Bioaccessibility Of Hg Research Articles

Green remediation of mercury-contaminated soil using iron sulfide nanoparticles: Immobilization performance and mechanisms, effects on soil properties, and life cycle assessment

Mercury (Hg) pollution in soil has grown into a severe environmental issue. Effective in situ immobilization techniques are crucially demanded. In this study, we explored the application of carboxymethyl cellulose stabilized iron sulfide nanoparticles (CMC-FeS) for in situ immobilization of Hg in soil. CMC-FeS (a CMC-to-FeS molar ratio of 0.0004) was prepared via the reaction between FeSO4 and Na2S using CMC as a stabilizer. Remedying the Hg-polluted soil using 0.03 % CMC-FeS via batch experiments effectively reduced the acid leachable Hg by 97.5 % upon equilibrium after 71 days. Column elution tests demonstrated that the addition of CMC-FeS decreased the peak Hg concentration by 89.9 % and the total Hg mass eluted by 94.9 % after 523 pore volumes. CMC-FeS immobilized Hg in soil via chemical precipitation, ion exchange, and surface complexation. After the CMC-FeS treatment, Hg was transformed from more available exchangeable, carbonate-bound, and organic material-bound forms into the less available residual fraction, reducing the environmental risk of soil Hg from medium to low. The application of CMC-FeS boosted the soil enzyme activities and enhanced the soil bacterial diversity whereas decreased the production of methylmercury. CMC-FeS also facilitated long-term immobilization of Hg in soil. The acid leachable Hg and relative Hg bioaccessibility was decreased. Lift cycle assessment indicated that the preparation and application of CMC-FeS for in situ Hg remediation in soil met green chemistry principles. The present study confirms that CMC-FeS can be applied as an efficient and “green” amending agent for long-term Hg immobilization in soil/sediment.

Quantification of trace heavy metals in environmental water, soil and atmospheric particulates with their bioaccessibility analysis

In this work, sulfhydryl (SH) functionalized magnetic covalent organic framework (COF) was synthesized by using 4-aldehyde phenyl butadiyne (DEBD) and 1,3,5-tris(4-aminophenyl) benzene (TAPB) as the monomers and ethanedithiol as the modifier, with the aid of thiol-alkyne “click” reaction. The prepared Fe3O4@COFTAPB-DEBD@SH exhibited relatively strong magnetism (32.8 emu g−1), good stability and selectivity to target analytes with a high sulfhydryl content (0.24 mmol g−1). Based on Fe3O4@COFTAPB-DEBD@SH, a method combining magnetic solid phase extraction with inductively coupled plasma mass spectrometry (ICP-MS) was developed for the quantitative analysis of trace metals. Under the optimal conditions, the method merited fast desorption kinetics (<2 min), adsorption kinetics (<20 min), fast phase separation (<1 min), high enrichment factor (100), and the detection limits for Cd, Hg, Pb and Bi were determined to be 1.18, 0.51, 4.91 and 0.39 ng L−1, respectively. A good resistance to complex matrices was demonstrated for the method in the analysis of soil, atmospheric particles and simulated pulmonary fluids samples. Certified reference materials (coal fly ash GBW08401 and soil GBW07427) were employed to validate the accuracy of the method. Four target metals in the range of 12.9–215 ng L−1, 0.06–24.6 μg g−1 and 0.52–33.1 ng m−3 were found in local water, soil and atmospheric particulates (PM), respectively. Additionally, artificial lysosome solution and gamble's solution were used to simulate human pulmonary fluid and the bioaccessibility of Cd, Hg, Pb and Bi in PM2.5 was evaluated to be 58.6–73.1 % and 1.3–7.1 %, respectively.

The effect of selenium co-ingestion on mercury bioaccessibility in contaminated fish of the Amazon region

Mercury (Hg) is a toxic element that contaminates humans by consuming fish with high concentrations due to biomagnification in the food chain. This situation primarily impacts the riverside population in the Amazon region, as fish is their staple food. The interaction between selenium (Se) and Hg is well known due to their respective conceptual Pearson (soft-soft) characteristics. However, there needs to be more understanding of the impact of Se co-ingestion on Hg bioaccessibility. This scenario has prompted the investigation into the effects of consuming Se-rich food on the potential bioaccessibility of Hg when simultaneously ingesting contaminated fish. Cold vapor atomic absorption spectrometry (CV-AAS) measured Hg, and a hydride generator (HG-AAS) was used for Se. The results indicated that the piscivorous species Cichla sp. (Tucunaré fish) exhibited a Hg concentration over twice the limit established by the European Commission: 2.94 ± 0.21 μg g−1 for raw fish and 2.64 ± 0.16 μg g−1 for cooked fish. Concomitant ingestion of beans can reduce the potential bioaccessibility of Hg by 42% (68.4 to 25.8), and Brazil nuts co-ingestion can be reduced by 45% (68.4 to 23.1). However, due to the high fish consumption in the riverside population's diet, the Hazard Index (HI) and Target Hazard Quotient (THQ) values, including beans and Brazil nuts, exceeded the safe limit, even though THQ had decreased by 55%, and 66% with adding beans and Brazil nuts, respectively. These findings underscore the significant potential of Se in reducing Hg bioaccessibility through co-ingestion of foods containing this element. Additionally, it highlights the importance of considering regional dietary habits when assessing potential health risks. The results also sound like a warning about the food safety of the local communities.

Oral and inhalation bioaccessibility of mercury in contaminated soils and potential health risk to the kidneys and neurodevelopment of children in Taiwan.

Health risk assessments of exposure to mercury (Hg) from soils via ingestion and inhalation are indispensable for Taiwanese people living in the vicinity of Hg-contaminated sites. In this study, anthropogenic soils were collected from various polluted sources in Taiwan. In vitro oral and inhalation bioaccessible fractions of Hg were analyzed to avoid from overestimating the exposure risk. Discrepancies in oral and inhalation bioaccessible levels of Hg in soils were found using different in vitro assays with different pH levels and chemical compositions. The freshly contaminated soil (soil S7) polluted by chlor-alkali production activity sampled before the site was remediated had the highest total Hg concentration of 1346mg/kg, with the highest oral bioaccessibility of 26.2% as analyzed by SW-846 Method 1340 and inhalation bioaccessibility of 30.5% as analyzed by modified Gamble's solution. The lesser extent of aging of Hg in soil S7 increased the Hg availability for humans, which was also found based on results of a sequential extraction procedure. Results of the hazard quotient showed that soil ingestion was the main pathway causing non-carcinogenic risks for children and adults. Children were also exposed to higher risks than were adults due to higher frequencies of hand-to-mouth behaviors and lower body weights. Furthermore, hazard index results adjusted for oral and inhalation bioaccessible Hg were lower than those obtained based on the total Hg content; however, an unacceptable value of the non-carcinogenic risk (> 1) for children living near soil S7 was still observed. This study suggests that children living near sites polluted for a short period of time may suffer potential renal effects regardless of the bioaccessibility. Our findings provide suggestions for decision makers on setting new strategies for managing risks of Hg-contaminated soils in Taiwan.

Effects of cooking methods and co-ingested foods on mercury bioaccessibility in pontic shad (Alosa immaculata)

Human mercury (Hg) exposure is mostly caused by eating fish. However, there are major differences between the measured and predicted mercury concentration on Hg bioavailability. This study investigated the effects of cooking (steaming, baking, frying, marinating, and smoking) and selected components' co-ingestion on Hg bioaccessibility. Baking and frying reduced Hg bioaccessibility compared to the raw sample. The bioaccessible Hg fraction in fish was assessed through in vitro digestion method. Hg bioaccessibility varied from 4.31 to nearly 24.95% and the Hg recovery rate varied from 63.44 to 78.74%. Co-ingested garlic and broccoli with pontic shad had a positive effect on decreasing fish Hg bioaccessibility. The antioxidant activity of co-ingested food items was also calculated and correlated with mercury bioaccessibility. These results highlighted a possible positive role of plant-based foods and other food processing techniques in the bioaccessibility reduction of other chemical contaminants found in food sources.

Bioaccessibility and health risk assessment of trace metals in Nanjing park dust

The bioaccessibility, chemical fractions, and total concentrations of Hg, As, Mn, Ni, Cd, Cr, Cu, Pb and Zn were determined in 17 urban park dust samples collected from a megacity in China. The geoaccumulation index indicated heavy Hg pollution, moderate Cd pollution, and slight to moderate Cu, Pb and Zn pollution. The inhalation bioaccessibility measured by the Artificial Lysosomal Fluid method decreased in the order of Cd > Zn > Mn > Ni > Pb > As > Cr > Cu. The ingestion bioaccessibility measured by the Physiologically Based Extraction Test decreased in the order of Cd > Zn > Mn > Cu > Pb > As > Ni > Cr. The modified European Community Bureau of Reference method was used to extract the chemical fractions of trace metals. As (87%), Cr (87%), and Hg (99%) were predominantly found in residual fraction (F4), whereas Cd was predominantly found in water soluble and exchangeable fraction (F1 34%) and carbonate, oxidizable and reducible fraction (F2 27%). The first two chemical fractions of the trace metals were closely correlated with their bioaccessibilities. The carcinogenic and non-carcinogenic risks of exposure to trace metals in park dust were assessed using inhalation bioaccessibility and ingestion bioaccessibility. The hazard indexes of all investigated trace metals were below the safe level of 1. The carcinogenic risks of As, Ni, Cd and Cr were also below the acceptable level (10−6), indicating that there was no non-carcinogenic or carcinogenic risk from trace metals in the park dust.

Mercury bioaccessibility in fish and seafood: Effect of method, cooking and trophic level on consumption risk assessment

The bioaccessible Hg fraction in fish and seafood commonly present in the Mediterranean diet was assessed through three distinct in vitro extraction schemes. Each extraction method provided different results, highlighting the lack of a universal methodology to estimate mercury (Hg) bioaccessibility in those matrices. Bioaccessible Hg fractions ranged from 10 to nearly 90% of total mercury (T-Hg) and increased in predator species (Swordfish - Xiphias gladius, Blue Shark - Prionace glauca and Tuna - Thunnus sp.). Among the three extractions tested, the Unified Bioaccessibility Method (UBM) provided the highest estimation of Hg bioaccessibility for consumers. The tested cooking procedures (frying, grilling and steaming) considerably reduced the bioaccessible fraction. Results indicate that bioaccessible Hg found in ingested fish and seafood is far below the levels set by the current safety risk assessment legislation. These findings highlight the importance of integrating bioaccessibility measurements in food safety legislation.

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 new method of predicting the contribution of TGM to Hg in white rice: Using leaf THg and implications for Hg risk control in Wanshan Hg mine area

Rice plants accumulate Hg from the soil and ambient air, however, evaluating the contribution of Hg from these two sources remains challenging. Here, we proposed a practical method to predict the contribution of total gaseous mercury (TGM) to Hg in white rice in Wanshan Hg mine area (WMM). In this study, rice was planted in the same low-Hg soil at different sites of WMM with varying TGM levels. Comparing to the control sites at IG (Institute of Geochemistry, Guiyang), TGM is the dominant source of Hg in rice leaves and white rice at TB (Tianba) and ZJW (Zhangjiawan) sites of WMM. Subsequently, a good correlation between the Hg concentrations in rice leaves and the concentration contributions of TGM to Hg in white rice was obtained. Such a correlation enabled feasible quantification of the contribution of TGM to Hg in white rice collected from the Wanshan Hg mine. The contribution of TGM to Hg in white rice across the WMM area was also estimated, demonstrating that white rice receives 14–83% of Hg from the air. Considering the high contribution of TGM to Hg in white rice, we compared the relative health risks of Hg via inhalation and rice consumption and found that inhalation, rather than rice consumption, was the major pathway for bioaccessible Hg exposure in adults at high-TGM sites. This study provides new knowledge of Hg biogeochemistry in Hg-mining areas.

Contamination, oral bioaccessibility and human health risk assessment of thallium and other metal(loid)s in farmland soils around a historic Tl[sbnd]Hg mining area

In this study, tweenty-nine soil samples were collected from a historic TlHg mining area, located in southwest Guizhou, China. Total concentrations of metal(loid)s in soils and in vitro extracts were analysed by ICP-MS, and the bioaccessibility of metal(loid)s was conducted by two often used in vitro extraction methods, Simplified bioaccessibility Extraction Test (SBET) and Physiologically Based Extraction Test (PBET). The health risk assessment based on total concentrations of metal(loid)s, bioaccessibility of SBET and PBET through soil ingestion were investigated. Results indicated that the collected cultivated soils contained elevated concentrations of Tl (44.8 ± 67.7 mg kg−1), Hg (110 ± 193 mg kg−1), As (84.4 ± 89.2 mg kg−1) and Sb (14.8 ± 24.8 mg kg−1), exceeding the regional background values of Guizhou province, China and the Chinese farmland risk screening values. However, the bioaccessibility of Tl, Hg, As and Sb were relatively low, usually less than 30% for most samples and varied greatly among metal(loid)s and sampling sites. The average bioaccessibility values of Tl, Hg, As and Sb by SBET were lower than those by PBET. The non-carsinogenic risk (HQ and HI) and Carcinogenic Risk (CR) values were significantly reduced when incorporating the bioaccessibiltiy of metal(loid)s into health risk assessment. It is worth noting that the health risk to children exceeded adults. Moreover, Tl and As contributed the most to the risk, indicating that more attention should be paid on Tl and As during the daily environmental regulation and management of contaminated soils in Lanmuchang.

Green tea infusion reduces mercury bioaccessibility and dietary exposure from raw and cooked fish

Human exposure to mercury (Hg) and methylmercury (MeHg) through the ingestion of seafood raises human health-related concerns. In contrast, green tea has health benefits and its consumption potentially reduces bioaccessibility of dietary Hg. The present study aimed to assess the effect of green tea in total mercury (THg) and MeHg bioaccessibility in raw and cooked marine fish species commonly having high Hg levels. Preliminary results demonstrated that significantly higher reductions of bioaccessible THg were attained after the co-ingestion of green tea infusion (1 cup or more) in the oral and intestinal phases. Overall, the present findings clearly show that the co-ingestion of green tea along with seafood grilling strongly reduces THg and MeHg bioaccessibility in all fish species and consequently diminishes the probability of exceeding MeHg provisional tolerable weekly intakes through the consumption of these species with high Hg levels. Such results point out the need to better understand the beneficial/preventive role of green tea infusions and other food processing techniques in bioaccessibility reduction of other chemical contaminants present in food products. Such information is certainly useful to help consumers to wisely select their food, and to enable food safety authorities to integrate such information in risk assessment.

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.

Mercury fractionation in tropical soils: A critical point of view

Problems related to specificity and re-precipitation of metals in sequential chemical extractions can impair their routine use. In order to test the efficiency of a sequential chemical procedure, model compounds composed by soil components commonly found in tropical soils such as goethite, Al-goethite, ferrihydrite, hematite, bauxite, and humic acid were incubated with either Hg(NO3)2 or HgSO4 and submitted to chemical extraction. The procedure aims to assess: (i) water soluble Hg; (ii) bioaccessible Hg at pH near human stomach; (iii) Hg associated with organic matter; (iv) reduced Hg; (v) Hg associated with Fe, Al, and Mn oxides; and, (vi) residual Hg. This procedure was also tested via single and sequential extractions using the surface and subsurface samples of two tropical soils, i.e., a Rhodic Acrudox and a Typic Hapludox, with and without lime application. Soil samples were submitted to an adsorption experiment with HgCl2 and a high adsorption percentage was observed. The majority of Hg at both single and sequential procedure was extracted by an acetic acid solution (pH = 2). Liming, soil depth, and soil type were not determinative on Hg extractability. The sequential extraction applied showed a lack specificity of Hg fractions, confirmed by the model components.

Innovative health risk assessments of heavy metals based on bioaccessibility due to the consumption of traditional animal medicines.

Few studies reported the extent of heavy metal accumulation in traditional Chinese medicines (TCMs). Currently, oral bioaccessibility of lead (Pb), cadmium (Cd), arsenic (As), mercury (Hg), and copper (Cu) present in traditional animal medicines was investigated with physiologically based extraction test-extracted in vitro model. We are the first to develop a health risk assessment strategy by combinational analysis of bioaccessible heavy metal levels to calculate target hazard quotient (THQ), target hazard index (THI) and cancer risk (CR), which has capacity to evaluate the heavy metal associated heath risk of traditional animal medicines. To precisely acquire a realistic risk assessment, questionnaire data was adopted to measure the frequency and duration of the exposure to traditional animal medicines, and the safety factor was highlighted as well. Our data revealed that the bioaccessibility of Hg was the lowest among the five heavy metals. After the adjustment with the bioaccessibility of each heavy metal to target hazard index (THI) values, excitingly, the results manifested that the consumption of traditional animal medicines might not exert an unacceptable health risk in a broad community. In addition, the CR values of As and Pb indicated that the risk of developing cancers was quite lower than their acceptable levels in the clinic.

Does the addition of ingredients affect mercury and cadmium bioaccessibility in seafood-based meals?

Despite the bioaccessibility of nutrients and contaminants present in individual seafood products has been thoroughly studied, information is extremely limited in what concerns complete seafood-based meals, where interactions between ingredients may occur. Hence, this study aimed to evaluate the effect of different ingredients and cooking processes in mercury (Hg) and cadmium (Cd) bioaccessibility in complete meals of tuna (Thunnus spp.) and edible crab (Cancer pagurus), respectively. The addition of ingredients/side dishes decreased Hg levels in cooked tuna meals, but increased Hg bioaccessibility (up to 31% of bioaccessible Hg in complete meals, against 13.5% in stewed tuna alone). Cd levels in edible crab meals were significantly decreased by the addition of ingredients (~36% and ~65% decrease in boiled crab and paté, respectively), but its' bioaccessibility was not significantly affected (>94% in all cases). Results showed that the weekly consumption of 2 complete tuna meals does not exceed MeHg tolerable weekly intake (TWI), whereas Cd's TWI is largely surpassed with the consumption of 50 g/week of edible crab meals. This highlights the importance of determining contaminant levels and bioaccessibility in a whole seafood-based meal context, as such approach enables a more realistic assessment of the risks that seafood can pose to consumers.

Food safety risk assessment of metal pollution in crayfish from two historical mining areas: Accounting for bioavailability and cooking extractability

Here we characterize the bioaccumulation of mercury (Hg) and lead (Pb) in red swamp crayfish (Procambarus clarkii) from two river courses in Central Spain that are impacted by historical Hg and Pb mining activities, respectively. We estimate the absolute oral bioavailability of metals in crayfish tissues by means of in vitro bioaccessibility simulations, and assess whether their consumption may imply a health risk for humans by estimating target hazard quotients and safe consumption rates. We also study the effect of cooking crayfish on the mobilization of the metal body burden in the context of the traditional Spanish cuisine. The results showed that crayfish from the mining districts accumulated a high level of Hg and Pb pollution in both the tail muscle and the carcass. The in vitro bioaccessibility of Hg and Pb in the edible part was 27.86 ± 4.05 and 33.73 ± 5.91%, respectively. Absolute bioavailability was estimated to be 38.31 for Hg, and 20.21 (adults) and 67.35% (children) for Pb. Risk indices indicated that, even after adjusting for bioavailability, it is not safe to consume crayfish from the mining-impacted rivers because of their high levels of Hg and Pb. Using the carcass as a condiment for flavouring should also be avoided. The cooking procedure extracted relatively small amounts of the total Hg (8.92 ± 2.13%) and Pb (1.68 ± 0.29%) body burden. Further research that will support human and ecological risk assessment, along with the implementation of advisory measures for the local population as regards crayfish consumption, are recommended.

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.

Chemical Form and Bioaccessibility of Mercury in Traditional Tibetan Medicines

Extremely high mercury (Hg) concentrations have been identified in traditional Tibetan medicine (TTM) products, but the chemical form and bioaccessibility of Hg remain unknown. We conducted experiments to explore whether the Hg contained in TTM is toxic. We determined that HgS is not the exclusive form of Hg in TTM; other compounds could be present in substantial quantities, ranging from 2 to 52% of the total Hg in commonly used TTMs. A substantial amount of Hg could be released from TTM after ingestion. In total, an average of 12 μg of Hg (mostly inorganic)/g (range of 0.41–25 μg of Hg/g) in TTMs was released into the liquid phase in simulated human gastrointestinal environments. However, different from the results from ingestion by fish, the release of Hg from TTM in the intestinal environment is larger than that in the gastric environment by a factor of 2. In the case of joint ingestion with protein-rich products, releases of methyl Hg and inorganic Hg from TTM in gastrointestinal environments could be...

Effect of Cooking on Speciation and In Vitro Bioaccessibility of Hg and As from Rice, Using Ordinary and Pressure Cookers.

Rice is the most widely consumed staple food for a large part of the world's human population, and owing to environmental pollution, it is a major source of human exposure to mercury (Hg) and arsenic (As). We evaluated the impact of cooking on the speciation and bioaccessibility of Hg and As from rice in this study. Results show that the dominant Hg and As species in rice from Guangzhou market in China were their inorganic forms (iHg and iAs), respectively. The cooking process modified the levels of Hg and As. Average Hg and As bioaccessibility in raw rice was 69.74 and 80.32%, respectively. Hg bioaccessibility decreased to 46.22 and 42.37% for pressure- and ordinary-cooked rice, respectively. In contrast, As bioaccessibility remained unchanged except after cooking with a large amount of water. Protein denaturation and the amount of soluble and volatile forms determine the bioaccessibility of Hg and As in cooked rice by being released into the cooking water or into the air. From the bioaccessibility data, the average established daily intake (EDI) values of Hg and As from pressure-cooked rice for children and adults were 0.034 and 0.025μgkg-1day-1 (Hg), and 0.735 and 0.559μgkg-1day-1 (As), respectively. This study provides novel insights into Hg and As exposure due to rice cooking.

MERCURY POLLUTION ASSESSMENT OF MINING WASTES AND SOILS FROM FORMER SILVER AMALGAMATION AREA IN NORTH-CENTRAL MEXICO

Mining wastes and soils from Cedral, San Luis Potosi, Mexico, were studied to assess mercury (Hg) pollution in areas of historical silver (Ag) amalgamation and in areas where amalgamation mining wastes were recently reprocessed for Hg and Ag recovery. The total, soluble and bioaccessible Hg concentrations from eight mining waste and nine soil cores were determined at varying depths, which fluctuated from the surface up to 1.0 m depth. The total Hg concentrations in the mining wastes samples ranged from 8 to 548 mg/kg. The total Hg concentrations in the soil samples were lower (1 to 116 mg/kg) than those in the mining wastes. Eighty percent of the soil samples exceeded the maximum permissible limit for residential soils according to the Mexican regulations, demonstrating the impacts of the amalgamation process in Cedral. The soluble Hg concentrations were low, from 0.009 to 0.32 mg/kg in the mining wastes, and from 0.003 to 0.02 mg/kg in soils. The latter represents 0.007 % to 0.54 % and < 0.03 % of total Hg, from mining wastes and soils, respectively, indicating low aqueous Hg transport during rainfall events. The bioaccessible Hg concentrations in the mining waste samples (0.1 to 60 mg/kg) and soil samples (0.1 to 17 mg/kg), suggested that humans could be exposed to this toxic element through the accidental ingestion of mining wastes and soil particles. Although the total Hg concentrations in the mining wastes decreased after reprocessing, the soluble and bioaccessible Hg concentrations increased.