Time filter

Source Type

Singapore, Singapore

Yihdego Y.,La Trobe University | Yihdego Y.,Snowy Mountains Engineering Corporation SMEC | Webb J.,La Trobe University | Leahy P.,Applied science Group
Hydrological Sciences Journal | Year: 2016

Lake Purrumbete is a deep volcanic freshwater lake, cylindrical in shape, located within an extensive basalt plain in southeastern Australia. A modified difference water budget method for lakes, that estimates net groundwater flux through the difference between the level of the lake and the water table, along with the specific yield and area of the aquifer, successfully modelled the lake level fluctuations. The major influences are evaporation and direct precipitation; however groundwater fluxes are significant (~17%). The salt balance modelling shows that the salinity in Lake Purrumbete is largely controlled by groundwater and surface water fluxes. Lake Purrumbete has a greater interaction with the surrounding groundwater system than other nearby volcanic lakes due to its significant depth and the presence of highly permeable basalts along the upgradient shoreline. Its low salinity reflects the substantial salt export in the groundwater and surface outflow, as well as the lake’s relatively small evaporation due to the low surface area/volume ratio. The fluctuations in lake level and salinity for Lake Purrumbete are much less than for other lakes in the region, even during the 1997–2010 drought, due partly to the large, relatively constant groundwater flux. Low salinity, deep water and estimated depth of stratification from this study, which leads to a distinct limnology, implies that the creatures need to adapt to a different habitat to survive in the vicinity of Lake Purrumbete. Thus, Lake Purrumbete will be an important aquatic ecosystem refugium if climate change causes frequent seasonal drying of other lakes in the plain, and it is important to develop management strategies to maintain its water resources and quality. Editor D. Koutsoyiannis Associate editor Not assigned © 2015 IAHS. Source

Lintern A.,Monash University | Deletic A.,Monash University | Leahy P.,Applied science Group | McCarthy D.,Monash University
Marine and Freshwater Research | Year: 2015

Negative effects of urbanisation on the health of aquatic environments are well recognised; but more data are needed for an accurate assessment of the particular effects of residential development on the health of aquatic systems. This study explores the relationship between residential growth and increasing pollution, by analysing temporal trends of chemical fluxes into Willsmere Billabong-an urban floodplain lake of the Yarra River in South-East Australia. Sediment cores were extracted to reveal depositions over three centuries (∼1700-2012). The cores were sub-sampled at high resolution and analysed for heavy metals, polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCPs). Pollutant concentrations in the sediments appear to have been significantly affected by residential development in the local catchment. Normalised concentration profiles show these effects to be exacerbated from the mid-20th century, after a stormwater drain was installed in the billabong. The study suggests that urban stormwater management techniques are critical for the protection of aquatic systems incorporated into residential zones. © 2015 CSIRO. Source

Bay L.J.,National University of Singapore | Chan S.H.,Applied science Group | Walczyk T.,National University of Singapore
Journal of Analytical Atomic Spectrometry | Year: 2015

A new approach to normalize measured isotope ratios (carbon and nitrogen) by elemental analyser continuous flow isotope ratio mass spectrometry (EA-CF-IRMS) was evaluated. Isotope ratios of samples are altered during the IRMS measurement and must be corrected for both instrumental drifts as well as instrumental isotope fractionation for comparing data within and between laboratories. Traditionally, the isotope ratio of a reference gas is measured intermittently to correct for time dependent changes in isotope fractionation over the course of the measurement. However, this step appears to be redundant as bracketing standards are usually included in a measurement run for comparisons between measurements and laboratories and they can serve, in principle, the same purpose. Here we show that measurements without normalization to the reference gas are on a par in terms of accuracy and precision with those where the reference gas was used when employing an optimized strategy for bracketing samples with reference standards. Abolishment of intermittent reference gas measurements in EA-CF-IRMS analysis has the potential to cut short the analysis time significantly, can help to save costs in commercial IRMS laboratories and may open a new door for instrument developers to design high through-put IRMS instruments. This journal is © The Royal Society of Chemistry. Source

Yong S.,Applied science Group | Yong S.,National University of Singapore | Chen Y.,Applied science Group | Lee T.K.,Applied science Group | Lee H.K.,National University of Singapore
Talanta | Year: 2014

Determination of total thyroxine in human serum using hollow fiber liquid-phase microextraction (HF-LPME) has been accomplished for the first time. HF-LPME serves as an inexpensive sample pretreatment and the cleanup method that is nearly solvent-free. Thyroxine was extracted through a water immiscible organic solvent immobilized in the wall pores of a polypropylene hollow fiber into 20 μl of an aqueous acceptor phase inside the lumen of the hollow fiber. This technique produced extracts that had comparable cleanness with those obtained using solid-phase extraction (SPE). Serum samples with endogenous thyroxine were spiked with isotopically-labeled thyroxine and analyzed by liquid chromatography-tandem mass spectrometry after HF-LPME extraction. Extraction parameters including the organic phase, acid/base concentration of acceptor phase, stirring speed and extraction time were optimized. The calibration range was found to be linear over 1-1000 ng/g with the limit of detection (LOD) of 0.3 -ng/g. For quantification of total thyroxine in human serum, 6 subsamples were prepared and the results indicated very good precision with a relative standard deviation of <1.3%. The difference from the SPE method was less than 1.2%, with independent t-test showing insignificant bias. Two reference materials of human serum were analyzed, and our obtained values were compared with the reference values. The results showed very good precision with RSD around 0.2% and the deviation from the reference values were -3.1% and -2.1%. The newly developed method is precise, accurate, inexpensive, and environmentally friendly. © 2014 Elsevier B.V. Source

Cheah N.P.,Applied science Group | Chong N.W.L.,Health Products Regulation Group | Tan J.,Applied science Group | Morsed F.A.,Applied science Group | Yee S.K.,Health Products Regulation Group
Tobacco Control | Year: 2014

Objective: Many electronic nicotine delivery systems (ENDS) are marketed as safer tobacco alternative products or effective cessation therapies. ENDS samples were evaluated for design features, including nicotine and glycols content. This could be useful in developing a legal framework to handle ENDS. Methods: Identification of the nicotine, glycerol and propylene glycol (PPG) contents was conducted using gas chromatography mass spectrometry with quantification performed using flame ionisation techniques. Results: Varying nicotine amounts were found in ENDS cartridges which were labelled with the same concentration. Chemicals such as PPG and glycerol were found to be present in the nicotine-containing liquid of the cartridges. ENDS varied in their contents and packaging information. Limited information was available on the contents of nicotine and other chemicals present in a variety of ENDS sampled. Conclusions: Based on samples tested in this study, many contain misleading information on product ingredients. The results show poor consistency between actual nicotine content analysed on ENDS cartridges and the amount labelled. These findings raise safety and efficacy concerns for current and would-be recreational users or those trying to quit smoking. Source

Discover hidden collaborations