[Characteristics of Heavy Metals Pollution of Farmland and the Leaching Effect of Rainfall in Tianjin].

The leaching effect of the rainfall process for removing heavy metals from farmland soils is a critical physical process. To study the leaching effect of the rainfall process on heavy metals in soil, the pollution characteristics of seven heavy metals in farmland soil have been investigated in the suburban Tianjin region by combining the current data with previously reported runoff data in the same region. There is a large difference for these tested heavy metals in soils, with Zn having the highest concentration at 106.61±56.24 mg·kg-1 and Cd having the lowest concentration at 0.31±0.31 mg·kg-1. Compared with the background value in Tianjin, only the content of Cd is at higher levels (a four-fold increase). The results from a single factor pollution index and comprehensive pollution index analysis indicate that the comprehensive pollution index ranking is Cd > Cu > Ni > Zn > As ≈ Cr > Pb. Cd, Cu, Ni, and Zn are in the moderate pollution, mild pollution, and alert level categories, respectively. Except for As, the results from a correlation analysis, the principal component analysis (PCA), and the cluster analysis indicate the possible similar origins of Cr, Ni, Cu, Zn, Cd, and Pb. The multivariate statistical analysis indicates that Cd is mainly derived from human activities, Zn, Cu, Cr, Ni, and Pb are affected by anthropogenic and natural sources, and As is mainly influenced by natural conditions. By comparing the ratios of individual heavy metals to Cr in soils and runoffs, the leaching behaviors have been studied, with the leaching capacity ranked as Cd > As > Cu ≈ Pb > Ni > Cr ≈ Zn. In summary, Cd pollution in soil is more prominent than pollution from other metals and should receive attention.

Distribution of mercury in coastal marine sediments of China: sources and transport.

A total of 220 surface sediments and eight sediment cores were analyzed to study the distribution and transport of Hg in Chinese marginal seas. Spatial distribution showed a general offshore decreasing trend towards the outer continental shelf. Vertical profiles of sediment cores displayed a general increasing trend from bottom to surface layers. Coastal land-based discharges and river-derived inputs are probably the main sources of Hg in coastal sediments of China seas, while TOC, pH, ocean currents and sediment characteristics could play important roles in the transport and spatial distribution of Hg in sediment. The influence of TOC on Hg concentration is more significant than that of pH. The mud deposits on the coastal shelves are main sinks of Hg in the region. The results showed that sedimentary Hg was affected by regional anthropogenic activities and riverine runoffs, and was also influenced by long-range atmospheric transport and ocean current circulations.

Coating Fe3O4 magnetic nanoparticles with humic acid for high efficient removal of heavy metals in water.

Humic acid (HA) coated Fe3O4 nanoparticles (Fe3O4/HA) were developed for the removal of toxic Hg(II), Pb(II), Cd(II), and Cu(II) from water. Fe3O4/HA were prepared by a coprecipitation procedure with cheap and environmentally friendly iron salts and HA. TOC and XPS analysis showed the as-prepared Fe3O4/HA contains approximately 11% (w/w) of HA which are fractions abundant in O and N-based functional groups. TEM images and laser particle size analysis revealed the Fe3O4/HA (with approximately 10 nm Fe3O4 cores) aggregated in aqueous suspensions to form aggregates with an average hydrodynamic size of approximately 140 nm. With a saturation magnetization of 79.6 emu/g, the Fe3O4/HA can be simply recovered from water with magnetic separations at low magnetic field gradients within a few minutes. Sorption of the heavy metals to Fe3O4/HA reached equilibrium in less than 15 min, and agreed well to the Langmuir adsorption model with maximum adsorption capacities from 46.3 to 97.7 mg/g. The Fe3O4/HA was stable in tap water, natural waters, and acidic/ basic solutions ranging from 0.1 M HCl to 2 M NaOH with low leaching of Fe (< or = 3.7%) and HA (< or = 5.3%). The Fe3O4/HA was able to remove over 99% of Hg(ll) and Pb(ll) and over 95% of Cu(II) and Cd(II) in natural and tap water at optimized pH. Leaching back of the Fe3O4/HA sorbed heavy metals in water was found to be negligible.

A novel fiber coating for solid phase microextraction and its application for the extraction of n-alkane from aqueous sample.

Base on the previous work in laboratory, a novel polyaniline doped with polydimethylsiloxane coating was developed on a stainless steel wire for solid phase microextraction(SPME) by electroplating method. This electroplating method not only has advantages of ease preparation and simple equipments required, but also increases the lifetime of the SPME fiber. The composite fiber (polyaniline/ polydimethylsiloxane(PANI/PDMS)) was evaluated by analyzing n-tridecane, n-tetradecane and n-pentadecane in aqueous sample. The new fiber coating showed comprehensive abilities to extract alkanes compounds. The relative standard deviations were found to be 6.8%-10.33%.