An extensive survey was conducted in this study to determine the spatial distribution and possible sources of heavy metals in the agricultural soils in Shunyi, a representative agricultural suburb in Beijing, China. A total of 412 surface soil samples were collected at a density of one sample per km 2 , and concentrations of As, Cd, Cu, Hg, Pb and Zn were analyzed. The mean values of the heavy metals were 7.85± 2.13, 0.136 ±0.061, 22.4 ±6.31, 0.073 ±0.049, 20.4 ±5.2, and 69.8 ±16.5 mg kg − 1 for As, Cd, Cu, Hg, Pb, and Zn, respectively, slightly higher than their background values of Beijing topsoil with the exception of Pb, but lower than the guideline values of Chinese Environmental Quality Standard for Soils. Multivariate and geostatistical analyses suggested that soil contamination of Cd, Cu and Zn was mainly derived from agricultural practices. Whereas, As and Pb were due mainly to soil parent materials, and Hg was caused by the atmospheric deposits from Beijing City. The identification of heavy metal sources in agricultural soils is a basis for undertaking appropriate action to protect soil quality.

Time effect on the fractionation of Cu, Zn, Pb, and Cd in three typical Chinese soils was investigated. A total of 500 mg kg À1 of Cu, Zn, Pb and 2.5 mg kg À1 of Cd were added to soils as nitrates. Metals in the incubated soils were fractionated termly from 3 h to 8 weeks by the sequential extraction procedure, in which the metal fractions were experimentally defined as exchangeable, carbonate-, Fe-Mn oxide-, organic matter-bound and residual fractions. Results showed that the changes of Cu, Pb and Zn in fraction distribution were biphasic by an initial rapid step followed by a slow one. Metals in exchangeable fraction were increased in the first 3 h, and then decreased, such decreases could be simulated by a diffusion equation and the decrease rate followed the order PbNCuNZnNNCd. Metals bound to Fe-Mn oxides and organic matter increased consistently in the 8-week incubation. There were almost no changes for the metals in the residual fraction. After 3-h incubation most of Cd added to soils presented in the exchangeable fraction. The content of Cd in each fraction changed slightly in the 8-week incubation. Soil pH played an important role in metal fraction distribution patterns. Jiangxi soil, with low soil pH, tended to keep more metals added in exchangeable fraction and the changes of metals in each fraction were not as remarkable as in other two soils. High organic matter content resulted in the increased organic matter-bound fraction. D

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Debrominated, hydroxylated and methoxylated metabolism in maize (Zea mays L.) exposed to lesser polybrominated diphenyl ethers (PBDEs) Sen" Debromination, hydroxylation and methoxylation of PBDEs in plant occurred rapidly. " The introduction of a hydroxyl/methoxy group at the ortho-positions was easier. " PBDEs are more susceptible to metabolism in leaves and stems than in roots." P MeO-PBDEs concentration was significantly higher than P OH-PBDEs concentration. a r t i c l e i n f o a b s t r a c tA hydroponic experiment was conducted to investigate the debrominated, hydroxylated and methoxylated metabolism of polybrominated diphenyl ethers (PBDEs, BDE-15, -28 and -47) in maize. A total of six debrominated metabolites (de-PBDEs), seven hydroxylated PBDEs (OH-PBDEs, including two unidentified OH-di-PBDEs and one unidentified OH-tri-PBDE) and four methoxylated PBDEs (MeO-PBDEs) were determined in the exposed plants. The metabolic products were detected in maize only after 12 h of exposure to the PBDEs. However, the concentration of each type of the metabolites (de-PBDEs, OH-PBDEs or MeOPBDEs) decreased at the later exposure time, possibly due to further metabolism. The removal of a bromine atom or the introduction of a hydroxyl/methoxy group was easier at the ortho-positions on the biphenyl structure than at the para-positions. Concentration ratios of the total debrominated, hydroxylated or methoxylated metabolites to the parent congener (BDE-28 or -47) generally followed the order of leaves > stems ) roots, and MeO-PBDEs > de-PBDEs ) OH-PBDEs. These results suggest that metabolism occurred preferentially in leaves and stems than in roots. Less transformation and shorter elimination half-life of OH-PBDEs would contribute to the lower concentrations of OH-PBDEs than of de-PBDEs or MeO-PBDEs in maize.

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A label-free aptamer-based assay for the highly sensitive and specific detection of Ochratoxin A (OTA) was developed using a cationic polymer and gold nanoparticles (AuNPs). The OTA aptamer was used as a recognition element for the colorimetric detection of OTA based on the aggregation of AuNPs by the cationic polymer. By spectroscopic quantitative analysis, the colorimetric assay could detect OTA down to 0.009 ng/mL with high selectivity in the presence of other interfering toxins. This study offers a new alternative in visual detection methods that is rapid and sensitive for OTA detection.

Antibiotic abuse is becoming increasingly serious and the potential for harm to human health and the environment has aroused widespread social concern. Aminoglycoside antibiotics (AGs) are broad-spectrum antibiotics that have been widely used in clinical and animal medicine. Consequently, their residues are commonly found in animal-derived food items and the environment. A simple, rapid, and sensitive detection method for on-site screening and detection of AGs is urgently required. In recent years, with the development of molecular detection technology, nucleic acid aptamers have been successfully used as recognition molecules for the identification and detection of AGs in food and the environment. These aptamers have high affinities, selectivities, and specificities, are inexpensive, and can be produced with small batch-to-batch differences. This paper reviews the applications of aptamers for AG detection in colorimetric, fluorescent, chemiluminescent, surface plasmon resonance, and electrochemical sensors for the analysis in food and environmental samples. This study provides useful references for future research.