Development of biofilters to treat the pesticides wastes from spraying applications

Several studies carried out in Europe showed the importance of direct losses to the contamination of surface water by pesticides. These pesticides losses can occur at the farm site when the sprayer equipment is filled with the pesticide formulation (spills, overflowing, leaking) and during the clean-up (rinsing) of the sprayer after the treatment. In Belgium studies are carried out on biofilters to treat in an efficient way effluents containing pesticides. The biofilter substrate is elaborated from a homogenised mixture of local soil, chopped straw and peat or composted material, able to absorb or degrade the active substances. Biofilters consist in systems of 2 or 3 units depending on the spray equipment of the farmer and on the configuration of the farmyard. Each unit is made from a 1 m3 plastic container and the different units are stacked in a vertical pile and connected between them using plastic valves and pipes. Eight pilot systems were installed in March 2002 in seven farms and in one agricultural school, all selected in the loamy region of Belgium specialised in arable crops such as cereals, sugar beets and vegetables. The efficacy (yield) of the systems was determined by measuring the balance of the inputs and outputs of the pesticides. Results were expressed in percent of pesticide retained on the biofilters. The results obtained after two years with 5 tracer pesticides (atrazine, carbofuran, diuron, lenacil and simazine) brought on the biofilter installations are very satisfactory since the percentage of retention is generally higher than 95% of the amount applied. In the beginning of 2004, ten new pilot biofilters were installed in several farms or agricultural technical centres (producing cereals, sugar beets, potatoes, vegetables, fruits or ornamental plants), and in a municipal maintenance service. Some biofilters were installed in duplicate in order to compare the efficacy of different substrates. The efficacy of the biofilters was studied for the 5 classical tracer pesticides but also for other chemical classes of herbicides (sulfonylurea, aryloxyalcanoic acids, chloroacetanilides), insecticides (pyrethroids, carbamates) and fungicides (dicarboximides, phenylamides, triazoles and strobilurines). To monitor these pesticides in elutes and substrates, two analytical methods were developed, optimised and validated : the first one by Gas Chromatography with Mass Spectrometry Detection (GC-MS), and the second one by High Performance Liquid Chromatography with UV Diode Array Detection (HPLC-DAD). The micro-organisms activity in the substrate was also measured in some situations.     

Exposure risks to pesticide applicators posed by the use of electric backpack sprayers and stretcher-mounted sprayers in orchards

Abstract

The introduction of the pesticide registration system in pesticide risk assessments has promoted the scientific and safe use of pesticides, and the assessment of occupational exposure risk. In the present study, we performed an experiment in a citrus orchard subject to normal orchard management practices. By measuring the exposure of applicators’ (farmers and technicians) body parts to 45% malathion emulsifiable concentrate during its application using electric backpack sprayers (0.25?KPa) and stretcher-mounted sprayers (1.5?KPa), the unit exposure (UE) was determined. The risks of exposure for pesticide applicators who adopted five different protective measures (A: no personal protective equipment (PPE), i.e., no clothes, no gloves, no caps, and no socks; B: short-sleeved top and shorts; C: short-sleeved top, shorts, and a single pair of gloves; D: short-sleeved top, shorts, a single pair of gloves, and a cap; E: long-sleeved top, long pants, a single pair of gloves, and a cap) were also assessed. The results were as follows: 1) The total levels of exposure for pesticide applicators using electric backpack sprayers and stretcher-mounted sprayers were 3613.63?µg and 5654.28?µg, respectively. When electric backpack sprayers were used, the body parts that had the highest exposure were the head (13.8%), hands (19.9%) and back (14.0%), and when stretcher-mounted sprayers were used, the hands (32.5%) and lower legs (21.1%) had the highest level of exposure; 2) In the absence of PPE, the UE values for farmers who used electric backpack sprayers and farmers who used stretcher-mounted sprayers were significantly different. However, when PPE was used, the difference in UE values between the farmers using the two different types of sprayers was not significant; 3) When protective measure A was adopted, the risk quotient (RQ) values of the farmers and technicians who used electric backpack sprayers for the application of malathion were 1.44 and 0.54, respectively; the corresponding RQ values when protective measure B was adopted were 0.97 and 0.28, respectively. When stretcher-mounted sprayers were used for the application of chlorpyrifos, the RQ value of the farmers who adopted protective measure E was 0.43 while other types of PPE use resulted in RQ values greater than 1. In contrast, the RQ value for technicians was 1.62 when protective measure A was used and 1.02 when protective measure B was adopted, whereas other types of PPE use resulted in RQ values less than 1. Therefore, besides increasing the awareness of personal protection among pesticide applicators, improvement in the management of pesticide use and the enhancement of standard operations are of practical significance for controlling occupational exposure to pesticides.     

Impact of pesticides on soil microbiological parameters and possible bioremediation strategies

Intensive agriculture is spectacularly successful since last couple of decades due to the inputs viz; fertilizers and pesticides along with high yielding varieties. The mandate for agriculture development was to feed and adequate nutrition supply to the expanding population by side the agriculture would be entering to into new area of commercial and export orientation. The attention of public health and proper utilization natural resources are also the main issues related with agriculture development. Concern for pesticide contamination in the environment in the current context of pesticide use has assumed great importance [1]. The fate of the pesticides in the soil environment in respect of pest control efficacy, non-target organism exposure and offsite mobility has been given due consideration [2]. Kinetics and pathways of degradation depend on abiotic and biotic factors [6], which are specific to a particular pesticide and therefore find preference. Adverse effect of pesticidal chemicals on soil microorganisms [3], may affect soil fertility [4] becomes a foreign chemicals major issue. Soil microorganisms show an early warning about soil disturbances by foreign chemicals than any other parameters. But the fate and behavior of these chemicals in soil ecosystem is very important since they are degraded by various factors and have the potential to be in the soil, water etc. So it is indispensable to monitor the persistence, degradation of pesticides in soil and is also necessary to study the effect of pesticide on the soil quality or soil health by in depth studies on soil microbial activity. The removal of metabolites or degraded products should be removed from soil and it has now a day’s primary concern to the environmentalist. Toxicity or the contamination of pesticides can be reduced by the bioremediation process which involves the uses of microbes or plants. Either they degrade or use the pesticides by various co metabolic processes.     

Adverse Respiratory Health and Hematological Alterations among Agricultural Workers Occupationally Exposed to Organophosphate Pesticides: A Cross-Sectional Study in North India

Background

Non-protective work practices followed by farm workers during spraying of pesticides lead to occupational exposure among them.

Objective

This study is designed to explore the respiratory health and hematological profile of agricultural workers occupationally exposed to OP pesticides.

Materials and Methods

A cross sectional study was undertaken among 166 pesticide sprayers working in mango orchards of Lucknow district in North India compared with 77 controls to assess the respiratory illness, lung functions, cholinesterase levels and hematological profile. A questionnaire based survey and clinical examination for respiratory health were conducted among study subjects. Lung function test was conducted among study subjects by using spirometer. Cholinesterase level as biomarker of OP pesticides and hematological profile of study subjects were investigated in the laboratory by following the standard protocols.

Results

Overall respiratory morbidity observed among exposed subjects was 36.75%. Symptoms for respiratory illness like dry cough, productive cough, wheezing, irritation of throat and blood stained sputum were found to be significantly more (p<0.05) among pesticide sprayers than controls. Lung function parameters viz. PEFR, FEV₁, %PEFR predicted, %FEV₁ predicted and FEV₁/FVC were found to be significantly decreased (p<0.05) among pesticide sprayers as compared to controls. Exposure wise distribution of respiratory illness and lung functions among pesticide sprayers show that the exposure duration significantly elevates (p<0.05) the respiratory problems and significantly decreases (p<0.001) lung functions among pesticide sprayers. Activities of acetylcholinesterase and butyrylcholinesterase were found to be significantly depleted (p<0.001) among pesticide sprayers as compared to controls which show the exposure of OP pesticides among them. The hematological profile viz. RBC, WBC, monocytes, neutrophils, MCV, MCH, MCHC and platelet count were significantly altered (p<0.001) in pesticide sprayers than controls.

Conclusion

This study shows that the unsafe occupational exposure of OP pesticides causes respiratory illness, decreased lung functions and hematological alterations among pesticide sprayers.     

Possible mechanism of pesticide toxicity-related oxidative stress leading to airway narrowing

The study was conducted to assess the magnitude of oxidative stress and lung function abnormalities in 34 male pesticide sprayers on exposure to pesticides in mango plantations. Biochemical studies on blood antioxidant enzymes revealed an unchanged glutathione level and increased level of malondialdehyde (P < 0.001), which indicates that pesticide sprayers may have suffered from oxidative stress. Decreased acetyl-cholinesterase levels (P < 0.001) in sprayers compared to the controls suggest inhibition of cholinesterase activity. The present study shows that pesticide toxicity might lead to oxidative stress and airway narrowing resulting in decreased peak expiratory flow rate.     

Fungicides degradation in an organic biomixture: impact on microbial diversity

Biological systems are being developed all over EU countries to protect water-bodies from pesticide contamination at farm level. A laboratory experiment was carried out to test the efficiency of a mixture of compost and straw in bio-degrading different mixtures of fungicides usually applied in vineyards. At the same time the effects of fungicide applications on microbial community of biomixture were also evaluated. Results showed that the biomixture had a good capability of degrading pesticides. Indeed, at the end of the experiment (112 days), the concentration of most of the pesticides was close to complete degradation. Denaturing gradient gel electrophoresis (DGGE) analysis showed an evident modification of microbial diversity after the addition of fungicides. However, at the end of degradation process, no significant changes in the composition of microbial community were seen. In this specific substrate used in the biomixture, yeast flora and ascomycete filamentous fungi seemed to be involved in the degradation activity.     

Possible mechanism of pesticide toxicity-related oxidative stress leading to airway narrowing

Abstract

The study was conducted to assess the magnitude of oxidative stress and lung function abnormalities in 34 male pesticide sprayers on exposure to pesticides in mango plantations. Biochemical studies on blood antioxidant enzymes revealed an unchanged glutathione level and increased level of malondialdehyde (P < 0.001), which indicates that pesticide sprayers may have suffered from oxidative stress. Decreased acetyl-cholinesterase levels (P < 0.001) in sprayers compared to the controls suggest inhibition of cholinesterase activity. The present study shows that pesticide toxicity might lead to oxidative stress and airway narrowing resulting in decreased peak expiratory flow rate.     

Nanoporous impedemetric biosensor for detection of trace atrazine from water samples

Trace contamination of ground water sources has been a problem ever since the introduction of high-soil-mobility pesticides, one such example is atrazine. In this paper we present a novel nanoporous portable bio-sensing device that can identify trace contamination of atrazine through a label-free assay. We have designed a pesticide sensor comprising of a nanoporous alumina membrane integrated with printed circuit board platform. Nanoporous alumina in the biosensor device generates a high density array of nanoscale confined spaces. By leveraging the size based immobilization of atrazine small molecules we have designed electrochemical impedance spectroscopy based biosensor to detect trace amounts of atrazine. We have calibrated the sensor using phosphate buffered saline and demonstrated trace detection from river and bottled drinking water samples. The limit of detection in all the three cases was in the femtogram/mL (fg/mL) (parts-per-trillion) regime with a dynamic range of detection spanning from 10 fg/mL to 1 ng/mL (0.01 ppt to 1 ppm). The selectivity of the device was tested using a competing pesticide; malathion and selectivity in detection was observed in the fg/mL regime in all the three cases.     

Dual-level toxicity assessment of biodegradable pesticides to aquatic species

The use of ecological models to assess the effects of pesticides on the structure and function of aquatic ecosystems is of growing interest. Of utmost concern is assessment of pesticides that have the potential to biodegrade into metabolites that are as toxic as the parent pesticide. In this work, a mathematical model to predict and evaluate the effect of two pesticides on the population of aquatic biospecies where both pesticides are bio-available in water and sediments with one of the pesticides capable of biodegrading into the other but not vice versa is formulated and analyzed. Conditions for nonlinear stability, instability and Hopf-bifurcation are obtained. The model undergoes a Hopf-bifurcation when the rate of discharge of pesticides crosses a critical value, so that the population of the aquatic species follows an oscillatory pattern. Four hypotheses involving the concentration of the pesticides and the population of the aquatic species where qualitatively investigated: the aquatic species will completely die out with time, the population of the aquatic biospecies will remain under certain conditions, the pesticide will continually remain in water and there will be a periodic variation in the population of the aquatic species over time. Results also indicate that the biodegradation potential of one of the pesticides had significant effect on the population dynamics of the aquatic species.     

微生物降解农药的研究新进展*

农药中,尤其化学农药中高毒、高残留、难降解的农药是重要的环境污染物,而微生物治理农药污染是一项有效手段,几十年来,在这方面已进行了大量研究。从农药降解菌的种类、工程菌的构建、微生物降解农药的机理、降解特性、影响因素及应用效果等几方面综述了近年这些方面的研究进展,并提出农药微生物降解研究领域的发展趋势和有待进一步解决的问题。     

Buffer strip width and agricultural pesticide contamination in Danish lowland streams: Implications for stream and riparian management

According to the European Water Framework Directive, member states are obliged to ensure that all surface water bodies achieve at least good ecological status and to identify major anthropogenic stressors. Non-point source contamination of agricultural pesticides is widely acknowledged as one of the most important anthropogenic stressors in stream ecosystems.We surveyed the occurrence of 31 pesticides and evaluated their potential toxicity for benthic macroinvertebrates using Toxic Units (TU) in 14 Danish 1st-and 2nd-order streams in bed sediments and stream water during storm flow and base flow. Total pesticide concentrations and toxic potential were highest during storm flow events with maximum TU ranging from −6.63 to −1.72. We found that minimum buffer strip width in the near upstream area was the most important parameter governing TU. Furthermore, adding a function for minimum buffer strip width to the Runoff Potential (RP) model increased its power to predict measured TUs from 46% to 64%. However, including a function for tile drainage capacity is probably equally important and should be considered in future research in order to further optimise the RP model. Our results clearly emphasise the importance of considering buffer strips as risk mitigation tools in terms of non-point source pesticide contamination. We furthermore apply our results for discussing the minimum dimensions that vegetated buffer strips should have in order to sufficiently protect stream ecosystems from pesticide contamination and maintain good ecological status.     

Pesticide relevance and their microbial degradation: a-state-of-art

The extensive use of pesticide causes imbalance in properties of soil, water and air environments due to having problem of natural degradation. Such chemicals create diverse environmental problem via biomagnifications. Currently, microbial degradation is one of the important techniques for amputation and degradation of pesticide from agricultural soils. Some studies have reported that the genetically modified microorganism has ability to degrade specific pesticide but problem is that they cannot introduce in the field because they cause some other environmental problems. Only combined microbial consortia of indigenous and naturally occurring microbes isolated from particular contaminated environment have ability to degrade pesticides at faster rate. The bioaugumentation processes like addition of necessary nutrients or organic matter are required to speed up the rate of degradation of a contaminant by the indigenous microbes. The use of indigenous microbial strains having plant growth activities is ecologically superior over the chemical methods. In this review, we have attempted to discuss the recent challenge of pesticide problem in soil environment and their biodegradation with the help of effective indigenous pesticides degrading microorganisms. Further, we highlighted and explored the molecular mechanism for the pesticide degradation in soil with effective indigenous microbial consortium. This review suggests that the use of pesticide degrading microbial consortia which is an eco-friendly technology may be suitable for the sustainable agriculture production.     

Comparison of Pesticide Sorption by Physicochemically Modified Soils with Natural Soils as a Function of Soil Properties and Pesticide Hydrophobicity

The objectives of this paper were to determine the efficiency of physicochemically modified soils with a surfactant in the sorption of pesticides, the stability against washing of the pesticides sorbed, and the effective sorption capacity of surfactant adsorbed by soils as a function of pesticide hydrophobicity and soil characteristics. Five soils of different characteristics and five pesticides (penconazole, linuron, alachlor, atrazine and metalaxyl) with different Kow values were selected and octadecyltrimethylammonium bromide (ODTMA) was chosen as model of cationic surfactants. Sorption-desorption isotherms were obtained and constants Kf and Kfd for natural soils (from Freundlich equation) and K and Kd for ODTMA-soils (from linear equation) were determined. Sorption on ODTMA-soils was higher than on natural soils. K increased 27–165 times for penconazole, 22–77 times for linuron, 7–14 times for alachlor, 9–23 times for atrazine, and 21–333 times for metalaxyl in relation to Kf. Sorption coefficients normalized to 100% of total organic matter (TOM) from organo soils K_OM (K 100/%TOM), were always higher than those from natural soils Kf_OM (Kf 100/%OM), indicating that the organic matter (OM) derived from the ODTMA (OM_ODTMA) had a greater sorption capacity than the OM of the natural soil. K_OM values were also higher than the Kow (octanol/water distribution coefficient) value for each pesticide. The similarity of the high K_OM values for the sorption of each pesticide by the five soils and the linearity of isotherms point to a partitioning of the pesticides between surfactant and water. The use in this work of different soils and various pesticides, unusual in this type of investigation, allowed us to obtain equations to know the sorbed amount of a given pesticide by the surfactant-modified soils as a function of the OM content derived from the cation and the Kow of the pesticide. The results obtained are of interest when it becomes necessary to increase the sorption capacity of soils with low OM contents with a view to delaying pesticide mobility in soils from pollution point sources (high concentration in small area), and preventing the pollution of waters.     

Comparative assessment of growth and biodegradation potential of soil isolate in the presence of pesticides

In Pakistan, to increase agricultural production, higher amounts of fertilizers and pesticides are being used. The residues of the applied pesticides stay in the environment and therefore causing contamination of air, water and land. Moreover, agricultural industries are also contributing relatively high quantities of toxic pesticides into the environment. Since most of them have no treatment facilities. These pesticides may be toxic, mutagenic or carcinogenic. They may be bioaccumulated or biomagnified by the biota. Therefore its removal from environmental systems needs special attention. In this study, bacterial isolate, Pseudomonas, designated as IES-Ps-1, was used to assess its potential for pesticide removal from industrial wastewater using the biosimulator (activated sludge process). During experimental studies conducted in the flask as well as in biosimulator, it was observed that IES-Ps-1 grows normally at low concentrations of added insecticides when compared with the control test (without pesticide). However, at high concentrations the microbial count decreased but no death occurred and the culture remained in lag phase. In many cases, the growth of organisms in the presence of the particular substrate serves as an indication about its metabolic potential. However, to confirm these results, chemical oxygen demand (COD) and HPLC analysis were performed. Under aerobic culture conditions using mechanical aerators in biosimulator, almost complete removal of Cypermethrin at 20 mg/L dose occurred during 48 h. The study findings indicate that IES-Ps-1 strain, can be used for the treatment of the pesticide contaminated environment. Such study may be valuable to scientist and engineers, who are trying to develop methods for the treatment of toxic organic waste using the biological treatment process.     

Use of diatom life-forms and ecological guilds to assess pesticide contamination in rivers: Lotic mesocosm approaches

The persistence of pesticides in the environment and their effects are a cause of concern to more and more people, and so in 2009 the French government announced plans to reduce pesticide use in agriculture over the next 10 years. Water managers are to monitor the beneficial impact of this reduction on aquatic environments. It has been suggested that diatoms may be good indicators of pesticides, and more particularly of herbicides, in water. Diatoms have been routinely used to assess organic and nutrient pollution for more than 10 years. The general approach is to develop a diatom-based tool to assess pesticide contamination. Diatom indices are usually based on specific pollution sensitivity. Other metrics, such as life-forms, ecological guilds, or cell size offer other advantages. For instance, the relationships between trends in these metrics and environmental gradients are more robust, and make it easier to establish ecological hypotheses. We have therefore opted for this approach.To develop such a tool, outdoor, lotic mesocosm experiments lasting about 2 months were conducted from 2006 to 2008. Herbicides (diuron) and fungicides (azoxystrobin, tebuconazole) were tested at environmental concentrations (sum of pesticides concentrations from 1.11 to 3.01 μg L^?1 for chronic pollutions and from 20.25 to 29.50 μg L^?1 for short-term acute pollutions). Diatom communities in artificial channels were analyzed by light microscopy using standard European methods. The various parameters structuring diatom communities were assessed, and colonization time appeared to be the most important. However, pesticide contamination was the second most important, and had a more significant impact on the composition of ecological guilds than on species composition. Some metrics did not display any significant trends (benthic/planktonic, colonial, pedunculate, pioneer), but others looked promising for use in pesticide contamination assessment: the abundances of motile guild, low-profile guild and mucous tubule diatoms all increased in contaminated channels, whereas high-profile diatoms showed the opposite trend. Some possible explanations, such as a protective effect of the exopolysaccharide matrix, can be advanced: diatoms living inside a mucous tubule may be shielded from dissolved pesticides, as are motile diatoms, which have a micro-habitat preference for thick matrices which also allows them to withstand higher levels of water contamination. In the same way, high-profile guild diatoms are exposed to dissolved pesticides to a greater extent, and this could explain their lower abundance in contaminated channels.     

Specifics and challenges of assessing exposure and effects of pesticides in small water bodies

Small water bodies (SWB) are freshwater ecosystems of high ecological relevance. However, they receive considerably higher inputs of pesticides compared to larger water bodies owing to their close connection to adjacent agricultural fields in combination with their low water volume or discharge. Monitoring of the pesticide contamination of lentic and lotic SWB is a challenging task as various spatial and temporal factors affect pesticide’s maximum peak concentrations in the water bodies. We present an overview of the major challenges that can complicate the detection of exceedances of regulatory acceptable concentrations. Pesticide data from streams encompassed by the Danish pesticide monitoring program show that the highest pesticide concentrations are found in SWB. A ditch monitoring in a German orchard reveals that event-driven sampling following spray application outperforms the widely used automatic water sampling at fixed intervals, and we therefore suggest that the latter should replace the former in SWB. Furthermore, we suggest that gathering of quantitative data on pesticide pollution of lentic SWB should be given priority in future research.     

Toxicity and bioremediation of pesticides in agricultural soil

Pesticides are one of the persistent organic pollutants which are of concern due to their occurrence in various ecosystems. In nature, the pesticide residues are subjected to physical, chemical and biochemical degradation process, but because of its high stability and water solubility, the pesticide residues persist in the environment. Moreover, the prevailing environmental conditions like the soil characteristics also contribute for their persistence. Bioremediation is one of the options for the removal of pesticides from environment. One important uncertainty associated with the implementation of bioremediation is the low bioavailability of some of the pesticides in the heterogeneous subsurface environment. Bioavailability of a compound depends on numerous factors within the cells of microorganism like the transportation of susbstrate across cell membrane, enzymatic reactions, biosurfactant production etc. as well as environment conditions such as pH, temperature, availability of electron acceptor etc. Pesticides like dichlorodiphenyltrichloroethane (DDT), hexachlorocyclohexane (HCH), Endosulfan, benzene hexa chloride (BHC), Atrazine etc. are such ubiquitous compounds which persist in soil and sediments due to less bioavailability. The half life of such less bioavailable pesticides ranges from 100 to 200 days. Most of these residues get adsorbed to soil particles and thereby becomes unavailable to microbes. In this review, an attempt has been made to present a brief idea on ‘major limitations in pesticide biodegradation in soil’ highlighting a few studies.     

Inoculation with a Mixed Degrading Culture Improves the Pesticide Removal of an On-Farm Biopurification System

To investigate whether the pesticide removal in on-farm biopurification systems (BPS) filled with two different types of substrata (biomix and plastic carriers) is affected by inoculation with a pesticide-degrading strain or mixed culture, lab-scale BPS used to treat chloropropham point source contaminations were bioaugmented with either a specialized chloropropham-degrading strain or a chloropropham-degrading enrichment culture. Application of both inoculum types leads to an accelerated degradation activity in the columns filled with plastic carriers. For both substratum types, inoculation with the mixed culture resulted in a lower breakthrough of the toxic intermediate 3-chloroaniline at high hydraulic loads, compared to inoculation with the pure isolate and no inoculation. This study suggests that the use of plastic carrier materials could be a proficient alternative to the use of a conventional biomix as a substratum in on-farm BPS and that inoculation with a mixed degrading culture can reduce the leaching of more mobile toxic intermediates.     

多种农药与次氯酸钠、高锰酸钾和高铁酸钾的反应活性

为探究4类,10种广泛使用的农药(苯氧羧酸类,芳香酸类,取代脲类和烟碱类)与3种氧化剂(次氯酸钠,高锰酸钾和高铁酸钾)的反应活性,本研究在温度(25±2)℃、pH值为8的条件下,分析10种农药分别与3种氧化剂NaClO、KMnO4、K2Fe O4在不同浓度下的反应活性,采用HPLC检测法,对比降解效能,探究氧化剂性质与有机物结构导致的反应活性的差异。实验结果表明,不同种类农药的结构性质对反应活性有重要影响,3种氧化剂的氧化降解能力有明显差异。苯氧羧酸类和芳香酸类农药结构较简单,并含有稳定的苯环或吡啶环结构,氧化降解较困难。取代脲类和烟碱类农药结构较复杂,氧化剂可攻击其不饱和官能团,反应活性较高。NaClO对取代脲类农药的降解率明显优于其他2种氧化剂,3种氧化剂对烟碱类农药的氧化降解效果依次为NaClO>KMn O4>K2Fe O4。研究多种农药与次氯酸钠、高锰酸钾和高铁酸钾的反应活性对降解去除水体中的农药残留对水环境的治理具有重要意义。     

植物-微生物联合修复毒死蜱污染的土壤

本试验以毒死蜱污染土壤为研究材料,利用降解菌DSP-A分别与高丹草、紫花苜蓿、多花黑麦草进行联合修复,探讨了植物-微生物联合修复毒死蜱污染土壤的效果,以及影响联合修复的因素,结果表明,植物．微生物联合修复的效果优于单一的植物修复及单一的微生物修复效果。与DSP—A菌群较合适的植物是高丹草,该组合对毒死蜱的降解率达到96．44％,其次是多花黑麦草。研究了微生物数量、植株密度以及土壤湿度对联合修复效果的影响,结果表明,DSP．A菌菌液稀释倍数越大,联合修复的效果越差。植株密度对联合修复的影响,主要表现为对植物根系生长的影响。植株密度越大,对生存环境的竞争越激烈,植物根系的生长越不好。除了紫花苜蓿外,高丹草和多花黑麦草根系的生长均受到影响。高丹草种植密度为12株／盆时,与DSP—A菌的联合修复效果最好,多花黑麦草则为10株／盆。土壤湿度是影响联合修复的重要因素,不仅影响植物的生长,对微生物的生长也有影响。土壤湿度过大,造成土壤的含氧量降低,不利于植物根系和好氧细菌的生长,从而影响土壤中农药的降解。土壤湿度过小,容易造成植株缺水,根系生长和微生物的生长。高丹草与DSP．A菌、多花黑麦草与DSP—A菌联合修复最适浇水量都为20mL／d,紫花苜蓿与DSP—A菌联合修复最适浇水量都为15mL／d。