Methylmercury In Soils Research Articles

Selenium–phosphorus modified biochar reduces mercury methylation and bioavailability in agricultural soil

Biochar is a frequently employed for solidifying and stabilizing mercury (Hg) contamination in soil. However, it often results in an elevated presence of soil methylmercury (MeHg), which introduces new environmental risks. Consequently, there is a necessity for developing a safer modified biochar for use in Hg-contaminated soil. This study employed sodium selenite (at a safe dosage for soil) and hydroxyapatite to modify straw biochar (BC) based on the interaction between selenium (Se) and phosphorus (P). This process led to the formation of Se-modified biochar (Se-BC), P-modified biochar (P-BC), and Se and P co-modified biochar (Se-P-BC). Additionally, solvent adsorption experiments and pot experiments (BC/soil mass ratio: 0.5 %) were conducted to investigate the impacts of these soil amendments on soil Hg methylation and bioavailability. Se and P co-modification substantially increased the surface area, pore volume, and Hg adsorption capacity of BC. BC treatment increased the simulated gastric acid-soluble Hg, organo-chelated Hg, and MeHg in the soil. Conversely, Se-P-BC significantly reduced these forms of Hg in the soil, indicating that Se-P-BC can transform soil Hg into less bioavailable states. Among the different biochar treatments, Se-P-BC exhibited the most pronounced reductions in soil MeHg, total Hg, and MeHg in water spinach, achieving reductions of 63 %, 71 %, and 70 %, respectively. The co-modification of Se and P displayed a synergistic reduction effect in managing soil Hg pollution, which is associated with the increase of available Se in the soil due to phosphorus addition. The significantly reduced dissolved organic carbon and the abnormally high SO42− concentration in the soil of Se-P-BC treatment also inhibited Hg methylation and bioavailability in the soil. In summary, Se-P-BC substantially increased reduction percentage in plant Hg content while mitigating the risk of secondary pollution arising from elevated soil MeHg.

Methylmercury content in soil and litter from the Amazonian rainforest and its potential fate during forest fires

Methylmercury in soils and vegetation from the Amazonian rainforest is still poorly studied. Hence, the aim of this work was to determine the total mercury [THg] and methylmercury [MeHg] concentrations in litter and surface soil, MeHg deposition via litterfall, and the MeHg fate during a forest fire in the Amazonian rainforest. Sampling of litter, soil (0–1, 1–2, and 2–5 cm), and ash was carried out before (BB) and after (AB) a prescribed forest fire. The results showed a low [THg] (34 ± 8 ng g-1) and [MeHg] (0.16 ± 0.03 ng g-1) value in litter, with a correspondingly low estimate of the MeHg litterfall flux (0.13 ± 0.03 μgm-2yr-1) which has been probably underestimated due to potential losses during the field experiment. In ashes, [THg] and [MeHg] values were 23 ± 8 ng g-1and 0.11 ± 0.04 ng g-1, respectively. Although a significant part of Hg contained in the biomass was lost during the fire, the [MeHg]/[THg] ratio was not affected by it and was the same in litterfall and ash (∼0.5%). In soil, the average [THg] BB value was 149 ± 12 ng g-1in the three layers and [MeHg] was between 0.8 and 1.0 ng g-1. The forest fire only affected the superficial soil, with a significant decrease of [THg] and [MeHg] in the 0-1 cm layer. Similarly, the decrease of the [MeHg]/[THg] ratio in the surface soil layer suggested that MeHg was more readily emitted or degraded than the other Hg species present.

Development of a Solid Phase Extraction-Based Method for the Quantitative Analysis of Methylmercury in Soil and Sediment.

A simple, universal method to quantify soil methylmercury (MeHg) is not available. Here, we developed a solid-phase extraction-based method using gas chromatography mass spectrometry. MeHg was purified from the soil matrix using an optimized solid-phase extraction method, which reduced the use of organic solvents and eliminated the requirement for harmful reagents. The sample limit of quantification was 7.5ng/g. MeHg recovery in the reference samples was 96.2%-102.6%; the intra- and inter-assay coefficients of variation were 3.4%-7.1% and 4.3%-7.1%, respectively, indicating high validation performance. This analysis method is simple as it can be performed using general-purpose reagents and instruments; has a high degree of trueness and accuracy; could be useful for soil MeHg quantification with improved sensitivity; and can provide reliable data to prevent MeHg contamination and improve food safety.

Assessment of the Bioavailability of Mercury Sulfides in Paddy Soils Using Sodium Thiosulfate Extraction - Results from Microcosm Experiments

Mercury sulfides (HgS), one of the largest Hg sinks in the lithosphere, has long been considered to be highly inert. Recently, several HgS speciation (e.g., nano- or micro-sized HgS particles) in paddy soils have been found to be reactive and bioavailable, increasing the possibility of methylation and bioaccumulation and posing a potential risk to humans. However, a simple and uniform method for investigating HgS bioavailability is still lacking. To address this issue, we extracted dissolved Hg from HgS particles by sodium thiosulfate (Na2S2O3) in paddy soils and analyzed the correlation between extracted Hg and soil methylmercury (MeHg). Results showed that the amounts of Hg extracted by Na2S2O3 had a strong positive correlation with the levels of soil MeHg (R 2 adj = 0.893, p < 0.05). It is suggested that Na2S2O3 extraction may be a good method of predicting Hg bioavailability in paddy soils. Our results would help to give clues in better predicting Hg risk in natural environments.

Extraction and Quantification of Nanoparticulate Mercury in Natural Soils.

Nanoparticulate mercury (Hg-NPs) are ubiquitous in nature. However, the lack of data on their concentration in soils impedes reliable risk assessments. This is due to the analytical difficulties resulting from low ambient Hg concentrations and background interferences of heterogeneous soil components. Here, coupled to single particle inductively coupled plasma-mass spectrometry (spICP-MS), a standardized protocol was developed for extraction and quantification of Hg-NPs in natural soils with a wide range of properties. High particle number-, particle mass-, and total mass-based recoveries were obtained for spiked HgS-NPs (74-120%). Indigenous Hg-NPs across soils were within 107-1011 NPs g-1, corresponding to 3-40% of total Hg on a mass basis. Metacinnabar was the primary Hg species in extracted samples from the Wanshan mercury mining site, as characterized by X-ray absorption spectroscopy and transmission electron microscopy. In agreement with the spICP-MS analysis, electron microscopy revealed comparable size distribution for nanoparticles larger than 27 nm. These indigenous Hg-NPs contributed to 5-65% of the measured methylmercury in soils. This work paves the way for experimental determinations of indigenous Hg-NPs in natural soils, which is critical to understand the biogeochemical cycling of mercury and thereby the methylation processes governing the public exposure to methylmercury.

Geochemistry of mercury in soils and water sediments

&lt;abstract&gt; &lt;p&gt;Our paper reviews the current understanding of mercury in the environment of soil and sediment, including sampling, mobilization phases and analyzing methods. As a dangerous trace element, mercury has been shown to have several harmful effects on the environment. Mercury is released into the environment in a variety of chemical forms by both geogenic and human activities, with the majority of it coming from anthropogenic sources. It is affected by environmental conditions such as pH, redox potential, light and temperature-all of which determine its final chemical form-reactivity and toxicity. Methylmercury is considered one of the most poisonous forms found in nature. Considering the methodologies of the studies carried out we have found that the best technique for preserving methylmercury in soil and sediment samples is to freeze it immediately after collection. Organically rich soils are related to higher total mercury levels. Plants, such as Solanum nigrum (BR3) and Cynodon dactylon (BR2), can play an important role in mercury transport and accumulation. Solid-phase selenium causes faster demethylation and slower methylation of mercury. Methylmercury can increase by climate change and thawing; arctic permafrost is a potential source of Hg. Chemical vapor generation inductively coupled plasma mass spectrometry was used to develop a simple and quick method for measuring methylmercury; ultrasonic agitation and HNO&lt;sub&gt;3&lt;/sub&gt; were used for the process, the last of which proved to be the most efficient for selective extraction of methylmercury.&lt;/p&gt; &lt;/abstract&gt;

Distribution of total and organic mercury in soils around an artisanal and small-scale gold mining area in West Java, Indonesia

This study was conducted to understand the environmental behavior of mercury released by artisanal and small-scale gold mining (ASGM) activities. For this purpose, we attempted to assess the effect of diffused mercury on mercury concentrations in soil, demonstrate the presence of methylmercury in soil affected by the deposited mercury and determine the reactions associated with methylmercury production. The vertical profiles of mercury were obtained from two sites in the forest of the ASGM village in Pongkor (West Java, Indonesia) and from two sites in Mount Halimun-Salak National Park, which is approximately 12 km from the ASGM village. The highest total mercury concentration, 8.9 mg kg−1, was observed for soil samples collected at the ASGM village. The mercury was concentrated at the surface or in the subsurface layers, and the concentrations were several times to more than ten times higher than the lowest values observed in the deeper layers at each site. Even in the national park, the highest concentration of 1.9 mg kg−1 was observed in the upper soil layer. These results suggest that the primary source of mercury in the forest soil is atmospheric deposition; fallen plant leaves also deliver accumulated mercury to the soil surface. The organic mercury percentages of the total mercury were 0.2 ± 0.1% for the national park and 0.3 ± 0.2% for ASGM sites. The vertical variation in organic mercury concentration did not always match that in total mercury concentration, which suggested that the formation of methylmercury in soil was closely related to the decomposition of organic matter near the surface. The soil surface is an important reaction field for methylmercury production in forested areas.

Inhibition and Remediation of Methylmercury Contaminated Soil by Use of Modified Montmorillonite

Montmorillonite was modified by 3-mercaptopyl trimethoxysilane and chitosan. The modified montmorillonite was characterized by XRD technology. The effects of thiol montmorillonite and chitosan montmorillonite on the inhibition and remediation of methylmercury contaminated soil under different water conditions were studied using laboratory simulation. XRD results showed that both thiol and chitosan were successfully loaded on the montmorillonite. The results of simulation tests showed that the addition of the remediation material to soil contaminated with methylmercury produced a better remediation effect. Compared with the blank control, the content of methylmercury in the soil was reduced by 82.10% (thiol montmorillonite) and 45.20% (chitosan montmorillonite), respectively, in the flooded condition. Under dry/wet alternation, the content of methyl mercury in soil decreased by 66.70% (thiol montmorillonite) and 49.79% (chitosan montmorillonite), respectively. Under drought conditions, the content of methylmercury in soil decreased by 44.66% (thiol montmorillonite), and the concentration of methylmercury in soil decreased by 54.37% after adding chitosan montmorillonite for 4 weeks. Compared with single modified montmorillonite, the repair effect of combined modified montmorillonite and lime treatment was not improved significantly.

Effects of Wetland Types on Distribution of Soil Methylmercury Based on the Region of Nanweng River in the Greater Xing'an Mountains

Methylmercury (MeHg) is the most toxic organic matter of all mercury (Hg) compounds. Its toxicity is far higher than that of inorganic Hg. Methylmercury can enter the human body through food, threatening human health. Based on the Nanweng River National Nature Reserve in the Greater Xing'an Mountains, the differences in the distribution of MeHg in soil samples collected from four types of wetlands, including medium swamp, low swamp, island forest, and forest soil, and the effect of the soil properties on the MeHg content were investigated in this study. The results show that:① the trends of the total Hg and MeHg levels are inconsistent. The order of the mean total Hg content is island forest (138.76 mg·kg-1±101.97 mg·kg-1) > forest soil (117.57 mg·kg-1±32.44 mg·kg-1) > low swamp (71.8 mg·kg-1±1.42 mg·kg-1) > median swamp (65.11 mg·kg-1±26.69 mg·kg-1), while the mean MeHg content is in the order of island forest (1.14 μg·kg-1±1.15 μg·kg-1) > medium swamp (0.87 μg·kg-1±1.06 μg·kg-1) > low swamp (0.28 μg·kg-1±0.06 μg·kg-1) > forest soil (0.1 μg·kg-1±0.05 μg·kg-1); ② the contents of MeHg in the island forest and medium swamp were relatively high and fluctuated dramatically, whereas the contents of MeHg in the low swamp and forest soil were lower and showed little change between each sampling point; ③ the longer the marsh wetland formation was, the higher was the MeHg content, that is, median swamp (0.87 μg·kg-1±1.06 μg·kg-1) > low swamp (0.28 μg·kg-1±0.06 μg·kg-1); the soil pH was positively correlated with MeHg (P<0.05); in the medium swamp area, the content of MeHg was positively related to the water content (WC), organic matter (OM%), carbon (C%), and total mercury (THg; P<0.05); in the island forest areas, the MeHg content showed a linear relationship with the soil pH and NH4+-N (P<0.05). This study reveals the distribution characteristics of MeHg and its influencing factors for different wetland ecosystems, providing data supporting the comprehensive evaluation of MeHg accumulation in wetland ecosystems.

Biochar and nitrate reduce risk of methylmercury in soils under straw amendment

There is growing evidence that incorporating crop straw into soils, which is being widely encouraged in many parts of the world, could increase net methylmercury (MeHg) production in soils and MeHg accumulation in crops. We explored the possibility of mitigating the risk of increased MeHg levels under straw amendment by transforming straw into biochar (BC). Greenhouse and batch experiments were conducted, in which soil MeHg concentrations, MeHg phytoavailability and accumulation in rice, dynamics of sulfate, nitrate and abundances of sulfate reducing bacteria (SRB) were compared in ‘Control’ (Hg contaminated soil), ‘Straw’ (soil with 1% rice straw), ‘Straw+BC’ (soil with 1% straw and 1% biochar), and ‘Straw+BC+N’ (soil with 1% straw, 1% biochar and 0.12% nitrate). Our results indicate that straw amendment increased MeHg concentrations in soils (28–136% higher) and rice plants (26% higher in grains, ‘Straw’ versus ‘Control’), while co-application of biochar with straw reduced grain MeHg levels (60% lower, ‘Straw+BC’ versus ‘Straw’). This could be mainly attributed to the reduced MeHg availability to rice plants (phytoavailability, extraction rates of MeHg by ammonium thiosulfate) under biochar amendment (64–99% lower, ‘Straw+BC’ versus ‘Straw’). However, biochar amendment enhanced soil MeHg levels (5–75% higher, ‘Straw+BC’ versus ‘Control’). Interestingly, nitrate addition helped reduce soil MeHg concentrations (11–41% lower, ‘Straw+BC+N’ versus ‘Straw+BC’) by facilitating nitrate reduction while inhibiting SRB activities. Subsequently, addition of nitrate with biochar, compared with biochar alone, further reduced grain MeHg levels by 34%. Therefore, straw biochar together with nitrate could possibly be effective in mitigating the risk of MeHg under straw amendment. Furthermore, the results evidence the impacts of straw management on the risk posed by MeHg in soils and emphasize the necessity to carefully consider the straw management policy in Hg-contaminated areas.

Deposition of mercury in forests across a montane elevation gradient: Elevational and seasonal patterns in methylmercury inputs and production

AbstractGlobal mercury contamination largely results from direct primary atmospheric and secondary legacy emissions, which can be deposited to ecosystems, converted to methylmercury, and bioaccumulated along food chains. We examined organic horizon soil samples collected across an elevational gradient on Whiteface Mountain in the Adirondack region of New York State, USA to determine spatial patterns in methylmercury concentrations across a forested montane landscape. We found that soil methylmercury concentrations were highest in the midelevation coniferous zone (0.39 ± 0.07 ng/g) compared to the higher elevation alpine zone (0.28 ± 0.04 ng/g) and particularly the lower elevation deciduous zone (0.17 ± 0.02 ng/g), while the percent of total mercury as methylmercury in soils decreased with elevation. We also found a seasonal pattern in soil methylmercury concentrations, with peak methylmercury values occurring in July. Given elevational patterns in temperature and bioavailable total mercury (derived from mineralization of soil organic matter), soil methylmercury concentrations appear to be driven by soil processing of ionic Hg, as opposed to atmospheric deposition of methylmercury. These methylmercury results are consistent with spatial patterns of mercury concentrations in songbird species observed from other studies, suggesting that future declines in mercury emissions could be important for reducing exposure of mercury to montane avian species.

Effect of Sewage Sludge Compost Products Application on Total Mercury and Methylmercury in Soil and Plants

Two different sludge composting products (with and without biochar) were applied in field to study the variations of total mercury (THg) and methylmercury (MeHg) in soil and plants,as well as their migration in the soil-plant system and accumulation ability in plants during the sludge compost land use process.The results indicated that the concentrations THg and MeHg in soil increased after applying sewage sludge compost products,while the THg level was still lower than the secondary standard of national soil environmental quality.Biochar was speculated to probably promote the soil mercury methylation with lower MeHg/THg ratios in different soil treatments.THg concentrations in mature plants were significantly lower than those in seedling stage,but MeHg levels were higher than those in seedling stage.An obvious influence of composting on MeHg enrichment in plants was observed,and this similar effect was not found for THg enrichment.MeHg concentration in the soils applied with biochar compost was significantly higher than that without applying biochar compost soil,while MeHg in plant presented a contrary trend with higher level observed in no-biochar compost soil,suggesting that the addition of biochar could be in favour of soil MeHg formation and inhibit the MeHg accumulation in plants by influencing its migration.Since a strong MeHg accumulation ability with BCF of 1.24-14.63 was present in plant,the mercury ecological risk in soil environment caused by long-term fertilizing should be noticed.

Biogeochemical controls on methylmercury in soils and sediments: Implications for site management.

Management of Hg-contaminated sites poses particular challenges because methylmercury (MeHg), a potent bio-accumulative neurotoxin, is formed in the environment, and concentrations are not generally predictable based solely on total Hg (THg) concentrations. In this review, we examine the state of knowledge regarding the chemical, biological, and physical controls on MeHg production and identify those most critical for contaminated site assessment and management. We provide a list of parameters to assess Hg-contaminated soils and sediments with regard to their potential to be a source of MeHg to biota and therefore a risk to humans and ecological receptors. Because some measurable geochemical parameters (e.g., DOC) can have opposing effects on Hg methylation, we recommend focusing first on factors that describe the potential for Hg bio-accumulation: site characteristics, Hg and MeHg concentrations, Hg availability, and microbial activity, where practical. At some sites, more detailed assessment of biogeochemistry may be required to develop a conceptual site model for remedial decision making. Integr Environ Assess Manag 2017;13:249-263. © 2016 SETAC.

Effects of incorporating differently-treated rice straw on phytoavailability of methylmercury in soil.

Differently-treated crops straw is being widely used to fertilize soil, while the potential impacts of straw amendment on the biogeochemistry and phytoavailability of mercury in contaminated soils are largely unknown. In the present study, differently-treated rice straw (dry straw, composted straw, straw biochar, and straw ash) was incorporated into mercury-contaminated soil at an environment relevant level (1/100, w/w), and mercury speciation, methylmercury (MeHg) phytoavailability (using ammonium thiosulfate extraction method, validated elsewhere) and bioaccumulation (in Indian mustard Brassica junceas) were quantified. Our results indicated that incorporating straw biochar or composted straw into soil would decrease phytoavailable MeHg levels, possibly due to the strong binding of MeHg with particulate organic matter in amended straw ('MeHg immobilization effect'). Consequently, MeHg accumulation in aboveground tissue of Indian mustard harvested from straw biochar-amended soil decreased by 20% compared to the control. Differently, incorporation of dry straw resulted in elevated MeHg levels in soil ('Mercury methylation effect'). Decomposition of amended dry straw in soil would evidently increase DOC levels (averagely 40%-195% higher than the control), which may subsequently mobilize MeHg in the soil ('MeHg mobilization effect'). Accordingly, incorporation of dry straw led to increased phytoavailable MeHg levels in the soil and doubled MeHg accumulation in Indian mustard. Our results provided the first evidence that incorporating differently-treated rice straw into soil could have diverse effects on mercury biogeochemistry and phytoavailability, which should be taken into account in risk assessment or soil remediation.

Investigation of the potential for mercury release from flue gas desulfurization solids applied as an agricultural amendment.

The potential for beneficial use of flue gas desulfurization-derived gypsum (FGDG), a coal combustion byproduct, as an agricultural soil amendment is currently being debated. This study investigated the hypothesis that Hg released to air from FGDG will be reduced when amended to planted and bare soils. The potential for enhanced methylmercury (MeHg) production and Hg uptake by plants in soils amended with FGDG was also investigated. Flue gas desulfurization-derived gypsum from three sources was homogenized into three soils at 4.5, 45, and 170 t ha and applied at 4.9 t ha as a thin layer to simulate tilled and no-till applications, respectively. Twenty-four-hour Hg flux was measured from unamended and FGDG-amended soils on a seasonal time step over 1 yr and after disturbing, watering, and planting. Methylmercury in soil, irrigation drainage, and total Hg in plant tissues were quantified. Results should be interpreted within the confines of the experimental setting and materials used for this study. Total Hg concentrations in soils, homogenized with FGDG, were below that considered representative of soil with background values (<100 ng g). Emissions from amended soils were higher initially relative to unamended soils but became similar over time. Significantly less Hg (2%) was lost to the air from FGDG-amended soils (90 g FGDG added for lowest application) than that released from the FGDG alone (30-70%) (50 g FGDG) over 1 yr. Total Hg and MeHg in irrigation drainage and total Hg concentrations measured in plants were similar for amended and unamended soils.

Mercury concentrations in oligohaline wetland vegetation and associated soil biogeochemistry

Concentrations of mercury were determined in above- and below-ground tissues of dominant plant species, as well as soils, in the wetlands of Lake Maurepas, Louisiana. Indicators of wetland soil biogeochemical status, such as soil redox potential, pore-water nutrient concentrations, and pore-water total sulfides, were also determined. Total mercury concentrations in plant tissues were within the typical range for vegetation not exposed to mercury contamination. Similarly, total mercury concentrations in soils were typical of uncontaminated wetlands within this geographic region. Soil methyl mercury levels in this study are slightly lower than those reported in other studies of nearby wetlands. This may reflect the less extensive geographic sampling in this study, or the low water levels in the Lake Maurepas system immediately prior to and during this study, which would have altered soil biogeochemical status. This is corroborated by measurements of soil redox potential and soil pore-water nitrogen and sulfur constituents conducted during this study that suggest minimal sulfate reduction was occurring in surficial soils. This study indicates that the wetlands surrounding Lake Maurepas are typical of many uncontaminated oligohaline wetlands in the southeastern U.S. in regard to mercury concentrations.

Total mercury and methylmercury in freshwater and salt marsh soils of the Mississippi river deltaic plain

Mercury entering wetland environments can be microbially methylated to methylmercury. The purpose of this study was to investigate the historical rate of mercury accumulation and distribution of total and methylmercury in soil profile of Louisiana coastal marshes. Two sediment cores each were taken from Louisiana freshwater marsh and salt marsh. Vertical accretion was determined using the 137Cs dating technique. Total and methylmercury were determined with depth in the soil profiles. The fresh marsh soil on a dry weight basis contained more total and methylmercury than the salt marsh. Average vertical accretion rates in freshwater marsh and salt marsh were 0.90 and 0.75 cm year −1, respectively. Average total and methylmercury content (to a depth of 30 cm) was 140 and 4.19 μg kg −1 and 80 and 1.34 μg kg −1 for the fresh and salt marsh, respectively. Due to greater sediment input resulting in a higher bulk density the salt marsh contained more total mercury per m 2 (to 30 cm depth) than the fresh water marsh (5340 μg m −2 as compared to 2929 μg m −2). The amount of methylmercury per m 2 to depth of 30 cm was approximately the same for each marsh.

Development of a microwave-assisted extraction method and isotopic validation of mercury species in soils and sediments

An efficient and rapid closed vessel microwave-assisted extraction method based on an acidic extractant has been developed to determine inorganic mercury and methylmercury in soils and sediments. Parameters optimized during this study were nitric acid concentration, amount of sample, extraction temperature and irradiation time. The results suggest that the nitric acid concentration and the irradiation temperature are statistically significant both for extraction efficiency and for stability of mercury species. A processed topsoil (Hg < 0.01 ng g−1) spiked with inorganic mercury and methylmercury and SRM 2711 (spiked with methylmercury) were used during the method development. The sample preparation was optimized in a closed-vessel system by heating 1.0 g of sample in 10.0 ml of 4.0 mol l−1 HNO3 for 10 min at 100 °C with magnetic stirring. Analyses of the extracts were carried out by using three types of instruments, Direct Mercury Analyzer-80 (DMA-80), inductively coupled plasma mass spectrometer (ICP-MS) and high-performance liquid chromatograph coupled with inductively coupled plasma mass spectrometer (HPLC-ICP-MS). The results obtained from each of these detection techniques agreed significantly at the 95% confidence level. The method was validated by the analyses of two types of specifically prepared reference soil samples and four certified reference materials (BCR 580, SRM 2704, SRM 2709 and SRM 1941a). The inorganic mercury and methylmercury concentrations found were in good agreement at the 95% confidence level with the certified or “made-to” value. The method was also validated using EPA Method 6800 as a diagnostic tool to check whether interconversion of inorganic mercury to methylmercury or vice versa took place during or after extraction; the amount of such interconversions was found to be statistically negligible. The method is in the process of consideration and adopted by the United States Environmental Protection Agency (US EPA) as a primary mercury species extraction protocol from soils and sediments in EPA draft Method 3200.