Eco-toxicological Effects Of Mercury In Soil-Maize System

As a result of the rapid development of our country, the large discharge of threeindustrial wastes and abuses of pesticide and fertilizer, a large number of heavy metals areadded into the soil, which environment is suffered and is polluted increasingly seriously. Oncemercury and mercury compounds of high toxicity flow into the soil, they can't bedecomposed by microorganism and stay steadily in the soil. The soil ecology environment isdamaged, which does harm to human health through the food chain, so eco-toxicologicaleffects of mercury are hot issues in environmental science research.Soil enzyme is one of important components of the soil, which plays a significant role innutrient cycling, energy metabolism and other soil biochemical processes. In recent years,domestic and foreign scholars carried out researches on relations of heavy soil metals andenzyme activity. However, the most discussions only refer to a single or a few soil sample andlong-term eco-toxicological effects of mercury are few.This paper, analyzing the samples of18main soil types, discusses the change rules ofsoil enzyme activity, variations of available mercury in the soil and their effects to soilmicrobiology indicators and the growth of corn by indoor simulation experiment as well aspot experiment. The main conclusions are as follows:(1)The relationship between the content of Hg (C) and soil enzyme activity (U) weresignificant or highly significant correlation. That revealed soil invertase, urease,dehydrogenase, arylsulfatase and phosphatase enzyme activity can be used as indicators of Hgpollution degree. ED10closely related to soil properties and negatively correlated with soilorganic matter. Because organic matter have the adsorption and coordination effect on Hg, theinhibition of high organic soil enzyme activity was less and ED10was higher. Total activityparameters can provide a more comprehensive evaluation of the toxic effects of Hg pollution.The mechanism about the action of Hg and soil enzyme is completely inhibition (competitiveinhibition and noncompetitive inhibition).(2) After long-term Hg pollution, Hg morphological changes was as follows: In the sametype soil, the contents of water soluble Hg, Mgcl2extractable Hg and EDTA extractable Hgwere increased with the increasement of exogenous Hg concentration. the content of Hg inthree forms was positive correlation with The total amount of mercury and was negatively correlated with PH. water soluble, the Mgcl2extraction state and EDTA extraction state of Hgwere lower in soil of high organic matter content than that of low organic matter content. thecontent of Hg in three forms declined with the time prolonged. The fitting formula on thecontent of Hg in three forms and the incubation time were fitted showed their relationship wassignificant or very significant negative correlation(r=-0.713*-0.984**, r=-0.717*-0.970**).(3) under long-term Hg pollution, With the aging time prolonged the variation ofdifferent soil dehydrogenase was inconsistent. The experimental results showed asfollows:,the relative dehydrogenase activity firstly decreased and then increased in acidic soilsand Jiangsu Wushan soil. It was slightly lower in Anhui yellow-brown soil. With increasing ofthe concentration of Hg, the inhibitory of soil urease activity rate was increased, and it overallperform first decreasing and then increasing as the aging time prolonged.(4)Under Hg stress, corn stalks fresh weight and panicle weight in many soils reducedexcept Gansu irrigation silt soil and Anhui yellow-brown.The influence of the corn grainweighe was different in different soil types. In Hunan red soil, Anhui yellow brown soil andShaanxi loess soil, grain weight improve in low concentrations of Hg and reduce in highconcentrations of Hg.(5)Corn grain weight decreased as the Hg concentration increasing in other soils.Microbial biomass carbon and organic matter, total nitrogen, alkali solution nitrogen and CECreached significant or very significant correlation, correlation coefficients were0.728**,0.771**,0.513*and0.701**. Under Hg pollution, Microbial biomass carbon was lowercompare with CK,but metabolic quotient increased in many soils.Respiration intensityincreased in low Hg concentration, and decreased in high Hg concentration.(6) The dehydrogenase activity was inhibited in many soil types polluted by Hg exceptindividual soil samples of alkaline soil.The variation of urease activity was different.Arylsulfatase activity was inhibited in acid and neutral soils,but it was activated in low Hgconcentrations and inhibited in high Hg concentrations.