Accumulation Of Microcystin-LR In Soil-vegetable System

Microcystins(MCs) is a biotoxin produced by aquatic cyanobacteria bloom. It can be transferred into farmland via irrigation, overflow or fertilization. Crops could uptake and accumulate MCs from the irrigation water and contaminated soil, which is harmful to agricultural products and consequently to human health. The studies available now are focused on the pollution characteristics and environmental behavious of MCs in water. But the accumulation of MCs in soil-vegetable system is rarely been reported. In this paper, the accumulation and the physiological, biochemical effects of vegetables under the MC-LR contamination via irrigation, water overflow and algae fertilization were studied. The concentration of MC-LR in different vegetable organs, individual growth, chlorophyll contents and antioxidant system index(contents of total protein(TP) and malondialdehyde(MDA), activities of superoxide dismutase(SOD) and peroxidase(POD)) were investigated and analysized using three leafy vegetables(Ipomoea batatas leaves、Brassica juncea and Brassica alboglabra) as tested materials by the pot culture experiments. It could provide the basic data for ensuring the security of agricultural products. The rusults were as follows:(1)The residual quantity in the tested soils ranged from 13.51 μg/kg to 138.59 μg/kg, which were higher than its soil predicted no effect concentration(PNECsoil)of 13.7 μg/kg. The degradation rate of MC-LR was followed the order of contaminated soil > irrigation >using algae fertilizer. The ecological risk and health risk assessment indicated that the ecological risk(RQs was 0.99~10.12) was high. Humen exposure risk index of MC-LR in soil ranged as 0.06×10-6~5.56×10-3 via skin, oral and breathe contact, which indicated a low health risk.(2)The accumulation of MC-LR in vegetables was followed the order of using algae fertilizer> irrigation> contaminated soil. Generally, MC-LR was mainly accumulated in the root than that in the leaf and stem. The accumulation of MC-LR in the root of Brassica juncea and Brassica alboglabra was higher(0.66~24.39 μg/kg, 2.82~28.45 μg/kg) and Ipomoea batatas leaves MC-LR accumulation was lower(4.47~10.70 μg/kg). The transport capacity of Brassica juncea and Brassica alboglabra was weaker, MC-LR content of aboveground was lower(0.62~6.78 μg/kg、0.23~1.72 μg/kg). The transport ability of Ipomoea batatas leaves was strong, which has a high concentration of 3.07~5.83 μg/kg. MC-LR mainly distributed in cell wall and soluble fraction under tested treatments and less MC-LR distributed in the organelle. MC-LR distributed in the three subcellular structures uniformly when cultivated using algae fertilizer. Health risk was acceptable when eating the vegetables when compared to the acceptable daily intake(ADI) value.(3)The antioxidant system of vegetable organs had the obvious stree effect when suffered the MC-LR pollution. The contents of MDA increased significantly. The MC-LR contamination reduced the vegetable height and yield, slowed the growth and wilting leaves. Results showed that the MC-LR resistance ability of the three tested vegetables were similar.