Occurrence of organotins in the aquatic environment during an operating cycle of the Three Gorges Reservoir, China.

Organotins (OTs) pollution in the aquatic environment of the Three Gorges Reservoir (TGR) was assessed during the reservoir's operating cycle. Butyltins (BTs) and phenyltins (PhTs) in the water phase and suspended particulate matter (SPM) at different water levels were analysed. It was found that the distribution of OTs in the surface and bottom water phases were similar, with the dominant OTs being BTs at the low water level and PhTs at the high water level. The detection rates and concentrations of OTs in the water phase at the high water level were both higher than those at the low water level, with most OTs being monobutyltin (MBT) at the low water level and monophenyltin (MPhT) at the high water level. The concentrations of OTs in SPM at the low water level were higher than those at the high water level, and BTs, especially dibutyltin (DBT) and tributyltin (TBT), were the predominant OTs whether surface or bottom layer at each water level. The BTs and SPM concentrations had a significant positive relationship in all samples, indicating that the SPM concentration would determine the distribution of BTs in the aquatic environment of the TGR region (TGRR). The difference in the distribution of OTs at the different water levels indicated that the hydrological and hydraulic behaviour of the TGR influences OTs transport in the aquatic environment of the TGRR.

A new method to measure and model dynamic oxygen microdistributions in moving biofilms.

Biofilms in natural environments offer a superior solution to mitigate water pollution. Artificially intensified biofilm reactors represented by rotating biological contactors (RBCs) are widely applied and studied. Understanding the oxygen transfer process in biofilms is an important aspect of these studies, and describing this process in moving biofilms (such as biofilms in RBCs) is a particular challenge. Oxygen transfer in RBCs behaves differently than in other biological reactors due to the special oxygen supply mode that results from alternate exposure of the biofilm to wastewater and air. The study of oxygen transfer in biofilms is indispensable for understanding biodegradation in RBCs. However, the mechanisms are still not well known due to a lack of effective tools to dynamically analyze oxygen diffusion, reaction, and microdistribution in biofilms. A new experimental device, the Oxygen Transfer Modeling Device (OTMD), was designed and manufactured for this purpose, and a mathematical model was developed to model oxygen transfer in biofilm produced by an RBC. This device allowed the simulation of the local environment around the biofilm during normal RBC operation, and oxygen concentrations varying with time and depth in biofilm were measured using an oxygen microelectrode. The experimental data conformed well to the model description, indicating that the OTMD and the model were stable and reliable. Moreover, the OTMD offered a flexible approach to study the impact of a single-factor on oxygen transfer in moving biofilms. In situ environment of biofilm in an RBC was simulated, and dynamic oxygen microdistributions in the biofilm were measured and well fitted to the built model description.

Heavy metals in sediments, soils, and aquatic plants from a secondary anabranch of the three gorges reservoir region, China.

We investigated the occurrence of cadmium (Cd), copper (Cu), chromium (Cr), nickel (Ni), lead (Pb), Znic (Zn), iron (Fe), manganese (Mn), and magnesium (Mg) in sediments, as well as in related soils and aquatic plants in the Liangtan River, a typical secondary anabranch of the Yangtze River in the Three Gorges Reservoir Region (TGRR) of China. We found that sediments accumulated more metals than soils and aquatic plants. Concentrations of the nine metals in sediments and soils followed the same sequence, while their concentrations in aquatic plants followed a different sequence. Potential adverse effects of contaminated sediments on benthic fauna were evaluated, and the results showed that the toxic effect on benthic organisms followed the sequence Zn > Ni > Cr > Cu > Cd > Pb. The potential ecological risk index analysis indicated that Cd in sediments had considerable ecological risk, whereas Cr, Cu, Zn, Ni, and Pb had low ecological risk. The potential ecological risk index (RI) of the heavy metals in sediments of the Liangtan River was 174.9, indicating moderate ecological risk. The transfer factor trend of metals for aquatic plants showed that Cd and Ni had the most and least accumulation, respectively. For Cu, Cd, Mg, Pb, and Cr, a significant positive correlation of the metal concentrations was observed between sediments and soils, but no correlations (excluding Cr) were detected between sediments and aquatic plants. Our study indicated that anthropogenic input may be the primary source of metal contamination in the Liangtan River, and that Zn and Cd pollution in the Liangtan River should be further explored.