Tilapia were exposed to sublethal concentrations of 0, 0.2, 2, 20, or 200 μg/L for 30 days, and then transferred to methomyl-free water for 18 days. GST, GPx, GR, GSH, and GSSG in tilapia serum were examined at 0, 6, 12, 18, 24, and 30 days after methomyl exposure and at 18 days after transferring to methomyl-free water. There were no significant changes in antioxidants activities and contents in serum of tilapia exposed to 0.2 μg/L. Significant increases in GST, GR, GPx, and GSSG accompanied by a decrease in GSH were observed following methomyl exposure to 2, 20, or 200 μg/L, suggesting the presence of oxidative stress. Thus, it would appear the 0.2 μg/L methomyl might be considered the no observed adverse effect level. Recovery data showed that the effects produced by lower concentration of 20 μg/L were reversible but not at the higher 200 μg/L concentration.

Hepatic antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT) of Nile tilapia in response to pesticide methomyl and recovery pattern were researched by exposing tilapia to sub-lethal methomyl concentrations of 0, 0.2, 2, 20 and 200 μg/L for 30 days, and then transferred to methomyl-free water for 18 days. Hepatic SOD and CAT were measured at 10 min (day 0), 6, 12, 18, 24 and 30 days after starting the experiment and at 18 days after transferring to methomyl-free water. The results showed hepatic SOD and CAT activities in 2, 20 and 200 μg/L groups were affected significantly, however, that in 0.2 μg/L group didn't change significantly compared to control during 30-day exposure period. Thus it would appear the 0.2 μg/L methomyl might be considered the no observed adverse effect level. Recovery data showed that, for SOD, the effects produced by lower concentration of methomyl 2 μg/L were reversible but not at concentrations higher than 20 μg/L, however, for CAT, the effects produced by all the concentrations were reversible.

Bacterial diseases are one of the major problems in freshwater fish culture and have been linked to significant losses and high mortality rate. In this study, Nile tilapia Oreochromis niloticus was infected by Providencia rettgeri to evaluate the oxidative stress and antioxidant responses in the fish tissues. Juvenile Nile tilapia was divided into two groups, as follow: control (uninfected) and experimentally infected with 100 μL of P. rettgeri suspension containing 2.4 × 10⁷ viable cells/fish, and the liver and kidney tissues were collected on days 7 and 14 post-infection (PI). Liver and kidney ROS and lipid peroxidation levels were high in infected fish on day 14 PI compared to control group, while superoxide dismutase activity was lower in liver (days 7 and 14 PI) and kidney (day 14 PI) compared to their respective control groups. Liver and kidney antioxidant capacity against peroxyl radicals, non-proteic, and proteic thiols levels was lower in infected tilapia on day 14 PI compared to control group. Based on these results, P. rettgeri infection may elicit oxidative damage via increased ROS production, decreased ROS elimination and inhibits enzymatic and non-enzymatic antioxidant defense systems; which may contribute directly to disease pathophysiology of infected animals.

The chronic effect of methomyl on the antioxidant system in tilapia (Oreochromis niloticus) was investigated. Fish were exposed to sub-lethal concentrations of 0.2, 2, 20 and 200μgL(-1) for 30 days, and then transferred to methomyl-free water for 18 days. Hepatic antioxidant parameters, including Glutathione-S-transferase (GST), Glutathione peroxidase (GPx), Glutathione reductase (GR), Reduced glutathione (GSH) and oxidized glutathione (GSSG), were measured at 10min (day 0), 6, 12, 18, 24 and 30 days after starting the experiment and at 18 days after transferring to methomyl-free water. There were no significant changes in enzymatic activity and content of antioxidants in liver of tilapia exposed to 0.2μgL(-1) methomyl compared to controls. However, the results showed significant increases in activities of GST, GR, GPx and levels of GSSG accompanied by a decrease in GSH levels following methomyl exposure in tilapia to 2, 20 or 200μgL(-1) over the 30-day exposure period and the highest induction rates in GST, GR, GPx and GSSG were 150.87%, 163.21%, 189.76%, and 179.56% of the control respectively, and the highest inhibition rate in GSH was 50.67% of the control, suggesting the presence of oxidative stress. Thus it would appear that the 0.2μgL(-1) methomyl might be considered as the no observed adverse effect level (NOAEL). Recovery data showed that the effects produced by lower concentration of methomyl 20μgL(-1) were reversible but not at the higher 200μgL(-1) concentration.

Tilapia were exposed to 0, 0.2, 2, 20, 200 µg/L methomyl for 30 days, and then transferred to methomyl-free water for 18 days. Caspase-8 in serum, apoptosis rate, microstructure and ultra-microstructure of testis were checked after methomyl exposure and at 18 days after transferring to methomyl-free water. There were no significant changes in Caspase-8 activity, apoptosis rate, and tissue structure in testis exposed to 0.2 and 2 µg/L compared with control. However, when tilapia exposed to 20 and 200 µg/L, the Caspase-8 activity and apoptosis rate were induced significantly, and tissue damage happened compared with the control. Thus it would appear 2 µg/L methomyl might be considered as the no observed adverse effect level. Recovery data showed that the effects produced by lower concentration of 20 µg/L were reversible but not at the higher 200 µg/L concentration.

采用高效液相色谱法,系统地对灭多威在蔬菜中残留与降解进行动态检测.结果表明:灭多威在蔬菜中能够迅速降解,半衰期为30h.5d以后蔬菜中残留量基本低于0.01mg/Kg.

研究了农药灭多威在TiO₂光催化下的降解产物、反应动力学及影响降解速率的因素.灭多威在TiO₂催化下10min内可被完全转换为无机物而失去毒害作用.IR研究表明,灭多威的分解产物为NH₄⁺、SO₄^2-和CO₂,其分解过程为准一级反应.除铜和氯离子在低浓度时有促进作用,而高浓度为阻碍作用外,大部分阴、阳离子对降解均有不利影响.

There were few reports on the antioxidant response of aquatic organisms exposed to 2,4-dichlorophenol (2,4-DCP). This research explored the hepatic antioxidant responses of fish to long-term exposure of 2,4-DCP for the first time. Freshwater fish Carassius auratus were chosen as experimental animals. The fish were exposed to six different concentrations of 2,4-DCP (0.005-1.0 mg/l) for 40 days and then liver tissues were separated for determination. As shown from the results, 40 days afterwards, the activities of catalase (CAT) and selenium-dependent glutathione peroxidase (Se-GPx) and the content of oxidized glutathione (GSSG) were induced significantly on the whole compared to control group; superoxide dismutase (SOD) responded to 2,4-DCP exposure at only 0.005 mg/l; the content of reduced glutathione (GSH) was suppressed continuously except Group 7; the activity of glutathione reductase was inhibited initially and then restored to control level from Group 4 on; glutathione S-transferase had only slight responses in Groups 3 and 4. Total glutathione (tGSH) and GSH/GSSG ratio were also calculated to analyze the occurrence of oxidative stress. Besides, good dose-effect relations, which cover most of the exposure concentration range, were found between 2,4-DCP level and CAT activity, GSSG content, Se-GPx activity, respectively. In conclusion, SOD and Se-GPx may be potential early biomarkers of 2,4-DCP contamination in aquatic ecosystems, and further studies will be necessary.

Recently, residual fungicides are generally recognized as relevant sources of aquatic environmental pollutants. However, the toxicological effects of these contaminants have not been adequately researched. In this study, the chronic effect of PCZ, a triazole-containing fungicide commonly present in aquatic environment, on GSH-related antioxidant system and oxidative stress indices of rainbow trout (Oncorhynchus mykiss) were investigated. Fish were exposed at sub-lethal concentrations of PCZ (0.2, 50 and 500 microg/L) for 7, 20 and 30 days. GSH levels and GSH-related enzyme activities, including GPx, GR and GST, were quantified in three tissues-liver, gill and muscle. The levels of LPO and CP were also measured as makers of oxidative damage. In addition, the correlations of the measured parameters in various tissues were evaluated by using PCA. The results of this study indicate that chronic exposure of PCZ has resulted in different responses in various tissues and the gill was the most sensitive tissue; however, before these parameters are used as potential biomarkers for monitoring residual fungicides in aquatic environment, more detailed experiments in laboratory need to be performed in the future.

The insecticide methomyl, an oxime carbamate, was first introduced in 1968 for broad spectrum control of several insect classes, including Lepidoptera, Hemiptera, Homoptera, Diptera, and Coleoptera. Like other carbamates, it inhibits AChE activity, resulting in nerve and/or tissue failure and possibly death. Considered highly toxic to insects (larval and adult stages), methomyl is thought to be metabolically degraded via mixed-function oxidase(s). Methomyl has both a low vapor pressure and Henry's law constant; hence, volatilization is not a major dissipation route from either water or moist or dry soils. Photolysis represents a minor dissipation pathway; however, under catalytic conditions, degradation via photolysis does occur. Methomyl possesses a moderate-to-high water solubility; thus hydrolysis, under alkaline conditions, represents a major degradation pathway. Methomyl has a low-to-moderate sorption capacity to soil. Although results may vary with soil type and organic matter content, methomyl is unlikely to persist in complex soils. Methomyl is more rapidly degraded by microbes, and bacterial species have been identified that are capable of using methomyl as a carbon and/or nitrogen source. The main degradation products of methomyl from both abiotic and biotic processes are methomyl oxime, acetonitrile, and CO₂. Methomyl is moderately to highly toxic to fishes and very highly toxic to aquatic invertebrates. Methomyl is highly toxic orally to birds and mammals. Methomyl is classed as being highly toxic to humans via oral exposures, moderately toxic via inhalation, and slightly toxic via dermal exposure. At relatively high doses, it can be fatal to humans. Although methomyl has been widely used to treat field crops and has high water solubility, it has only infrequently been detected as a contaminant of water bodies in the USA. It is classified as a restricted-use insecticide because of its toxicity to multiple nontarget species. To prevent nontarget species toxicity or the possibility of contamination, as with all pesticides, great care should be taken when applying methomyl-containing products for agricultural, residential, or other uses.