A stainless steel hand auger with a Teflon® coated-core sampler was used to collect the soil samples. To minimize cross contamination, a polyethylene core liner was utilized. Soil samples were obtained from the topsoil and composited. The forage soil samples were obtained by utilizing a topographic soil zone sampling pattern using a random zig-zag pattern. Soil samples were weighed at 100 g. Physicochemical properties such as temperature, pH, Munsell color, depth, and moisture were obtained. The sheep tissue samples were paired with the forage, soil, and water samples. The mean age of adult sheep harvesters was 58.67 ± 2.89 years; two of three participants were male. All sheep parts were consumed by the participants for a mean of 52.33 ± 10.78 years. The sheep harvesters reported that 35% of their overall meat intake came from sheep they raised and harvested locally. On average, all the participants reported consuming locally raised sheep once a week. The local harvesters reported other important non-food uses for sheep. All participants reported selling wool, and two reported using the locally harvested wool to create textiles to sell for income. One of three harvesters reported selling live sheep to market, and two reported selling sheep or lamb cuts to market. All the participants reported sharing sheep meat for free with others. On average, each sheep harvester distributed free meat to two households. Multiple sheep parts were reportedly used for various ceremonial or cultural purposes by all harvesters.The existing literature reports HM levels in kidney tissue,ebb flow table but typically there is no comparison between the kidney medulla and the renal cortex. In this study, the kidney medulla rather than the kidney cortex showed an increased uptake of U, Se, Mo, and As.
The renal proximal tubule epithelia arechemically damaged by high acute levels or prolonged low doses of U; the proximal tubules are housed in the renal cortex. The administration of toxic doses of Se demonstrated histopathological changes in the proximal tubules of the sheep. The kidneys maintain Se homeostasis. Renal compromise may cause dysregulation of Se. Our study indicates there may be a difference between HM accumulation in the medulla and the cortex. The renal toxic effects of U and Cd are well supported in the literature. The effects of associated heavy metals on the sheep kidney need further exploration. Meat protein is richer in Se than plants. The literature supports that Se commonly concentrates in the liver and kidneys of animals. Of all sheep organs, elevated Se levels were found in the liver and kidney medulla . In a lamb tissue study, it was reported that Se concentrations in the kidneys were seven to 44 times higher than in other tissue and organs. Similarly, in our study, the medullary levels contained the higher concentrations of Se . The above lamb study reported that leg muscle contained the lowest Se concentrations of the tissues sampled. We also found that leg muscle contained the lowest Se concentrations in our examination . There is a narrow margin between Se requirement and toxicity. Therefore, taking an accurate measure of food intake containing Se, particularly meat protein, is important. Food processing such as cooking via baking, boiling, and grilling may alter the amount of Se in food. Whether food processing has an additive or minimizing effect on Se concentrations in food is to be determined by research. Adjusting food intake and cooking habits based on various HM measurements and bio-availability may be a plausible intervention once it is informed by research. Elevated levels of Se and Pb were found in sheep wool in the current study. Further, though Th was negligible in all other sheep tissue, it was detected in sheep wool .
This finding may indicate that Th may be accumulating across time in sheep wool. Direct dirt and dust aerosol capture and the effects of lanolin may be contributing exposure factors. We did not measure the effects of lanolin in this study. The current study community relies on wool to create textiles. It is common practice to place local plants in hot water to pigment the wool. The wool is handled often by weavers once the wool is removed from the animal, hand-carding the wool, hand-spinning, dyeing, and weaving the textile. The entire process often takes weeks to months, suggesting a potential lengthy human exposure to heavy metals. A considerable amount of time is spent outdoors for such activities, and exposure to various sources of contaminants such as soil, water, and air is a concern. Although this study of three sheep provided interesting insight, future studies should focus on determining the speciation of heavy metals and evaluate which metals have a greater affinity to wool. The majority of the time for this study, heavy metals were found in the greatest amounts in soil > forage roots > above-ground forage parts, respectively. The current study mean Se soil concentrations were equivalent or exceeded the exposed soil and were greater than the control concentrations reported by Dreesen and Cokal. The above-ground forage parts contained the least amount of heavy metals, except for Mo and Cd. The bio-accumulation ratio can partially demonstrate the ability of particular plants to absorb soil heavy metals and transport them to the above ground portions of a plant. The data shows that the uptake of Cd, Mo, and Se by most plants sampled were high under current soil conditions. The highest BF ratios were seen in most forage for Mo , Cd , and Se , which needs further exploration. The high BF ratios seen may indicate a low tolerance of various plants to high concentrations of Mo and Cd. In particular, B. gracilis the most abundant plant, was associated with elevated BF ratios for Cd, Mo, and Se.
Generally, in the biota samples there were greater heavy metal concentrations in the plant roots than the above-ground portions, which is consistent with several other plant studies that found that U translocates in greater amounts to the roots than the shoots. Similar to the current study, Soudek et al. reported that U was more localized in the root system. Uranium accumulation was less in grasses than root crops and Brassica spp.. Uranium uptake was found to be 3.9 or 4.5higher in the presence of phosphate deficiency. The micro and macro-nutrients available in soil affected the uptake of Cd in one source. Geochemical characteristics have an important influence on HM plant uptake. Future investigations can focus on the interactions between trace elements or other factors that may demonstrate an influence on HM plant uptake. Forage and water intake are important considerations in livestock,air pruning pots and soil ingestion must also be considered. In the current examination, the soil samples showed greater HM concentration than sheep tissue and forage samples. It has been demonstrated that sheep, a ground feeding animal, eat one to two percent of soil when good forage is available and about 18% when low quality forage is available. It has been shown that sheep intake and digestibility of more mature plant material decreases with advancing maturity due to greater effort and time in chewing by the animal; sheep selectively graze in high-quality forage areas when they are available. The forage environment of the sheep in the current study area exhibited high stocking rates, sparse vegetation, and mature forage samples, which may have contributed to higher HM concentrations in forage. Dung analysis can evaluate the amount of inorganic material in sheep diets and may be useful in future studies in the current study area. Previous studies have reported the concentrations of HMs in sheep tissues, plants, and soil in the target study area . In most categories, our study results were comparable to or less than what was previously found.
The current study tissue measurements were below the exposure and control concentrations reported by Millard et al. and Ruttenber et al. in the 1980s. No excess cancer risk was calculated to be attributed to eating sheep meat, liver, kidney, and soup bone by humans; researchers recommended continued monitoring at that time. The highest HM metal concentration in the diet was used for each animal to calculate and compare to the maximum tolerable concentrations, and the lowest concentration for each HM was used to compare to the requirements for Mo and Se. The calculations are based only on the forage samples collected and are not representative of the complete sheep intake. Maximum tolerable concentrations are established for sheep intake for As Cd, Pb, Mo, and Se. All study animals did not exceed the calculated maximum tolerable concentrations for As, Cd, Mo, and Pb. All study sheep met the Mo and Se dietary requirements. Liver is the organ of choice to diagnose Se deficiency, and concentrations less than 0.21 mg/kg in sheep liver are considered deficient. All study sheepliver concentrations did not indicate deficiency. In sheep, Se toxicity was reported at 0.25 mg/kg of body weight chronically. However, the National Research Council set the maximum tolerable concentrations for Se at 5.0 mg/kg of DM. Of the donated sheep, the shepherds did not report indicators of acute or chronic Se poisoning . Other supplementary sources of forage were not reported at the time of sampling; sheep harvesters reported relying on alternative fodder sources for their sheep in the late winter months only . New Mexico is one state that was reported to have high Se concentrations in soils and those in areas with low annual rainfall or alkaline soil. The mean study soil pH was 7.31 ± 0.51. Primarily, most of the Se is absorbed in the small intestines of ruminants and less absorption is seen in forage based diets versus diets based on concentrate. Plants that accumulate Se may be unpalatable to grazing animals, but if there is lack of more palatable forage, animals may develop signs of toxicity from ingestion. According to one study calculation, selenosis can occur in lambs ingesting 0.2% BW of Se accumulating plants. Soil ingestion during foraging, seasonal soil forage adhesion , pulling up of roots while foraging, and licking snouts by livestock may also contribute to higher HM concentrations. The forage plants that we sampled were not known Se obligate or secondary accumulator plants. Aside from Se, whether study plants accumulate Mo and Cd needs further evaluation. Selenosis diagnosis is primarily based on Se measurements , anemia and the presence of physical examination findings identifying toxic levels.One source reported that plant forage containing >3–5 mg/kg induced toxicity in sheep. In our study, several plant roots exceeded 3 mg/kg, which is a concern with the pulling up of roots when sheep forage. The amount of root consumption in relation to the total sheep forage intake is important to determine. Further work examining these factors is an area of future research. Based on drinking water standards for livestock, none of the heavy metal concentrations were above maximum tolerable concentrations . Heavy metal water measurements collected by the DiNEH study from two of the water sources identified for Sheep 3 contained lower concentrations of Pb in comparison to our data ; the remaining HM data were less than what the DiNEH researchers found. Most of the shepherds obtained public water for sheep consumption, which was reflected in the concentration levels found in sheep water. Harvesters in the study reported a history of consuming unregulated water intended for livestock. However, the As, Cd, Pb, Se, and U concentrations did not exceed the maximum contaminant levels set for human consumption. The implementation of water use maps may have contributed to the use of safer alternative water sources for these shepherds. Continued emphasis on the use of safe alternatives for water use in sheep and human consumption put forth by deLemos et al. is essential. Harvested food selling and sharing was common among the participants in the study. Emphasis should be placed on determining the incidence and frequency of food selling and sharing when assessing food chain contamination. Harvesting locations and activities can overlap in mining impacted areas. A few important factors to consider include the availability of harvest items based on seasonal variation and peak consumption periods . It is important to consider the consumption of contaminated food not only by individuals and their families but potentially the whole community and beyond.