Methiocarb Degradation by Electro-Fenton: Ecotoxicological Evaluation.

This paper studies the degradation of methiocarb, a highly hazardous pesticide found in waters and wastewaters, through an electro-Fenton process, using a boron-doped diamond anode and a carbon felt cathode; and evaluates its potential to reduce toxicity towards the model organism Daphnia magna. The influence of applied current density and type and concentration of added iron source, Fe2(SO4)3·5H2O or FeCl3·6H2O, is assessed in the degradation experiments of methiocarb aqueous solutions. The experimental results show that electro-Fenton can be successfully used to degrade methiocarb and to reduce its high toxicity towards D. magna. Total methiocarb removal is achieved at the applied electric charge of 90 C, and a 450× reduction in the acute toxicity towards D. magna, on average, from approximately 900 toxic units to 2 toxic units, is observed at the end of the experiments. No significant differences are found between the two iron sources studied. At the lowest applied anodic current density, 12.5 A m-2, an increase in iron concentration led to lower methiocarb removal rates, but the opposite is found at the highest applied current densities. The highest organic carbon removal is obtained at the lowest applied current density and added iron concentration.

Acute effects of methiocarb on oxidative damage and the protective effects of vitamin E and taurine in the liver and kidney of Wistar rats.

Methiocarb (MC) is a widely used carbamate pesticide in agriculture and health programs. Although the main molecular mechanism of carbamate toxicity involves acetylcholinesterase inhibition, studies have also implicated the induction of oxidative stress. Therefore, the present study was aimed to evaluate the effect of acute MC exposure on lipid peroxidation, antioxidant defense systems, histological changes in Wistar rats and the protective effect of pretreatment with vitamin E and taurine. A total of 48 rats were randomly divided into six groups. Rats in group I were given corn oil, while those in group III were dosed with vitamin E (100 mg/kg body weight (b.w.)) and in group V were dosed with taurine (50 mg/kg b.w.). Rats in group II were administered with MC only (25 mg/kg b.w., 1/4 of median lethal dose (LD(50))), while those in groups IV and VI were pretreated with vitamin E (100 mg/kg b.w.) and taurine (50 mg/kg b.w.) for 20 days, respectively, and then exposed to MC (25 mg/kg b.w.). The rats administered with MC showed significant increase in the levels of malondialdehyde in the liver and kidney as an index of lipid peroxidation. Levels of glutathione and activities of superoxide dismutase, catalase and glutathione peroxidase were significantly increased, while activity of glutathione reductase remained unchanged in both the tissues after MC treatment. Mild degenerative histological changes were observed in liver tissue, while the changes in kidney tissue were more severe then liver after MC treatment. Pretreatment with vitamin E and taurine resulted in a significant decrease in the lipid peroxidation and alleviating effects on antioxidant defense systems in both the tissues, while protective effects on the histological changes were shown only in kidney when compared with liver. In conclusion, the study has demonstrated that the acute MC exposure in Wistar rats caused oxidative damage on liver and kidney, which were partly ameliorated by the pretreatment of vitamin E and taurine.

Neuropathological effect of carbamate molluscicides on the land snail, Eobania vermiculata.

The present study was designed to investigate the neuropathological effect of the two carbamate pesticides: methomyl and methiocarb on the neurons of the buccal ganglia in the land snail Eobania vermiculata using topical application and baiting technique. Their in vivo effects on acetylcholinesterase (AChE, EC 3.1.1.7) activity were also investigated. Sublethal dose and concentration (1/4 LD(50) and 1/4 LC(50)) of both pesticides were used, and the experiment lasted for 14 days. Histopathological and ultrastuctural alterations in the buccal ganglia were more obvious after the baiting technique treatment than after the topical application method, and methomyl was found to be more toxic than methiocarb. These alterations included shrinkage of the perikarya of neurons, increased cytoplasmic basophilia, and extreme indentation of the plasma membrane. In addition, the nuclei appeared karyolitic, eccentric, and highly shrunken with an irregular nuclear envelope. The most outstanding symptom observed after topical application of methiocarb was a highly vacuolated cytoplasm with a peripheral increase in electron density associated with dense accumulations of free ribosomes. On the other hand, an increased number of lysosomes and autophagosomes were observed after topical application of methomyl. Mitochondrial damage, increased number of lipid droplets, and myelin figures were frequently observed in ganglia treated with either methomyl or methiocarb. Moreover, it was noticed that both compounds induced reductions in AChE activity. However, methomyl exhibited more potency in reducing AChE activity than methiocarb.

Increased expression of the testicular estrogen receptor alpha in adult mice exposed to low doses of methiocarb.

Methiocarb is a widely used carbamate pesticide and a suspected endocrine disrupter. The objective of this study was to examine the in vivo effects of methiocarb at low doses on testicular expression of steroid receptors, spermatogenesis and sperm quality in adult mice. Eighteen-week-old DBA/2 males were treated with daily intraperitoneal injection of methiocarb (0, 0.03, 0.3, 1.0 or 3.0 microg kg(-1) of body weight) for 20 days. Kidney and liver weights were significantly increased in the 1.0 or 3.0 microg kg(-1) treatment groups (P < 0.05). The testicular expression of estrogen receptor alpha (ERalpha) was significantly increased in mice treated with methiocarb as confirmed by Western blot analysis. The sperm production and sperm quality of the methiocarb-exposed mice were not significantly altered as determined using a computer-assisted sperm analysis system. Therefore, these results demonstrate, that although the exposure to methiocarb at low doses alters testicular ERalpha expression in adult mice, both sperm production and quality remain unaffected.

Pollutant-induced alterations of granulocyte morphology in the earthworm Eisenia foetida.

Earthworms are considered convenient indicators of land use and soil fertility. Recently the use of biomarkers in earthworms has been increasingly investigated. The aim of this work was to study possible pollutant-induced morphometric alterations in Eisenia foetida granulocytes in view of future applications as a sensitive, simple, and quick biomarker for soil monitoring and assessment applications. Results showed consistent enlargement of earthworm granulocytes induced by exposure to either copper sulfate or methiocarb. The increase of cellular size was time-dependent and was about 100% after 14 days of exposure for both treatments. In order to verify the applicability of morphometric granulocyte alteration, a battery of standardized biomarkers such as lysosomal membrane stability, metallothionein induction, or acetylcholinesterase (AChE) inhibition were also determined. We recommend the use of morphometric alterations of granulocytes as a suitable biomarker of pollutant effect to be included in a multibiomarker strategy including responses at different levels of biological organization.

Metabolism of methiocarb and carbaryl by rat and human livers and plasma, and effect on their PXR, CAR and PPARα activities.

The oxidative, reductive, and hydrolytic metabolism of methiocarb and the hydrolytic metabolism of carbaryl by liver microsomes and plasma of rats or humans were examined. The effects of the metabolism of methiocarb and carbaryl on their nuclear receptor activities were also examined. When methiocarb was incubated with rat liver microsomes in the presence of NADPH, methiocarb sulfoxide, and a novel metabolite, methiocarb sulfone were detected. Methiocarb sulfoxide was oxidized to the sulfone by liver microsomes and reduced back to methiocarb by liver cytosol. Thus, the interconversion between methiocarb and the sulfoxide was found to be a new metabolic pathway for methiocarb by liver microsomes. The product of methiocarb hydrolysis, which is methylthio-3,5-xylenol (MX), was also oxidized to sulfoxide form by rat liver microsomes. The oxidations were catalyzed by human flavin-containing monooxygenase isoform (FMO1). CYP2C19, which is a human cytochrome P450 (CYP) isoform, catalyzed the sulfoxidations of methiocarb and MX, while CYP1A2 also exhibited oxidase activity toward MX. Methiocarb and carbaryl were not enzymatically hydrolyzed by the liver microsomes, but they were mainly hydrolyzed by plasma and albumin to MX and 1-naphthol, respectively. Both methiocarb and carbaryl exhibited PXR and PPARα agonistic activities; however, methiocarb sulfoxide and sulfone showed markedly reduced activities. In fact, when methiocarb was incubated with liver microsomes, the receptor activities were decreased. In contrast, MX and 1-naphthol showed nuclear receptor activities equivalent to those of their parent carbamates. Thus, the hydrolysis of methiocarb and carbaryl and the oxidation of methiocarb markedly modified their nuclear receptor activities.

Effects of the pesticides prochloraz and methiocarb on human estrogen receptor alpha and beta mRNA levels analyzed by on-line RT-PCR.

Exposure to endocrine disrupters such as dioxins, PCBs and certain pesticides are suspected to affect human reproductive health. We have analyzed the effect of the currently used pesticides prochloraz and methiocarb on the estrogen receptor (ER)alpha and beta mRNA levels in parallel with the natural ligand, 17beta-estradiol (E2). Using the highly sensitive on-line RT-PCR technique we were able to quantify the ERalpha and ERbeta mRNA levels in the human breast cancer cell line, MCF7-BUS. Upon exposure with E2 or prochloraz a down regulation of ERalpha and ERbeta mRNAs was observed after 48 h of treatment. Co-treatment with the ER antagonist ICI 182,780 abolished these mRNA down regulations. Western blot analyses elicited a decreased ER protein level after 3 h of exposure with prochloraz but after 24 h the ERalpha protein level had recovered to basal level. Methiocarb exposure had no effect on the ERalpha mRNA level, whereas an increase in the ERbeta mRNA level was observed after 3 h of exposure. Our study demonstrates that like E2, prochloraz had the potential to down regulate the expression of ERalpha and ERbeta mRNAs as well as the ERalpha protein level in MCF7-BUS cells.

Novel field sampling procedure for the determination of methiocarb residues in surface waters from rice fields.

Methiocarb was extracted from surface water samples collected at experimental rice field sites in Louisiana and Texas. The sampling system consisted of a single-stage 90-mm Empore extraction disk unit equipped with a battery-powered vacuum pump. After extraction, the C-18 extraction disks were stored in an inert atmosphere at -10 degrees C and shipped overnight to the laboratory. The disks were extracted with methanol and the extracts analyzed by reversed-phase high-performance liquid chromatography with a methanol/water mobile phase. Methiocarb was detected by ultraviolet absorption at 223 nm and quantified with the use of calibration standards. Recoveries from control surface water samples fortified at 5.0, 10, 50, and 100 ng/mL methiocarb averaged 92 +/- 7%. A method limit of detection for methiocarb in rice field surface water was estimated to be 0.23 ng/mL at 223 nm.

Seed dressings to control slug damage in oilseed rape.

Slugs are major pests of oilseed rape that are poorly controlled by conventional bait pellets. A series of laboratory experiments investigated the potential of seed-dressings to control slug damage in this crop. Four compounds: metaldehyde, methiocarb, cinnamamide and 3,5-dimethoxycinnamic acid (DMCA) were tested at a range of doses for phytotoxicity and ability to reduce damage by Deroceras reticulatum (Müller). Metaldehyde and methiocarb were not phytotoxic at any doses, whereas all doses of cinnamamide and DMCA were. All compounds reduced slug damage, but metaldehyde and methiocarb consistently performed better than cinnamamide and DMCA. Metaldehyde and methiocarb seed-dressings were compared with baited pellets containing the same active ingredients at recommended field doses. The seed-dressings protected plants from damage by D reticulatum and Arion subfuscus (Draparnaud) as well as, or better than, baited pellets. We therefore recommend that metaldehyde and methiocarb should be field-tested as seed dressings to control slugs in oilseed rape.

Biomarker response in the earthworm Lumbricus terrestris exposed to chemical pollutants.

Earthworms are important organisms for the soil ecosystem. They are sensitive to toxic chemicals and represent useful bioindicator organisms for soil biomonitoring. Recently the use of biomarkers in earthworms has been increasingly investigated for soil monitoring and assessment purpose. The aim of the preset paper was to analyze the pollutant-induced response of a suite of cellular and biochemical biomarkers in the earthworm Lumbricus terrestris exposed to copper sulphate or methiocarb in OECD soil at the maximal concentrations recommended in agriculture. These responses were compared to lifecycle parameters such as survival, growth and reproduction. Granulocyte morphometric alteration, lysosomal membrane stability, metallothionein concentration, and acetylcholinesterase activity were considered. In either copper sulphate or methiocarb exposure conditions the mean percentage variation of the pollutant-induced molecular and cellular biomarkers was consistent with the whole organism end-point responses. In particular pollutant-induced granulocyte enlargement, detected in either copper sulphate or methiocarb exposed organisms, showed to be a potential general biomarker that may be directly linked to organism health. Compared to the other biological responses to pollutants, it showed high sensitivity to pollutant exposure suggesting its possible applications as a sensitive, simple, and quick general biomarker for monitoring and assessment applications.

Kinetics and mechanism for methiocarb degradation by chlorine dioxide in aqueous solution.

The kinetics and mechanism for methiocarb (MC) degradation by aqueous ClO2 were investigated under simulated water treatment conditions. Experimental results indicate that the reaction between MC and ClO2 was of second-order overall, and the rate constant rapidly increased from 0.56 to 4.5 M(-1) s(-1) as the solution pH increased from 6.0 to 9.1 at 23 degrees C. The activation energy was determined to be 75 kJ mol(-1) in the studied temperature range of 7-35 degrees C. Methiocarb sulfoxide (MCX) and methiocarb sulfone (MCN) were quantified to be the major byproducts from MC degradation. Unlike the sequential formation of sulfoxide and sulfone during the oxidation of many thioethers, the two byproducts were formed simultaneously during MC degradation by ClO2. The solution pH significantly affected the type and quantity of the degradation byproducts. For example, at pH 6.5 MCX and MCN accumulated as the reaction proceeded and finally accounted for 71% and 28% of MC degraded, respectively; while at pH 8.6 three more minor byproducts were identified. Though ClO2 can effectively oxidize MC in water, the significant increase in toxicity raises a potential risk to consumers.

Methiocarb-induced oxidative damage following subacute exposure and the protective effects of vitamin E and taurine in rats.

Methiocarb, is used worldwide in agriculture and health programs. Besides its advantages in the agriculture, it causes several toxic effects. In this study, we aimed to investigate subacute effects of methiocarb on lipid peroxidation, reduced glutathione (GSH), antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px) and glutathione reductase (GSH-Rd) and histopathological changes in rat tissues. Moreover, we examined the possible protective effects of vitamin E and taurine on methiocarb-induced oxidative damage in rat tissues. Rats were randomly divided into six groups as follows; I-control group; II-methiocarb group; III-vitamin E group; IV-vitamin E+methiocarb group; V-taurine group and VI-taurine+methiocarb group. Methiocarb significantly increased lipid peroxidation in liver and kidney when compared to control groups. Levels of GSH and activities of SOD, CAT and GSH-Px were found to be decreased, while GSH-Rd remained unchanged in rat liver and kidney treated with methiocarb. Pretreatment of vitamin E and taurine resulted in a significant decrease on lipid peroxidation, alleviating effects on GSH and antioxidant enzymes. The degenerative histological changes were less in liver than kidney of rats treated with methiocarb. Pretreatment of vitamin E and taurine showed a protective effect on the histological changes in kidney comparing to the liver of rats treated with methiocarb.

Histopathology of rainbow trout exposed to sublethal concentrations of methiocarb or endosulfan.

Liver, spleen, trunk kidney, gills, and brain of rainbow trout (Oncorhynchus mykiss) were examined histologically after exposure to different concentrations of methiocarb (2.5 and 3.75 mg/L) or endosulfan (0.6 and 1.3 micro g/L) for 21 days. Histological recovery was also studied by maintaining the pesticide-exposed fish in a freshwater system for an additional 30 d. Lesions were not evident in liver, kidney, spleen, or brain of fish exposed to either concentration of methiocarb for 21 d. Lesions were observed in gills, liver, spleen, and trunk kidney (but not brain) of rainbow trout exposed to either concentration of endosulfan. There was no concentration-related effect observed on the histopathological lesions. After 30 days of recovery, fish had no histological lesions in gills, kidney, spleen, liver, or brain. Therefore all the changes observed during exposure were reversible.

Factors influencing discrimination between insecticide-treated and untreated foods by northern bobwhite.

Tests were conducted to determine at what dietary concentrations northern bobwhite (Colinus virginianus) chicks (14 days old) could discriminate between pesticide-treated and untreated food using an organophosphate (OP) insecticide, parathion, and two carbamates, carbofuran and methiocarb. Results from subacute dietary LC50 tests (one feeder of treated food per cage) were compared to tests where birds were presented with two feeders (one treated and one untreated, 1:1) or 10 feeders (five treated and five untreated, 5:5; or nine treated and one untreated, 9:1). The dietary concentration above which birds discriminate between feeders by consuming a greater proportion of untreated food is defined as the discrimination threshold (DT). The DT occurred at sublethal concentrations in all 1:1 tests, with little mortality or reduction in food consumption. Little or no discrimination was observed in 9:1 tests, with mortality similar to the LC50 tests. The discrimination response in 5:5 tests was similar to the 1:1 tests for parathion and methiocarb, but with carbofuran the DT was higher than in the 1:1 test and higher mortality was observed. In all tests, mortality was inversely related to total food consumption. No relationship was found between mortality and the amount of active ingredient ingested/bird-day. Consequently, mortality was more a function of ability to locate untreated feeders than amount of chemical ingested. When alternative food choices exist, vulnerability to poisoning can be influenced by the number and relative abundance of those choices, as well as the bird's ability to detect the chemical.

The chronic toxicity of methiocarb to grackles, doves, and quail and reproductive effect in quail.

Methiocarb (4-methylthio-3, 5-xylyl N-methyl carbamate, Mesurol, Bay (3744), a bird repellent, was fed in concentrations of 100 to 1,000 ppm to common grackles (Quiscalus quiscula), mourning doves (Zenaida macroura), and breeding pairs of coturnix quail (Coturnix coturnix) to investigate the possibility of cumulative intoxication. Although aversion to treated diets was readily apparent in most of the tests, the 28- to 30-day median lethal concentration (LC50) was determined to be greater than 100 ppm for grackles, 630 ppm (95% confidence limits, 480-830 ppm) for doves, and greater than 1,000 ppm for coturnix quail. Methiocarb appeared to be noncumulative when measured by an index of chronicity: birds consumed several LD50 doses during a day's feeding, and when deaths occurred, they appeared to be due to acute intoxication. Egg production and live chick production were not affected in coturnix fed 100 ppm but were reduced at 316 and 1,000 ppm.