The present study examines the effect of carboxyl-CdSe/ZnS quantum dots (QDs) on Cu and Pb availability to microalgae with different cell wall characteristics: Chlorella kesslerii possessing a cellulosic cell wall and two strains of Chlamydomonas reinhardtii, a wall-less and a walled strain containing glycoproteins as the main cell wall component. Results demonstrated that QDs decreased Pb and Cu intracellular contents ({Cu}ᵢₙₜ and {Pb}ᵢₙₜ) in walled strains by a factor of 2.5 and 2, respectively, as expected by the decrease of about 70% and 40% in the dissolved Cu and Pb concentrations. QDs increased {Cu}ᵢₙₜ and {Pb}ᵢₙₜ in wall-less strain by a factor of 4 and 3.5. These observations were consistent with the observed association of QDs to the wall-less C. reinhardtii, and lack of association to walled algal strains. Suwannee River humic acid did not influence metal association to QDs, but decreased {Cu}ᵢₙₜ and {Pb}ᵢₙₜ in all microalgae.

The environmental behavior of antibiotics is not well known and the precise environmental risk assessment is not practical. This study investigated the sorption kinetics of ofloxacin, a widely used antibiotics, on soil particles with different organic carbon contents as well as soil components (a humic acid, ferric oxide and kaolinite). Two-compartment sorption kinetics were mathematically recognized (except ferric oxide because of its very fast sorption). The apparent sorption rate and the contribution of fast sorption compartment decreased with the increased organic carbon content with the exception of humic acid, suggesting that the slow sorption sites were partially located in organo-mineral complex. The OFL concentration-dependent sorption kinetics suggested that the slow sorption compartment was not controlled by diffusion process as indicated by slower sorption at higher OFL loading. The difference between OFL sorption kinetics and those of hydrophobic organic contaminants was discussed and possible mechanism of OFL two-compartment sorption was proposed.

To advance the knowledge of environmental fate of nanomaterials, we systematically investigated the dissolution of polymer-coated CdSe/ZnS quantum dots (QDs) under UV (254 nm) irradiation. The environmental effects (i.e., irradiation intensity, dissolved oxygen, temperature, and humic acid), as well as the coating effects on dissolution kinetics of QDs were investigated. Our results showed that higher irradiation intensity and temperature increased ion release rates (Cd²⁺, SeO₄ ²⁻, and Zn²⁺), whereas the different polymer coatings varied the dissolution rates. The absence of dissolved oxygen inhibited the dissolution of QDs, and we further demonstrated that the dissolution was a photo-oxidative process involved superoxide radical formation. Humic acid had a twofold effect on dissolution due to its photosensitization and photoabsorption for UV irradiation. Finally, an empirical kinetic law was proposed to interpret the above environmental effects. This study lays groundwork to better understand the environmental fate of QDs.

Solid humic acid (HA) particles were dissolved and subsequently coated on a type of multiwalled carbon nanotubes (MWCNTs). Pb²⁺ sorption from water by the solid HA, the MWCNTs and the obtained HA-MWCNT complexes was compared. The underlying mechanism of the difference in the sorption was discussed with the data at different pHs, results of desorption in the presence and absence of Ca²⁺ and the characterizations using inductively coupled plasma mass spectrometry, X-ray energy dispersion spectroscopy and X-ray absorption fine structure spectroscopy. The effect of MWCNT-contained impurities on the sorption was also examined. It was shown that the surface-bound HA introduced oxygen-containing functional groups and negative charges on the MWCNTs, thus greatly increasing Pb²⁺ sorption on the MWCNTs. Pb²⁺ could be electrostatically attracted into outer-sphere of the electric double layer of the HA-MWCNT complexes, a fraction of which would form coordination complexes with carboxyl groups in the inner- and/or outer-sphere.

Sorption of two herbicides, fluridone (FLUN) and norflurazon (NORO), by two types of biochars, whole sediment, and various soil/sediment organic matter (OM) fractions including nonhydrolyzable carbon (NHC), black carbon (BC) and humic acid (HA) was examined. The single-point organic carbon (OC)-normalized distribution coefficients (KOC) of FLUN and NORO at low solution concentration (Cₑ=0.01SW, solubility) for HA, NHC, and BC were about 3, 14, and 24 times and 3, 16, and 36 times larger than their bulk sediments, respectively, indicating the importance of different OM fractions in herbicide sorption. This study revealed that aliphatic moieties of the hydrothermal biochars and aromatic moieties of NHC samples, respectively, were possibly responsible for herbicide sorption. The hydrothermal biochar and condensed OM (i.e., NHC and BC) showed relatively high or similar herbicide sorption efficiency compared to the thermal biochar, suggesting that the hydrothermal biochar may serve as an amendment for minimizing off-site herbicide movement.

Photolysis rates of phenanthrene as a function of ionic strength (salinity), oxygen levels and humic acid concentrations were measured in aqueous solution over the range of conditions found in fresh to marine waters. Photolysis followed first order kinetics, with an estimated photodegradation half-life in sunlight in pure water of 10.3±0.7h, in the mid-range of published results. Photolysis rate constants decreased by a factor of 5 in solutions with humic acid concentrations from 0 to 10mgCL⁻¹. This decrease could be modeled entirely based on competitive light absorption effects due to the added humics. No significant ionic strength or oxygen effects were observed, consistent with a direct photolysis mechanism. In the absence of significant solution medium effects, the photodegradation lifetime of phenanthrene will depend only on solar fluxes (i.e. temporal and seasonal changes in sunlight) and not vary with a freshwater to marine environment.

This work assesses the use of immobilized humic acid (ImHA) onto aminopropyl silica (APS) as a sorbent for the removal and preconcentration of trace amounts of cobalt ions by on-line solid phase extraction (SPE) technique in the column system prepared in our laboratory. Different parameters, such as the effect of the pH, concentration, and flow rate, were studied and throughput was observed by a UV detector. All SPE steps were monitored by breakthrough curves used to visualize distribution of cobalt concentration between mobile and solid phase. The solutions collected from stripping steps were analyzed in atomic absorption spectrometer (AAS) and the amount of sorbed ions was calculated. Sorption characteristics were evaluated by using common adsorption isotherms and Scatchard plot analysis. From the obtained results, it was seen that sorption mechanism of cobalt ions were fitted to Langmuir model on a large scale and thought to be localized. Mean free energy (E = 40.82 kJ mol⁻¹) calculated from D-R isotherm showed that chemical interactions are more effective than physical interactions. This investigation reveals a new, simple, environmentally friendly, and cost-effective method for removal and preconcentration of cobalt ions from aqueous solutions by a new aminopropyl silica-immobilized humic acid material.

Synthetic and persistent endocrine disrupting chemicals (EDCs) such as 17α-ethinylestradiol (EE2) have been frequently detected in the effluent of wastewater treatment plants and induce hazards to humans and wildlife. In this study, biogenic Mn oxides were tested for the removal of EE2, and factors affecting the reaction were also investigated. The biogenic Mn oxides produced by Pseudomonas putida strain MnB1 were nano-sized and poorly crystallized particles. A concentration of 7.9 mg l−1 biogenic Mn oxides showed 87% EE2 (1 mg l−1) removal efficiency in 2 h, which confirms the excellent potential of biogenic Mn oxides for removal of estrogens. EE2 removal was enhanced at high Mn oxide doses and at low pH. Co-existing heavy metals significantly inhibit EE2 removal, due to their competition for the reactive sites of biogenic Mn oxides. Humic acid (HA) also obstructed EE2 removal, but the adverse effect was alleviated as HA concentration increased, possibly due to the formation of soluble complexes with the released Mn2+, of which adsorption onto Mn oxides reduces surface reactive sites.

The effect of different humic fractions on polychlorinated biphenyl (PCB) contamination in soils was tested in the field by means of 53 soil samples from a high-altitude grassland plateau in the Italian Alps. Three humic fractions (humin, humic acids, and fulvic acids) were characterized in parallel by quantifying 12 PCB congeners to establish a direct relationship between PCB levels and humic fraction concentrations. Humin (the most hydrophobic fraction) appears to be the most closely correlated with the amount of PCBs in soil (R ²â€‰= 0.83), while fulvic acid shows the lowest correlation (R ²â€‰= 0.49). The idea of preferential sorption of hydrophobic compounds in the humin fraction is discussed, and the humin carbon content (f ₕᵤₘᵢₙC) is proposed as an improved parameter for evaluating the potential for POP accumulation in soils, replacing total organic carbon (f ₒc). Congener studies revealed that penta- and hexa-substituted-CBs show the optimal combination of physicochemical properties for equilibrating with the humin content in soil. Moreover, f ₕᵤₘᵢₙC/f ₒc is conceptually equivalent to the empirical coefficients used in predictive K ₛₐ equations. In our samples, the f ₕᵤₘᵢₙC/f ₒc was 0.55, a value in between the empirical coefficients proposed in the literature. In predictive equations, the use of f ₕᵤₘᵢₙC instead f ₒc avoids the necessity of using an empirical parameter for a ‘generic’ condition by introducing an experimental parameter (f ₕᵤₘᵢₙC) that takes into account local conditions (organic matter composition).

PURPOSE: The oxone process for azo dye decolorization has drawbacks such as difficulties with reuse, risks of secondary pollution, and high costs associated with UV irradiation. This study aims to explore the use of oxone for decolorization in the absence of catalyst and under natural sunlight conditions (i.e., oxone/natural sunlight system) and evaluate the impacts of operating parameters (reagent dosage, initial methyl orange (MO) concentration, and initial pH) and coexisting substances (humic acid, NO 3 − , metal ions) on the system’s decolorization efficiency. METHODS: Four levels of operating parameters were configured under a Taguchi L16 orthogonal array design to examine their effects on decolorization efficiency. Fractional factional design was then used to derive the optimal combination of operating parameters, under which the effects of coexisting substances at various concentrations were examined. In addition, H2O2, CH3OH, and (CH3)3COH were used to derive the possible reaction mechanisms in the oxone/sunlight system, while ultrasonic power was used to shorten the reaction time. RESULTS: In the oxone/sunlight system, (1) the MO decolorization efficiency reaches 96.4% under the optimal operating conditions: initial concentration, 100 mg L−1; initial pH 6.04; dosage of reagent, 3 mmol L−1; and reaction time, 30 min. (2) Coexisting substances do not affect the overall decolorization efficiency. (3) The decolorization of MO in the oxone/sunlight system takes place mainly via oxidation by SO 4 [Symbol: see text]− . (4) Ultrasonic irradiation could remarkably accelerate the MO decolorization process. CONCLUSION: Effective for MO decolorization, the oxone/sunlight system improves over the traditional oxone process with advantages of lower costs and avoiding secondary pollution by catalyst.