Speciation and accumulation pattern of heavy metals from soil to rice at different growth stages in farmland of southwestern China

Soil-mustard revitalization via rice husk ash, a promising soil amendment material for sustainable management of heavy metal contamination in tropical ecosystem

Prolonged wastewater irrigation in agriculture has led to the accumulation of heavy metals in soil, endangering both the soil quality and food safety, thereby posing a potential threat to human health through the consumption of contaminated crops. The present study aimed to enhance the yield of mustard (Brassica juncea L. cv. Varuna and NRCHB 101) plants and stabilize heavy metals (Cd, Cr, Ni, Cu, and Zn) in wastewater-irrigated soil using rice husk ash (RHA), rice mill by-product, collected from Chandauli region of Eastern Uttar Pradesh, India. Results demonstrated significant improvements in growth, biomass, physiology, and yield of mustard plant with increasing RHA application in wastewater irrigated soil (p ≤ 0.05). Heavy metal accumulation in different parts of mustard plants decreased as RHA application rate increased. Applying RHA at 2% in soil proved to be most effective in reducing Cd, Cr, Ni, Cu, and Zn accumulation in seeds by 29%, 29.6%, 23.1%, 21.3% and 20.1%, respectively in Varuna and 30.1%, 21.4%, 11.1%, 12.1%, and 28.5%, respectively in NRCHB 101cultivars. The present findings showed that RHA amendment in wastewater irrigated soil had reduced bioaccumulation of Cd, Cr, Ni, Cu, and Zn and consequently their toxicity in cultivated mustard plants. A novel application of RHA is unveiled in this research, offering a promising solution to promote sustainable agriculture and to reduce heavy metal associated health risks within the soil-mustard system.

Co-exposure of heavy metals in rice and corn reveals a probabilistic health risk in Guizhou Province, China

The adverse effects of heavy metals have arousing concern in the high geological background area, especially in southwestern Guizhou, China. However, the pollution status of heavy metals are still unclear when exposed to rice and corn in Guizhou province. Therefore, the concentration, pollution level, spatial distribution, and probabilistic health risks of Ni, Cr, Pb, Cu, and Zn are estimated in rice and corn. A total of 241 samples (117 for rice and 124 for corn) were collected from Guizhou province and measured by a method of inductively coupled plasma-mass spectrometry (ICP-MS). The results showed that rice and corn were contaminated with Ni and Cr. High concentrations of Ni were presented in the southeast of rice. It indicated that 22.0 % of rice samples were contaminated with Ni. HI values for children and adults exceeded 1.0 in rice and corn, suggesting that humans might be subject to probabilistic non-carcinogenic risks. FTCR demonstrated that rice and corn might cause probabilistic carcinogenic risks to children and adults, which were both greatly higher than 1.0 × 10-4. Moreover, the contributions of Ni to the HI and FTCR were the highest for adults and children. Therefore, more attention should be paid to the exposure of heavy metals in rice and corn, especially in Ni. The results would provide a novel prospective for pollution control and be helpful for environmental regulation.

Product safety aspects of plant molecular farming

Plant molecular farming (PMF) has been promoted since the 1990s as a rapid, cost-effective and (most of all) safe alternative to the cultivation of bacteria or animal cells for the production of biopharmaceutical proteins. Numerous plant species have been investigated for the production of a broad range of protein-based drug candidates. The inherent safety of these products is frequently highlighted as an advantage of PMF because plant viruses do not replicate in humans and vice versa. However, a more nuanced analysis of this principle is required when considering other pathogens because toxic compounds pose a risk even in the absence of replication. Similarly, it is necessary to assess the risks associated with the host system (e.g., the presence of toxic secondary metabolites) and the production approach (e.g., transient expression based on bacterial infiltration substantially increases the endotoxin load). This review considers the most relevant host systems in terms of their toxicity profile, including the presence of secondary metabolites, and the risks arising from the persistence of these substances after downstream processing and product purification. Similarly, we discuss a range of plant pathogens and disease vectors that can influence product safety, for example, due to the release of toxins. The ability of downstream unit operations to remove contaminants and process-related toxic impurities such as endotoxins is also addressed. This overview of plant-based production, focusing on product safety aspects, provides recommendations that will allow stakeholders to choose the most appropriate strategies for process development.

Translocation pattern of heavy metals in soil-rice systems at different growth stages: A case study in the Taihu region, Eastern China

Rice production is crucial for human nutrition and food safety globally. However, it has been a significant sink for potentially harmful metals because of intensive anthropogenic activities. The study was conducted to characterize heavy metal translocation from soil to rice at the filling, doughing and maturing stages, and influencing factors of their accumulation in rice. The distribution and accumulation patterns varied for metal species and growth stages. Cd and Pb accumulation mainly occurred in roots, Cu and Zn were readily transported to stems. Cd, Cu, and Zn accumulation in grains had a descending order of filling > doughing > maturing. Soil heavy metals, TN, EC, and pH exerted important impacts on heavy metals uptake by roots during the period from filling stage to maturing stage. Concentrations of heavy metals in grains were positively correlated with the translocation factors TF_stem-grain (from stem to grain) and TF_leaf-grain (from leaf to grain). Grain Cd exhibited significant correlations with total Cd and DTPA-Cd in the soil at each of the three growth stages. Moreover, Cd in maturing grain could be effectively predicted by soil pH and DTPA-Cd at the filling stage.

Uptake and Transport of Different Concentrations of PPCPs by Vegetables

In many parts of the world, water resources are scarce or even extremely scarce, and the reuse of water resources has become mainstream in today's world. Many regions use treated wastewater for agricultural irrigation, aquaculture, and other activities. However, in recent years, wastewater has been found to contain large amounts of pharmaceuticals and personal care products (PPCPs). Therefore, there is a potential risk of PPCPs being transported in the environment and affecting human health. In this study, we compared the uptake, transport, and accumulation of 27 PPCPs in three types of sprouts (radish, buckwheat, and okra).The bioaccumulation of amantadine, diphenhydramine, chlorpheniramine maleate, sibutramine, hemosibutramine, chlorosibutramine, N-monomethyl sibutramine, N, N-desmethyl sibutramine, and carbamazepine was found to be significantly higher in plants grown for 12 days in media containing 0.5, 5.0, and 50.0 ng/mL PPCPs. With increasing concentration of PPCPs in the culture solution, the amount of PPCPs absorbed by plants and the degree of accumulation also showed an increasing trend. At the same time, it was demonstrated that there was an obvious uptake transfer phenomenon of PPCPs by plants, and the trend of uptake transfer became more and more obvious as the concentration of external environmental pollutants increased. In addition, amantadine, chlorpheniramine maleate, carbamazepine, N, N-desmethyl sibutramine, hemosibutramine, and chlorosibutramine showed more active translocation in some plants (TF > 1.0).

Spatial distribution of heavy metals in rice grains and human health risk assessment in Hunan Province, China

Rice is the main food in China, and its pollution by heavy metals has attracted widespread attention. In this study, rice grain samples were collected from 14 prefecture-level cities in Hunan Province, China. The contents of 9 heavy metals (i.e., As, Cr, Co, Ni, Cu, Zn, Cd, Pb, and Sb) were measured using graphite digestion-inductively coupled plasma mass spectrometry (ICP-MS). Pearson correlation analysis and principal component analysis were performed to evaluate the correlation among these heavy metals. In addition, ordinary kriging interpolation were applied to investigate the spatial distribution pattern of the heavy metals. Results showed that the average concentrations of these heavy metals were 0.48 (As), 1.28 (Cr), 0.03 (Co), 0.84 (Ni), 2.39 (Cu), 15.73 (Zn), 0.28 (Cd), 0.66 (Pb), and 0.0043 (Sb) mg/kg, respectively. The single-factor pollution index (SFPI) contamination assessment showed that As, Pb, Cr, Ni, and Cd accumulated significantly in the rice grain, with over-standard rates of 100%, 100%, 64.70%, 47.05%, and 44.12%, respectively. The Sb concentrations at the sampling sites were low, and there was no obvious pollution. Health risk assessment showed that the target hazard quotient followed the order of As> Cr> Cd> Pb> 1.0> Co> Cu> Zn> Ni> Sb, and the carcinogenic risk value was in the order of Cd> Ni> As> Cr> 1.0×10^-4> Pb. In particular, quick actions should be taken to regulate As, Cr, and Cd contents in rice because they posed greater non-carcinogenic and carcinogenic health risks than the others to the local residents.

Effects of water salinity on cadmium availability at soil-water interface: implication for salt water intrusion

Low-lying paddy fields in estuaries can be affected by salt water intrusion; however, it remains unclear how salt water intrusion influences the availability of heavy metals in paddy soil. In this study, batch adsorption and incubation experiments of soil were conducted with different salt water sampled along the estuary to investigate the effects of salt water intrusion on cadmium (Cd) availability. The surface complexation model (SCM) was established to assess the effects of pH on Cd adsorption behavior, which presented typical pH-dependent characteristics. The results of SCM also showed that Cd-chloro complexes became the dominant species when the ionic strength increased. The results of Cd fractions in the incubation experiments revealed a significant increase in dissolved Cd with increasing ionic strength. This may be attributed to the increased point of zero charge (pH_pzc) in the presence of salt water with higher salinity, which likely formed more positive charges on soil surfaces, causing an inhibition of Cd adsorption via electrostatic repulsion. Moreover, higher concentrations of Cl^- in salt water favored the formation of Cd-chloro complexes, facilitating Cd release from soil particles. This study provides mechanistic insights into the impact of salt water intrusion on Cd availability at the soil-water interface of paddy soil along the estuary.

Distribution, bioavailability, and human health risk assessment of arsenic in groundwater-soil-rice system in the Jianghan Plain, Central China

Many studies have reported high arsenic concentrations in the groundwater and soil of the Jianghan Plain (JHP), an important rice production base in China. However, no comprehensive study on the occurrence and risk of As in groundwater-soil-rice systems in this region has been conducted. In this study, As concentrations in groundwater, soil, rice straw, and rice grain samples were analyzed. Arsenic concentrations were found to range from BDL to 42.88 μg/L (median 0.34 μg/L) in phreatic water, BDL to 41.77 μg/L (median 8.64 μg/L) in soil pore water, 10.20 to 21.90 mg/kg (mean 16.52 mg/kg) in soil, 0.204 to 2.860 mg/kg (mean 0.847 mg/kg) in rice straw, and 0.131 to 0.951 mg/kg (mean 0.449 mg/kg) in rice grain. Arsenic uptake by rice from soils was evaluated according to bioavailable As defined by chemical extraction and diffusive gradients in thin films. The results indicated that owing to the low content of highly mobile As fractions, the less mobile As fraction (mainly bound with amorphous Fe/Al (hydr)oxides) also contributed to bioavailable As, suggesting that amorphous Fe/Al bound As should be considered in analyzing bioavailable As. In terms of the geoaccumulation index and the Chinese paddy soil standard (GB15618-2018) limit (25 mg/kg), As pollution in water and soils in the study area is at a low level and can be considered relatively safe. However, the target hazard quotients and cancer risk assessment indicated that As pollution is at a dangerous level with potential human health risk. According to the bioconcentration factor, the bioavailability of soil is higher in JHP compared with other rice-growing areas owing to the unique hydrogeological conditions and irrigation using groundwater with high As content. Rice planting areas in JHP should be set as far away from large rivers as possible, and groundwater with high As concentrations must be pre-treated prior to irrigation.

Single and mixed effects of metallic elements in maternal serum during pregnancy on risk for fetal neural tube defects: A Bayesian kernel regression approach

Studies of the association between prenatal exposure to metal elements and risk for neural tube defects (NTDs) have produced inconsistent results. Little research has examined the joint effects and interactions of multiple elements. This study examined 273 women with NTD-affected pregnancies and 477 controls. Cadmium, cobalt, chromium, copper, iron, mercury, manganese, molybdenum, lead, and zinc were quantified in maternal serum. Single and mixed effects of these elements on NTD risk were evaluated with Bayesian kernel machine regression, and the effects of individual elements were validated using logistic regression. As a result, NTD risk increased with the concentration of the mixture of the 10 elements. NTD risk rose as the levels of the five toxic elements increased, with effect sizes larger than the overall analyses, but they decreased, albeit non-significantly, as the levels of the five essential elements increased. Lead and manganese showed risk effects on NTDs, with odds ratios (ORs) of 1.94 (1.76-2.13) and 1.25 (1.14-1.38), respectively, with the remaining nine elements remaining at their median. Molybdenum showed a protective effect against NTDs with an OR 0.87 (0.90-0.94). The single-element results were validated using logistic regression. In conclusion, NTD risk increased with concentrations of the five toxic elements, with lead and manganese being the major contributors. Essential elements showed protective effects against NTD risk.

Health risk assessment of heavy metals in soils and screening of accumulating plants around the Wanshan mercury mine in Northeast Guizhou Province, China

The Wanshan mercury mine, which is an abandoned mine located in northeastern Guizhou Province in Southwest China, has introduced serious Hg pollution to the local ecosystem resulting from previous mining and smelting activities. However, it is not clear to date whether soil pollution has actually improved after treatment by related departments. Therefore, the present study investigates the vegetation community and heavy metal contents of the soil and plants in the Wanshan mercury mining area. The results showed that most of Hg, Cd, As, Cu, and Zn contents in soil samples were higher than those of Soil Environment Quality Risk Control Standard for Soil Contamination of Agricultural Land in China (GB15618-2018). The observed plant species mainly consisted of Compositae, followed by Leguminosae. Unfortunately, this investigation found that heavy metal concentrations in these plants were not extremely high and far below the standard of hyperaccumulator. Despite all this, the maximum values of bioaccumulation factor for Pb, Cd, Hg, As, Cu and Zn were Serissa japonica (Thunb.) Thunb., Rhus chinensis Mill., Potentilla sibbaldii Haller f., Erigeron canadensis L., Clerodendrum bungei var. bungei. and Rhus chinensis Mill., respectively. Regardless of the carcinogenic or noncarcinogenic risk index, the potential risk to urban children is higher. Our results suggest that heavy metal pollution was indeed relieved since their contents in soil significantly decreased in comparison with those reported in other previous studies. This finding provides a reference for the long-term treatment of heavy metal pollution in the local environment and other areas employing analogous environmental protection measures.

Speciation Variation and Bio-Activation of Soil Heavy Metals (Cd and Cr) in Rice-Rape Rotation Lands in Karst Regions

Heavy metals in soil are in a high background state in Karst areas, and agricultural activities will affect the bioactivity of heavy metals. The heavy metal (Cd and Cr) bioactivity and their activation effects in rice-rape rotation lands in Karst areas were studied based on field experiments and laboratory analysis, and the influencing factors of heavy metal activity were analyzed based on the physical and chemical properties of soil. The results suggest that the residual fraction was the largest and the exchangeable fraction was the smallest for both Cr and Cd in rice-rape rotation lands in Karst areas. During the rice-rape rotation process, Cd and Cr tended to be released from the residual fraction and transformed into the other four fractions. The fractions with high bioactivity, including the exchangeable fraction and carbonate fraction, increased to different degrees. Rice-rape rotation could activate the activity of soil Cd and Cr in Karst areas. It is also revealed that the activity of soil Cd and Cr in Karst areas was closely associated with soil pH and electric potential (Eh). In the 0–20 cm soil layer, Cr showed a significant negative correlation with pH (r = −0.69, p < 0.05), while both Cr and Cd showed significant negative correlations with Eh, and the correlation coefficients were −0.85 (p < 0.01) and −0.83 (p < 0.01), respectively. In the 20–40 cm soil layer, Cr showed significant negative correlations with Eh, and the correlation coefficient was −0.95 (p < 0.01). No significant correlation between the activity of soil Cd and Cr and soil mechanical composition was observed. This study revealed that special attention should be paid to changes in pH and Eh in consideration of heavy metal activity in the rice-rape rotation process.

Arsenic and Heavy Metals in Vietnamese Rice: Assessment of Human Exposure to These Elements through Rice Consumption

In this work, twelve heavy metals and arsenic, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, and Zn, in a rice sample collected from some areas of Vietnam have been quantified and implemented by using multiple analytical platforms such as ICP-MS, AAS, and mercury analyser. Seventy rice samples collected from the Red River Delta and mining zone activity were analysed. Concentration of heavy metals and arsenic in rice was analysed after appropriated sample digestion using internal or external calibration curves. The mean concentration (mg kg^-1 dried weight) of the analysed elements in rice samples decreased on the order of Mn (19.268) > Fe (13.624) > Zn (8.163) > Cu (3.138) > Ni (0.384) > Cr (0.296) > Co (0.279) > As (0.115) > Cd (0.111) > Pb (0.075) > Hg (0.007) > Se (<LOD). Mercury, a highly toxic element, has been only found in rice samples collected in the mining activity zone (frequency detection 14.5% of total samples). The experimental results indicated that the heavy metals and arsenic found in rice collected from mining activity zone were higher than those in rice harvested from normal cultivated areas like the Red River Delta. The heavy metals and arsenic content in Vietnamese rice samples were also compared with the concentration of heavy metals in other foreign rice samples in some recent publications. The estimated daily intake through rice consumption was calculated and compared with the level proposed by the Food and Agriculture Organization of the United Nations. The results indicated that the provisional daily intake of Cd was higher than the level proposed by FAO, while the intake of other heavy metals was in an acceptable range of CODEX standard.

Health Risk Assessment of Heavy Metals in Soils before Rice Sowing and at Harvesting in Southern Jiangsu Province, China

Rice, one of the most important staple crops in China, is easily contaminated by heavy metal pollution from industrial development. In this work, we systematically investigated the heavy metal (Cr, Cd, Pb, Zn, and Cu) and metalloid (Hg and As) concentrations in paddy soils and different rice tissues in southern Jiangsu Province, China. The potential ecological hazard index method and in vitro simulation test were used to evaluate the influence of heavy metals on local resident health. The results showed that, before rice sowing and at the harvesting period, the order of Eri values was EriCd>EriHg>EriAs>EriPb>EriCu>EriCr>EriZn. The low-risk index values (91.63 and 30.29) for the heavy metals indicated the low risk at the two stages in the study area based on the potential ecological hazard index. As determined with Tessier’s five-stage sequential extraction procedure, the proportions of the chemical speciation of the heavy metals were as follows: residual > organic matter-bound > iron-manganese oxide-bound > carbonate-bound > exchangeable. The order of the values of the accumulation and transfer factors was Cd (3.16) > Cu (0.42) > Zn (0.28) > Pb (0.25) > As (0.07) > Cr (0.04) > Cr (0.03) and root > stem > leaves, respectively. In vitro simulation tests showed that, in both adults and children, the daily amount of Pb and Cd intake through the soil-oral cavity route in the study area did not exceed the daily tolerance for Pb and Cd proposed by the WHO. In summary, although there is no obvious danger to local adults and children, it is necessary to be aware of the possibility of rice contamination from Cd in the soil.

Adsorption of Heavy Metals on Soil Collected from Lixisol of Typical Karst Areas in the Presence of CaCO3 and Soil Clay and Their Competition Behavior

The content of heavy metals in the soil in Guizhou Province, which is a high-risk area for heavy metal exposure, is significantly higher than that in other areas in China. Therefore, the objective of this study was to evaluate the ability of CaCO3 and clay to accumulate heavy metals in topsoil sample collected from Lixisol using the method of indoor simulation. The results showed that the contents of Cu, Zn, Cd, Cr, Pb, Hg and As in the soil sample were 10.8 mg/kg, 125 mg/kg, 0.489 mg/kg, 23.5 mg/kg, 22.7 mg/kg, 58.3 mg/kg and 45.4 mg/kg, respectively. The soil pH values increased with the CaCO3 concentration in the soil, and the fluctuation of the soil pH values was weak after the CaCO3 concentrations reached 100 g/kg. The adsorption capacity of lime soil increased by approximately 10 mg/kg on average, and the desorption capacity decreased by approximately 300 mg/kg on average. The desorption of all heavy metals in this study did not change with increasing clay content. Pseudo-second-order kinetics were more suitable for describing the adsorption kinetics of heavy metals on the soil material, as evidenced by the higher R2 value. The Freundlich model can better describe the adsorption process of As on lime soil. The process of As, Cr, Cd and Hg adsorption on the soil sample was spontaneous and entropy-driven. Additionally, the process of Cu and Pb adsorption on the soil materials was spontaneous and enthalpy-driven. Generally, the adsorption and desorption of heavy metals in polluted soil increased and decreased, respectively, with increasing CaCO3 content. The effect of calcium carbonate on the accumulation of heavy metals in soil was greater than that of clay. In summary, CaCO3 and pH values in soil can be appropriately added in several areas polluted by heavy metals to enhance the crop yield and reduce the adsorption of heavy metals in soils.