Polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), dioxin-like polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in waterbird eggs of Hong Kong, China

Concentrations of PCDD/Fs, PCBs and PBDEs were measured in 56 egg samples collected from waterbirds of different species (Great Egret, Little Egret, Night Heron and Chinese Pond Heron) from different regions of Hong Kong (Ho Sheung Heung, Mai Po Village and Mai Po Lung Village) during 2000 and 2006. Dominance of 2,3,4,7,8-PeCDF indicates a signature associated with commercial usage of PCBs. Although no significant variations were observed within- and between-site in the levels of PCDD/Fs, coplanar PCBs and PBDEs, the concentrations of coplanar PCBs were much higher than PCDD/Fs. Similarity in composition profiles of PCDD/F and coplanar PCBs from different egretries is possibly associated with non-point sources of these contaminants to Hong Kong. Predominant accumulation of BDE-47, BDE-99 and BDE-100 suggested the penta-BDE technical mixtures usage in Hong Kong and its vicinity. Toxic equivalency and Monte Carlo simulation technique showed potential risks on waterbirds due to their exposure to PCDD/Fs.     

Persistent organic pollutants in food items collected in Hong Kong

This study aims to investigate levels of POPs in meat, edible oils, nuts, milk and wine collected from Hong Kong. Naphthalene, pp-DDE, beta-, gamma-HCH and PBDE 47 were detected in most of the food items. Goose liver accumulated the highest PAHs (47.9 ng g⁻¹ wet wt), DDTs (25.6), HCHs (13.0), PCBs (4.17), PBDEs (468 pg g⁻¹ wet wt) among all the selected food. Meat and nut groups had significant (p < 0.01 or 0.05) correlations between lipid contents and concentrations of PAHs (meat: r = 0.878), HCHs (meat: r = 0.753), DDTs (meat: r = 0.937; nuts: r = 0.968) and PCBs (meat: r = 0.832; nut: r = 0.946). The concentrations of DDTs, HCHs and PCBs in vegetable oil were lower, but HCHs in fish oil were higher, when compared with other countries. The concentrations of PAHs, DDTs, PCBs and PBDEs in food tested in the present study were all below various safety guidelines.     

Photocatalytic degradation of methyl orange by a multi-layer rotating disk reactor

Introduction

Solar wastewater treatment based on photocatalytic reactions is a green process that utilizes renewable energy resources and minimizes secondary pollution. Reactor design plays an important role in promoting treatment efficiency and throughput density (based on unit volume of the reactor).

Experimental

A rotating disk reactor that significantly increases the process efficiency has been designed and evaluated for application to photocatalytic decomposition of dye pollutants in aqueous solutions. In this process, a novel multi-layer rotating disk reactor (MLRDR) was presented. Photocatalyst (TiO₂) particles are immobilized on the surfaces of disks. Within each layer of the reactor, methyl orange aqueous solution is allowed to flow from the center of the disk in a radial direction along the surface of the disk, which is rotating at high speed and is irradiated with UV lamps. The effluent is then directed to the center of another layer that lies underneath. Up to four stacked layers have been tested in this study, and the effects due to the number of the layers and volumetric flow rate on reaction conversion are investigated.

Results and discussion

The efficiency of this photocatalytic reactor exhibits complex dependence on these parameters. With selected operating conditions, conversions greater than 95% can be achieved within seconds of residence time. Design equations of the reactor have been derived based on fluid dynamics and kinetic models, and the simulation results show promising scale-up potential of the reactor.     

A Modal Approach to Vehicular Emissions and Fuel Consumption Model Development

Abstract

This study reports on the analysis of emissions and fuel consumption from motor vehicles using a modal approach. The four standard driving modes are idling, accelerating, cruising, and decelerating. On‐road data were collected using instrumented test vehicles traveling many times through the urban areas of Hong Kong. A model was developed for estimating vehicular fuel consumption and emissions as a function of instantaneous speed and driving mode. Piecewise interpolation functions were proposed for each nonidling driving mode. Idling emission and fuel consumption rates were estimated as negative exponential functions of idling time. Preliminary modeling results showed good agreements for the test vehicles and indicated that the on‐road measurements are feasible for the development of modal emission and fuel consumption models.     

Preparation of Sulfurized Powdered Activated Carbon from Waste Tires Using an Innovative Compositive Impregnation Process

Abstract

The objective of this study is to develop an innovative compositive impregnation process for preparing sulfurized powdered activated carbon (PAC) from waste tires. An experimental apparatus, including a pyrolysis and activation system and a sulfur (S) impregnation system, was designed and applied to produce sulfurized PAC with a high specific surface area. Experimental tests involved the pyrolysis, activation, and sulfurization of waste tires. Waste-tire-derived PAC (WPAC) was initially produced in the pyrolysis and activation system. Experimental results indicated that the Brunauer-Emmett-Teller (BET) surface area of WPAC increased, and the average pore radius of WPAC decreased, as water feed rate and activation time increased. In this study, a conventional direct impregnation process was used to prepare the sulfurized PAC by impregnating WPAC with sodium sulfide (Na₂S) solution. Furthermore, an innovative compositive impregnation process was developed and then compared with the conventional direct impregnation process. Experimental results showed that the compositive impregnation process produced the sulfurized WPAC with high BET surface area and a high S content. A maximum BET surface area of 886 m²/g and the S content of 2.61% by mass were obtained at 900°C and at the S feed ratio of 2160 mg Na₂S/g C. However, the direct impregnation process led to a BET surface area of sulfurized WPAC that decreased significantly as the S content increased.     

Effects of As levels on radial oxygen loss and As speciation in rice

Greenhouse experiment was conducted to examine effects of arsenic (As) on iron plaque formation, radial oxygen loss, As accumulation, and speciation in rice. Three genotypes were grown in soil with three different concentrations of As. The stress of As caused a slight increase of iron plaque formation (P?>?0.05) and a decrease in the rates of radial oxygen loss (ROL; P?<?0.01). The results of As speciation showed that the percentages of DMA increased from 19–28 % to 53–58 %, while the percentages of inorganic As decreased from 53–58 % to 36–42 % with the increasing soil As concentrations, indicating a strong environmental influence on As species in rice grain. The present study showed that elevated soil As may induce As toxicity towards rice plants, leading to the decrease of ROL; environmental factors could influence As methylation or As species transportation. Our study provided useful information on As tolerance and accumulation in rice which may contribute to reducing the health risk posed by As contamination in rice.     

Gas permeability of biochar-amended clay: potential alternative landfill final cover material

Compacted biochar-amended clay (BAC) has been proposed as an alternative landfill final cover material in this study. Biochar has long been proposed to promote crop growth, mitigate odor emission, and promote methane oxidation in field soils. However, previous studies showed that soil-gas permeability was increased upon biochar application, which will promote landfill gas emission. The objective of the present study is to investigate the possibility of using compacted BAC as an alternative material in landfill final cover by evaluating its gas permeability. BAC samples were prepared by mixing 425-μm-sieved peanut shell biochar with kaolin clay in different ratios (0, 5, 10, and 15 %, w/w) and compacting at different degrees of compactions (DOC) (80, 85, and 90 %) with an optimum water content of 35 %. The gas permeability of the BACs was measured by flexible wall gas permeameter and the microstructure of the BACs was analyzed by SEM with energy-dispersive x-ray spectroscopy (EDX). The results show that the effects of biochar content on BAC gas permeability is highly dependent on the DOC. At high DOC (90 %), the gas permeability of BAC decreases with increasing biochar content due to the combined effect of the clay aggregation and the inhibition of biochar in the gas flow. However, at low DOC (80 %), biochar incorporation has no effects on gas permeability because it no longer acts as a filling material to the retard gas flow. The results from the present study imply that compacted BAC can be used as an alternative final cover material with decreased gas permeability when compared with clay.     

Trophic relationships and health risk assessments of trace metals in the aquaculture pond ecosystem of Pearl River Delta,China

Cadmium, lead, zinc, Chromium, copper, nickel and manganese in sediments and in aquatic organisms were collected from the aquaculture pond ecosystem of the Pearl River Delta (PRD), China and analyzed to evaluate bioaccumulation and trophic transfer in food chains, as well as the potential health risk of exposure to the Hong Kong residents via dietary intake of these aquatic products. The results revealed that based on the biota–sediment accumulation factor, omnivorous fish and zooplankton accumulated more trace metals from sediment than carnivorous fish. Concentrations of seven trace metals in aquaculture pond of PRD significantly decreased with increasing trophic levels, showing that these trace metals were trophically diluted in predatory and omnivorous food chains. The hazard index values of all fish species were smaller than 1 for adults and children, indicating there was no health risk from the multiple metals via ingestion of the freshwater fish for the inhabitants.     

Evaluation of diffusive gradients in thin films technique (DGT) for measuring Al, Cd, Co, Cu, Mn, Ni, and Zn in Amazonian rivers

Studies concerning the lability and bioavailability of trace metals have played a prominent role in the search for contamination of water resources. This work describes the first application yet of the diffusive gradients in thin films technique (DGT) to the determination of the fraction of free plus labile metals in waters from the Amazon Basin. Due to the complexity of the use of DGT for samples with low ionic strength and high organic matter content (characteristic of Amazonian rivers), a new analytical procedure was developed. The method is based on the determinations of apparent diffusion coefficients (D_ap) in the laboratory, by performing deployments in samples collected in the corresponding sites of study. The D_ap thereby determined is then used for in situ measurements. The suitability of the proposed approach for determination of labile Al, Cd, Co, Cu, Mn, Ni, and Zn in the Amazon River and Rio Negro (English: Black River) was evaluated. Except for Co, Mn (in a deployment at Rio Negro), Ni and Zn (in a deployment at Amazon River), labile in situ measurements were lower or similar to dissolved concentrations, indicating suitability of the proposed approach.     

Microbiological risk infection assessment using QMRA in agriculture systems in Côte d’Ivoire,West Africa

Poor wastewater management that results from a lack of appropriate sanitation infrastructure contributes to increasing health risks in urban areas in Côte d’Ivoire. We assessed the health risks associated with the use of wastewater for watering salad destined for human consumption, to help local authorities in developing appropriate risk mitigation measures for Yamoussoukro, the political capital of Côte d’Ivoire. We applied a stochastic approach based on quantitative microbiological risk assessment (QMRA), focusing on wastewater for farming activities and salad consumption at the household level. Farming activities rely on a large degree on contaminated water and are conducted without any protection. The QMRA highlights that the poor quality of watering water increased the microbiological risk of the two assessed groups of urban farmers and individual households. The annual risk of infection due to watering wastewater in the city is estimated at 0.01 per person per year (pppy) for Giardia lamblia and 0.2 pppy for Escherichia coli O157:H7. The annual risk from salad consumption is 0.01 pppy for G. lamblia and 0.9 pppy for E. coli O157:H7. Both the annual risks from farming activities and salad consumption were higher than the tolerable standard of risk of 10^?4 pppy as defined by the World Health Organization. There is a need to conduct a risk analysis and a cost-effectiveness study on intervention to improve public health and the livelihoods of the producers which are women in majority in Yamoussoukro.