W.K. Liu

Heavy metal pollution in roadside urban parks and gardens in Hong Kong

An ecological survey was conducted on metal contamination (including Cd, Pb, Ni, Zn, Cu, Mn and Fe) of vegetation (leaf of Bauhina variegata), surface soil (0-1 cm) and dust (from road curbs) collected at 13 urban parks near busy roads (with heavy traffic volume) in Hong Kong. Samples from roadside parks had significantly higher metal contents than the control site (away from automobile traffic). A close correlation was found between traffic volume and metal contents of leaf, soil and dust. Washing of leaf samples reduced the levels of Cu, Mn, Zn and Fe contamination and suggested that the source of heavy metal pollution was mainly due to aerial deposition from motor vehicles.

Toxic effects of mosquito coil (a mosquito repellent) smoke on rats: I. Properties of the mosquito coil and its smoke

The physical and chemical properties of the mosquito coil, a commonly used mosquito repellent in Asia and South America, were analysed. The smoke emitted from the burning mosquito coil consists of submicron particles (diameter less than 1 micron) coated with a considerable amount of heavy metals, allethrin and a wide range of organic vapors, such as phenol and o-cresol. Therefore, a lengthy exposure to this smoke will cause adverse effects on the consumers.

Ultrastructural changes of tracheal epithelium and alveolar macrophages of rats exposed to mosquito coil smoke

The volatile organic compounds of mosquito coil smoke were analysed by a combination of gas chromatography and mass spectrometry. 67 volatile organic compounds were detected and 46, including allethrin, phenol, benzene, toluene, xylene, etc. could be identified. Allethrin, a common name for (+/-)-3-allyl-2-methyl-4-oxocyclopent-2-enyl (+/-)-cis,trans-chrysanthemate, is a synthetic pyrethroid, which is used as an insecticide or repellent in subtropical countries. The vapors also contain other aromatic and aliphatic hydrocarbons which are combustion products of other mosquito coil constituents, including wood dust, coconut flour and other fillers and dyes. An exposure to the mosquito coil smoke for 60 days (8 h per day, 6 days per week) resulted in a focal deciliation of the tracheal epithelium, metaplasia of epithelial cells, and morphological alterations of the alveolar macrophages of exposed rats.

Toxic effects of mosquito coil (a mosquito repellent) smoke on rats: II. Morphological changes of the respiratory system

A group of 20 female albino rats was exposed to mosquito coil smoke, 8 h a day, 6 days per week, for 60 days. An additional group receiving air exposure served as control. The smoke-exposed animals had a lower body weight than the controls. Smoke-induced histopathological lesions, including an inflammation of the tracheal epithelium, atelectasis of the lung parenchyma, emphysema, increase of alveolar macrophages in the alveolar space and perivascular infiltration of polymorphonuclear cells were observed in the experimental rats. An elevation of enzyme activities of lactate dehydrogenase, glutamate pyruvate transaminase, glutamate oxoacetate transaminase and acid phosphatase were found in the serum of the smoke-exposed rats indicating the enzymes were released from the damaged tissues into the blood stream.

Comparison of hemolytic activities of coal fly ash and its soluble and insoluble fractions

Coal fly ash of a particle diameter smaller than 10 micron was collected from the precipitator of a power plant in Hong Kong. Comparison of hemolytic activities between fly ash and free silica showed that fly ash had a lower biological effect than free silica. The hemolytic activities of the soluble and insoluble fractions of fly ash were further compared by two methods: total hemoglobin method and cyanmethemoglobin method. An analysis of results showed significant differences for fly ash and its soluble fraction between methods (P less than 0.05 and P less than 0.01, respectively). Fly ash, which contained a silicate level similar to its insoluble fraction, had a hemolytic activity higher than the summation of both its soluble and insoluble fractions. This indicates that the hemolytic activity was independent of the silicate content in the fly ash samples.

Ultrastructural changes in gills of Sarotherodon mossambicus treated with chicken manure.

Sarotherodon mossambicus were fed a chicken manure (60%) supplementary diet for 4 weeks under laboratory conditions, and significantly higher (P less than 0.05) concentrations of Mn, Fe, Cu, Pb, and Zn were obtained in the gills of the treated fish. Ultrastructural changes including separation of the epithelium from the pillar cell system and subsequently increasing the blood-water barrier, necrosis of lamellar cells, collapse of lamellar blood spaces, and hyperplasia of interlamellar cells were found in the lamellae of the gills of the treated fish.

Cytotoxicity of airborne particles from roadside urban gardens

Airborne particles were collected in two small urban gardens along the roads with heavy traffic in Hong Kong. The chemical and physical properties of the particles of a diameter about 1 micron were analysed by a scanning electron microscope incorporated with a x-ray energy dispersive microanalyzer and an atomic absorption spectrophotometer. The cytotoxicities of particles were compared using an in vitro alveolar macrophage culture assay. It was found that both particles significantly increase (p less than 0.05) the release of lactate dehydrogenase and acid phosphatase into the medium in addition to damage the surface morphology and intracellular structures of the macrophages to a variable extent after exposure to the particles.

Properties and toxicity of airborne wood dust in woodworking establishments

The total suspended dust levels, particle shape and size distributions and metal concentrations (Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn) of wood dust in the breathing zone of 3 small wood-working establishments were monitored. In vitro culture assay indicated that the mortality of alveolar macrophage was related to the metal content of dust collected from these 3 workplaces.

Fly ash hemolysis as related to its alkalinity.

Fly ash particles were collected from the precipitator of a power plant in Hong Kong and the hemolytic activity of the particles of the respirable range (smaller than 10 micron) was studied using a rat red blood cell assay system. It was revealed that coal-fired fly ash had a high hemolytic activity which was dose independent. The hemolysate changed from red to brownish-green. Chemical analyses, including scanning electron microscopy incorporated with energy dispersive X-ray microanalysis, inductively coupled plasma spectrophotometry, and X-ray power diffractometry, showed that a considerable amount of calcium salt coated the surface of the particles. The high alkalinity of the calcium salt initially damaged the red blood cell membrane and then destroyed the hemoglobin molecules released from the damaged cells. This phenomenon only caused a discrepancy if the amount of hemoglobin which remained in the incubation medium was taken into account for the measurement of hemolytic activity of fly ash particles.