Effect Of Dissolved Organic Matter On Mercury Release From Soil/air Interface

Since the Minamata disease happened in Japan in the 1950s', environmental mercury pollution has been one of the hot issues study in the field of the environmental science. In the recent 10 years, it was discovered that long-distance transmission of mercury could lead to contamination through the circulation of the atmosphere and the stock of the mercury in the atmosphere and the flux of its input and output were paid special attention. It is estimated that the total amount of mercury that entered the atmosphere every year in the world is about 6000-75001, of which the natural released mercury is about 1/3. Soil is the main source of the natural released mercury. After the mercury is transmited for a certain period of time and distance in the atmosphere, over 90 percent of it would eventually come down to terrestrial ecosystems, and threat human health through terrestrial food chain. Application of organic fertilizer is a widely adopted agronomic method in the agricultural activity. It is found that there would be a large amount of dissolved organic matter (DOM) when the organic fertlizer enter into the soil. The chemical properties of DOM is very active, and it has great impact on the adsorption and desorption, migration and conversion even biological toxicity on the heavy metal Hg. Accordingly, this trial choose Chongqing's typical soil-purple tide soil, yellow soil and purple soil as the object of investigation, test the impact that DOM has on the exchange of mercury in the soil/air interface under a variety of conditions by the simulation test, analyse the forms of mercury in purple soil before the simulation, research the impact that DOM has on the change of mercury's forms in the purple soil under a variety of condition, and finally inspect whether there is relationship between the changes of mercury's form in the purple soil and the release amount of mercury from the soil/air interface under the effect of DOM. The results are as follows:From the monitoring results of the mercury amount from the soil/air interface, it is found that: adding DOM to the three kinds of soils would reduce the mercury release amount from the soil/air interface; different DOMs have different impact on the mercury release amount from the soil/air interface, and the compost DOM have the strongest inhibit effect on the amount of mercury release. The DOM's impact on the mercury release amount from the soil/air interface is related to the adding amount(that is the last concentration adding to the soil). With the increasing concentration of the DOM in the soil, the inhibit effect on the mercury release amount from the soil/air interface would be stronger.Under the two kinds of the exotic mercury's concentration, the three sorts of DOM mainly have different degrees of restraining effect to the mercury release amount from the soil/air interface of the three kinds of soil, and this restraining effect becomes more obvious as the concentration of the exotic mercury becomes stronger.DOM's impact on the mercury release amount from the soil/air interface is related to the reaction time(that is the aged time) between DOM and soil mercury. As the aged time's growing, whether the DOM is added or not, the trend of the mercury release amount from the soil/air interface drops. The dropping degrees of the mercury release amount from the soil/air interface of soil samples with no DOM is greater than the one with DOM.As the physical and chemical properties of different soils are different, such as their differrent pH, mechanical components ,that make the mercury release amount from the soil/air interface of three kind of soils is diffenrent under the same condition. Basically ,the sequence is purple tide soil> purple soil> yellow soil.From the result of analysing the forms of mercury in purple soil before the simulation we know that: the content of the chemicals in the purple soil would change after adding DOM. Compared with the soil samples in which DOM is not added, DOM from humic soil would make the content of water-soluble and acid-soluble form decline, but make the content of alkali-soluble form,organic matter form and residual form increase; DOM from compost would make the content of water-soluble form,acid-soluble form and organic matter form decline, but make the content of alkali-soluble form and residual form increase; DOM from straw would make the content of water-soluble form and acid-soluble form decline, but make the content of alkali-soluble form,organic matter form and residual form increase;As the increasing of the adding amount of the three kinds of DOM, there is a declining tendency of the content of water-soluble form and acid-soluble form, the tendency of straw is particularly obvious, and there's an obvious rising tendency in the content of residual form when the straw DOM's adding amount is increased.The soil samples with no DOM and compost DOM added are rarely effected by the aged time. The contents of mercury of acid-soluble form in purple soils with straw DOM and compost DOM added drop obviously as the time grows, while the residual form rises; the contents of acid-soluble form mercury in purple soils with straw DOM added drops obviously, the amount of declining is 0.0276mg/kg from 1d to 3d, 0.0097mg/kg from 3d to 5d, the amount varied 0.0373 mg/kg in total.Compared with the soil sample with no exotic mercury added into, the one that add the exotic mercury made the allocation of the mercury's form change; Differrent concentration of the exotic mercury makes varied allocation of the mercury's form, and with DOM added into the soil, contradistinguishing with that with no DOM added into, the more concentrated the mercury, the greater change the allocation of the content of the mercury' form would have.The relation between the mercury release amount from the soil/air interface and the corresponding content of soil mercury form is analyzed. It's found that there's relationship between mercury release amount from the soil/air interface and content of water-soluble form mercury and alkali-soluble form mercury. There's a significant positive corresponding with content of water-soluble form mercury, the correlation coefficient is 0.479**, and a significant negative corresponding with alkali-soluble form mercury, the correlation coefficient is -0.524**.