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The Effects of Continuous Exposure to Organophosphorus and Carbamate Insecticides on Cholinesterase (Che) Levels in Humans
63
THE EFFECTS OF CONTINUOUS EXPOSURE TO ORGANOPHOSPHORUS AND CARBAMATE INSECTICIDES ON CHOLINESTERASE (CHE) LEVELS IN HUMANS J. NGATIA*and A.Y. MGENI
**
Tropical Pesticides Research Institute, Arusha, Tanzania
** Ministry
of Health, Department of Preventive Medicine, Dar Es Salaam, Tanzania
ABSTRACT To assess the effects of continuous exposure to organophosphorus and carbamate insecticides on the cholinesterase levels in humans, the whole-blood cholinesterase from each clinically examined subject was determined using the tintometric method. The plasma cholinesterase level was spectrophotometrically determined in the laboratory. Our results show a reduction of the plasma cholinesterase enzyme, statistically significant at the 0.025 probability level, in subjects working in the Agricultural Entomology Sections at the Tropical Pesticides Research Institute (TPRI) Arusha, and Lyamungu Agricultural Research Institute, Moshi. No statisticall] significant reduction in the concentration of the whole-blood cholinesterase enzyme was observed in the subjects examined. These results show the degree of sensitivity of the second method rather than the actual inhibition of the cholinesterase enzyme.
INTRODUCTION In the past 15 years the use of pesticides has increased tremendously in Kenya, Uganda and Tanzania. These chemicals are toxic to humans and animals and thus pose a potential hazard to those individuals who because of the nature of their work (farmers and spray operators) constantly run the risk of being exposec to these chemicals. Although some form of protective measure against such hazards is practised by those who use pesticides constantly, poisoning, be it accidental or intentional, cannot be completely ruled out. The toxicity of organophosphorus and carbamate insecticides is mainly due to their ability to inhibit cholinesterase enzyme. Some of these compounds are readily absorbed into the human body through the skin, lungs and gastrointestinal tract.
* National Agricultural Laboratories, P.O. Box 14733, Nairobi, Kenya
64
T h i s experiment w a s d e s i g n e d s p e c i f i c a l l y f o r s c r e e n i n g p u r o o s e s t o r e v e a l t h e p r e s e n c e of c h o l i n e s t e r a s e i n h i b i t o r s i n t h e whole-blood
and plasma.
MATERIALS AND METHODS Employees from f o u r s e c t i o n s of t h e T r o p i c a l P e s t i c i d e s Research I n s t i t u t e , Arusha, ( A g r i c u l t u r a l Entomology, P h y s i c s , Botany and A d m i n i s t r a t i o n ) and employees from two s e c t i o n s of Lyamungu A g r i c u l t u r a l R e s e a r c h I n s t i t u t e , Moshi ( A d m i n i s t r a t i o n and A g r i c u l t u r a l Entomology) v o l u n t e e r e d t o p a r t i c i p a t e i n t h i s e x p e r i m e n t . The A d m i n i s t r a t i v e p e r s o n n e l from t h e two I n s t i t u t i o n s s e r v e d
as t h e c o n t r o l group of t h e i r r e s p e c t i v e I n s t i t u t i o n w h i l e t h o s e who mix and s p r a y p e s t i c i d e s i n t h e two I n s t i t u t i o n s were i n t h e e x p e r i m e n t a l group. A t t h e time t h i s experiment w a s c a r r i e d o u t (March and A p r i l 1977), o n l y
t h e A g r i c u l t u r a l Entomology S e c t i o n of Lyamungu w a s a c t i v e l y engaged i n s p r a y i n g c o f f e e p l a n t s u s i n g a m i x t u r e of f e n t h i o n , carbendazim and e n d o s u l f a n . During t h e p r e c e d i n g two months, however, TPRI S e c t i o n s had h a n d l e d t h e compounds shown i n T a b l e I.
TABLE I Chemicals h a n d l e d a t TPRI s-ection
chemicals
A g r i c u l t u r a l Entomology Botany Physics
The whole-blood
chlorpyrifos, dimethoate, fenthion, t r i c h l o r p h o n , methomyl, d i c h l o r v o s , c a r b o f u r a n DNOC, 2,4-D, a t r a z i n e , oxadiazon dichlorvos
c h o l i n e s t e r a s e l e v e l s were determined u s i n g t h e t i n t o m e t r i c
method. T h i s i s a f i e l d method developed and d e s c r i b e d by Edson ( r e f . 2 ) . The plasma c h o l i n e s t e r a s e l e v e l s were determined i n t h e l a b o r a t o r y s p e c t r o p h o t o m e t r i c a l l y u s i n g t h e method d e s c r i b e d b y Ellman e t a l . ( r e f .
3 ) . One o r two
c h o l i n e s t e r a s e d e t e r m i n a t i o n s were performed f o r e a c h c l i n i c a l l y examined person.
RESULTS I n t h e r e s u l t s shown i n Table 11, t h e whole-blood c h o l i n e s t e r a s e i s expressed a s a p e r c e n t a g e of t h e a c t i v i t y o f t h e normal pre-exposure v a l u e .
65
TABLE I T The whole-blood cholinesterase activity determined tintometrically section
date
Administration
24 March & 4 April 18 March 28 March 25 March
TPRI
19 April 6 April
Lyamungu
Botany Physics Agricultural Entomology Administration Agricultural Entomology Agricultural Entomology
institution
11
I, !I
,,
19 April
t,
+_
S.D.
(n)
95.8
+_
9.4
(19)
93.5 93.1 94.0
+_
+ -
8.5 6.6 9.9
( 7) ( 9)
mean Z
+_
(16)
94.8 94.8
+_ +_
7.1 8.2
(12) (27)
91.2
+_
7.6
(29)
S.D. - Standard deviation (n) - No of individuals The plasma cholinesterase activity (Table 111) is expressed in the kinetic units per litre (ku/l), using butyrylthiocholine at 25OC and at a pH of 7.7. The normal range is 3.0-8.0 ku/l. TABLE 111 The plasma cholinesterase activity determined by Ellman's SDeCtrODhOtOmetriC method institution
mean ku/1
+
S.D.
(n)
29 March & 4 Anril 18 March 28 March 25 March
TPRI
4.34
2
1.94
(17)
4.10 4.37*
z2
0.75 1.13
( 7) ( 9)
0.98
(14)
19 April 6 April
Lyamungu
0.75 1.14
(10)
1.02
(22)
section
date
Administration Botany Physics Agricultural Entomology Administration Agricultural Ent om0 logy Agricultural Entomology
19 April
1
,I 11
$1
11
* Statistically significant at the 0.025
2.94
2
3.77 2.80*
+
3.08
(24)
orobability levei
DISCUS SION Our results show a statistically significant reduction of the olasma cholinesterase enzyme at the 0 , 0 2 5 mobability level (Table 111) but no significant reduction in the concentration of the whole-blood cholinesterase in all persons examined (Table 11). The inconsistency of the results shown by the two methods suggest that Ellman's soectroohotometric method enablesthe detection of a slight but significant reduction of the plasma enzyme whereas by using the
tintometric method, Dlasma and erythrocyte cholinesterase activities are not
66 determined s e p a r a t e l y . It should be mentioned t h a t some of t h e mixers and spraymen we examined from
t h e two I n s t i t u t i o n s have been applying t h e s e chemicals f o r many y e a r s w i t h o u t t h e use of any a p p r o p r i a t e p r o t e c t i v e c l o t h i n g and w i t h o u t any s p e c i a l c l e a n s i n g r o u t i n e a f t e r a d a y ' s work. The s i g n i f i c a n c e of t b i s type of working h a b i t t o t h e d e p r e s s i o n of blood o r plasma c h o l i n e s t e r a s e enzyme i s u n c e r t a i n . S i n c e t h e r e h a s been l i t t l e i n f o r m a t i o n published on t h e e f f e c t s of continuous exposure of organophosphorus and carbamate p e s t i c i d e s on t h e c h o l i n e s t e r a s e l e v e l s i n humans i n t h e t r o o i c s , we f e e l t h a t more d a t a w i l l be needed b e f o r e any c o n c l u s i o n i s reached on t h i s s u b j e c t .
On t h e r e a c t i v a t i o n of t h e c h o l i n e s t e r a s e enzyme a f t e r i n h i b i t i o n by t h e s e p e s t i c i d e s , however, t h e r e have been r e p o r t s t h a t a comDlete r e v e r s a l of t h e c h o l i n e s t e r a s e enzyme i n h i b i t i o n by organophosphorus o r carbamate i n s e c t i c i d e s does occur by t h e h y d r o l y s i s of t h e phosphorylated o r carbamylated enzyme a t d i f f e r e n t r a t e s depending upon t h e physiochemical p r o p e r t i e s of t h e i n h i b i t o r (refs. l,4). ACKNOWLEDGEMENT
We wish t o thank D r . Hamon, D r . Vandekar and D r . Copplestone of WHO Geneva, S w i t z e r l a n d , f o r purchasing t h e c h o l i n e s t e r a s e t e s t k i t used i n t h i s experiment, and t h e D i r e c t o r s , T r o p i c a l P e s t i c i d e s Research I n s t i t u t e , Arusha and Lyamungu A g r i c u l t u r a l Research I n s t i t u t e , Moshi f o r making i t p o s s i b l e t o perform t h i s experiment. The t e c h n i c a l a s s i s t a n c e of M r . G.C.G.
S e b i k a l i and Miss A. Tarimo
i s g r a t e f u l l y acknowledged. We a r e a l s o i n d e b t e d t o J . Bujulu, R. Lubega and W.
I s h a r a z a f o r t h e i r c r i t i c a l review of t h e manuscript.
REFERENCES C a s a r r e t and J . Doull, Toxicology, The Basic Science of Poison, Macmillan p u b l i s h i n g Co., New York, N . Y . , 1975 p. 425. 2 E.F. Edson, World Crops, 10 (1958)' 49. 3 G.L. Ellman, K.D. Courtney, V . Andreas J r . , and R.M. F e a t h e r s t o n e , Bioch. Pharmacol., 1 (1961) 88. 4 E. Reiner, B u l l . WHO 44 (1971) 109-112. 1 L.J.
THE EFFECTS OF CONTINUOUS EXPOSURE TO ORGANOPHOSPHORUS AND CARBAMATE INSECTICIDES ON CHOLINESTERASE (CHE) LEVELS IN HUMANS J. NGATIA*and A.Y. MGENI
**
Tropical Pesticides Research Institute, Arusha, Tanzania
** Ministry
of Health, Department of Preventive Medicine, Dar Es Salaam, Tanzania
ABSTRACT To assess the effects of continuous exposure to organophosphorus and carbamate insecticides on the cholinesterase levels in humans, the whole-blood cholinesterase from each clinically examined subject was determined using the tintometric method. The plasma cholinesterase level was spectrophotometrically determined in the laboratory. Our results show a reduction of the plasma cholinesterase enzyme, statistically significant at the 0.025 probability level, in subjects working in the Agricultural Entomology Sections at the Tropical Pesticides Research Institute (TPRI) Arusha, and Lyamungu Agricultural Research Institute, Moshi. No statisticall] significant reduction in the concentration of the whole-blood cholinesterase enzyme was observed in the subjects examined. These results show the degree of sensitivity of the second method rather than the actual inhibition of the cholinesterase enzyme.
INTRODUCTION In the past 15 years the use of pesticides has increased tremendously in Kenya, Uganda and Tanzania. These chemicals are toxic to humans and animals and thus pose a potential hazard to those individuals who because of the nature of their work (farmers and spray operators) constantly run the risk of being exposec to these chemicals. Although some form of protective measure against such hazards is practised by those who use pesticides constantly, poisoning, be it accidental or intentional, cannot be completely ruled out. The toxicity of organophosphorus and carbamate insecticides is mainly due to their ability to inhibit cholinesterase enzyme. Some of these compounds are readily absorbed into the human body through the skin, lungs and gastrointestinal tract.
* National Agricultural Laboratories, P.O. Box 14733, Nairobi, Kenya
64
T h i s experiment w a s d e s i g n e d s p e c i f i c a l l y f o r s c r e e n i n g p u r o o s e s t o r e v e a l t h e p r e s e n c e of c h o l i n e s t e r a s e i n h i b i t o r s i n t h e whole-blood
and plasma.
MATERIALS AND METHODS Employees from f o u r s e c t i o n s of t h e T r o p i c a l P e s t i c i d e s Research I n s t i t u t e , Arusha, ( A g r i c u l t u r a l Entomology, P h y s i c s , Botany and A d m i n i s t r a t i o n ) and employees from two s e c t i o n s of Lyamungu A g r i c u l t u r a l R e s e a r c h I n s t i t u t e , Moshi ( A d m i n i s t r a t i o n and A g r i c u l t u r a l Entomology) v o l u n t e e r e d t o p a r t i c i p a t e i n t h i s e x p e r i m e n t . The A d m i n i s t r a t i v e p e r s o n n e l from t h e two I n s t i t u t i o n s s e r v e d
as t h e c o n t r o l group of t h e i r r e s p e c t i v e I n s t i t u t i o n w h i l e t h o s e who mix and s p r a y p e s t i c i d e s i n t h e two I n s t i t u t i o n s were i n t h e e x p e r i m e n t a l group. A t t h e time t h i s experiment w a s c a r r i e d o u t (March and A p r i l 1977), o n l y
t h e A g r i c u l t u r a l Entomology S e c t i o n of Lyamungu w a s a c t i v e l y engaged i n s p r a y i n g c o f f e e p l a n t s u s i n g a m i x t u r e of f e n t h i o n , carbendazim and e n d o s u l f a n . During t h e p r e c e d i n g two months, however, TPRI S e c t i o n s had h a n d l e d t h e compounds shown i n T a b l e I.
TABLE I Chemicals h a n d l e d a t TPRI s-ection
chemicals
A g r i c u l t u r a l Entomology Botany Physics
The whole-blood
chlorpyrifos, dimethoate, fenthion, t r i c h l o r p h o n , methomyl, d i c h l o r v o s , c a r b o f u r a n DNOC, 2,4-D, a t r a z i n e , oxadiazon dichlorvos
c h o l i n e s t e r a s e l e v e l s were determined u s i n g t h e t i n t o m e t r i c
method. T h i s i s a f i e l d method developed and d e s c r i b e d by Edson ( r e f . 2 ) . The plasma c h o l i n e s t e r a s e l e v e l s were determined i n t h e l a b o r a t o r y s p e c t r o p h o t o m e t r i c a l l y u s i n g t h e method d e s c r i b e d b y Ellman e t a l . ( r e f .
3 ) . One o r two
c h o l i n e s t e r a s e d e t e r m i n a t i o n s were performed f o r e a c h c l i n i c a l l y examined person.
RESULTS I n t h e r e s u l t s shown i n Table 11, t h e whole-blood c h o l i n e s t e r a s e i s expressed a s a p e r c e n t a g e of t h e a c t i v i t y o f t h e normal pre-exposure v a l u e .
65
TABLE I T The whole-blood cholinesterase activity determined tintometrically section
date
Administration
24 March & 4 April 18 March 28 March 25 March
TPRI
19 April 6 April
Lyamungu
Botany Physics Agricultural Entomology Administration Agricultural Entomology Agricultural Entomology
institution
11
I, !I
,,
19 April
t,
+_
S.D.
(n)
95.8
+_
9.4
(19)
93.5 93.1 94.0
+_
+ -
8.5 6.6 9.9
( 7) ( 9)
mean Z
+_
(16)
94.8 94.8
+_ +_
7.1 8.2
(12) (27)
91.2
+_
7.6
(29)
S.D. - Standard deviation (n) - No of individuals The plasma cholinesterase activity (Table 111) is expressed in the kinetic units per litre (ku/l), using butyrylthiocholine at 25OC and at a pH of 7.7. The normal range is 3.0-8.0 ku/l. TABLE 111 The plasma cholinesterase activity determined by Ellman's SDeCtrODhOtOmetriC method institution
mean ku/1
+
S.D.
(n)
29 March & 4 Anril 18 March 28 March 25 March
TPRI
4.34
2
1.94
(17)
4.10 4.37*
z2
0.75 1.13
( 7) ( 9)
0.98
(14)
19 April 6 April
Lyamungu
0.75 1.14
(10)
1.02
(22)
section
date
Administration Botany Physics Agricultural Entomology Administration Agricultural Ent om0 logy Agricultural Entomology
19 April
1
,I 11
$1
11
* Statistically significant at the 0.025
2.94
2
3.77 2.80*
+
3.08
(24)
orobability levei
DISCUS SION Our results show a statistically significant reduction of the olasma cholinesterase enzyme at the 0 , 0 2 5 mobability level (Table 111) but no significant reduction in the concentration of the whole-blood cholinesterase in all persons examined (Table 11). The inconsistency of the results shown by the two methods suggest that Ellman's soectroohotometric method enablesthe detection of a slight but significant reduction of the plasma enzyme whereas by using the
tintometric method, Dlasma and erythrocyte cholinesterase activities are not
66 determined s e p a r a t e l y . It should be mentioned t h a t some of t h e mixers and spraymen we examined from
t h e two I n s t i t u t i o n s have been applying t h e s e chemicals f o r many y e a r s w i t h o u t t h e use of any a p p r o p r i a t e p r o t e c t i v e c l o t h i n g and w i t h o u t any s p e c i a l c l e a n s i n g r o u t i n e a f t e r a d a y ' s work. The s i g n i f i c a n c e of t b i s type of working h a b i t t o t h e d e p r e s s i o n of blood o r plasma c h o l i n e s t e r a s e enzyme i s u n c e r t a i n . S i n c e t h e r e h a s been l i t t l e i n f o r m a t i o n published on t h e e f f e c t s of continuous exposure of organophosphorus and carbamate p e s t i c i d e s on t h e c h o l i n e s t e r a s e l e v e l s i n humans i n t h e t r o o i c s , we f e e l t h a t more d a t a w i l l be needed b e f o r e any c o n c l u s i o n i s reached on t h i s s u b j e c t .
On t h e r e a c t i v a t i o n of t h e c h o l i n e s t e r a s e enzyme a f t e r i n h i b i t i o n by t h e s e p e s t i c i d e s , however, t h e r e have been r e p o r t s t h a t a comDlete r e v e r s a l of t h e c h o l i n e s t e r a s e enzyme i n h i b i t i o n by organophosphorus o r carbamate i n s e c t i c i d e s does occur by t h e h y d r o l y s i s of t h e phosphorylated o r carbamylated enzyme a t d i f f e r e n t r a t e s depending upon t h e physiochemical p r o p e r t i e s of t h e i n h i b i t o r (refs. l,4). ACKNOWLEDGEMENT
We wish t o thank D r . Hamon, D r . Vandekar and D r . Copplestone of WHO Geneva, S w i t z e r l a n d , f o r purchasing t h e c h o l i n e s t e r a s e t e s t k i t used i n t h i s experiment, and t h e D i r e c t o r s , T r o p i c a l P e s t i c i d e s Research I n s t i t u t e , Arusha and Lyamungu A g r i c u l t u r a l Research I n s t i t u t e , Moshi f o r making i t p o s s i b l e t o perform t h i s experiment. The t e c h n i c a l a s s i s t a n c e of M r . G.C.G.
S e b i k a l i and Miss A. Tarimo
i s g r a t e f u l l y acknowledged. We a r e a l s o i n d e b t e d t o J . Bujulu, R. Lubega and W.
I s h a r a z a f o r t h e i r c r i t i c a l review of t h e manuscript.
REFERENCES C a s a r r e t and J . Doull, Toxicology, The Basic Science of Poison, Macmillan p u b l i s h i n g Co., New York, N . Y . , 1975 p. 425. 2 E.F. Edson, World Crops, 10 (1958)' 49. 3 G.L. Ellman, K.D. Courtney, V . Andreas J r . , and R.M. F e a t h e r s t o n e , Bioch. Pharmacol., 1 (1961) 88. 4 E. Reiner, B u l l . WHO 44 (1971) 109-112. 1 L.J.