Selenium Content In Soil Research Articles

Investigation of seleniummetabolites in Se-enriched kale, Brassica oleracea A, viaHPLC-ICPMS and nanoESI-ITMS

Kale (Brassica oleracea A.) can accumulate high concentrations of Se, as well as lutein and β-carotene, which have important human health benefits and possess strong antioxidant properties. In the present study, kale plants were cultivated in soil supplemented with sodium selenite or sodium selenate. The plants accumulated over 20 times higher concentration of selenium in the selenate-enriched soil compared with selenite-enriched soil. Selenium accumulation did not suppress the plant's uptake of the essential metals, Fe, Cu and Zn. Speciation of selenium in the plant was performed via size-exclusion chromatography and ion-pairing reversed phase chromatography using inductively coupled plasma mass spectrometry (ICPMS) and nano-electrospray ion trap mass spectrometry (nanoESI-ITMS) for detection. In ion-pairing reversed phase chromatography, 0.02% HFBA was found to facilitate separating the selenium metabolites without hampering ESI-ITMS ionization. MS2/MS3 spectra were successfully obtained for identification of Se-methylselenocysteine (MeSeCys). MeSeCys was the prominent selenium metabolite formed in kale, which has been suggested as a chemopreventive food supplement. The Se species in leaf are significantly different from those in stem. The leaf shows higher content of high molecular weight selenium than the stem, while the stem produced higher amounts of MeSeCys than the leaf, indicating the metabolism to MeSeCys competes with the production of high molecular weight selenium forms. The plant leaf, when supplemented with Se(IV), contained the highest amount of high molecular weight selenium (49%) as well as the lowest amount of MeSeCys (4%).

Nest Box and Site Use by, and Selenium Concentrations in, American Kestrels at Kesterson Reservoir, Central California

Abstract During 1997 and 1998, we studied American Kestrels (Falco sparverius) using nest boxes at Kesterson Reservoir (Merced County, central California), a site with elevated soil selenium concentrations. We radiotagged male kestrels to determine their foraging ranges. Nest-box use was lower than expected; eleven nest boxes at Kesterson were used during the two years (16% and 20% occupancy) and five offsite nest boxes were used (60 and 40% occupancy). Kestrel pairs in 60% and 67% of onsite nest boxes that were used successfully fledged chicks in 1997 and 1998, respectively; pairs in offsite nest boxes had 100% (1997) and 50% (1998) success. Concentrations of Se in blood and eggs of kestrels at Kesterson were similar to concentrations in offsite kestrels. We analyzed 31 pellets and we used previously measured selenium concentrations in prey items from Kesterson to estimate dietary Se exposure of 8.1 µg Se/g for kestrels at Kesterson. We estimated that radiotagged male kestrels foraged onsite 58% of the t...

Assessment of selenium pollution in agricultural soils in the Xuzhou District, Northwest Jiangsu, China

Xuzhou City is an important base for coal production and coal-fired power. To evaluate selenium contamination in this area, we sampled agricultural soil, soil profile, irrigation water, bedrock, coal, fly ash, paddy rice, and vegetables from the north of Xuzhou City, and determined their selenium contents. The background level of selenium in the soil profile was 0.08 mg/kg. The selenium concentrations in agricultural soils and irrigation water were in the range of 0.21-4.08 mg/kg and 0.002-0.29 mg/L, respectively. Soils with high selenium content were located closely to coalmines and power plants. The average selenium concentrations in coal and coal fly ash were 5.46 and 2.81 mg/kg, respectively. In contrast, the concentrations of selenium in bedrock and in the soil profile were very low. These results imply that the high selenium level in agricultural soils is mainly caused by anthropogenic activities, rather than by parent material. The arithmetic mean of selenium concentration in paddy rice was 0.116 mg/kg, and in cabbage was 0.05 mg/kg. The selenium concentration in rice was positively correlated with total selenium concentration in soil, suggesting that selenium in soil is readily transferred into the crops. Furthermore, the estimated dietary intake (88.8 microg) of selenium from paddy rice and cabbage exceeds the recommended dietary allowance (55 microg). Therefore, there is a potential health risk from consumption of local staple food in the study area.

Soil selenium concentration and Kashin-Beck disease prevalence in Tibet, China

In order to investigate the correlation between the prevalence of Kashin-Back disease (KBD) and Se concentrations, natural soil samples and cultivated soil samples were collected from southeastern Tibet, China; and the soil Se concentrations were measured by atomic fluorescent spectrophotometer. It was found that the mean Se concentrations of natural soil samples in KBD areas, from the first layer to the third layer, were 0.17 mg/kg, 0.11 mg/kg, and 0.10 mg/kg, respectively, and in nondisease areas were 0.21 mg/kg, 0.24 mg/kg, and 0.13mg/kg, respectively. The mean Se concentrations of cultivated soil samples were 0.10 mg/kg in KBD areas and 0.23 mg/kg in non-disease areas, respectively. Soil Se concentrations in KBD areas were lower than that in non-disease areas, and the mean concentrations of soil Se in Tibet were lower than the average of China (0.29 mg/kg). Therefore, there is a close relationship between soil Se concentrations and KBD in Tibet. More studies should be concentrated on the impacts of Se deficiency in soils and its relationship with Se concentrations in food-grain and the human body in Tibet areas.

The biogeochemistry of selenium in Sunan grassland, Gansu, Northwest China, casts doubt on the belief that Marco Polo reported selenosis for the first time in history

In order to clarify the historic academic problem of whether or not livestock poisoning in ancient Suzhou of Northwest China, recorded by Marco Polo in 1295, was selenosis, this study deals with the biogeochemistry of selenium in Sunan County in the Hexi Corridor, which is part of ancient Suzhou in China. It was found that quite a number of farm animals had suffered from intoxication and died as a result of grazing poisonous grasses, mostly Oxytropis DC, Stellera chamaejasme, and Achnatheru inebrians. Toxic symptoms of livestock grazing on Oxytropis DC are similar to those of selenium toxicity, for instance, hair loss and hoof lesions as described by Marco Polo. Therefore, we thought that toxic grass, probably Oxytropis DC, led to the intoxication of livestock recorded by Marco Polo. Average Se concentrations in two members of this species were 0.112 +/- 0.038 mg/kg for the root of Oxytropis glabra, 0.102 +/- 0.027 mg/kg for the stem and leaf of Oxytropis glabra, and 0.066 +/- 0.009 mg/kg for Oxytropis ochrocephala. The average soil selenium concentration was 0.205 +/- 0.127 mg/kg on grassland producing Oxytropis glabra and 0.152 +/- 0.024 mg/kg on grassland producing Oxytropis ochrocephala. The average Se concentration in other plants was 0.076 mg/kg in the root of Ephedra monosperma Mey, 0.029 mg/kg in the root of Rheum palmatum, 0.031 mg/kg in the root of Stellera chamaejasme, 0.037 mg/kg in Achnatherum inebrians, and 0.067 mg/kg in forage grass (Achnatherum splendens ohwi). Selenium concentrations in soils and plants in Sunan County are far less than the thresholds causing selenium toxicity in livestock. As a result, this study concludes that the livestock poisoning recorded by Marco Polo in 1295 might not have been selenosis.

Environmental behaviors of selenium in soil of typical selenosis area, China

Daba Mountain area is one of the two endemic selenosis areas in China, which may relate with the environmental behaviors of selenium (Se) in soil. This study focuses on the concentraion and distribution of Se and its relationships with some other elements in natural soil in the area. The average concentration of Se in Daba Mountain soils was 14.3 times higher than the value cited for natural soil background worldwide, suggesting that soils in the region were contaminated by the element. The finding was confirmed by Miller geoaccumulation index assessment with 22% slightly polluted, 15% moderately polluted, 11% highly to very highly polluted and 8% moderately polluted to highly polluted. Soil Se is generally enriched in topsoil, and its distribution is extremely uneven and significantly site-specific. However, the concentrations of Se in soils have significant positive correlation with them in corresponding parent materials (r = 0.995, P < 0.01). Besides of Se, the concentrations of elements, such as Ca, Sr, V, Cu, Zn, Ni, Mg, Co, and Fe are also obviously abnormal compared with their background values of Chinese soil. Selenium behaviors in the region were controlled by multifactors: in addition to the parent material, pedogenic processes, biologic processes, and element geochemical behaviors also impacted the concentration and distribution of selenium in soil.

Historical changes in the concentrations of selenium in soil and wheat grain from the Broadbalk experiment over the last 160 years

Selenium (Se) intake has decreased substantially in the UK population since 1970s. To investigate whether Se concentration in wheat grain has changed as a result of yield improvement or environmental changes, we analyzed archived wheat grain from the Broadbalk Wheat Experiment at Rothamsted, England, which has been run continuously for over 160 years. Wheat grain and soil samples were selected from plots receiving different fertilizer or manure treatments. Grain Se concentration varied from 11 to 236 ng g − 1 , with a mean and median of 44 and 32 ng g − 1 , respectively. Grain samples from the unfertilized control plot had significantly higher concentrations of Se than those from fertilized or manured plots; the latter received various amounts of S and also had higher grain yield. No significant trends in grain Se concentrations were detected in the fertilized or manured plots, in spite of a dramatic increase in grain yield since the introduction of modern short-straw cultivars in the mid 1960s. In the control plot, grain samples had higher Se concentrations in the periods before 1920 or after 1970 than those during 1920–1970. This temporal pattern mirrored that of SO 2 emissions and atmospheric S deposition. Soil Se concentrations showed an increasing trend in all plots over 160 years. The results show that the Se concentration of wheat grain from the Broadbalk experiment was influenced by S inputs from fertilizers and atmospheric deposition, and that improving grain yield through plant breeding has not resulted in a significant decrease in grain Se concentration in the fertilized plots.

SOIL REDOX CHEMISTRY LIMITATION OF SELENIUM CONCENTRATION IN CAREX SPECIES SEDGES

Soil samples from normally wet and normally dry locations on an alpine study site were analyzed for total selenium, available selenium, pH, and oxidation-reduction potential (ORP). The selenium concentration of Carex species sedges from the same sample locations were also analyzed. Total selenium concentrations in soil were variable, and not correlated with Carex selenium concentration. However, soil available selenium and Carex selenium concentrations were found to be related to soil ORP. Similarly, soil samples maintained in a saturated condition in the laboratory showed rapid decreases in ORP and in available selenium. The conditions that favor the thermodynamic transition between available and nonavailable Se occur within the range of pH and ORP found naturally in soil at this location. Water-saturated soil conditions and the resulting low ORP appear to limit the Se concentration in Carex, a forage plant used by wildlife at the study area.

Characterizing Spatial and Environmental Determinants of Prostate Cancer Using a Geographic Information System

ISEE-652 Objective: Prostate cancer (PrCA) incidence in South Carolina (SC) exceeds the national average, particularly among African Americans (AAs). A Geographic Information System (GIS) was used to evaluate spatial and environmental determinants of PrCA in SC, a cancer for which there are few established risk factors. Materials and Methods: Age-adjusted PrCA incidence, standardized incidence ratios (SIRs), and 95% confidence intervals were calculated for census tracts using SC Central Cancer Registry data (1996–2002). Demographic data (groundwater consumption, age, race, median income, land use) were obtained from census data. Metal concentrations in groundwater and soil were obtained from existing federal and state databases to test hypotheses that zinc and selenium are protective, and that cadmium and uranium increase PrCA incidence. Census tract-specific exposure estimates included: geometric mean groundwater and soil metal concentrations, proportion of samples exceeding background, and census tract-centroid concentration obtained via spatial modeling (kriging). A GIS was used to map incidence rates, SIRs, and exposures. Statistical procedures (linear and Poisson regression) were applied with and without censoring of tracts with <50% groundwater consumption per capita (N = 173 and 854, respectively). An adjacency matrix was generated and spatial statistical models were performed using WinBUGS software, with adjustment for correlated and uncorrelated heterogeneity. Results: There were 18,091 PrCA cases; 30% AA and 69% European American. Among uncensored tracts with elevated groundwater zinc, 7 had PrCA rates below expected incidence, and this inverse relationship also was observed using linear regression (P = 0.02). There were 96 census tracts with both elevated soil selenium concentrations and reduced SIRs. Three tracts had both elevated soil cadmium and higher SIRs. Conclusions: A decreasing trend in PrCA rates was observed among SC census tracts with elevated zinc in soil or groundwater. Relationships between environmental factors and cancer incidence can be efficiently explored using GIS, spatial statistics, and existing population databases.

The Level of Selenium and Some Other Trace Elements in Different Libyan Arable Soils Using Instrumental Neutron Activation Analysis

Elemental analysis of soils from two different arable regions in Libya was carried out to measure the level of many trace elements. Instrumental neutron activation analysis was used for the determination of 10 elements, viz., (Ba, Ce, Co, Cr, Cs, Fe, Sc, Se, Th, and Zn), using their long-lived radionuclides. The accuracy of the measurements has been evaluated by analyzing two IAEA soil reference materials: IAEA Soil-7 and IAEA leak sediment SL-1; precision has been estimated by triplicate analysis of the sample and that of the reference material. Irradiations were carried out at the Tajura Research Center reactor, at 5-MW power level. It is clear that in the Libyan soil selenium concentration is somewhat lower than in other countries. The results show that trace metal concentrations in Libyan clay surface soil are higher than the sandy soil.

Study on the Relationship between Soil Selenium and Plant Selenium Uptake

Various extraction methods have been used to determine selenium (Se) concentrations in soils and plants in the second seleniferous regions of China. Our results show tea Se contents in the study area range from 1.009 to 2.6 mg/kg, which reveal that the tea areas in Ziyang County are in seleniferous regions. The four extraction methods evaluated in this study provide different information concerning soil and plant Se levels. The quality control/quality assurance program for this project indicated there is excellent agreement between total soil Se and extractable Se. For example, phosphate extractable Se results from the field investigation and greenhouse study were found to be highly correlated (R 2 > 0.91) by linear regression analyses. Results from rye seedling experiments further show phosphate extractable Se has significant correlations with plant Se uptake and that a 0.1 M solution of KH2PO4 can be used as the extractant of soil available Se. In the acid soil, the Brassica campestris yield could be significantly reduced when the content of Se 6+ –Se ‡ 0.5 mg/kg, and the influence on the yield was not as obvious when the content of Se 6+ –Se reached up to 2.0 mg/kg. The uptake by Brassica campestris of Se 6+ –Se is higher than that of Se 4+ –Se. The main factors influencing the biological availability of soil Se, in order of their importance are CaCO3, the presence of silt grains, organic matter and the presence of clay grains. pH could affect KH2PO4 extractable Se through CaCO3.

English

The occurrences of low levels of selenium (<25 µg/l) were detected in central Appalachian streams during the data collection for the Mountaintop Mining Environmental Impact Study. The study was conducted as part of a settlement in a lawsuit alleging Clean Water Act and SMCRA violations related to the construction of valley fills. Most of the areas east of the Mississippi River have been characterized as being low or even deficient in selenium. During the past twenty-five years the role of selenium has changed from being considered a toxic element to now being considered a necessary micronutrient that is important for biological functions. The current water quality standard for selenium is 5 µg/l, which is lower than the levels measured in some streams in the study area of central Appalachia. Typically, areas west of the Mississippi River have higher naturally occurring soil selenium concentrations. In a few areas some streams have selenium concentrations as high as 500 to 1000 µg/l. The sources of selenium in the central Appalachian area are related to several anthropogenic activities. These sources can range from the weathering of exposed soil and rock created from various surface disturbance activities to runoff from domestic animal feedlots. The concentrations in soil, rock, and coal can range from < 0.5 mg/kg to as high as 21 mg/kg. The exact path in which the selenium becomes part of the water column is currently being evaluated. The impacts of these low levels of selenium on aquatic life are nearly indistinguishable from other contaminants (high suspended solids or high total dissolved solids), which also occur in these streams. Elevated levels of these parameters will usually result in more significant aquatic degradation than can be correlated with low selenium concentrations.

Elevated selenium and other mineral element concentrations in soil and plant tissue in bone coal sites in Haoping area, Ziyang County, China

The Shuang'an site is the most serious selenosis site in Ziyang County, Shaanxi Province, which was the second selenosis site in China. In order to investigate the relationships between Se and other mineral elements and selenosis, bone coals, V-Mo ores, rocks, soils and plants were sampled from each site. The higher mean concentrations of Se, Mo, V and F in bone coals and ores may be the main environmental geochemical sources for soils and plants in this local ecosystem. Inappropriate revegetation in the Shuang'an mining site have posed the greatest risk of pollution, resulting in elevated mean concentrations of Se (16.9 μg/g), Mo (99 μg/g), V (1134 μg/g), F (1041 μg/g) and As (111 μg/g) in the soil directly derived from bone coal and V-Mo ore dumps. Most plants, which grow in the revegetated soil, contain elevated Se, Mo, V and F concentrations. The revegetated soil derived from bone coal and V-Mo ore dumps with excess Se, Mo, V and F concentrations in this ecosystem might have been essentially responsible for selenosis incidence of Shuang'an site in Ziyang County, Shaanxi Province. It is proposed that this selenosis area coincides with Mo, F and V toxicity based on their higher concentrations in rocks, soils and plants.

Selenium in a Wyoming grassland community receiving wastewater from an in situ uranium mine.

Water, soil, vegetation, grasshoppers, bird eggs, and bird livers collected at a 23.5-ha (58 acres) grassland irrigated with wastewater from an in situ uranium mine (study area) and a reference site in 1998 were analyzed for selenium and other trace elements. Selenium concentrations in the uranium mine wastewater applied onto the grassland ranged from 340 to 450 microg/L. Selenium in the upper 15 cm (6 in) of soil from the irrigated grassland at the mine ranged from 2.6 to 4.2 microg/g dry weight (DW). Mean selenium concentrations in soil and water were 5 and 15 times higher at the study area than at the reference site. Selenium concentrations in grasses and grasshoppers ranged from 6.8 to 24 microg/g and 11 to 20 microg/g DW, respectively. Selenium in red-winged blackbird eggs and livers collected from the study area ranged from 13.2 to 22 microg/g and 33 to 53 microg/g DW, respectively, and concentrations were well in excess of toxic thresholds. Mean selenium concentrations in grasses, grasshoppers, and bird eggs and livers were 5.8 to 30 times higher at the study area than at the reference site. Elevated selenium concentrations in water, soil, grasshoppers, and red-winged blackbird eggs and livers collected from the study area demonstrate that selenium is being mobilized and is bioaccumulating in the food chain.

Lambs with White Muscle Disease and Selenium Content of Soil and Meadow Hay in the Region of Kars, Turkey

Lambs with White Muscle Disease and Selenium Content of Soil and Meadow Hay in the Region of Kars, Turkey

The Behaviour of Selenium in Geological Processes

Selenium contents were analyzed from a total of 244 soil samples collected over different rock types at a sampling density of one sample per 4 km2 around Geita gold mining areas, Northwestern Tanzania. Comparisons using literature survey contents of selenium in geological materials and some implications on the selenium in soils are compiled and discussed. Most selenium occurs as simple selenides in small quantities in low temperature hydrothermal deposits devoid of sulphur. It has been observed that to a large extent selenium content is increased more than most trace elements in the upper parts of the Earth perhaps through extraterrestrial deposition. In deep-seated rocks selenium is associated with sulphur but being volatile selenium and sulphur do not behave according to the crystallochemical law. Due to the higher stability of S6+, Se4+ and Se0 separate during migration. Thus, selenium is especially found in deep-seated plutonic rocks where large magma bodies cooled slowly and sulphur is available to precipitate sulphides. Selenium, which occurs with sulphides, is inhomogeneously deposited into continental margins. It is increased during magmatic differentiation and is highest in basic rocks. In magmatic and metamorphic conditions, selenium is found in the crystal structures of sulphides while in pneumatolytic and hydrothermal processes, it is relatively enriched into the late differentiates compared to sulphur. In metamorphic rocks selenium is more widely distributed. Selenium content in soils in the investigated area varies from (0.3–0.5 μ gg−1) in laterite and in black cotton soil 0.4 μ gg−1. Of all volcanic rocks selenium is highest in volcanogenic rocks especially the basalts. Surface waters are enriched in selenium, which they leach from volcanic materials. Selenium in sediments containing clay and organic matter is elevated but the content decreases with increased metamorphism. Selenium in volcanic areas can be used as a pathfinder in prospecting for volcanogenic ore deposits. S/Se ratios are distinct in different rock types and can thus be used to elucidate the origin of rocks, ores, and sediments.

Map of Selenium Content in Soil in Japan.

We present a new selenium (Se) map of Japan in more detail than in our previous report (J. Health Sci., 42, 360-366). It contains 150 measured points, especially in the northeast of Japan. In the new sampling points, we did not find high Se levels and most of the measurements were generally at values below 1 mg/kg. In the Se map of Japan, there are two particularly high measurements, at Mt.Zao (10 mg/kg) and Tateyama Murodo Jigokudani (148 mg/kg). These two areas are the origin of a minor branch of the Abukuma River and the Jouganji River, respectively. We also analyzed the Se levels near two major copper mines, Asio and Besshi. We detected high Se content in rocks at both copper mines and an average Se level in soil from the area near the Asio copper mine. The Se level in soil at Besshi was slightly higher than that at the area near the Asio copper mine. We also measured the Se levels of some pyrites in Japan. The Se levels of most pyrites were some ten mg/kg higher than the general Se level in soil. This study provides information about the fundamental background values of Se levels in soil and rocks to correlate with Se pollution if it occurs in the future

Distribution of selenium in corn and its relationship with soil selenium in Yutangba mini-landscape

Within the range of 0.01 km mini-landscape in Yutangba, Enshi, Hubei Province, the content of Se in corn is very high. The average Se contents in root, stem, leaf and seed of corn were estimated to be 4.36±3. 27mg/kg, 3.08±2.24 mg/kg, 9.74±7.62mg/kg, and 8.07±5.02mg/kg, respectively. The research results show that there is a significantly positive correlation between corn selenium and soil selenium, and thus according to the distribution of Se in corn, three subregions can be divided in Yutangba. The content of selenium in corn is controlled by that of soil. A little variation in selenium content in soil will lead to a considerable corresponding variation in corn. So it is deduced that the organs that contain relatively high Se in plants may be used as a sensitive selenium indicator of Se levels in the environment.

Environmental factors, health-related habits, and serum selenium levels in cancer patients and healthy controls.

Previous studies conducted in Yugoslavia indicated that the concentration of selenium in soil, food items, and serum of the population is very low. The aim of the study was to investigate the possible relationship among environmental, health-related habits, nutrition, and selenium serum levels in cancer patients and the healthy population. The case-control study included a group of cancer patients and a matched group of healthy controls: 57 cancer patients and 41 healthy controls living in Stari Grad (an urban area of Belgrade), as well as 17 cancer patients and 13 healthy controls living in Barajevo (a rural community in the vicinity of Belgrade). The healthy controls were matched to cancer patients in sex and age; they were not blood related. The selenium serum levels were measured by atomic absorption spectrophotometry. Health-related habits and relevant dietary factors ("food frequency" method) that may influence the selenium serum levels were assessed by questionnaires. The differences in average values of selenium serum levels between the cancer patients and healthy controls were not significantly different, but both were below the lowest recorded in referential studies. A significant difference between the values obtained from urban and rural subgroups was noted. The most important factors that influenced the level of selenium included the residence place in the region with selenium deficiency (Barajevo), age, associated chronic diseases, and some dietary factors potentially related to the intake of selenium. The results obtained in this investigation pointed out that use of selenium supplementation in this area should be seriously considered.

Soil Selenium: Laboratory Comparisons and Soil/ Backfill Variability

Various analytical methods have been used to determine selenium (Se) in soils, overburden, and plants. Inter-Mountain Laboratories and the Soil and Environmental Chemistry Laboratory at the University of Wyoming conducted a study to determine the variability of soil Se by independently analyzing 20% of the soil/backfill samples from an Abandoned Coal Mine Land research project {open_quotes}Relationship Between Soil Selenium Concentrations and Selenium Uptake by Vegetation on Surface Coal Mine Lands in Wyoming{close_quotes}. The quality control/quality assurance program for this project revealed excellent agreement between the two laboratories. For example, hot water, AB-DTPA, and phosphate extractable Se results from the two laboratories were found to be highly correlated (R{sup 2} {ge} 0.95) by linear regression analyses. Both laboratories followed {open_quotes}Standard Operating Procedures{close_quotes} which included determination of Se by atomic adsorption spectroscopy with hydride generation (Varian HGA-76). Five methods used to determine soil Se (i.e., total Se and four methods of extractable Se - hot water, AB-DTPA, phosphate, and saturated paste) were compared among three cores sampled within a one meter triangle at different sites (native and reclaimed locations) and depths (5 at native and 3 at unclaimed sites). A wide range in the coefficient of variation (CV) was noted (0 tomore » 118%); however, the larger CV`s tended to be grouped at specific sites and depths, and with certain extractants. Of 831 CV`s calculated, only 10 (or 1.2%) were greater than 100%. Average CV`s for mine type and ecological system (i.e., native versus reclaimed) were approximately 25%. Overall, total Se varied the least among the five Se variables followed by phosphate < AB-DTPA < hot water < saturated paste extractable Se.« less