Study Of Heavy Metals Pollution In Sediments Of Lakeside Belt

Because of the persistence, bio-accumulation and toxicity, heavy metal pollution of lake has been one hot research topic in the international environment community. This study relied on the National Water Pollution Control and Management (2008ZX07101), investigated the surface sediments from lakeside belt of Lake Taihu and Lake Dianchi, analyzed species distribution and ecological risk of heavy metal pollution, and studied the release mechanism of heavy metals(Pb, Cd, Cu, Zn) in the different environmental factors. Aim of this study is to control heavy metal pollution in Lake Taihu and Lake Dianchi, and provide the basic information of ecosystem recovery of lakeside belt. The main research results obtained are listed below:(1)The surface sediment from lakeside belt of Lake Taihu was mainly polluted by Cd compared with the《Environmental quality standard for soils》(GB-15618-1995), while Lake Dianchi was mainly polluted by Cd and Cu, and the Lake Dianchi pollution was stronger than Lake Taihu, with the four heavy metals in Lake Dianchi having a higher concentration. The overall intensity of heavy metal pollution of Lake Taihu was northern estuaries>southern estuaries, outflow estuaries>inflow estuaries, and of Lake Dianch was Lake Caohai>northern Lake Waihai>southern Lake Waihai.(2)According to the correlation analysis of various heavy metals and TOC, there was no positive correlation between these heavy metals and TOC in Lake Taihu, there was a remarkable correlation between Cu and Cd, Cu and Zn, Zn and Cd in Lake Dianchi, but the correlation of heavy metals with TOC was weak.(3)The bioavailability of four heavy metals in Lake Taihu varied in the descending order of Zn, Cu, Cd and Pb, while the bioavailability of heavy metals in Lake Dianchi varied in descending order of Zn, Cd, Pb and Cu. Need to be noted that the extractable concentrations of four heavy metals in Lake Taihu all exceeded 60%, which indicated the heavy metals in Lake Taihu had a higher second release potential and a reactivity than Lake Dianchi.(4)Based on the potential ecological risk assessment results, Cd was the main ecological risk factor in Lake Taihu, reaching a strong ecological risk, the ecological risk of other three heavy metals was low, and order of ecological risk of heavy metals in lakeside belt of Lake Taihu in the descending order was Cd, Cu, Pb and Zn. Cd was also the main ecological risk factor in Lake Dianchi, but the average Eri reached 533.61, with a much higher ecological risk than Lake Taihu, the order of ecological risk of heavy metals in lakeside belt of Lake Dianchi was same with Lake Dianchi. Lake Taihu only slightly exceeded medium ecological risk, while Lake Dianchi reached a very strong ecological risk.(5)The pH values had significant effect on the release of all four heavy metals in sediments. In the condition of six pH values, the higher pH values, the release amount was more. When pH value reached to 2, the release amount of four heavy metals reached the most. When pH value was in alkaline region, the release amount almost did not change. Temperature also had effect on the release of heavy metals from the sediments. The higher temperature, the release amount was more. When the temperature reached to 35℃, the four heavy metals release amount also reached the most. Organic acids tend strongly to combine with heavy metals and had an effect on the release of heavy metals from the sediments, of which the effect of citric acid on the release of Zn was the strongest, and the highest release rate reached to 77.53%, the effect of tartaric acid on the release of Zn was the strongest, and the highest release rate reached to 90.65%, and the effect of oxalate acid on the release of Pb was the strongest, the highest release rate reached to 43.16%. The order of extraction capacity of this three organic acids was tartaric acid>citric acid>oxalate acid. In the condition of same amount of organic acids and different pH values, the release amount of all four heavy metals in sediment decreased with the pH values increased. But compared with the condition of no additional organic acids, the release rate of the four heavy metals increased, and the release rate all exceeded 70% at pH=2. The higher concentration of NaCl, the release amount was more. When the concentration was below 60mmol/L, the change range was small, but when the concentration exceeded 60mmol/L, the change range was very obvious.