Heavy Metals Bioavailability On Sediments Of The Baotou Section Of The Yellow River

Natural water is one of the main ecosystems contaminated by heavy metal. Since sediments of the natural water contaminated by heavy metal are usually called as "Chemical Time Bomb", the sediments are chosen as an indicator of heavy metal contamination. With the developing economy of drainage basin, environmental problem becomes a key factor restricting the sustainable development of Nature-Economy-Society system. The civilization and industrialization have destroyed the natural conditions around human, as nearly all of the rivers, lakes and sea were polluted with heavy meals. Many countries all over the world regulate the heavy metal contents as important indicator for water quality monitoring and assessment.Baotou city is a typical heavy industrialized city on the drainage basin of the Yellow River. Therefore, the Baotou section of The Yellow River is a typical and representative section for studying the contribution of urban industrial waste water on heavy metal pollution of the Yellow River.Speciation analysis is a basis for bioavailability research, it is used to identify potential hazards of heavy metals in sediments. Natural water is a complex multi-ion system. Research about competitive adsorption dynamics of heavy metals onto natural sediments in multi-ion solution (simulate the natural conditions) and about impacts of competitive adsorption on transformation of heavy metal species are of great importance for revealing heavy metal pollution mechanism. Exposure experiments of micro-ecosystem, study about acid-volatile sulfide and heavy metal concentrations in pore water are of propitious to systematically study the heavy metal pollution characteristics.Based on the mechanism and effect of heavy metal pollution in the Yellow River, the transition and transformation characteristics of heavy metals in the Yellow River are discussed; the relation between speciation, bioavailability and toxicity of heavy metal in sediments are revealed and identified; the potential hazards of heavy metal contamination in the sediments are evaluated. The paper could provide strategy and scientific basis for the prevention and cure of heavy metal contamination in the Baotou section of the Yellow River, and could also provide reference for the study about water quality protection of the Yellow River and study about impacts of urban industrial inputs on heavy metal pollution in rivers.Based on the theories of Environmental Geochemistry, Biogeochemistry, Pollution Ecology, and Modern Sedimentology, this work is focused on geochemical characteristics and bioavailability of heavy metals. The overlying water, pore water, suspended particulate matter, sediment core and fish samples are collected at nine sections of the mainstream and the tributaries in low water period, medium water period and high water period in 2004 and 2005. We obtained 17287 data through experimental test. The mechanisms of competitive adsorption and transformation of heavy metals in multi-ion system (simulate the natural conditions of the Yellow River), the pollution characteristics of heavy metals, the relation of heavy metals in water-sediment-fish micro-ecosystem and the bioaccumulation of heavy metals in fishes are discussed in detail. This is the first research that carries out lots of exposure experiments of fish of the Baotou section of the Yellow River to the urban industrial waste water, and provides large amounts of basic data for bioavailability, biogeochemical cycle and ecological risk assessment of heavy metal. Additionally, according to the consanguinity between the Yellow River and the Nanhai lake, the geochemical characteristics of heavy metals in the sediments of the Nanhai lake are studied. The conclusions are as follows:1. The exposure experiments of micro-ecosystem to fishes is carried out first time by simulating the condition of the Yellow River; the response relation of heavy metals between water-sediment-fish system is identified; the linear model which can identify the relation between heavy metal speciation in water and toxicity in fish organs is established, which maybe provide a new effective methods for the biological monitoring of heavy metal pollution.2. The pollution level of nine Yellow River fishes are assessed first time, it ranked as: Hemiculter leucisclus > Carassius auratus auratus > Hemibarbus maculatus > Megalobrama amblycephala > Abbottina rivularis Basilewsky > Cyprinus carpio >Squaliobarbus curriculus> Perccottus glehni > Saurogobio dabryi. By developing the concept of bioaccumulation factors, the train of thought of the mechanism research about the bioaccumulation is broadened.3. The sediments of the Yellow River function as a sink of heavy metal in low water period, whereas a source in high water period. The sediment quality criteria of heavy metals are used here to study the potential risk of the Yellow River sediments. The study indicates that the industrial inputs from Baotou city have a large contribution on heavy metal enrichment in the mainstream of the Yellow River.4. The competitive adsorption capacities are ranked as: Pb²⁺ > Cu²⁺ >> Zn²⁺ > Cd²⁺ ; whereas the release capacities are ranked as: Cd>Zn?Cu>Pb. This result is of great importance for the research about heavy metal transformation mechanism in water-sediment system.5. The Nanhai lake presents notorious consanguinity with the Yellow River. In pore water of the surface sediments, Cu and Cd (especially Cu) present releasing trends towards overlying water. The pore water functions as a bridge in heavy metal transition process from sediments to overlying water.Different from normal fresh water lakes, the vertical distribution of acid-volatile sulfide of the Nanhai lake shows the maximum downward shifting because of oxidation. The acid-volatile sulfide is the key factor controlling heavy metal precipitation of the Nanhai lake, and the organic agent is the main factor promoting the release of Cu from sediment to water phase.6. The conception of spatial effect of heavy metal speciation distribution is introduced. Furthermore, the Cu pollution of water in the Nanhai lake and the transformation mechanism of sink/source of the sediments in different water periods are well discussed based on the conception of spatial effect.