'-hexachlorobiphenyl ( r = 0.58, p < 0.01). trans-Nonachlor, a chlordane residue, was observed in serum in all of the 180-min samples and in 24 other cases. The correlation of skin concentration with serum concentration of trans-nonachlor was statistically significant (r = 0.70, n = 47). Hexachlorobenzene was also usually observed in serum, but the relationship with skin concentration was significant only for 180-min samples (n = 23, r = 0.60).
SUMMARY Collection of skin oil (sebum) as a noninterventivesampling method for halogenated hydrocarbons has potential applicability as an indicator of body burden. For DDE, where a range of 1-75 ng/mL in serum was observed, typical of the U.S. population, the use of skin oil provided an acceptable means of body burden estimation for 30-, 60-, or 180-min sampling times. This conclusion is based on (1) similar correlation coefficients for the regression of skin oil concentration with serum DDE (Figures 4 and 5) and (2) similar correlation coefficients among the variables adipose, serum, and skin oil
1496
Anal. Chsm. 1984, 56, 1496-1502
concentration. However, for trans-nonachlor and hexachlorobenzene, typically 1 ng/mL in serum, and for PCBs, where analytical variance is multiplied by the summation of several GC peaks, skin oil analysis was not well correlated with adipose or serum concentration, except for PCBs among highly exposed individuals. For low-level residues, the exploratory studies reported suggest that a 3-h sampling time may be necessary to provide reliable results, since the amount of lipid collected (in the range of 3 mg) affords sufficient residue to achieve reproducible instrumental detection and quantitation. The results obtained indicate that, without further refinement,skin oil analysis cannot supercede the accepted methods of blood or adipose analysis. However, the passive, uninterventive nature of skin oil collection may provide a convenient screening method in appropriate circumstances. Where significant ambient or dermal exposure occurs in the workplace, skin oil may contain chemicals representative of exposure, but not of body burden, as was found with Aroclor 1016 in capacitor manufacture and with polycyclic aromatic hydrocarbons in roofing workers (16).
ACKNOWLEDGMENT Provision of clinical material by A. Fischbein, M. Moses, A. L. Frank, K. Rosenman, and S. Levin is gratefully acknowledged. Particular thanks go to F. Camper, C. Rice, and H. A. Anderson for collaboration, criticism, and discussion during the development of this project. Technical assistance and manuscript preparation by M. Rivera, K. Keever, B. Taffe, J. Nicholson, S. Sibel, and V. Josephson are greatly appreciated.
Registry No. p,p’-DDE,72-55-9; hexachlorobenzene,118-74-1; trans-nonachlor, 39765-80-5;2,2‘,4,4’,5,5’-hexachlorobiphenyl, 35065-27-1. LITERATURE CITED (1) Wolff, M. S. Am. J . Ind. Med. 1983, 4 , 259-261. (2) Matthews, H. B.; Tuey, D. B. Toxicol. Appl. Pharmacol. 1980, 53, 377-386. (3) Cunliffe, W. J.; Shuster, S. Br. J. Dermatol. 1969, 81, 697-704. (4) Strauss, J. S.;Pochi, P. E. J . Invesf. Dermatol. 1961, 36, 293-298. (5) Matthews, H. B.; Domanskl, J. J.; Guthrie, F. E. Xenobiotica 1978, 6, 425-429. (6) Wolff, M. S.; Anderson, H. A.; Selikoff, I. J. J . Am. Med. Assoc. 1982, 247, 2112-2116. (7) Wolff, M. S.; Fischbein, A.; Thornton, J.; Rice, C.; Lilis, R.; Selikoff, I . J. Int. Arch. Occup. Environ. Health 1982, 49, 199-206. (6) Webb, R. G.; McCall, A. C. J . Chromafogr. Sci. 1973, 1 1 , 366-373. (9) Cunliffe, W. J.; Shuster, S. Lancet 1989, 1 , 665-687. (10) Wolff, M. S.;Anderson, H. A.; Camper, F.; Nikaido, M. N.; Daum, S. M.; Haymes, N.; Selikoff, I. J. J. Environ. Pathol. Toxicol. 1979, 2, 1397- 1411. (11) Baumann, K.; Angerer, J.; Heinrich, R.; Lehner, G. Int. Arch. Occup. Environ. Health 1980, 47, 119-127. (12) Lawton, R., General Electric Corp., personal communication. (13) Wolff, M. S.;Thornton, J.; Fischbein, A,; Lilis, R.; Selikoff, I. J. Toxicol. Appl. Pharmacol. 1982, 62, 294-306. (14) Smith, A. B.; Schloemer, J.; Lowry, L. K.; Smallwood, A. W.; Ligo, R. N.;Tanaka, S.;Stringer, W.; Jones, M.; Hemin, R.; Glueck, C. J. Br. J . Ind. Med. 1982, 39, 361-369. (15) Maronl, M.; Colombi, A.; Cantoni, S.;Ferioli, E.; Foa, V. Br. J. Ind. Med. 1981, 338, 49-54. (16) Wolff, M. S.; Taffe, B.; Boesch, R. R.; Selikoff, I. J. Chemosphere 1982, 11, 595-599.
RECEIVED for review December 27,1983.Accepted March 19, 1984. This research was supported by the National Institute of Environmental Health Sciences, Grant No. ES 02305.
Measurement of Atmospheric Peroxy Radicals by Chemical Amplification Christopher A. Cantrell,’ Donald H. Stedman,*2and Gregory J. Wende12 Department of Chemistry, The University of Michigan, Ann Arbor, Michigan 48109
Presented herein Is a new technique for the contlnuous measurement of peroxy and oxy radicals in air, based on the chain reaction in which these molecules participate to oxidize NO and CO to NO, and CO,. Under typical instrument conditions, more than 1000 NO, molecules can be produced from each measurable redlcal enterlng the system. The NO, produced is measured by iuminoi chemliuminescence, based on the gas-surface reactlon of NO, wlth a pH 12,3 mM aqueous lumlnol soiutlon. NOP produced from sources other than the chain reactlon Is measured by substltutlon of N, for CO half of the tlme. Therefore the radical slgnal is modulated and determined by difference. The detection ilmlt of radkais with this system is a strong function of the variabiilty of amblent NO, and 0,, but usually less than 1 pptv (parts In 10” by volume) can be detected, with a precision of a few percent and an overall estlmated accuracy of f50%. Callbratlon procedures as well as results of some preliminary experlments using this method are presented. ‘Present address: National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307. Present address: Department of Chemistry, University of Den-
ver, Denver, CO 80208.
The chemistry of trace species in polluted and unpolluted atmospheres is fundamentally dependent on the reactions of free radicals. In air with low hydrocarbon content, the most important radicals are the odd hydrogen radicals: hydroxyl, HO, and hydroperoxy, HOz (organic peroxy radicals become more abundant as the hydrocarbon concentration increases). Major loss mechanisms for many species are initiated by reaction with HO (E.g., CH, and higher hydrocarbons, SOz and NOz). Hydroperoxy oxidizes NO to NOz and is the major homogeneous source of H202in clean atmospheres. There has been considerable interest in the measurement and modeling of HO and HOz, since 1969,when the importance of odd hydrogen free radicals to smog chemistry was recognized by Weinstock (1) and Heicklen (2). Subsequently the interaction between the odd hydrogen family and other atmospheric cycles was recognized as important in the clean troposphere (3-5). There have been a large number of laboratory kinetic studies of reactions of HO and HOz with various radical and nonradical species (6). In the atmosphere, measurements of HO have mostly been limited to the upper troposphere and the stratosphere. Laser-induced fluorescence is used by several groups around the world for stratospheric balloon measurements (7), tropospheric aircraft measurements (8), and some
0003-2700/84/0356-1496$01.50/00 1964 American Chemical Society
