Long-term Aging Behavior Of Soil Added Nickel And Copper And Ecological Thresholds Based On Extractable Copper In Soils

As the scientific basis of ecological risk threshold and environmental standards,the availability of heavy metals in soil was widely investigated to evaluate the ecological risk and phytotoxicity.In the present study,the chemical extractability and bioavailability of copper(Cu)and nickel(Ni)were used to evaluate the influence of soil properties on availability of Cu and Ni in long-term aging field soils.Based on the quantitative relationship between EDTA-extractable and added total Cu and its phytotoxicity model,the species sensitivity distribution(SSD)was established to derive the soil-type ecological thresholds.Firstly,the chemical phytotoxicity and extractability were used to indicate the long-term aging of Cu and Ni.According to the results of aging experiment in field soils from 1 to 6 years,long-term decreases in added Cu and Ni phytotoxicity was only significantly identified in a neutral soil.As an aging indicator of Cu and Ni,chemical extractability was better than phytotoxicity.On the one hand,there was not big difference between biological variance and aging effect on phytotoxicity of Cu and Ni in field soils.On the other hand,the heavy metals rapidly partitioned between soil solution and solid phases when water-solubel metals were added to soils;comparing with short-term,the availability of Cu and Ni decreased slower during long-term aging.As a better indicator,the extractability of Cu was more than Ni in neutral and alkaline soils,but similar in acidic soils.Secondly,the EDTA-extraction of Cu from 17 Chinese soils was used to study the influence of soil properties on extractability of Cu.The result of multible EDTA-extactations,both in unleached and leached soils,first EDTA-extactable Cu was 60%～70%to total added Cu;the sum of three sequential EDTA-extractable Cu was more than 80%,especially in neutal soil,it was 97%.Combining with soil properties,the linear regression relationship between EDTA-extractable and added total Cu concentration was established based on 1 or 3 equential extractions.When more soil properties parameters were incorporated,the multiple linear models were not improved to predict the EDTA-extractability of Cu.And as a single factor,the totol added Cu concentration could explain 95%of variance of EDTA-extractale Cu concentration.Based on the EDTA-extractable Cu,the phytotoxicity model for different ecotoxicological endpoints was established.The soil properties affecting the Cu phytotoxicity for different ecotoxicological endpoints were different.For barley root elongation,the pH,CEC and OC were the most important factors in the model based on 3 sequential extractions.For tomato biomass,the soil pH,OC and citrate dithionate extractable Fe were the most important factors.For bok choy biomass,the soil OC and CaC03 content was the most important facors,and as a single factor,the soil OC could explain 41.9%～60.7%of variance of Cu phytotoxicity.According to the leaching factors and phytotoxicity models for three ecotoxicological endpoints,the correcting phytotoxicity data were used to fit species sensitivity distribution(SSD)with Weibul or BurrⅢ distribution fuction.The soil-type ecological thresholds for Cu were derived from SSD curves to propose the recommendation for updating the Chinese current soil environmental qulity standards.