I N S E C T I C I D E TOXICOLOGY
Mammalian Toxicity of 1-Naphthyl-Nmethylcarbamate (Sevin Insecticide)
C. P. CARPENTER, C. S. WEIL, P. E. PALM, M. W. WOODSIDE, J. H. NAlR 111, and H. F. SMYTH, Jr. Mellon Institute, Pittsburgh, Pa.
The apparent effectiveness of 1 -naphthyl-N-methylcarbamate against a wide variety of insects encouraged the study of its mammalian toxicology. Information is presented on metabolism, cholinesterase inhibition, alleviation of symptoms with atropine sulfate and their aggravation by pyridine-2-aldoxime methiodide, and the absence of neuromuscular degenerative potential, carcinogenic activity, and sensitizing propensity. The responses of several species to single doses by oral, parenteral, percutaneous, and respiratory routes are presented. A 2-year rat feeding study demonstrates that 200 p.p.m. in the total dietary is tolerated by this species without significant deviation from suitable controls, while dogs tolerate 400 p.p.m. in their diet on the same basis.
T
HE INSECTICIDE 1-naphthy1-'trmethylcarbamate (Crag Sevin, Union Carbide Corp.) is of particular interest because it is a cholinesterase inhibitor, completely free of phosphorus, but possessing greater anticholinesterase activity against insects than against mammals (70, 77, 74). Sevin is a wide spectrum insecticide effective against insects attacking fruit trees, bean and cotton crop insect pests, and forest insects. Performance results give promise of wide use in substantial quantities.
Structural formula of Sevin : 0- CO-NH-CH,
Average analysis batches of Sevin:
of
commercial
1-Naphthyl-N-methylcarbarnate
1-Naphthol Bis(naphthy1carbonate) Water
98.0%
0.7% 1. O %
0.3%
The technical material is a slightly colored, nearly odorless crystalline solid. Its melting point is 142' C., vapor pressure is less than 0.005 m m . of Hg a t 26' C., and density is 1.232 a t 20'/20" C. Solubility ranges from 40% in organic solvents to approximately 0.01% in water. I t is sparingly soluble in hydrocarbons, somewhat more soluble in chlorinated hydrocarbons and alcohols, moderately soluble in ketones, and quite soluble in dimethylformamide, pyridine, die thanolamine, and dimethylsulfoxide. Methoxy triethylene glycol is a useful solvent for parenteral studies, as i t will carry 20% of Sevin. Unless otherwise specified, the term Sevin refers to the technical grade.
30
Metabolism
22.4 i. 4.4. Expressed in terms of the I-naphthol content of Sevin, the percentage would be 31.3 + 6.1. The 1naphthol was excreted almost completely in the conjugated form possibly as the glucuronide. The observation that lethan one third of the 1-naphthol content of Sevin was found in the urine is substantiated by work of others (2, 3, 5 ) involving the administration of 1naphthol directly to experimental animals. The fate of the hydrolyzed carbamate amine moiety is not known. No analytical procedure was found that would distinguish methylamine from other amines present, or that would indicate its particular metabolic fate.
T o demonstrate the hypothesis that a substantial portion of a n oral dose of Sevin would appear in the urine as free or conjugated 1-naphthol, a recovery experiment was performed. Six groups of three rats each were dosed with 0.015 gram of Sevin and urinary naphthol excretion followed 4 days after dosing. Control urine was collected during 48 hours prior to dosing. The collections from each cage were pooled to provide three sets of six samples representing 48 hours after dosing. The naphthol analyses were made on 0.1-ml. portions of urine diluted to 1.0 ml. Conjugated naphthols were hydrolyzed by heating each sample with 0.1 ml. of ION hydrochloric acid a t Cholinesterase lnhibition 100" C. for 1 hour. Neutralization of the A variety of studies was undertaken to hydrolyzates was made with the dropassess the extent of cholinesterase inwise addition of 0.5 ml. of 2 M h'a&O,. hibition by Sevin in mammals. The One milliliter of 0.1MNa2Bd07 and 10.0 work covered both in vitro and in vivo ml. of 1-butanol were added. The color experiments on several species. In was developed by the addition of 0.2 ml. of .4~,2,6-trichloroquinoneimine some of the work parathion ( 0 , O diethyl 0-b-nitrophenyl phosphorothi(0.5% in 95% ethyl alcohol) to each oate), which is representative of the tube and allowing it to stand 30 minorganic phosphate-type cholinesteraseutes. The butyl alcohol extracts were inhibiting insecticide, was used for separated by centrifugation for 15 mincomparison with Sevin. utes and transferred to cuvettes. ColorAfter Parenteral Doses to Dogs. imetric readings were made a t 620 The initial in vivo studies involved a mM against a water blank carried determination of the inhibitory effects throughout the procedure. of Sevin. Two groups of three beagleThere was a slight rise in free and a type dogs each were injected intradefinite rise in conjugated naphthol in venously with 10 and 15 mg. per kg., 48 hours following doses of Sevin. Conrespectively, of body weight of Sevin centrations fell rapidly to values near as an 8% solution in 950/, ethyl alcohol. or below the controls after this period. Ethyl alcohol is a notoriously poor The excess in the 24- to 48-hour convehicle for intravenous use because it centration over the control excretion damages blood vessels and denatures has been calculated in terms of the inprotein, but as propylene glycol initial 0.015 gram per rat dose. The creased plasma and erythrocyte chomean percentage and the standard error linesterase levels and ethyl alcohol did of this mean for Sevin recovered was
AGRICULTURAL AND FOOD CHEMISTRY
not, the latter was used. Heparinized syringes were used to collect blood samples taken several days prior to dosing and a t intervals of 0.5 to 1.0, 2.0, 5.0, and 23 hours after the Sevin doses. These blood samples were immediately centrifuged to separate plasma and erythrocytes and individual determinations of the inhibition of cholinesterase were made according to the method of Frawley et al. ( 9 ) . The values expressed in this paper, in terms of percentage inhibition, were measured after a 2-hour incubation of plasma samples and 0.17M substrate while a 1-hour period was used with erythrocytes and 0.1 1M substrate. Varying the quantities of substrate from ' / ? to 4 times the amount used for the routine determinations did not appreciably alter the apparent percentage inhibition a t the 2- and I-hour time intervals. In agreement with Burgen ( 4 ) , percentage inhibitions with both plasma and erythrocytes changed markedly within the first 30 minutes of the in vitro incubation, but soon thereafter equilibrium was reached. Burgen points out that readings made after equilibrium may underestimate grossly the extent of cholinesterase inhibition, but results obtained prior to 30 minutes are influenced in a complex manner by both the inhibitor and substrate concentration making the quantitative significance doubtful. Because of these inherent difficulties it was decided arbitrarily to make the measurements after equilibrium was attained. Admittedly, the values obtained are not a n exact measure of cholinesterase activity but they do present the relative picture of the effect of the several routes of administration. Table I presents the results of intravenous dosing. The values are given as mean percentage of the cholinesterase activity of each subject animal prior to dosing. Intravenous administration of ethyl alcohol a t levels of 0.125 or 0.1875 ml. per kg. had no measurable effect on the plasma or erythrocyte cholinesterase values. These dosage levels approximated the amount of ethyl alcohol given when the Sevin was administered as a n 8% solution in ethyl alcohol. No significant effect was found on erythrocyte or plasma cholinesterase after single dosages of 10 or 1 5 mg. of Sevin per kg. of body weight had been injected. Twenty days later one of these dogs was started on daily repeated intravenous doses of variable size and before all accessible vessels were sclerosed by the ethyl alcohol a total of 88.3 mg. per kg. of Sevin in 11 doses was injected. Typical symptoms of cholinesterase inhibition were produced by dosages of 10 and 15 mg. per kg., but only slight reactions by 5 mg. per kg. The greatest depression over predose control values
of plasma and erythrocyte cholinesterase occurred after the first four injections consisting of 9.3, 15.0, 6.7: and 15.0 mg. per kg., respectively. O n the fifth day the plasma value was depressed 25% and the erythrocyte 40%; on the sixth day, after a n additional 5 mg. per kg. dosage, there was a 17% depression of plasma but the erythrocyte cholinesterase level was normal. Urinary 1naphthol excretion reached a peak on the morning of the third day. I t was variable from that time on until the dog died after a rapid intravenous dose by jugular vein following anesthetization with pentobarbital sodium. The jugular vein was used because it was no longer possible to enter the sclerosed leg veins. I n the depressed state of surgical anesthesia the additional shock of intravenously administered alcoholic solution of Sevin probably caused the animal to expire. Artificial respiration might have saved this animal had it been given. I n our opinion Sevin alone was not responsible for this death. Pathological examination of the internal organs established the fact that no tissue damage had occurred. Cholinesterase determinations on brain tissue from the circle of Willis showed no abnormal value when compared with three parallel determinations on dogs that had never been dosed with a chemical, but had served as controls on another study. Two more dogs were then started on intravenous injections of 8% Sevin solution in 95% ethyl alcohol. The dosage schedule, following a week of collecting control data, was 10 mg. per kg. per day. This regimen was followed until six doses had been given and all superficial vessels had become inflamed or sclerosed. Sevin was then ground in lard melting a t or below 37" C. (body temperature) and injected subcutaneously into the scapular area, a t a dosage of SO mg. per kg. per week, in one injection on each subsequent Monday morning. A total of 60 mg. per
Table 1.
kg. of Sevin in ethyl alcohol was given intravenously and 640 mg. per kg. of Sevin subcutaneously in lard, which is a total dosage of 700 mg. per kg. An unsuccessful attempt was made to collect all urine excreted so that 1-naphthol excretion could be followed. This failed because the male dog was notorious for voiding a t each injection and frequently when handled otherwise. The female was not so excitable and fairly consistent trends were established for her. Plasma and erythrocyte cholinesterase levels and blood counts were followed daily the first week, every other day the second week. and twice weekly thereafter. Means, standard deviations, and 95% fiducial limits were calculated for the predose values of each of these criteria. Plasma cholinesterase values were below the lower fiducial limit range for the female dog on only four of 27 occasions. T h e inhibition was never more than 20 to 30%. These values occurred 48 hours after the first, second, and fourth subcutaneous injection and 24 hours after the third. The male dog had only one correspondingly low value, 55% inhibition, 48 hours after the third subcutaneous injection. Four other values were above the upper fiducial limit by as much as 20%. The importance of the 55% inhibition is tempered when offset by the four values which exceeded the upper limits by as much as 20%. Neither dog showed any values beyond the fiducial limits as regards erythrocyte cholinesterase, which was determined on these same blood samples. Blood urea nitrogen was below the lower fiducial limit for the female dog on three separate occasions about a month apart with normal values intervening. They are not. therefore, interpreted as indicating any significant trend. Total 1-naphthol in the urine of the female dog exceeded the upper fiducial
Mean and Range of Percentage of Predose Values
Intravenous administration of ethyl alcohol or Sevin in ethyl alcohol to groups of 3 dogs each Hours, after Dose
0.7 2.5 5.0 23.0 47.0 95.0
Plasma Cholinesferose
0.725
101 (100 to 101) 99 (96 to 102) 102 (100 to 103) 99 ( 96 to 102) 104 (101 to 106) 100 ( 99 to 101) 10.0
0 . 5 to 1 . 0 2.0 5.0 23.0
82 ( 74 to 86) 87 ( 77 to 99) 93 ( 82 to 98) 95 ( 90 to 102)
Erythrocyte Cholinesterase
95% Ethyl Alcohol, MI./Kg. 0.7875 0.125
99 ( 98 ( 96 ( 95 (
98 to 96 to 93 to 94 to 100 (100 to 98 ( 95 to
100) 100) 98) 96) 101) 101)
103 ( 95 ( 100 ( 99 ( 106 ( 105 (
0.1875
98 to 106)
92 to 94 to 98 to 94 to 98 to
99) 107) 100)
113) 111)
97 ( 95 ( 94 ( 96 ( 100 ( 98 (
8% S e h i n Ethyl Alcohol, M g . / K g . o f Sevin 75.0 70.0
96 ( 87 ( 97 ( 98 (
90 to 102)
78 to 98) 87 to 104) 91 to 103)
88 ( 78 to 111 (105 to 112 (107 to 117 (108 to
100) 120) 116) 127)
V O L . 9, NO. 1 , J A N . - F E B .
91 to 91 to 84 to 82 to 74 to 82 to
100) 104) 106) 110) 120) 114)
75.0
97 ( 80 to 102 ( 81 to 104 (100 to 113 (105 to
1961
31
109) 120) 109) 120)
limit 24 to 48 hours after the Monday morning 50-mg.-per-kg. subcutaneous injection of Sevin in lard in 9 of the 13 weeks it was injected. The urine collection from the male was so erratic that the highs cannot be documented, but the same pattern of increased 1naphthol in urine 24 to 48 hours after the injection was found. It is unlikely that Sevin had any marked effect upon the blood picture of these dogs. Both were troubled with subcutaneous abscesses a t the site of these injections. This was reflected in leucocyte counts that were elevated to over 26,000 cells per cubic mm. for the female and 21,000 for the male, but hematocrits, reticulocyte enumerations, and complete differential white blood cell counts fell within the predose fiducial limits. The fact that the female of this last pair received 12.6 grams of Sevin by injection over a 3-month period without any serious effect on cholinesterase levels in blood or in plasma and without weight loss is convincing evidence that repeated dosing with Sevin is well tolerated in the dog. After Single Peroral Doses of Sevin and Parathion. The relative inhibition of Sevin and parathion on the in vivo cholinesterase activity in plasma, erythrocytes, and brain tissue was compared. Each insecticide was administered by stomach intubation in corn oil solution to groups of seven to 10 rats at a dosage slightly above their respective LDFA’snamely, 0.56 gram per kg. of Sevin and 0.0093 gram per kg. of parathion. LDjo determinations made immediately prior to this study were 0.50 and 0.007 gram per kg. for a 5% suspension of Sevin and a 0.034% solution of parathion in corn oil. The rats were anesthetized with 0.1 ml. of pentobarbital sodium given intraperitoneally immediately prior to killing, which was done a t intervals of 0.5, 4, and 24 hours after dosing. Blood for plasma and erythrocyte cholinesterase determinations was withdrawn by heart puncture using heparin as an
anticoagulant. The rats were then decapitated and the brain was removed and divided across the arterial circlr of Willis. The anterior portion, including the optic lobes, was transferred to a small amount of distilled water, then blotted, weighed, and homogenized in 50 times its weight of water. An aliquot was analyzed for cholinesterase activity. The cholinesterase response of rats following a single dose of Sevin or parathion is summarized in Table 11. Plasma cholinesterase was not significantly depressed by these large oral doses of Sevin. O n the other hand, parathion produced a 30 and 43y0 inhibition of this nonspecific pseudocholinesterase at 4 and 24 hours after dosing. The pattern of inhibition of true cholinesterase in the cellular components of blood was different for Sevin and parathion. Sevin caused a 427, inhibition of erythrocyte cholinesterase in 0.5 hour which returned essentially to normal within 24 hours after dosing. Parathion resulted in a 13% inhibition in 0.5 hour, 45% in 4 hours, and 75% in 24 hours. Similarly. brain cholinesterase values were initially depressed about 307, by Sevin a t 0.5 hour, but were back to normal in rats that survived 24 hours after this dosage. While parathion depressed brain cholinesterase only 67, a t 0.5 hour. a mean value of 85% inhibition was measured 24 hours after dosing. Therefore, while the depression of all three cholinesterase systems was slower but definitely progressive after oral administration of parathion, no important depression of plasma cholinesterase was produced by Sevin, and only slight but significant and transitory inhibition of erythrocyte and brain cholinesterase was found. Control of Symptoms by Atropine Sulfate, Six female mongrel dogs. averaging 8 kg. in weight, were force-fed dry Sevin in gelatin capsules as follo\vs: One dog received 0.5 gram per kg.,
Table 11. Cholinesterase Response of Rats Single peroral dose of 0.56 gram/kg. of Sevin or 0.0093 gramikg. of parathion Sevin rime After Dose, Hours
Sevin-Dosed Rats Mean of Std. dev. N o . confrol
0.5 4 24
9
Erythrocyte
0.5 4 24
8 7
Brain
0.5 4 24
Cholinesferase
Plasma
32
70
Parathion-Dosed Rafs Mean of Std. No. confrol dev.
70
94.9 86.5 92.9
22.8 19.8 15.6
8 8 9
91.0 69.6 57.1
14.8 7.8 10.3
9
57.9 69.1 86.1
9 8 9
70.0 80.8 91.2
24.0 22.6 15.5 10.0 12.9 13.5
8 8 9 8 7 10
86.9 54.6 25.2 93.9 83.6 15.1
15.2 18.5 13.8 8.2 23.3 9.3
8 9
AGRICULTURAL AND FOOD CHEMISTRY
M~~~ Minus Parathion Mean
+ 3.9
f16.9 +35.8 -29.0 f14.5 +60.9 -23.9 - 2.8 f76.1
p for t Jest
0.70 0.06
