Effects of foliar application of Zn combined with organic matters on Cd accumulation and its chemical forms in rice.

Rice consumption is a key Cd exposure pathway, which poses a health risk to humans. Reducing cadmium (Cd) concentrations in rice remains challenging. In this study, a pot experiment was conducted to examine the effects of foliar spray of Zn combined with organic matters (including Zn-lysine (Zn-Lys), Zn-fulvic acid (Zn-FA), Zn-amino acid (Zn-AA), and Zn combined with glutathione (Zn + GSH)) on Cd accumulation in rice grains. Compared with the control group, all treatment groups exhibited reduced Cd concentration in rice grains, while improving plant growth, and reducing Cd transport from other tissues to the grains. Zn-FA was found to be the most effective fertilizer, which considerably reduced Cd concentrations in grains from 0.77 ± 0.068 to 0.14 ± 0.021 mg/kg and yielded reductions of up to 81%, which is within the Chinese food maximum tolerable limit of 0.2 mg/kg. Furthermore, the analysis of the chemical forms of Cd of rice tissues indicated that the treatment groups had increased proportions of integrated with pectates and protein in the stems. Except for the group treated with Zn-Lys spray, the percentages of undissolved Cd phosphate in the leaves were increased in all treatment groups, which reduced Cd toxicity to rice plants. The foliar application of Zn combined with organic matters may be a promising strategy to decrease Cd concentration in rice grains cultivated in severely Cd-contaminated agricultural soil, particularly in the karst area in southwest China with limited available cultivable agricultural land.

Significant biomagnification of methylmercury in songbird nestlings through a rice-based food web: Insights from stable mercury isotopes.

To elucidate the sources and transfer of mercury (Hg) in terrestrial food chains, particularly in heavily Hg-contaminated rice paddy ecosystems, we collected rice leaves, invertebrates, and Russet Sparrow nestlings from a clear food chain and analyzed the dietary compositions and potential Hg sources using stable Hg isotopes coupled with a Bayesian isotope mixing model (BIMM). Our findings indicated that MeHg exposure is dominant through the dietary route, with caterpillars, grasshoppers, and katydids being the main prey items, while the less provisioned spiders, dragonflies, and mantises contributed the most of the Hg to nestlings. We found minimal MIF but certain MDF in this terrestrial food chain and identified two distinct MeHg sources of dietary exposure and maternal transfer. We firstly found that the dietary route contributed substantially (almost tenfold) more MeHg to the nestlings than maternal transfer. These findings offer new insights into the integration of Hg from the dietary route and maternal transfers, enhancing our understanding of fluctuating Hg exposure risk during the nestling stage. Our study suggested that Hg isotopes combined with BIMM is an effective approach for tracing Hg sources in birds and for gaining in-depth insight into the trophic transfers and biomagnification of MeHg in food chains.

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.

Home-produced eggs: An important pathway of methylmercury exposure for residents in mercury mining areas, southwest China.

In light of the documented elevated concentrations of total mercury (Hg) and methylmercury (MeHg) in poultry originating from Hg-contaminated sites, a knowledge gap persists regarding the levels of Hg found in home-produced eggs (HPEs) and the associated dietary exposure risks in regions affected by Hg mining. To address this knowledge gap, a comprehensive investigation was undertaken with the primary objectives of ascertaining the concentrations of THg and MeHg in HPEs and evaluating the potential hazards associated with the consumption of eggs from the Wanshan Hg mining area in Southwest China. The results showed that THg concentrations in HPEs varied within a range of 10.5-809 ng/g (with a geometric mean (GM) of 64.1 ± 2.7 ng/g), whereas MeHg levels spanned from 1.3 to 291 ng/g (GM, 23.1 ± 3.4 ng/g). Remarkably, in half of all eggs, as well as those collected from regions significantly impacted by mining activities, THg concentrations exceeded the permissible maximum allowable value for fresh eggs (50 ng/g). Consumption of these eggs resulted in increased exposure risks associated with THg and MeHg, with GM values ranging from 0.024 to 0.17 µg/kg BW/day and 0.0089-0.066 µg/kg BW/day, respectively. Notably, the most substantial daily dosage was observed among children aged 2-3 years. The study found that consuming HPEs could result in a significant IQ reduction of 34.0 points for the whole mining area in a year. These findings highlight the potential exposure risk, particularly concerning MeHg, stemming from the consumption of local HPEs by residents in mining areas, thereby warranting serious consideration within the framework of Hg exposure risk assessment in mining locales.

The mercury flow through a terrestrial songbird food chain in subtropical pine forest: Elucidated by Bayesian isotope mixing model and stable mercury isotopes.

In order to comprehend the transfer of inorganic mercury (IHg) and methylmercury (MeHg) within food chains in terrestrial pine forests, we collected samples of Great Tit nestlings, common invertebrates, plants, and soil in a subtropical pine forest and used Bayesian isotope mixing model analysis, Hg daily intake, and stable Hg isotopes to elucidate the flow of MeHg and IHg in these food chains. Results indicate that caterpillars and cockroaches are the predominant prey items for nestlings, accounting for a combined contribution of 81.5%. Furthermore, caterpillars, cockroaches, and spiders were found to contribute the most (∼80%) of both IHg and MeHg that dietary accumulated in nestlings. The provisoned invertebrates tend to supply more IHg and diluting the proportion of MeHg as total Hg (MeHg%). Notably, nestling feathers displayed the highest Δ199Hg values but a relatively lower MeHg%, suggesting an imbalanced incorporation of Hg from maternal transfer and dietary accumulation during the nestling stage. This study highlights the efficacy of nestlings as indicators for identifying Hg sources and transfers in avian species and food chains. However, caution must be exercised when using Hg isotope compositions in growing feathers, and the contribution of maternally transferred Hg should not be ignored.

Aquatic methylmercury is a significant subsidy for terrestrial songbirds: Evidence from the odd mass-independent fractionation of mercury isotopes.

In contrast to aquatic food chains, knowledge of the origins and transfer of mercury (Hg) and methylmercury (MeHg) in terrestrial food chains is relatively limited, especially in songbirds. We collected soil, rice plants, aquatic and terrestrial invertebrates, small wild fish, and resident songbird feathers from an Hg-contaminated rice paddy ecosystem for an analysis of stable Hg isotopes to clarify the sources of Hg and its transfer in songbirds and their prey. Significant mass-dependent fractionation (MDF, δ202Hg), but no mass-independent fractionation (MIF, ∆199Hg) occurred in the trophic transfers in terrestrial food chains. Piscivorous, granivorous, and frugivorous songbirds and aquatic invertebrates were all characterized by elevated Δ199Hg values. The estimated MeHg isotopic compositions obtained using linear fitting and a binary mixing model explained both the terrestrial and aquatic origins of MeHg in the terrestrial food chains. We found that MeHg from aquatic habitats is an important subsidy for terrestrial songbirds, even those that feed mainly on seeds, fruits, or cereals. The results show that MIF of the MeHg isotope is a reliable tool to reveal MeHg sources in songbirds. Because the MeHg isotopic compositions was calculated with a binary mixing model or directly estimated from the high proportions of MeHg, compound-specific isotope analysis of Hg would be more useful for the interpretation of the Hg sources, and is highly recommended for future studies.

Soil exposure is the major fluoride exposure pathways for residents from the high-fluoride karst region in Southwest China.

In the karst areas of southwest China, soil fluoride levels are higher than in China (478 mg kg-1) and world (200 mg kg-1). High levels of F in the environment might pose a health risk to humans. The comprehensive exposure risk must be studied in this area. Herein, samples of crops and soil were collected from Bijie City, a typical karst area in southwest China, to investigate the pollution level and evaluate the comprehensive F exposure risk. The single-factor index (PFw) and the geological accumulation index (Igeo) were used. The hazard index (HI) was applied to assess exposure risk from multiple exposure routes. The results revealed that there is considerable F contamination in soil and crops in the study area. Average soil total fluorine (Ft) was 1139.13 mg kg-1, and soil water soluble F (Fw) was 3.792 mg kg-1. In corn, rice, wheat, and potatoes, F contents were 1.167-9.585, 1.222-6.698, 1.587-9.976, and 1.797-9.143 mg kg-1, respectively. The mean values of HI were 4.45 and 2.42 for children and adults, respectively, > 1, showing potential health risk exists. Youngsters are at a greater exposure risk than adults. From the results of contribution ratios of different exposure routes for health risk, the major exposure risk was determined to be from soil exposure. Based on this, we suggest that risk managers mainly strive to control the soil fluoride level and implement the risk education and communication.

Cadmium exposure as a key risk factor for residents in a world large-scale barite mining district, southwestern China.

Cadmium (Cd) contamination is easily generated during the mining and manufacturing of barium (Ba). In this study, concentrations of both Ba and Cd in rice, vegetables, pork, fish, drinking water, and soil samples from an active barite mining district were determined. Daily intakes of Ba and Cd, as well as corresponding health risks, were evaluated. The average total daily exposure doses of Cd were 0.0035 and 0.0012 mg/kg BW/day (geometric mean) in the mining zone (MZ) and the chemical plant zone (PZ), respectively. These values significantly exceed the provisional tolerable monthly intake (25 µg/kg BW/month, equal to 0.00083 mg/kg BW/day). Based on the daily exposure doses, vegetable consumption was the most significant Ba exposure route for residents, contributing around 66.1% of the total exposure. In contrast, rice consumption was the major Cd exposure pathway, accounting for about 85.6% of the total exposure. Although the geometric mean (0.17) and 95th percentile (P95, 0.75) of the total hazard quotient (HQ) for Ba were below the acceptable level (1), suggesting that there were no significant health effects caused by Ba exposure, Cd exposure was associated with significant health risks, with the geometric mean of the HQ (1.7) and the P95 (21) well above the acceptable limit (1), indicating the unacceptable non-carcinogenic risk of Cd exposure. In summary, high Cd exposure risk, rather than Ba, was observed for populations living in a large-scale active Ba mining area.

Multi-pathway mercury health risk assessment, categorization and prioritization in an abandoned mercury mining area: A pilot study for implementation of the Minamata Convention.

This is a systematic study of human health risk assessment (HHRA) and risk categorization for inorganic mercury (IHg) and methylmercury (MeHg) in Hg mining areas. A multi-pathway exposure model coupled with Monte Carlo simulation was constructed for the Wanshan Hg mining area (WSMM), Southwestern China, with consideration of oral ingestion (foodstuffs, water and soil), dermal contact (water and soil), and inhalation (gaseous Hg and particulate Hg). The results show that dietary intake (food and water), gaseous Hg inhalation, oral ingestion of soil particles, dermal contact, and particulate Hg inhalation comprised 88.3-96.3%, 3.49-6.14%, 0.14-5.3%, 0.02%, and <0.01% of total IHg ingestion, respectively. As expected, rice consumption contributed the highest proportion (86.3-92.7%) of MeHg. The study shows that the elevated MeHg exposure risk is the most significant issue in Hg mining areas. In addition, Hg risk categorization and prioritization in the WSMM are established for the first time based on rice-based exposure doses of IHg and MeHg. Target areas for future treatment and/or remediation are characterized according to thresholds of reference dose and provisional tolerable weekly intake for exposure doses, as well as risk screening values and risk control values for contaminated soil. The proposed multi-pathway exposure model is strongly recommended for the HHRA of Hg-contaminated sites worldwide and helps facilitate the implementation of the Minamata Convention on Mercury.

Dietary exposure assessment of cadmium, arsenic, and lead in market rice from Sri Lanka.

Rice is frequently reported to be contaminated with heavy metals (HMs); thus, the human health risks from its consumption have received increasing attention. A total of 165 commercial rice samples from Sri Lanka were collected to determine their cadmium (Cd), arsenic (As), and lead (Pb) concentrations. The exposure risk for Sri Lankans from the estimated daily intakes (EDIs) of these toxicants was assessed. Simultaneously, non-carcinogenic and carcinogenic risks were evaluated using hazard quotients (HQs) and the hazard index (HI). The results revealed that the average levels of Cd, As, and Pb in commercial rice were 0.080 ± 0.130, 0.077 ± 0.040, and 0.031 ± 0.050 mg/kg, respectively, with ranges of 0.003-0.727, 0.019-0.217, and 0.001-0.345 mg/kg (expressed on a dry weight basis), respectively. The average EDIs of Cd, inorganic As (iAs), and Pb were 0.772, 0.490, and 0.306 µg/kg body weight (bw)/day, respectively; these were below provisional tolerable weekly intake (PTWI) values recommended by the Joint FAO/WHO Expert Committee on Food Additives (JECFA), but iAs was above the recommended reference doses (RfDs) recommended by the United States Environmental Protection Agency (USEPA). However, approximately 25% and 75% of the Cd and iAs HQs for the Sri Lankan population, respectively, were greater than 1, suggesting a potential health risk, whereas the HQs for Pb was less than 1. Considering the additive effect, HI values of the P90, P95, P97.5, and P99 percentiles would reach 4.773, 6.458, 8.392, and 11.614, implying that intake of the combined metals might result in potential health risks.

Comparison and Risk Assessment for Trace Heavy Metals in Raw Pu-erh Tea with Different Storage Years.

This research conducted an exploration of the content of microelements (As, Cr, Cd, Pb, Cu, Zn, Mn, and Hg) in raw Pu-erh tea with different storage years. The contents of As, Cr, Cd, Pb, Cu, Zn, Mn, and Hg were 0.14, 0.82, 0.02, 0.52, 14.59, 33.51, 564.02, and 0.01 µg/g, respectively, and were all less than the national standard limit values in China. The target hazard quotients (THQs) of each heavy metal were all lower than 1, and the value of combined risk hazard index (HI) of all to adults was 0.221, which presents no health risk when consumed properly by adults of the raw Pu-erh tea infusions. Interestingly, there was no significant correlation between the heavy metal element (As, Cr, Cd, Pb, Cu, Zn, Mn, and Hg) contents and the THQ values of raw Pu-erh tea samples and storage years; the correlation coefficients (R2) range from 0.01 to 0.33 and from 0.01 to 0.57, respectively. The result showed that the storage years showed no effect on the exposure risk of heavy metals; the heavy metal elements in tea samples come from the atmosphere and soil.

Cadmium contamination in a soil-rice system and the associated health risk: An addressing concern caused by barium mining.

Cadmium (Cd) is associated with barite; however, its biogeochemical characteristics in environments impacted by barium (Ba) mining are not known. Here, we first revealed the characteristics of Cd concentrations, distributions, and chemical forms in the soil-rice system in Ba mining areas. The associated exposure and risk assessments of Cd via rice consumption were also conducted. Elevated levels of Cd with a wide range of 0.054-91 mg/kg were found in paddy soils, approximately 63% of which exceeded the national Grade II value for soil Cd levels in China (0.3 mg/kg). A significant positive correlation between the soil Cd and soil Ba demonstrated that large amounts of Cd were released into the environment from Ba mining. Cadmium accumulated remarkably in the rice grains (0.007-3.5 mg/kg). The chemical forms in the rice plants indicated that most of the Cd was in the pectate/protein fraction (F2, 92% in the grains and 61-71% in the other tissues), followed by the residual fraction (F3, 7.1% in the grains, 27-38% in the other tissues). A minor portion of Cd was in the soluble and aminophenol fraction (F1, 0.44% in the grains, 0.26-1.4% in the other tissues). The positive correlations observed between the grain Cd and F2 in the roots, stems and leaves suggested that Cd in the rice grain was mainly from F2. Similarly, the root F2 was also positively correlated with that in the stems/leaves, indicating the critical role of F2 in Cd2+ migration in rice tissues. The estimated average hazard quotient (2.5) and annual excess lifetime cancer risk (21 × 10-5 a-1) were higher than the safety levels of 1 and 5.0 × 10-5 a-1, respectively, showing that the dietary intake of Cd via rice consumption posed high health risks to residents. Our study demonstrated that more concerns should be paid to Cd contamination in Ba mining areas.

Impacts of selenium supplementation on soil mercury speciation, and inorganic mercury and methylmercury uptake in rice (Oryza sativa L.).

Rice grain is known to accumulate methylmercury (MeHg) and has been confirmed to be the major pathway of MeHg exposure to residents in mercury (Hg) mining areas in China. Selenium (Se) supplementation has been proven to be effective in mitigating the toxicity of Hg. To understand how Se supplementation influences soil Hg speciation, a wide range of Se (0-500 mg/kg) was applied to Hg polluted paddy soils in this study, which decreased MeHg concentration in soil from 2.95 ±â€¯0.36 to 0.69 ±â€¯0.16 µg/kg (or 77%). After Se addition, humic acid state Hg (F4) was transformed into strong-complexed state Hg (F5), indicating that Hg bound up to the non-sulfur functional groups of humic acid (non-RSH) was released and reabsorbed by strong binding Se functional group (F5). As a result, inorganic Hg (IHg) was reduced by >48%, 18%, and 80% in root, stem, and grain, respectively, however, the reduction was not apparent in leaf. Substantial reductions were also found for MeHg in grain and root, but not in stem and leaf. Soil is suggested to be the main source of both MeHg and IHg in rice grain. Such a finding may provide an idea for improving Hg-polluted paddies through controlling soil IHg and MeHg. Further research on the molecular structure of the strong-complexed Hg in F5 should be conducted to elucidate the mechanism of Hg-Se antagonism.

New insights into the chemical forms of extremely high methylmercury in songbird feathers from a contaminated site.

The chemical forms of mercury (Hg), particularly methylmercury (MeHg), in songbird feathers from an abandoned mining region were analyzed via X-ray absorption near-edge structure analysis (XANES). In feathers, proportions of MeHg as total mercury (75.6-100%) quantified by the XANES were directly comparable to the chemical extraction values (74.1-95.9%). Most of MeHg were bound with cysteine (Cys) and reduced glutathione (GSH), whereas inorganic mercury (IHg) was mainly bound with GSH. These results were consistent with those found in fish muscles and human hairs of both fish consumers and occupational Hg exposure populations. Our study suggested that chemical forms and speciation of Hg were highly dependent on the exposure sources and food consumption, respectively. Bird feathers were able to selectively accumulate MeHg due to their special binding ways. However, detailed mechanisms of Hg accumulation in bird feathers remain to be further elucidated.

Weir building: A potential cost-effective method for reducing mercury leaching from abandoned mining tailings.

To mitigate mercury (Hg) pollution and reduce Hg downstream transportation, a weir was designed by a river system that had been inflicted by leachate from the slagheap of the Yanwuping Hg mine in Wanshan Hg mining area. A whole year monitoring of Hg species was conducted, and the efficiency of Hg reduction by the weir application was evaluated. The Hg concentrations in the river water were significantly higher in the wet season than in the dry season. Waterflow was confirmed to be the main driving factor for Hg mobilization and transportation, and an episode study revealed that most Hg was released in times of storms. Increased monitoring and preventive maintenance measures need to be taken on barriers in advance of storms. A large proportion of the total Hg (THg) and methylmercury (MeHg) is associated to particles. During the study period, approximately 412 g THg and 4.04 g total MeHg (TMeHg) were released from the YMM slagheap, of which 167 g THg and 1.15 g TMeHg were retained by the weir. Annually, 40.4% THg and 38.4% TMeHg was retained by the weir. Weir construction is considered as a potential cost-effective measure to mitigate Hg in river water and should be promoted and extended in the future after optimization.

Barium concentrations and speciation in surface waters collected from an active barium mining area in Guizhou Province, southwestern China.

Barium (Ba) is a toxic element and can cause serious health effects. Humans have experienced increased exposure to Ba due to its intensive usage in industrial areas and daily life. Anthropogenic activities of Ba mining and the manufacture of Ba containing products introduce the element into surrounding areas, posing environmental concerns. Concentrations of total Ba (TBa) and dissolved Ba (DBa) in water samples collected from active Ba mines in Tianzhu, east Guizhou Province, southwestern China were measured to show the regional dispersion of Ba contamination. Aqueous Ba species in water were calculated using the PHREEQC program. The results showed that TBa and DBa concentrations ranged from 6.7 to 483.1 µg/L and from 7.5 to 222.7 µg/L, respectively. TBa concentrations presented a high average value of 126.6 µg/L and greatly exceeded the reported common value of 10 µg/L Ba in surface water set by the Ministry of Environment Protection of China. PHREEQC results indicated that Ba species in water were present as Ba2+, BaSO4, BaHCO3, BaCO3, and BaOH+. The distribution of Ba species in water is controlled by pH and total organic carbon (TOC), and the lower pH (pH < 7) the higher the dissolved fractions. The log K d values (K d , dissolved-particulate distribution coefficients) varied from 2.41 to 6.32. Significant correlations were observed among Ba2+ and K+, Na+, Cl-, NO3-, with Pearson correlation coefficients of 0.425, 0.531, 0.853, 0.612, and 0.329, respectively (p < 0.01). Elevated Ba concentrations in water indicated that the Ba contamination and its distribution pattern in local aquatic ecosystems are derived from Ba mining sites in the Tianzhu area.