Study On The Effect Of Soil Chromium To Plants And The Threshold Value Of Soil Chromium

The toxic effect of soil chromium to plants is one of the necessary basis for establishing environmental benchmark of soil Cr. Water culture experiments were first carried out to to select the most sensitive vegetable to Cr toxicity among 15 vegetable species. The most sensitive vegetable species was then tested by soil culture experiments in order to determine the threshold values for Cr toxicity in the soil. The main results were as follows:1. Low concentrations of Cr in the culture solutions had hormesis effects to same vegetable species. However, when Cr concentrations increased, toxic effects to the vegetables appeared. The general Cr toxicity symptoms were withering in old leaves, chlorosis in new leaves, and crinkle of young leaves and difficult leaf emergence for leaf vegetables, darkness in root tops or rot of roots, even death of plants.2. The shoot height, shoot fresh weight and root length of the vegetables decreased as the Cr concentration in the solution increased. The dry weight of shoot increased at first, and then decreased with the increasing concentration of Cr. The Cr content of plants increased with increasing Cr concentrations in the solution, with much higher Cr content in the roots than in the shoots.3. Water spinach (Ipomiea aquatica Forsk) and three-colored amaranth (Brassica juncea Coss) showed the most serious symptoms to Cr toxicity than the others. However, cabbage(B.oleracea L. var. capitata L.) would be the most sensitive vegetable species and water spinach (Ipomiea aquatica Forsk) the second sensitive species to Cr toxicity based on the EC10 values (effect Cr concentration in the solution causing a 10% reduction of shoot biomass). Therefore, water spinach (Lpomoea aquatica Forsk.) was selected as the most sensitive vegetable to Cr species based on the comprehensive effects.4. The shoot height, root length, shoot weight (fresh), root weight (fresh), dry weight of shoot and root of water spinach under soil culture condition decreased as the Cr concentration in the soil increased. The fresh weights of shoot had most significant correlation with the available soil Cr among the 15 vegetables while the dry weight of root showed the poorest correlation with the available soil Cr.5. The threshold value of soil available Cr (0.1 mol/L HCl extractable) was 3.36 mg/kg when the shoot biomass of water spinach under soil culture decreased 10%. The corresponding threshold values of soil total Cr was 91.7 mg/kg, which was calculated from the regression equation between the 0.1 mol/L HCl extractable Cr and the total Cr in the vegetable soils in Fujian Province.