Effect of quantity and fractionation of loaded humic acid (HA) on biochar sorption for sulfonamides was investigated. The HA was applied in two different modes, i.e. pre-coating and co-introduction with sorbate. In pre-coating mode, the polar fractions of HA tended to interact with low-temperature biochars via H-bonding, while the hydrophobic fractions were likely to be adsorbed by high-temperature biochars through hydrophobic and π-π interactions, leading to different composition and structure of the HA adlayers. The influences of HA fractionation on biochar sorption for sulfonamides varied significantly, depending on the nature of interaction between HA fraction and sorbate. Meanwhile, co-introduction of HA with sulfonamides revealed that the effect of HA on sulfonamide sorption was also dependent on HA concentration. These findings suggest that the amount and fractionation of adsorbed HA are tailored by the surface properties of underlying biochars, which differently affect the sorption for organic contaminants.

Fluorescence quenching includes dynamic and static quenching, and both processes can alter the behavior and reactivity of the fluorescer. However, dynamic quenching is seldom quantified. This study combined dialysis equilibrium and fluorescence quenching methods to compare the contribution of dynamic and static quenching. The results indicate that phenanthrene (PHE)-DHA binding increased with DHA hydrophobicity, while ofloxacin (OFL)-DHA interaction showed the opposite effect. For PHE, the contribution of dynamic quenching to the overall fluorescence quenching was in the range of 50%∼82% and decreased to 11%∼58% with increased DHA hydrophobicity. However, OFL dynamic quenching increased from 2%∼27% to 31%∼61% with DHA hydrophobicity. Combining the results using model chemicals, we concluded that the carboxyl groups in DHA might be the primary components for PHE dynamic quenching and might be responsible for both dynamic and static quenching of OFL. Extensive study is needed to explore the quantitative relationship of dynamic quenching and chemical/DHA properties.

It is known that 17β-estradiol (E2) can be transformed by reactions mediated by some oxidoreductases such as laccase in water. Whether or how such reactions can happen in soil is however unknown although they may significantly impact the environmental fate of E2 that is introduced to soil by land application of animal wastes. We herein studied the reaction of E2 in a model soil mediated by laccase, and found that the reaction behaviors differ significantly from those in water partly because of the dramatic difference in laccase stability. We also examined E2 transformation in soil using 14C-labeling in combination with soil organic matter extraction and size exclusion chromatography, which indicated that applied 14C radioactivity was preferably bound to humic acids. The study provides useful information for understanding the environmental fate of E2 and for developing a novel soil remediation strategy via enzyme-enhanced humification reactions.

The effects of chloride on dissolution and toxicity of silver nanoparticles (AgNPs) have been well studied. However, their intermediate shapes during the transition have not been illustrated to-date. Herein, the chloride-induced shape transformation process of AgNPs under long-term, low-concentration conditions is explored. A unique triangular Ag–AgCl heterostructure is observed. The structure then evolves into a symmetric hexapod and finally into a smaller AgNP. This transformation process could be affected by other environmental conditions, such as 0.4 mg/mL humic acid, 5% surfactants and 1 mg/mL bovine serum albumin protein. Our results offer new knowledge regarding the shape transformation process of AgNPs in the presence of chloride, which can be valuable in relevant studies concerning the effect of water chemistry on the behavior of AgNPs.

Sorption of organic contaminants on organo-mineral complexes has been investigated extensively, but the sorption contribution of mineral particles was not properly addressed before calculating KOC, especially for ionic organic contaminants. We measured the surface coverage of a humic acid (HA) on nano iron oxides (n-Fe2O3) in a series of synthesized organo-mineral complexes. The contribution of the coated HA to ofloxacin (OFL) and norfloxacin (NOR) sorption in HA–n-Fe2O3 complexes was over 80% of the total sorption with the surface coverage of 36% and fOC of 1.6%. All the coated HA showed higher sorption to NOR and OFL in comparison to the original HA, suggesting HA fractionation and/or physical re-conformation during organo-mineral complex formation. The decreased KOC with multilayer coating may suggest the importance of site-specific interactions for OFL sorption, while the increased KOC with multilayer coating may suggest the importance of partitioning in hydrophobic region for NOR sorption.

As one kind of phosphorus species, polyphosphate (poly-P) is ubiquitous in natural environments, and the potential interactions between poly-P and humic substances in the sediments or natural waters would influence the fate of poly-P in the environments. However, the mechanism of the interactions has not yet been understood clearly. In this work, the characteristics and mechanisms of the interactions between humic acids (HA) and two model poly-P compounds with various chain lengths have been investigated. Results show that a stable polyphosphate-HA complex would be formed through the noncovalent interactions, and hydrogen bond might be the main driving force for the binding process, which might be formed between the proton-accepting groups of poly-P (e.g., PO and P–O−) and the oxygen containing functional groups in HA. Our findings implied that the presence of humic substances in natural waters, soils and sediments would influence the potential transport and/or mobility of environmental poly-P.

Heavy metals in urban soils can compromise human health, especially in urban gardens, where gardeners may ingest contaminated dust or crops. To identify patterns of urban garden metal contamination, we measured concentrations and bioavailability of Pb, As, and Cd in soils associated with twelve community gardens in Los Angeles County, CA. This included sequential extractions to partition metals among exchangeable, reducible, organic, or residual fractions. Proximity to road increased all metal concentrations, suggesting vehicle emissions sources. Reducible Pb increased with neighborhood age, suggesting leaded paint as a likely pollutant source. Exchangeable Cd and As both increased with road proximity. Only cultivated soils showed an increase in exchangeable As with road proximity, potentially due to reducing humic acid interactions while Cd bioavailability was mitigated by organic matter. Understanding the geochemical phases and metal bioavailability allows incorporation of contamination patterns into urban planning.

The impact of Fe₂O₃and TiO₂nanoparticles (NPs) on the removal of trichloroethylene (TCE) in a granular activated carbon (GAC)-fixed bed adsorber was investigated in the presence of humic acid (HA). The surface charges of GAC and NPs were obtained in the presence and absence of HA with the NPs behaving similarly. Isotherm and column studies were conducted in the presence and absence of the NPs and HA. NPs had no effect on TCE adsorption during isotherm studies. However, in the column studies conducted with organic-free water, the presence of NPs resulted in a reduction in TCE capacity most likely due to pore blockage by aggregating NPs. This effect was completely mitigated in the presence of HAs that prevented an association between the GAC and the NPs, and between NPs. The presence of HA provided a high negative charge on the GAC and on the nanoparticles resulting in repulsive forces between the GAC and the NPs, and between NPs, thereby preventing pore blockage. Both Fe₂O₃and TiO₂NPs demonstrated that charge characteristics are more important than chemical characteristics. Pore-size distribution of the fresh and the spent GAC confirmed the adsorption data but points to some HA and NP interaction with the carbon.

The current study focuses on the removal of perchlorate in water using single-walled carbon nanotubes (SWCNTs) and granular ferric hydroxide as sorbents. The randomly distributed tubes were observed by scanning electron microscopy. The influence of temperature and content of natural humic acid on the perchlorate adsorption capacity was examined at pH 3. The adsorption data were fitted with three models: modified Freundlich, pseudo-first order, and pseudo-second order. The modified Freundlich model produced the best fit to describe the kinetic adsorption processes. The adsorption capacities of perchlorate measured at 25 °C and pH 3 using single-walled carbon nanotubes and granular ferric hydroxide were about 6 and 3 mg/g, respectively. The influence of natural humic acid on perchlorate adsorption by SWCNTs was examined. Natural humic acid was derived from raw water in Gao-Ping River in south Taiwan. Lower adsorption reaction rates of perchlorate were obtained at higher humic acid concentrations. High humic acid concentrations induce the compression of the electric double layer that consequently reduces the surface potential energy and electrostatic repulsion.

To develop an efficient adsorbent for humic acid, the present study represents the first attempt to investigate the capability of zeolitic imidazole frameworks to remove humic acid from water. Zeolitic imidazole framework-8 (ZIF-8) is particularly selected as a prototype ZIF to adsorb humic acid owing to its high stability in aqueous solutions. ZIF-8 was synthesized and characterized using scanning electronic microscopy (SEM), powder X-ray diffraction pattern (PXRD), Fourier transform infrared spectroscopy (FT-IR), and thermogravimetric analyzer (TGA) and then used to adsorb humic acid under various conditions. The structure of ZIF-8 was found to remain intact after the exposure to humic acid in water. Factors affecting the adsorption were examined, including solid-to-liquid ratio, mixing time, temperature, pH, presence of salt, and surfactants. The adsorption capacity of ZIF-8 was found to be much higher than that of activated carbon, fly ash, zeolites, graphite, etc., showing its promising potential for removal of humic acid. The adsorption mechanism could be attributed to the electrostatic interaction between the positive surface of ZIF-8 and the acidic sites of humic acid, as well as the π–π stacking interaction between imidazole of ZIF-8 and benzene rings of humic acid. The humic acid adsorption to ZIF-8 could be enhanced in the acidic conditions, and the adsorption process remained highly stable in the solutions of a wide range of NaCl concentrations. ZIF-8 can be also regenerated by simple ethanol-washing process and reused for humic acid adsorption. These features enable ZIF-8 to be an efficient and stable adsorbent to remove humic acid from water.