| Heavy metal copper, chromium （Ⅵ） combined pollution is serious all of the world. Inthis study, pot experiments, culture experiments combined with indoor chemical analysis wereperformed to investigate the bio-toxicity of copper and chromium （Ⅵ） on pakchoi both insolution and in soil mediums, and the transformation and bioavailability for pakchoi ofadditional copper and hexavalent chromium in co-contaminated soil. Meanwhile, theinteraction typy between the two heavy metals was also evaluated, in order to providescientific base for predication, evaluation and repair of copper and chromium combinedpollution. The results were as follows:1. The chromium was present mainly on residual and organic boned form while copperwas mainly bound to hydrated oxides of iron and manganese as well as residual form.Lowerconcentrations copper (≤400mg·kg-1) in soil could promoted chromium transformed fromother forms to exchangeable form while higher concentrations copper in soil would inhibit thetransformation. Similarly, chromium in low concentrations could facility copper whoseconcentration was400mg·kg-1transformed to residual form while chromium in highconcentrations (≥20mg·kg-1) would reduce the transformation process. However, thevariation trend was opposite when added copper was more or less than400mg·kg-1in soil.Both added chromium to soil polluted by high concentrations copper or added copper to highchromium content soil could promote the polluted soil reach quasi-equilibrium state.Additionally, copper inhibited pakchoi absorption of chromium by promoting soil OM-Crtransformed into RES-Cr. While chromium reduced copper uptake of pakchoi by stimulatingthe EXE-Cu transformed into the RES-Cu.2. The effect of seed germination indexes was not significant in low concentrations of Cuand Cr treatments, whereas the root enlogation inhibition rate was remarkable in highconcentrations of Cu (≥800mg·kg-1) and Cr(≥60mg·kg-1) treatments （p<0.05）. It was foundthat there were significant liner relationships between concentrations of Cr （Ⅵ） and rootelongation （p<0.01） and low concentrations of Cu (≤200mg·kg-1) could accelerate the rootelongation while high concentration of Cu could inhibit it significantly. In conclusion, thetoxicity of the pollutants to seed germination is lower than to root elongation. Therefore，weproposaled that the seed root length inhibition rate as indicator to determine heavy metal biological toxicity.3. The contamination by single Cu and Cr （Ⅵ） could all inhibit the root elongation ofpakchoi. The EC50values for Cu were2.02mg·L-1and195.8mg·kg-1in solution and soil,respectively, while those for Cr （Ⅵ） were6.88mg·L-1and8.08mg·kg-1. In the case ofcombined tests, toxic unit （TU） was introduced to determine the combined outcomes, anddifferent behaviors were obtained in solution culture and soil condition experiment. Thecoexistence of Cu and Cr （Ⅵ） appeared a less than additive toxicity both in solution and insoil cultivation with EC50mixvalues of3.31TUmixand1.24TUmix, respectively.4. Factor analysis was applied to data on pak choi growth and physiological parameters[root length, plant height, root fresh weight （RFW）, shoot fresh weight （SFW）, root dryweight （RDW）, shoot dry weight （SDW）, malondialdehyde （MDA）, proline content andSPAD] to extract principal factors for better characterization of the combined effects ofCu–Cr （Ⅵ）. In the Cu–Cr （Ⅵ） treatment, the first factor was also classified as a “biomass”factor, accounting for30.6%of the total variance. The second factor was “growth” factoraccounted for21.7%and the third factor, called the “resistance” factor, and explained14.0%.SDW were ultimately selected as indicators of the combined effects of Cu–Cr （Ⅵ）. In thecombined tests, the antagonist ratio was calculated to characterize the combined effects.Results showed that the coexistence of low concentrations of Cu （2.5and5mg·L1） and Cr（Ⅵ） exhibited an additive effect, while, an antagonist effect was found when Cr （Ⅵ）combined with high concentration of Cu （10mg·L1） in the solution culture. |
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