Sorption of atrazine onto humic acids (HAs) coated nanoparticles
With the development of nanotechnologies, a large number of nano-materials with novel properties are being released into the environment. However, little is known about their fate, transport, toxicity and interactions with organic matters in aqueous environment. In this study, nano-SiO2 or kaolinite, coated with soil humic acid (SHA) and peat humic acid (PHA), were used as sorbents. The original and HA-coated nanoparticles were characterized for particle size, TEM and electrophoretic mobility. Sequential ultrafiltration (UF) was used to characterize the molecular size fractionations of dissolved HAs. Sorption data of atrazine (AT) under various solution concentration, ionic strength and pH were well fitted with Freundlich model. Sorption amount of AT on HA-coated nanoparticles was significantly lower than that on original particles. The sorption maximum appeared at I = 0.001 mol/l (NaNO3), pH 3. Size of nanoparticle aggregates, conformation of HA and specific surface area were factors affecting the sorption process. The compressed conformation of HA was more favorable for HA sorption than expanded one. Size of aggregation was not a determinant factor for the sorption process, while the specific surface areas of nano-sorbent was an important one. Results indicated that HA plays an important role in the transport and toxicity of nanoparticles and AT in aqueous environment.
Available from: Weihua Zhang
- "The decrement became more substantial under a higher atrazine loading. In fact, the similar phenomenon was also reported by Lu et al. (2009), who observed the amount of sorbed atrazine on humic acid-coated nanoparticles was significantly lower than that on the original ones. This can be Environ Sci Pollut Res "
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ABSTRACT: Pyrolyzing municipal wastewater treatment sludge into biochar can be a promising sludge disposal approach, especially as the produced sludge-derived biochar (SDBC) is found to be an excellent sorbent for heavy metals and atrazine. The aim of this study was to investigate how and why the coexisting humic acids influence the sorption capacity, kinetic, and binding of these contaminants on SDBC surface. Results showed humic acids enhanced Pb(II)/Cr(VI) sorption binding, and increased the corresponding Pb(II) Langmuir sorption capacity at pH 5.0 from 197 to 233 μmol g−1, and from 688 to 738 μmol g−1 for Cr(VI) at pH 2.0. It can be mainly attributed to the sorbed humic acids, whose active functional groups can offer the additional sites to form stronger inner-sphere complexes with Pb2+, and supply more reducing agent to facilitate the transformation of Cr(VI) to Cr(III). However, humic acids reduced the atrazine adsorption Freundlich constant from 1.085 to 0.616 μmol g−1. The pore blockage, confirmed by the decreased BET-specific surface area, as well as the more hydrophilic surface with more sorbed water molecules may be the main reasons for that suppression. Therefore, the coexisting humic acids may affect heavy metal stabilization or pesticide immobilization during SDBC application to contaminated water or soils, and its role thus should be considered especially when organic residues are also added significantly to increase the humic acid content there.
Available from: Ahmet Topal
- "Humic substances are structurally complex large to macromolecules which occur in soils and natural waters as a consequence of the breakdown of plant and animal residues by microbial activity (Jones, 1998). Aquatic humic substances are a category of the most widely distributed organic matters that constitute 30–50% of dissolved organic matter (DOM) in natural aquatic systems (Lu et al., 2009). Humic acid is ubiquitous in the environment and has been found to influence physiological functions of aquatic organisms (Andersson et al., 2010). "
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ABSTRACT: This study was conducted to determine the histopathological and biochemical effects of humic acid on cadmium stress in liver and kidney tissues of Salmo trutta fario, L. The fish were treated in four groups as follows and were exposed to chemicals for 7 days: control (C), cadmium (2 ppm) (Cd), humic acid (5 ppm) (HA) and humic acid + cadmium (Cd + HA). At the end of the experimental period, liver and kidney samples were taken from all fish for histopathological examination and determination of antioxidant enzyme (glutathione peroxidase, superoxide dismutase) and malondialdehyde (MDA) levels. Activity of GPx and SOD in the tissues of fish exposed to the stress of Cd was significantly lower than the control groups (P<0.05). MDA level increased (P<0.05) in cadmium exposed groups, whereas fish receiving cadmium with humic acid returned to normal MDA levels in the liver. The cadmium-induced histopathological alterations were also decreased with humic acid. These results suggest that humic acid may mediate cadmium toxicity.
Available from: Dong-Mei Zhou
- "cts might occur independently or in combination , so it is difficult to predict their net effect on contaminant degradation kinetics ( Tratnyek et al . , 2001 ) . However , limited studies have reported the effects of NOM on the decomposition of some other contaminants by Fe 0 ( Tratnyek et al . , 2001 ; Zhang et al . , 2009 ; Rao et al . , 2009 ; Lu et al . , 2009 ; Giasuddin et al . , 2007 ) . Zhang et al . ( 2009 ) found the introduction of HA de - creased the removal of 2 , 4 - DCP . Rao et al . ( 2009 ) reported that the removal rate of arsenic by Fe 0 was inhibited in the presence of HA probably because of the formation of soluble Fe - humate in the groundwater which hindered the formation o"
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ABSTRACT: Transformation of polychlorinated biphenyls (PCBs) by zero-valent iron represents one of the latest innovative technologies for environmental remediation. The dechlorination of 4-chlorobiphenyl (4-ClBP) by nanoscale zero-valent iron (NZVI) in the presence of humic acid or metal ions was investigated. The results showed that the dechlorination of 4-ClBP by NZVI increased with decreased solution pH. When the initial pH value was 4.0, 5.5, 6.8, and 9.0, the dechlorination efficiencies of 4-ClBP after 48 hr were 53.8%, 47.8%, 35.7%, and 35.6%, respectively. The presence of humic acid inhibited the reduction of 4-ClBP in the first 4 hr, and then significantly accelerated the dechlorination by reaching 86.3% in 48 hr. Divalent metal ions, Co2+, Cu2+, and Ni2+, were reduced and formed bimetals with NZVI, thereby enhanced the dechlorination of 4-ClBP. The dechlorination percentages of 4-ClBP in the presence of 0.1 mmol/L Co2+, Cu2+ and Ni2+ were 66.1%, 66.0% and 64.6% in 48 hr, and then increased to 67.9%, 71.3% and 73.5%, after 96 hr respectively. The dechlorination kinetics of 4-ClBP by the NZVI in all cases followed pseudo-first order model. The results provide a basis for better understanding of the dechlorination mechanisms of PCBs in real environment.
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