Arch. Environm. Contam. Toxicol. 8,433-440 (1979)
Archives of
Environmental Contamination and Toxicology
Exposure of Field Workers to Organophosphorus Insecticides: Cotton G. W. Wicker, W. A. Williams 1, J. R. Bradley, Jr., and F. E. Guthrie Department of Entomology, North Carolina State University, Raleigh, North Carolina 27650 Abstract. The red blood cell and plasma cholinesterase (ChE) levels of cotton scouts inspecting foliage for insect infestation and damage were monitored. Group means for ChE activity were significantly depressed at one or more time(s) during four of the eight growing seasons studied. Although no symptoms of organophosphate poisoning were confirmed, several scouts exhibited ChE depressions over 50% of pre-exposure levels. Organophosphorus (OP) insecticides, including the relatively toxic compounds methyl parathion, EPN (O-ethyl-O-p-nitrophenylphenyl phosphonothioate), monocroptophos, and azinphosmethyl, are used extensively as foliage sprays for the control of insect pests of cotton in North Carolina and other cottongrowing states. Approximately 50% of the cotton in North Carolina is assessed at three to seven day intervals for pest population levels and crop damage to determine when treatment is economically justified. A worker may scout from 700 to 1400 acres of cotton per week, depending on proximity and size of fields and frequency of scouting. These cotton scouts are exposed to insecticide residues on foliage from eight to ten hours per day. Although it is recommended that scouts avoid reentering a field for at least 48 hr after application of insecticides, it is not always possible for the scouts to do this while maintaining their scheduled activities. Although scouting in pest management programs is now common on alfalfa, tobacco, fruit, and other crops, few studies have been reported on possible hazards of reentry into treated areas from these programs. Several investigators have monitored blood cholinesterase (ChE) levels or conducted reentry experiments involving individuals inspecting cotton (Quinby et al. 1958, E1-Refai et al. 1971, Barry and Womack 1973, Nemec et al. 1%8, Ware et al. 1973, 1974, 1975, Burns and Parker 1975). These studies suggest no appreciable health hazard to cotton scouts. Also, fourteen tobacco scouts in two areas of North Carolina were monitored during 1973, and neither plasma
1 North Carolina Department of Human Resources, Pesticides Program, Raleigh, North Carolina 27602
0090-4341/79/0008-0433 $01.60 9 1979 Springer-Verlag New York Inc.
434
G . W . Wicker et al.
nor red blood cell (RBC) ChE levels were significantly reduced (Ellis and Ganyard 1973). The present study was directed to a monitoring program of cotton scouts in North Carolina over an 8-year period by determination of RBC and plasma ChE levels during the season when exposure to OP insecticides was maximal.
Methods Cholinesterase levels of cotton scouts from several locations throughout North Carolina were monitored over an eight-year period. The monitoring program did not permit close surveillance of individuals because of the number of individuals involved, the distances required in sampling, and the impossible tasks of ascertaining pesticide residue levels (hence exposure) in the multi-field situation dictated by such an activity. Scouts were primarily males (>95%)between the ages of 17-25 (>95%) most of whom were entering college or already enrolled. The dress of scouts was variable, but the most usual mode was long trousers, short-sleeved shirts, and boots (tennis shoes in some instances) with rare individuals wearing hats and gloves. Although clothes were changed daily (except in very unusual instances), the workers seldom washed their hands and arms upon leaving the fields. Scouts were instructed to follow a minimal 48-hr reentry schedule, but the date of application was often unknown to the scouts. A measure of exposure was impossible to obtain for individuals, since insecticide treatment depended upon insect activity, the number of fields scouted by each individual varied, weathering of residues was variable, and the rates of application differed according to the problem in a specific field, etc. The insecticides primarily used were toxaphene-methyl parathion (applied at the per acre rate of 2 + 1 lb oftoxaphene and methyl parathion, respectively), EPN-methyl parathion (applied at the rate of 0.5 lb of each chemical per acre), monocrotophos (applied at 0.6 to 0.9 lb/acre), or azinphosmethyl (applied at 0.25 lb/acre). Applications normally began as early as late June and continued as late as mid-September. Insecticides were applied at 5 to 7 days intervals, and individual fields were sprayed 3 to 15 times on an "as needed" basis. Supervisors and scouts were instructed to periodically check for pin-point pupils (miosis) as an indication of excess exposure, and scouts were warned to temporarily cease scouting activities if ChE levels fell below 25% of pre-exposure determinations. The blood collection schedules for individuals scouting cotton in Scotland, Halifax, Northampton, Edgecombe, Nash, and Chowan counties in 1971-78 are shown in Table 1. Blood samples were collected by staff nurses of the North Carolina Department of Human Resources at one to four week intervals, and pre-exposure baseline activity was determined for each group. Samples were collected by venipuncture in a heparinized vacutainer (7 or 10 ml) or by finger stick in duplicate hematocrit tubes (75 mm) and placed immediately into ice chests for transport to the laboratory. RBC and plasma ChE activities were determined within 24 hr of blood collection by an automated pH stat method (Nabb and Whitfield 1967) or by the micro colorimetric method described by Ellman et al. (1961). Individuals scouting cotton with no known exposure to organophosphorus or carbamate insecticides served as controls. Comparisons of RBC and plasma ChE values between group pre-exposure means and postexposure means were made by using unpaired " t " tests. Group means and standard deviations (SD) also were calculated for each sampling date.
Results 1971. Group means and SD of the means for RBC and plasma ChE activity for cotton scouts on each sampling date are shown in Table 2. In 1971, there were no significant group differences in ChE inhibition; however, two scouts in Scotland and Northampton counties exhibited RBC ChE inhibition of more than
1978
1976 1977
1975
1974
Northampton Edgecombe Nash Scotland Chowan Scotland Scotland
Scotland Halifax Northampton Scotland Halifax Northampton Edgecombe Halifax Northampton Edgecombe Scotland Halifax
1971
1972 1973
County
Year
11 14 25 21
8
12
7 3 0 0
1
1
0
0
35
42
0
2
20
5
2
No. controls
8
Total No. scout volunteers
weekly weekly weekly weekly
bi-weekly
weekly
monthly
bi-weekly
bi-weekly
bi-weekly
bi-weekly
Sample collection schedule
8 4 8 10
3
7
3
5
4
5
6
Total samples
100/zl 100/xl !0 m! 5 ml
100/zl
100/zl
10 ml
10 ml
10 ml
7 ml
7 ml
Sample volume
finger stick finger stick venipuncture venipuncture
finger stick
finger stick
venipuncture
venipuncture
venipuncture
venipuncture
venipuncture
Method of blood collection
Ellman Ellman E!!man Ellman
et et et et
al. al. a!. al.
(1961) (1961) (!961) (1961)
Ellman et al. (1961)
Ellman et al. (1961)
Nabb & Whitfield (1967)
Nabb & Whitfield (1967)
W
cn
O
Nabb & Whitfield (1967) Ellman et al. (1961)
O
O
O
Nabb & Whitfield (1967)
Method of ChE analysis
Table 1. Blood collection schedules and methods for ChE determination for cotton scouts in Scotland, Northampton, Edgecombe, Nash, Halifax and Chowan Counties in 1971-1978
436
G . W . Wi c ke r et al.
Table 2. Group m e a n s and standard deviations for RBC and pl a s ma C h E a c t i vi t y for cotton scouts on e a c h blood sampling date (/xmoles/ml/min) C h o l i n e s t e r a s e A c t i v i t yb
Year
County
1971
Scotland Northampton
Halifax
1972
Scotland
1973
Halifax Northampton Edgecombe
1974
1975
Halifax Northampton Edgecombe Scotland Halifax Northampton Edgecombe Nash
1976
Scotland
1977
Chowan
Sampling a Period
Scouts Sampled
RBC Mean _+ S.D.
Plasma Me a n _+ S.D.
1+
16
12.1 • 2.7
4.6 ___ 0.6
2 3 4 5 6 1+ 2 3 4 5 1• 2 3 4 1 +-
20 19 19 14 2 6 4 4 3 3 4 2 3 3 28
14.1 13.1 12.5 12.8 12.4 12.0 12.8 13.0 13.1 12.9
• 3.5 -+ 1.9 -4- 1.4 -+ 2.4 -+ 0.5 +- 1.5 -+ 3.0 -+ 1.9 -+ 0.8 • 1.7 ----14.4 _+ 2.6
5.0 _+ 0.7 5.1 -+ 1.0 4.6 _+ 0.8 4,3 -+ 1.1 5,2 _+ 1.6 4,8 _+ 0.5 5,0 _+ 0.2 4,6 + 0.4 4,1 _+ 0.3 4,4 _+ 0.1 3.1 _+ 0.5 1.7 -+ 0* 3.0_+ 0.1 3.1 _+ 0.1 5.6 _+ 1.0
2 3 4 5
29 21 28 19
11.8 15.4 12.4 12.8
_+ _+ -+ _+
1.6 1.5 1.9 1.2
4.7 6.0 4.8 5.4
_+ 1.1 +_ 1.2 _+ 0.9 _+ 1.0
1• 2 3 1+-
33 32 16 12
13.2 14.0 11.4 17.8
+ + + •
2.7 2.7 1.2 1.9
4.9 5.2 4.7 1.9
_+ 0.9 _+ 1.0 -+ 0.9 _+ 0.5
2
10
17.0 _+ 1.9
2.0 _+ 0.3
3 4 5 6 7 1_+ 2_+ 3 4 5 6 7 8 I_+ 2 3 4
10 11 15 5 4 11 7 10 10 7 9 8 4 14 8 14 8
18.0 17.0 15.0 16.0 16.7 21.3 20.1 19.0 21.4 18.7 17.5 19.1 16.6 22.3 22.8 21.6 23.3
1.9 1.8 1.7 1.8 1.6 2.8 2.6 2.5 2.7 2.4 2.4 2.8 2.4 2.2 2.9 3.3 3.4
• 2.2 • 1.6 --- 3.0** + 2.4 • 1.7 • 2.4 • 2,4 _+ 2.6 _+ 2.4 -+ 2.3* • 1.0"* _+ 0.7* _+ 2.0** _+ 3.9 • 1.8 -+ 1.8 -+ 2.2
-+ 0.5 -+ 0.4 _+ 0.5* -+ 0.4 _+ 0.4 _+ 0.4 • 0.4 _+ 0.5 --- 0.5 • 0.3* + 0.5* -+- 0.3 • 0.4 • 1.4"* • 0.6 _+ 0.6 -+ 0.7
Exposure of workers to organophosphorus insecticides
437
Table 2. Continued Cholinesterase Activity b
Year 1977
1978
County Scotland
Scotland
Sampling a Period 1-+ 2 3 4 5 6 7 8 1 +2 3 4 5 6 7 8 9 10
Scouts Sampled 15 17 21 18 15 16 11 2 21 4 2 13 13 13 16 11 8 10
RBC Mean -+ S.D.
m
i
m
m
m
m
m
m
m
m
D
m
B
m
Plasma Me a n -+ S.D.
2.6 -+ 0.8 3.3 -+ 0.5 2.8 -+ 0.6 2.7 -+ 0.6 3.1 -+0.4 2.5 -+ 0.5 2.3 -+ 0.4 2.7-+0.1 2.8 +- 0.6 2.5 -+ 0.4 2.1 -+0.4 2.5 -+ 0.5 2.4 -+ 0.6 2.3 -+ 0.6* 2.3 -+ 0.8* 2.0 -+ 1.0" 2.3 -+ 1.0 1.9 -+ 0.7**
a The first and second sampling dates (_+) were for we-exposure estimates (except as noted for 1977) b* ChE activity significantly different from the pre-exposure level p < .05 ** ChE activity significantly different from the pre-exposure level p < .001
20%, and five scouts exhibited plasma ChE inhibitions of more than 25% of their pre-exposure levels. Two of these individuals had depressions of plasma ChE which approached 50% by the end of the study period when no subsequent exposure followed. The ChE depressions of these latter individuals correlated with personal habits, such as lack of daily changing of clothing and disregard for reentry intervals, especially in dew-wet fields. A group of scouts in Halifax County was also monitored. No OP insecticides were used on fields scouted in that county and no ChE inhibition was noted. This group and two other individuals not exposed to OP compounds served as controls. 1972. Plasma ChE activity was significantly reduced (50%) in the two scouts monitored at the second sampling date. No ChE depression was noted during the rest of the season. 1973. No significant ChE inhibition was noted for the group means in 1973. Twenty-eight percent of the workers showed RBC ChE depressions of at least 20%, and 19% of the workers showed plasma ChE depressions of 20% or greater. 1974. No significant group differences were found between pre-exposure and post-exposure ChE activity. Only three cotton scouts exhibited depressed RBC ChE activity, ranging from 34 to 43%.
438
G . W . Wicker et al.
1975. Over 40% of the scouts in Scotland County showed RBC ChE reductions
of 20% to 45%, and 33% of the scouts had plasma reductions ranging from 20% to 56%. The group RBC ChE activity on the fifth sampling date was significantly lower than the pre-exposure level. The control RBC ChE varied by only 1% between the first and fifth sampling dates. 1976. Approximately 50% of the workers had ChE depressions of at least 20% in Scotland County. The group RBC ChE activity was significantly lower than the baseline level for the last four weeks in the study. The plasma ChE was significantly reduced the fifth and sixth weeks of sampling. The reduced ChE activity in the latter part of the growing season correlates with the increased use of OP insecticides during that time period. The ChE depression may also reflect the cumulative action of OP compounds on enzyme inhibition. 1977. Four scouts from Chowan County were exposed to residues approximately three hr before pre-exposure blood collection was scheduled when they inadvertently entered a field that had been treated less than 24 hr before with monocrotophos. Three other scouts entered a monocrotophos-treated field within 48 hr after treatment. Both groups showed plasma ChE activity significantly lower than any subsequent samples taken and significantly lower than the seven unexposed scouts. No reduction in RBC ChE activity was detected. This would be expected, since their exposure occurred just prior to blood sample collection, and RBC ChE levels decline more slowly than plasma ChE after exposure to OP compounds (Hayes and Durham 1954). Since RBC values have been shown to parallel closely those of the brain (Freedman et al. 1949), early detection of plasma ChE inhibition allowed corrective measures to be taken before poisoning became more advanced. Several of the highly exposed workers complained of "not feeling well" the evening after exposure, but no other symptoms of poisoning were noted. No significant ChE depressions were noted between the exposed and unexposed groups for the subsequent sampling dates. No significant ChE depressions were noted for scouts in Scotland County during 1977. 1978. The group plasma ChE activity of the scouts in Scotland County was significantly lower than the baseline level for four of the last five weeks in 1978. ChE depressions greater than 20% were found in 57% of the scouts. Twenty four percent of the scouts had ChE depressions greater than 45% of their pre-exposure levels, including three scouts with ChE activity reduced 59 to 68%. Discussion
Although few confirmed illnesses and no deaths have been reported among cotton scouts, a number of investigators have detected ChE depressions in some workers. Two workers who entered a field two hr after treatment with methyl parathion showed a marked reduction in ChE activity (Nemec et al. 1968). Burns and Parker (1975) reported a significant depression of ChE levels in a group of 12 cotton scouts exposed to methyl parathion-treated fields. Ware et al. (1973) estimated that an average of 3.5 mg of methyl parathion accumulated on the hands of workers (30 min exposure) entering a field immediately
Exposure of workers to organophosphorus insecticides
439
after treatment for 30 min. Leaf residues of parathion were -~ 10 ~g/cm ~ immediately after treatment. Ware et al. (1974) reported reduced RBC ChE in four volunteers exposed to monocrotophos residues ( 2 10/zg/cm 2) on cotton; however, the ChE levels were not below the "normal" range. Quinby et al. (1958) postulated that the main exposure by 25 scouts to malathion, methyl parathion, and azinophosmethyl residues was to the hands. Although no significant ChE changes were noted for these scouts, our observations are not in agreement with this prediction. In fields where cotton was dense and three to five feet tall, the legs and hips of the workers were also subject to exposure, especially when plants were wet with dew or rain. Contaminated clothing may act as an occlusive dressing and aid in dermal absorption of OP insecticides (Milby 1974). Clothing worn by scouts on the first reentry day (after 24 hr) was found to contain methyl parathion residues of 21.9 (all-cotton) and 32.0 ppm (cotton polyester). Residues on clothing on the fourth reentry day were only 1 to 1.5% of those estimated for the first reentry day (Finley et al. 1976). High ambient temperatures to which scouts are exposed may increase absorption of some insecticides (Funckes et al. 1%3, Baetjer and Smith 1956). This report, and the findings of several other studies, has not detected a serious health hazard for cotton scouts exposed to 10 or more applications (1.0 lb/appl/ac) of OP insecticides per season. When recommended procedures are followed (i.e., 48-hr reentry interval, daily clothing changes, avoidance of dew-wet fields, frequent check for miosis, forced absence from further exposure when ChE depression exceeds 25%, etc.), no adverse effects seem likely. Nonetheless, a hazard is ever-present for the unusual circumstances, especially for the careless worker who enters several recently-treated fields on a number of occasions. Precautions must be taken to avoid such an event, and routine monitoring of ChE in individuals exposed during normal work routine would appear to be a minimal precaution. Acknowledgments. The authors are grateful to the cotton scouts who volunteered to participate in this study, to the staff nurses of the North Carolina Department of Human Resources for their aid in blood collection, and to Henry L. McLeod, Jr., K. V. Perkins, and Milton C. Ganyard for their cooperation. This work was supported by ES-00044 and ES-07046 from the National Institute of Environmental Health Sciences. Paper No. 2661 of the Journal Series of the North Carolina Agricultural Experiment Station, Raleigh, North Carolina.
References Baetjer, A. M., and R. Smith: Effect of environmental temperature on reaction of mice to parathion, an anticholinesterase agent. Amer. J. Physiol. 186, 39 (1956). Barry, R. M., and H. Womack: Cholinesterase activity determinations for personnel engaged in a cotton-scouting program. Environ. Entomol. 2, 961 (1973). Burns, J. E., and R. D. Parker: An investigation of the safety of cotton reentry after organophosphate application. Arch. Environ. Contain. Toxicol. 3, 344 (1975). Ellis, H. C., and M. C. Ganyard, Jr.: North Carolina Tobacco Pest Management Third Annual Report. Raleigh, NC, North Carolina Agricultural Extension Service (1973).
440
G . W . Wicker et al.
Ellman, G. L., K. D. Courtney, V. Andres, and R. M. Featherstone: A new and rapid colorimetric determination of acetyl cholinesterase activity. Biochem. Pharmacol. 7, 88 (1961). E1-Refai, A. R., M. E1-Essawi, N. E1-Esnawi, and R. Risk: Hazards from spraying in cotton culture area of the Nile River. Arch. Environ. Health 15, 147 (1971). Finley, E. L., J. M. Bellon, J. B. Graves, and K. L. Koonce: Pesticide contamination of clothing in cotton fields. Louisiana Agr. 20, 9 (1976). Freedman, A. M., A. Willis, and H. E. Himwich: Correlation between signs of toxicity and cholinesterase level of brain and blood during recovery from di-isopropyl phosphate (DFP) poisoning. Amer. J. Physiol. 157, 80 (1949). Funckes, A. J., G. R. Hayes, and W. V. Hartwell: Urinary excretion of paranitropbenol by volunteers following dermal exposure to parathion at different ambient temperatures. J. Agr. Food Chem. 11, 455 (1963). Hayes, W. J., Jr., and W. Durham: Studies .of organic phosphorus insecticide poisoning. VI Congress of Comparative Pathology, Madrid, May 4-11, 1952. II. Actas Y. Communications, p. 231 (1954). Milby, T. H., Editor: Report of the Task Group on Occupational Exposure to Pesticides. United States Government Printing Office (1974). Nabb, D. P., and F. Whitfield: Determination of cholinesterase by an automated pH-stat method. Arch. Environ. Health 15, 147 (1967). Nemec, S. J., P. L. Adkisson, and H. W. Dorough: Methyl parathion absorbed on the skin and blood cholinesterase levels of persons checking cotton treated with ultra-low-volume sprays. J. Econ. Entomol. 61, 1740 (1968). Quinby, G. E., K. C. Walker, and W. F. Durham: Public health hazards involved in the use of organic phosphorus insecticides in cotton culture in the Delta Area of Mississippi. J. Econ. Entomol. 51, 831 (1958). Ware, G. E., D. P. Morgan, B. J. Estesen, W. P. Cahill, and D. M. Whitacre: Establishment of reentry intervals for organophosphate-treated cotton fields based on human data: I. Ethyl- and methyl-parathion. Arch. Environ. Contam. Toxicol. 1, 48 (1973). Ware, G. W., D. P. Morgan, B. J. Estesen, and W. P. Cahill: Establishment of reentry intervals for organopbosphate-treated cotton fields based on human data. II. Azodrin, ethyl and methyl parathion. Arch. Environ. Contam. Toxicol. 2, 117 (1974). , , , : Establishment of reentry intervals for organophosphate-treated cotton fields based on human data. III. 12 to 72 hours post-treatment exposure to monocrotophos, ethyl- and methyl-parathion. Arch. Environ. Contam. Toxicol. 3, 289 (1975).
Manuscript received August 18, 1978; accepted November 7, 1978.
Archives of
Environmental Contamination and Toxicology
Exposure of Field Workers to Organophosphorus Insecticides: Cotton G. W. Wicker, W. A. Williams 1, J. R. Bradley, Jr., and F. E. Guthrie Department of Entomology, North Carolina State University, Raleigh, North Carolina 27650 Abstract. The red blood cell and plasma cholinesterase (ChE) levels of cotton scouts inspecting foliage for insect infestation and damage were monitored. Group means for ChE activity were significantly depressed at one or more time(s) during four of the eight growing seasons studied. Although no symptoms of organophosphate poisoning were confirmed, several scouts exhibited ChE depressions over 50% of pre-exposure levels. Organophosphorus (OP) insecticides, including the relatively toxic compounds methyl parathion, EPN (O-ethyl-O-p-nitrophenylphenyl phosphonothioate), monocroptophos, and azinphosmethyl, are used extensively as foliage sprays for the control of insect pests of cotton in North Carolina and other cottongrowing states. Approximately 50% of the cotton in North Carolina is assessed at three to seven day intervals for pest population levels and crop damage to determine when treatment is economically justified. A worker may scout from 700 to 1400 acres of cotton per week, depending on proximity and size of fields and frequency of scouting. These cotton scouts are exposed to insecticide residues on foliage from eight to ten hours per day. Although it is recommended that scouts avoid reentering a field for at least 48 hr after application of insecticides, it is not always possible for the scouts to do this while maintaining their scheduled activities. Although scouting in pest management programs is now common on alfalfa, tobacco, fruit, and other crops, few studies have been reported on possible hazards of reentry into treated areas from these programs. Several investigators have monitored blood cholinesterase (ChE) levels or conducted reentry experiments involving individuals inspecting cotton (Quinby et al. 1958, E1-Refai et al. 1971, Barry and Womack 1973, Nemec et al. 1%8, Ware et al. 1973, 1974, 1975, Burns and Parker 1975). These studies suggest no appreciable health hazard to cotton scouts. Also, fourteen tobacco scouts in two areas of North Carolina were monitored during 1973, and neither plasma
1 North Carolina Department of Human Resources, Pesticides Program, Raleigh, North Carolina 27602
0090-4341/79/0008-0433 $01.60 9 1979 Springer-Verlag New York Inc.
434
G . W . Wicker et al.
nor red blood cell (RBC) ChE levels were significantly reduced (Ellis and Ganyard 1973). The present study was directed to a monitoring program of cotton scouts in North Carolina over an 8-year period by determination of RBC and plasma ChE levels during the season when exposure to OP insecticides was maximal.
Methods Cholinesterase levels of cotton scouts from several locations throughout North Carolina were monitored over an eight-year period. The monitoring program did not permit close surveillance of individuals because of the number of individuals involved, the distances required in sampling, and the impossible tasks of ascertaining pesticide residue levels (hence exposure) in the multi-field situation dictated by such an activity. Scouts were primarily males (>95%)between the ages of 17-25 (>95%) most of whom were entering college or already enrolled. The dress of scouts was variable, but the most usual mode was long trousers, short-sleeved shirts, and boots (tennis shoes in some instances) with rare individuals wearing hats and gloves. Although clothes were changed daily (except in very unusual instances), the workers seldom washed their hands and arms upon leaving the fields. Scouts were instructed to follow a minimal 48-hr reentry schedule, but the date of application was often unknown to the scouts. A measure of exposure was impossible to obtain for individuals, since insecticide treatment depended upon insect activity, the number of fields scouted by each individual varied, weathering of residues was variable, and the rates of application differed according to the problem in a specific field, etc. The insecticides primarily used were toxaphene-methyl parathion (applied at the per acre rate of 2 + 1 lb oftoxaphene and methyl parathion, respectively), EPN-methyl parathion (applied at the rate of 0.5 lb of each chemical per acre), monocrotophos (applied at 0.6 to 0.9 lb/acre), or azinphosmethyl (applied at 0.25 lb/acre). Applications normally began as early as late June and continued as late as mid-September. Insecticides were applied at 5 to 7 days intervals, and individual fields were sprayed 3 to 15 times on an "as needed" basis. Supervisors and scouts were instructed to periodically check for pin-point pupils (miosis) as an indication of excess exposure, and scouts were warned to temporarily cease scouting activities if ChE levels fell below 25% of pre-exposure determinations. The blood collection schedules for individuals scouting cotton in Scotland, Halifax, Northampton, Edgecombe, Nash, and Chowan counties in 1971-78 are shown in Table 1. Blood samples were collected by staff nurses of the North Carolina Department of Human Resources at one to four week intervals, and pre-exposure baseline activity was determined for each group. Samples were collected by venipuncture in a heparinized vacutainer (7 or 10 ml) or by finger stick in duplicate hematocrit tubes (75 mm) and placed immediately into ice chests for transport to the laboratory. RBC and plasma ChE activities were determined within 24 hr of blood collection by an automated pH stat method (Nabb and Whitfield 1967) or by the micro colorimetric method described by Ellman et al. (1961). Individuals scouting cotton with no known exposure to organophosphorus or carbamate insecticides served as controls. Comparisons of RBC and plasma ChE values between group pre-exposure means and postexposure means were made by using unpaired " t " tests. Group means and standard deviations (SD) also were calculated for each sampling date.
Results 1971. Group means and SD of the means for RBC and plasma ChE activity for cotton scouts on each sampling date are shown in Table 2. In 1971, there were no significant group differences in ChE inhibition; however, two scouts in Scotland and Northampton counties exhibited RBC ChE inhibition of more than
1978
1976 1977
1975
1974
Northampton Edgecombe Nash Scotland Chowan Scotland Scotland
Scotland Halifax Northampton Scotland Halifax Northampton Edgecombe Halifax Northampton Edgecombe Scotland Halifax
1971
1972 1973
County
Year
11 14 25 21
8
12
7 3 0 0
1
1
0
0
35
42
0
2
20
5
2
No. controls
8
Total No. scout volunteers
weekly weekly weekly weekly
bi-weekly
weekly
monthly
bi-weekly
bi-weekly
bi-weekly
bi-weekly
Sample collection schedule
8 4 8 10
3
7
3
5
4
5
6
Total samples
100/zl 100/xl !0 m! 5 ml
100/zl
100/zl
10 ml
10 ml
10 ml
7 ml
7 ml
Sample volume
finger stick finger stick venipuncture venipuncture
finger stick
finger stick
venipuncture
venipuncture
venipuncture
venipuncture
venipuncture
Method of blood collection
Ellman Ellman E!!man Ellman
et et et et
al. al. a!. al.
(1961) (1961) (!961) (1961)
Ellman et al. (1961)
Ellman et al. (1961)
Nabb & Whitfield (1967)
Nabb & Whitfield (1967)
W
cn
O
Nabb & Whitfield (1967) Ellman et al. (1961)
O
O
O
Nabb & Whitfield (1967)
Method of ChE analysis
Table 1. Blood collection schedules and methods for ChE determination for cotton scouts in Scotland, Northampton, Edgecombe, Nash, Halifax and Chowan Counties in 1971-1978
436
G . W . Wi c ke r et al.
Table 2. Group m e a n s and standard deviations for RBC and pl a s ma C h E a c t i vi t y for cotton scouts on e a c h blood sampling date (/xmoles/ml/min) C h o l i n e s t e r a s e A c t i v i t yb
Year
County
1971
Scotland Northampton
Halifax
1972
Scotland
1973
Halifax Northampton Edgecombe
1974
1975
Halifax Northampton Edgecombe Scotland Halifax Northampton Edgecombe Nash
1976
Scotland
1977
Chowan
Sampling a Period
Scouts Sampled
RBC Mean _+ S.D.
Plasma Me a n _+ S.D.
1+
16
12.1 • 2.7
4.6 ___ 0.6
2 3 4 5 6 1+ 2 3 4 5 1• 2 3 4 1 +-
20 19 19 14 2 6 4 4 3 3 4 2 3 3 28
14.1 13.1 12.5 12.8 12.4 12.0 12.8 13.0 13.1 12.9
• 3.5 -+ 1.9 -4- 1.4 -+ 2.4 -+ 0.5 +- 1.5 -+ 3.0 -+ 1.9 -+ 0.8 • 1.7 ----14.4 _+ 2.6
5.0 _+ 0.7 5.1 -+ 1.0 4.6 _+ 0.8 4,3 -+ 1.1 5,2 _+ 1.6 4,8 _+ 0.5 5,0 _+ 0.2 4,6 + 0.4 4,1 _+ 0.3 4,4 _+ 0.1 3.1 _+ 0.5 1.7 -+ 0* 3.0_+ 0.1 3.1 _+ 0.1 5.6 _+ 1.0
2 3 4 5
29 21 28 19
11.8 15.4 12.4 12.8
_+ _+ -+ _+
1.6 1.5 1.9 1.2
4.7 6.0 4.8 5.4
_+ 1.1 +_ 1.2 _+ 0.9 _+ 1.0
1• 2 3 1+-
33 32 16 12
13.2 14.0 11.4 17.8
+ + + •
2.7 2.7 1.2 1.9
4.9 5.2 4.7 1.9
_+ 0.9 _+ 1.0 -+ 0.9 _+ 0.5
2
10
17.0 _+ 1.9
2.0 _+ 0.3
3 4 5 6 7 1_+ 2_+ 3 4 5 6 7 8 I_+ 2 3 4
10 11 15 5 4 11 7 10 10 7 9 8 4 14 8 14 8
18.0 17.0 15.0 16.0 16.7 21.3 20.1 19.0 21.4 18.7 17.5 19.1 16.6 22.3 22.8 21.6 23.3
1.9 1.8 1.7 1.8 1.6 2.8 2.6 2.5 2.7 2.4 2.4 2.8 2.4 2.2 2.9 3.3 3.4
• 2.2 • 1.6 --- 3.0** + 2.4 • 1.7 • 2.4 • 2,4 _+ 2.6 _+ 2.4 -+ 2.3* • 1.0"* _+ 0.7* _+ 2.0** _+ 3.9 • 1.8 -+ 1.8 -+ 2.2
-+ 0.5 -+ 0.4 _+ 0.5* -+ 0.4 _+ 0.4 _+ 0.4 • 0.4 _+ 0.5 --- 0.5 • 0.3* + 0.5* -+- 0.3 • 0.4 • 1.4"* • 0.6 _+ 0.6 -+ 0.7
Exposure of workers to organophosphorus insecticides
437
Table 2. Continued Cholinesterase Activity b
Year 1977
1978
County Scotland
Scotland
Sampling a Period 1-+ 2 3 4 5 6 7 8 1 +2 3 4 5 6 7 8 9 10
Scouts Sampled 15 17 21 18 15 16 11 2 21 4 2 13 13 13 16 11 8 10
RBC Mean -+ S.D.
m
i
m
m
m
m
m
m
m
m
D
m
B
m
Plasma Me a n -+ S.D.
2.6 -+ 0.8 3.3 -+ 0.5 2.8 -+ 0.6 2.7 -+ 0.6 3.1 -+0.4 2.5 -+ 0.5 2.3 -+ 0.4 2.7-+0.1 2.8 +- 0.6 2.5 -+ 0.4 2.1 -+0.4 2.5 -+ 0.5 2.4 -+ 0.6 2.3 -+ 0.6* 2.3 -+ 0.8* 2.0 -+ 1.0" 2.3 -+ 1.0 1.9 -+ 0.7**
a The first and second sampling dates (_+) were for we-exposure estimates (except as noted for 1977) b* ChE activity significantly different from the pre-exposure level p < .05 ** ChE activity significantly different from the pre-exposure level p < .001
20%, and five scouts exhibited plasma ChE inhibitions of more than 25% of their pre-exposure levels. Two of these individuals had depressions of plasma ChE which approached 50% by the end of the study period when no subsequent exposure followed. The ChE depressions of these latter individuals correlated with personal habits, such as lack of daily changing of clothing and disregard for reentry intervals, especially in dew-wet fields. A group of scouts in Halifax County was also monitored. No OP insecticides were used on fields scouted in that county and no ChE inhibition was noted. This group and two other individuals not exposed to OP compounds served as controls. 1972. Plasma ChE activity was significantly reduced (50%) in the two scouts monitored at the second sampling date. No ChE depression was noted during the rest of the season. 1973. No significant ChE inhibition was noted for the group means in 1973. Twenty-eight percent of the workers showed RBC ChE depressions of at least 20%, and 19% of the workers showed plasma ChE depressions of 20% or greater. 1974. No significant group differences were found between pre-exposure and post-exposure ChE activity. Only three cotton scouts exhibited depressed RBC ChE activity, ranging from 34 to 43%.
438
G . W . Wicker et al.
1975. Over 40% of the scouts in Scotland County showed RBC ChE reductions
of 20% to 45%, and 33% of the scouts had plasma reductions ranging from 20% to 56%. The group RBC ChE activity on the fifth sampling date was significantly lower than the pre-exposure level. The control RBC ChE varied by only 1% between the first and fifth sampling dates. 1976. Approximately 50% of the workers had ChE depressions of at least 20% in Scotland County. The group RBC ChE activity was significantly lower than the baseline level for the last four weeks in the study. The plasma ChE was significantly reduced the fifth and sixth weeks of sampling. The reduced ChE activity in the latter part of the growing season correlates with the increased use of OP insecticides during that time period. The ChE depression may also reflect the cumulative action of OP compounds on enzyme inhibition. 1977. Four scouts from Chowan County were exposed to residues approximately three hr before pre-exposure blood collection was scheduled when they inadvertently entered a field that had been treated less than 24 hr before with monocrotophos. Three other scouts entered a monocrotophos-treated field within 48 hr after treatment. Both groups showed plasma ChE activity significantly lower than any subsequent samples taken and significantly lower than the seven unexposed scouts. No reduction in RBC ChE activity was detected. This would be expected, since their exposure occurred just prior to blood sample collection, and RBC ChE levels decline more slowly than plasma ChE after exposure to OP compounds (Hayes and Durham 1954). Since RBC values have been shown to parallel closely those of the brain (Freedman et al. 1949), early detection of plasma ChE inhibition allowed corrective measures to be taken before poisoning became more advanced. Several of the highly exposed workers complained of "not feeling well" the evening after exposure, but no other symptoms of poisoning were noted. No significant ChE depressions were noted between the exposed and unexposed groups for the subsequent sampling dates. No significant ChE depressions were noted for scouts in Scotland County during 1977. 1978. The group plasma ChE activity of the scouts in Scotland County was significantly lower than the baseline level for four of the last five weeks in 1978. ChE depressions greater than 20% were found in 57% of the scouts. Twenty four percent of the scouts had ChE depressions greater than 45% of their pre-exposure levels, including three scouts with ChE activity reduced 59 to 68%. Discussion
Although few confirmed illnesses and no deaths have been reported among cotton scouts, a number of investigators have detected ChE depressions in some workers. Two workers who entered a field two hr after treatment with methyl parathion showed a marked reduction in ChE activity (Nemec et al. 1968). Burns and Parker (1975) reported a significant depression of ChE levels in a group of 12 cotton scouts exposed to methyl parathion-treated fields. Ware et al. (1973) estimated that an average of 3.5 mg of methyl parathion accumulated on the hands of workers (30 min exposure) entering a field immediately
Exposure of workers to organophosphorus insecticides
439
after treatment for 30 min. Leaf residues of parathion were -~ 10 ~g/cm ~ immediately after treatment. Ware et al. (1974) reported reduced RBC ChE in four volunteers exposed to monocrotophos residues ( 2 10/zg/cm 2) on cotton; however, the ChE levels were not below the "normal" range. Quinby et al. (1958) postulated that the main exposure by 25 scouts to malathion, methyl parathion, and azinophosmethyl residues was to the hands. Although no significant ChE changes were noted for these scouts, our observations are not in agreement with this prediction. In fields where cotton was dense and three to five feet tall, the legs and hips of the workers were also subject to exposure, especially when plants were wet with dew or rain. Contaminated clothing may act as an occlusive dressing and aid in dermal absorption of OP insecticides (Milby 1974). Clothing worn by scouts on the first reentry day (after 24 hr) was found to contain methyl parathion residues of 21.9 (all-cotton) and 32.0 ppm (cotton polyester). Residues on clothing on the fourth reentry day were only 1 to 1.5% of those estimated for the first reentry day (Finley et al. 1976). High ambient temperatures to which scouts are exposed may increase absorption of some insecticides (Funckes et al. 1%3, Baetjer and Smith 1956). This report, and the findings of several other studies, has not detected a serious health hazard for cotton scouts exposed to 10 or more applications (1.0 lb/appl/ac) of OP insecticides per season. When recommended procedures are followed (i.e., 48-hr reentry interval, daily clothing changes, avoidance of dew-wet fields, frequent check for miosis, forced absence from further exposure when ChE depression exceeds 25%, etc.), no adverse effects seem likely. Nonetheless, a hazard is ever-present for the unusual circumstances, especially for the careless worker who enters several recently-treated fields on a number of occasions. Precautions must be taken to avoid such an event, and routine monitoring of ChE in individuals exposed during normal work routine would appear to be a minimal precaution. Acknowledgments. The authors are grateful to the cotton scouts who volunteered to participate in this study, to the staff nurses of the North Carolina Department of Human Resources for their aid in blood collection, and to Henry L. McLeod, Jr., K. V. Perkins, and Milton C. Ganyard for their cooperation. This work was supported by ES-00044 and ES-07046 from the National Institute of Environmental Health Sciences. Paper No. 2661 of the Journal Series of the North Carolina Agricultural Experiment Station, Raleigh, North Carolina.
References Baetjer, A. M., and R. Smith: Effect of environmental temperature on reaction of mice to parathion, an anticholinesterase agent. Amer. J. Physiol. 186, 39 (1956). Barry, R. M., and H. Womack: Cholinesterase activity determinations for personnel engaged in a cotton-scouting program. Environ. Entomol. 2, 961 (1973). Burns, J. E., and R. D. Parker: An investigation of the safety of cotton reentry after organophosphate application. Arch. Environ. Contain. Toxicol. 3, 344 (1975). Ellis, H. C., and M. C. Ganyard, Jr.: North Carolina Tobacco Pest Management Third Annual Report. Raleigh, NC, North Carolina Agricultural Extension Service (1973).
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Ellman, G. L., K. D. Courtney, V. Andres, and R. M. Featherstone: A new and rapid colorimetric determination of acetyl cholinesterase activity. Biochem. Pharmacol. 7, 88 (1961). E1-Refai, A. R., M. E1-Essawi, N. E1-Esnawi, and R. Risk: Hazards from spraying in cotton culture area of the Nile River. Arch. Environ. Health 15, 147 (1971). Finley, E. L., J. M. Bellon, J. B. Graves, and K. L. Koonce: Pesticide contamination of clothing in cotton fields. Louisiana Agr. 20, 9 (1976). Freedman, A. M., A. Willis, and H. E. Himwich: Correlation between signs of toxicity and cholinesterase level of brain and blood during recovery from di-isopropyl phosphate (DFP) poisoning. Amer. J. Physiol. 157, 80 (1949). Funckes, A. J., G. R. Hayes, and W. V. Hartwell: Urinary excretion of paranitropbenol by volunteers following dermal exposure to parathion at different ambient temperatures. J. Agr. Food Chem. 11, 455 (1963). Hayes, W. J., Jr., and W. Durham: Studies .of organic phosphorus insecticide poisoning. VI Congress of Comparative Pathology, Madrid, May 4-11, 1952. II. Actas Y. Communications, p. 231 (1954). Milby, T. H., Editor: Report of the Task Group on Occupational Exposure to Pesticides. United States Government Printing Office (1974). Nabb, D. P., and F. Whitfield: Determination of cholinesterase by an automated pH-stat method. Arch. Environ. Health 15, 147 (1967). Nemec, S. J., P. L. Adkisson, and H. W. Dorough: Methyl parathion absorbed on the skin and blood cholinesterase levels of persons checking cotton treated with ultra-low-volume sprays. J. Econ. Entomol. 61, 1740 (1968). Quinby, G. E., K. C. Walker, and W. F. Durham: Public health hazards involved in the use of organic phosphorus insecticides in cotton culture in the Delta Area of Mississippi. J. Econ. Entomol. 51, 831 (1958). Ware, G. E., D. P. Morgan, B. J. Estesen, W. P. Cahill, and D. M. Whitacre: Establishment of reentry intervals for organophosphate-treated cotton fields based on human data: I. Ethyl- and methyl-parathion. Arch. Environ. Contam. Toxicol. 1, 48 (1973). Ware, G. W., D. P. Morgan, B. J. Estesen, and W. P. Cahill: Establishment of reentry intervals for organopbosphate-treated cotton fields based on human data. II. Azodrin, ethyl and methyl parathion. Arch. Environ. Contam. Toxicol. 2, 117 (1974). , , , : Establishment of reentry intervals for organophosphate-treated cotton fields based on human data. III. 12 to 72 hours post-treatment exposure to monocrotophos, ethyl- and methyl-parathion. Arch. Environ. Contam. Toxicol. 3, 289 (1975).
Manuscript received August 18, 1978; accepted November 7, 1978.
