Biomedical subjects

L M Chu

Publications and source records attributed to L M Chu.

11 recordsLinked to original sources

PubMed2006

Phytotoxicity data safeguard the performance of the recipient plants in leachate irrigation.

Leachates from an operating and a closed landfill were examined for their phytotoxicity by seed germination/root elongation tests using seeds of Brassica chinensis and Lolium perenne. Their EC50s ranged from 3% to 46% v/v, which varied remarkably with the operating status of the landfills. Seedlings of twelve tree species were grown in pots, which were irrigated with landfill leachate at the EC50 levels, with tap water as control. No tree mortality or growth inhibition was observed after 90 days of leachate application. Chlorophyll fluorescence measurement also showed that plants receiving leachate did not suffer from a decline in photosynthetic efficiency. Litsea glutinosa and Hibiscus tiliaceus had remarkable growth, and other non-N-fixers were not inferior to the N-fixing Acacia auriculiformis. Leachate irrigation improved soil N content, though P deficiency is still a problem. The seed bioassay provided a conservative estimate of the phytotoxicity of landfill leachate. Plants irrigated can be protected from growth inhibition when the leachate irrigation plan is designed with reference to phytotoxicity data.

Acacia↗

PubMed2005

Influence of glyphosate and its formulation (Roundup) on the toxicity and bioavailability of metals to Ceriodaphnia dubia.

This study examined the toxicological interaction between glyphosate (or its formulation, Roundup) and several heavy metals to a freshwater cladoceran, Ceriodaphnia dubia. We demonstrated that all binary combinations of Roundup and metals (Cd, Cu, Cr, Ni, Pb, Se and Zn) exhibited "less than additive" mixture toxicity, with 48-h LC50 toxic unit > 1. Addition of glyphosate alone could significantly reduce the acute toxicity of Ag, Cd, Cr, Cu, Ni, Pb and Zn (but not Hg and Se). The ratio between glyphosate and metal ions was important in determining the mitigation of metal toxicity by glyphosate. A bioaccumulation study showed that in the presence of glyphosate the uptake of some metals (e.g. Ag) was halted but that of others (e.g. Hg) was increased significantly. Therefore, our study strongly suggests that glyphosate and its commercial formulations can control the toxicity as well as the bioavailability of heavy metals in aquatic ecosystems where both groups of chemicals can co-occur.

Adsorption↗

PubMed2004

Comparative toxicity of glyphosate-based herbicides: aqueous and sediment porewater exposures.

Glyphosate-based herbicides are widely used for aquatic weed control. However, their aquatic toxicity data, especially those on sediment, are relatively scarce. In this study, the water-only acute toxicity of three formulations based on glyphosate (Rodeo, Roundup Biactive, and Roundup) were compared using a water-column organism (cladoceran: Ceriodaphnia dubia) and a benthic organism (amphipod: Hyalella azteca). In addition, Roundup Biactive and Roundup were spiked into a clean sediment which was amended with appropriate amounts of peat moss to study the effect of different organic carbon levels (0, 0.4, 1.2, and 2.1%) on their sediment toxicity, with C. dubia exposed to overlying water or porewater prepared from the contaminated sediments. Results showed that the toxicity based on 48-h LC50s for the three herbicides in the water-only tests was Roundup (1.5-5.7 mg L(-1)) > Roundup Biactive (82-120 mg L(-1)) > Rodeo (225-415 mg L(-1)), and H. azteca was generally more sensitive than C. dubia to these herbicides. Toxicity differences between formulations were due to the different surfactant components in these herbicides. From the porewater toxicity tests, Roundup Biactive (340 mg kg(-1)) and Roundup (244 mg kg(-1)) were similarly toxic in the sediment tests at 0% organic carbon, indicating that the surfactants in Roundup were considerably more adsorptive than those in Roundup Biactive to the sediment of the same organic carbon. Also, an increase in organic carbon significantly decreased the toxicity of Roundup in sediment, but not for Roundup Biactive. Sediment-porewater partitioning of glyphosate was found to be influenced by sediment organic carbon (i.e., glyphosate adsorption increased with sediment organic carbon).

Adsorption↗

PubMed2003

Aquatic toxicity of glyphosate-based formulations: comparison between different organisms and the effects of environmental factors.

Glyphosate-based herbicides (e.g. Roundup) are extensively used in the aquatic environment, but there is a paucity of data on the toxicity of the formulated products and the influences by environmental factors. In this study, the acute toxicity of technical-grade glyphosate acid, isopropylamine (IPA) salt of glyphosate, Roundup and its surfactant polyoxyethylene amine (POEA) to Microtox bacterium (Vibrio fischeri), microalgae (Selenastrum capricornutum and Skeletonema costatum), protozoa (Tetrahymena pyriformis and Euplotes vannus) and crustaceans (Ceriodaphnia dubia and Acartia tonsa) was examined and the relative toxicity contributions of POEA to Roundup were calculated. The effects of four environmental factors (temperature, pH, suspended sediment and algal food concentrations) on the acute toxicity of Roundup to C. dubia were also examined. Generally, the toxicity order of the chemicals was: POEA>Roundup>glyphosate acid>IPA salt of glyphosate, while the toxicity of glyphosate acid was mainly due to its high acidity. Microtox bacterium and protozoa had similar sensitivities towards Roundup toxicity (i.e. IC50 from 23.5 to 29.5 mg AE/l). In contrast, microalgae and crustaceans were 4-5 folds more sensitive to Roundup toxicity than bacteria and protozoa. Except photosynthetic microalgae, POEA accounted for more than 86% of Roundup toxicity and the toxicity contribution of POEA was shown to be species-dependent. Increase in pH (6-9) and increase of suspended sediment concentration (0-200 mg/l) significantly increased the toxicity of Roundup to C. dubia, but there were no significant effects due to temperature change and food addition.

Animals↗

PubMed2003

Microbial enhancement of Cu2+ removal capacity of Eichhornia crassipes (Mart.).

Bacteria resistant to Cu2+, Ni2+ or Zn2+ were isolated from the rhizosphere of water hyacinth (Eichhornia crassipes (Mart.)) and their metal ion removal capacities (RCs) were determined. The Ni2+ and Zn2+ RCs of the respective metal ion-resistant bacteria were less than 4.1 mg g(-1), while one of the Cu2+-resistant bacteria (Strain CU-1) showed a significant high Cu2+ RC of 10.6 mg g(-1). The effect of inoculating water hyacinth with Strain CU-1 on its Cu2+ RC was further studied. Water hyacinths were treated with an antibiotic, oxytetracycline (OTC), to remove most rhizospheric bacteria of plant roots. Inoculation of Strain CU-1 increased the Cu2+ RC of the plant root by 1.91 (OTC-treated) and 1.56 (OTC-untreated) folds respectively when compared with the control. Results also showed that Strain CU-1 colonized onto the plant root and led to the increase of Cu2+ RC of the roots of water hyacinth.

Bacteria↗

PubMed2002

Effects of leachate recirculation on biogas production from landfill co-disposal of municipal solid waste, sewage sludge and marine sediment.

Leachate recirculation is an emerging technology associated with the management of landfill. The impact of leachate recirculation on the co-disposal of three major wastes (municipal solid waste, sewage sludge and sediment dredgings) was investigated using a laboratory column study. Chemical parameters (pH, COD, ammoniacal-N, total-P) and gas production (total gas volume, production rates and concentrations of CH4 and CO2) were monitored for 11 weeks. Leachate recirculation reduced waste-stabilization time and was effective in enhancing gas production and improving leachate quality, especially in terms of COD. The results also indicated that leachate recirculation could maximize the efficiency and waste volume reduction rate of landfill sites.

Carbon Dioxide↗

PubMed2001

Heavy metal concentrations in marine fishes collected from fish culture sites in Hong Kong.

The levels of six heavy metals (Cd, Cr, Cu, Ni, Pb, and Zn) in different tissues of three species of cultured marine fishes (Epinephelus areolatus, Lutjanus russelli, and Sparus sarba) collected from three fish culture sites in Hong Kong were evaluated. Metal pollution problems in the fish culture sites were serious, as reflected by the high metal concentrations recorded in sea water, sediments, and the biomonitor Perna viridis. In general, tissues of all three species contained high concentrations of Zn and Cu, but much lower concentrations of Ni, Pb, Cd, and Cr. Similar pattern of heavy metal concentrations was observed in sea water, sediment, and P. viridis. Metal concentrations in various tissues varied greatly among species and among fish culture sites. Different tissues showed different capacity for accumulating heavy metals. Gonad of all three species contained high concentrations of Zn. On the other hand, liver seemed to be the primary organ for Cu accumulation. Overall, metal concentrations in the tissues of culture marine fishes were much lower than those in P. viridis. Despite high metal levels in sea water and sediments, concentrations of Cd, Cr, and Pb in edible tissues, including muscle and skin, did not exceed permissible levels recommended by the Hong Kong Government for human consumption.

Animals↗

PubMed1999

Codisposal of municipal refuse, sewage sludge and marine dredgings for methane production.

As marine disposal of sewage sludge and dredged sediments may impose serious adverse effects to marine ecosystems, landfilling seems to be the most feasible method for the final disposal of these wastes. A batch experiment was conducted to study waste degradation and gas production after sewage sludge and marine dredgings were mixed with municipal refuse at 13 different ratios for 36 days. The addition of sludge and dredgings to municipal refuse enhanced gas production, compared with the degradation of refuse or sludge alone. A proper mixing ratio of wastes can also shorten the time to reach the final phase of anaerobiosis. The highest gas production was obtained from the ratio of 75-20-5 (refuse-sludge-dredgings) (wet weight basis). Its average daily gas production rate was 1.42 l kg(-1) waste mixture; methane content was 68.3%. The results indicated that codisposal of the three wastes would be beneficial for energy recovery from landfill gas.

Journal Article↗

PubMed1997

Influence of landfill factors on plants and soil fauna-an ecological perspective.

An ecological study was conducted on two landfill sites in Hong Kong. Both sites were contaminated by landfill gas and leachate, as indicated by the high concentrations of CH(4) and CO(2) and the presence of high concentration of NH(4)-N in the cover soil layer. Their plant diversity and performance, as well as the soil and litter animals, were compared with three derelict sites as references. The landfill sites had higher plant coverage and plant diversity, and higher densities of soil and litter animals than the reference sites. Similarly, the microbial activities at the landfill sites were higher than those at reference sites. The results showed that the landfill sites possessed an effective food web, starting from microbes to macroinvertebrates. Woodland establishment seems feasible at these landfill sites, and natural succession appears to take place at a higher rate at these landfill sites when compared with the reference sites.

Journal Article↗

PubMed1994

Inhibition of glioma cell growth by a truncated platelet-derived growth factor-beta receptor.

Abnormal expression of platelet-derived growth factor (PDGF) receptors has been observed in malignant glioma and other tumors such as osteosarcomas and malignant melanomas. However, their role in the development and maintenance of the tumors is not understood. Signaling through the PDGF receptors is activated by ligand-induced dimerization. Thus, introduction of mutant receptors that are kinase deficient but still dimerization competent is one strategy to study the importance of PDGF receptors in glioma cell growth. A truncated PDGF-beta receptor was introduced into C6 rat glioma cells and the PDGF-mediated signaling and subsequent cell growth studied. In clones expressing the mutant receptor, PDGF-BB-induced tyrosine phosphorylation of the endogenous receptor was significantly reduced. In addition, these cells grew to lower density in culture and formed smaller colonies in soft agar than the C6 parental cells. Furthermore, the ability of cells expressing the truncated receptor to grow as xenografts in nude mice was significantly impaired. These results support the important role for the PDGF-beta receptor in C6 glioma cell growth. They also demonstrate the usefulness of dominant-negative mutants of the PDGF receptor for the evaluation of the role of the receptor in tumorigenesis.

Animals↗

PubMed1986

Relation between plasma creatinine and body size.

We studied the relationship between creatinine concentration in plasma and body size in 673 healthy individuals (385 women, 288 men). Weight, height, and skinfold thickness were measured and blood was sampled (after a short fast) for estimations of urea and creatinine in plasma. Lean body mass was calculated according to Durnin and Wormsley (Br J Nutr 1974; 32:77-97). Concentrations of urea and creatinine in plasma were significantly lower in women than in men and were significantly correlated with age in both sexes. For neither sex was there a significant correlation between lean body mass and creatinine concentration, even after we took age into account either by multiple linear-regression analysis or by considering subjects at decade intervals.

Adult↗