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Zhao C.-M.,Sun Yat Sen University | Zhao C.-M.,Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology | Campbell P.G.C.,INRS - Institute National de la Recherche Scientifique | Wilkinson K.J.,University of Montreal
Environmental Chemistry | Year: 2016

Environmental contextThe concentration of a free metal cation has proved to be a useful predictor of metal bioaccumulation and toxicity, as represented by the free ion activity and biotic ligand models. However, under certain circumstances, metal complexes have been shown to contribute to metal bioavailability. In the current mini-review, we summarise the studies where the classic models fail and organise them into categories based on the different uptake pathways and kinetic processes. Our goal is to define the limits within which currently used models such as the biotic ligand model (BLM) can be applied with confidence, and to identify how these models might be expanded. AbstractNumerous data from studies over the past 30 years have shown that metal uptake and toxicity are often best predicted by the concentrations of free metal cations, which has led to the development of the largely successful free-ion activity model (FIAM) and biotic ligand model (BLM). Nonetheless, some exceptions to these classical models, showing enhanced metal bioavailability in the presence of metal complexes, have also been documented, although it is not yet fully understood to what extent these exceptions can or should be generalised. Only a few studies have specifically measured the bioaccumulation or toxicity of metal complexes while carefully measuring or controlling metal speciation. Fewer still have verified the fundamental assumptions of the classical models, especially when dealing with metal complexes. In the current paper, we have summarised the exceptions to classical models and categorised them into five groups based on the fundamental uptake pathways and kinetic processes. Our aim is to summarise the mechanisms involved in the interaction of metal complexes with organisms and to improve the predictive capability of the classic models when dealing with complexes. © CSIRO 2016. Source

Zhang W.,Sun Yat Sen University | Zhang W.,Oak Ridge National Laboratory | Zhang W.,Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology | Tsang D.C.W.,University of Canterbury | Tsang D.C.W.,Hong Kong Polytechnic University
Chemosphere | Year: 2013

Understanding the transport of metal-chelant complexes is a challenging but necessary task for assessing the in situ chelant applications for land remediation and the potential environmental risks. This study presented an integrated conceptual framework for delineating primary and secondary interactions between target metals, chelants and soil components. The mathematical transport model based on primary interactions reasonably simulated the breakthrough curves of multiple target metals (Cu, Zn, Pb, Cr, and Ni) and mineral cations (Fe, Al, Mg, Mn, and Ca) during EDTA flushing of a field-contaminated soil. The first-order extraction rates of target metals were on the order of 10-6s-1, except Zn (10-4s-1) due to exceptionally large extractable amount in the soil. These rates compared well with previously reported values for field-contaminated soil, but were much smaller than those for artificially contaminated soil. The first-order dissolution rates of mineral cations (10-6-10-5s-1) were similar to the reported values for crystalline minerals, except Ca (10-4s-1) because of substantial proton-induced dissolution of carbonates. Nevertheless, due to a wide spectrum of extraction and dissolution rates at different stages, the model provided a more conservative prediction (i.e., overestimation) of metal-chelant transport while underestimated the transport of free chelant. Further revision of the proposed model may improve its prediction accuracy but attention should be paid to the model complexity and the number of adjustable parameters. © 2013 Elsevier Ltd. Source

Yang X.,Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology | Yang X.,Sun Yat Sen University | Shen Q.,Sun Yat Sen University | Guo W.,Sun Yat Sen University | And 2 more authors.
Chemosphere | Year: 2012

The formation of trichloronitromethane (TCNM) and dichloroacetonitrile (DCAN) was investigated during chlorination and chloramination of 31 organic nitrogen (org-N) compounds, including amino acids, amines, dipeptides, purines, pyrimidones and pyrroles. Tryptophan and alanine generated the greatest amount of TCNM during chlorination process and asparagine and tyrosine yielded the highest amount of TCNM during chloramination process. Tryptophan, tyrosine, asparagine, and alanine produced more DCAN than other org-N compounds regardless of chlorination or chloramination. TCNM and DCAN formation was higher by chlorination than by chloramination. NH 2Cl:org-N molar ratios, reaction time, and pH affected N-DBPs formation in varying degrees. TCNM and DCAN yields were usually high during chloramination of tyrosine, asparagine, and methylpyrrole under the following reaction conditions: NH 2Cl:org-N molar ratios greater than 10, reaction time for 1d, and at pH 7.2. NH 2Cl as a major nitrogen origin in TCNM and DCAN was confirmed via labeled 15N-monochloramine during chloramination of tyrosine, asparagine and methylpyrrole. In contrast, the majority of nitrogen in TCNM originated from glycine, and that in DCAN originated from pyrrole. Based on the intermediates identified by gas chromatography/mass spectrometry (GC/MS), a pathway scheme was proposed for TCNM and DCAN formation. © 2012 Elsevier Ltd. Source

Yang X.,Sun Yat Sen University | Yang X.,Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology | Guo W.,Sun Yat Sen University | Shen Q.,Sun Yat Sen University
Journal of Hazardous Materials | Year: 2011

Algal cells and extracellular organic matter (EOM) of two algae species, Microcystis aeruginosa (blue-green algae) and Chlorella vulgaris (green algae), were characterized. The low specific UV absorbance (SUVA) values of EOM and cells from both algae species indicated the very hydrophilic nature of algal materials. Fluorescence excitation-emission matrix showed that algal EOM and cells were enriched with protein-like and soluble microbial by-product-like matters. The formation potential of a variety of disinfection by-products (DBPs) during chlorination and chloramination of algal cells and EOM were evaluated. Algal cells and EOM of Microcystis and Chlorella exhibited a high potential for DBP formation. Yields of total DBPs varied with the algae cultivation age. Cellular materials contributed more to DBP formation than EOM. The presence of bromide led to higher concentrations of total trihalomethanes (THMs), haloacetonitriles (HANs), and halonitromethanes (HNMs). Bromide also shifted the DBPs to brominated ones. Bromine incorporation was higher in HNMs than in THMs and HANs. Compared to natural organic matter, algae under bloom seasons can contribute significantly to the DBP precursor pool. © 2011 Elsevier B.V. Source

Qian J.,Hong Kong University of Science and Technology | Lu H.,Sun Yat Sen University | Lu H.,Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology | Cui Y.,Hong Kong University of Science and Technology | And 4 more authors.
Water Research | Year: 2015

Thiosulfate, as an intermediate of biological sulfate/sulfite reduction, can significantly improve nitrogen removal potential in a biological sulfur cycle-based process, namely the Sulfate reduction-Autotrophic denitrification-Nitrification Integrated (SANI®) process. However, the related thiosulfate bio-activities coupled with organics and nitrogen removal in wastewater treatment lacked detailed examinations and reports. In this study, S2O3 2- transformation during biological SO4 2-/SO3 2- co-reduction coupled with organics removal as well as S2O3 2- oxidation coupled with chemolithotrophic denitrification were extensively evaluated under different experimental conditions. Thiosulfate is produced from the co-reduction of sulfate and sulfite through biological pathway at an optimum pH of 7.5 for organics removal. And the produced S2O3 2- may disproportionate to sulfide and sulfate during both biological S2O3 2- reduction and oxidation most possibly carried out by Desulfovibrio-like species. Dosing the same amount of nitrate, pH was found to be the more direct factor influencing the denitritation activity than free nitrous acid (FNA) and the optimal pH for denitratation (7.0) and denitritation (8.0) activities were different. Spiking organics significantly improved both denitratation and denitritation activities while minimizing sulfide inhibition of NO3 - reduction during thiosulfate-based denitrification. These findings in this study can improve the understanding of mechanisms of thiosulfate on organics and nitrogen removal in biological sulfur cycle-based wastewater treatment. © 2014 Elsevier Ltd. Source

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