Assessment of heavy metal pollution and health risks in a main river in Huayuan County,Xiangxi, Hunan Province北大核心CSCD

To study heavy metal pollution and assess the health risk of river water in Huayuan County, Xiangxi, Hunan Province, 11 water samples were collected from the Huayuan River and Brother Rivers in August and December 2016. Heavy metal (Pb, Zn, Cr, Cu, Fe, and Ni) concentrations were determined from the samples. The health risk assessment model recommended by the U.S. Environmental Protection Agency (USEPA) was applied to assess the health risk of heavy metals in the main surface waters of Huayuan County. The results indicated that the concentrations of heavy metals (Pb, Zn, Cr, Cu, Fe, and Ni) of surface water in the research area were 2.57 × 10-3, 4.66 × 10-4, 1.65 × 10-3, 6.27 × 10-4, 0.19, and 8.50 × 10-4 mg/L, respectively. The health risk of surface waters with heavy metals was high. Therefore, the chemical carcinogenic substance (Cr) health risk index was five or six times higher than that of chemical non-carcinogens (Pb, Zn, Cu, and Ni). The average health risk indices of non-carcinogenic substances were in the order Pb > Cu > Zn > Ni. The correlation and principal component analysis of surface water showed that the six heavy metal elements were composed of three main components in the main surface waters of the county. The first principal component was comprised of Fe and Ni (33.28%), which was mainly from internal pollution. The second component was comprised of Cu and Cr (26.98%), which was primarily due to industrial waste water, rainwater leaching mineral waste produced by heavy metal mining, and smelting enterprises. The third component, resulting from geochemical pollution, was Zn (17.10%). The health risk indices triggered by heavy metal in surface waters was high. Heavy metal pollutants in the research area need to be controlled in the order Cr, Pb, Cu, Zn and Ni. © 2018 Science Press. All rights reserved.     

Assessment of metals in dry-toilet collected matters from suburban areas of Ulaanbaatar,Mongolia, using biosolids quality guidelines and potential ecological risk index

Dry-toilet collected matter （DCM） from traditional dry-toilet pits are a potential health and ecological risk in suburban areas. In this study, the characteristics of metals in DCMs from suburban areas of Ulaanbaatar were surveyed. The results indicate that DCMs contain a high percentage of organic matter and nutrients, while heavy metals are at low levels, which shows good agricultural potential. The concentration ranges of Cr, Cu, Hg, Ni, Pb, and Zn were 11±5, 46±9, 0.08±0.05, 9±3, 17±9, and 338±86mg·kg^-1, respectively. The concentration of Cd was below 0.5 mg.kgl, and a high positive relation was shown between chromium and nickel concentrations. The heavy metals in DCMs were safe for land application but Zn in DCMs was close to the effects range median （ERM）, which is toxic in some cases, such as amphipod bioassays. Because it is mandatory to treat DCMs to reduce pathogens, in the case of heavy metal enrichment and agricultural reuse, composting or pyrolysis are better choices than incinera- tion. Compared with global soil background values, the heavy metals in DCMs showed a low level of ecological risk, but a medium level when compared with Mongolian soil background values. The ecological risk of six heavy metals was in the descending order Hg 〉 Cu 〉 Zn 〉 Pb 〉 Ni 〉 Cr and the contribution rate of Hg exceeded 60%.     

Reuse of heavy metal-accumulating Cynondon dactylon in remediation of water contaminated by heavy metals

Phytoremediation technology is regarded as a simple and efficient way to remove heavy metals from contaminated soil. A reasonable disposal of metal hyperaccumulators is always and resource-saving. The a major issue in waste reuse heavy metal-accumulating Cynondon dactylon （L.） was investigated where heavy metals were desorbed by a facile acid-treatment. The result indicated that more than 90% of heavy metals （Zn, Pb and Cu） was extracted from Cynondon daetylon with 0.2 mmol· L^-1 HCl. The plant residue was used to adsorb heavy metals ions. The adsorption fitted the Langmuir isotherm model with the saturation adsorption capacity of 9.5 mg·g^-1 Zn^2＋, 36.2 mg·g^-1 Pb2＋ and 12.9 mg·g^-1 Cu^2＋, and the surface eomplexation and the backfilling of heavy metal imprinting cavities existed simultaneously during the adsorption. The treatment of wastewaters indicated that the plant residue exhibited a high removal rate of 97% for Cu. Also, the material could be recycled. The method offers a new disposal approach for heavy metal hyperaccumulator.     

Current status and developing trends of the contents of heavy metals in sewage sludges in China

It is essential to determine the heavy metal concentrations in sewage sludge to select appropriate disposal methods. We conducted a national survey of heavy metal concentrations of sewage sludge samples from 107 municipal sewage treatment plants located in 48 cities covering the 31 provinces and autonomous regions, as well as Hong Kong, Macao and Taiwan by Xinjiang Production and Construction Corps in 2006, and identified the temporal trends of heavy metal contents in sewage sludge by comparison with surveys conducted in 1994-2001. In 2006, the average concentrations of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn in sewage sludge were 20.2, 1.97, 93.1, 218.8, 2.13, 48.7, 72.3, and 1058mg.kg-1, respectively. Because of the decreased discharge of heavy metals into industrial wastewater in China and the increasingly stringent regulations governing the content of industrial wastes entering sewers, the average concentrations of Cd, Cr, Cu, Hg, Ni, Pb, and Zn have decreased by 32.3%, 49.7%, 54.9%, 25.0%, 37.2%, 44.8%, and 27.0%, respectively, during the past 12 years. The concentrations of Cd, Cr, Cu, Ni, and Zn in the samples exceeded the heavy metal limits of the Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant in China （GB 18918-2002） by 6.5%, 3.7%, 6.5%, 6.5%, and 11.2%, respectively. From these results, 85 of the 107 municipal sludges analyzed would be considered suitable for land application.     

Effects of in situ biological treatments on heavy metal release of urban river sediment

A typical fiver in Yangzhou City was used to study the effects of artificial aeration, eco-brick cover, biological packing cover, and low-sited plant floating beds on the release of heavy metals from urban river sediments. This work showed that 1） the Cr release rate was decreased by 50.3%-89.6%, with an average of 59.3%, thereby reducing the Cr pollution load to the overlying water by 36.6%-82.7%, with an average of 53.3%; 2） the Zn release rate was reduced by 21.0%-88.9%, with an average of 42.3%, and the Zn pollution load of the overlying water was reduced by 38.0%-67.1%, with an average of 55.0%; 3） the Cu release rate was reduced by 27.5%-91.0%, with an average of 55.3%, and the Cu load of the overlying water was reduced by 57.1%-83.7%, with an average of 71.7%; 4） the Pb release rate was reduced by 11.8%- 79.3%, with an average of 41.2%, and the Pb pollution load of the overlying water was reduced by -1.3%-70.7%, with an average of 29.8%. We also found that the effects of in situ biological treatments on the release of heavy metals were affected by the extent of sediment disturbance. For integrated applications, high-disturbance treatments should be combined with low-disturbance treatments to reduce the explosive release of pollutants caused by sediment disturbance during the treatment operation to achieve better overall treatment effects.     

Concentrations of Heavy Metals in Muscle with Relation to the Growth of Two Marine Fish Species

Heavy metal concentrations in muscle and their relation to thegrowth of two marine fish species,including tonguefish( Cynoglossus arel) and mullet( Mugil cephalus),were studied. The samples were collected in Bach Dang estuary andconcentrations of heavy metals( As,Cd,Co,Mn,Cu,Zn,Pb,and V) in muscle of the fisheswere determined. The result showed that the accumulated trend of heavy metal is different between fish species. The concentration of As,Zn,Mn,V,Cu,Pb,Co and Cd in tonguefish were 73. 7 ± 30. 6,22. 82 ± 4.87,3. 44 ± 2. 13,1. 61 ± 0. 15,0. 71 ± 0. 13,0. 45 ± 0. 24,0. 03 ± 0. 02 and 0. 02 ± 0. 02 mg·g-1,respectively. Meanwhile the concentration of Zn,As,V,Mn,Cu,Pb,Co and Cd in mullet were 83. 41 ±19. 68,9. 78 ± 1. 92,1. 36 ± 0. 54,1. 29 ± 0. 51,0. 65 ± 0. 12,0. 42 ± 0. 20,0. 06 ± 0. 03 and0. 03 ± 0. 01mg·g-1,respectively. Comparison of metal levels among thesespecies indicated that the concentrations of As and Mn in tonguefish were significantly higher than those in mullet,whereas Zn levels in mullet were found to be higher than that in tonguefish. There is no significant differences of Cd,Co,Cu,Pb and V levels in muscle between two species. Significant inversed relationshipsbetween concentration levels of metals and lengths of tonguefish were found for Mn,Cu and Zn,butnot for As,Cd,Pb,and V. There were no significant relationships between the heavy metal concentrations and the length of mullet. In general,decreasesof the heavy metal concentrations corresponded to the increases of fish body lengths,particularly for As,Co,Cu,Mn and V and the exception for Cd. Terefore reduced risks were associated with consuming biggermullet fish,and increased risks of As and Cd were associated with consuming bigger tonguefish in Bach Dang river mouth.     

Speciation evolutions of target metals （Cd,Pb） influenced by chlorine and sulfur during sewage sludge incineration

In sludge incineration, the thermal behavior of heavy metal is a growing concern. In this work, the combined analysis of metal partitioning behavior between vapor phase and condensed phase, speciation redistribu- tion in condensed phase and the difference of metal species in binding energy was carried out to investigate the possible volatilization-condensation mechanism of heavy metals in high-temperature sludge incineration. It was found that there were two steps in metal volatilization. The initial volatilization of heavy metal originated from their exchangeable （EXC）, carbonate bound （CAR） and iron- manganese bound （FM） fractions, which is primarily composed of simple substance, chlorides, oxides and sulfides. With the increase of chlorine and sulfur in sludge, the inner speciation redistribution of heavy metals occurred in condensed phase, which was an important factor affecting the potential volatility of heavy metals. A partial of metal species with complexed （COM） and residual （RES） fractions gradually decomposed into simple substance or ions, oxides and carbonates, which signifi- cantly strengthened the second volatility. In presence of chlorine, about 46% of Cd with the RES fraction disappeared when the volatility rate of Cd increased by 44.89%. Moreover, about 9% of Pb with COM fraction disappeared when there was an increase of nearly 10% in the volatilization rate. Thus, the second volatilization was mainly controlled by the decomposition of metal species with COM and RES fractions. By virtue of XRD analysis and the binding energy calculation, it was found that metal complex and silicates were inclined to decompose under high temperature due to poor thermo stability as compared with sulfates.     

Genotoxicity evaluation of surface waters located in urban area of Xi’an City using Vicia faba bioassays

In this study, micronucleus （MCN） and chromosome aberration （CA） tests in Vicia faba root tip cells were carried out in order to assess the water quality and the comprehensive genotoxic potential of surface waters located in the urban area of Xi＇an City, China. For these evaluations, water samples from different surface waters （four rivers, two lakes, two biological treatment plant effluents） were collected, the ultra-pure water and methyl methanesulfonate solution was used as the negative and positive control, respectively. In our results, highly significant differences in MCN perrnillage （average number of micronuclei per 1000 cells）, CA frequencies and PI （pollution index） values were found among three rivers and two WWTP effluents, the tested samples from two rivers caused the decrease of mitotic index over 22% compared with the negative control. No significant changes were observed in micronuclei and chromosome aberrations frequencies at one river and two lakes during the period of test （wet season）. These results point out a poor state of the water quality and genotoxic activity of the main surface waters in Xi＇an City. It is recommended to establish a monitoring program for the presence of genotoxic agents in these surface waters.     

Heavy metal accumulation and phytostabilization potential of dominant plant species growing on manganese mine tailings

Screening plants that are hypertolerant to and excluders of certain heavy metals plays a fundamental role in a remediation strategy for metalliferous mine tailings. A field survey of terrestrial higher plants growing on Mn mine tailings at Huayuan, Hunan Province, China was conducted to identify candidate species for application in phytostabilization of the tailings in this region. In total, 51 species belonging to 21 families were recorded and the 12 dominant plants were investigated for their potential in phytostabilization of heavy metals. Eight plant species, Alternanthera philoxeroides, Artemisia princeps, Bidens frondosa, Bidens pilosa, Cynodon dactylon, Digitaria sanguinalis, Erigeron canadensis, and Setaria plicata accumulated much lower concentrations of heavy metals in shoots and roots than the associated soils and bioconcen- tration factors （BFs） for Cd, Mn, Pb and Zn were all 〈 1, demonstrating a high tolerance to heavy metals and poor metals translocation ability. The field investigation also found that these species grew fast, accumulated biomass rapidly and developed a vegetation cover in a relatively short time. Therefore, they are good candidates for phytostabilization purposes and could be used as pioneer species in phytoremediation of Mn mine tailings in this region of South China.     

Cadmium and lead toxicity and bioaccumulation in Microcystis aeruginosa

The growth of human population leads to intensification of agriculture and promotes, through eutrophication, development of cyanobacteria. One of the most widespread and bloom-forming species in freshwater is toxic Microcystis aeruginosa （M. aeruginosa）. Combustion of fossil fuels and metallurgical processes are the main sources of heavy metals contamination in surface water including cadmium （Cd） and lead （Pb）. The following study was conducted in order to determine the effect of 1- 20 mg. L-1 of Cd and Pb on photochemistry （using flow cytometry） and growth （based on chlorophyll concentra- tion） ofM. aeruginosa as well as to estimate levels of metal bioaccumulation. We have found that 1-10mg.L-1 of Cd and 1-5 rag. L1 of Pb induced continuous enhancement of chlorophyll fluorescence during 24 h of incubation. No significant degradation of chlorophyll was observed in these samples. At higher concentrations of 20 mg. L-1 of Cd and 10-20 mg.L-1 of Pb chlorophyll level significantly decreased and its fluorescence was quenched. M. aeruginosa demonstrated high capability of Cd and Pb bioaccumulation, proportionally to initial metal concentration. In samples with initial concentration of 20 mg. L-1 of Cd and Pb bioaccumulation of 87.3% and 90.1% was observed, respectively. Our study demonstrates that M. aeruginosa can potentially survive in highly metals polluted environments, be a primary source of toxic metals in the food chain and consequently contribute to enhanced toxicity of heavy metals to living organisms including human.     

Quantitative characterization of Cu binding potential of dissolved organic matter （DOM） in sediment from Taihu Lake using multiple techniques

Dissolved organic matter （DOM） plays an important role in heavy metal speciation and distribution in the aquatic environment especially for eutrophic lakes which have higher DOM concentration. Taihu Lake is the third largest freshwater and a high eutrophic lake in the downstream of the Yangtze River, China. In the lake, frequent breakout of algae blooms greatly increased the concentration of different organic matters in the lake sediment. In this study, sediment samples were collected from various part of Taihu Lake to explore the spatial difference in the binding potential of DOM with Cu. The titration experiment was adopted to quantitatively characterize the interaction between Cu（II） and DOM extracted from Taihu Lake sediments using ion selective electrode （ISE） and fluorescence quenching technology. The ISE results showed that the exogenous DOM had higher binding ability than endogenous DOM, and DOM derived from aquatic macrophytes had a higher binding ability than that derived from algae. The fluorescence quenching results indicated that humic substances played a key role in the complexation between DOM and Cu（II） in the lake. However, because of the frequent breakout of algae blooms, protein-like matters are also main component like hnmic matters in Taihu Lake. Therefore, the metals bound by protein-like substances should be caused concern as protein-like substances in DOM were unstable and they will release bound metal when decomposed.     

Effects of phosphorus concentration on Cr（VI） sorption onto phosphorus-rich sludge biochar

To investigate effects of phosphorus content on Cr（VI） sorption onto phosphorus-rich biochar, sewage sludge of different phosphorus concentrations from 4 to 60 mg.g-1 by dry weight were prepared and carbonized to make biochar for batch sorption experiments. Test results revealed that different phosphorous concentration of raw sludge had respective impacts on surface area, pore surface area, average pore diameter and pH value of derived biochar. The adsorption kinetics of phosphorus-rich biochar could be described by the pseudo-second-order model. The sorption isotherm data followed Langmiur model better than Freundlich model. Biochar produced from sludge with phosphorus concentration of 20 mg. gl gave the largest chromium sorption capacity, which could be attributed to its largest surface area and pores surface area comparing with those of＇biochars from sludge with other phosphorus concentrations. The chromium loaded biochar was analyzed using Fourier Transform Infrared Spectroscopy and X-ray Diffraction measurement. The results indicated that chemical functional groups hydroxyl and methyl on surface of biochar were involved in Cr（VI） binding and its reducing to Cr（III）. Then, a portion of Cr （III） in form of various phosphate precipitates was bound onto biochar surface and the rest was released into the solution. The experimental results suggested that phos- phorus played an important role in pore and surface area development of sludge biochar during pyrolytic process. It also could react with Cr（III） on the biochar surface that impacted on capacity of Cr（VI） removal from solution by sludge biochar. Therefore, phosphorus concentration in sludge should be considered when sludge pyrolytic residue would be reused for heavy metals sorbing.     

Total phosphorus concentrations in surface water of typical agro- and forest ecosystems in China, 2004–2010

The concentrations of total phosphorus （TP） from 83 surface water sampling sites in 29 of the Chinese Ecosystem Research Network （CERN） monitored ecosystems, representing typical agro- and forest ecosystems, were assessed using monitoring data collected between 2004 and 2010 from still and flowing surface water. Results showed that, TP concentrations were significantly higher in agro-ecosystems than those in forest ecosystems both for still and flowing surface water. For agro- ecosystems, TP concentrations in the southern area were significantly higher than those in the northern and north- western areas for both still and flowing surface water, however no distinct spatial pattern was observed for forest ecosystems. In general, the median values of TP within agro- and forest ecosystems did not exceed the Class V guideline for still （0.2mg.L-1） or flowing （0.4mg.L-1） surface water, however, surface water at some agro- ecosystem sampling sites was frequently polluted by TE Elevated concentrations were mainly found in still surface water at the Changshu, Fukang, Linze and Naiman monitored ecosystems, where exceedance （〉 0.2 mg.L-1） frequencies varied from 43% to 78%. For flowing water, elevated TP concentrations were found at the Hailun, Changshu and Shapotou monitored ecosystems, where exceedance （〉 0.4 mg. L-1） frequencies varied from 29% to 100%. Irrational fertilization, frequent irrigation and livestock manure input might be the main contributors of high TP concentrations in these areas, and reduced fertilizer applications, improvements in irrigation practices and centralized treatment of animal waste are necessary to control P loss in these TP vulnerable zones.     

Diversity and vertical distributions of sediment bacteria in an urban river contaminated by nutrients and heavy metals

The aim of this study was to investigate the benthic bacterial communities in different depths of an urban river sediment accumulated with high concentrations of nutrients and metals. Vertical distributions of bacterial operational taxonomic units （OTUs） and chemical para- meters （nutrients： NH4＋, NO3, dissolved organic carbon, and acid volatile sulfur; metals： Fe, Zn, and Cu） were characterized in 30 cm sediment cores. The bacterial OTUs were measured using the terminal restriction fragment length polymorphism analysis. Biodiversity indexes and multivariate statistical analyses were used to characterize the spatial distributions of microbial diversity in response to the environmental parameters. Results showed that concentrations of the nutrients and metals in this river sediment were higher than those in similar studies. Furthermore, high microbial richness and diversity appeared in the sediment. The diversity did not vary obviously in the whole sediment profile. The change of the diversity indexes and the affiliations of the OTUs showed that the top layer had different bacterial community structure from deeper layers due to the hydrological disturbance and redox change in the surface sediment. The dominant bacterial OTUs ubiquitously existed in the deeper sediment layers （5-27 cm） corresponding to the distributions of the nutrients and metals. With much higher diversity than the dominant OTUs, the minor bacterial assemblages varied with depths, which might be affected by the sedimentation process and the environmental competition pressure.     

Distribution characteristics of dinoflagellate cysts in the Yantian Port,Shenzhen, China北大核心CSCD

An annual quarterly survey of six stations in Yantian Port, Shenzhen, China was conducted from January 2020 to October 2020 to investigate the spatial and temporal distribution of dinoflagellate cysts in the surface sediment of Yantian Port. In total, 36 species representing five groups and two uncertain taxa were identified. The dominant species were Scrippsiella trochoidea, Alexandrium spp., Gymnodinium catenatum, Cochlodinium spp., and Lingulodinium polyedrum. The seasonal difference was not obvious in terms of temporal distribution. The number of species ranged from 32 to 36, and the abundance varied from 297 to 996 cysts/g. The annual average values of the diversity index, richness index, and evenness index were 3.65, 1.55, and 0.93, respectively. The annual number and abundance of heterotrophic species were higher than those of autotrophic species. The number and abundance of species at stations near the dock zone were lower than those near the adjacent area. Notably, six toxic dinoflagellate cysts were found in the surface sediment of Yantian Port, indicating a potential outbreak risk for their vegetative cells in the local coastal area. This study provides a picture of the “Seed Bank” of dinoflagellates near Yantian Port, Shenzhen, and provides a reference value for predicting the occurrence of algal blooms. © 2022 Science Press. All rights reserved.     

Identification and ranking of the risky organic contaminants in the source water of the Danjiangkou reservoir

The Danjiangkou reservoir was selected to provide the source water for the middle routes of the South to North Water Transfer Project, which has provoked many environmental concerns. To date, investigations of water contamination of the source water of the Danjiangkou reservoir with organic micro-pollutants have been limited. This study was conducted to identify and rank organic contaminants that pose risks in the Danjiangkou reservoir. To this end, the Chemical Hazard Evaluation and Manage- ment Strategies （CHEMS-1） approach was adapted to integrate the deconvolution technology of qualitative identifying contaminants for site-specific environmental matrices. The samples were screened for the presence of 1093 contaminants using deconvolution technologies and the hazard values of the identified contaminants were calculated using the adapted CHEMS-1 approach accord- ing to their hazardous properties and occurrence in source water. The results showed that 46 contaminants from 1093 targets were present in Danjiangkou water, 23 of which appeared at frequencies higher than 50%, and 15 of which were identified as priorities. Over half （53%） of the high- ranked contaminants were polycyclic aromatic hydrocar- bons （PAHs）, with chrysene ranked highest on the list. Health risk assessment of the top-ranked PAHs was conducted and revealed that cancer risks of PAHs detected in the source water of Danjiangkou to different populations ranged from 10-7 to 104, indicating a low cancer risk to consumers. The results of this study indicated that the adapted CHEMS-1 approach was feasible for site-specific screening of organic contaminants to identify and rank potential priority pollutants.     

High specificity detection of Pb2+ ions by p-SCN-Bz-DTPA immunogen and p-NH2-Bn-DTPA coating antigen

Only one bifunctional metal-chelator was used to prepare immunogen and coating antigen in all of the previous researches. However, the antibody-specific recognition to the spacer arm of the bifunctional metal- chelator might lower the specificity of heavy metal ions immunoassay. Two different bifunctional metal-chelators were adopted to prepare the immunogen and coating antigen respectively in our study to avoid this problem. The conjugates of keyhole limpet hemocyanin （KLH） and p-SCN-Bz-DTPA-Pb were used as immunogen, whereas the conjugates of bovine sentrn albumin （BSA） and p- NH2-Bn-DTPA-Pb were used as coating antigen. Poly- clonal antibodies specific to DTPA-Pb chelates were obtained from rabbits. Indirect competitive enzyme-linked immunosorbent assay （ELISA） was adopted to detect Pb^2＋ ion solutions prepared by Pb^2＋ standard solution and ultrapure water. In the mixing microplate, DTPA and Pb2＋ ions formed chelates and combined with specific anti- bodies. After incubation, the DTPA-Pb and the antibodies complex were added into the wells of the reaction microplate. The reaction microplate was coated by the conjugates ofBSA andp-NH2-DTPA-Pb, which competed for the specific antibodies. The result signals presented a good sigmoid curve when the Pb^2＋ concentration ranges from 0.01 to 100mg·L^-1 The IC50 of the indirect competitive ELISA is 0.23±0.04mg·L^-1 Pb2＋ ion. The cross-reaction with Cd^2＋, Cu^2＋, Fe^2＋, Mn^2＋, Zn^2＋, and other divalent ions were less than 5%.     

Role of biologic components in a novel floating-bed combining Ipomoea aquatic,Corbicula fluminea and biofilm carrier media

A novel floating-bed incorporated with water spinach （Ipomoea aquatica）, Asiatic clam （Corbicula fluminea）, and carrier media supported biofilm was developed for eutrophic water purification. The contribu- tions of each biologic component to the removals of total nitrogen （TN）, total phosphorus （TP） and Chl.a were examined. The nutrient removals due to the direct uptake by either water spinach or Asiatic clam were less than 10%, suggesting a negligible role of biologic assimilation and leaving the biofilm as the indispensable biologic compo- nent in the floating-bed. Chl.a was reduced mainly by Asiatic clams via filter-feeding. Meanwhile, the digestion and excretion of Asiatic clams benefited the proliferation of nitrifying and denitrifying bacteria, resulting in the improvement of TN removal. In summary, the synergetic effects of water spinach, Asiatic clams and biofilms would promote the eutrophic water treatment performance of floating-bed in comparison with the conventional floating- bed with vegetation as the single biologic component.     

A 14-year measurement of toxic elements in atmospheric particulates in Hong Kong from 1995 to 2008

Toxic elements in the atmosphere can enter and accumulate in the human body, seriously impacting human health. In this study, we analyzed a 14-year （1995-2008） measurement of three toxic elements （As, Cd and Cr） in PMlo in Hong Kong, China. The pollution of these toxic elements in Hong Kong was not serious. The trend analysis showed that As and Cr in PM10 increased at a statistically significant level （p〈0.05） during the 14-year period, while the Cd in PM10 did not change significantly. Typical seasonal variations were observed for all three toxic elements, largely in relation to the Asian monsoon. Hourly 10-day backward trajectories were computed and cate- gorised into four groups. The continental air masses showed much higher concentrations of the three toxic elements than the marine air masses. The abundances of As and Cd in the PM10 were much higher in the continental air masses than those in the marine air masses, while the abundances of Cr showed an opposite pattern. The trends of the three toxic elements in East China＇s air mass were consistent with those in the overall data set ofHong Kong. Examination of the toxic element data recorded at urban sites and a roadside site also indicated a large contribution of external air masses to particulate As and Cd in Hong Kong. These results suggest that the long-range transport from the mainland of China is the dominant contributor to particulate As and Cd, while both local and long-distance sources determine the particulate Cr in Hong Kong.     

Modeling agricultural non-point source pollution in a high-precipitation coastal area of China

Non-point source （NPS） pollution simulation in the high-precipitation coastal areas of China is difficult because varying annual typhoon incidence leads to highly contrasting rainfall patterns in dry years and wet years. An IMPULSE （Integrated Model of Non-point Sources Pollution Processes） based NPS model of the Changtan Reservoir watershed, which is a typical high-precipitation coastal area in China, was established based on the analysis of point and NPS pollution data, a digital elevation model, and data on land-use, soil, meteorology, economy, and agricultural management practice. Pre-processed pre-rain- fall soil moisture levels were introduced during the simulation to model the effects of typhoons on hydrology. Rainfall events were simulated sequentially through the year and the model was calibrated and verified using hydrological and water quality data. Accuracy of the simulated rainfall runoff and water quality in the Changtan watershed was found to be acceptable. The study showed that the NPS modeling system could be applied to the simulation and prediction ofNPS loadings in the Changtan Reservoir watershed.