Xinhui Liu

Assessment of heavy metal pollution in wetland soils from the young and old reclaimed regions in the Pearl River Estuary, South China.

Soils were sampled in three types of wetlands from the young (A) and old (B) reclaimed regions of the Pearl River Estuary. They were analyzed for total concentrations of heavy metals to investigate their distributions and pollution levels in both regions. Results showed that most heavy metals in ditch and riparian wetlands did not significantly differ from those in reclaimed wetlands in A region, while significantly lower for Cd, Cu, Pb, and Zn in reclaimed wetlands in B region, suggesting higher effects of long-term reclamation. Iron, Cr and Cu were identified as metal pollutants of primary concern and had higher contributions to the total toxic units compared to other metals. Almost all metals exceeded their lowest effect levels and Fe and Cr even exceeded the severe effect levels. Multivariate analysis shows that Fe and Mn are controlled by parent rocks and other metals mainly originate from anthropogenic source.

Photosonochemical degradation of Phenol in water

The combination of ultrasound (US) and photochemistry has been used to degrade an aqueous solution of phenol. It was considerably more effective than ultrasound or ultraviolet (UV) light alone. Based on the results of total organic carbon (TOC) removal, it was shown that the synergistic action of ultrasound and ultraviolet light existed. Identification of the first intermediates of the reaction (hydroquinone, catechol, benzoquinone and resorcin) indicates that OH radicals are involved in the photosonochemical degradation mechanisms. The effects of parameters such as pH, saturating gases, and Fe2+ on the photosonochemical degradation have been studied. The experimental results have shown that lower pH and higher concentration of dissolved oxygen favor the phenol degradation and that the presence of Fe2+ enhanced TOC removal of phenol solutions.

Analyzing trophic transfer of heavy metals for food webs in the newly-formed wetlands of the Yellow River Delta, China

Nine heavy metals sampled from water, sediments, and aquatic organisms in the newly-formed wetlands of the Yellow River Delta (YRD) of China were analyzed to evaluate their concentrations and trophic transfer in food webs. The stable carbon (δ13C) and nitrogen (δ15N) isotopes were used to investigate trophic interactions. Results show that most of heavy metals detected in water and sediments are lower than that in Yangtze River Delta and Pearl River Delta. The longest food web is approximately 4 with the highest trophic level of birds. The difference of heavy metal concentrations between endangered Saunderss Gull and other three kinds of protected birds is not obvious. Cd, Zn, and Hg were identified to have an increase with the trophic level (TL), while As, Cr, Cu, Mn, Ni and Pb show an opposite trend, however, the biomagnification of the selected nine heavy metals in the food webs is not significant.

Distribution and pollution, toxicity and risk assessment of heavy metals in sediments from urban and rural rivers of the Pearl River delta in southern China

Sediments were collected from the upper, middle and lower reaches of both urban and rural rivers in a typical urbanization zone of the Pearl River delta. Six heavy metals (Cd, Cr, Cu, Ni, Pb and Zn) were analyzed in all sediment samples, and their spatial distribution, pollution levels, toxicity and ecological risk levels were evaluated to compare the characteristics of heavy metal pollution between the two rivers. Our results indicated that the total contents of the six metals in all samples exceeded the soil background value in Guangdong province. Based on the soil quality thresholds of the China SEPA, Cd levels at all sites exceeded class III criteria, and other metals exhibited pollution levels exceeding class II or III criteria at both river sites. According to the sediment quality guidelines of the US EPA, all samples were moderately to heavily polluted by Cr, Cu, Ni, Pb and Zn. Compared to rural river sites, urban river sites exhibited heavier pollution. Almost all sediment samples from both rivers exhibited moderate to serious toxicity to the environment, with higher contributions from Cr and Ni. A “hot area” of heavy metal pollution being observed in the upper and middle reaches of the urban river area, whereas a “hot spot” was identified at a specific site in the middle reach of the rural river. Contrary metal distribution patterns were also observed along typical sediment profiles from urban and rural rivers. However, the potential ecological risk indices of rural river sediments in this study were equal to those of urban river sediments, implying that the ecological health issues of the rivers in the undeveloped rural area should also be addressed. Sediment organic matter and grain size might be important factors influencing the distribution profiles of these heavy metals.

Seasonal variation and sediment-water exchange of antibiotics in a shallower large lake in North China.

The occurrence of four antibiotics, including oxytetracycline (OTC), tetracycline (TC), norfloxacin (NOR) and ofloxacin (OFL), in surface water, overlying water, pore water and sediment samples were studied in the Baiyangdian Lake from February to November in 2009. The total concentrations of these antibiotics ranged among 17.73-281.82, 22.98-258.45, 22.43-198.95 ng L(-1) and 131.65-750.27 ng g(-1) in surface water, overlying water, pore water and sediments, respectively. Seasonal variation might be impacted by the frequency of different pattern of antibiotics and the water temperatures of different seasons, where the higher concentrations appeared at different seasons. In addition, the regions with significant sewage discharge or human agricultural activities exhibited high concentrations of antibiotics in water and sediments. The highest accumulation rates of the four antibiotics ranged from 11.27 to 29.71%, which indicated that these compounds exhibited strong adsorption to the sediment. However, higher concentrations of antibiotics in pore water and even overlying water may result in the release of these compounds from the sediment acting as a secondary contaminant source in a certain time period, especially for TC. The pseudo-partitioning values of fluoroquinolones (FQs) ranged from 4493 to 47,093 L kg(-1) and were much higher than those of tetracyclines (TCs), which ranged from 277 to 1880 L kg(-1) indicating that the FQs are prone to accumulation in the sediment.

Fractionation, transfer, and ecological risks of heavy metals in riparian and ditch wetlands across a 100-year chronosequence of reclamation in an estuary of China

The effect of reclamation on heavy metal concentrations and the ecological risks in ditch wetlands (DWs) and riparian wetlands (RWs) across a 100-year chronosequence in the Pearl River Estuary of China was investigated. Concentrations of 4 heavy metals (Cd, Cu, Pb, and Zn) in soil and plant samples, and sequential extracts of soil samples were determined, using inductively coupled plasma atomic absorption spectrometry. Results showed that heavy metal concentrations were higher in older DW soils than in the younger ones, and that the younger RW soils contained higher heavy metal concentrations compared to the older ones. Although the increasing tendency of heavy metal concentrations in soil was obvious after wetland reclamation, the metals Cu, Pb, and Zn exhibited low or no risks to the environment based on the risk assessment code (RAC). Cd, on the other hand, posed a medium or high risk. Cd, Pb, and Zn were mainly bound to Fe-Mn oxide, whereas most of Cu remained in the residual phase in both ditch and riparian wetland soils, and the residual proportions generally increased with depth. Bioconcentration and translocation factors for most of these four heavy metals significantly decreased in the DWs with older age (p<0.05), whereas they increased in the RWs with younger age (p<0.05). The DW soils contained higher concentrations of heavy metals in the organic fractions, whereas there were more carbonate and residual fractions in the RW soils. The non-bioavailable fractions of Cu and Zn, and the organic-bound Cd and Pb significantly inhibited plant growth.

The use of carbon black to catalyze the reduction of nitrobenzenes by sulfides.

Using carbon black (CB) as catalyst, the reduction of nitrobenzenes (NBs) to anilines by sulfides at room temperature was studied. In the reactions, CB serves as an intermedium to accelerate the reduction of NBs by sulfides. In the presence of 0.3g/L CB and 3.0 mM sulfides at pH 7.0 and 25°C, our results showed that CB-catalyzed reduction of NBs were pseudo-first order. The reduction rate constant of nitrobenzene was 0.0367 h(-1) in the presence of CB-1, which was 10 times more than the reduction rate constant in the absence of CB-1. Other experiments of different CB samples produced by different methods and different raw materials indicated that some active oxygenated functional groups on CB surface should be the reactive sites and play the dominant role in catalyzing the reduction of NBs. The catalytic reactions of different NBs by sulfides indicated that the reduction rate constants of chloronitrobenzenes to chloroanilines were greater than those of methylnitrobenzenes to methylanilines. And due to the effect of different substituent positions, the nitro group with meta substituent was reduced most easily while the nitro group with ortho substituent was reduced most difficulty.

Acute toxicity and quantitative structure–activity relationships of α-branched phenylsulfonyl acetates to Daphnia magna

The acute toxicity (48 h-EC50, microM) of 20 alpha-substituted phenylsulfonyl acetates was measured using Daphnia magna with a static method. On the basis of physicochemical parameters (octanol/water partition coefficient logK(ow) and aqueous solubility logS(w)), the theoretical linear solvation energy relationships (TLSER) and Charge model descriptors, QSARs were calculated for the immobilization of D. magna. For the models with the physicochemical parameters logK(ow) and logS(w), the low squared correlation coefficients indicate that hydrophobicity plays a dominant role on the toxicity and hydrophobicity is not the only factor that influences the activity of the compounds. For the TLSER model and the Charge model, the great squared correlation coefficients suggest that the models have good predictive capability. The higher activity of the compounds can be explained with the disruption of van der Waals interactions between lipid and/or protein compounds within the membrane and the possibility of the compounds to form hydrogen bonds with the receptor molecules. The models may more completely illustrate the toxicity mechanisms.

China’s Coastal Wetlands: Understanding Environmental Changes and Human Impacts for Management and Conservation

Anthropogenic activities are substantially changing coastal wetland ecosystems globally. In developing countries such as China, a number of anthropogenic factors associated with rapid population growth and economic development threaten coastal wetlands. In China, notably, coastal wetlands have been increasingly lost to reclamations that are widely adopted to meet the increasing demand for land under rapid economic development. Coastal wetland management requires understanding the patterns of and the mechanisms underlying such human impacts. In this special issue, we synthesize current understanding of environmental changes and human impacts on China’ coastal wetlands, focusing on reclamation. Coastal human activities in China are found to change shoreline evolution and wetland hydrology, to deteriorate soil and water quality, to alter vegetation succession, benthic animal and microbial communities, and fisheries, and to impair ecosystem functioning and services. For some of those impacts, new models and indices are developed or applied. We also outline key research areas that should be further studied for effective management of coastal wetlands and successful wetland restoration. We suggest that developing a multi-objective, multi-scenario, and multi-scale framework of integrated management will be crucial to the success of China’s coastal wetland conservation with increasing human dominance of the nation’s coasts.

Polycyclic aromatic hydrocarbons (PAHs) in wetland soils under different land uses in a coastal estuary: toxic levels, sources and relationships with soil organic matter and water-stable aggregates.

The concentrations of 16 polycyclic aromatic hydrocarbons (PAHs) were determined in the soils from industrial, wharf, cropland, milldam and natural wetland sites to characterize their distributions, toxic levels and possible sources in the Pearl River Estuary and identify their relationships with soil organic matter (SOM) and water-stable aggregates (WSAs). Our results indicate that the average concentration of total PAHs in this region reached a moderate pollution level, which was higher than that in other larger estuaries in Asia. The average level of total PAHs in industrial soils was 1.2, 1.5, 1.6 and 2.3 times higher than those in soils from wharf, cropland, milldam and natural wetland sites, respectively. Greater accumulation of PAHs occurred in the middle and/or bottom soil layers where 3-ring PAHs were dominant. Industrial soils also exhibited the highest toxic levels with the highest toxic equivalent concentrations of PAHs, followed by wharf and milldam soils, and the cropland and wetland soils had the lowest toxicity. The diagnostic ratios suggested that PAHs primarily originated from biomass and coal combustion at industrial and milldam sites, and petroleum combustion was determined to be the primary source of PAHs at the wharf, cropland and wetland sites. Both 3-ring and 4-ring PAHs in the milldam and wharf soils were significantly positively correlated with the SOM, whereas the 4,5,6-ring PAHs and total PAHs in industrial soils and the 2-ring PAHs in cropland soils were significantly negatively correlated with the SOM. In addition, large WSAs also exhibited a significant positive correlation with PAHs.