Environmental and Biological Assessment of Exposure to Benzene in Petroleum Workers

Occupational exposure to benzene was measured in two gasoline marketing terminals and five major refineries in Singapore. A total of 280 workers were monitored over two years. This assessment was carried out with two primary objectives: (1) To find out the extent of occupational exposure to benzene in the petroleum industry in Singapore, (2) To identify suitable biomarkers for monitoring of low levels of benzene exposure. The exposure was measured in five different categories of petroleum and petrochemical workers, i.e., truck drivers, despatch assistant, process operators, oil movements operators and laboratory technicians. The results revealed wide variations in exposure, from 0.01 to 13.6 ppm for personal time weighted average (TWA) exposure over the whole workshift. The exposure of truck drivers appeared to be the highest, with geometric mean (GM) of 1.98 ppm (ranged from 0.25 to 13.6 ppm). The average benzene exposure for process operators was relative low with a GM of 0.04 ppm. Lowest benzene exposure was found in the laboratory technicians, with a GM of 0.02 ppm. As cigarette smoking is known to affect metabolism of benzene, data analyses on the relationships with environmental exposure were conducted only on the 190 nonsmokers. The results showed that urinary trans, trans-muconic acid (ttMA), unmetabolized benzene in urine (UBZ) and benzene in blood (BBZ) were better biomarkers for low level benzene exposure as compared to urinary phenolic metabolites in urine, such as hydroquinone, phenol and catechol.     

Does the wood-borer Sphaeroma terebrans (Crustacea) shape the distribution of the mangrove Rhizophora mucronata?

Field surveys were conducted to evaluate the occurrence of the isopod borer Sphaeroma terebrans (Crustacea) in aerial roots (prop roots) of the red mangrove Rhizophora mucronata on several different spatial scales (m to 100 km) in East Africa. In 6 out of 17 sites studied in Kenya and on Zanzibar Island, Tanzania, no signs of the isopods were found. When the isopods were present the frequency of infestation was high. Trees in muddy substrates in the lower intertidal, in particular at fringing channels or the open sea, showed high prevalence and intensity of infestation, with large part of their roots damaged or dead. Trees at the upper range of Rhizophora, in sandy and muddy areas, showed no signs of isopod infestation. This pattern recurred in mangrove forests on large spatial scales and there was no indication that island forests differed from the mainland forests. This indicates that sediment characteristics, vertical height in the tidal zone, and direct exposure to incoming water are the major factors controlling the abundance of S. terebrans. The isopod may play an important role in determining the lower intertidal limits of R. mucronata. Trees with numerous dead or nongrowing roots, as result of Sphaeroma attack, are likely to tumble due to a lack of root support and this is most likely to occur along channels at the lower, muddy intertidal. Tumbled trees were frequently observed along channels in the lower, muddy intertidal, but rarely in the mid or high intertidal. Implications for management of mangrove forests are discussed.     

蛀木生物钻刺团水虱是否改变红茄冬红树林的分布形状?

为了评价东非不同空间尺度(1m尺度～l00km尺度)红树林分布区等足类甲壳动物蛀木虫钻刺团水虱(团水虱属)在美国红树红茄冬气生根中出现的情况,进行了野外调查研究.     

蛀木生物钻刺团水虱是否改变红茄冬红树林的分布形状?

为了评价东非不同空间尺度(1m尺度～l00km尺度)红树林分布区等足类甲壳动物蛀木虫钻刺团水虱(团水虱属)在美国红树红茄冬气生根中出现的情况,进行了野外调查研究.