The Ecotoxicity Assessment Of Water And Sediments From The Suzhou Creek During Ecological Restoration

The Suzhou Creek is originated from Taihu Lake of Jiangshu Province and connecting with Huangpu River near Waibaidu Bridege. As the main watercourse of Shanghai, the Suzhou Creek played an important role in the development of Shanghai. In early twentieth century, it began to be polluted seriously with a great amount of domestic sewage and industrial wastewater discharged. By 1970s, it had been polluted within Shanghai Municipality with "black and stink" all year around in the city. The ecological structure and function had been destroyed thoroughly. In the end of 1980s, the government established the objective of Suzhou Creek Rehabilitation Project and gradually put it into practice. Through more than ten years' efforts, the water quality in the Suzhou Creek has been improved greatly. However, the ecological function and structure has not been restored yet. The Suzhou Creek was heavily polluted by organic materials and heavy metals. When the amount of oxygen in the creek increased, the organic materials adhering to sediments were degraded and released into the water. Some of them would induce toxic effect in organism. Moreover, owing to the biodiversity has been destroyed heavily; the process of restoration of ecological structure and function is still slow.The study, taking advantage of ecotoxicity tests combined in a hierarchical strategy, analyzed the feature of ecological risk in the fields of the ecotoxicity of plant and animal and bidegradation ability; then the toxic character of surface water and sediments was confirmed by means of Microtox and SOS-chromotest. After obtained the ecotoxiclogical data, an assessment of ecological risk of the Suzhou Creek was made.ECOTOXICITY CHARACTERISTICThe toxicity tests on algae (Selenastrum capricornutum), embryos and lavals (Danio rerio) were carried out on water samples collected from Huangdu, Beixinjing and Caojiadu sites. Three waters induced inhibition of growth of algal, but stimulated the test algal growth after filtered. Among them, sample from Beixinjing showed the significant effect. Three waters didn't induce obvious acute and teratogenic effect on zerbafish embryos. But the times of spontaneous movements in 20s of embryos exposed to water collected from Beixinjing were significant less than other groups. Larval mortalities in three waters were 3,12,2 seperately. Three kinds of organic compounds, sodium acetate, diethylene glycol and paraldehyde, were screened out in the lab condition as additives into natural surface water samples which were separately collected from the Huangdu and Caojiadu in the Suzhou Creek to evaluate the bacterial purification ability of the Creek. The results suggested that the difference appeared in bacterial purification ability between upriver and downriver when the chemical structures of the additives became more and more complex. Lag periods of sodium acetate, diethylene glycol, paraldehyde in Huangdu were 0, 3.8, 9.1 days, respectively; while those in Caojiadu were 0.1, 4.9, 14. And the biodegradation rates of three additives were all around 80%-90% and half-lives were less than 2 days. It was suggested that the species of microorganisms of upriver is more abundant than that of downstream and the biodegradation potential was greater than the latter.TOXICITY IDENTIFICATIONMicrotox tests were carried out on the surface water and sediment samples collected from Baihe, Huangdu, Huacao, Beixinjing, Caojiadu and Zhapulu. The results suggested that waters from Huangdu, Caojiadu and Zhapulu were not toxic; water from Baihe was little toxic; water from Huachao was toxic; water from Beixinjing was middle toxic. The EC₅₀ of Microtox tests decreased along from Baihe to Beixinjing, and then increased from Caojiadu to Zhapulu. The toxicities of surface sediments collected from Caojiadu and Zhapulu decreased compared to the middle and bottom parts. The sediments collected were heavily polluted, and the toxicity increased from bottom to surface.20L of waters collected from Huangdu, Beixinjing, Caojiadu, Zhapulu were absorbed on XAD resins and concentrated to 200μl to detect the genotoxins using SOS-chromotest. The results suggested that Huangdu, Beixinjing and Caojiadu sections existed genotoxins. Genotoxity was not detected in sediments collected from six sections.To sum up, the surface water and sediments collected from Beixinjing showed acute toxicity and genotoxicity. The sediment quality of Caojiadu has improved, but the surface water collected from Huangdu and Caojiadu showed genotoxicity.