Yingwen Li

Assessment of influences of cooking on cadmium and arsenic bioaccessibility in rice, using an in vitro physiologically-based extraction test.

The health risks associated with rice consumption may decrease if consumers use cooking practices which can reduce the bioaccessibility of metal(loid)s. The effects of cooking on the Cd and As bioaccessibility, at three contamination levels of rice, were studied. Results indicated that cooking reduced bioaccessibility of Cd and As in rice. Cooking resulted in a significant increase (p<0.01) of Cd and As concentrations in the residual fraction. Low volume water-cooking of rice to dryness reduced total Cd by about 10% for rices A and B, while medium or high volume water-cooking had no effect on Cd bioaccessibility in all rice types. In contrast, low volume cooking did not remove As, but a significant decrease (p<0.05) was observed when cooking with higher volumes of water. This study provides information for a better understanding of more realistic estimation of metal(loid)s exposure from rice and the possible health risks.

Response of plant nutrient stoichiometry to fertilization varied with plant tissues in a tropical forest

Plant N:P ratios are widely used as indices of nutrient limitation in terrestrial ecosystems, but the response of these metrics in different plant tissues to altered N and P availability and their interactions remains largely unclear. We evaluated changes in N and P concentrations, N:P ratios of new leaves (<1 yr), older leaves (>1 yr), stems and mixed fine roots of seven species after 3-years of an N and P addition experiment in a tropical forest. Nitrogen addition only increased fine root N concentrations. P addition increased P concentrations among all tissues. The N × P interaction reduced leaf and stem P concentrations, suggesting a negative effect of N addition on P concentrations under P addition. The reliability of using nutrient ratios as indices of soil nutrient availability varied with tissues: the stoichiometric metrics of stems and older leaves were more responsive indicators of changed soil nutrient availability than those of new leaves and fine roots. However, leaf N:P ratios can be a useful indicator of inter-specific variation in plant response to nutrients availability. This study suggests that older leaf is a better choice than other tissues in the assessment of soil nutrient status and predicting plant response to altered nutrients using nutrients ratios.

Influences of calcium silicate on chemical forms and subcellular distribution of cadmium in Amaranthus hypochondriacus L.

A pot experiment was conducted to investigate the effects of calcium silicate (CS) on the subcellular distribution and chemical forms of cadmium (Cd) in grain amaranths (Amaranthus hypochondriacus L. Cv. ‘K112’) grown in a Cd contaminated soil. Results showed that the dry weight and the photosynthetic pigments contents in grain amaranths increased significantly with the increasing doses of CS treatments, with the highest value found for the treatment of CS3 (1.65 g/kg). Compared with the control, application of CS4 (3.31 g/kg) significantly reduced Cd concentrations in the roots, stems and leaves of grain amaranths by 68%, 87% and 89%, respectively. At subcellular level, CS treatment resulted in redistribution of Cd, higher percentages of Cd in the chloroplast and soluble fractions in leaves of grain amaranths were found, while lower proportions of Cd were located at the cell wall of the leaves. The application of CS enhanced the proportions of pectate and protein integrated forms of Cd and decreased the percentages of water soluble Cd potentially associated with toxicity in grain amaranths. Changes of free Cd ions into inactive forms sequestered in subcellular compartments may indicate an important mechanism of CS for alleviating Cd toxicity and accumulation in plants.

Synergistic improvement of crop physiological status by combination of cadmium immobilization and micronutrient fertilization.

Wollastonite application in cadmium-contaminated soils can reduce cadmium concentrations in plant, while the side effect is the synchronous immobilization of micronutrients, which reduces micronutrient uptake in plant, inducing micronutrient deficient symptoms. Accordingly, we investigated whether the supplement of Zn and Mn fertilizers after the wollastonite addition could promote the growth and photosynthesis in amaranth (Amaranthus tricolor L.). In this study, plants were cultivated in cadmium-contaminated soil under micronutrient fertilization alone, wollastonite addition, and combination of wollastonite and micronutrient fertilization treatments. Then, plant biomass; photosynthesis parameters; and total Cd, Zn, and Mn concentrations were investigated. Moreover, chemical extractions were performed on soil samples. The results show that application of wollastonite decreased Cd, Zn, and Mn concentrations in plant and availability in soil and it increased the gas exchange ability of plants. But, it reduced the chlorophyll content in leaves and had no positive influence on plant biomass. In comparison, Zn and Mn fertilization after wollastonite application greatly increased plant biomass and photosynthetic ability. It also reduced Cd phytoavailability more efficiently. Therefore, synergistic improvement of physiological status of farmland crop by sequential treatment with first wollastonite for cadmium immobilization, and then micronutrient fertilization to avoid micronutrient deficiency, was demonstrated.

Oral Bioaccessibility and Exposure Risk of Metal(loid)s in Local Residents Near a Mining-Impacted Area, Hunan, China

Metal(loid) contamination of food crops and soils resulting from mining activities has been a major concern due to the potential risk to humans. In this study, a total of 36 rice (home-grown and market rice), 38 vegetable, 10 drinking water, 4 river water, 18 soils and 30 urine samples were collected from an abandoned mining area or the local residents in China. Results showed that metal(loid) levels in some of the soil and drinking water samples exceeded the Chinese standard. Rice Cd concentration, rice Pb levels, and vegetable Pb levels exceeded the maximum permissible concentrations in 49%, 68%, and 42% of the samples, respectively. In gastric phases, the average Cd, Pb and As bioaccessibilities in rice were 72%, 70%, and 82%. In gastrointestinal phases, the average Cd, Pb and As bioaccessibilities in rice were 49%, 39%, and 94%. Vegetables (pak choi was selected) showed lower metal(loid) bioaccessibility than rice. The median concentrations of Cd, Pb and As in urine were 3.99, 4.82 and 64.8 µg L−1, respectivley. Rice had the highest contribution rates of Cd and Pb for daily intake, accounting for 114% and 210%, respectively. Vegetables contributed less, and very little contribution came from drinking water. Based on the bioaccessibility data, metal(loid) contamination around the mining area poses a great exposure risk to the local residents through consumption of food crops.