Distribution of Cu and Pb in particle size fractions of urban soils from different city zones of Nanjing, China

Soil samples from 4 defined city zones of Nanjing were randomly collected at 0-5 cm and 5-20 cm intervals and size fractions of soil particles were separated from undisturbed bulk soils by low energy dispersion procedure. The total contents of Cu and Pb in the different particle size fractions of the urban soils were analyzed by HNO3-HF-HClO4 digestion and flame atomic absorption spectrophotometer determination. The total content of Cu and Pb in soil particle size fractions varied with their size and with city zones as well. Both the content and variation with the size fractions of Pb was bigger than of Cu supporting our previous finding that there was Pb pollution to different degrees in the urban soils although the two elements were generally enriched in clay-sized fraction. Contaminated Pb tended to be preferentially enriched in the size fraction of 2000-250 μm and clay-sized fraction. While the size fractions of the soils from newly developed and preserved area contained smaller amount of Cu and Pb, the partitioning of them in coarse and fine particle size fractions were insignificant compared to that from inner residence and commercial area. The very high Pb level over 150 mg/kg of the fine particle fractions from the soils of the inner city could be a cause of high blood Pb level reported of children from the city as acute exposure to Pb of fine particles of the urban soil might occur by soil ingestion and inhalation by young children. Thus, much attention should be paid to the partitioning of toxic metals in fine soil particles of the urban soils and countermeasures against high health risk of Pb exposure by soil ingestion and dust inhalation should be practiced against the health problem of blood Pb for young children from the cities.

Influence of soil physicochemical properties,particle size fractions and mineralogy on the leaching potentials of arsenic and antimony in abandoned mine soils

At abandoned mine sites,arsenic(As)-and antimony(Sb)-enriched soils are often disposed of through onsite burial or capping.In highly weathered mine sites,the mobility of As and Sb is typically controlled by iron(Fe)(III)/Fe(II)phases;thus,the suitability of such disposal methods and appropriate testing techniques are questionable.In the present study,leaching potentials of As and Sb were examined using the toxicity characteristic leaching procedure(TCLP),waste extraction test(WET),and WET-extended procedure(WET-EXT)at three abandoned mine site soils in Australia.The leached concentration of As regularly exceeded USEPA criteria(5 mg L^(-1)).The highest leached concentrations of As and Sb were observed in the finest particle size fraction(<0.053 mm)by WET-EXT(1040 mg L^(-1)for As and 21.10 mg L^(-1)for Sb)followed by WET(800 mg L^(-1)for As and 20.90 mg L^(-1)for Sb).The TCLP method resulted in the lowest concentrations of leached As(0.0009 mg L^(-1))and Sb(0.0003 mg L^(-1)).Crystalline and amorphous As-bearing Fe oxides were the main phases in the soils studied.However,the best correlations of leached As determined by TCLP(0.832),WET(0.944),and WET-EXT(0.961)were found with the non-specifically sorbed(NS1)As fraction.The mineralogical and sequential extraction data clearly indicate the dominant role of Fe geochemistry in controlling leachability of As and Sb.The TCLP method was unlikely to be suitable for assessing leachability,as it exhibited no relationship with leachable Fe and substantially lower leached As and Sb than the other two methods.Given the high to extremely high leachable As and Sb concentrations,most of the soil samples would not be recommended for placement in capping works,old shafts,or reduction systems(e.g.,collection in drainage basins).

Behavior of different phosphorus species in suspended particulate matter in the Changjiang estuary

Suspended particulate matter （SPM） collected in the Changjiang （Yangtze River） estuary in June 2006 was separated into five fractions via water elutriation： clay-very fme silt （〈8 μm）, fine silt （8-16 μm）, medium silt （16--32 μm）, coarse silt （32~53 μm） and sand （〉63 μm）. The SPM and fractionated particles were sequentially analyzed by a modified SEDEX sequential extraction method to obtain six species of phosphorus： exchangeable or loosely-sorbed P, organic P, Fe-bound P, authigenic P, detrital P and refractory P. The results indicated that all particulate phosphorus species except for detrital P were negatively correlated to particle size; a high detrital P content was found in coarse silt and very coarse silt. From the inside of the river mouth to the gate of the fiver mouth, organic P, Fe-bound P and refractory P in the suspended particles decreased and a higher amount of exchangeable P appeared around the gate of the fiver mouth. From the gate of the river mouth to the sea, exchangeable P and organic P in suspended panicles increased distinctly. The total particulate P flux into the estuary from the Changjiang River was about 45.45×10^8μmol/s during sampling. Of this, about 8.27×10^8μmol/s was associated with the ＂truly suspended＂ fraction. The bio-available particulate P flux was about 13.58×10^8μmol/s. Of this, about 4.24 ×10^8μmol/s w as transported by ＂truly suspended＂ particles.

Distribution and Accumulation of Major and Trace Elements in Gypsum Samples from Lignite Combustion Power Plant

Flue gas containing volatile elements, fine fly ash particulates not retained by particle control devices, and limestone are the most important sources of trace and major elements (TMEs) in wet flue gas desulphurization (WFGD) gypsum. In this study, samples of gypsum slurry were separated into fine and coarse fractions. Multi-elemental analysis of 45 elements in the different size fractions of gypsum, slurry waters and lignite were performed by k0-INAA (k0-instrumental neutron activation analyses). The study found that the volatile elements (Hg, Se and halogens) in the flue gas accumulate in the fine fractions of gypsum. Moreover, the concentrations of most TMEs are considerably higher in the fine fractions compared to the coarse fractions. The exceptions are Ca and Sr that primarily originate from the limestone. Variations of TMEs in the finer fractions are dependent on the presence of CaSO4·2H2O that is the main constituent of the coarse fraction. Consequently, the content of TMEs in the fine fraction is highly dependent on the efficiency of separating the fine fraction from the coarse fraction. Separation of the finer fraction, representing about 10% of the total gypsum, offers the possibility to remove effectively TMEs from WFGD slurry.

Degradation of the fungicide metalaxyl and its non-extractable residue formation in soil clay and silt fractions

The proportion of organic matter and mineral composition are important factors determining the formation and type of non-extractable residues(NERs) of pesticides in soil. In this study, we investigated the enantioselectivity in degradation and NER formation of the chiral fungicide metalaxyl in soil particle size fractions(silt and clay). Microbial and extracellular enzyme activities during these processes were monitored in incubation of silt and clay samples isolated from sterilized and non-sterilized soil samples collected from a long-term agricultural field experimental site in Ultuna, Sweden. The temporal influence on the fate of the fungicide was noted by short-term(10-d) and long-term(92-d) incubations. Besides the acquisition of quantitative data with gas chromatography-mass spectrometry(GC/MS), stereoselective analyses were performed with chiral GC/MS. Quantitative results pointed to a higher metabolism rate of the pesticide through microbial activity than through extracellular enzyme activity. This was also confirmed by the enantioselective depletion of R-metalaxyl and the subsequent formation of R-metalaxyl acid in microbially active samples from non-sterilized soil. The silt fraction containing a high amount of organic matter exhibited a significant hydrolyzable proportion of metalaxyl NERs that was releasable under alkaline conditions. On the contrary, the clay fraction showed an enhanced affinity for covalently bound residues. Based on our results, we recommend differentiating between reversibly and irreversibly bound proportions of pesticides in persistence and environmental risk assessment because the reversible fraction contained potentially bioavailable amounts of residues that may be released under natural conditions.