[Critical Review on Heavy Metal Contamination in Urban Soil and Surface Dust].

With the rapid urbanization and industrialization, heavy metal contamination in urban soil and surface dust has received particular attention due to its negative effects on the eco-environment and human health. Contamination and spatio-temporal characteristics, contamination sources, and source apportionment methods, as well as the ecological and health risks of heavy metals in urban soil and surface dust were reviewed. The knowledge gaps in current research and prospects of future works were proposed. Four key points were presented, including improving the research on the interaction mechanism of heavy metals in urban soil and surface dust under complex conditions, enriching verification methods to improve the source apportionment reliability of anthropogenic metals by receptor models, strengthening the research on chemical forms of heavy metals from different sources and their short-term accumulation processes in surface dust, and raising the credibility of ecological and health risk forecast of heavy metals by integrating the improved exposure parameters and chemical forms.

[Spatial-temporal Variations and Pollution Assessment of Heavy Metals in Sediments of Qionghai Lake in Xichang City].

Based on the analysis of the total concentrations of 10 metals in the sediment core and total concentrations and chemical fractions of seven metals in the surface sediments of Qionghai Lake in Xichang City, Sichuan Province, the spatial-temporal characteristics of metal accumulation and pollution over the past century and the potential ecological risk of metals in surface sediments were studied. Before the 1970s, metal concentrations in the sediment core were stable. The total concentrations of Al, Fe, K, and Cr in the sediment core exhibited visible peaks in the 1970s, which were related to the enhanced input of fine-grained topsoil caused by increasing precipitation, lake reclamation, and deforestation. Since the 1990s, the total concentrations of Al, Fe, K, and Cr decreased with the reduced topsoil erosion, whereas the total concentrations of As, Cd, Cu, Pb, and Zn gradually increased or remained stable. The enrichment factor results showed that Cd, Pb, and Zn were the main contaminants, with Cd as the typical contaminant in the sediment core. The Cd contamination started in the 1960s and has remained at a moderate level since the 1990s. In the surface sediments, the total concentrations of Cd were higher in the northwest lake area, and no visible spatial concentration trends of the other metals were displayed. The bioavailable fractions of Cd, Pb, and Zn accounted for 95%, 63%, and 48% of the total metal concentrations on average. Among the bioavailable fractions, Cd was mainly in the acid-soluble fraction, and Pb and Zn were mainly in the reducible and oxidized fractions. The bioavailable fractions of the other metals were less than 27%. The results of total concentrations and bioavailable fractions of metals revealed that Pb and Zn in the surface sediments were slightly or moderately contaminated, and Cd was moderately contaminated on average. Cd contamination was at a severe level in the northwest lake area. The concentrations of anthropogenic Cd, Pb, and Zn in the surface sediments estimated from the total and bioavailable concentrations were comparable (P>0.05), indicating that anthropogenic metals primarily existed in bioavailable fractions in the sediment. Integrating the assessment results from sediment quality guidelines, potential ecological risk index, and chemical forms of metals, Cd in surface sediments may pose a high ecological risk, whereas the other metals has a low ecological risk.

Purification, Chemical Characterization, and Bioactivity of an Extracellular Polysaccharide Produced by the Marine Sponge Endogenous Fungus Alternaria sp. SP-32.

Marine sponges are ancient and simple multicellular filter-feeding invertebrates attached to solid substrates in benthic habitats and host a variety of fungi both inside and on their surface because of its unique ingestion and digest system. Investigation on marine sponge-associated fungi mainly focused on the small molecular metabolites, yet little attention had been paid to the extracellular polysaccharides. In this study, a homogeneous extracellular polysaccharide AS2-1 was obtained from the fermented broth of the marine sponge endogenous fungus Alternaria sp. SP-32 using ethanol precipitation, anion-exchange, and size-exclusion chromatography. Results of chemical and spectroscopic analyses showed that AS2-1 was composed of mannose, glucose, and galactose with a molar ratio of 1.00:0.67:0.35, and its molecular weight was 27.4 kDa. AS2-1 consists of a mannan core and a galactoglucan chain. The mannan core is composed of (1→6)-α-Manp substituted at C-2 by (1→2)-α-Manp with different degrees of polymerization. The galactoglucan chain consists of (1→6)-α-Glcp residues with (1→6)-ß-Galf residues attached to the last glucopyranose residue at C-6. (1→6)-ß-Galf residues have additional branches at C-2 consisting of disaccharide units of (1→2)-ß-Galf and (1→2)-α-Glcp residues. The glucopyranose residue of the galactoglucan chain is linked to the mannan core. AS2-1 possessed a high antioxidant activity as evaluated by scavenging of 1,1-diphenyl-2-picrylhydrazyl and hydroxyl radicals in vitro. AS2-1 was also evaluated for cytotoxic activity on Hela, HL-60, and K562 cell lines by the MTT and SRB methods. The investigation demonstrated that AS2-1 was a novel extracellular polysaccharide with different characterization from extracellular polysaccharides produced by other marine microorganisms.

Extracellular polysaccharide with novel structure and antioxidant property produced by the deep-sea fungus Aspergillus versicolor N2bc.

An extracellular polysaccharide, N1, was obtained from the culture medium of the deep-sea fungus Aspergillus versicolor N2bc by a combination of ethanol precipitation, ion-exchange and gel filtration chromatography. N1 was a mannoglucogalactan with molecular weight of about 20.5kDa. Results of chemical and spectroscopic analyses, including Fourier-transform infrared, one- and two-dimensional nuclear magnetic resonance spectroscopy showed that the main chain of N1 consisted of →2)-α-d-Glcp-(1→, →2)-ß-d-Glcp-(1→ and →6)-ß-d-Manp-(1→ units, substituted at C-6 position of →2)-α-d-Glcp-(1→ units. The branches were composed of galactofuranose-oligosaccharides built up of →5)-ß-d-Galf-(1→, →6)-ß-d-Galf-(1→ and terminal ß-d-Galf units. At an average, there were two branching points for every five sugar residues in the backbone. N1 possessed a high in vitro antioxidant activity as evaluated by scavenging assays involving superoxide, 1,1-diphenyl-2-picrylhydrazyl, hydroxyl radicals and reducing power. The investigation revealed that N1 was a novel antioxidant polysaccharide differing from previously described extracellular polysaccharides and could be a potential antioxidant.

Preparation and characterization of a novel extracellular polysaccharide with antioxidant activity, from the mangrove-associated fungus Fusarium oxysporum.

Marine fungi are recognized as an abundant source of extracellular polysaccharides with novel structures. Mangrove fungi constitute the second largest ecological group of the marine fungi, and many of them are new or inadequately described species and may produce extracellular polysaccharides with novel functions and structures that could be explored as a source of useful polymers. The mangrove-associated fungus Fusarium oxysporum produces an extracellular polysaccharide, Fw-1, when grown in potato dextrose-agar medium. The homogeneous Fw-1 was isolated from the fermented broth by a combination of ethanol precipitation, ion-exchange, and gel filtration chromatography. Chemical and spectroscopic analyses, including one- and two-dimensional nuclear magnetic resonance spectroscopies showed that Fw-1 consisted of galactose, glucose, and mannose in a molar ratio of 1.33:1.33:1.00, and its molecular weight was about 61.2 kDa. The structure of Fw-1 contains a backbone of (1 → 6)-linked ß-D-galactofuranose residues with multiple side chains. The branches consist of terminal α-D-glucopyranose residues, or short chains containing (1 → 2)-linked α-D-glucopyranose, (1 → 2)-linked ß-D-mannopyranose, and terminal ß-D-mannopyranose residues. The side chains are connected to C-2 of galactofuranose residues of backbone. The antioxidant activity of Fw-1 was evaluated with the scavenging abilities on hydroxyl, superoxide, and 1,1-diphenyl-2-picrylhydrazyl radicals in vitro, and the results indicated that Fw-1 possessed good antioxidant activity, especially the scavenging ability on hydroxyl radicals. The investigation demonstrated that Fw-1 is a novel galactofuranose-containing polysaccharide with different structural characteristics from extracellular polysaccharides from other marine microorganisms and could be a potential source of antioxidant.