Behavior Of Organic Contaminants Research Articles

The Role of Biocomposites and Nanocomposites in Eliminating Organic Contaminants from Effluents

Many contaminants such as heavy metals, dyes and hydrocarbon compounds are annually generated by industrial activities and discharged into water sources. They have destructive impacts on the environment. To eliminate these toxic contaminants from aqueous media, sorption can be considered a proper and efficient process, as it has indicated high efficiency for removing organic contaminants. This paper entails a comprehensive evaluation of different organic pollutants, pros and cons of the sorption process in removing these pollutants, comparing different types of adsorbents and investigating the recyclability of different types of composites. Moreover, the sorption mechanism and kinetic behavior of organic contaminants are investigated using biocomposites and nanocomposites. Moreover, the future perspectives of biocomposites and nanocomposites in eliminating organic compounds are discussed. Based on investigations, a large number of nanocomposites have been utilized for removing organic contaminants with high performance so far, including SiO2/MnFe2O4/ZIF-8 MOF, magnetite/MWCNTs, nano zerovalent iron, barium/Cobalt/polyethylene glycol (PEG), graphene oxide/Fe3O4, kaolin/CuFe2O4 and Fe3O4@UiO-66. Moreover, polyaniline/sodium alginate/Oscillatoria filamentous cyanobacterium biomass, cow bones/zeolite/coconut biocomposite and AC derived from melamine and sucrose are excellent biocomposites in the removal of organic pollutants. Moreover, the reusability study shows that poly(N-isopropylacrylamide)/Fe3O4 and corn stalk biomass/chitosan/Fe3O4 biocomposites have significant stability compared to other composites in the elimination of organic pollutants.

Enhanced oxidation of aromatic hydrocarbons by ozone micro-nano bubble water: Mechanism and influencing factors

Aromatic hydrocarbons are common contaminants in groundwater, which could threat human health through multiple ways and have low degradation rates. Micro-nano bubble ozonation has been developed as a novel technology to oxidize organic contaminants effectively. Since most technologies such as dissolved air flotation (DAF) could only produce ozone micro-nano bubble water (OMBW) instead of independent ozone micro-nano bubbles, the comparison between OMBW and ozonated water (OW) had more significant implications. This study investigated the oxidation rate of four aromatic hydrocarbons (AHs) including toluene, ethylbenzene, o-xylene and p-xylene by both OW and OMBW at the same dissolved ozone concentration through a series of batch experiments. Results showed that the oxidation rate of AHs by OMBW was 13.6–22.6% higher than that by OW when solution pH was 8, which was mainly caused by the promoted contact between AHs and OH·at the micro-nano bubble interface. This conclusion was also validated by the faster increase of reaction rate between OH·and AHs for OMBW when solution pH increased from 5 to 9, leading to the increase of OH·utilization rate in alkaline environment. The inhibition effect by anions (Cl-, SO42- and HCO3-) as well as dissolved organic matter, and the promotion effect by Mg2+ were both magnified in OMBW, which was also caused by the interfacial effect of micro-nano bubble. This study was critical to our understanding of the removal behavior of organic contaminants by OMBW, and it would also guide the design of more efficient oxidation technologies based on micro-nano bubbles.

Predicting laterite redox potential with iron activity and electron transfer term

Predicting the redox behavior of organic contaminants and heavy metals in soils is challenging because there are few soil redox potential (Eh) models. In particular, current aqueous and suspension models usually show a significant deviation for complex laterites with few Fe(II). Here, we measured the Eh of simulated laterites over a range of soil conditions (2450 tests). The impacts of soil pH, organic carbon, and Fe speciation on the Fe activity were quantified as Fe activity coefficients, respectively, using a two-step Universal Global Optimization method. Integrating these Fe activity coefficients and electron transfer terms into the formula significantly improved the correlation of measured and modeled Eh values (R2 = 0.92), and the estimated Eh values closely matched the relevant measured Eh values (accuracy R2 = 0.93). The developed model was further verified with natural laterites, presenting a linear fit and accuracy R2 of 0.89 and 0.86, respectively. These findings provide compelling evidence that integrating Fe activity into the Nernst formula could accurately calculate the Eh if the Fe(III)/Fe(II) couple does not work. The developed model could help to predict the soil Eh toward controllable and selective oxidation-reduction of contaminants for soil remediation.

Heavy metal-mediated adsorption of antibiotic tetracycline and ciprofloxacin on two microplastics: Insights into the role of complexation

Microplastics (MPs) have recently become an emerging environmental concern. Nevertheless, limited information is known about the adsorption of MPs for organic contaminants under combined heavy metals pollution, with an emphasis on the role of complexation. Thus, this study aims to comprehensively compare and investigate the adsorption performance of antibiotic tetracycline (TC) and ciprofloxacin (CIP) on two polar MPs (polyamide (PA) and polyvinyl chloride (PVC)) affected by Cu(II) and Cd(II) with contrasting complexation abilities. Batch adsorption experiments were used in combination with speciation calculation, zeta potential determination, FTIR spectroscopy characterization and investigation of the affinity of MPs for heavy metals. Results showed that the sorption kinetics and isotherms of TC and CIP on PA and PVC could be well fitted to pseudo-second-order and Langmuir models, respectively, both in the absence and presence of Cu and Cd, suggesting that multiple interactions and monolayer adsorption played an important role in the adsorption process. The presence of Cu substantially improved TC and CIP adsorption and obviously changed the pH dependence of their adsorption onto both MPs, which may result from the Cu-induced strong complexation with TC and CIP. The presence of Cd slightly enhanced TC adsorption on both MPs while reduced CIP adsorption especially on PVC, which may be ascribed to the Cd-induced cationic bridging effects in TC adsorption and the competitive adsorption of Cd in CIP adsorption. Therefore, the heavy metal-mediated complexation effects may play a dominant role in antibiotic adsorption by MPs only in the presence of heavy metals with strong complexation ability while the adsorption performance in the presence of heavy metals with negligible complexation capacity may be influenced by effects other than complexation. This study helps further understand the heavy metal-mediated adsorption behavior of organic contaminants on polar MPs and the role of complexation reactions therein.

Influence of shallow geothermal energy on the behaviour of organic contaminants of emerging concern in urban aquifers

Abstract. Urban aquifers are a valuable resource of freshwater for cities, however, their quality is degraded due to the presence of organic contaminants of emerging concern (CECs). The effects of organic CECs are largely unknown, but there is evidence that they pose a risk for human health, soil, plants and animals. Organic CECs are naturally degraded in aquifers and their degradation rates depend on the physico-chemical properties, i.e., redox conditions and groundwater temperature. Some anthropogenic activities, like low-enthalpy geothermal energy (LEGE), may modify subsurface physico-chemical conditions altering the behaviour of organic CECs. LEGE is a renewable and carbon-free energy that allows obtaining cooling and heating energy. The utilization of LEGE is currently growing and it is expected that in a near future the density of LEGE systems will increase. LEGE modifies the groundwater temperature and in some situations the redox state (i.e., if the dissolved oxygen increases when groundwater is returned to the aquifer as a result of a poorly design), thus, it is of paramount importance to determine the impact of LEGE related activities on the behaviour of organic CECs. The behaviour of organic CECs under the influence of LEGE is investigated by means of thermo-hydro-chemical numerical modelling. Simulation output shows that LEGE activities have the potential to modify the degradation rates of organic CECs, and thus, their concentrations in aquifers. In the simulated scenario, the concentration of the chosen CEC decreases by the 77 % at the downgradient boundary of the model. The results of this study have significant implications for predicting the behaviour of organic CECs in urban aquifers and suggest specific changes in the design of LEGE facilities aiming to improve the quality of urban groundwater by boosting in-situ attenuation mechanisms.

Coupled model for consolidation and organic contaminant transport in GMB/CCL composite liner under non-isothermal distribution condition

The transport behavior of organic contaminants in the composite liner is affected by both consolidation and thermal diffusion. However, research on the coupled theory is still limited. In this study, the governing equations for consolidation and organic contaminant transport in GMB/CCL (geomembrane and compacted clay liner) composite liner are developed under non-isothermal distribution condition, and the corresponding coupled model is established. Meanwhile, the numerical method is adopted to obtain the finite difference solutions for consolidation and organic contaminant transport, respectively. Besides, the correctness of the proposed coupled model is validated by comparing the existing analytical solution with the theoretical model. Finally, the effects of different factors on the transport behaviors are discussed, in which trichloroethylene is chosen as the research object. It is found that the influence of non-isothermal distribution on the transport process is amplified when consolidation is neglected rather than considered. Moreover, the effects of consolidation on the transport behaviors are more remarkable under the non-isothermal distribution condition than under the isothermal distribution condition, where the volume compressibility coefficient plays a vital role. Overall, the coupled influences of multi-factors such as thermal diffusion and consolidation should be considered simultaneously to properly evaluate the transport characteristics of organic contaminants.

Sorption and desorption behavior of four antibiotics at concentrations simulating wastewater reuse in agricultural and forested soils

Due to rises in antibiotic resistance, fate and transport of antibiotics in soil systems requires greater understanding to determine potential risks to human and animal health. Adsorption coefficients (Kd and Kf) are standard measures for determining sorption capacity and partitioning behavior of organic contaminants in solid matrices. Frequently, sorption studies use higher antibiotic concentrations (mg L−1) and larger spiked water volume to mass of soil (>5:1), which may not reflect sorption behaviors of antibiotics at low concentrations (ng L−1 - μg L−1) in natural soils. The aim of this study was to determine sorption and desorption behaviors of four antibiotics commonly found in soils due to wastewater reuse using parameters replicating typical soil conditions. Concentrations (μg L−1) of sulfamethoxazole (SMX), trimethoprim (TMP), lincomycin (LIN) and ofloxacin (OFL) were equilibrated with four soil types at a 2:1 ratio of spiked water volume to mass of soil, which better represents field conditions. Log Kf and log Kfoc value ranges in this study were 1.88–1.95 and 3.2–4.7 for TMP, 0.43–1.4 and 2.7–3.2 for SMX, and 0.65–1.4 and 2.0–4.1 for LIN, respectively. Ofloxacin adsorbed tightly to soil particles, and adsorption coefficients could not be calculated. Sorption values were higher than previous studies that used similar soil types but had higher ratios of spiking solution to mass of soil (>5:1). Overall, OFL and TMP are expected to strongly interact with soil particles and be less mobile, while SMX and LIN are expected to be more mobile due to weaker sorption interactions.

Sorption Behavior and Mechanisms of Organic Contaminants to Nano and Microplastics.

Nano and microplastics (NPs/MPs) have received widespread attention in recent years. Because of their large specific surface area and hydrophobicity, NPs/MPs can adsorb various organic contaminants. This article gives a brief review of the sorption behavior of organic contaminants to NPs/MPs, summarizes the possible sorption mechanisms, and analyzes the influencing factors in the environment on the sorption behavior and mechanisms of NPs/MPs. The main mechanisms of sorption of organic contaminants to NPs/MPs are partitioning, surface sorption (hydrogen bonding, π–π interaction, electrostatic interaction, and van der Waals force), and pore filling. The sorption behavior of organic contaminants to NPs/MPs is not only affected by the properties of the NPs/MPs and the organic contaminants, but also by the solution chemistry, such as the pH, ionic strength, and dissolved organic matter.

Numerical investigation of naphthalene deposition dynamics during CO2 leakage

An important leakage risk associated with CO2 geological sequestration is the potential transport and fate of organic contaminants due to the CO2 leakage. In this paper, a precipitation and deposition dynamic model was constructed using COMSOL to evaluate the potential impacts of organic contaminants in response to the leakage of CO2 and brine into a shallow aquifer. The Span-Wagner equation and Peng-Robinson equations were adopted to estimate the partitioning behavior of organic contaminants. Numerical simulations with naphthalene as a representative contaminant show that the dissolved component is transported with the equilibrium concentrations at the thermodynamic conditions built by the fluid phase, while the precipitated solid particles are either transported with carrier fluid or deposited in the leakage pathway according to the deposition dynamic model. The sharp decrease of solubility promotes the precipitation impetus while the deposition rate mainly depends upon the leakage velocity and pore structure. Local blockage may occur due to the accumulation of deposited particles, and the potential location is most likely to be near the outlet of the leakage pathway in current scenario. Sensitivity analyses indicate that pressure difference and temperature buildup would influence both the leakage velocity and deposition dynamics, while the pore structure of leakage pathway, represented by porosity and permeability, will affect the leakage characteristic so as to the deposition rate. The presented models are generic in nature for naphthalene transport, demonstrating a methodology that can explore the generation of a potential third organic phase in contaminant transport for risk assessments.

Adsorption of bisphenol A on dispersed carbon nanotubes: Role of different dispersing agents

Although the adsorption of organic contaminants on carbon nanotubes (CNTs) and the dispersion of CNTs have been extensively investigated separately, the adsorption behavior of organic contaminants on dispersed CNTs, which may be a missing link to understanding their environmental behavior and risks, remain unclear yet rarely studied. In this study, the effect of the dispersing agent structure on the adsorption characteristics of BPA (a representative organic contaminant) on dispersed CNTs were investigated using tannic acid (TA), sodium dodecylbenzenesulfonate (SDBS), and gallic acid (GA) as model dispersing agents. Our results showed that at low dispersing agent concentrations, adsorption of TA could lead to higher CNT suspension than adsorption of SDBS and GA due to greater steric hindrance. However, the presence of TA reduced the adsorption of BPA due to strong competitive adsorption on dispersed CNTs. At high concentrations of TA, the suspension of CNTs was reduced by the “bridging effect,” in which adjacent dispersed CNTs form hydrogen bonds and re-aggregate. However, the adsorption of BPA dramatically increased due to the enhanced partition of BPA into pseudomicelles of TA on dispersed CNTs, as indicated by the significantly increased index of heterogeneity at high TA concentration. Transmission electron microscopy images confirmed the formation of TA pseudomicelles. This study highlights the key role of the dispersing agent structure on CNT dispersion and adsorption of organic contaminants. The high mobility and transport of CNT-adsorbed contaminants may lead to higher environmental risks compared with aggregated CNTs.

Correlations and adsorption mechanisms of aromatic compounds on biochars produced from various biomass at 700°C.

Knowledge of adsorption behavior of organic contaminants on high heat temperature treated biochars is essential for application of biochars as adsorbents in wastewater treatment and soil remediation. In this study, isotherms of 25 aromatic compounds adsorption on biochars pyrolyzed at 700°C from biomass including wood chips, rice straw, bamboo chips, cellulose, lignin and chitin were investigated to establish correlations between adsorption behavior and physicochemical properties of biochars. Isotherms were well fitted by Polanyi theory-based Dubinin-Ashtakhov (DA) model with three parameters, i.e., adsorption capacity (Q0) and adsorption affinity (E and b). Besides the negative correlation of Q0 with molecular maximum cross-sectional areas (σ) of organic compounds, positive correlations of Q0 with total pore volume (Vtotal) and average diameter of micropore (D) of biochars were observed, indicating that adsorption by biochars is captured by the pore-filling mechanism with molecular sieving effect in biochar pores. Linear solvation energy relationships (LSERs) of adsorption affinity (E) with solvatochromic parameters of organic compounds (i. e., αm and π∗) were established, suggesting that hydrophobic effect, π-π interaction and hydrogen-bonding interaction are the main forces responsible for adsorption. The regression coefficient (π1) and intercept (C) of obtained LSERs are correlated with biochar H/C and Rmicro, respectively, implying that biochars with higher aromaticity and more micropores have stronger π-π bonding potential and hydrophobic effect potential with aromatic molecule, respectively. However, hydrogen-bonding potential of biochars for organic molecules is not changed significantly with properties of biochars. A negative correlation of b with biochar H/C is also obtained. These correlations could be used to predict the adsorption behavior of organic compounds on high heat temperature treated biochars from various biomass for the application of biochars as sorbents and for the estimating of environmental risks of organic compounds in the present of biochars.

Impact of Polymer Colonization on the Fate of Organic Contaminants in Sediment.

Plastic pellets and microbes are important constitutes in sediment, but the significance of microbes colonizing on plastic pellets to the environmental fate and transport of organic contaminants has not been adequately recognized and assessed. To address this issue, low-density polyethylene (LDPE), polyoxymethylene (POM) and polypropylene (PP) slices were preloaded with dichlorodiphenyltrichloroethanes (DDTs), polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) and incubated in abiotic and biotic sediment microcosms. Images from scanning electron microscope, Lysogeny Broth agar plates and confocal laser scanning microscope indicated that all polymer slices incubated in biotic sediments were colonized by microorganisms, particularly the LDPE slices. The occurrence of biofilms induced higher dissipation rates of DDTs and PAHs from the LDPE slice surfaces incubated in the biotic sediments than in the abiotic sediments. Plastic colonization on LDPE slice surfaces enhanced the biotransformation of DDT and some PAHs in both marine and river sediments, but had little impact on PCBs. By comparison, PP and POM with unique properties were shown to exert different impacts on the physical and microbial activities as compared to LDPE. These results clearly demonstrated that the significance of polymer surface affiliated microbes to the environmental fate and behavior of organic contaminants should be recognized.

Thiacloprid adsorption and leaching in soil: Effect of the composition of irrigation solutions

Pressure on groundwater resources has increased during the last decades due to the growing demand, especially in arid and semiarid regions, such as the Mediterranean basin, with frequent drought periods. In order to partially remediate this environmental problem of world concern, irrigation of agricultural lands with adequately treated wastewaters (TWW) is becoming a common management practice. The complex composition of these low-quality waters may influence the behavior of organic contaminants in soils. A calcareous soil with low organic carbon content was selected for the assessment of the adsorption and leaching of the neonicotinoid insecticide thiacloprid (THC). Different solutions were evaluated: TWW after a secondary treatment, a saline solution and solutions with a range of dissolved organic carbon concentration (DOC, 3–300mgL−1). The addition of an organic fertilizer (fertiormont) to the soil was also assessed, in an attempt to reduce THC mobility. Sorption of thiacloprid, a relatively polar pesticide, was similar under all the conditions considered, though an adsorption decrease was observed when DOC concentration increased. The transport of THC through soil columns was retarded with all the treatments, with the lower effects corresponding to TWW and the saline solution. Addition of fertiormont and irrigation with DOC at 3mgL−1 resulted in a reduction of pesticide leached (34% and 38%, respectively) in comparison with the control (66%), but surprisingly not for DOC at high concentration (55%), possibly due to co-elution of the pesticide with DOC. Therefore the transport of polar compounds, like THC, could be affected by the composition of the irrigation solutions, altering their impact to environmental water resources.

Reactive mineral removal relative to soil organic matter heterogeneity and implications for organic contaminant sorption

Soil organic matter (SOM) is generally treated as a static compartment of soil in pollutant fate studies. However, SOM might be altered or fractionated in soil systems, and the details of SOM property/composition changes when coupled with contaminant behavior are unknown. In this study, a mild acid treatment was adopted to remove reactive minerals and partially remove SOM components. After acid treatment, biomarker signatures showed that lignin-derived phenols were released and black carbon (as suggested by benzene-polycarboxylic acids) and lipids were enriched. The biomarker information was consistent with common bulk chemical characterization. The sorption coefficient Kd for PHE was two times higher after acid treatment, whereas Kd for OFL was three times lower. The organic carbon normalized sorption coefficient KOC values for PHE were higher for soils after acid treatment, indicating stronger interactions between PHE and SOM. The linear regression line between Kd and fOC for OFL showed lower intercepts and slopes after reactive mineral removal, suggesting a decreased contribution of minerals and reduced dependence on SOM. These results were attributed to the release of polar compositions in SOM accompanied by reactive mineral removal. Our results suggest that the mobility of ionic organic contaminants increases, whereas that of hydrophobic organic contaminants decreases after acid treatment with respect to reactive mineral depletion. This study emphasized that new insights into the coupling of SOM dynamics should be incorporated into organic contaminant behavior studies. SOM molecular biomarkers offer a useful technique for correlating SOM composition and sorption property changes.

Simulation Experiment: Effect of Organic Colloid on Carbamazepine Transport in Porous Media

The behavior of organic contaminants in subsoil can be affected by their interactions with organic colloids. In order to explore the impact of organic colloids on the mobility of emerging contaminants in porous media, especially pharmaceutical and personal care products (PPCPs), column experiment was conducted to investigate the migration behavior of target compound carbamazepine (CBZ). In the experiments, quartz sand, standard soil and natural field-collected soil were selected as three types of porous media respectively, and organic colloids were prepared with commercial humic acid. The results showed that, the two-site chemical nonequilibrium model in CXTFIT could better describe the migration behavior of CBZ in all soil columns. This results demonstrated that chemical nonequilibrium adsorption happened in CBZ's migration process. After colloid was added to the sand column, results of CBZ's adsorption process had no significant changes, however, desorption hysteresis was weaker. The reason for that can be explained as the formation of colloid-CBZ complexes by the combination of colloid with CBZ. These complexes could not significantly influence CBZ's adsorption process, however, they could accelerate CBZ's desorption process by solubilization. When organic colloids existed, the migration of CBZ in natural soil and standard soil columns was more hysteretic than sand column, indicating that the sorption capacity of soil column was higher than sand column. The soil organic matter and clay should play a crucial role in the transportation: low/high energy adsorption sites in organic matter and clay surface all could bond with CBZ. Compared with standard soil, the magnitude of sorption and desorption hysteresis of CBZ in natural soil was higher. It was mainly because of the higher organic content in natural soil. Based on the migration behavior of the contaminant in this study, a concept model for various interactions during the transport of hydrophobic organic contaminants in porous media in the presence of organic colloids was then proposed.

Deriving in vivo biotransformation rate constants and metabolite parent concentration factor/stable metabolite factor from bioaccumulation and bioconcentration experiments: An illustration with worm accumulation data.

Growing concern for the biological fate of organic contaminants and their metabolites and the urge to connect in vitro and in vivo toxicokinetics have prompted researchers to characterize the biotransformation behavior of organic contaminants in biota. The whole body biotransformation rate constant (kM ) is currently determined by the difference approach, which has significant methodological limitations. A new approach for determining kM from the kinetic observations of the parent contaminant and its intermediate metabolites is proposed. In this method, kM can be determined by fitting kinetic data of the parent contaminant and the metabolites to analytical equations that depict the bioaccumulation kinetics. The application of the proposed method is illustrated using worm bioaccumulation-biotransformation data collected from the literature. Furthermore, a metabolite parent concentration factor (MPCF) is also proposed to characterize the persistence of the metabolite in biota. Because both the proposed kM method and MPCF build on the existing theoretical framework for bioaccumulation, they can be readily incorporated into standard experimental bioaccumulation protocols or risk assessment procedures or frameworks. Possible limitations, implications, and future directions are elaborated. Environ Toxicol Chem 2016;35:2903-2909. © 2016 SETAC.

Degradation of p-Nitrophenol on Biochars: Role of Persistent Free Radicals.

Generation of environmentally persistent free radicals (EPFRs) on solid particles has recently attracted increasing research interest. EPFRs potentially have high reactivity and toxicity. However, the impact of EPFRs on organic contaminant behavior is unclear. We hypothesized that EPFRs in biochars can degrade organic contaminants and play an important role in organic contaminant behavior. We observed obvious degradation of p-nitrophenol (PNP) in the presence of biochars, through the detection of NO3(-) as well as organic byproducts. The extent of PNP degradation was correlated to the intensity of EPR signals of biochar particles. tert-Butanol (a •OH scavenger) did not completely inhibit PNP degradation, indicating that •OH could not fully explain PNP degradation. The decreased PNP degradation after tert-butanol addition was better correlated with reduced PNP sorption on biochars. PNP degradation through the direct contact with EPFRs in biochar particles could be an important contribution to the PNP concentration reduction in the aqueous phase. The coating of natural organic matter analogue (tannic acid) on biochars did not considerably inhibit PNP degradation, suggesting the ability of biochars to degrade PNP in soil and natural water. Similar EPFR-promoted degradation was observed for five different types of biochars and one activated carbon, as well as one additional chemical (p-aminophenol). Therefore, organic chemical degradation by EPFRs in biochars can be a common process in the environment and should be incorporated in organic chemical fate and risk studies.

Comparative Adsorption of Phenanthrene, Bisphenol A, and Sulfamethoxazole on Humic Acid-Iron Oxide Nanoparticle Complexes

Abstract Organo-mineral complexes are important components of soil and can greatly affect the behavior and fate of organic contaminants. Properties of organic components play important roles in organic coating on mineral surfaces. However, the dominant property and mechanism controlling organic contaminant behavior are still unclear. In this study, adsorption of various organic contaminants on humic acid-nano-Fe2O3 complexes with different properties were investigated. Nonpolar, aromatic, and high-molecular-weight fractions of humic acid (HA) were preferentially adsorbed on nano-Fe2O3, forming various HA-nano-Fe2O3 complexes with different properties. According to a correlation analysis between the adsorption of organic contaminants and properties of HA-nano-Fe2O3 complexes, the organic carbon content, aromaticity, and hydrophobicity, were believed to be the dominant properties controlling the organic contaminant adsorption. Organic carbon contents and π-π bonds might contribute to sulfamethoxazole (SMX) ...

In situ impacts of a flooding event on contaminant deposition and fate in a riparian ecosystem

Floodwaters contain a mixture of organic contaminants which affect both the water and soil quality within flooded regions. This study is the first to describe the chemical behavior of organic contaminants mobilized during the 2010 flooding event of the Rio Grande. The study compares two sites: one directly impacted by outfall from municipal sources and one primarily impacted by rural runoff. This study characterized the in situ cycling of organic contaminants (triclosan, ciprofloxacin, and atrazine), their depositional mechanisms, and the post-flood dynamics within riparian soils over 6 months. Water quality (pH, salinity, alkalinity, turbidity, N, and P) of the Rio Grande at four sites within Webb County, TX, was monitored for 3 months pre-flooding and 6 months post-flooding in order to determine contaminant levels along the Webb County border. Soil physicochemical properties (pH, CEC, and EC) were assessed for 6 months at two sites post-flooding: within the municipal area of both Laredo, TX, USA, and Nuevo Laredo, Mexico (LCC site), and upstream of the site near the edge of Laredo, TX (MR site). Low levels of contaminants were detected in the watershed year-round with levels increasing during the flood. Floodwaters had a lower pH than nonflooding conditions, resulting in greater partitioning of both triclosan and ciprofloxacin to particles within the water column with no change detected in atrazine behavior. Soil samples (0–2-cm depth) showed an increase in clay-sized particles (up to 6–14 %) and contaminant concentrations similar to that of water column particles. Organic contaminants were uniform in concentration throughout the soil profile (2–30 cm), demonstrating the impact of infiltration. Both triclosan and atrazine decayed away at rates of 23 ± 2 and 16 ± 1 days, respectively, with no decay of ciprofloxacin detected. Vertical mobility of contaminants within soils was not detected. This study was able to distinguish the influx of contamination contributed by particle deposition from that due to infiltration of the contaminated floodwaters. Further, our data indicates that outfall/effluent contaminants, such as ciprofloxacin, may persist in riparian soils post-flooding. Agricultural management should consider potential exposure and accumulation of floodwater contaminants in crops.

Organic contaminants and carbon nanoparticles: sorption mechanisms and impact parameters

Carbon nanoparticles (CNPs) are novel manufactured materials with unique properties and have potential for a variety of applications. Adsorption of organic contaminants by discharged CNPs may affect the fate and transport of organic contaminants in the environment. This review summarizes the present research progress regarding organic contaminant adsorption on CNPs, and provides important information for the evaluation of the environmental behavior of organic contaminants and the risks associated with the use of CNPs. The main adsorption mechanisms involve hydrophobic interactions, π-π interactions, hydrogen bonds, and electrostatic interactions. These interactions may exist simultaneously, while the controlling adsorption mechanism differs depending on the properties of both the organic contaminants and the CNPs along with environmental conditions. The status of CNPs in the environment greatly affects or even controls their characteristics for adsorption of organic contaminants. The mobility and transport of dispersed CNPs and CNP-adsorbed organic contaminants could be promoted in natural aqueous environments, potentially increasing the spread of various organic contaminants and their associated environmental risks. Investigating the adsorption mechanisms and impact parameters is vital in predicting the environmental behaviors of both organic contaminants and CNPs and their associated risks.