Effects Of FeSO₄ And MnSO₄ On The Growth And Hexavalent Chromium Transformation Of Rice Seedlings

As an essential trace element for humans and animals,chromium（Cr）is often present in living organisms in the valence state of Cr（III）,but the hazards of excess Cr have not been taken seriously.Cr（VI）is also a high hazard to the environment.At present,there are more studies on Fe SO₄and Mn SO₄as heavy metal remediation materials,but there are fewer studies on the application of Cr pollution remediation.In this study,rice（TUE63）was selected as the test plant and potassium dichromate（K₂Cr₂O₇）as the Cr source.Using Fe SO₄and Mn SO₄to reduce Cr（VI）,the specific remediation effects of different doses of Fe SO₄（Fe SO₄·7H₂O）and Mn SO₄（Mn SO₄·H₂O）on Cr（VI）were studied by hydroponic and soil cultivation tests,respectively,and the main results are as follows:（1）In the hydroponic experiment,the Cr（VI）concentration in the aqueous solution gradually decreased with the increase of Fe SO₄addition at the same initial Cr（VI）concentration,in which the Fe3（25 mg/L）and Fe4 treatments（50 mg/L）decreased 97%and 99%,respectively,compared with CK.However,there was no significant change in the Cr（VI）concentration in the aqueous solution after the addition of Mn SO₄.（2）In the hydroponic experiment,the p H decreased with the increase of Fe SO₄addition at the same Cr（VI）concentration,in which the p H of Fe2-Fe4 treatment decreased by 8%-41%compared with the control;the Eh value of Fe SO₄solution added at the same Cr（VI）concentration level showed an increasing trend,and the Eh values of Fe3 and Fe4 treatments increased by 73%,58%.（3）In the hydroponic experiment,the Cr content of the above-ground（straw）and below-ground parts（roots）of rice seedlings decreased gradually with the increase of Fe SO₄addition after the application of Fe SO₄treatment at the same initial Cr（VI）concentration.Among them,the Cr content of Fe1-Fe5 treated straw ranged from6.96-11.05μg/g,which decreased by 58.61%-73.93%compared with CK,both reaching a significant level（P<0.05）.The Cr content of Fe3 and Fe4 treated rice roots decreased by 33.5%and 22%compared with CK,both reaching a significant level（P<0.05）.The Cr content of rice seedling straw and root system also decreased with the addition of Mn SO₄,where the Cr content of Mn1,Mn3,and Mn4 straw decreased by 22.5%,23.59%,and 41.6%,respectively,compared with CK.The Cr content of Mn4 root system decreased by 25.6%compared with CK,with significant differences（P<0.05）.Compared with CK,the application of Fe SO₄and Mn SO₄significantly reduced the Cr translocation coefficient（P<0.05）and slowed down the translocation of Cr from the roots of the underground part to the rods of the above-ground part of rice.（4）In the soil culture experiment,the soil Cr（VI）content of each treatment showed a decreasing trend with the increase of Fe SO₄and Mn SO₄at the same Cr（VI）concentration,and the decreasing trend was more obvious in the treatment with Fe SO₄addition.There was no significant change in the total soil Cr content of each treatment.（5）In the soil culture experiment,Fe SO₄and Mn SO₄were significantly effective in reducing the Cr content of rice plants at the same Cr（VI）concentration.After the application of Fe SO₄,the Cr content of rice straw decreased by 35.6%-66.8%and the Cr content of rice roots decreased by 54.52%-70.29%compared with CK,which were significantly lower than CK（P<0.05）;the Cr content of Mn1,Mn3 and Mn4 rice seedling straw decreased by 22.5%,23.59%and 41.6%compared with the control;The Cr content of Mn4 treated roots decreased by 25.6%compared with CK,with significant differences（P<0.05）;meanwhile,the total accumulation of Cr in rice seedlings was significantly lower（P<0.05）than the control after the application of Fe SO₄or Mn SO₄.（6）In the soil culture experiment,the GST activity of rice was increased to different degrees after the application of Fe SO₄or Mn SO₄,and the GST activity of Fe1-Fe5treatment increased by 93%-285.2%compared with CK;the GST activity of Mn1-Mn4treatment increased by 198.3%-315.1%compared with CK,in which Fe4（160 mg/kg）and Mn4（160 mg/kg）treated rice seedlings had the highest values of GST vigor.The CAT vigor of Fe1,Fe2 and Fe3 treated rice seedlings increased by 53.6%,31.8%and 40.5%,respectively,compared with CK,where the highest antioxidant stress capacity and the highest CAT vigor values were achieved with Fe²⁺addition of 40mg/kg;the CAT vigor of Mn1-Mn4 treated rice increased by 87%-197.1%,respectively,compared with the control.The highest CAT vigor value was obtained with Mn²⁺addition of 80 mg/kg.After the application of Fe SO₄and Mn SO₄,the POD activity of rice in each treatment increased to different degrees compared with CK,with the POD activity of Fe1-Fe5treatment increasing by 14.4%-45.3%compared with CK and the Mn1-Mn4 treatment increasing by 80.2%-193.6%compared with CK.The highest values of POD activity were achieved in Fe2（80 mg/kg）and Mn2（80 mg/kg）treated rice seedlings.Both S-CAT and S-UE values increased after the application of Fe SO₄or Mn SO₄compared with CK.