| Since the rapid development of modern industry, agriculture, science and technology, lots of pollutants were discharged into the water environment, heavy metals are parts of the sewage. Mercuric ions (Hg2+) and methylmercury are major, human-generated, toxic contaminants present in our waterbody. They can be accumulated through food chain to a toxic concentration level which can lead to impairment in the quality of human life.1. The cell numbers, photosynthetic pigment and biomarkers of Scenedesmus obliquus exposed in different concentrations of HgCl2Toxic compounds may affect microalgal growth, photosynthesis pigment, enzyme activity, and respiration. The effective concentration of toxicants that inhibits 50% microalgal growth at 96h (96h EC50) is widely used as an index of toxicity. It has been reported that microalgal production of glutathione, thiols, or superoxide dismutase (SOD) activity can be stimulated by heavy metals, which may also be a defense mechanism against heavy metal toxicity. Pigments have often been used as biomarkers of herbicides exposure in plants, including algae. We report in this paper the effects of HgCl2 on S. obliquus.5 concentrations of HgCl2,0.01,0.1,0.5,1.0,1.5 mg-L-1, were added to the flasks and a control group was set for determining the 96h EC50 of mercury on S. obliquus. Algal growth, photosynthetic pigments, super oxide dismutase (SOD) activity, Malondialdehyde (MDA) content in the algal cells were measured in the exponential phase. It showed that higher concentration of HgCl2 is inhibitory for growth and other metabolic indices and the 96h EC50 of HgCl2 to S. obliquus was 0.986±0.027 mg-L-1. Compared with the control, the chlorophyll a, b and carotenoids content decreased obviously. The SOD activity increased at low concentration, then dropped with the concentration increasing. It was significant that the MDA content was stimulated by HgCl2. The potential application of MDA and carotenoids in S. obliquus as a sensitive biomarker for HgCl2 exposure assessment was also discussed in this paper.2. Determination of the 96h-LC50 of HgCl2 and biomarkers on the zebrafishZebrafish were exposed to 0,158.49,199.53,251.19,316.23,398.11g·L-1 of HgCl2. The aquarium water was semi-renewable and the dead fish was removed everyday at the duration time. The 96h-LC50 was dertermined to be 244.06g·L-1 by using the logarithm-probit method. Zebrafish were exposed to 0,0.1LC50, 0.4LC50,0.8LC50 of HgCl2 respectively. The muscle was obtained for further measurment on the 1 st day and 7th day.The AChE activity was inhibited as the concentration increasing on the 1st day and the 7th day. The SOD activity was basically unchanged on the 1 st day, while showed a dose-response effect on the 7th day. It showed that HgCl2 the enzyme activities were affected significantly with prolonged exposure time.3. The effect of HgCl2 to the relative amount of gene transcription of zebrafishThe amount of AChE transcription was declined significantly compared with the control on the first day, which was in accordance with the enzyme activity. The gene transcription of 0.1LC50, 0.4LC50 groups were stimulated significantly compared with the control on the 7th day, but not for the 0.8LC50 group. The gene transcription of CYP450 IA was declined compared with the control on the first day (*, p< 0.05), the gene transcription of 0.1 LC50 group increased, and 0.4LC50,0.8LC50 groups decreased on 7th day, which shows a effect of stimulation at low concentration and inhibition at high concentration. The Cu/Zn-SOD transcription was delined compared with the control on the first day. The 0.1LC50,0.4LC50 groups had a significant difference compared with the control (*, p< 0.05). It showed an stimulation effect at low concentration and inhibition effect at high concentrations. Therefore HgCl2 was highly toxic for zebrafish, both the enzymatic activities and the gene transcription amount were affected significant. |
PDF Full Text Request