Due to strong affinity for the solid phase, pyrethroid bioavailability is reduced considerably in surface water containing dissolved organic matter or suspended solids. The bioavailable fraction for water column invertebrates is often considered to be the freely dissolved fraction, because it is that fraction which can cross the cellular membrane. Thus, selective methods that measure the freely dissolved concentration are good indicators of the bioavailability of pyrethroids in surface waters. Solid phase microextraction (SPME) was used in several studies as a selective sampling approach to evaluate the bioavailability of pyrethroids in surface water. The SPME measurements correlated well with the pyrethroid bioaccumulation by Daphnia magna. The LC50 estimated by SPME also correlated well with the observed LC50 to Ceriodaphnia dubia. These results indicate the usefulness of SPME as a tool for evaluating the bioaccumulation and toxicity of pyrethroids to water column invertebrates in the presence of dissolved organic matter or suspended solids. Results from these studies suggest that the presence of dissolved organic carbon and suspended solids should be taken into account when evaluating organism exposure to pyrethroids, especially when monitoring runoff or irrigation effluent which usually contain high levels of dissolved organic matter and suspended solids.

<正>为指导农药的使用,避免对后茬作物的影响、优化农药的施用量以及减少环境污染,研究了土壤、腐植酸、粘土矿对莠去津的吸附,借助IR和ESR技术研究了腐植酸与莠去津的作用机理。结果表明,吸附强弱与土壤理化特性密切相

Pyrethroids are widely used insecticides in both agricultural and urban environments, and their potential movement to surface streams and toxicity to susceptible aquatic species is an emerging concern. Natural surface waters usually contain low levels of dissolved organic matter (DOM). Limited data have shown that DOM preparations can significantly alter the bioavailability and toxicity effects of pyrethroids. However, the importance of these effects in natural waters has not been investigated. In this study we measured uptake and acute toxicity of permethrin and cyfluthrin by Daphnia species in 15 surface water samples. Low levels of DOM (3-20 mg L(-1)) inhibited cyfluthrin uptake by Daphnia magna and acute toxicity to Ceriodaphnia dubia in most samples. For permethrin, the effects of DOM on bioavailability and toxicity were generally not significant. The effects of DOM on bioavailability of cyfluthrin could not be explained from the DOC concentration alone, suggesting that properties of DOM were also important in regulating bioavailability. Regression of K DOC with selected DOM properties revealed significant dependence of K DOC on the carboxylic acid content of DOM. Moreover, concentrations sensed by solid-phase microextraction (SPME) fibers were well correlated with the observed changes in bioaccumulation by D. magna and acute toxicity to C. dubia. Therefore, selective sampling methods such as SPME may be used for measuring the bioavailable concentrations of pyrethroids in waters with naturally occurring DOM levels and predicting the actual toxicity effects.

The use of pyrethroid insecticides is increasing in both agricultural and urban environments. Although pyrethroids display very high acute toxicities to water column organisms in laboratory tests, environmental water samples typically contain suspended sediment (SS) that can reduce the freely dissolved concentration of pyrethroids, hence their bioavailability. Consequently, phase distribution could play an important role in pyrethroid aquatic toxicology. In this study, we evaluated the effect of SS on the acute toxicity of four widely used pyrethroid insecticides to Ceriodaphnia dubia . In all assays, median lethal concentrations (LC50s) consistently increased with increasing SS, demonstrating the pronounced inhibitory effects of SS on pyrethroid toxicity. The LC50s in the 200 mg/L SS solutions were 2.5 to 13 times greater than those measured in sediment‐free controls. Solid‐phase microextraction (SPME) was used to determine the apparent distribution coefficient K d for the pyrethroids in the water samples. Under the assumption that only the freely dissolved fraction is bioavailable, the measured K d was used to predict C. dubia LC50s in the water samples. The predicted LC50s were within a factor of two of the measured values for 95% of the treatments. Results from this study suggest that the inhibitory effect of SS can be highly significant and must be considered in estimating exposures to pyrethroids in aquatic systems. The SPME methodology could be used effectively to measure bioavailable concentration and to predict the actual ecotoxicologic effects of pyrethroids.

Runoff and surface-water effluents commonly contain suspended solids. Adsorption to suspended particles and the associated dissolved organic matter (DOM) may significantly decrease the freely dissolved concentration of a hydrophobic compound and, hence, its availability to aquatic organisms. In the present study, we evaluated phase distribution and bioaccumulation of two synthetic pyrethroids, bifenthrin and permethrin, in water samples containing suspended solids from different source sediments. Uptake of [14C]bifenthrin or [14C] permethrin by Daphnia magna after 24 h consistently decreased with increasing levels of suspended solids in the range of 0 to 200 mg/L. The trend of decrease was closely mimicked by pesticide accumulation on polydimethylsiloxane (PDMS) fibers exposed under the same conditions, and the ratio of body residues in D. magna to the concentration detected in the PDMS fiber was consistently around 2.4. Regression analysis showed that the pesticide adsorbed on particles or DOM was completely unavailable to D. magna for uptake during the 24-h exposure. The relative contribution of particles and DOM to the reduced bioavailability depended on the organic matter content and the texture of the source sediment. The influence from particles was predominant for sandy sediments, but contribution from DOM became comparable to or even greater than particles when the organic matter content of the source sediment was 1% or greater. The inhibitory effects of suspended solids on bioavailability should be considered when monitoring runoff and surface-water effluents for synthetic pyrethroids. The proposed PDMS method is simple and inexpensive, and it may serve as an effective option for obtaining ecotoxicologically relevant concentrations.

Synthetic pyrethroids are widely used insecticides in both agricultural and urban environments. Recent studies show frequent appearances of pyrethroid residues in runoff effluents and sediments, which stimulated concerns over the potential ecotoxicological implications. Pyrethroids are known to have two contrasting characteristics, high aquatic toxicity and strong affinity for the solid phase, that may negate the actual toxicity in a multiphased system. This study evaluated the effect of dissolved organic matter (DOM) on the pyrethroid uptake by and acute toxicity to water-column invertebrates using permethrin as a model compound. During the bioassays, the freely dissolved permethrin concentration was simultaneously measured using poly(dimethylsiloxane) (PDMS) fibers as a biomimetic surrogate. The presence of DOM consistently decreased permethrin uptake and increased its LC(50). For instance, compared to the DOM-free treatment, the LC(50) of permethrin to Ceriodaphnia dubia in a pond water containing DOM at 10 mg L(-)(1) increased from 0.56 to 1.03 microg L(-)(1), whereas the bioaccumulation factor by Daphnia magna decreased by 56%. Permethrin accumulation on the PDMS fiber closely mimicked permethrin uptake by D. magna. Statistical analyses suggest that permethrin associated with DOM was completely unavailable to D. magna or C. dubia. The effect of DOM on permethrin bioavailability appeared to depend also on the source of the DOM. These results indicate that the inhibitory role of DOM should be considered in the development of toxicologically relevant water quality limits and in monitoring protocols for permethrin and other pyrethroids in runoff effluents and surface streams that ubiquitously contain DOM.

研究了除草剂莠去津对土壤过氧化氢酶活性的影响.试验结果表明,莠去津浓度不同对土壤过氧化氢酶活性影响会不同,随着浓度的升高,对过氧化氢酶活性激活作用有所增强,莠去津对离体过氧化氢酶有一定的激活;336 nm处的相对荧光强度不断减弱,酶分子的构象发生了变化,过氧化氢酶分子渐趋紧密.莠去津对过氧化氢酶荧光的猝灭作用主要是由于静态猝灭引起的.

N-nitrosodimethylamine (NDMA), a potential carcinogen, was commonly found in treated wastewater as a by-product of chlorination. As treated water is increasingly used for landscape irrigation, there is an imperative need to understand the leaching risk for NDMA in landscape soils. In this study, adsorption and incubation experiments were conducted using landscape soils planted with turfgrass, ground cover, and trees. Adsorption of NDMA was negligibly weak (K(d) < 1) in all soils, indicating that NDMA has a high potential for moving with percolating water in these soils. Degradation of NDMA occurred at different rates among these soils. At 21 degrees C, the half-life (t(1/2)) of NDMA was 4.1 d for the ground cover soil, 5.6 d for the turfgrass soil, and 22.5 d for the tree soil. The persistence was substantially prolonged after autoclaving or when incubated at 10 degrees C. The rate of degradation was not significantly affected by the initial NDMA concentration or addition of organic and inorganic nutrient sources. The relative persistence was inversely correlated with soil organic matter content, soil microbial biomass, and soil dehydrogenase activity, suggesting the importance of microorganisms in NDMA degradation in these soils. These results suggest that the behavior of NDMA depends closely on the vegetation cover in a landscape system, and prolonged persistence and increased leaching may be expected in soils with sparse vegetation due to low organic matter content and limited microbial activity.

The binding of metolachlor and S-Isomer to urease in aqueous solution was studied using UV difference spectrum and fluorescence spectrum. According to the results of the UV difference spectrum curve, the UV difference adsorption deltaA changed rapidly when herbicide concentration increased from 0.0 to 1.6 micromol x L(-1) x UV difference spectra were red-shifted and absorb-peaks became lower. It was shown that herbicide can quench the urease fluorescence mainly through a static quenching procedure. The binding constant K and the number of binding site n were calculated according to the fluorescence quenching results. For metolachlor, K = 1.49 x 10(3) L x mol(-1) and n was 0.84; for S-isomer, K=2.22 x 10(3) L x mol(-1) and n was 0.89.

Triazine herbicides are among the most widely used herbicides in the United States. Many triazine compounds are relatively stable under natural conditions and have become prominent contaminants in hydrologic systems. It was previously reported that chloro-s-triazine compounds were rapidly dechlorinated in water by polysulfides, and the reaction was assumed to be aromatic nucleophilic substitution (SNAr). In this study, we evaluated the effect of free radical inhibitors on the reaction rate of polysulfides with herbicides atrazine, simazine, and cyanazine. The reaction was significantly inhibited by radical scavengers oxygen and 1,4-benzoquinone, suggesting involvement of free radicals in the reaction. Spectral analysis of the reaction mixture using electron spin resonance showed that after the reaction, the free radical concentration in polysulfide solution substantially decreased. These evidences indicate that radical sulfur anions may also be involved in the reaction, likely via a free radical substitution reaction (S(RN)1) mechanism. Amendment of sodium tetrasulfide significantly reduced the leaching of atrazine or simazine from packed sand columns. Therefore, polysulfide salts may be potentially used to remove residues of triazine herbicides in environmental media.

The binding of triazine herbicide to catalase in aqueous solution was studied using fluorescence spectroscopy. It was shown that the herbicide has a strong ability to quench the CAT fluorescence mainly through a static quenching procedure. The binding constant K and the number of binding site n were calculated according to the fluorescence quenching results. For prometryn, K = 6.17 X 10(6) L.mol(-1) and n was 1.45; for prometon, K = 2.12 X 10(6) L.mol(-1) and n was 1.19. Based on the mechanism of energy transfer, the distances between acceptor herbicide and CAT were obtained. The distances are r (prometryn) = 0.140 nm and r (prometon) = 0.155 nm. It is clear that the binding of prometryn with catalase is stronger than that of prometon. It is inferred that the binding site between herbicides and catalase was Tyr-214.

The adsorption of prometryne and prometon on 4 kinds of soil colloids was studied and compared using z electric potential technique. The results showed that the z electric potentials of soil surface raised somewhat as the positively charged herbicides were adsorpted on the soil surface charged negatively. The herbicides affect the z electric potential even causing its change from negative to positive. Through calculating the point of zero charge, Gibbs energies and adsorption constants between the herbicide and soil was obtained, and the results were similar to those calculated with batch oscillation equilibration technique.

研究了均三氮苯类除草剂扑灭通和氰草津各0、1、10、100 μg g-1和扑灭通+氰草津50+50 μg g-1对土壤过氧化氢酶活性和多酚氧化酶活性的影响,结果表明扑灭通和氰草津施用后对过氧化氢酶活性和多酚氧化酶活性均有一定的激活作用,氰草津对过氧化氢酶和多酚氧化酶的激活作用比扑灭通的激活作用更强.两者混施没有产生明显的协同作用.

A chemiluminescence suppression method for the determination of catalase activity based on Luminol-KIO_4-H_2O_2-catalase system was established. The linear range of the method for the determination of the catalase activity is 2~200 unit/L and the detection limit is 0.7 unit/L. The relative standard deviation(n=10) is 0.4% for 50 unit/L catalase. The method was used to determine the activity of catalase in soil with satisfactory results as compared with the standard method, potassium permanganate titration.

By the UV difference spectrum and fluorescence spectrum technique, the influence of atrazine on tyrosine environment of catalase was studied. According to the results of the UV difference spectrum curve, the UV difference adsorption delta A260nm showed changing rapidly when pH ranging from 9.1 to 9.9. UV difference spectrum and fluorescence spectrum of atrazine-catalase were red shift that maybe caused by effect of hydrogen bonding. The fluorescence spectrum was sensitive to SDS and quenchable by KI. The results indicated that the tyrosine residues of catalase reside in hydrophilic core, and there is hydrogen bonding between atrazine and catalase probably. Atrazine has little effect on tyrosine environment of catalase.

Adsorption of chloroacetanilide herbicides on homoionic montmorillonite, soil humic acid, and their mixtures was studied by coupling batch equilibration and FT-IR analysis. Adsorption isotherms of acetochlor, alachlor, metolachlor and propachlor on Ca(2+)-, Mg(2+)-, Al(3+)- and Fe(3+)-saturated clays were well described by the Freundlich equation. Regardless of the type of exchange cations, Kf decreased in the order of metolachlor > acetolachlor > alachlor > propachlor on the same clay. FT-IR spectra showed that the carbonyl group of the herbicide molecule was involved in binding, probably via H-bond with water molecules in the clay interlayer. The type and position of substitutions around the carbonyl group may have affected the electronegativity of oxygen, thus influencing the relative adsorption of these herbicides. For the same herbicide, adsorption on clay increased in the order of Mg2+ < Ca2+ < Al3+ < or = Fe3+ which coincided with the increasing acidity of homoionic clays. Acidity of cations may have affected the protonation of water, and thus the strength of H-bond between the clay water and herbicide. Complexation of clay and humic acid resulted in less adsorption than that expected from independent adsorption by the individual constituents. The effect varied with herbicides, but the greatest decrease in adsorption occurred at a 60:40 clay-to-humic acid ratio for all the herbicides. Causes for the decreased adsorption need to be characterized to better understand adsorption mechanisms and predict adsorption from soil compositions.

The binding of simazine to catalase (CAT) in aqueous solution was studied using fluorescence spectroscopy and high performance liquid chromatography ( HPLC) with microdialysis sampling technique. It was shown that herbicide had a strong ability to quench the CAT fluorescence mainly through a static quenching procedure. The binding constant K and the number of hinging site n were calculated according to the fluorescence quenching results and Scatchard equation from the results of HPLC with microdialysis sampling technique. Based on the mechanism of energy transfer, the distance between acceptor herbicide and CAT wes obtained. The distance are r = 0.164 nm. It is proposed clearly that the interaction between simazine and CAT has been verified as consistent with static quenching procedure and the quenching mechanism is related to the energy transfer. It is inferred that the binding sites between simazine and catalase is Tyr-214.

The binding of atrazine to catalase(CAT) in aqueous solution was studied with fluorospectroscopic method. The results show that atrazine has a strong ability to quench the CAT fluorescence mainly through a static quench procedure. The binding constant K and the number of binding site n were calculated according to the fluorescence quenching results. Based on the mechanism of energy transfer, the donor-acceptor distance of the herbicide and CAT was calculated as 0.159. It is inferred that the binding site of CAT to atrazine is Tyr-16.