Measurement of Atmospheric Levels of Pesticides Charles W. Stanley’ and James E. Barney 11% Midwest Research Institute, Kansas City, Mo. 641 10 Michael R. Heltona and Anne R. Yobs Pesticides Office, Environmental Protection Agency, Atlanta, Ga. 30341
rn In a pilot study to establish a system for measuring the extent of atmospheric contamination by pesticides, air was sampled at nine localities in the US.,and the samples were analyzed for 19 pesticides and metabolites. The localities were Baltimore, Md.; Buffalo, N.Y.; Dothan, Ala. ; Fresno, Calif. ; Iowa City, Iowa; Orlando, Fla.; Riverside, Calif.; Salt Lake City, Utah; and Stoneville, Miss. These sites are representative of both urban and agricultural areas. Detected pesticide levels ranged from the lower limit of detection of 0.1 ng of pesticide per cm3 of air to as high as 2520 ng/m3. Only DDT was detected at all localities. At least one chlorinated pesticide was found at all localities, while organophosphate pesticides were found only in the three localities in the South-Dothan, Orlando, and Stoneville; levels were much lower in the urban areas-Baltimore, Fresno, and Riverside.
M
any differentman-made contaminants are introduced into the ambient air. One important group of these is pesticides, which are being used in increasing amounts for the control of insects, fungi, nematodes, rodents, and weeds. The air pollution aspects of pesticides have recently been reviewed (Finkelstein, 1969). Until the present study, however, no detailed investigation has been made to measure the levels of some common pesticides in the ambient air by the most sensitive available analytical techniques. There are few places where residues of pesticides have not been found (West, 1966). They are present in water, soil, air, animals, people, as well as food and other commodities. Although pesticides are generally present in small amounts, their variety, toxicity, and persistence are affecting biological systems in nature and may eventually affect human health (President’s Science Advisory Committee, 1963). There is much known about acute poisoning by pesticides, but comparatively little is known of the relationships that may exist between environmental exposure and chronic human health effects (Anderson, 1966). The Division of Pesticide Community Studies of the En-
Present address, Chemagro Corp., Kansas City, Mo. 64120. Present address, Stauffer Chemical Co., Richmond, Calif. 94804. Present address, Department of Interior, Federal Water Pollution Control Administration, Colorado River Basin Water Quality Control Project, Denver, Colo. 80225. 1
430 Environmental Science & Technology
vironmental Protection Agency is responsible for determining the effects of exposure to pesticides on human health. In discharging its responsibilities, the division conducts many activities, one of which is monitoring pesticides in air. To assist in defining the extent of atmospheric contamination by pesticides, a pilot study was conducted in 1967 and 1968 for the Division of Pesticide Community Studies by Midwest Research Institute. This study has provided information about the scope of pesticide contamination and the kinds of pesticides in the air. Experimental
Sampling Sites. An air sampling program was established at nine localities: Baltimore, Md. (urban); Buffalo, N.Y. (rural); Dothan, Ala. (rural); Fresno, Calif. (urban); Iowa City, Iowa (rural); Orlando, Fla. (rural); Riverside, Calif. (urban); Salt Lake City, Utah (urban); and Stoneville, Miss. (rural). The actual sampling sites of the rural localities were located up to 20 miles from these communities. From a study of topographic and micrometeorological factors, four sampling sites were selected at each locality. The sampling sites were arranged in a box design of the type widely used in air pollution studies; the sampling grid was about 1 mile on a side. Where possible, the sampling units were located 10 to 15 ft above the ground to avoid local effects caused by small topographical differences. The filter was unimpregnated glass cloth (Hess, Goldsmith and Co., N.Y., N.Y.), about 0.5-mm thick, cut into circles 8 cm in diameter; 5.2 cm of the glass cloth was exposed to the airstream. The impinger was a Greenburg-Smith impinger modified by the addition of O-ring joints at the inlet and outlet (Ace Glass, Inc.). The trapping liquid was hexylene glycol (2-methyl 2,4-pentanediol) (Eastman Organic Chemicals). This was purified before use by passage through a Norit-A charcoal column; 100 ml was used in the impinger. An adsorbent tube, 417-cm diameter by 9-cm long, was filled with 120 g of alumina (Fisher Scientific Co., catalog no. A-540) which had been heated to 545°C for 2 hr before use. The alumina was held in the tube by a glass wool pad at each end. The alumina was reused after ignition, but the filter and the hexylene glycol were discarded after use. Analytical Method. The 19 pesticides and metabolites sought in the air samples are listed in Table I. In addition, any unidentified peaks in the gas chromatograms were checked to determine if they were produced by pesticides not on this list. The extraction and cleanup procedure was based on one developed for measuring pesticide residues in foods (Stanley and Post, 1967). The pesticides were extracted from the filter, the alumina, and the hexylene glycol and passed through a
Table I. Pesticides Sought in Air Samples Chemical name Pesticide 1,2,3,4,10,10-Hexachloro-l,4,4a,5,Dieldrin 8,8a-hexahydro-endo-exo-5,8-dimethanonaphthalene
Pesticide Aldrin
BHC
(4 isomers)
Chlordane 2,4-~ p,p '-DDT O,~'-DDT DDD
(TDE)
p,p '-DDE O,P'-DDE
1,2,3,4,5,6-Hexachlorocyclohexane (benzene hexachloride), CY-, fi-, y, and &isomers. 1,2,4,5,6,7,8,8-Octachloro-3a,4,7,7,7a-tetrahydro-4,7-methanoindane 2,4-Dichlorophenoxyaceticacid (including esters and salts) 1,1,1-Trichloro-2,2-bis@-chlorophenyl)-ethane 1,1,1-Trichloro-2-(o-chlorophenyl)-2(p-chlorophenyl) ethane 2,2-Bis(p-chlorophenyl)-l,l-dichloroethane 1,l-D~chloro-2-bis-(p-chlorophenyl)ethylene 1,l-Dichloro-2-(o-chlorophenyl)-2(p-chloropheny1)-ethylene
Endrin
Heptachlor Heptachlor epoxide
Malathion Methyl parathion Parathion
Chemical name 1,2,3,4,10,10-Hexachloro-6,7-epoxy1,4,4a,5,6,7,8,8a-octahydro-l,4endo-exo-5,8-dimethanonaphthalene 1,2,3,4,10,10-Hexachloro-6,7-epoxy1,4,4a,5,6,7,8,8a-octahydro-l,4endo-endo-5,8-dimethanonaphthalene 1,4,5,6,7,8,8-Heptachlor0-3a,4,7,7atetrahydro-4,7-methanoindene 1,4,5,6,7,8,8-Heptachloro-2,3epoxy-3a,4,7,7a-tetrahydro-4,7methanoindene Diethyl mercaptosuccinate, S-ester with 0,O-dimethyl-phosphorodithioate 0,O-Dimethyl 0-p-nitrophenyl phosphorothioate 0,O-Diethyl 0-p-nitrophenyl phosphorothioate
Table 11. Gas Chromatographic Conditions
Co1u mn s
Chlorinated pesticides No.1. 2 m X 6 m m 0.d. glass, 5% SE-30 on 100/120 Mesh Gas Chrom Q No.2. 1 m X 6 m m 0.d. glass, 2.5% SE-30, 3.5% OV-17 on 100/120 Mesh Gas Chrom Q Organophosphate pesticides No. 1. 1 m X 6 m m 0.d. glass, 5% QF-1 on 100/120 Mesh Gas Chrom Q No. 2. l m X 6 m m 0.d. glass, 5% OV-1 on 100/120 Mesh Gas Chrom Q
Injection port temp, "C
Oven temp, 'C
Detector temp., "C
Nitrogen carrier gas flow rate, ml/min
200
185
200
120
Detector
Electron-capture
200
185
200
100
200
140
160
100 Flame photometric
200
140
Florisil column cleanup step, during which the chlorinated pesticides were separated from the organophosphate pesticides. Pesticides in the cleaned up samples were determined by gas chromatography with the columns and conditions given in Table 11. The chlorinated pesticides were determined with a Micro-Tek 2000R gas chromatograph equipped with two columns, two electron-capture detectors, two electrometers, and a dual-channel recorder, so that a sample could be run on the two columns at one temperature at the same time. A known sample containing aldrin was run immediately before and after each sample, and peak retention times were calculated
160
100
relative to aldrin. Pesticides were identified by a comparison of the relative retention times of the unknown peaks with those of known pesticides on the two columns. Quantitative results were obtained by comparing the area calculated from the peak height and half width with that of a known run on the same day. Organophosphate pesticides were determined with a MicroTek 2500R gas chromatograph equipped with a Aame-photometric detector operating in the phosphorus mode. Samples were screened on one column, and if a peak was obtained with a retention time which agreed with that of a known pesticide, the pesticide identity was confirmed by analyzing the sample Volume 5, Number 5, May 1971 431
Sample 505 506 507 508 509 510 511 540 541 542 543 544 545 546
Sample 110 111 112 113 114 174 175 210 21 1 212 213 214 643 644 645 690 691 692 729 730 731 776 777 778 821 822 823 824 a
Table 111. Correlation of Pesticide Levels with Rain and Reported Spraying Dothan Orlando Pesticide level, Pesticide level, ng/m3 ng/m3, Rain, in. ~,~‘-DDT Sample Rain, in. P,P’-DDT Parathion no 2.1 693 3.3 468 9.7 0.2 5.2 694 4.3 143 5.2 2.3 0.2 695 4.2 117 3.9 no 2.0 696 0.2 728 68.0 1.4 no 697 no 1430 465.0 0.3 3.2 no 698 1560 224.0 0.5 2.7 699 no 1250 132.0 no 7.2 741 no 340 27.2 2.0 0.3 742 0.3 480 99.0 0.3 2.9 743 3.7 470 36.0 no 1.7 744 0.2 430 90.5 1.3 no 745 no 310 9.5 2.9 1. o 746 no 360 27.0 3.5 0.5 747 no 390 50.0 Stoneville Pesticide level, ng/m3 Rain Spraying reported p,P’-DDT Methyl parathion none 80.0 64.5 Yes no 50.0 16.1 Yes no none 117.0 14.8 489.0 148.0 yes Yes none no 124.0 4.3 no 16.9 ... Yes none 33.8 Yes none 15.6 4.3 Yes 6.0 none ... Yes 7.0 Yes Yes no none 15.0 0.5 no 19.5 none 4.1 no none 12.9 none 15.5 Yes no 12.8 none ... no none 13.4 11.3 none Yes no none 28.8 no 19.1 22.8 Yes none 18.8 Yes no 32.8 Yes no ... 26.3 yes 27.2 yes Yes no 10.8 Yes no 5.2 69.4 Yes 3.0 75.5 Yes Yes no none 57.4 none 46.8 ... yes Q
None detected.
on the other column. If enough of the pesticide was present, its identity was also confirmed by the use of the detector in the sulfur mode. Sampling Method. Samples were taken according to the following schedule. Either 12- or 24-hr samples were collected for seven days at two of the four sampling sites a t each locality. The sampling units were then moved to the other two sites, and samples were collected for another seven days. Selection of the order in which sites at a locality were to be sampled was made on a random basis. Usually, all samples collected 432 Environmental Science & Technology
during a 24-hr period at one locality were combined to give one sample for analysis. Sampling was conducted a t each locality over a six-month period during which samples were taken during two weeks out of each month. This six-month sampling period was not continuous, permitting sampling at each locality during both the growing season and at a time when pesticide usage would be at a minimum level. An air sampling unit was designed at Midwest Research Institute for the collection of air samples based on the tech-
Table IV. Correction Factors for Losses Incurred during Extraction and Cleanup Correction Correction Pesticide factor Pesticide factor a-BHC 1.51 &BHC 1.24 1.06 Lindane 1.31 o,p '-DDE Heptachlor 1.13 Dieldrin 1.53 o,p '-DDT Aldrin 1.27 1 .oo Heptachlor 1.37 P-BHC 1.19 1.01 epoxide Toxaphene 2.15 1.19 Methyl P,P'-DDE 1.30 Endrin parathion p,p '-DDD 1.26 Malathion 2.82 1.79 P,P~-DDT 1.30 Parathion 1.36 DEF
nique previously devised (Miles et al., 1970). An absorption tube containing activated alumina was added to trap pesticides that might pass through the scrubber (Hornstein and Sullivan, 1953). This unit is now commercially available from Electro-Neutronics/Technical Assoc. The units were operated at a flow rate of 29 liters/min, giving an air sample of about 40 m a in 24 hr. The collection train consisted of a filter, an impinger with a
trapping liquid, and an adsorbent. All parts of the collection train that would contact the airstream were glass to lessen the probability of loss of pesticides, and all connections between component parts were by O-ring joints. Because of the selectivity of the flame photometric detector, more unequivocal results were obtained with the organophosphate pesticide samples than with the chlorinated pesticide samples. Chromatograms with the electron-capture detector showed more extraneous peaks and interferences than did chromatograms with the flame-photometric detector. Correlation of Pesticide Level with Rainfall and Spraying. Pesticide levels varied from day to day and with the season. Highest levels were found at those times pesticide spraying was reported in the area. Changes in levels in the area could be better correlated with reported spraying than with rain. Thus, the lower amount of pesticide found on a day when rain was reported as compared with the previous day could be due to the fact that no spraying was carried out on that day rather than to the rain itself. In Table I11 are given some pesticide levels for Dothan, Orlando, and Stoneville for periods during which there was rain. With several days of rain, the pesticide level usually decreased; a rise afterward could be ascribed to renewed spraying. The levels at Dothan show little difference between rainy days and no-rain days. The reason for this may be either that spraying continued because the rainfall was light or that the pesticide level remained nearly constant. There were no reports of spraying at any time when samples
Table V. Recovery of Pesticides from Atmosphere Pesticide CY-BHC
Lindane Heptachlor Aldrin Heptachlor epoxide P,P'-DDE
Endrin DDD P,P!-DDT
Methyl parathion Malathion Parathion
Amount used, c(g 4 4 4 4 20 20 20 20 20 5 5 5
2-Methyl 2,4pentanediol, p g 2.02 2.38 1.84 2.04 6.77 2.94 4.45 4.20 4.75 1.19 0.36 0.68
Alumina, pg 0.44 1.02 0.64 0.44 3.52 2.32 4.09 3.82 3.80 0.41 0.22 0.20
Material balance, 64.6 97.4 76.5 82.4 88.2 59.9 88.2 94.6 100.0 53.4 58.0 58.0
Inlet wash, p g 0.13 0.50 0.59 0.82 7.36 6.72 9.10 10.91 12.00 1 .05 2.32 2.02
Table VI. Distribution of Pesticides in Collection Media Pesticide level, ng/m3 Locality Baltimore
Iowa City Salt Lake City Stoneville
Sample l09f 109h 109a 90f 90h 90a 123f 123h 123a 113f 113h 113a
P,P'-DDT
0.9 1 .o 0.9 1.7 0.8 1.2 1.8 3.9 0.8 417.0 52.0 19.5
O,~'-DDT
0.5 0.5
...
4
0.9 0.5 0.3
... 0.1 80.0 20.0 8.0
~ , ~ ' - D D E CY-BHC
Lindane
0.8 1.1 ...
... ...
1.7
...
...
...
0.7
...
...
...
...
...
... 5.0 1.4 ...
0.4 1.4 0.7 ...
...
...
... 2.1
...
... ... 7.1 2.4
...
Toxaphene
Methyl parathion
... ...
... ...
... ...
...
...
...
...
... 9.4 8.9
1110 151 81
...
None detected.
Volume 5, Number 5, May 1971 433
Date Aug. 14-15 Aug. 21-22 Sept. 11-12 Oct. 2-3 Oct. 16-17 Jan. 15-16 Jan. 30-31 May 30-31 June 6-7 June 17-18 July 1-2 July 15-1 6 July 29-30 Aug. 12-13
Table VII. Pesticide Levels Found at Stoneville the First Day of Each Sampling Week Pesticide level, ng/ma Methvl P,P'-DDT P,P'-DDE Toxaphene Endrin parathion
950.0 156.0 104.0 52.0 15.6 7.0 14.4 11.2 7.6 9.9 26.3 41.1 37.4 71.5
... 7.1 4.7 14.2 2.4
... ... 6.2 3.9 6.9 5.3 4.7 5.6 2.6
Table VIII. Pesticide Levels Found at Orlando First Day of Each Sampling Week Pesticide level, ng/ms Date P,P'-DDT Dieldrin Parathion Oct. 16-17 2.9 5.0 Oct. 30-31 29.9 ... Jan. 8-9 10.4 ... ... Jan. 22-23 17.9 ... 19.4 15.5 Jan. 29-30 13.4 ... Feb. 12-13 5.7 ... 22.7 10.4 Feb. 26-27 25.4 2.0 13.0 Mar. 11-12 ... ... Apr. 1-2 14.2 ... 15.3 28.3 Apr. 15-16 12.6 4.5 10.2 1.2 May 6-7 5.3 May 20-21 7.3 104.0 ... May 3-4 9.7 468.0 ... 27.2 340.0 June 17-18 ...
DEF
283 373 701 161
... 6.5 3.9
32.2 71.0 64.5
...
... ...
...
...
0.8
4.3
16.0 4.8
... ... ... ...
...
...
...
... ...
... ... 68 116 62 135
...
...
,..
... ... ... .,.
...
...
... 7.3 20.6
...
... ...
of pesticide sprayed into the inlet and the amount of pesticide recovered. The material balance was better than 50% in all cases. Low values may have resulted from vaporization of pesticide from the inlet walls and so may not necessarily indicate the pesticides are not being trapped in the collection train. To determine the distribution of pesticides in the train under actual operating conditions, the components of the sampling train from four actual samples were analyzed separately. Results are shown in Table VI in whichf is the filter, h is the liquid from the impinger, and a is the alumina. Appreciable amounts of pesticide were on the filter, indicating that the pesticide was probably absorbed on particulate matter trapped by the filter. In the Stoneville sample, about 80 % of the chlorinated pesticides was present in the filter; the proportion varied for other samples. These results and those in Table V support the studies of Miles et al. (1970), but also show that the activated alumina trap must be added to increase the collection efficiency. Results and Discussion
were collected in Dothan. At Orlando and Stoneville, both rainfall and spraying were reported for some days. Pesticide levels tended to be higher on these days than on rainy days when no spraying was reported. Loss Correction Factors. Correction factors for losses during extraction and cleanup were determined for the pesticides of interest by adding known amounts of pesticides to the collection media and extracting them. The correction factors are given in Table IV. Distribution of Pesticides in Collection Media. Pesticides were usually extracted from all three parts of the sampling train and combined into one sample for analysis. To show that the collection train was trapping essentially all the pesticides entering the train, several tests were made in which known amounts of pesticides were sprayed into the inlet of a collection train while air was being drawn through the train by a pump. There was no glass cloth filter in the collection train. The impinger liquid and the alumina were extracted and analyzed for pesticides; the glass tube into which the pesticide solution was sprayed was washed with solvent, which was also analyzed for pesticides. Typical results are given in Table V. A material balance was calculated based on the known amount 434 Environmental Science & Technology
There were 880 composite samples analyzed during the study; usually each represented one day's sampling at two sites at a locality. Selected results for the first day of each week of sampling for Stoneville are given in Table VI1 and for Orlando in Table VIII. These results were selected for presentation because they illustrate the degree of qualitative and quantitative variation. A comprehensive report containing all of the results will also be published. Of the pesticides that are listed in Table I, the only ones that were found at all localities were P,P'-DDT and O,P'-DDT. Heptachlor epoxide, chlordane, DDD, and 2 , 4 - ~esters were not found in any samples; aldrin was found in one sample, and 2 , 4 - ~was found in one sample. Two other pesticides, toxaphene (chlorinated camphene containing 67 to 69 % chlorine) and DEF (S,S,S-tributylphosphorotrithioate, Chemagro Corp.), were also found. Organophosphate pesticides were found only in samples from Dothan, Orlando, and Stoneville; methyl parathion was found in samples from these three localities, while parathion and malathion were found only at Orlando. DEF, a cotton defoliant, was found in samples from Stoneville. Maximum pesticide levels found in air samples at the nine locations are presented in Table IX.
Table IX. Maximum Pesticide Levels Pound in Air Samples (Levels in ng/m3)
Total samples Pesticides p,p ‘-DDT o,p ‘-DDT P,P‘-DDE
o,p ’-DDE (r-BHC
Lindane
0-BHC 6-BHC Heptachlor Aldrin Toxaphene 2,4-~ Dieldrin Endrin Parathion Methyl parathion Malathion
Baltimore
Buffalo
Dothan
Fresno
123
57
90
120
19.5 (89). 11.0 (40) 177.0 (88) 3 . 0 (59) 2 . 9 (24) 88.0 (72) 2 . 4 (4) 13.2 (32) 3 . 9 (13) 4 . 5 (27) 2 . 6 (4) 2 . 2 (4)
94
11.2 (62) 5 . 5 (28) 6 . 4 (3) 4 . 5 (4)
68.0 (11)
99
Riverside 94
2 . 7 (56) 1560 (99) 24.4 (85) 2 . 1 (21) 500 (95) 6 . 2 (44) 3 . 7 (10) 131 (29) 1 1 . 3 (6) 9 . 6 (7) 4 . 4 (9) 0 . 1 (1)
19.2 (37) 8 . 0 (1)
Salt Lake City 100
Stoneville 98
8 . 6 (62) 950 (98) 1 . 4 (29) 250 (98) 47 (76) 1 . 9 (25) 9 . 9 (30) 7 . 0 (24) 1 . 8 (3) 9 . 9 (5)
2 . 3 (7) 2520 (9)
1340 (55) 4.0 (1)
29.7 (50) 58.5 (25) 29.6 (9)
DEF a
Iowa City Orlando
465 (37) 5 . 4 (3) 2 . 0 (4)
129 (40) 16 (12)
Number of samples containing detectable amounts of the pesticide.
The levels varied greatly from one locality to another and with the season. They were generally lower in urban areas than in agricultural areas. The highest pesticide levels were found in the agricultural areas of the South-Dothan, Orlando, and Stoneville. Relatively low levels were detected in other agricultural areas-Buffalo and Iowa City. Appreciable levels were found in Salt Lake City, an urban area in which there is considerable mosquito control activity. The levels were quite low in other urban areas-Baltimore, Fresno, and Riverside. In Fresno and Riverside, it had been anticipated that higher levels would be found. One explanation for the low levels may be that sampling operations were conducted too far from spraying operations for appreciable amounts of pesticides to be present. The sites were selected to give samples representative of the population exposure in the area. The levels of pesticides that were found are extremely low when compared with pesticide residue levels in foodstuffs. Any detailed analysis of the significance of the results is premature because the proportion of these pesticides that are retained in the body and the long-term effects of these levels of pesticides on humans are unknown. One approach to placing the results in perspective is to compare the levels with those found in “total diet” surveys (Duggan, 1969). Even if all the pesticides in the air breathed by an adult at these locations were retained in the body, the intake from air for the highest level measured (DDT, Orlando) would only approximate the intake from total diet, while more typical levels measured (10 to 30 ng/m3) would be at least two orders of magnitude below the intake from total diet. Conclusions
The levels of pesticides found in the ambient air were almost entirely far below levels that might add to the total human intake of pesticides. Odyp,p‘-DDT and O,P’-DDTwere found in the atmosphere at all localities, in both urban and agricultural areas. Levels are highest in the agricultural areas of the South, and are generally lower in urban areas. Levels vary from the
lower limit of detection of 0.1 ng of pesticide per m 3 of air to as high as 1560 ng ofp,p‘-DDT 2520 ng of toxaphene, and 680 ng of parathion per m 3 of air. Higher pesticide levels were found when pesticide spraying was reported than when no spraying was reported. There was no apparent correlation of level with rainfall. Kinds and levels of pesticides changed with time, with higher levels being found during the summer at all locations except Orlando, where there are agricultural activities throughout the year. The pesticide distribution in the components of the sampling train indicates that most pesticides are present in the atmosphere as particulates. Literature Cited Anderson, R. J., “Scientific Aspects of Pest Control,” National Academv of Sciences. NAC-NRC 1402. Washington. D.C., 1966, p f67. Duggan, R. E., Lipscomb, G. Q., Pestic. Monit. J . 2 (4), 153162 (1969). Finkelstein,’M., “Air Pollution Aspects of Pesticides,” U S . Department of Commerce, National Bureau of Standards, PB188091, September 1969. Hornstein, I., Sullivan, W. N., Anal. Chem. 25, 496 (1953). Scr. Miles, J. W., Fetzer, L. E., Pearce, G. W., ENVIRON. TECHNOL. 4(5), 420 (1970). President’s Science Advisory Committee, “Use of Pesticides,” U.S. Government Printing Office, Washington, D.C., 1963. Stanley, C. W., Post, A. P., “Determination of Carbaryl, Chlorinated Hydrocarbon Pesticides, and Organophosphate Residues in Foodstuffs,” 153rd Meeting, ACS, Miami Beach, Fla., April 1967. West, I., Advan. Chem. Ser. 60, 38 (1966). -
I
Receioed for reciew July 28, 1969. Resubmitted Sept. 28, 1970. Accepted Jan. 11, 1971. Commercial sources are given for identification only and does not constitute endorsement by the Pns or HEW. This work was supported by the Division of Pesticide Community Studies, Ofice of Product Safety, Bureau of Medicin?, Food and Drug Administration, Consumer Protection and Environmental Health Service, Pns, HEW, under contract PH 21-2006. Volume 5, Number 5, May 1971 435
