Endosulfan and quinalphos residues and toxicity to soil microarthropods after repeated applications in a field investigation

Biodegradation and metabolic pathway of quinalphos by Cunninghamella elegans ATCC36112

Quinalphos is a long-term, wide-spectrum organophosphate insecticide with residual problems in the natural environment. Cunninghamella elegans (C. elegans) is a member of Mucoromycotina. Since the degradation products of its exogenous compounds are similar to those of mammals, it is often used to simulate the metabolism pathways of mammals. In this study, the detailed metabolic pathways of quinalphos were investigated with C. elegans. Quinalphos was degraded by 92% in 7 days, while ten metabolites were produced. The metabolites were analyzed and identified by GC-MS. To determine the responsible enzymes in quinalphos metabolism, piperonyl butoxide (PB) and methimazole included in the culture flasks, and the kinetic responses of quinalphos and its metabolites by C. elegans were measured. Results indirectly demonstrated that cytochrome P450 monooxygenases were involved in the metabolism of quinalphos, but that methimazole inhibited the metabolism less efficiently. Comprehensive metabolic pathways can be deduced from the detailed analysis of metabolite profiles in control and inhibitor assays.

Quinalphos Tolerant Endophytic Bacillus sp. Fcl1 and its Toxicity-Alleviating Effect in Vigna unguiculata

In order to meet the agricultural requirement for the expanding population, pesticides have been used regularly even with their severe threat. The uncontrolled use of these pesticides can cause irreparable damage to both soil and plant-associated microbiome. Therefore, an environment friendly alternative to enhance plant productivity and yield is highly important. Here comes the importance of endophytic microorganisms with multi-plant beneficial mechanisms to protect plants from the biotic and abiotic stress factors. However, their performance can be negatively affected under pesticide exposure. Hence the present study was conducted to analyse the tolerating ability of a Bacillus sp. Fcl1 which was originally isolated from the rhizome of Curcuma longa towards the pesticide quinalphos and also its ability to reduce the quinalphos-induced toxicity in Vigna unguiculata. The results revealed that the viability of endophytic Bacillus sp. Fcl1 depended on the concentration of quinalphos used for the study. Further, Fcl1 supplementation was found to alleviate the quinalphos-induced toxicity in Vigna unguiculata seedlings. The study is environmentally significant due to the pesticide tolerating and alleviating effect of Bacillus sp. Fcl1 in quinalphos-induced plant toxicity. This could suggest the application of microbes of endophytic origin as an efficient bioinoculant for field application even in the presence of pesticide residues.

Influence of environmental factors on biodegradation of quinalphos by Bacillus thuringiensis

BACKGROUND

The extensive and intensive uses of organophosphorus insecticide-quinalphos in agriculture, pose a health hazard to animals, humans, and environment because of its persistence in the soil and crops. However, there is no much information available on the biodegradation of quinalphos by the soil micro-organisms, which play a significant role in detoxifying pesticides in the environment; so research is initiated in biodegradation of quinalphos.

RESULTS

A soil bacterium strain, capable of utilizing quinalphos as its sole source of carbon and energy, was isolated from soil via the enrichment method on minimal salts medium (MSM). On the basis of morphological, biochemical and 16S rRNA gene sequence analysis, the bacterium was identified as to be Bacillus thuringiensis. Bacillus thuringiensis grew on quinalphos with a generation time of 28.38 min or 0.473 h in logarithmic phase. Maximum degradation of quinalphos was observed with an inoculum of 1.0 OD, an optimum pH (6.5-7.5), and an optimum temperature of 35-37 °C. Among the additional carbon and nitrogen sources, the carbon source-sodium acetate and nitrogen source-a yeast extract marginally improved the rate of degradation of quinalphos.

CONCLUSIONS

Display of degradation of quinalphos by B. thuringiensis in liquid culture in the present study indicates the potential of the culture for decontamination of quinalphos in polluted environment sites.

Decay profile and metabolic pathways of quinalphos in water, soil and plants

The widespread occurrence of pesticide residues in different agricultural and food commodities has raised concern among the environmentalists and food chemists. In order to keep a proper track of these materials, studies on their decay profiles in the various segments of ecosystem under varying environmental conditions are needed. In view of this, the metabolites of quinalphos in water and soil under controlled conditions and in plants, namely tomato and radish in field conditions have been analysed and possible pathways suggested. In order to follow the decay of the pesticide, an HPLC procedure has been developed. Studies conducted in water at different temperatures, pH and organic content reveal that the persistence of the pesticide decreases with the increase in all the three variables. In the three different types of soils studied, the effect of pH is more or less apparent on a similar line. On an average a faster decay is observed in the case of plants than in water and soil. The decay profiles in all these cases follow first order kinetics. The metabolites were identified by GC-MS. The investigations reflect that degradation occurs through hydrolysis, S-oxidation, dealkylation and thiono-thiol rearrangement. The pathways seem to be complex and different metabolites were observed with the change in the matrix. Quinalphos oxon, O-ethyl-O-quinoxalin-2-yl phosphoric acid, 2-hydroxy quinoxaline and quinoxaline-2-thiol were observed in all the matrices. Results further indicate that the metabolites, 2-hydroxy quinoxaline and oxon, which are more toxic than parent compound, persist for a longer time.

Application of statistical design of experiment with desirability function for the removal of organophosphorus pesticide from aqueous solution by low-cost material

This paper deals with the multiple response optimization for the removal of organophosphorus pesticide quinalphos [QP: O,O-diethyl O-2-quinoxalinyl phosphorothioate] from the aqueous solution onto low-cost material and tried to overcome the drawbacks of univariate optimization. Used tea leaves were used as low-cost adsorbent and batch equilibration method was followed for this study. A Box-Behnken design was used to develop response model and desirability function was then used for simultaneous optimization of all affecting parameters in order to achieve the highest removal% of quinalphos. The optimum conditions of factors predicted for quinalphos removal% were found to be: pH 8.83, concentration 7 mg L(-1) and dose 0.40 g. Under these conditions, maximum removal% of quinalphos was obtained 96.31%. Considering the above optimum conditions, the adsorption isotherms were developed and provided adsorption capacity of 196.07 microg g(-1) by using Langmuir equation, indicating that used tea leaves may be applied as a low-cost material for pesticides removal from aqueous matrices.

Optimization of environmental parameters for biodegradation of alpha and beta endosulfan in soil slurry by Pseudomonas aeruginosa

AIM

To determine optimal environmental conditions for achieving biodegradation of alpha- and beta-endosulfan in soil slurries following inoculation with an endosulfan degrading strain of Pseudomonas aeruginosa.

METHODS AND RESULTS

Parameters that were investigated included soil texture, soil slurry: water ratios, initial inoculum size, pH, incubation temperature, aeration, and the use of exogenous sources of organic and amino acids. The results showed that endosulfan degradation was most effectively achieved at an initial inoculum size of 600 microl (OD = 0 x 86), incubation temperature of 30 degrees C, in aerated slurries at pH 8, in loam soil. Under these conditions, the bacterium removed more than 85% of spiked alpha- and beta-endosulfan (100 mg l(-1)) after 16 days. Abiotic degradation in noninoculated control medium within same incubation period was about 16%. Biodegradation of endosulfan varied in different textured soils, being more rapid in course textured soil than in fine textured soil. Increasing the soil contents in the slurry above 15% resulted in less biodegradation of endosulfan. Exogenous application of organic acids (citric acid and acetic acid) and amino acids (L-methionine and L-cystein) had stimulatory and inhibitory effects, respectively, on biodegradation of endosulfan.

CONCLUSION

The results of this study demonstrated that biodegradation of endosulfan by Ps. aeruginosa in soil sediments enhanced significantly under optimized environmental conditions.

SIGNIFICANCE AND IMPACT OF THE STUDY

Endosulfan is a commonly used pesticide that can contaminate soil, wetlands and groundwater. Our study demonstrates that bioaugmentation of contaminated soils with an endosulfan degrading bacterium under optimized conditions provides an effective bioremediation strategy.

Non-omnia moriantur-toxicity of mancozeb on dead wood microarthropod fauna

The effect of Dithane M-45 (dithiocarbamate fungicide; active substance: mancozeb) was studied on microarthropod fauna inhabiting dead wood. Although the exposure was almost never 100% lethal for the majority of observed taxa, almost all (Mesostigmata, Oribatida, some Uropodina, Actinedida, Collembola and Diplopoda) showed very high correlation between concentration of the fungicide and mortality (r > 0.86). Only Stigmaeidae showed low correlation (r = 0.293). For the majority of taxa LC(50 )values were close to the concentrations used during agrochemical activities in woods. Only Trachytes aegrota showed full susceptibility to the fungicide within the range of recommended field concentrations used in forestry (characterised by the low LC(95 )value). Tolerance of mesostigmatid and oribatid mites was found to differ between juveniles and adults, but not consistently. Related Uropodina species varied in susceptibility to the fungicide.