Effects of cyclodextrins on photodegradation of organophosphorus pesticides in humic water

Cyclodextrin (CyD) effects on photodegradations of organophosphorus pesticides in humic water were monitored on the basis of the increase percentage of the photodegradation rate constant for CyD-containing humic water. Remarkable promotion effects of CyDs were observed in humic water for photo-induced radical generation. The promotion effects could be mainly assigned to the inclusion effects of CyDs to catalyze interactions of pesticides with reactive radicals generated by the humin photosensitizer and inclusion-trapped in CyDs.     

Fate of parathion in artificially fortified grape juice processed into wine

"Semellon" grape juice fortified with a high level of 25 ppm parathion was fermented using Saccharomyces cerevisiae var. ellipsoideus. After 12 days inte parathion levels in the wine and lees were 10.3 and 156 ppm, respectively; the paraoxon, aminoparathion, and p-nitrophenol levels in the wine were 0.16, 0.20, and 4.5 ppm, respectively, and in the lees were 0.04, 3.1 and 10 ppm, respectively. Thus, hydrolysis of parathion to p-nitrophenol and parathion sorption to sedimented particulate matter were important pathways for parathion residue reduction in the wine. The 56-day-old finished wine just prior to bottling contained 8.8 ppm parathion, 0.04 ppm paraoxon, 0.21 ppm aminoparathion, and 3.0 ppm p-nitrophenol. Two months storage at 24 degrees, 12 degrees, 4 degrees, and -20 degrees C had no effect on paraoxon and aminoparathion residue levels in the wine; parathion residues in wine decreased at all storage temperatures.     

Structural study on inclusion complexes of cyclodextrins with organophosphorus pesticides by use of rotational strength analysis method

For inclusion complexes of cyclodextrins with parathinons and paraoxon, inclusion depths were estimated with the rotational strength analysis method. The inclusion depths of pesticides were sensitive to the difference in the hydrophobic properties of the phosphate and monothiophosphate groups and were in close correlations with the substrate-specificity for the cyclodextrin-catalyzed hydrolysis of pesticides. The inclusion depths were also characteristically affected by surfactant material having high solubilization functions to aquatic environmental chemicals.     

Photochemical behavior of parathion in the presence of humic acids from different origins

This paper reports the effect of ultraviolet radiation on the degradation of pesticide ethyl parathion in the presence of humic acids. Ethyl parathion was completely degraded in 300 min using an artificial lamp of 7.41 x 10(-10) einstein/s. Humic acid from peat did not influence the photochemical rate (k = 8.92 x 10(-3) min). However, in the presence of aquatic humic acid, the photochemical rate was higher (11.5 x 10(-3) min). The analytical determinations show the presence of p-nitrophenol and aminophenol in the reaction medium during the photochemical experiments. The kinetic of degradation in all experiments obeyed a first-order reaction pattern.     

Removal of mixed pesticides from drinking water system by photodegradation using suspended and immobilized TiO2

Lindane (1α, 2α, 3β, 4α, 5α, 6β-hexachloro cyclohexane), methyl parathion (O,O-dimethyl-O-4-nitrophenyl phosphorothioate) and dichlorvos (2,2-dichlorovinyl-O-O-dimethyl phosphate) are removed from water individually and as a mixture by photo degradation using suspended and immobilized forms of TiO₂ (Degussa P-25). Studies were conducted to optimize the coating thickness of immobilized photo catalyst. The rate of degradation of pesticides was compared in both suspended and immobilized TiO₂ systems. Degradation studies of mixed pesticides were carried out with low concentrations (1.0 and 2.5 mg/L) of pesticides. Only three intermediate byproducts such as methyl paraoxon, O,O,O-trimethyl phosphonic thionate and p-nitrophenol were observed during the methyl parathion degradation in suspended, immobilized TiO₂ systems and mixed pesticides degradation studies. At the end of the reaction methyl parathion and its by-products were completely degraded. During lindane degradation hexachloro cyclohexane, pentachloro cyclohexane, hexachloro benzene, 1-hydroxy 2,3,4,5,6-chlorocyclohexane, 1-hydroxy 2,3,4,5,6-chlorobenzene, pentachloro cyclopentadiene, 1,2,3,4,5-hydroxy cyclopentene and 1,2,3-hydroxy cyclobutane were identified in suspended and immobilized TiO₂ systems, whereas only hexachloro cyclohexane, pentachloro cyclohexane, hexachloro benzene and pentachloro cyclopentadiene were observed during mixed pesticides degradation. No intermediate by-product was observed during the photo degradation of dichlorvos. Langmuir-Hinshelwood pseudo first order kinetic equation showed that there was not much change in the rates of degradation in both suspended and immobilized TiO₂ systems irrespective of the pesticide. During mixed pesticides degradation, the degradation pattern was not similar to that of single pesticide.     

Parathion degradation and its intermediate formation by Fenton process in neutral environment

The purpose of this study is to investigate parathion degradation by Fenton process in neutral environment. The initial parathion concentration for all the degradation experiments was 20 ppm. For hydrogen ion effect on Fenton degradation, the pH varied from 2 to 8 at the [H₂O₂] to [Fe²⁺] ratio of 2-2 mM, and the result showed pH 3 as the most effective environment for parathion degradation by Fenton process. Apparent degradation was also observed at pH 7. The subsequent analysis for parathion degradation was conducted at pH 7 because most environmental parathion exists in the neutral environment. Comparing the parathion degradation results at various Fenton dosages revealed that at Fe²⁺ concentrations of 0.5, 1.0 and 1.5 mM, the Fenton reagent ratio ([H₂O₂]/[Fe²⁺]) for best-removing performance were found as 4, 3, and 2, resulting in the removal efficiencies of 19%, 48% and 36%, respectively. Further increase in Fe²⁺ concentration did not cause any increase of the optimum Fenton reagent ratio for the best parathion removal. The result from LC-MS also indicated that hydroxyl radicals might attack the PS double bond, the single bonds connecting nitro-group, nitrophenol, or the single bond within ethyl groups of parathion molecules forming paraoxons, nitrophenols, nitrate/nitrite, thiophosphates, and other smaller molecules. Lastly, the parathion degradation by Fenton process at the presence of humic acids was investigated, and the results showed that the presence of 10 mg L⁻¹ of humic acids in the aqueous solution enhanced the parathion removal by Fenton process twice as much as that without the presence of humic acids.     

Photochemical Behavior of Parathion in the Presence of Humic Acids from Different Origins

This paper reports the effect of ultraviolet radiation on the degradation of pesticide ethyl parathion in the presence of humic acids. Ethyl parathion was completely degraded in 300 min using an artificial lamp of 7.41 × 10^{? 10} einstein/s. Humic acid from peat did not influence the photochemical rate (k = 8.92 × 10^?3 min). However, in the presence of aquatic humic acid, the photochemical rate was higher (11.5 × 10^?3 min). The analytical determinations show the presence of p-nitrophenol and aminophenol in the reaction medium during the photochemical experiments. The kinetic of degradation in all experiments obeyed a first-order reaction pattern.     

Biodegradation of lindane, methyl parathion and carbofuran by various enriched bacterial isolates

In the present study, lindane (1,2,3,4,5,6-hexachlorocyclohexane), methyl parathion (O-dimethylO-(4-nitro-phenyl) phosphorothioate) and carbofuran (2,3-dihydro-2,2-dimethyl-7-benzofuranyl methylcarbamate) degradation potential of different enriched bacterial cultures were evaluated under various environmental conditions. Enriched cultures behaved differently with different pesticides. Degradation was more in a facultative anaerobic condition as compared to that in aerobic condition. A specific pesticide enriched culture showed maximum degradation of that pesticide irrespective of pesticides and environmental conditions. Lindane and endosulfan enriched cultures behaved almost similarly. Degradation of lindane by lindane enriched cultures was 75 +/- 3% in aerobic co-metabolic process whereas 78 +/- 5% of lindane degradation occurred in anaerobic co-metabolic process. Degradation of methyl parathion by methyl parathion enriched culture was 87 +/- 1% in facultative anaerobic condition. In almost all the cases, many intermediate metabolites were observed. However, many of these metabolites disappeared after 4-6 weeks of incubation. Mixed pesticide-enriched culture degraded all the three pesticides more effectively as compared to specific pesticide- enriched cultures. It can be inferred from the results that a bacterial consortium enriched with a mixture of all the possible pesticides that are present in the site seems to be a better option for the effective bioremediation of multi-pesticide contaminated site.     

Photochemical nitro-nitrite rearrangement in methyl parathion decay under tropical conditions

This work presents a study of the abiotic degradation of commercially available methyl parathion in aqueous solution at two different concentrations (88 mg/L and 200 μg/L). The effects of solar irradiation and the presence of humic acids were evaluated and revealed a synergistic response between them. The half-life of methyl parathion ranged from 4.9 to 37 days, and the experimental data also show that photochemical processes were the most relevant in this case. The only byproduct found in samples submitted to shadowed conditions was 4-nitrophenol. On the other hand, 4-nitrophenol, methyl paraoxon and a new degradation product (O,O-dimethyl O-p-hydroxyphenyl phosphorothioate) were detected when the samples were exposed directly to sunlight. This newly identified compound was prepared in the laboratory by thiophosphorylation of hydroquinone, and coelution experiments with authentic samples provided unambiguous confirmation of the presence of O,O-dimethyl O-p-hydroxy phenylphosphorothioate in samples.     

Influence of sorption to dissolved humic substances on transformation reactions of hydrophobic organic compounds in water. Part II: hydrolysis reactions

The effect of dissolved humic acid (HA) on two types of hydrolysis reactions was investigated: (I) dehydrochlorination of gamma-hexachlorocyclohexane (HCH) and 1,1,2,2-tetrachloroethane (TeCA) as a reaction involving hydroxide ions (OH(-)) and (II) hydrolysis of 1-octyl acetate (OA) which is catalyzed by H(+) at the applied pH value (pH 4.5). The rate of TeCA hydrolysis was not affected by addition of 2 g l(-1) of HA at pH 10 (k' = 0.33 h(-1)) but HCH hydrolysis was significantly inhibited (k' = 4.6 x 10(-3) h(-1) without HA and 2.8 x 10(-3)h(-1) at 2 g l(-1) HA). HCH is sorbed by 51% whereas TeCA sorption is insignificant at this HA concentration. Sorbed HCH molecules are effectively protected due to electrostatic repulsion of OH(-) by the net negative charge of the HA molecules. In contrast, OA hydrolysis at pH 4.5 (k' = 1.6 x 10(-5) h(-1)) was drastically accelerated after addition of 2 g l(-1) HA (k' = 1.1 x 10(-3) h(-1)). The ratio of the pseudo-first-order rate constants of the sorbed and the freely dissolved ester fraction is about 70. H(+) accumulation in the microenvironment of the negatively charged HA molecules was suggested to contribute to the higher reaction rate for the sorbed fraction in case of this H(+)-catalyzed reaction. Analogous effects from anionic surfactants are known as micellar catalysis.     

Influence of suspended clay minerals and humic matter on the solid phase extraction efficiency of selected pesticides from water

The purpose of this investigation was to determine the influence of humic acids (HA) and Ca-montmorillonite (CaM) on the solid-phase extraction (SPE) efficiency of atrazine, alachlor and alpha-cypermethrin from water samples at various pH-values. The nature and intensity of binding of the studied pesticides to CaM were determined by X-ray diffraction analysis and termogravimetric analysis (TGA) test. The studied pesticides eluted from discs were analysed by thin-layer chromatography (TLC). The effects of CaM and humic acid were generally pH-dependent and acted independently in extraction efficiency influence. Lower recovery of pesticides was observed at higher pH values when CaM was > or =0.1 g and was attributed to greater dispersion of clay, increased surface area and subsequent adsorption. Concentrations of dissolved organic carbon (DOC) in humic acid had less effect on the extraction efficiency when water was at pH 8 compared to water at pH 2, which was probably due to greater nonpolar interactions of the pesticides to the charge-neutralized humic acid molecule.     

On the dissolution kinetics of humic acid particles. Effect of monocarboxylic acids

The dissolution kinetics of humic acid particles has been studied in batch experiments, and the effects of monocarboxylic (formic, acetic, and propionic) acids are reported. The dissolution rate of the particles is significantly affected by the presence of monocarboxylic acids in the pH range 4–10. At pH 7, for example, propionic acid increases 30 times this dissolution rate. The capacity of increasing the dissolution rate is in the order formic acid < acetic acid < propionic acid, and this dissolving capacity of carboxylics seems to be directly related to their affinity for HA molecules located at the surface of the solid particles. The results indicate that carboxylics and related compounds may affect markedly the mobility and transport of humic substances in the environment.     

Divergent toxicity of parathion in two freshwater invertebrates, orconectes rusticus and viviparus malleatus

The toxicity of parathion and its metabolite paraoxon was examined in the crayfish Orconectes rusticus and the snail Viviparus malleatus and attempts were made to relate this to parathion uptake and metabolism. The crayfish was found to be very susceptible with all animals tested dying at 0.1 ppb of parathion in 48 hours. The snail was resistant to exposure to 1000 ppm. The absence of lethality even to injected (50 mg/kg) parathion and paraoxon suggests an innate lack of susceptibility. Metabolism of the compounds could not be detected in vitro or in vivo in either species.     

Degradation mechanism and the toxicity assessment in TiO2 photocatalysis and photolysis of parathion

The photocatalytic degradation of methyl parathion was carried out using a circulating TiO2/UV reactor. The experimental results showed that parathion was more effectively degraded in the photocatalytic condition than the photolysis and TiO2-only condition. With photocatalysis, 10mg/l parathion was completely degraded within 60 min with a TOC decrease exceeding 90% after 150 min. The main ionic byproducts during photocatalysis were measured. The nitrogen from parathion was recovered mainly as NO3-, NO2- and NH4+, 80% of the sulfur as SO4(2-), and less than 5% of the phosphorus as PO4(3-). The organic intermediates 4-nitrophenol and paraoxon were also identified, and these were further degraded. Two different bioassays (Vibrio fischeri and Daphnia magna) were used to test the acute toxicity of solutions treated by photocatalysis and photolysis. A Microtox test using V. fischeri showed that the toxicity, expressed as the relative toxicity (%), was reduced almost completely after 90 min under photocatalysis, whereas only an 83% reduction was achieved with photolysis alone. Another toxicity test using D. magna also showed that the relative toxicity disappeared after 90 min under photocatalysis, whereas there was a 65% reduction in relative toxicity with photolysis alone. The pattern of toxicity reduction parallels the decrease in parathion and TOC concentrations.     

Bioavailability and mass balance studies of a commercial pentabromodiphenyl ether mixture in male Sprague-Dawley rats

Cyanogenic glycosides are common plant toxins. Toxic hydrogen cyanide originating from cyanogenic glycosides may affect soil processes and water quality. In this study, hydrolysis, degradation and sorption of dhurrin (4-hydroxymandelonitrile-beta-d-glucoside) produced by sorghum has been studied in order to assess its fate in soil. The log K(ow) of dhurrin was -1.18+/-0.08 (22 degrees C). Hydrolysis was a first-order reaction with respect to dhurrin and hydroxyl ion concentrations. Half lives ranged from 1.2h (pH 8.6; 25 degrees C) to 530d (pH 4; 25 degrees C). The activation energy of hydrolysis was 112+9kJ. At pH 5.8 and room temperature, addition of humic acids (50gl(-1)) increased the rate of hydrolysis tenfold, while addition of kaolinite or goethite (100-250gl(-1)) both decreased the rate considerably. No significant sorption to soil components could be observed. The degradation rates of dhurrin in top and subsoils of Oxisols, Ultisols, Alfisols and Mollisols were studied at 22 degrees C (25mgl(-1), soil:liquid 1:1 (w:V), pH 3.8-8.1). Half-lives were 0.25-2h for topsoils, and 5-288h in subsoils. Hydrolysis in solution explained up to 45% of the degradation in subsoils whereas the contribution in topsoils was less than 14%, indicating the importance of enzymatic degradation processes. The highest risk of dhurrin leaching will take place when the soil is a low activity acid shallow soil with low content of clay minerals, iron oxides and humic acids.     

Assessment of pesticide contamination in three Mississippi Delta oxbow lakes using Hyalella azteca

Three oxbow lakes in northwestern Mississippi, USA, an area of intensive agriculture, were assessed for biological impairment from historic and current-use pesticide contamination using the amphipod, Hyalella azteca. Surface water and sediment samples from three sites in each lake were collected from Deep Hollow, Beasley, and Thighman Lakes from September 2000 to February 2001. Samples were analyzed for 17 historic and current-use pesticides and selected metabolites. Ten-day H. azteca survival and growth (as length and dry weight) were measured to determine the degree of biological impairment. Maximum number of detectable pesticides in surface water from Deep Hollow, Beasley and Thighman Lakes was 10, 11, and 17, respectively. Maximum number of detectable pesticides in lake sediments was 17, 17, and 15, respectively. Bioassay results indicated no observable survival effects on H. azteca exposed to surface water or sediment from any lake examined and no growth impairment in animals exposed to lake sediments. However, growth was significantly impaired in surface water exposures from Deep Hollow Lake (2 sites) and Beasley Lake (1 site). Statistically significant relationships between growth impairment (length) and cyanazine, methyl parathion, λ-cyhalothrin, chlorfenapyr, and pp′DDE surface water concentrations in Deep Hollow Lake as well as trifluralin, atrazine, and methyl parathion in Beasley Lake were observed. Although pesticide frequency and concentrations were typically greater in sediment than surface water, bioassay results indicated decreased availability of these pesticides in sediment due to the presence of clay and organic carbon. Growth impairment observed in surface water exposures was likely due to complex interaction of pesticide mixtures that were present.     

The influence of cosolvent and heat on the solubility and reactivity of organophosphorous pesticide DNAPL alkaline hydrolysis

The presented research concerned the compatibility of cosolvents with in situ alkaline hydrolysis (ISAH) for treatment of organophosphorous (OPP) pesticide contaminated sites. In addition, the influence of moderate temperature heat increments was studied as a possible enhancement method. A complex dense non-aqueous phase liquid (DNAPL) of primarily parathion (~50 %) and methyl parathion (~15 %) obtained from the Danish Groyne 42 site was used as a contaminant source, and ethanol and propan-2-ol (0, 25, and 50 v/v%) was used as cosolvents in tap water and 0.34 M NaOH. Both cosolvents showed OPP solubility enhancement at 50 v/v% cosolvent content, with slightly higher OPP concentrations reached with propan-2-ol. Data on hydrolysis products did not show a clear trend with respect to alkaline hydrolysis reactivity in the presence of cosolvents. Results indicated that the hydrolysis rate of methyl-parathion (MP3) decreased with addition of cosolvent, whereas the hydrolysis rate of ethyl-parathion (EP3) remained constant, and overall indications were that the hydrolysis reactions were limited by the rate of hydrolysis rather than NAPL dissolution. In addition to cosolvents, the influence of low-temperature heating on ISAH was studied. Increasing reaction temperature from 10 to 30 °C provided an average rate of hydrolysis enhancement by a factor of 1.4–4.8 dependent on the base of calculation. When combining 50 v/v% cosolvent addition and heating to 30 °C, EP3 solubility was significantly enhanced and results for O,O-diethyl-thiophosphoric acid (EP2 acid) showed a significant enhancement of hydrolysis as well. However, this could not be supported by para-nitrophenol (PNP) data indicating the instability of this product in the presence of cosolvent.

     

Role of cupric ions in the H2O2/UV oxidation of humic acids

The purpose of this study is to reveal the role of cupric ions as a natural water contaminant in the H2O2/UV oxidation of humic acids. Humic acids are naturally occurring organic matter and exhibit a strong tendency of complexation with some transition metal ions. Chlorination of humic acids causes potential health hazards due to formation of trihalomethane (THM). The removal of THM precursors has become an issue of public concern. The H2O2/UV process is capable of mineralizing humic acids due to formation of a strong oxidant, hydroxyl radicals, in reaction solution. Experiments were conducted in a re-circulated photoreactor. Different cupric concentrations (0-3.8 mg/l) and different pH values (4-9) were controlled to determine their effects on the degradation of humic acids, UV light absorbance at 254 nm, and H2O2. The presence of cupric ions inhibits humic mineralization and decreases the rate of destruction of humic acids which absorb UV light at 254 nm. On the other hand, the higher the cupric concentration, the lower the H2O2 decomposition rate. In the studied pH range, the minimum of total organic carbon (TOC) removal occurs at pH = 6 in the presence of 2.6 mg/l of cupric ions; both acidification (pH = 4) and alkaline condition (pH = 9) lead to a better removal of TOC. It is inferred from this study that the cupric-complexed form of humic acids is more refractory than the non-complexed one.     

Solubilization of substituted indole compounds by beta-cyclodextrin in water

The solubilization of four pairs of substituted indole compounds (SICs) by β-cyclodextrin (β-CD) in water was investigated. The results show that 1,2,3,4-tetrahydrocarbazole and N-methyl-1,2,3,4-tetrahydrocarbazole form 1:1 inclusion complexes with β-CD, while the other six SICs form 1:2 inclusion complexes, respectively. To each pair of SICs with similar structures, the differences between their solubilization in β-CD/water solutions has been explained by the difference of their contact area within the β-CD cavity, the difference of their molecule polarity, or the presence of hydrogen bond between SIC molecule and β-CD molecule.     

Influence of Suspended Clay Minerals and Humic Matter on the Solid Phase Extraction Efficiency of Selected Pesticides from Water

The purpose of this investigation was to determine the influence of humic acids (HA) and Ca-montmorillonite (CaM) on the solid-phase extraction (SPE) efficiency of atrazine, alachlor and α-cypermethrin from water samples at various pH-values. The nature and intensity of binding of the studied pesticides to CaM were determined by X-ray diffraction analysis and termogravimetric analysis (TGA) test. The studied pesticides eluted from discs were analysed by thin-layer chromatography (TLC). The effects of CaM and humic acid were generally pH-dependent and acted independently in extraction efficiency influence. Lower recovery of pesticides was observed at higher pH values when CaM was ≥0.1 g and was attributed to greater dispersion of clay, increased surface area and subsequent adsorption. Concentrations of dissolved organic carbon (DOC) in humic acid had less effect on the extraction efficiency when water was at pH 8 compared to water at pH 2, which was probably due to greater nonpolar interactions of the pesticides to the charge-neutralized humic acid molecule.