Cadmium Uptake By Different Vegetable Cultivars And Their Root Morphological Traits

Environmental issue has become one of the greatest concerns in this world today. Moreover, heavy metal contamination in soil is one of the most serious global environment problems. As their unique biological toxicity and easy accumulation, heavy metals pose a serious threat to ecosystem and human health, cadmium is more easily to be absorbed by crops and enriched by food chain, and then threaten food security and affect human health. There are two strategies to solve heavy metal pollution problems. One is remediation and the other is selection and breeding of heavy metal pollution-safe cultivars. As plants uptake and accumulate heavy metals present significant differences among and within species, it provides the possibility of species selection. In this study a pot experiment was used to study the influence of three degrees of Cd to 71 usual vegetables'growth, and differences of absorption and accumulation of cadmium and vegetable root morphology characters. Statistical analysis was carried out by Anova and Cluster analysis. Meanwhile, Target Hazard Quotient (THQ) was used to evaluate the health risks of Cd in these vegetables, and Environmental Security Decision Assistant System was build to evaluate field Environmental security. The pot experiment results show that:1. Cd concentration in the shoots of Ipomoea aquatica(Ipomoea aquatica Forsk.),Leaf-used lettuce(Lactuca sativa L.) and Romaine (Lactuca sativa L.var.capitata L.) changes during their vegetative growth generally followed the order:increased (8 leaves stage)——stabilized (12 leaves stage)——increased (16 leaves stage)——stabilized (20 leaves stage),the highest concentration appears in the late vegetative stage (16 leaves stage in this study), no obvious injured symptom was observed.2. Effects of Cd on the vegetable biomass showed significant differences within and among species,differences in the situation can be classified into highly sensitive, sensitive, high tolerant, tolerant, and the other.3. It could be concluded that different vegetables had different accumulation abilities for Cd. According to the concentration of Cd in the shoots, these 71 leafy vegetables can be classified into low, medium, high, higher and highest clusters.Under 2.12 mg kg-1Cd exposure,concentrations of Cd in Low-level was in a range of 0.45-1.16 mg kg-1, medium-leve 11.27～2.29 mg kg-1, high-level 2.36-2.66 mg kg-1, higher-level 1.49～4.11 mg kg-1 and highest-level 4.69-5.04 mg kg-1. The bioconcentration factors of these 71 vegetables can be divided into low, medium and high categories.we also find that Cd can significantly affect the transfer coefficient of the same vegetable. When exposure to 0.31,1.20 and 2.12 mg kg-1 of Cd, the transfer coefficient of various vegetables has decreased in turn, ascended in turn, first increased and then decreased, first decreased and then increased, and no effect totally 5 types, Circumstances vary for different varieties of vegetables.4. In this study, it was concluded that leafy vegetables have little potential on the phytoremediation of cadmium contaminated soil,the highest concentration of Cd in shoots of vegetables is 5.04 mg kg-1, the highest intake of Cd by vegetable cultivars was 7.81μgpot-1, the highest purification ratio of cadmium in soil was 0.74% (soil Cd:2.12 mg kg-1).5. Under 2.12 mg kg-1 Cd exposure, Cd concentration in shoots of these vegetables were weakening followed the order:Leaf-used lettuce>Romaine> Flowering chinese cabbage(Brassica campestris L. ssp.chinensis var.utilis Tsen et Lee)> Lettuce (Lactvca saiva L. lettuce)> Ipomoea aquatica> Celery(Apium graveolens L. celery)> Cole (Brassica campestris L. var. communis Tsen et Lee)> Chinese cabbage(Brassica campestris L. ssp. Pekinensis(Lour.) Olsson)> Shepherd's purse(Brassica juncea)> Coriander(Herba Coriandri Sativi)>Common sowthistle(Cichorium endiviaL. common) >Chive(Allium porrum L.leek)>Kale(Brassica oleracea var.capitata f.rubra)> Malabar spinach(Gynura cusimbua(D. Don) S. Moore)> Chrysanthemum (Chrysanthemum soronarium L.garland chrysanthemum)> Amaranth(Amaranthus mangostanus L. edible amaranth)>Leek(A.tuberosum Rott, ex Spr. Chinese chive)。6. Different vegetables have different risks due to different cultivars, urban residents have higher risks than rural residents by eating the same vegetables. Under 2.12 mg kg-1 Cd exposure, leaf-used lettuce, romaine, lettuce, celery, coriander and ipomoea aquatica showed high risks to human health, however, kale, chrysanthemum, leek, malabar spinach and amaranth were safer than others.7. Root volume, length, surface area, tip numbers were significantly effected by the presence of Cd. they were inhibited or stimulated, determined by cultivars and soil Cd concentration. It was feasible to assess field environmental by Environmental Security Decision Assistant System, But it's further application need more raw data accumulation and improvement of restricted conditions.The results of this study can provide detailed information to the primary production of agricultural soils, assessment of environmental heavy metal pollution and phytoremediation.