Sediment Pollution Characteristics And Interstitial Water Toxicity Identification For The Wujin'gang River

The input of pollutants from the Wujin,gang River directly affects the pollution status of Lake Taihu as it is one of the mam rivers flowing into Meiliang Bay of Lake Taihu.The input amount of CODMn,TP,TN and ammonia nitrogen into Lake Taihu were 2765 t,88.48 t,3149 t and 2143 t per year,respectively.Because the Wujin'gang River was received long-term industrial wastewater and domestic sewage from villages and towns,the sediments become the source and sink of pollutants.At the same time,the pollutants in the sediments could cause a "second pollution" on water body by diffusion,resuspension and bioturbation.Nitrogen,phosphorus,metals and polycyclic aromatic hydrocarbons are selected as the target pollutants in this study according to the situation of water quality,the Wujin'gang River routine monitoring sections,pollution sources and distribution of sewage outfall.First,the pollution characteristics of sediments from the Wujin'gang River are studied;Then,the biological toxicity effects of sediment are analyzed through the toxicity of interstitial water on three organisms;Further,toxic substances are identified by toxicity identification evaluation method.The research results have an important significance for sediment dredging on inflowing rivers,environmental management decision,etc.The main results are as follows:1.The total nitrogen contents for sediments from the Wujin'gang River ranged from 1909.38 to 4539.58 mg/kg;the content of total phosphorus ranged from 895.41 to 1919.57 mg/kg;the content of total heavy metals ranged from 599.7 to 2086.3 mg/kg;and the contents of total polycyclic aromatic hydrocarbons(?PAHs)are at the range of 1175.96 to 3890.65 ?g/kg.Sediments from the Wujin,gang River are polluted by nitrogen and phosphorus,heavy metals and polycyclic aromatic hydrocarbons.The content of pollutants in sediments were higher than those in Meiliang Bay,presumably,showing that the Wujin'gang River is an important input source for the pollution of Meiliang Bay of Lake Taihu.The study shows that discharge of nitrogen and phosphorus are from the same source of pollution;emissions of total metals have correlation with nitrogen and phosphorus emissions to some extent.The accumulation of PAHs is different from the above pollutants,illustrating that there may be existed other pollution sources.Toxicity assessment results indicate that four kinds of heavy-metals(Cd,Cr,Ni,Cu)in sediment form the Wujin,gang River can induce harmful toxic effects on the organism,while PAHs may be toxic to organisms.Sediment dredging operation can be used to remove total nitrogen and heavy metals in sediments from the Wujin'gang River.2.The total nitrogen and total phosphorus contents in sediment from the Wujin'gang River after centrifugation were less than before centrifugation through double centrifugation method,illustrating that nitrogen and phosphorus are transferred from sediment phase to interstitial water phase.After centrifugation,the content of six kinds of heavy metals is slightly higher than that before centrifugation,demonstrating that a small amount of heavy metals is also transferred to interstitial water phase.However,double centrifugation operation has little influence on the total polycyclic aromatic hydrocarbons.The toxicity of interstitial water among three organisms is similar,i.e.the toxicity of S5,S9,S12 and S3 are small,and the toxicity of S6,S1,and S13 are larger.At the same time,the toxicity among three organisms have specificity,which is that the toxicity difference between S7 and S8 is large,due to the different effectiveness of different and pollutant chemical biological samples.Comparing the biological endpoints of three organisms,the toxicity order is Limnodrilus hoffmeisteri,Daphnia magna,Photobacterium phosphoreum.Toxicity sediment interstitial water from the Wujin,gang River among the three organisms has significant relationship,showing that one of three species can reflect the toxicity of interstitial water.3.The toxicity of sediment interstitial water(such as S6,S7)from the Wujin,gang River on Daphnia magna,is not caused by metals.After zeolite treatment,the toxicity of interstitial water samples decreased significantly,which means that one toxic substance is ammonia nitrogen.After air and nitrogen aeration treatment,the toxicity of interstitial water samples decline than prior to aeration,indicating the existence of volatile toxic substances.In addition,the C18 manipulation results show that non-polar organic toxic is a cause of toxicity for S6 and S7.To sum up,the toxicity of sediment interstitial water from the Wujin'gang River on organisms is mainly due to the existence of ammonia nitrogen,volatile toxic substances and non-polar organic toxicant.We also figure out these three kinds of compounds exist in sediment from the Wujin'gang River.