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PubMed1983

Kinetics of aqueous base and acid hydrolysis of aldicarb, aldicarb sulfoxide and aldicarb sulfone.

The kinetics of degradation of aqueous solutions of aldicarb, aldicarb sulfoxide and aldicarb sul fone by base hydrolysis were investigated. Pseudo first order rate constants of 37 micrograms/l solutions were determined at different hydroxide concentrations by acid-base titration. Second order rate constants were calculated, and it was found that aldicarb sulfone is more sensitive to hydroxide ion concentration than aldicarb sulfoxide which is more sensitive than aldicarb. Temperature effects were determined by measuring the base hydrolysis rate constant for aldicarb sulfone at 5, 15, 20, 25, 30, and 35 degrees C. An activation energy of 15.2 +/- 0.1 kcal/mole was calculated. Addition of a neutral electrolyte decreased the rate constant for base hydrolysis. Acid catalyzed hydrolysis rate constants were also measured for aldicarb sulfone, and, as expected, the reaction was much slower. The second order (reaction) rate constant for base hydrolysis of aldicarb sulfone is 40.3 (+/- 0.5) liter mole-1min-1; for acid catalyzed hydrolysis it is 7.33 (+/- 0.06) X 10(-4) liter mole-1min-1.

Aldicarb↗
PubMed2000

Determination of aldicarb, aldicarb sulfoxide and aldicarb sulfone in some fruits and vegetables using high-performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry.

An analytical method for the determination of aldicarb, and its two major metabolites, aldicarb sulfoxide and aldicarb sulfone in fruits and vegetables is described. Briefly the method consisted of the use of a methanolic extraction, liquid-liquid extraction followed by solid-phase extraction clean-up. Afterwards, the final extract is analyzed by liquid chromatography-atmospheric pressure chemical ionization mass spectrometry (LC-APCI-MS). The specific fragment ion corresponding to [M-74]+ and the protonated molecular [M+H]+ ion were used for the unequivocal determination of aldicarb and its two major metabolites. The analytical performance of the proposed method and the results achieved were compared with those obtained using the common analytical method involving LC with post-column fluorescence detection (FL). The limits of detection varied between 0.2 and 1.3 ng but under LC-FL were slightly lower than when using LC-APCI-MS. However both methods permitted one to achieve the desired sensitivity for analyzing aldicarb and its metabolites in vegetables. The method developed in this work was applied to the trace determination of aldicarb and its metabolites in crop and orange extracts.

Aldicarb↗
PubMed1981

High pressure chromatography determination of aldicarb, aldicarb sulfoxide, and aldicarb sulfone in potatoes.

An ion-suppression reverse phase high pressure liquid chromatographic method is described for the determination of aldicarb, aldicarb sulfoxide, and aldicarb sulfone in potatoes. Samples are extracted with methylene chloride and Na2SO4, evaporated to dryness, and cleaned up using Sep-Pak silica and Sep-Pak-C18 cartridges. The extract can be successfully analyzed by high pressure liquid chromatography on either a mu LiChrosorb RP-18 or mu Bondapak C18 column and quantitated using a variable wavelength ultraviolet detector set at either 220 or 247 nm. The mobile phase is acetonitrile-buffer (4 + 96) and (30 + 70), buffered to pH 7.6 and flowing at 2 mL/min. Recoveries ranged from 80 to 100%. The minimum detectable amount was 37.5 ng, which easily permitted the quantitation of 0.1 ppm aldicarb sulfone in 75 g sample. The recovery of aldicarb was low because of its rapid enzymatic oxidation to aldicarb sulfoxide and sulfone.

Aldicarb↗
PubMed1994

Determination of aldicarb, aldicarb sulfoxide and aldicarb sulfone in tobacco using high-performance liquid chromatography with dual post-column reaction and fluorescence detection.

A screening method for the determination of aldicarb (AS) and its sulfoxide (ASX) and sulfone (ASN) metabolites in tobacco at low ppm levels is described. Tobacco samples are extracted using methanol with the aid of sonication at ambient conditions. The extract is filtered and then injected into a high-performance liquid chromatograph equipped with a dual post-column reaction system and a fluorescence detector. Chromatographic separation is performed on a C18 column with a mixture of methanol-acetonitrile-water containing 0.1% of triethanolamine as the mobile phase. Triethanolamine is added to improve peak shape of AS residues and to reduce the undesired interaction between residual silanols and interferences, mainly amino acids and other amines. The average recoveries for AS residues spiked in tobacco are higher than 95% for AS, 91% for ASN and 85% for ASX at levels of 0.5-10 ppm (w/w). The detection limit is 0.5 ppm for each of the target compounds.

Aldicarb↗
PubMed2001

Nonlethal method for forensic evaluation of aldicarb exposure in wildlife.

Forensic evaluation of aldicarb exposure is difficult due to the rapid hydrolysis and oxidation of the parent compound. Oxidation products-aldicarb sulfoxide and aldicarb sulfone-are commonly analyzed, but hydrolytic products-aldicarb nitrile, aldicarb nitrile sulfoxide, aldicarb nitrile sulfone-are infrequently analyzed even though they are the primary stable products of aldicarb degradation. Nitrile analyses provide an important avenue to verify aldicarb exposure or aldicarb-induced mortality. Our aproach allows lethal and sublethal exposure assessment. Extraction of samples with acetonitrile:water is followed by chromatographic determination. Sublethal exposure assessment utilizes excreta samples, which is nonlethal and requires holding animals in captivity for 12 h or less. Sublethal exposures of northern bobwhite Colinus virginianus to aldicarb can be identified with greater than 80% confidence for 6 h after dosing. By analyzing GI tracts, lethal exposures of bobwhite to aldicarb can be identified with greater than 90% confidence for 4 days post mortem and with 75% confidence for 8 days post mortem. Sublethal exposures to aldicarb was identified in greater than 80% of Peromyscus maniculatis for 6 h after dosing. Aldicarb and its transformation products were detected for 8 days post mortem in all mice that received aldicarb doses at or above the LD50.

Aldicarb↗
PubMed1998

Potential mechanisms of the enhancement of aldicarb toxicity to Japanese medaka, Oryzias latipes, at high salinity.

In an attempt to understand underlying mechanism(s) of salinity-induced aldicarb toxicity in Japanese medaka (Oryzias latipes), aldicarb uptake, biotransformation, and its effect on acetylcholinesterase (AChE) were examined. Salinity had no effect on aldicarb uptake. However, gill microsomal flavin-containing monooxygenase (FMO) activity and a 57-kDa FMO1-like protein increased as the salinity was raised from 0.15 to 2.0%. Sulfoxidation of 14C-aldicarb by liver and gill microsomal incubations showed ninefold and 1.8-fold increases, respectively, as the salinity was raised from 0.15 to 2.0%. Formation of aldicarb sulfoxide was not affected by incubation with carbon monoxide, indicating that cytochrome P450 (CYP450) was not a primary pathway in the formation of the sulfoxide. Muscle AChE activity showed no significant relationship with salinity, although the IC50 of aldicarb to muscle AChE differed significantly between 6.21 +/- 1. 253 and 2.97 +/- 0.597 microM for 0.15 and 2.0% salinity, respectively. Aldicarb sulfoxide was 40 times more potent than aldicarb in inhibiting muscle AChE in Japanese medaka. Based on these results, we conclude that salinity-induced enhancement of aldicarb toxicity to Japanese medaka might be partly attributed to the upregulation of FMO(s), which, in turn, increase the biotransformation of aldicarb to aldicarb sulfoxide, which is a more potent inhibitor of AChE than aldicarb. In addition, salinity also seems to potentiate the anticholinesterase activity of aldicarb (the parent) through an unknown mechanism.

Acetylcholinesterase↗
PubMed1990

Aldicarb treatment inhibits the stimulatory activity of macrophages without affecting the T-cell responses in the syngeneic mixed lymphocyte reaction.

Aldicarb, a carbamate pesticide used extensively throughout the United States, has been shown in several areas to contaminate drinking water at levels exceeding 100 p.p.b. Recent studies have suggested that aldicarb at levels well below these found in drinking water may lead to alterations in mammalian health. In the present study, we investigated the possible toxic effects of aldicarb on the mammalian immune system. Specifically examined in these studies were the effects of aldicarb on syngeneic mixed lymphocyte reaction (SMLR) in which CD4+ T-helper cells (autoreactive T-cells) respond to self or syngeneic Ia molecules expressed on macrophages. The effect of aldicarb was delineated at both the responder and stimulator cell-level. When C3H mice were injected intraperitoneally with a single dose of 0.1-1000 p.p.b. of aldicarb, it was observed that there was a decrease in the stimulatory functions of macrophages, as studied by decreased capacity to stimulate normal autoreactive T-cells. Further analysis revealed that the decreased stimulatory capacity of macrophages from aldicarb-treated mice was not due to decrease in the expression of Ia antigens, since flow cytometric analysis of macrophages from aldicarb-treated mice demonstrated normal levels of Ia expression. Also, cell-mixing experiments failed to demonstrate any suppressor macrophages in aldicarb treated mice. Addition of exogenous interleukin-1, however, completely reconstituted the defective stimulatory activity of macrophages from aldicarb-treated mice. In contrast to these effects on macrophages, it was observed that in C3H mice treated intraperitoneally with single dose of 1-1000 p.p.b. of aldicarb, there was no evidence of alteration in the ability of autoreactive T-cells to respond to syngeneic Ia molecules expressed on normal macrophages. In addition, responsiveness of T-lymphocytes obtained from aldicarb-treated mice to allogeneic Ia antigens was also unaltered. These data suggested that aldicarb may selectively suppress the stimulatory activity of macrophages by inhibiting IL-1 mediated signal to the T-cells without directly affecting the T-cell functions.

Aldicarb↗
PubMed2000

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.

Acetylcholinesterase↗
PubMed2001

Effects of salinity on aldicarb toxicity in juvenile rainbow trout (Oncorhynchus mykiss) and striped bass (Morone saxatilis x chrysops).

Fluctuations in several environmental variables, such as salinity, can influence the interactions between organisms and pollutants in aquatic organisms, and, therefore, affect the toxicity of xenobiotics. In this study, after 2 species of fish, rainbow trout (Oncorhynchus mykiss) and hybrid striped bass (Morone saxatilis x chrysops) were acclimated to 4 salinity regimens of 1.5, 7, 14, and 21 ppt for 1 week and then exposed to 0.5 mg/l aldicarb. Mortality, brain, and muscle cholinesterase levels were measured after 96 h. Rates of (14)C-aldicarb sulfoxide formation were determined in kidney (trout only), liver, and gill microsomes from each species acclimated to the 4 salinity regimens. Salinity significantly enhanced aldicarb toxicity, cholinesterase inhibition, and (14)C-aldicarb sulfoxide formation in rainbow trout but not in striped bass. In vitro incubations with (14)C-aldicarb and the cytochrome P450 (CYP) inhibitor, N-benzylimidazole, did not significantly alter aldicarb sulfoxide formation in tissue microsomes from either species of fish, indicating CYP did not contribute to aldicarb sulfoxidation. Salinity increased flavin-containing monooxygenase (FMO) mRNA expression and catalytic activities in microsomes of liver, gill, and kidney of rainbow trout, which was consistent with the salinity-induced enhancement of aldicarb toxicity. Salinity did not alter FMO mRNA expression and catalytic activities in striped bass, which was also consistent with the lack of an effect of salinity on aldicarb toxicity in this species. These results suggest that salinity-mediated enhancement of aldicarb toxicity is species-dependent, and at least partially due to the salinity-related upregulation of FMOs, which, in turn, increases the bioactivation of aldicarb to aldicarb sulfoxide, which is a more potent inhibitor of cholinesterase than aldicarb.

Adrenergic alpha-Antagonists↗
PubMed1995

Microbial aldicarb transformation in aquifer, lake, and salt marsh sediments.

The microbial transformation of [N-methyl-(sup14)C]aldicarb, a carbamate pesticide, occurred in aquifer, lake, and salt marsh sediments. Microbial degradation of aldicarb took place within 21 days in aquifer sediments from sites previously exposed to aldicarb (Jamesport, Long Island, N.Y.) but did not occur in sediments which were not previously exposed (Connetquot State Park, Long Island, N.Y.). At the Jamesport sites, higher aldicarb transformation rates occurred in deep, anoxic sediments than in shallow, oxic sediments. There was a significant negative relationship (P < 0.05) between transformation rates and ambient dissolved O(inf2) levels. Aldicarb hydrolysis rates in Jamesport sediments were 10- to 1,000-fold lower than rates previously reported for soils. In addition, aldicarb degradation rates were not significantly correlated with measurements of bacterial activity and density previously determined in the same sediments. Substantially higher aldicarb degradation rates were found in anoxic lake and salt marsh than in aquifer sediments. Furthermore, we investigated the anaerobic microbial processes involved in aldicarb transformation by adding organic substrates (acetate, glucose), an alternative electron acceptor (nitrate), and microbial inhibitors (molybdate, 2-bromoethanesulfonic acid) to anoxic aquifer, lake, and salt marsh sediments. The results suggest that a methanogenic consortium was important in aldicarb transformation or in the use of aldicarb-derived products such as methylamine. In addition, microbial aldicarb transformation proceeded via different pathways under oxic and anoxic conditions. In the presence of O(inf2), aldicarb transformation was mainly via an oxidation pathway, while in the absence of O(inf2), degradation took place through a hydrolytic pathway (including the formation of methylamine precursors). Under anoxic conditions, therefore, aldicarb can be transformed by microbial consortia to yield products which can be of direct benefit to natural populations of methanogens present in sediments.

Journal Article↗
PubMed2005

Pulsed losses and degradation of aldicarb in a South Florida agricultural watershed.

The objectives of these studies were to characterize patterns of movement of aldicarb, aldicarb sulfoxide, and aldicarb sulfone from a typical canalized South Florida watershed and to evaluate aldicarb dissipation in surface water in situ within a citrus grove. Surface water samples were collected daily or every other day from the discharge point for the watershed beginning May 15, 2001, through August 15, 2002. Of 457 samples collected, aldicarb, aldicarb sulfoxide, and aldicarb sulfone were detected in 6, 1, and 13, respectively. Aldicarb was detected from February through May 2002, corresponding to the legal application season of January 1 through April 30 in Florida. Aldicarb concentrations ranged from <0.16 to 4.97 ng ml(-1). A single detection (0.99 ng ml(-1)) of aldicarb sulfoxide occurred in March 2001. The majority of aldicarb sulfone detections occurred during June and July, 2001, after the application season, and ranged from <0.22 to 0.89 ng ml(-1). The half-life for aldicarb in fortified, native surface water ranged from 1.86 to 3.64 days depending on the source of water and the presence of sediments. These results demonstrated the utility of sampling on a frequent basis (compared with monthly or quarterly) for better characterizing pesticide discharges, especially in flashy systems such as canal-drained watersheds within South Florida.

Agriculture↗
PubMed1990

Immunosuppression by aldicarb of T cell responses to antigen-specific and polyclonal stimuli results from defective IL-1 production by the macrophages.

In the present study we investigated the immunomodulatory effects of aldicarb, a carbamate pesticide, on T cells activated by a number of different ways. When C3H mice were injected intraperitoneally with a single dose of Aldicarb, 0.005-50 micrograms/kg body wt, and their spleen cells were stimulated with T cell mitogens such as concanavalin A (ConA)3 or anti-CD3 monoclonal antibodies (mAb), a decreased responsiveness was detected when compared to the control mice. Aldicarb administered at concentrations less than 0.005 microgram/kg body wt failed to cause significant immunosuppression. Interestingly, when purified T cells from immunosuppressive doses of aldicarb-treated mice were stimulated with ConA in the presence of irradiated control macrophages, the defective T cell response was no longer demonstrable. Also, purified control T cells stimulated with ConA in the presence of irradiated macrophages from aldicarb-treated mice showed decreased responsiveness. Similar observations were made using anti-CD3 mAb to activate the T cells, inasmuch as whole spleen cells from aldicarb-treated mice showed decreased responsiveness to anti-CD3 stimulation, whereas purified T cells in the presence of irradiated control macrophages showed normal reactivity. The fact that aldicarb did not directly affect the T cell functions was further confirmed by stimulating purified T cells from aldicarb-treated mice with phorbol myristate acetate and calcium ionophore, a response which is independent of the accessory cells and which was found to be normal in aldicarb-treated mice. It was observed that the macrophages from aldicarb-treated mice demonstrated a decreased capacity to stimulate conalbumin-specific T helper cell clone, D10.G4, and when activated produced decreased amounts of IL-1 when compared to control macrophages. Also, the decreased stimulation of D10.G4 clone by aldicarb-treated macrophages was reconstituted when exogenous recombinant IL-1 was added to the cultures. These data together suggested that aldicarb affects the macrophage functions by interfering with IL-1 production and that it does not affect the T cell functions directly.

Aldicarb↗
PubMed2001

Residues of aldicarb in oranges: a unit-to-unit variability study.

Residues of aldicarb and its sulphoxide and sulphone oxidative metabolites in individual Navelino orange trees were determined at several time intervals after soil application of TEMIK 10G at 200 g formulated material per tree. Analysis was by HPLC with postcolumn derivatization giving average recoveries of 98% for aldicarb (RSD 6%), 34% for aldicarb sulphoxide (RSD 5%) and 77% for aldicarb sulphone (RSD 5%). Lowest calibrated levels (LCLs) were 0.02 mg/kg for aldicarb and aldicarb sulphone and 0.04 mg/kg for aldicarb sulphoxide. At the recommended preharvest interval (PHI) of 120 days no detectable residues of any compound, including the parent compound, were found in and of the samples analysed. In mature fruits (PHI of 88 days) detectable residues at the LCL for aldicarb sulphoxide and 0.03 or 0.04 mg/kg for aldicarb sulphone were found in only three of the 18 samples analYsed. In immature fruits detectable residues of aldicarb sulphoxide at concentrations ranging between 0.04 (LCL) and 0.51 mg/kg were detected in 70 out of 88 samples analysed, while residues of aldicarb sulphone at concentrations 0.02 (LCL) to 0.8 mg/kg were detected in 73 out of 88 samples. Indicative variability factors for sulphoxide and sulphone were estimated for immature fruits.

Aldicarb↗
PubMed1999

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.

Aldicarb↗
PubMed2002

Effect of 17beta-estradiol and testosterone on the expression of flavin-containing monooxygenase and the toxicity of aldicarb to Japanese medaka, Oryzias latipes.

Previous studies in our laboratory indicated gender differences in salinity-enhanced acute toxicity of aldicarb in Japanese medaka with females being more susceptible. In the current study, the effects of the sex steroids, 17beta estradiol (E2) and testosterone (T) on aldicarb toxicity was examined. Adult Japanese medaka were separated by sex and exposed to 100 microg/l E2 or T for 6 days followed by exposure to the 96-h LC50 (0.5 mg/l) of aldicarb. The toxicity of aldicarb to adult males was significantly lowered by E2 and T whereby the mortality percentage was reduced to 23.3 +/- 5.8% and 3.3 +/- 5.8%, respectively, compared to the fish not receiving steroids (46.7 +/- 5.8% mortality). In females, T caused significant reduction in aldicarb toxicity to 16.7 +/- 5.8%, while E2 significantly enhanced the toxicity to 96.7 +/- 5.8% mortality. Since the flavin-containing monooxygenase (FMO) enzyme system had been shown to play a critical role in aldicarb toxicity, the effect of E2 and T on FMO expression was examined. Gill FMO activity showed a direct correlation with the overall toxicity of aldicarb in both male and female medaka. Expression of FMO1-like protein was significantly reduced by T in male livers and gills, and T did not affect the expression of FMOs in female tissues. In contrast, E2 significantly reduced FMO1-like protein expression in male gills and female livers, as well as FMO3 expression in both male and female livers, but significantly increased gill FMO1 expression in females. Since aldicarb acts by inhibiting the enzyme cholinesterase (ChE), the effect of sex hormones on the activity of this enzyme was also examined. In both male and female medaka, T counteracted the inhibitory effect of aldicarb on muscle ChE. In male fish, E2 had similar effects but did not seem to counteract the ChE inhibition in females. In conclusion, E2 and T modulation of aldicarb toxicity in Japanese medaka seems to be mediated via alteration of gill FMO and ChE actitivies.

Aldicarb↗
PubMed2002

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.

Aldicarb↗