Abstract-The toxicity of a heavy metal in solution to a microorganism depends not only on its concentration but also on pH and the concentrations of any aqueous complexing ligands in the microorganism's environment. This paper reports on the use of different inorganic resuscitation media and effect of the chloride ion, Cl Ϫ , on the bioluminescence response of a bacterial biosensor, Escherichia coli HB101 (pUCD607), to four metals: Cd, Cu, Hg, and Pb. The toxicity tests were conducted at pH 4, using 0.1 M KNO 3 as resuscitation medium and adding KCl to investigate effect of Cl Ϫ concentration. The species distributions of metals as a function of Cl Ϫ concentration were calculated using GeoChem-PC. Resuscitation in 0.1 M KCl gave significantly higher light output than that in 0.1 M KNO 3 , demonstrating that Cl Ϫ in the resuscitation medium has a direct effect on the bioluminescence response of the E. coli biosensor. Increasing concentrations of Cl Ϫ ions increased the toxicity of Hg, apparently because of the formation of HgCl , and increased the toxicity of Pb because of PbCl ϩ formation. The toxicity of Cu decreased at high Cl Ϫ concentrations asfree Cu 2ϩ decreased, in accordance with the free ion model. Concentrations of Cl Ϫ had no significant effect on the toxicity of Cd. This study clearly demonstrates that the chloro-complexes of some heavy metals can be toxic and, for Pb and Hg, more toxic than the free ion.
This research investigated the effects of elevated ozone and carbon dioxide on photosynthesis of rice (Oryza sativa L.) cultivar Khao Dawk Mali 105. Seedlings were kept in indoor climate control chambers which were set to typically background level of ozone (<10 ppb) by passing inlet air from outside through charcoal filter prior to enter to the chambers. Plant samples were fumigated by ozone concentration level at 40 ppb, 70 ppb and carbon dioxide concentration level at 700 ppm. For combined effects, elevated carbon dioxide concentration 700 ppm was given into two combination treatments of ozone concentration level at 40 and 70 ppb. Control groups were grown in charcoal-filter chambers with no additional ozone. Plant samples then were fumigated with ozone and carbon dioxide for 28 days at tillering stage (at the rice age of 42 to 70 days), and analyzed weekly for photosynthesis rate, leaf chlorophyll, total soluble sugar and biomass. The results showed that ozone significantly caused reduction in photosynthesis, leaf chlorophyll, total soluble sugar and total biomass of rice. The ozone concentration level of 70 ppb significantly (p ≤ 0.05) affected rice more than 40 ppb treatment. Nevertheless, elevated carbon dioxide reduced the negative effects of ozone from both ozone concentration levels. Moreover, higher photosynthesis was observed in combined treatment, when compared with the control group. Finally, increasing of ozone caused reduction in rice photosynthesis; however, elevated carbon dioxide could significantly adverse the effects of ozone.
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