Weitao Liu

Cadmium tolerance and accumulation characteristics of Bidens pilosa L. as a potential Cd-hyperaccumulator.

Recently, researchers are becoming interested in using hyperaccumulators for decontamination of heavy metal polluted soils, whereas few species that hyperaccumulate cadmium (Cd) has been identified in the plant kingdom. In this study, the physiological mechanisms at the seedling stage and growth responses and Cd uptake and accumulation at flowering and mature stages of Bidens pilosa L. under Cd treatments were investigated. At the seedling stage, when soil Cd was lower than 16mgkg(-1), the plant did not show obvious symptom of phytoxicity, and the alterations of chlorophyll (CHL), superoxide dismutase (SOD), peroxidase (POD), malondialdehyde (MDA), and soluble protein (SP) did not have significant differences when compared with the control. At the flowering and mature stages, under low Cd treatments (</=16mgkg(-1)), the application of Cd could facilitate plant growth, resulting in 3.9-11.0% and 5.9-13.8%, respectively, increase in shoots dry biomass compared with the control. The Cd concentrations in stems, leaves and shoots exceeded 100mgkg(-1) when soil Cd was at 8mgkg(-1), and they were positively correlated with Cd concentration in soils, the bioaccumulation factor (BF) and translocation factor (TF) values were all greater than 1.0. Thus, it is clear that B. pilosa has the basic characteristics of a Cd-hyperaccumulator. All the results elementarily indicated that B. pilosa is a potential Cd-hyperaccumulating plant.

Variations in cadmium accumulation among Chinese cabbage cultivars and screening for Cd-safe cultivars.

Variations in cadmium accumulation and translocation among 40 Chinese cabbage cultivars were studied to identify and screen out Cd-safe cultivars (CSCs), i.e. cultivars with low enough accumulation of Cd in their edible parts even when grown in contaminated soils. It was observed in the pot-culture experiment that there was a significant difference (p<0.05) in shoot Cd concentrations under three Cd treatments (1.0, 2.5 and 5.0mg/kg), with corresponding average values 0.88, 4.45 and 7.76 mg/kg, respectively. Shoot Cd concentrations in 16 cabbage cultivars were lower than 0.50mg/kg. The translocation factors (TFs) and the extraction factors (EFs) in five cabbage cultivars were lower than 1.0 in the pot-culture experiment. The field-culture experiment further validated that New Beijing 3 and Fengyuanxin 3 could be considered as CSCs. In particular, the two cultivars can be cultivated in low to moderate Cd-contaminated soils (Cd concentration <1.25mg/kg) to minimize the Cd accumulation in the food.

JOINT EFFECTS OF ARSENIC AND CADMIUM ON PLANT GROWTH AND METAL BIOACCUMULATION: A POTENTIAL CD-HYPERACCUMULATOR AND AS-EXCLUDER BIDENS PILOSA L

Joint effects of arsenic (As) and cadmium (Cd) on the growth of Bidens pilosa L. and its uptake and accumulation of As and Cd were investigated using the field pot-culture experiment. The results showed that single Cd (<or=25 mg kg(-1)) and As (<or=50 mg kg(-1)) treatments could promote the growth of B. pilosa, resulting in 34.5-104.4% and 21.0-43.0%, respectively, increase in the dry biomass of shoots while compared with that under the control conditions. However, under the co-contamination of As and Cd, there was an antagonistic effect on the growth of the plant. The concentrations of As and Cd accumulated in tissues of the plant increased with an increase of As and Cd in soils. In particular, the levels of Cd in stems and leaves reached 103.0 and 110.0 mg kg(-1), respectively, when soil Cd was 10 mg kg(-1). Furthermore, the BF and TF values of Cd were greater than 1.0. However, the highest content of As in roots of the plant was only 13.5 mg kg(-1) when soil As was at a high level, i.e. 125 mg kg(-1), and the TF values of As were less than 0.1, indicating that B. pilosa can be considered as a potential Cd hyperaccumulator and As excluder. The presence of As had inhibitory effects on Cd absorption by the plant, in particular, the accumulation of Cd in stems, leaves and shoots decreased significantly, with 42.8-53.1, 49.3-66.4 and 37.6-59.5%, respectively, reduction when the level of soil As was up to 125 mg kg(-1) compared with that under no addition of As. Whereas, when Cd was added to soils, it could facilitate As accumulation in tissues of the plants and the As concentrations in shoots increased with increasing Cd spiked in soils. The interactive effects of Cd and As may be potential for phytoremediation of Cd and/or As contamination soils.

Identification of Chinese cabbage genotypes with low cadmium accumulation for food safety

The pot-culture experiment and field studies were conducted to screen out and identify cadmium (Cd) excluders from 40 Chinese cabbage genotypes for food safety. The results of the pot-culture experiment indicated that the shoot Cd concentrations under three treatments (1.0, 2.5 and 5.0 mg Cd kg(-1) Soil) varied significantly (p<0.05), with average values of 0.70, 3.07 and 5.83 mg kg(-1), respectively. The Cd concentrations in 12 cabbage genotypes were lower than 0.50 mg kg(-1). The enrichment factors (EFs) and translocation factors (TFs) in 8 cabbage genotypes were lower than 1.0. The field studies further identified Lvxing 70 as a Cd-excluder genotype (CEG), which is suitable to be planted in low Cd-contaminated soils (Cd concentration should be lower than 1.25 mg kg(-1)) for food safety.

Lead accumulation in different Chinese cabbage cultivars and screening for pollution-safe cultivars.

Recently, the concept of pollution-safe cultivars (PSCs) was proposed to minimize the influx of pollutants to the human food chain. Variations in lead (Pb) uptake and translocation among Chinese cabbage (Brassica pekinensis L.) cultivars were investigated in a pot-culture experiment and a field-culture experiment to screen out Pb-PSCs for food safety. The results of the pot-culture experiment showed that shoot Pb concentrations under two Pb treatments (500 and 1500mgkg(-1)) varied significantly (p<0.05) between cultivars, with average values of 3.01 and 6.87mgkg(-1), respectively. Enrichment factors (EFs) and translocation factors (TFs) in cultivars were less than 0.50 and varied significantly (p<0.05) between cultivars. Shoot Pb concentrations in 12 cultivars under treatment T(1) (500mgkg(-1)) were lower than 2.0mgkg(-1). The field-culture experiment further confirmed Qiuao, Shiboqiukang and Fuxing 80 as Pb-PSCs, which were suitable to be cultivated in low-Pb (<382.25mgkg(-1)) contaminated soils and harmless to human health as foods.

Evaluation of cadmium phytoremediation potential in Chinese cabbage cultivars.

Selecting a phytoextraction plant with moderate to high Cd-accumulating ability and high biomass based on the plants compatibility with mechanized cultivation techniques may yield more immediately practical results. In the present study, six Chinese cabbage cultivars were grown in three soils, ranging from 0.15 to 2.25 mg Cd kg(-1) soil, to examine uptake and translocation of Cd in their tissues. The results indicated that the order of the shoot Cd concentration values in the cultivars was as follows: Beijingxiaoza 56 > Suancaiwang > Quansheng and Qiubo 60 > Xianfengkuaicai and Chunkang. Similar order was also found in the bioaccumulation factor (BAF), translocation factor (TF), and metal extraction ratio (MER). Several soil Cd fractions after Beijingxiaoza 56 harvesting decreased most. Beijingxiaoza 56 is thus promising for phytoextraction of Cd from soils with low to moderate (<2.25 mg kg(-1)) Cd contamination.

Evaluation of the effectiveness of sepiolite, bentonite, and phosphate amendments on the stabilization remediation of cadmium-contaminated soils

A pot trial was conducted to assess the effectiveness of sepiolite, bentonite, and phosphate on the immobilization remediation of cadmium (Cd)-contaminated soils using a set of variables, namely, physiological traits, sequential extraction procedure, plant growth and Cd concentration, and soil enzymatic activities and microbial population. Results showed that superoxide dismutase and peroxidase activities in the leaves of Oryza sativa L. and catalase activities in soils were stimulated after applying the amendments. However, soluble protein contents in leaves and urease and invertase activities in soils were reduced from 7.1% to 31.7%, 1.0%-23.3%, and 21.1%-62.5%, respectively, compared with the control. Results of the sequence extraction procedures revealed that the exchangeable fraction of Cd in soils was mostly converted into carbonated-associated forms. The water soluble plus exchangeable fraction (SE) of Cd in soil decreased when treated with single and compound materials of sepiolite, bentonite and phosphate, which resulted in 13.2%-69.2% reduction compared with that of CK (control test). The amendments led to decreased Cd concentrations in roots, stems, leaves, brown rice, and rice hull by 16.2%-54.5%, 16.6%-42.8%, 19.6%-59.6%, 5.0%-68.2%, and 6.2%-20.4%, respectively. Higher bacterial and actinomycete amount indicated that remediation measures improved soil environmental quality. Composite amendments could be more efficiently used for the stabilization remediation of Cd contaminated soils with low Cd uptake and translocation in the plants and available contents of Cd in soil.

Joint effects of cadmium and lead on seedlings of four Chinese cabbage cultivars in northeastern China

In northeastern China, large area of vegetable land has been simultaneously polluted by cadmium (Cd) and lead (Pb). Joint effects of Cd and Pb on Chinese cabbage (Brassica pekinensis L.) were investigated using the seed germination and sand culture method. Four Chinese cabbage cultivars including Kangbingjinchun (KB), Dongyangchunxia (DY), Qinglvwang (QL) and Qiangshi (QS) from Shenyang in northeastern China were adopted in this study. The results showed that there were positive linear relationships between the inhibitory rate of biomass, root and shoot elongation and the concentrations of Cd and Pb. In particular, root elongation was more sensitive to joint stress of Cd and Pb. The activity of superoxide dismutase and the content of malondialdehyde (MDA), soluble protein (SP) and proline (PRO) changed significantly with increasing exposure concentration of Cd and Pb. The decrement in the activity of antioxidative enzymes, the content of SP and accumulation of MDA were relatively low in KB and QS. PRO played an important role in resisting Cd and Pb stress.

Uptake of Heavy Metals by Trees: Prospects for Phytoremediation

It is known that heavy metals are taken up and translocated by plants to different degrees. Phytoremediation, the use of plants to decontaminate soil by taking up heavy metals, shows considerable promise as a low-cost technique and has received much attention in recent years. However, its application is still very limited due to low biomass of hyperaccumulators, unavailability of the suitable plant species and long growing seasons required. Therefore, to maximize phytoextraction efficiency, it is important to select a fast-growing and high-biomass plant with high uptake of heavy metals, which is also compatible with mechanized cultivation techniques and local weather conditions. Trees in particular have a number of attributes (e.g. high biomass, economic value), which make them attractive plants for such a use. This paper reviews the potential for the phytoremediation of heavy metal-contaminated land by trees. In summary, we present the research progress of phytoremediation by trees and suggest ways in which this concept can be applied and improved.

Horizontal distribution and levels of heavy metals in the biggest snowstorm in a century in Shenyang, China

The horizontal distribution and levels of heavy metals in the biggest snowstorm in Shenyang since 1904 were investigated by analyzing 4 metals (As, Cd, Pb, and Cu) in a series of ultraclean samples collected from 17 sites distributed in different regions of the Shenyang area, China. The results showed that the concentrations of all the 4 heavy metals in snow from the industrial regions were high, up to 7.3 (As), 2.2 (Cd), 850.0 (Pb), and 0.197-20.2 (Cu) microg/kg, respectively. In the suburb, in contrast, their concentrations were not detected, except for As. Because of the long-term application of arsenical pesticides and herbicides, As was detected in the snow samples which collected on the farm. As, Cd, and Pb were also detected in the snow samples collected from the parks, the residential areas, and the commercial districts mainly by reason of human activities. In a sense, long-term industrial activities, traffic activities, coal combustion, and agricultural activities affected the horizontal distribution and levels of these heavy metals in snow differently. The data relating to the horizontal distribution and concentrations of heavy metals in the snow under extreme climatic conditions can provide with a unique snapshot of environmental pollution situation and behaviors in urban areas.