Acute and sublethal effects of two insecticides on earthworms (Lumbricus terrestris L.) under laboratory conditions

Earthworms (Lumbricus terrestris L.) were exposed to commercial formulations of endosulfan and aldicarb for 2, 7, and 15 days, and the LC(10), LC(25), and LC(50) were determined. Worms were then exposed to LC(10), LC(25), and LC(50) concentrations of endosulfan and LC(10) and LC(25) concentrations of aldicarb. The growth rate and total protein content were determined and related to endosulfan and aldicarb residues in soil and earthworms. Aldicarb was more toxic than endosulfan under the experimental conditions. The residues of endosulfan and aldicarb caused a significant reduction in the growth rate and total protein content of earthworms. The residues of endosulfan and aldicarb were monitored in soil and earthworms after 2, 7, and 15 days of exposure. The residues remaining in the soil after the experiments ranged between 37.75% and 68.54% of the applied concentration for endosulfan and between 10.13% and 67.71% of the applied concentration for aldicarb. Small amounts of both insecticides were detected in worms, and accumulation was more important for endosulfan. This study proposes the use of growth rate and total protein content as biomarkers for contamination by endosulfan and aldicarb.

Gender differences in the effect of salinity on aldicarb uptake, elimination, and in vitro metabolism in Japanese medaka, Oryzias latipes

Toxicity studies have shown that salinity enhances the toxicity of aldicarb to female Japanese medaka. Although previous studies indicated that biotransformation may be important in these effects, other dispositional factors may play a role in this scenario. Male and female medaka were separately acclimated to three salinity regimens: 1.5, 12, and 20 parts per thousand (per thousand) for 2 weeks. The fish were then aqueously exposed to 96 h LC(20) of [(14)C]aldicarb for 24 h. [(14)C]aldicarb equivalents (aldicarb and its metabolites) were measured in whole-fish homogenates of half the fish. The other half of the population was transferred to clean water for 48 h. During this 48 h period, fish were removed and whole animal homogenates were measured radiometrically at 0, 2, 4, 8, 12, and 24 h time points. Salinity did not have an effect on the uptake of aldicarb in either male or female medaka. Elimination data showed that elimination of [(14)C]aldicarb equivalents was biphasic. Salinity did not have an effect on the elimination half life in either males or females. In vitro metabolism using gill and liver microsomes from fish acclimated to three salinity regimens showed that aldicarb sulfoxide production by male gill microsomes increased 6-fold by salinity compared to a 9-fold increase in female gills. In conclusion, the increased sensitivity of female medaka to salinity enhanced toxicity seems to be caused by a higher metabolic activation of aldicarb to the sulfoxide compared to the males. This study supports the hypothesis that the differential expression and regulation of FMOs is an important factor in determining the sensitivity of euryhaline fish to aldicarb, especially at high salinity regimens.

The oxidative metabolism of aldicarb in pigs: in vivo-in vitro comparison

Aldicarb was administered (1 mg/kg b.w.) to four female pigs and the kinetics of its major oxidized metabolites (sulfoxide and sulfone) was followed for 6 hours. The in vitro transformations of the carbamate pesticide into these two still active metabolites were also investigated in hepatocytes and in microsomes from pig livers. In all cases, aldicarb was quickly oxidized to the sulfoxide (major metabolite) and only a minor quantity of sulfone was produced. The in vivo toxic symptomatology was related to the peak serum concentration of sulfoxide, suggesting that this metabolite is principally responsible for the aldicarb toxicity. Selective in vitro inhibition of flavin-containing and cytochrome P-450 monooxygenases confirmed that the former enzymes catalyze mainly sulfoxide production whereas the latter that of sulfone.

Repeated measurements of aldicarb in blood and urine in a case of nonfatal poisoning

A nonfatal case of poisoning involving aldicarb, an extremely toxic carbamate pesticide, is presented. A 39-year-old female ingested an unknown amount of aldicarb, together with alprazolam and sertraline. On admission to ICU (T0), she displayed marked cholinergic symptoms and a deep coma. The patient was given pralidoxime and atropine. Her condition gradually improved on days 2 and 3 and she was discharged at T0+80 h. Aldicarb was assayed by high-performance liquid chromatography on 21 blood and 8 urine samples successively taken during hospitalization. At the same time, serum pseudocholinesterase activity was followed on 21 successive samples. Blood aldicarb level was 3.11 microg/mL at T0 and peaked at T0+3.5 h (3.22 microg/mL), then followed a two-slope decay with a terminal half-life of ca. 20 h. Aldicarb was detected in all urine samples (peak level: 6.95 microg/mL at T0+31.5 h) and was still present at the time of discharge. Serum pseudo-cholinesterase activity remained low (< or = 10% of normal) until the 30th hour then rapidly increased and returned to normal after the 60th hour. The patient's clinical picture closely followed blood aldicarb levels and serum pseudo-cholinesterase activities. To our knowledge, this is the first report of an aldicarb poisoning documented by repeated measurements of the drug in the intoxicated person.

Effect of culture acclimation on the kinetics of aldicarb insecticide degradation under methanogenic conditions

This study reports on the kinetics of aldicarb transformation under methanogenic conditions using batch reactors containing acclimated and unacclimated cultures under controlled conditions. Culture acclimation was accomplished by exposing anaerobic microorganisms maintained in a semi-batch reactor to low concentrations of aldicarb. Results of the kinetic studies showed that in an anaerobic system aldicarb is converted to aldicarb nitrile by the hydrolytic pathway. Analysis of the hydrolysis/dehydration rate constants showed that anaerobic cultures enhanced the rate of conversion of aldicarb by 4-fold for acclimated cultures and by 2-fold for unacclimated cultures compared to the rate of abiotic hydrolysis (p < 0.05). Only the acclimated cultures were able to further mineralize the reaction intermediate aldicarb nitrile. Michaelis-Menten and Monod kinetics adequately defined the aldicarb nitrile degradation.

In vivo acetylcholinesterase inhibition, metabolism, and toxicokinetics of aldicarb in channel catfish: role of biotransformation in acute toxicity

The carbamate pesticide, aldicarb, demonstrates significant acute toxicity in mammals, birds, and fish through the inhibition of acetylcholinesterase (AChE), and may present high potential for exposure of aquatic organisms during periods of runoff. Toxicity studies have shown that channel catfish are less sensitive to the acute toxic effects of aldicarb than are rainbow trout or bluegill. An earlier in vitro study suggests that the aldicarb resistance in catfish may be related to a low level of bioactivation to the potent aldicarb sulfoxide. The current study examines the toxicity, AChE inhibition, plasma kinetics, and in vivo metabolism of aldicarb in channel catfish. A 48-h LC50 of 9.7 mg/l was determined for juvenile channel catfish. Mortality was accompanied by dramatic loss of brain AChE. Further characterization of tissue-level effects suggests that muscle AChE plays a causal role in mortality. Aldicarb was metabolized in channel catfish to aldicarb sulfoxide, along with the formation of minor hydrolytic products. The toxicokinetics of aldicarb in catfish are bi-compartmental with rapid elimination (t1/2 = 1.9 h). Plasma AChE was inhibited in a pattern similar to that of the elimination of total aldicarb-derived compounds. A comparison of aldicarb uptake between catfish and rainbow trout showed no difference in compound absorbed in 24 h. The pattern of in vivo metabolism, however, was quite different between these species. Rainbow trout produce significantly more hydrolytic derivatives and have a 3-fold higher aldicarb sulfoxide to aldicarb ratio at 3 h. These data give strength to the hypothesis that a slower rate of bioactivation in the catfish (vs. rainbow trout) is acting as a protective mechanism against the acute toxicity of aldicarb.

In vitro sulfoxidation of aldicarb by hepatic microsomes of channel catfish, Ictalurus punctatus

The carbamate pesticide, aldicarb, demonstrates significant acute toxicity in mammals, birds, and fish, and is readily biotransformed by most organisms studied. Metabolic products of aldicarb include the more toxic sulfoxide and the less toxic sulfone as two of the major products. Both the cytochrome P450 (CYP) and the flavin monooxygenase systems (FMO) are involved in this process. This study examined the capacities of liver microsomes of male channel catfish (Ictalurus punctatus), which lack FMO, to biotransform aldicarb in vitro. In addition, the acetylcholinesterase inhibitory potencies of aldicarb and its sulfoxide and sulfone derivatives were determined. For metabolism studies, incubations of [14C]-aldicarb (0.1mM) were carried out for up to 15-90 min using 1.0 mg/mL of hepatic microsomal protein. Total NADPH- dependent biotransformation was low (< 3.0% conversion to polar metabolites), and was inhibited by carbon monoxide. The only metabolite detected was aldicarb sulfoxide (Kmapp = 53.8 +/- 25.3 microM; Vmaxapp = 0.040 +/- 0.007 nmol/min/mg). Treatment of fish with the CYP modulators beta-naphthoflavone (BNF, 50 mg/kg) and ethanol (EtOH, 1.0% aqueous) had no effect on sulfoxide production. No correlation existed between CYP isoform expression (determined by western blot) and aldicarb sulfoxidation rates, suggesting the involvement of an unmeasured CYP isoform or involvement of several isoforms with low specificity. This study indicates that a low rate of bioactivation of aldicarb to aldicarb sulfoxide may be responsible for the resistance of channel catfish to aldicarb toxicity relative to that of other piscine species.

Determination of the rate of aldicarb sulphoxidation in rat liver, kidney and lung microsomes

1. The rate of sulphoxidation of aldicarb (2-methyl-2-(methylthio) propanal O-[(methylamino) carbonyl oxime], Temik) in rat hepatic, renal and pulmonary microsomes was determined by quantitating the levels of aldicarb sulphoxide and aldicarb sulphone produced during incubations. Under in vitro experimental conditions used in the present study, aldicarb sulphoxide was the only metabolite produced, and further metabolism of aldicarb sulphoxide to aldicarb sulphone was negligible. 2. The average maximal velocity (mumol/min/mg protein) for the sulphoxidation of aldicarb, based on measurements of product formation, in liver, kidney and lung microsomes was 5.41, 39.51 and 2.45 respectively. The corresponding values for the Michaelis constant (microM) were 184, 1050 and 188 respectively. 3. These results imply that under in vivo conditions (1) aldicarb sulphoxidation is not likely to be saturable even at lethal doses in the rat, and (2) aldicarb clearance in rat liver and kidney will be limited by the rate of blood flow and not metabolizing enzyme levels.

Use of aquatic organisms as models to determine the in vivo contribution of flavin-containing monooxygenases in xenobiotic biotransformation

In an attempt to understand the evolution and role of flavin-containing monooxygenases (FMOs) in xenobiotic biotransformation by aquatic organisms, a survey of hepatic FMO activity (N,N-dimethylaniline N-oxidase and thiourea oxidase) was performed in one brackish water fish and 17 species of freshwater fish, one of which was anadromous. Only hepatic microsomes from the brackish water medaka (Oryzia latipes), the freshwater centrarid Lepomis macrochirus, and the anadromous rainbow trout (Oncorhynchus mykiss) consistently demonstrated FMO activity. Previous studies in trout have shown that the carbarmate insecticide, aldicarb, is bioactivated through an FMO-catalyzed S-oxidation. The toxicity of aldicarb was examined in O. mykiss and one of the species that did not show measurable FMO activity or protein, the channel catfish (Ictalurus punctatus). Rainbow trout were approximately 100 times more sensitive to aldicarb toxicity compared with channel catfish after a 96-hour waterborne exposure or 24 hours following intraperitoneal injection. However, rainbow trout were only 10 times more sensitive to aldicarb S-oxide, the bioactivated metabolite, than catfish 24 hours following intraperitoneal injection. Elimination profiles of injected aldicarb in both species fit a two-compartment model, but half-lives were significantly different between each species. Aldicarb and metabolites were rapidly cleared from trout (respective alpha and beta half-lives being 3 and 28 hr), while half-lives in catfish were significantly longer (alpha and beta half-lives being 16 and 140 hr). The major metabolite from catfish after 24 hours was aldicarb sulfone, which was 9.3% of the total dose. In trout, aldicarb sulfoxide was the major metabolite (7.6% of total dose) without any measurable sulfone. Because cytochrome P450 monooxygenases also perform the S-oxidation of aldicarb and differences in aldicarb disposition exist, future experiments will attempt to transfect catfish with rainbow trout FMO cDNA in order to determine the role of FMOs in aldicarb biotransformation and toxicity.

In vitro comparison of aldicarb oxidation in various food-producing animal species

Aldicarb (ALD) metabolism was studied in vitro using hepatic microsomes from chickens, rabbits, sheep and pigs. The microsomal activities of mono-ooxygenase enzymes (flavin-containing and cytochrome P-450-dependent mixed function oxygenases) were compared by measuring the quantity of the 2 oxidized metabolites, ALD sulfoxide and ALD sulfone, produced during 60 min of incubation. Pig microsomes produced the greatest quantity of ALD sulfoxide and the lowest quantity of ALD sulfone; the latter being produced in greater quantities in sheep than in chickens and rabbits. Aldicarb and its metabolites were degraded fastest in rabbits, probably by hydrolytic reactions. These in vitro results, which are consistent both with the levels of cytochrome P450 found in hepatic microsomes and previous in vivo data on ALD kinetics in pigs, rabbits and chickens, indicate that preliminary in vitro studies can limit the necessary use of animals for drug metabolism experiments.

Development and optimization of reactivation techniques for carbamate-inhibited brain and plasma cholinesterases in birds and mammals

Two biochemical assays were developed which promote and measure the induced reactivation of carbamate-inhibited cholinesterases in avian and mammalian brain and plasma samples. The effects of inhibitor concentration, temperature, and the extent of dilution on the achievement of a steady state equilibrium and the subsequent level and rate of recovery of brain cholinesterase activity were investigated. A similar procedure for reactivation of carbamate-inhibited plasma cholinesterase activity involved the removal of excess carbamate from a small sample volume (< 400 microliters). Both methods begin by measuring cholinesterase activity immediately following dilution and involve an incubation period during which conditions for spontaneous reactivation of the inhibited enzymes are maximized. Both assays are suitable for large-scale, rapid use and appear able to restore inhibited cholinesterase activity to levels closely approximating that of control values for each species tested. These methods will not only maximize the usefulness of cholinesterases in monitoring carbamate pesticide exposure but should prove to be extremely useful tools in the forensic assessment of carbamate exposure in human and wildlife pesticide incidents.

The distribution, elimination, and in vivo biotransformation of aldicarb in the rainbow trout (Oncorhynchus mykiss)

The distribution and elimination of [14C]aldicarb, administered orally and by intraperitoneal (ip) injection, was examined in the rainbow trout (Oncorhynchus mykiss). Tissue residues were determined by monitoring radioactivity at various time periods up to 96 hr in trout administered [14C]aldicarb orally. Periodic water samples and a single tissue residue radioactivity level were obtained after 24 hr in free swimming and spinally transected fish which received [14C]aldicarb via intraperitoneal injection. Aldicarb appears to be absorbed rapidly (99% within 3 hr) and distributed to all tissues. Elimination profiles from both dosage groups demonstrate a rapid alpha phase (oral 24 hr; ip 3 hr) probably due to branchial excretion (96% after ip injection) followed by a slower beta phase (oral 107 hr; ip 28 hr) suggesting a deeper compartment such as muscle. [14C]Aldicarb and/or its metabolites were slowly being transported to the bile after 24 hr. The in vivo biotransformation of [14C]aldicarb was examined in spinally transected trout 24 hr after ip injection. The major metabolite found was aldicarb sulfoxide (7.6%) along with lesser amounts of aldicarb oxime (5.4%).

Role of flavin-containing monooxygenase in the in vitro biotransformation of aldicarb in rainbow trout (Oncorhynchus mykiss)

1. The in vitro biotransformation of 14C-aldicarb was examined in liver, kidney, and gill microsomes from the rainbow trout (Oncorhynchus mykiss). 2. In all tissues the major metabolite was aldicarb sulphoxide. Addition of the cytochrome P-450 inhibitor, N-benzylimidazole, failed to alter significantly aldicarb sulphoxide levels, while co-incubation with the flavin-containing monooxygenase substrates, N,N-dimethylaniline or methimazole, caused significant decreases in sulphoxide formation in liver and gill microsomes. 3. Aldicarb sulphoxide formation was optimal at pH 8.0, and had Michaelis-Menten kinetics with an apparent Km of 46.7 microM and a Vmax of 0.216 nmol/min per mg. 4. Aldicarb sulphoxide formation was competitively inhibited by co-incubation with N,N-dimethylaniline in liver microsomes. These data indicate that flavin-containing monooxygenase plays an important role in the in vitro biotransformation of aldicarb in rainbow trout.

Aldicarb toxicosis in a dairy herd

Aldicarb, an extremely toxic carbamate, caused sudden death of several lactating Holstein cows. Confirmation of this toxic agent as the cause of death was hindered by its rapid breakdown in biological tissue. Therefore, aldicarb was not detected in rumen contents of some of the dead cows, and brain acetylcholinesterase values were essentially normal. The analyses were conducted 2 to 4 days after death of the cows. Rapid testing of tissue samples is necessary if a carbamate insecticide is suspected.