| The carbonate rock widely distributed in Guizhou Province,which is the typical heavy metals geochemical anomaly karst terrain.The geochemical background value of Cd is 0.31×10-6 in sediments,which is 2.5~3.5 times higher than abundance value.So the accumulation,release and environmental risks of heavy metals should be studied.So the Yelang Lake that represented Karst geology background was chose.And the speciation distribution of Cd,release that based on the DGT(Diffusive Gradients in Thin Films)assembly and the risk assessment of Cd in sediment were studied.The main results are as follows.(1)The concentrations of Cd in dry and wet season in sediments were 0.16~4.17 mg·kg-1 and 1.32~6.54 mg·kg-1,respectively.The concentration of Cd in dry season was less than in wet season.In the same area,there was basically accordant laws of changes in different seasons.The concentration of Cd in Tianfen&Shawan,Dachuanbian area represented top half was higher than bottom half,and the Sanchahe area represented opposite.Cd in sediments were mainly dominated in dry season and wet season by the exchangeable fraction and reducible fraction,which accounted for 10.62%~64.37% and 28.33%~60.42%,respectively.(2)The concentrations of Cd in sedimrnts in dry and wet season by DGT assembly were 0.394 ~1.639 ?g·L-1 and 0.0328 ~ 0.885 ?g·L-1,respectively,which represented Cd in wet season was less than in dry season..Cd of pore water in dry and wet season were 0.284~0.605 ?g·L-1 and 0.247~3.995 ?g·L-1,respectively,which were higher than Cd concentrations by DGT.The ratio of Cd concentration by DGT and pore water was less than 1 and the changes rules were not same.These showed that lower replenishment of Cd from solid to the liquid and lower bioavailability in the sediment from Yelang Lake.(3)The median lethal concentration data gradually reduced with the increase of time,and the LC50 was 0.50 mg·L-1 for Cd present at 48 hours.Because of the chronic existence of heavy metals,so it was dangerous to aquatic organisms.The safe concentration is 1.2×10-3 mg·L-1.Cd in sediments were mainly dominated by exchangeable fraction,which accounted for 39.21%~76.51%.Exposed overlying water system and water-sediment coexistence syatem,Cd accumulation in Daphnia pulex both increated with the ambient increasing Cd concentrations in sediment,and when the Cd concentration was higher than 1500 mg·kg-1,the Daphnia pulex all dead..(4)The risk assessment of Cd in sediments showed that the results of geo-accumulation index(Igeo)and the potential ecological risk index(RI)were same to some extent.The span of Cd pollution in dry season was larger than in wet season.The Igeo showed that the degree of Cd pollution was zreo to three and the RI showed that degree of Cd pollution was light to serious harm.The most polluted degree of Cd was downstream,the following were upstream and midstream.The degree of Cd pollution in wet season was more serious than dry season.And the RSP showed that the result was little different from other methods,it considered cadmium speciation analysis,which was mainly affected by the exchangeable fraction and reducible fraction. |
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