Derivation of empirical model to predict the accumulation of Pb in rice grain.

Lead contamination in soil has become a worldwide threat on food security and human health. To assess the Pb bioavailability and evaluate the safe use of low Pb polluted soil for food production, the speciation of Pb in 19 types of paddy soil were investigated by chemical extraction and X-ray absorption near-edge structure (XANES), and the uptake and accumulation characteristics of Pb in different soil-rice systems were investigated. Moreover, an empirical model was established to predict the content of Pb in rice grain, and field validation was conduct to evaluate model performance. Results showed that the proportion of available Pb in different soil satisfied normal distribution N (0.47, 0.23). Pb(CH3COO)2, GSH-Pb, PbO, PbHPO4 and Pb3(PO4)2 performed well in characterizing the speciation of Pb in different rhizosphere soils, and PbHPO4 accounted for more than 70%. The exceedance of Pb in grain in CK, 0.5X and 1X treatment were 10.5%, 36.1% and 42.1%, respectively, and the accumulation of Pb in grain was significantly related with Pb content in root. Carbonate and organic bound Pb in rhizosphere soil were two major Pb species that influenced the accumulation of Pb in rice. Moreover, content of total Pb, clay and SOM performed well in predicting the Pb content in grain, both for pot and field samples. Above all, our predicting model worked well in evaluating Pb accumulation in rice grain among low polluted paddy farmland (Total Pb < 300 mg/kg).

Controlling Factors and Prediction of Lead Uptake and Accumulation in Various Soil-Pepper Systems.

Lead (Pb) is a typical toxic heavy metal element in soils and plants, which has a potential threat to human health through the food chain. Uptake of Pb in the soil-vegetable system has attracted broad attention, whereas reports on the main controlling factors of Pb uptake and accumulation in different soil-vegetable systems are limited. The effect of soil properties on Pb uptake and accumulation in pepper (Capsicum annuum L.) was studied by a pot experiment with 16 typical soils in China. The results showed that the Pb bioavailability was lower in alkaline soils, and that soil cation exchange capacity (CEC), CaCO3 , and total phosphorus contents might influence the uptake and transfer of Pb by peppers. Soil pH and CEC were the most significant factors affecting Pb accumulation in pepper fruits. Soil pH was negatively correlated with Pb uptake and accumulation due to its influence on Pb mobility and bioavailability. The accumulation of Pb decreased as soil CEC increased, which might inhibit the absorption and transfer of Pb in peppers. The multiple linear regression function based on soil Pb content, pH, and CEC could provide enough information for a good prediction of the accumulation of Pb in soil-pepper systems (R2 = 0.733). The results are in favor of developing a Pb threshold for vegetables in agricultural soils in China, thus improving the food safety of crops. Environ Toxicol Chem 2021;40:1443-1451. © 2021 SETAC.

Wheat (Triticum aestivum L.) grains uptake of lead (Pb), transfer factors and prediction models for various types of soils from China.

Lead (Pb) contaminated in farmlands has become a deep threat to global food security and human health. In this study, the bioavailability of Pb in 18 types of soil to wheat (Triticum aestivum L.) grains were investigated, and reliable empirical models of Pb in wheat grains were established based on soil properties. The results showed that the average bioconcentration factor (BCFgrain/total-Pb) in acidic soils was approximately 3.30 times than that in alkaline soils (ANOVA P < 0.05). Significant positive relationships between wheat grain Pb concentration and soil total Pb or EDTA extractable Pb were presented through the results of simple linear regressions (P < 0.001). The stepwise multiple linear regression models indicated that soil pH and soil total Pb were determined to be the two most reliable and reasonable factors in predicting wheat grain Pb concentration, with 83.8% explanation of variation. Soil total Pb compared with EDTA extractable Pb was applied to better improve prediction models in describing Pb transfer from soils to wheat grains. Furthermore, grouped models divided into two parts with pH of 7.5 also generated well prediction in wheat grain Pb concentration. Our prediction models were successfully verified within 95% prediction intervals for published literature data (including other wheat varieties). Moreover, the results indicated that ungrouped models performed better in predicting accuracy within 400 mg kg-1 of soil total Pb, and grouped models showed better extrapolation stability when Pb in soil were overly high. Our results in the study were conduce to evaluate food security of Pb in contaminated agricultural soils.

Transport and retention of copper oxide nanoparticles under unfavorable deposition conditions caused by repulsive van der Waals force in saturated porous media.

Currently, copper oxide nanoparticles (CuO NPs) have been widely used in industry, manufacturing and agriculture. The transport and retention of CuO NPs are vital to understanding the fate as well as the life cycle of CuO NPs in the environment. This study systematically investigates the transport and retention of CuO NPs in saturated porous media, and the experimental results were explained by the CFT and DLVO theory. The van der Waals force between CuO NPs and collector was repulsive, resulting in the unfavorable deposition condition. Column experiments were conducted with saturated quartz sand under environmentally relevant pH (6, 8, 9), ionic strength (IS, 1, 10, 50 mM), and humic acid (HA, 0.1-10 mg-C/mL). Experimental results show that the breakthrough curves (BCTs) were affected by different pH and IS. Under pH 6 and 9, the mobility of CuO NPs was enhanced by high IS while the mobility was inhibited by high IS under pH 8. The mobility of CuO NPs was enhanced by humic acid and the effect was best at 0.5 mg-C/mL HA. The experimental results were successfully explained by CFT and DLVO theory, the main mechanisms were aggregation of CuO NPs, interaction energy and collision between CuO NPs and collector. In general, these findings can improve our understanding of the transport and retention of CuO NPs in subsurface environments, and suggest pH, IS, HA may be key factors governing mobility and stability of CuO NPs in natural environment.

Influence of Humic Acid on Pb Uptake and Accumulation in Tea Plants.

A hydroponic experiment combined with synchronous radiation X-ray fluorescence (SRXRF) analysis was designed to understand the influence of humic acid (HA) in tea plants under lead stress. The results showed that the quantitative relationship (QR) between humic acid and Pb is an important factor affecting the regulation of humic acid with respect to the accumulation of Pb in tea plants. Besides, excess humic acid might stimulate the accumulation of Pb in the root cell wall and transfer to the shoot organs through undifferentiated casparian band structure. This study could provide a theoretical basis for the scientific evaluation of the effect of humic acid on tea uptake and the accumulation of Pb and the practical application of humic acid in reducing Pb pollution in the field.

Study of the potential of barnyard grass for the remediation of Cd- and Pb-contaminated soil.

In this study, the microwave digestion method was used to determine total cadmium (Cd) and lead (Pb) concentrations, the BCR method was used to determine different states of Cd and Pb, and atomic absorption spectroscopy (AAS) and inductively coupled plasma optical emission spectrometry (ICP-OES) were used to determine Cd and Pb concentrations in simulated soil and barnyard grass before and after planting barnyard grass to provide a theoretical basis for the remediation of Cd- and Pb-contaminated soil. The results showed that the bioconcentration factor changes with different Cd concentrations are relatively complex and that the removal rate increases regularly. The 100 mg kg-1 Cd treatment had the highest removal rate, which reached 36.66%. For Pb, the bioconcentration factor decreased and tended to reach equilibrium as the Pb concentration increased. The highest removal rate was 41.72% and occurred in the 500 mg kg-1 Pb treatment; however, this removal rate was generally lower than that of Cd. In addition, the reduction state had the highest change rate, followed by the residual, acid soluble and oxidation states. For Pb, the residual state has the highest change rate, followed by the acid soluble state, reduction state and oxidation state. In addition, a significant correlation was observed between the soil Pb and Cd concentrations and the concentrations of Pb and Cd that accumulated in the belowground biomass of the barnyard grass, but no significant correlation was observed between the soil Pb and Cd concentrations and the amounts of Pb and Cd that accumulated in the aboveground biomass of the barnyard grass. The highest transfer factor of Cd was 0.49, which occurred in the 5 mg kg-1 Cd treatment. The higher transfer factor of Pb was 0.48 in the 100 mg kg-1 Pb treatment. All of these factors indicate that the belowground biomass of barnyard grass plays a more important role in the remediation of Cd- and Pb-contaminated soils than the aboveground biomass of barnyard grass. Remediation should occur through phytostabilization. Thus, with its strong adaptability and lush growth, barnyard grass can be applied as a pioneer species for the phytoremediation of Cd- and Pb-contaminated soils.