The Research Of Species Sensitivity Distribution Of Cd Toxicity To Rice Cultivars And The Main Factors Affecting In Soils

This thesis mainly focused on the dose-response relationship of Cd toxicity to different ricecultivars and the main factors affecting the Cd-toxicity to rice species in soils, hydroponic and potexperiment were employed to investigate the Cd toxicity （ECx, x=10,50） to rice cultivars deducedfrom the dose-response relationship and the main influence factors (i.e. pH、CEC、OC in soils) using thelatest environment ecological risk assessment method for hazardous substances risk evaluation (e.g.Log-Logistic distribution models, species sensitivity distribution models (SSD) and the derivation ofthe toxicity thresholds etc). The results will provide fundmental data for the revision of the currentenvironmental quality standard for soils in China and for the development of environmental qualitystandard for Cd toxicity thresholds to rice cultivars in China.1. A hydroponic culture experiment was conducted to investigate to dose-response of Cadmium(Cd) to17different rice cultivars, thereafter the ecological hazard concentrations (HC5: the protection of95%rice species) of Cd to rice cultivars were determined with species sensitivity distribution model(Bur-III). The results indicated that, in general, the biologic concentration factor (BCFs) of Cd to ricespecies decreased with the addition level of Cd (with the range from0.30mg.L-1to6.0mg.L-1),however, the transfer factors (TFs) increased with the addition level of Cd in solution, and the higherTFs of Cd to the hybrid rice were observed than that of traditional rice cultivars. The observed halfinhibiting concentration (EC50) of Cd to rice cultivars ranged from0.552~24.01mg.L-1in solution, with1.18~43.49times variation among the tested species; in case of10%inhibiting concentration, theobserved EC10ranged from0.033~1.624mg·L-1with variation of1.758~49.21times. Significantdifferences of response of rice cultivars under Cd stress were observed in this study. The determinedmaximum concentration of10%inhibiting concentration of Cd to rice cultivars with protection of the95%rice species (HC510%) was0.045mg/L and0.594mg/L for50%inhibiting concentration (HC550%)with Burr-III model.2. The response relationships of Cd toxicity to18different rice species were fitted by cumulativeprobability distribution functions Log-logistic distribution model and the species sensitivitydistributions (SSD). The results show that The biomass of different rice species decreased with theincreasing concentrations of Cd in acidic soil from Qiyang, however, the stimulating effect of relativelylower level of Cd (1.2and4.8mg·kg-1) on rice growth was found. In alkaline soils from Guangzhou,there was no significant difference in the biomass of different rice species with increasingconcentrations of Cd. The biologic concentration factor (BCFs) of Cd to rice species decreased with theincreased spiked levels of Cd in both soils, however, the BCFs of rice in Qiyang soil was higher than inGuangzhou soil under the same Cd level. Rice X-45had the highest Cd toxicity threshold concentration(EC50, mg·kg-1), while rice X-42had the lowest EC50. The EC50of18rice species ranged from4.30~61.611mg·kg-1,with the variations differed from1.0to14.32folds. Rice X-42was the most sensitivespecies to Cd stress with the largest toxicity threshold, on the contrary, rice X-45showed strong patience to Cd stress. The maximum concentration of50%inhibiting concentration of Cd to ricecultivars with protection of the95%rice species (HC50%5) was4.93mg·kg-1determined by Burr-IIImodel.3.Four typical China soils with different properties were selected and added with six centrations ofCd2+to study the effects of different aging time (14,30,60and90days) on the form transformationtransformation and eco-toxicity threshold (ECx) of added Cd in the soils, with the main affecting factorsanalyzed. The results indicated that with the added Cd incresing, effective cadmium content in fourkinds of soil increased. effect Cd content of different added Cd contents decined rapidly in30d, andthen slowed down. When the soil with the same amount of foreign source added, Cd effective contentdecreased with the soil pH increasing. With the increase of aging time, Cd toxicity threshold EC50oftwo kinds of rice growing significantly improved. In the same aging time, with the soil pH decreasing,toxicity thresholds EC50of X-45and T-167decreased, which was a positive correlation. In differentaging times, soil pH, CEC and Org-C was the negative correlation with C∞and the positive correlationwith k2. pH and CEC are the main factors affecting soil aging, nothing to do with rice cultivars.