Kunde Lin

Oxidative removal of bisphenol A using zero valent aluminum–acid system

Bisphenol A (BPA), a controversial endocrine disruptor, is ubiquitous in the aquatic environment. In this study, the oxidative degradation of BPA and its mechanism using zero valent aluminum (ZVAl)-acid system under air-equilibrated conditions was investigated. Under pH <3.5 acidic conditions, ZVAl demonstrated an excellent capacity to remove BPA. More than 75% of BPA was eliminated within 12 h in pH 1.5 reaction solutions initially containing 4.0 g/L aluminum and 2.0 mg/L BPA at 25 ± 1 °C. The removal of BPA was further accelerated with increasing aluminum loadings. Higher temperature and lower initial pH also facilitated BPA removal. The addition of Fe(2+) into the ZVAl-acid system significantly accelerated the reaction likely due to the enhancing transformation of H(2)O(2) to HO via Fenton reaction. Furthermore, the primary products or intermediates including monohydroxylated BPA, hydroquinone, 2-(4-hydroxyphenyl)propane and 4-isopropenylphenol, were identified and a possible reaction scheme was proposed. The remarkable capacity of the ZVAl-acid system in removing BPA displays its potential application in the treatment of organic compound-contaminated water.

Single and Joint Acute Toxicity of Isocarbophos Enantiomers to Daphnia magna

Although enantioselectivity in the toxicity of chiral pesticides has received considerable attention over recent years, how coexisting enantiomers interact with each other during their toxic action remains unknown. In this study, we attempted to resolve the enantiomers of a chiral organophosphate insecticide, isocarbophos, and investigated the acute toxicity of individual enantiomers and various enantiomer mixtures. Baseline enantiomeric separation of isocarbophos was achieved on a Chiralcel OD column with the mobile phase of n-hexane/isopropanol (90/10, v/v) at a flow rate of 0.8 mL/min. The resolved enantiomers were differentiated by their responses on a circular dichroism detector. The median lethal concentrations (LC 50) of racemate, (+)-enantiomer, and (-)-enantiomer of isocarbophos toward Daphnia magna were 13.9, 7.08, and 353 microg/L, respectively, after 48 h of static exposure, displaying a 50-fold difference between the enantiomers. Toxic unit (TU) analysis was employed to evaluate the joint toxicity of isocarbophos enantiomer mixtures. The calculated TU mix for the acute toxicity (48 h test) of various binary mixtures ranged from 0.83 to 1.04, suggesting a mode of additive effect. Further evaluation of available literature data for chiral organophosphorus insecticides showed that the joint toxicity of enantiomers may be additive, synergistic, and antagonistic. Therefore, when significant enantioselectivity exists for a chiral pesticide, it is important to also evaluate the interaction of enantiomers in the joint toxicity effect when enantiomers are present in a mixture.

Transformation and sorption of fipronil in urban stream sediments.

Fipronil is an urban-use insecticide, and the increased use has led to its frequent detections in urban streams. Most studies on the environmental fate of fipronil so far have focused on soils, and little is known about its behavior in sediment-water systems. In this study, we investigated the transformation and sorption of fipronil in urban stream sediments from California, incubated under facultative and anaerobic conditions. Degradation of fipronil in sediments generally followed exponential decay kinetics, and the first-order half-lives of fipronil were only 4.6-18.5 days in anaerobic sediments. The persistence of fipronil under facultative conditions was considerably longer, with half-lives from 25 to 91 days. Sterilization generally decreased the dissipation of fipronil, indicating that microbial activity was an important factor in fipronil transformations in sediments. Under facultative conditions, fipronil sulfide and sulfone were observed, while only fipronil sulfide was detected in anaerobic samples. The sorption coefficient K d consistently increased with organic carbon contents of sediments. In the same sediment, K d usually also increased with contact time, suggesting decreased availability for aged residues. Results from this study showed that the stability of fipronil in sediments depends closely on the oxygen status and that due to the readily conversion of fipronil to the sulfone and sulfide metabolites, the overall risk assessment of fipronil in surface aquatic systems should take into consideration fipronil as well as its metabolites.

Wash‐off potential of urban use insecticides on concrete surfaces

Contamination of surface aquatic systems by insecticides is an emerging concern in urban watersheds, but sources of contamination are poorly understood, hindering development of regulatory or mitigation strategies. Hardscapes such as concrete surfaces are considered an important facilitator for pesticide runoff following applications around homes. However, pesticide behavior on concrete has seldom been studied, and standardized evaluation methods are nonexistent. In the present study, a simple batch method for measuring pesticide wash-off potential from concrete surfaces was developed, and the dependence of washable pesticide residues was evaluated on pesticide types, formulations, time exposed to outdoor conditions, and number of washing cycles. After application to concrete, the washable fraction of four pyrethroids (bifenthrin, permethrin, cyfluthrin, and cyhalothrin) and fipronil rapidly decreased, with half-lives < or =3 d, likely due to irreversible retention in micropores below the concrete surface. The initial fast decrease was followed by a much slower declining phase with half-lives ranging from one week to two months, and detectable residues were still found in the wash-off solution for most treatments after 112 d. The slow decrease may be attributed to a fraction of pesticides being isolated from degradation or volatilization after retention below the concrete surface. Wash-off potential was consistently higher for solid formulations than for liquid formulations, implying an increased runoff contamination risk for granular and powder formulations. Trace levels of pyrethroids were detected in the wash-off solution even after 14 washing-drying cycles over 42 d under outdoor conditions. Results from the present study suggest that pesticide residues remain on concrete and are available for contaminating runoff for a prolonged time. Mechanisms for the long persistence were not clearly known from the present study and merit further investigation.

Occurrence and toxicity of three classes of insecticides in water and sediment in two Southern California coastal watersheds.

The occurrence of chlorpyrifos, diazinon, pyrethroids, and fipronil was investigated in two watersheds along the southern California coast. Paired surface water and sediment samples were collected under dry and wet (after significant rain events) weather conditions. Insecticide concentrations in water and sediment were higher following rain events than during the dry season. Chlorpyrifos was the most frequently detected compound (>88%). Pyrethroids were detected in 74 and 100% of the water and sediment samples, respectively, with bifenthrin detected most frequently. Trans-permethrin was detected at the highest concentration followed by bifenthrin. Bifenthrin and trans-permethrin water concentrations were significantly correlated (P < 0.01) with the suspended solid level, suggesting transport facilitated by suspended particles. In 80% of the wet season samples with 100% of Ceriodaphnia dubia mortality, chlorpyrifos concentrations were >100 ng L(-1). Sediment pyrethroid levels (0.5-1100 ng g(-1)) were frequently higher than the respective Hyalella azteca LC(50) values, with bifenthrin as the primary contributor of H. azteca toxicity.

Oxidation of bisphenol F (BPF) by manganese dioxide

Bisphenol F (BPF), an environmental estrogen, is used as a monomer in plastic industry and its environmental fate and decontamination are emerging concern. This study focused on the kinetics, influencing factors and pathways of its oxidation by MnO(2). At pH 5.5, about 90% of BPF was oxidized in 20 min in a solution containing 100 μM MnO(2) and 4.4 μM BPF. The reaction was pH-dependent, following an order of pH 4.5 > pH 5.5 > pH 8.6 > pH 7.5 > pH 6.5 > pH 9.6. Humic acids inhibited the reaction at low (≤ pH 5.5) and high pH (≥ pH 8.6) at high concentrations. In addition, metal ions and anions also suppressed the reaction, following the order Mn(2+) > Ca(2+) > Mg(2+) > Na(+) and HPO(4)(2-) > Cl(-) > NO(3)(-) ≈ SO(4)(2-), respectively. A total of 5 products were identified, from which a tentative pathway was proposed.

Oxidative removal of acetaminophen using zero valent aluminum-acid system：Efficacy,influencing factors,and reaction mechanism

Commercial available zero valent aluminum under air-equilibrated acidic conditions (ZVA1/H+/air system) demonstrated an excellent capacity to remove aqueous organic compounds. Acetaminophen (ACTM), the active ingredient of the over-the-counter drug Tylenol, is widely present in the aquatic environment and therefore the treatment of ACTM-contaminated water calls for further research. Herein we investigated the oxidative removal of ACTM by ZVA1/H+/air system and the reaction mechanism. In acidic solutions (pH < 3.5), ZVA1 displayed an excellent capacity to remove ACTM. More than 99% of ACTM was eliminated within 16 hr in pH 1.5 reaction solutions initially containing 2.0 g/L aluminum and 2.0 mg/L ACTM at 25 +/- 1 degree C. Higher temperature and lower pH facilitated ACTM removal. The addition of different iron species Fe0, Fe2+ and Fe3+ into ZVA1/H+/air system dramatically accelerated the reaction likely due to the enhancing transformation of H2O2 to HO. via Fentons reaction. Furthermore, the primary intermediate hydroquinone and the anions formate, acetate and nitrate, were identified and a possible reaction scheme was proposed. This work suggested that ZVA1/H+/air system may be potentially employed to treat ACTM-contaminated water.

Enantioselectivity in fipronil aquatic toxicity and degradation

Fipronil and its transformation products are being increasingly detected in aquatic ecosystems as a result of widespread use. Fipronil is a chiral compound, and enantioselectivity may greatly impact its environmental fate and effects. In the present study, fipronil enantiomers were isolated and used to investigate the possibility of enantioselectivity in their acute toxicity to Japanese medaka (Oryzias latipes) and cytotoxicity to primary hepatocytes from rainbow trout (Oncorhynchus mykiss). Enantioselectivity was further evaluated in terms of fipronil degradation in sediments under aerobic and anaerobic conditions and in field-contaminated runoff water from urban watersheds. The 96-h median lethal concentrations to Japanese medaka were 94.2 (95% confidence interval [CI], 82.9-107.1), 98.3 (95% CI, 85.6-113.0), and 95.4 (95% CI, 74.7-121.9) microg/L for the racemic, R-(-)-, and S-(+)-fipronil, respectively, suggesting absence of enantioselectivity. The 24-h median effect concentration of racemic fipronil to primary rainbow trout hepatocytes was 26.7 (95% CI, 25.6-27.9) microg/ml. In contrast, exposure of the cells to the S-(+)- and R-(-)-enantiomers resulted in a 19.7 and 7.8% reduction in cell viability, respectively, at the highest treatment concentrations (100 microg/ml), potentially indicating a greater-than-additive interaction between enantiomers. Under aerobic or slightly reduced conditions, biodegradation of fipronil in sediments was essentially nonstereoselective, with the enantiomeric fraction (EF) similar to racemic (EF = 0.5) after 168 d of incubation. However, EF decreased to as low as less than 0.1 following short incubations under anaerobic conditions, suggesting preferential degradation of S-(+)-fipronil in strongly reduced sediments. A survey of urban runoff samples consistently showed near-racemic EF, indicating fipronil degradation that was not enantioselective. Results suggest that site-specific characteristics are critical in accurately predicting fipronil fate and toxicity in the environment.

Persistence and sorption of fipronil degradates in urban stream sediments.

Fipronil, an increasingly popular insecticide used for urban pest control, is known to readily transform into several degradates that generally have similar or greater toxicity to aquatic organisms than the parent compound. However, knowledge on the fate of these degradates in the environment is obscure. In the present study, degradation kinetics and sorption of desthiofipronil, fipronil sulfide, and fipronil sulfone were investigated in urban stream sediments. All degradates showed enhanced persistence in sediments compared to fipronil under facultative or anaerobic conditions. Under facultative conditions, the estimated half-lives of desthiofipronil, fipronil sulfide, and fipronil sulfone were 217 to 497, 195 to 352, and 502 to 589 d, respectively. Under anaerobic conditions, the corresponding half-lives were over one year in one sediment, while no detectable degradation occurred in the other two sediments after 280 d. Sorption isotherms of fipronil and its degradates in the sediments were linear, with mean K(OC) values of 802, 1,296, 3,684, and 3,543 L/kg for fipronil, desthiofipronil, fipronil sulfide, and fipronil sulfone, respectively, suggesting that the degradates generally have a higher sorption capacity than fipronil. Sorption coefficient K(d) increased up to fourfold over 280 d, suggesting an aging effect on sorption. The inherent toxicity, long persistence, and strong sorption potential highlight the importance for a better understanding of the sediment toxicity of fipronil degradates in surface water bodies.