Daqiang Yin

Aqueous photolysis of tetracycline and toxicity of photolytic products to luminescent bacteria.

The extensive utilization of antibiotics in the pharmaceutical therapies and agricultural husbandry has led to the worldwide pollution in environments. In this study the photolysis behaviors of tetracycline (TC) and toxicity of its degradation products were investigated. The results showed that TC photolysis followed first-order kinetics. The photolysis rate was found to be dependent on the initial TC concentration and increasing TC concentration from 10 to 40mgl(-1) led to the decrease of the photolysis rate constant from 0.0045min(-1) to 0.0014min(-1). TC photolysis was highly pH-dependent and strongly enhanced at high pH value. Markedly elevated TC photolysis was also observed in the presence of nitrate and dissolved organic matter. Upon irradiation for 300min, only 15% reduction of total organic carbon (TOC) occurred in spite of quick conversion of 73% of TC, suggesting that a majority of TC transformed into intermediate products without complete mineralization. The intermediate products from TC photolysis were analyzed using high-performance liquid chromatography-electrospray ionisation-mass spectrometry (HPLC-ESI-MS) and the main photolysis products of TC were proposed. The toxicity of the photolysis compounds was evaluated using luminescent bacterium, and the results revealed that the toxicity increased with irradiation, indicative of a higher adversity risk of the degradation products of TC on bacteria upon photolysis.

Aqueous oxytetracycline degradation and the toxicity change of degradation compounds in photoirradiation process

The extensive use of antibiotics has been a worldwide environmental issue. In this study the fate of oxytetracycline (OTC), under photoirradiation, was investigated. The results showed that OTC photolysis followed first order model kinetics. Direct photolysis rate was found to be dependent on the initial OTC concentration, with k value ranging from 0.0075 to 0.0141 min(-1), in the OTC concentration from 40 to 10 mg/L. OTC photolysis was highly pH-dependent and strongly enhanced at a high pH value, with a k value of 0.0629 min(-1) at pH 9. Enhanced OTC photolysis has also been observed in the presence of nitrate and low concentration of dissolved organic matter. Upon irradiation for 240 min, only 13.5% reduction of TOC occured in spite of a rapid consumption of 90% of OTC. The byproducts from OTC photolysis have been analyzed using high-performance liquid chromatography electrospray ionization mass spectrometry (LC-ESI-MS), and the degradation pathway of OTC in the photo process was proposed. By employing luminescent bacterium to assess the adversity of the degradation compounds, an increased effect of toxicity occured in spite of the great consumption of OTC in the photoirradiation process. After irradiation for 240 min, the inhibition rate was 47%, significantly higher than the initial rate of 21% (p < 0.05), revealing a potentially higher adversity risk on the microorganism upon OTC photolysis.

Ozone-biological activated carbon integrated treatment for removal of precursors of halogenated nitrogenous disinfection by-products

Pilot-scale tests were performed to reduce the formation of several nitrogenous and carbonaceous disinfection by-products (DBPs) with an integrated ozone and biological activated carbon (O(3)-BAC) treatment process following conventional water treatment processes (coagulation-sedimentation-filtration). Relative to the conventional processes alone, O(3)-BAC significantly improved the removal of turbidity, dissolved organic carbon, UV(254), NH(4)(+) and dissolved organic nitrogen from 98-99%, 58-72%, 31-53%, 16-93% and 35-74%, respectively, and enhanced the removal efficiency of the precursors for the measured DBPs. The conventional process was almost ineffective in removing the precursors of trichloronitromethane (TCNM) and dichloroacetamide (DCAcAm). Ozonation could not substantially reduce the formation of DCAcAm, and actually increased the formation potential of TCNM; it chemically altered the molecular structures of the precursors and increased the biodegradability of N-containing organic compounds. Consequently, the subsequent BAC filtration substantially reduced the formation of the both TCNM and DCAcAm, thus highlighting a synergistic effect of O(3) and BAC. Additionally, O(3)-BAC was effective at controlling the formation of the total organic halogen, which can be considered as an indicator of the formation of unidentified DBPs.

Trace determination of 13 haloacetamides in drinking water using liquid chromatography triple quadrupole mass spectrometry with atmospheric pressure chemical ionization

The haloacetamides (HAcAms) are disinfection by-products (DBPs) in drinking water which are currently receiving increased scientific attention due to their elevated toxicity relative to regulated disinfection by-products. A simultaneous determination method of 13 HAcAms, combining solid-phase extraction (SPE) enrichment, liquid chromatographic (LC) separation, and triple quadrupole mass spectrometry (tqMS) detection with atmospheric pressure chemical ionization (APCI) using selective reaction monitoring in positive mode, was developed to measure HAcAms, including chlorinated, brominated, and iodinated analogs. Ammonium chloride and Oasis HLB were selected as the dechlorinating reagent and polymeric SPE sorbent of HAcAm samples. The used tqMS apparatus showed higher sensitivity for the studied HAcAms in the APCI mode than electrospray ionization. 13 HAcAms were separated by LC in 9.0 min, and the detection limits ranged from 7.6 to 19.7 ng/L. The SPE-LC/tqMS method was successfully applied to quantify 13 HAcAms in drinking water samples for the first time, and first indentified tribromoacetamide and chloroiodoacetamide as DBPs in drinking water.

Ionic liquids as mobile phase additives for high-performance liquid chromatography separation of phenoxy acid herbicides and phenols

In this present study, 1-butyl-3-methylimidazolium chloride ([C(4)MIM]Cl), 1-octyl-3-methylimidazolium chloride ([C(8)MIM]Cl), and 1-decyl-3-methylimidazolium chloride ([C(10)MIM]Cl) were adopted as mobile phase additives in the high performance liquid chromatography (HPLC) to simultaneously separate phenoxy acid herbicides and phenols at neutral pH. It was found that by using 20 mM of [C(4)MIM]Cl, baseline separation and good chromatograms for all the acid compounds were obtained on a normal reversed-phase C(18) column. The retention time of the target acid compounds shortened with the increase of the alkyl chain length and the concentrations of ionic liquids, probably due to the delocalization of the positive charge on the imidazolium cation, the repulsion between chlorine ions of ionic liquids and the acid compounds, as well as the stereo-hindrance effect. The mechanism with ionic liquids as mobile additives for the separation of acid compounds was discussed.

Fe(III)–oxalate complexes mediated photolysis of aqueous alkylphenol ethoxylates under simulated sunlight conditions

Photolysis of octylphenol ethoxylates Triton X-100 (TX) in water under simulated sunlight conditions was investigated in the presence of Fe(III)-oxalate complexes. The results showed that Fe(III)-oxalate complexes mediated TX degradation followed the first-order kinetics and the photolysis efficiency was dependent on the pH, Fe(III) concentration, Fe(III)/oxalate ratio and initial TX concentration. The active oxygen species generated by photolysis of Fe(III)-oxalate complexes were monitored by electron paramagnetic resonance (EPR) method using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as the spin-trapping reagent. The steady-state concentration of OH radicals was 8.33x10(-14)M and the rate constant of TX reaction with OH radical was 1.29x10(9)M(-1)s(-1) under our experimental conditions. The degradation products were analyzed by the high-performance liquid chromatography-electrospray ionisation-mass spectrometry and the degradation mechanisms of TX in the presence of Fe(III)-oxalate complexes was proposed. The OH radical can react with the alkyl chain, ethoxy (EO) chain and the aromatic ring of TX molecule during TX photolysis process. The main degradation pathway of TX involves the OH radical addition to the aromatic ring and the cleavage of the alkyl chain followed by combination with OH radical. The OH radical also attacks the polyethoxylated chain to generate short polyethoxylated chains or formyl ethoxylates.

Bioavailability of organochlorine compounds in aqueous suspensions of fullerene: Evaluated with medaka (Oryzias latipes) and negligible depletion solid-phase microextraction

The wide application of engineered nanomaterials, such as fullerene (C(60)), will inevitably lead to their release into the aqueous environment, which may alter the bioavailability of organic compounds to aquatic organisms. Negligible depletion solid-phase microextraction (nd-SPME) together with medaka (Oryzias latipes) bioaccumulation were used to study the effects of aqueous suspensions of fullerene (nC(60)) on the bioavailability of eight organochlorine compounds (OCCs) (logK(OW) 3.76-6.96). Freely dissolved concentrations of OCCs decreased by 11.5-88.4% at addition of 5mgL(-1)nC(60) as indicated by reduced equilibrium concentrations in the SPME fiber coating, the highest reduction being observed for the most hydrophobic OCCs. Medaka bioaccumulation study demonstrated that at the kinetic uptake regime, nC(60) significantly decreased the bioaccumulation of the high hydrophobic OCCs (logK(OW)>6), but slightly enhanced the bioaccumulation of the less hydrophobic OCCs (logK(OW)<6). The OCC concentrations in medaka (C(fish)) at the kinetic uptake regime linearly correlated with that in nd-SPME fiber (C(fiber)) without nC(60) (p=0.007-0.013, R(2)=0.666-0.723), but this correlation deteriorated with the presence of nC(60) (p=0.073-0.081, R(2)=0.423-0.440). These results suggest that in nC(60) the uptake mechanism of OCCs to medaka is different from that to nd-SPME fiber. While only the freely dissolved OCCs are available to nd-SPME fiber, both the freely dissolved and the nC(60) associated OCCs contributed to the accumulation of OCCs to medaka.

Ionic liquid‐based single‐drop liquid‐phase microextraction combined with high‐performance liquid chromatography for the determination of sulfonamides in environmental water

A simple, rapid and environment-friendly technique of single-drop liquid-phase microextraction has been developed for the determination of sulfonamides in environmental water. Several important parameters including stirring rate, extraction solvent, extraction pH, salinity and extraction time were optimized to maximize the extract efficiency. Extraction solvent 1-octyl-3-methylimidazolium hexafluorophosphate [C(8) MIM][PF(6) ] ionic liquid showed better extraction efficiency than 1-butyl-3-methylimidazolium hexafluorophosphate [C(4) MIM][PF(6) ] and 1-octanol. The optimum experimental conditions were: pH, 4.5; sodium chloride content, 36% w/v; extraction time, 20 min. This method provided low detection limits (0.5-1 ng/mL), good repeatability (the RSD ranging from 4.2 to 9.9%, n=5) and wide linear range (1-1500 ng/mL), with determination coefficients (r(2) ) higher than 0.9989 for all the target compounds. Real sample analysis showed relative recoveries between 63.5 and 115.8% for all the target compounds.

Solid‐phase extraction coupled with ultra high performance liquid chromatography and electrospray tandem mass spectrometry for the highly sensitive determination of five iodinated X‐ray contrast media in environmental water samples

A highly sensitive method based on solid-phase extraction and ultra high performance liquid chromatography with electrospray tandem mass spectrometry has been developed for simultaneous determination of five iodinated X-ray contrast media in environmental water samples. Various solid-phase extraction cartridges have been evaluated and a combination of LiChrolute EN and ENVI-Carb solid phase extraction cartridges was selected for sample enrichment. The method was comprehensively validated on ground water, tap water, surface water, drinking water, and waste water by the conventional procedures: linearity, method detection limits, accuracy and precision, matrix effects. Good linearity (R(2) > 0.999), low detection limits (0.4-8.1 ng/L), satisfactory recoveries (55.1-109.5%) and precision (0.8-10.0% for intra-day precisions and 0.6-16.5% for inter-day precisions) were obtained for all the target compounds. Iopamidol, iohexol, and diatrizoate in some matrices were affected by matrix effects, which were slightly eased by using the isotope-labeled internal standard. The developed method was successfully applied for real samples collected in Shanghai, China, with detected concentrations up to 2200 ± 200 and 9000 ± 1000 ng/L for iohexol and iopamidol, respectively.

A predictive model for the formation potential of dichloroacetamide, a nitrogenous disinfection by-product formed during chlorination

Nitrogenous disinfection by-products have increasingly become a public health concern in the drinking water industry because they have been found to be more geno- and cytotoxic than most of the currently regulated disinfection by-products. Dichloroacetamide, a nitrogenous disinfection by-product which is formed during chlorination in water treatment, has increasingly received attention due to its elevated genotoxicity and cytotoxicity relative to the currently regulated disinfection by-products. In this study, a power function model with parameters of dissolved organic nitrogen, dissolved organic carbon, bromide, soluble microbial products, and aromatic proteins was developed to successfully predict dichloroacetamide formation potential. The inclusion of soluble microbial product and aromatic protein into the model significantly improved the prediction, suggesting that soluble microbial product and aromatic protein play a significant role in the formation of dichloroacetamide. Additionally, the performance of the predictive model appeared to be somewhat affected by the characteristics of raw water used to develop the model.