Bioavailability Of Mercury In Soil Research Articles

The Effects of Different Soil Component Couplings on the Methylation and Bioavailability of Mercury in Soil.

Soil composition can influence the chemical forms and bioavailability of soil mercury (Hg). However, previous studies have predominantly focused on the influence of individual components on the biogeochemical behavior of soil Hg, while the influence of various component interactions among several individual factors remain unclear. In this study, artificial soil was prepared by precisely regulating its components, and a controlled potted experiment was conducted to investigate the influence of various organic and inorganic constituents, as well as different soil textures resulting from their coupling, on soil Hg methylation and its bioavailability. Our findings show that inorganic components in the soils primarily exhibit adsorption and fixation effects on Hg, thereby reducing the accumulation of total mercury (THg) and methylmercury (MeHg) in plants. It is noteworthy that iron sulfide simultaneously resulted in an increase in soil MeHg concentration (277%). Concentrations of THg and MeHg in soil with peat were lower in rice but greater in spinach. A correlation analysis indicated that the size of soil particles was a crucial factor affecting the accumulation of Hg in plants. Consequently, even though fulvic acid activated soil Hg, it significantly increased the proportion of soil particles smaller than 100.8 μm, thus inhibiting the accumulation of Hg in plants, particularly reducing the concentration of THg (93%) and MeHg (85%) in water spinach. These results demonstrate that the interaction of organic and inorganic components can influence the biogeochemical behavior of soil Hg not only through their chemical properties, but also by altering the soil texture.

Potential bioavailability of mercury in humus-coated clay minerals

It is well-known that both clay and organic matter in soils play a key role in mercury biogeochemistry, while their combined effect is less studied. In this study, kaolinite, vermiculite, and montmorillonite were coated or not with humus, and spiked with inorganic mercury (IHg) or methylmercury (MeHg). The potential bioavailability of mercury to plants or deposit-feeders was assessed by CaCl2 or bovine serum albumin (BSA) extraction. For uncoated clay, IHg or MeHg extraction was generally lower in montmorillonite, due to its greater number of functional groups. Humus coating increased partitioning of IHg (0.5%–13.7%) and MeHg (0.8%–52.9%) in clay, because clay-sorbed humus provided more strong binding sites for mercury. Furthermore, humus coating led to a decrease in IHg (3.0%–59.8% for CaCl2 and 2.1%–5.0% for BSA) and MeHg (8.9%–74.6% for CaCl2 and 0.5%–8.2% for BSA) extraction, due to strong binding between mercury and clay-sorbed humus. Among various humus-coated clay particles, mercury extraction by CaCl2 (mainly through cation exchange) was lowest in humus-coated vermiculite, explained by the strong binding between humus and vermiculite. The inhibitory effect of humus on mercury bioavailability was also evidenced by the negative relationship between mercury extraction by CaCl2 and mercury in the organo-complexed fraction. In contrast, extraction of mercury by BSA (principally through complexation) was lowest in humus-coated montmorillonite. This was because BSA itself could be extensively sorbed onto montmorillonite. Results suggested that humus-coated clay could substantially decrease the potential bioavailability of mercury in soils, which should be considered when assessing risk in mercury-contaminated soils.

Green waste compost as an amendment during induced phytoextraction of mercury-contaminated soil.

Phytoextraction of mercury-contaminated soils is a new strategy that consists of using the higher plants to make the soil contaminant nontoxic. The main problem that occurs during the process is the low solubility and bioavailability of mercury in soil. Therefore, some soil amendments can be used to increase the efficiency of the Hg phytoextraction process. The aim of the investigation was to use the commercial compost from municipal green wastes to increase the efficiency of phytoextraction of mercury-contaminated soil by Lepidium sativum L. plants and determine the leaching of Hg after compost amendment. The result of the study showed that Hg can be accumulated by L. sativum L. The application of compost increased both the accumulation by whole plant and translocation of Hg to shoots. Compost did not affect the plant biomass and its biometric parameters. Application of compost to the soil decreased the leaching of mercury in both acidic and neutral solutions regardless of growing medium composition and time of analysis. Due to Hg accumulation and translocation as well as its potential leaching in acidic and neutral solution, compost can be recommended as a soil amendment during the phytoextraction of mercury-contaminated soil.

Modified Wallschläger Sequential Extraction as a Tool for Evaluating the Mobility of Mercury

Abstract The presented studies were focused on evaluating the utility of one of sequential extraction methods for evaluating the bioavailability of mercury in soils polluted by this element. Soil samples collected from horizons 0-20 cm and 20-80 cm were subject to analysis of the basic physical and chemical properties of soils. Moreover, the total content of mercury was determined and sequential extraction of mercury was conducted using a modified five-stage Wallschläger method. The analyses show that the studied soils are characterized by a variable mercury content, the highest in the surface soil horizons. Sequential extraction of mercury in the analyzed soils has indicated that the highest percentage content in the total content had mercury linked with sulphides. A high content of mercury linked with organic matter was also noted. The content of bioavailable mercury did not exceed 1.5% of the total content.

Current Views on the Oral Bioavailability of Inorganic Mercury in Soil: Implications for Health Risk Assessments

Due to the presence of mercury at a number of major contaminated sites in the United States, the bioavailability of inorganic mercury in soil following ingestion has emerged as an important public health issue. Studies of the leachability/solubility of inorganic mercury in soil have shown that it is largely immobile, thereby suggesting that it will not be readily available for absorption in the gastrointestinal tract. Ignoring the effect of the soil matrix on decreasing bioavailability may result in a substantial overprediction of risks due to ingestion of contaminated soil. This paper discusses current knowledge about the oral bioavailability of inorganic mercury in soil and offers suggestions about how these data may be applied in human health risk assessment. Though precise estimates are not available, in vivo and in vitro estimates of the bioavailability of different inorganic mercury species in different matrices suggest that the bioavailability of mercury in soil is likely to be significantly less, on the order of at least three- to tenfold, than the bioavailability of mercuric chloride, the species used to derive the toxicity criteria for inorganic mercury. Because bioavailability can vary significantly with soil type, soil aging, the presence of co-contaminants and other factors, it is suggested that whenever the fiscal aspects justify a more precise estimate of bioavailability, site-specific estimates be developed. To develop a database for identifying a less expensive and more efficient method for estimating bioavailability, it is suggested that in vivo studies be conducted concurrently with in vitro studies. However, due to the lack of precision associated with the derivation of the most widely-used health guidance value for inorganic mercury (the USEPA RfD), additional work to address the uncertainties in the RfD is recommended.

ATSDR science panel on the bioavailability of mercury in soils: lessons learned.

On the basis of discussion and analysis during and following an ATSDR science panel on the bioavailability of mercury in soils, it is apparent that the default assumption of 100% relative bioavailability for mercury-contaminated soils is excessively conservative. However, current knowledge does not allow the development of default assumptions or guidelines for determining relative bioavailability of mercury in soils. Until such default assumptions or guidelines can be developed, site-specific assays of bioavailability, preferably using either animal bioassays or validated in vitro techniques, may provide the best approach for estimating soil-mercury bioavailability.