Comparison of in vitro digestion methods for determining bioaccessibility of Hg in rice of China

A ratiometric fluorescent probe with a large Stokes shift for the detection of Hg2+ and its applications in environmental sample and living system analysis

Toxic mercury ions (Hg2+) can cause serious environmental pollution and accumulate in living organisms via the food chain. Therefore, monitoring Hg2+ is crucial in ensuring the safety of ecosystems and organisms. In this work, a novel ratiometric fluorescent probe CMT (5-(4-(diphenylamino)phenyl)-1-(7-hydroxy-coumarin-3-yl)-4-pentene-1,3-dione) based on coumarin was developed for detecting Hg2+, which displayed obvious fluorescence changes, a low detection limit (2.24 × 10-7 M), good selectivity, and a large Stokes shift (255 nm). The CMT probe could detect Hg2+ in real environmental soil and water samples. Furthermore, the CMT probe enabled the naked-eye detection of Hg2+ using test paper experiments. CMT was also applied for fluorescence imaging in living zebrafish and plants. This work provides a highly efficient tool for monitoring Hg2+ in environmental samples and biological systems.

Bioavailability-based risk assessment of various heavy metals via multi-exposure routes for children and teenagers in Beijing, China

Assessing the health risks of sensitive population, such as children and teenagers, through multiple exposure routes (MERs) such as ingestion, inhalation, and dermal contact is critical for policy creation that protects or reduces exposure to pollutants for all populations. Heavy metal (HM) contents in food and environmental media in Beijing, capital of China, were collected. Furthermore, on the basis of considering the bioavailability of HMs, we evaluated the multiple environmental routes and health risks to HMs in children and teenagers of eight age groups (2-<3, 3-<4, 4-<5, 5-<6, 6-<9, 9-<12, 12-<15, and 15-<18) in Beijing, China by Monte Carlo simulation approach. The main findings are as follows: lead exposure in children aged 2-<3 years exceeds the exposure dose (0.3 μg·kg-1·d-1) of 0.5 point reduction in intelligence quotient. Moreover, children aged 2-<3 and 6-<9 years have relatively high non-carcinogenic risk (NCR) of 1.32 and 1.30, respectively. The carcinogenic risk (CR) for children aged 6-<9 and 9-<12 years is 2.73×10-6 and 2.39×10-6, respectively. Specifically, the contributions of oral ingestion, dermal contact, and inhalation to the NCR were 69.5%, 18.9%, and 11.6%, respectively. Moreover, the combined NCR contributions of copper, cadmium, mercury, and arsenic (As) were about 69.4%. The contributions of the above three routes to the CR were 93.4%, 4.1%, and 2.5%, in that order, with the largest CR contribution of As being about 92.0%. This study can provide new ideas for accurately assessing the exposure and health risks of HMs in the population, and we believe that it is necessary to update the national standards for food and soil based on the bioavailability of HMs.

A high spatial resolution dataset for methylmercury exposure in Guangdong-Hong Kong-Macao Greater Bay Area

Dietary methylmercury (MeHg) exposure increases the risk of many human diseases. The Guangdong-Hong Kong-Macao Greater Bay Area (GBA) is the world's most populous bay area and people there might suffer a high risk of dietary MeHg exposure. However, there lacks a time-series high spatial resolution dataset for dietary MeHg exposure in the GBA. This study constructs a high spatial resolution (1 km × 1 km) dataset for dietary MeHg exposure in the GBA during 2009-2019. It first constructs the dietary MeHg exposure inventory for each county/district of the GBA, based on MeHg concentrations of foods (i.e., rice and fish in this study) and per capita rice and fish intake. Subsequently, this study spatializes the dietary MeHg exposure inventory at 1 km × 1 km scale, using gridded data for food consumption expenditure as the proxy. This dataset can describe the spatially explicit hotspots, distribution patterns, and variation trend of dietary MeHg exposure in the GBA. This dataset can support spatially explicit evaluation of MeHg-related health risks in the GBA.

Mercury and selenium co-ingestion assessment via rice consumption using an in-vitro method: Bioaccessibility and interactions

Mercury (Hg) was reported to accumulate in rice grains, and, together with the selenium (Se) was found in rice, the co-exposure of Hg-Se via rice consumption may present significant health effects to human. This research collected rice samples containing high Hg:high Se and high Se:low Hg concentrations from high Hg and high Se background areas. The physiologically based extraction test (PBET) in vitro digestion model was utilized to obtain bioaccessibility data from samples. The results showed relatively low bioaccessible for Hg (<60%) and Se (<25%) in both rice sample groups, and no statistically significant antagonism was identified. However, the correlations of Hg and Se bioaccessibility showed an inverse pattern for the two sample groups. A negative correlation was detected in the high Se background rice group and a positive correlation in the high Hg background group, suggesting various micro forms of Hg and Se in rice from different planting locations. In addition, when the benefit-risk value (BRV) was calculated, some "fake" positive results showed while Hg and Se concentrations were directly used, which indicated that bioaccessibility should not be neglected in benefit-risk assessment.

Bioaccessibility of Cu, Mn, Fe, and Zn in Fruit and Vegetables by the In Vitro UBM and Statistical Evaluation of the Results

The total, gastric, and gastro-intestinal Cu, Mn, Fe, and Zn concentrations in eight fruit and vegetable samples were investigated. The unified bioaccessibility method (UBM) developed by BARGE (Bioaccessibility Research Group of Europe) was performed for in vitro bioaccessibility experiments. Total and bioaccessible concentrations of Cu, Mn, Fe, and Zn were determined by ICP-OES and ICP-MS, respectively. The accuracy of the methods was verified using BGS 102 for the BARGE UBM and SRM 1573a for total analysis. The mean BF (%) order for Cu, Mn, Fe, and Zn was Mn (101) > Zn (88) > Fe (60) > Cu (30) in gastric phase and Mn (78) > Zn (69) > Fe (46) > Cu (29) in gastro-intestinal phase. The results show that Mn and Zn in all the samples have the greatest bioaccessible values, while the values for Cu are much lower. The relationships among total, gastric, and gastro-intestinal element concentrations were investigated using statistical analysis such as correlation analysis, principal component analysis (PCA), and cluster analysis (CA). Total and bioaccessible Cu, Mn, and Zn concentrations were significantly correlated with each other.

Assessing the factors impacting the bioaccessibility of mercury (Hg) in rice consumption by an in-vitro method

Mercury (Hg) in rice is drawing mounting concern since methylmercury (MeHg) was found capable of accumulating in rice. In-vitro bioaccessibility is a feasible and reliable method to assess the health effects of Hg in rice and has been utilized in a number of studies. This study was done to investigate the impact of cultivar, planting location, and cooking on the total mercury (THg) and MeHg bioaccessibility of rice, for which multiple statistical analysis methods were used to analyze the significance of their effects. The THg concentrations of rice samples taken from non-Hg contaminated areas of China were all below 15 ng/g and their MeHg concentrations were below 2 ng/g. Cooking could significantly reduce the MeHg bioaccessibility of rice because the MeHg was mainly combined with protein and the protein will be denatured during the cooking process, and then the denatured MeHg is difficult to be dissolved into the liquid phase. Indica- and japonica-type rice cultivars did not show significant differentiation in either the concentration of Hg or its bioaccessibility. However, the glutinous rice type differed significantly from the above rice types, and it showed greater bioaccessibility of THg and MeHg due to its distinct protein contents and starch properties. Planting location can affect the Hg concentration in rice and THg bioaccessibility but has a limited impact on MeHg bioaccessibility. Based on these results, two macro factors (rice cultivar, planting location) are presumed to impact Hg bioaccessibility by how they affect micro factors (i.e., Hg forms).

A fluorescent probe for rapid detection of low concentration mercury ions and its application in biological cells

As a toxic substance, mercury can easily cause harm to organisms and humans. The development of methods that allow rapid detection of low concentrations of mercury ions has a positive effect on the natural environment and human health. The fluorescent probe RBSH reported in this paper has a detection limit as low as 5.9 nM, and a fast response time and allows naked eye detection. We characterized its structure by nuclear magnetic resonance and mass spectrometry, and explored the response mechanism of the probe using Job's plot, and ¹H NMR and mass spectrometry. UV-vis spectrophotometry and fluorescence spectroscopy show the excellent optical properties of the probe RBSH. The low toxicity and high cell penetration capacity demonstrated by the cellular assay open up the possibility of biological experiments. By selecting hosts (natural water samples, soybean plants and zebrafish) where mercury ions are likely to be present in the biological chain for low concentration Hg²⁺ detection, the results all demonstrated the excellent performance of the probe RBSH.

Aging and phytoavailability of newly introduced and legacy cadmium in paddy soil and their bioaccessibility in rice grain distinguished by enriched isotope tracing

Phytoavailability of Cadmium (Cd) plays a critical role in its accumulation in soil-rice systems. However, differential aging and phytoavailability of newly introduced Cd (Cd_N) and legacy Cd (Cd_L) in the soil-rice system remains unknown. Moreover, distinguishing their aging and phytoavailability is challenging. Enriched ¹¹²Cd isotope was introduced into a series of pot experiments, combined with sequential extraction and isotope dilution (¹¹⁰Cd isotopic spike), to investigate the aging and distribution of Cd_N and Cd_L under different treatments. The treatments included simulated acid rain, slaked lime, and biochar. Cd_N aged quickly than Cd_L in flooded soil and its availability was similar to that of Cd_L after tillering stage. The grain Cd contents were positively correlated to Cd concentrations in the overlying water. Acid rain reduced the soil pH, increasing the grain Cd, while slaked lime reduced grain Cd content. The acidic biochar used in this study increased grain Cd, possibly through soil acidification-induced Cd release. The differences in bioaccumulation and translocation factors between Cd_N and Cd_L in rice plants under slaked lime and biochar treatments suggested their different in vivo complexations and translocations. Analysis of bioaccessibility of Cd_N and Cd_L in rice grains provided valuable insights regarding human Cd exposure.

An interlaboratory evaluation of the variability in arsenic and lead relative bioavailability when assessed using a mouse bioassay

Animal bioassays have been developed to estimate oral relative bioavailability (RBA) of metals in soil, dust, or food for accurate health risk assessment. However, the comparability in RBA estimates from different labs remains largely unclear. Using 12 soil and soil-like standard reference materials (SRMs), this study investigated variability in lead (Pb) and arsenic (As) RBA estimates employing a mouse bioassay in 3 labs at Nanjing University, University of Jinan, and Shandong Normal University. Two performances of the bioassay at Nanjing University in 2019 and 2020 showed reproducible Pb and As RBA estimates, but increasing the number of mouse replicates in 2020 produced more precise RBA measurements. Although there were inter-lab variations in diet consumption rate and metal accumulation in mouse liver and kidneys following SRM ingestion due to differences in diet composition, bioassays at 3 labs in 2019 yielded overall similar Pb and As RBA estimates for the 12 SRMs with strong linear correlations between each 2 of the 3 labs for Pb (R² = 0.95-0.98 and slope = 0.85-1.02) and As RBA outcomes (R² = 0.46-0.86 and slope = 0.56-0.79). The consistency in RBA estimates was attributed to the relative nature of the final bioavailability outcome, which might overcome the inter-lab variation in diet consumption and metal uptake in mice. These results increased the confidence of use of mouse bioassays in bioavailability studies.

Elevated CO2 and soil mercury stress affect photosynthetic characteristics and mercury accumulation of rice

This is a novel study about responses of leaf photosynthetic traits and plant mercury (Hg) accumulation of rice grown in Hg polluted soils to elevated CO₂ (ECO₂). The aim of this study was to provide basic information on the acclimation capacity of photosynthesis and Hg accumulation in rice grown in Hg polluted soil under ECO₂ at day, night, and full day. For this purpose, we analyzed leaf photosynthetic traits of rice at flowering and grain filling. In addition, chlorophyll content, soluble sugar and Malondialdehyde (MDA) of rice leaves were measured at flowering. Seed yield, ear number, grain number per ear, 1000-grain weight, total mercury (THg) and methylmercury (MeHg) contents were determined after harvest. Our results showed that Hg polluted soil and ECO₂ had no significant effect on leaf chlorophyll content and leaf mass per area (LMA) in rice. The contents of soluble sugar and MDA in leaves increased significantly under ECO₂. Mercury polluted soil treatment significantly reduced the light saturated CO₂ assimilation rate (A_sat) of rice leaves only at flowering, but not at grain filling. Night ECO₂ greatly improved rice leaf water use efficiency (WUE). ECO₂ greatly increased seed yield and ear number. In addition, ECO₂ did not affect THg accumulation in rice organs, but ECO₂ and Hg treatment had a significant interaction on MeHg in seeds, husks and roots.

Multiple metal(loid)s bioaccessibility from cooked seafood and health risk assessment

Seafood has been generally considered to be the main diet exposure source of metal(loid)s. We evaluated health risk of mercury (Hg), arsenic (As), cadmium (Cd), lead (Pb), chromium (Cr), nickel (Ni), copper (Cu), and zinc (Zn) through consumption of cooked seafood based on bioaccessibility, which was obtained by physiologically based extraction test method. Results showed that cooking practices could decrease metal(loid)s concentration from seafood (by 6.0-45.7%). Metal(loid)s release from seafood in this study followed the descending order of Hg > Zn > Ni > Cd > Pb > As > Cu > Cr. On average, cooking lowered the bioaccessibility of As, Hg, Cd, Pb, Ni, Cr, Cu, and Zn by 15.2, 26.1, 30.9, 30.7, 25.7, 31.2, 17.6, and 22.4%, respectively. Health risk calculation results showed that Cr, Ni, and Zn in seafood species in this study were within the human health benefits range. Hg, Cd, Pb, and Cu exposure from cooked seafood was within the safe dose. However, we found that there is a potential of having cancer (especially bladder and lung cancer) for people exposure to iAs from seafood based on bioaccessible contents the first time.

Methylmercury and inorganic mercury in Chinese commercial rice: Implications for overestimated human exposure and health risk

China is the largest rice producer and consumer in the world, and mercury (Hg) levels, particularly methylmercury (MeHg), in rice and health exposure risks are public concerns. Total Hg (THg) and MeHg levels in 767 (domestic = 709 and abroad = 58) Chinese commercial rice were investigated to evaluate Hg pollution level, dietary exposures and risks of IHg and MeHg. The mean rice THg and MeHg levels were 3.97 ± 2.33 μg/kg and 1.37 ± 1.18 μg/kg, respectively. The highest daily intake of MeHg and IHg were obtained in younger groups, accounted for 6% of the reference dose-0.1 μg/kg bw/day for MeHg, 0.3% of the provisional tolerance week intake-0.571 μg/kg bw/day for IHg. Residents in Central China and Southern China meet the highest rice Hg exposure, which were more than 7 times of those in Northwest China. Lower concentrations than earlier studies were observed along the implementations of strict policies since 2007. This may indicate that a declining temporal trend of Hg in Chinese grown rice and associated exposures could be obtained with the implementations of strict policies. Though there exist Hg pollution in commercial rice, Hg levels in Chinese commercial rice is generally safe compared with Hg polluted sites. Populations dwelling in China have relatively a quite low and safe MeHg and IHg exposure via the intake of commercial rice. Strict policies contributed to the decrease in THg and MeHg levels in Chinese-grown rice. More attention should be paid to younger groups.

Change in mercury speciation in seafood after cooking and gastrointestinal digestion

Mercury (Hg) is readily bioaccumulated in seafood, a common ingredient in indigenous cuisines throughout the world. This study investigates Hg speciation in cooked seafood after gastric and intestinal digestion. The results showed that the removal of Hg by washing was negligible. Additionally, the results of our calculations regarding the mass balance of Hg concentration indicated that cooking reduced Hg mainly by means of volatilization and that Hg²⁺ was more readily reduced than MeHg. Moreover, cooking lowered the bioaccessibility of Hg in seafood: the reduced percent of bioaccessible Hg²⁺ after cooking ranged from 2 to 35% (on average, 16%). The corresponding numbers were slightly lower compared with those for MeHg (on average, 19%). Furthermore, there might be a chemical transformation of Hg during in vitro gastrointestinal digestion. The results of in vivo tests in laboratory mice suggested that methylation of Hg mainly took place in the gastric tract, whereas demethylation of Hg occurred primarily during intestinal digestion. These findings indicate that the bioaccessibility of Hg²⁺ and MeHg was not only related to their initial concentrations in the food samples, but also that further studies on the mechanisms of Hg demethylation and methylation during gastrointestinal digestion are essential for more realistic risk assessments.

Occurrence and bioaccessibility of mercury in commercial rice samples in Montreal (Canada)

The objective of this study was to increase the understanding of mercury exposure via rice commonly consumed in a major North American city. Rice samples were collected from Montreal markets (n = 89) between 2016 and 2017 and analyzed for total mercury (THg) content. THg content ranged from 0.7 ± 0.1 to 9.3 ± 0.5 ng g^-1 dw. Significant differences (p < 0.05) were recorded among the various rice types and countries of origin. Overall, cooking had little effect on the THg concentrations in rice. Thiols play a major role in the fate of Hg, therefore thiol contents in rice were measured, and a weak but significant relationship between thiol and THg contents in rice (p < 0.05) was observed. An in vitro gastro-intestinal digestion method was used to assess the bioaccessibility rate of THg in cooked rice samples, and less than 44.5% of THg from the initial rice samples was bioaccessible after in vitro digestion. Dietary exposure to Hg through rice consumption was calculated for the typical Canadian population and values were all below current provisional tolerable weekly intake guidelines. This study improves our understanding of Hg exposures via rice in a large North American city.