Elemental and radionuclide exposures and uptakes by small rodents, invertebrates, and vegetation at active and post-production uranium mines in the Grand Canyon watershed.

The effects of breccia pipe uranium mining in the Grand Canyon watershed (Arizona) on ecological and cultural resources are largely unknown. We characterized the exposure of biota to uranium and co-occurring ore body elements during active ore production and at a site where ore production had recently concluded. Our results indicate that biota have taken up uranium and other elements (e.g., arsenic, cadmium, copper, molybdenum, uranium) from exposure to ore and surficial contamination, like blowing dust. Results indicate the potential for prolonged exposure to elements and radionuclides upon conclusion of active ore production. Mean radium-226 in deer mice was up to 4 times greater than uranium-234 and uranium-238 in those same samples; this may indicate a potential for, but does not necessarily imply, radium-226 toxicity. Soil screening benchmarks for uranium and molybdenum and other toxicity thresholds for arsenic, copper, selenium, uranium (e.g., growth effects) were exceeded in vegetation, invertebrates, and rodents (Peromyscus spp., Thomomys bottae, Tamias dorsalis, Dipodomys deserti). However, the prevalence and severity of microscopic lesions in rodent tissues (as direct evidence of biological effects of uptake and exposure) could not be definitively linked to mining. Our data indicate that land managers might consider factors like species, seasonal changes in environmental concentrations, and bioavailability, when determining mine permitting and remediation in the Grand Canyon watershed. Ultimately, our results will be useful for site-specific ecological risk analysis and can support future decisions regarding the mineral extraction withdrawal in the Grand Canyon watershed and elsewhere.

Terrestrial ecological risk analysis via dietary exposure at uranium mine sites in the Grand Canyon watershed (Arizona, USA).

The U.S. Department of the Interior recently included uranium (U) on a list of mineral commodities that are considered critical to economic and national security. The uses of U for commercial and residential energy production, defense applications, medical device technologies, and energy generation for space vehicles and satellites are known, but the environmental impacts of uranium extraction are not always well quantified. We conducted a screening-level ecological risk analysis based on exposure to mining-related elements via diets and incidental soil ingestion for terrestrial biota to provide context to chemical characterization and exposures at breccia pipe U mines in northern Arizona. Relative risks, calculated as hazard quotients (HQs), were generally low for all biological receptor models. Our models screened for risk to omnivores and insectivores (HQs>1) but not herbivores and carnivores. Uranium was not the driver of ecological risk; arsenic, cadmium, copper, and zinc were of concern for biota consuming ground-dwelling invertebrates. Invertebrate species composition should be considered when applying these models to other mining locations or future sampling at the breccia pipe mine sites. Dietary concentration thresholds (DCTs) were also calculated to understand food concentrations that may lead to ecological risk. The DCTs indicated that critical concentrations were not approached in our model scenarios, as evident in the very low HQs for most models. The DCTs may be used by natural resource and land managers as well as mine operators to screen or monitor for potential risk to terrestrial receptors as mine sites are developed and remediated in the future.

Biota Dose Assessment of Small Rodents Sampled Near Breccia Pipe Uranium Mines in the Grand Canyon Watershed.

The biotic exposure and uptake of radionuclides and potential health effects due to breccia pipe uranium mining in the Grand Canyon watershed are largely unknown. This paper describes the use of the RESRAD-BIOTA dose model to assess exposure of small rodents (n = 11) sampled at three uranium mine sites in different stages of ore production (active and postproduction). Rodent tissue and soil concentrations of naturally occurring uranium (U, U, and U), thorium (Th, Th, and Th), and radium (Ra) radioisotopes were used in the dose model. The dose assessment results indicated that the potential internal, external, and total doses to rodents were below the US Department of Energy's biota dose standard of 1 mGy d. As expected, tissue concentrations of U, U, and Th were in approximate equilibrium; however, Ra results in tissue were 1.25 to 5.75 times greater than U, U, and Th tissue results for 10 out of 11 samples. Soil at the three sites also displayed Ra enrichment, so it is likely that the Ra enrichment in the rodents was from soil via typical activities (i.e., burrowing, incidental ingestion, bathing, etc.) or by dietary uptake of translocated Ra. The results suggest that Ra is more mobile in this environment and bioaccumulates in these rodent species (e.g., in bones via the bloodstream). Internal dose accounting suggests that Ra is the radionuclide of most concern for rodent exposure and health.

Assessment of chronic low-dose elemental and radiological exposures of biota at the Kanab North uranium mine site in the Grand Canyon watershed.

High-grade U ore deposits are in various stages of exploitation across the Grand Canyon watershed, yet the effects of U mining on ecological and cultural resources are largely unknown. We characterized the concentrations of Al, As, Bi, Cd, Co, Cu, Fe, Pb, Hg, Mo, Ni, Se, Ag, Tl, Th, U, and Zn, gross alpha and beta activities, and U and Th radioisotopes in soil, vegetation (Hesperostipa comata, Artemisia tridentata, Tamarix chinensis), and rodents (Peromyscus maniculatus, P. boylii) to waste material at the Kanab North mine, a mine with decades-long surficial contamination, and compared the concentrations (P < 0.01) to those at a premining site (Canyon Mine). Rodent tissues were also analyzed for radium-226 and microscopic lesions. Radioactivities and some elemental concentrations (e.g., Co, Pb, U) were greater in the Kanab North mine biological samples than in Canyon Mine biota, indicating a mining-related elemental signature. Mean rodent Ra-226 (111 Bq/kg dry weight [dry wt]) was 3 times greater than expected, indicating radioactive disequilibrium. Multiple soil sample U concentrations exceeded a screening benchmark, growth inhibition thresholds for sensitive plants, and an EC20 for a soil arthropod. Lesions associated with metals exposure were also observed more frequently in rodents at Kanab North than those at Canyon Mine but could not be definitively attributed to U mining. Our results indicate that Kanab North biota have taken up U mining-related elements owing to chronic exposure to surficial contamination. However, no literature-based effects thresholds for small rodents were exceeded, and only a few soil and vegetation thresholds for sensitive species were exceeded; therefore, adverse effects to biota from U mining-related elements at Kanab North are unlikely despite chronic exposure. Integr Environ Assess Manag 2019;15:112-125. Published 2018. This article is a US Government work and is in the public domain in the USA.

Pre-mining trace element and radiation exposure to biota from a breccia pipe uranium mine in the Grand Canyon (Arizona, USA) watershed.

The risks to wildlife and humans from uranium (U) mining in the Grand Canyon watershed are largely unknown. In addition to U, other co-occurring ore constituents contribute to risks to biological receptors depending on their toxicological profiles. This study characterizes the pre-mining concentrations of total arsenic (As), cadmium (Cd), copper (Cu), lead (Pb), mercury (Hg), nickel (Ni), selenium (Se), thallium (Tl), U, and zinc (Zn); radiation levels; and histopathology in biota (vegetation, invertebrates, amphibians, birds, and mammals) at the Canyon Mine. Gross alpha levels were below the reporting limit (4 pCi/g) in all samples, and gross beta levels were indicative of background in vegetation (<10-17 pCi/g) and rodents (<10-43.5 pCi/g). Concentrations of U, Tl, Pb, Ni, Cu, and As in vegetation downwind from the mine were likely the result of aeolian transport. Chemical concentrations in rodents and terrestrial invertebrates indicate that surface disturbance during mine construction has not resulted in statistically significant spatial differences in fauna concentrations adjacent to the mine. Chemical concentrations in egg contents and nestlings of non-aquatic birds were less than method quantification limits or did not exceed toxicity thresholds. Bioaccumulation of As, Pb, Se, Tl, and U was evident in Western spadefoot (Spea multiplicata) tadpoles from the mine containment pond; concentrations of As (28.9-31.4 µg/g) and Se (5.81-7.20 µg/g) exceeded toxicity values and were significantly greater than in tadpoles from a nearby water source. Continued evaluation of As and Se in biota inhabiting and forging in the mine containment pond is warranted as mining progresses.

Derivation of soil-screening thresholds to protect the chisel-toothed kangaroo rat from uranium mine waste in northern Arizona.

Chemical data from soil and weathered waste material samples collected from five uranium mines north of the Grand Canyon (three reclaimed, one mined but not reclaimed, and one never mined) were used in a screening-level risk analysis for the Arizona chisel-toothed kangaroo rat (Dipodomys microps leucotis); risks from radiation exposure were not evaluated. Dietary toxicity reference values were used to estimate soil-screening thresholds presenting risk to kangaroo rats. Sensitivity analyses indicated that body weight critically affected outcomes of exposed-dose calculations; juvenile kangaroo rats were more sensitive to the inorganic constituent toxicities than adult kangaroo rats. Species-specific soil-screening thresholds were derived for arsenic (137 mg/kg), cadmium (16 mg/kg), copper (1,461 mg/kg), lead (1,143 mg/kg), nickel (771 mg/kg), thallium (1.3 mg/kg), uranium (1,513 mg/kg), and zinc (731 mg/kg) using toxicity reference values that incorporate expected chronic field exposures. Inorganic contaminants in soils within and near the mine areas generally posed minimal risk to kangaroo rats. Most exceedances of soil thresholds were for arsenic and thallium and were associated with weathered mine wastes.

Chemical contaminants, health indicators, and reproductive biomarker responses in fish from rivers in the Southeastern United States.

Largemouth bass (Micropterus salmoides) and common carp (Cyprinus carpio) were collected from 13 sites located in the Mobile (MRB), Apalachicola-Flint-Chattahoochee (ARB), Savannah (SRB), and Pee Dee (PRB) River Basins to document spatial trends in accumulative chemical contaminants, health indicators, and reproductive biomarkers. Organochlorine residues, 2,3,7,8-tetrachlorodibenzo-p-dioxin-like activity (TCDD-EQ), and elemental contaminants were measured in composite samples of whole fish, grouped by species and gender, from each site. Mercury (Hg) and polychlorinated biphenyls (PCBs) were the primary contaminants of concern. Concentrations of Hg in bass samples from all basins exceeded toxicity thresholds for piscivorous mammals (>0.1 microg/g ww), juvenile and adult fish (>0.2 microg/g ww), and piscivorous birds (>0.3 microg/g ww). Total PCB concentrations in samples from the MRB, ARB, and PRB were >480 ng/g ww and may be a risk to piscivorous wildlife. Selenium concentrations also exceeded toxicity thresholds (>0.75 microg/g ww) in MRB and ARB fish. Concentrations of other formerly used (total chlordanes, dieldrin, endrin, aldrin, mirex, and hexachlorobenzene) and currently used (pentachlorobenzene, pentachloroanisole, dacthal, endosulfan, gamma-hexachlorocyclohexane, and methoxychlor) organochlorine residues were generally low or did not exceed toxicity thresholds for fish and piscivorous wildlife. TCDD-EQs exceeded wildlife dietary guidelines (>5 pg/g ww) in MRB and PRB fish. Hepatic ethoxyresorufin O-deethylase (EROD) activity was generally greatest in MRB bass and carp. Altered fish health indicators and reproductive biomarker were noted in individual fish, but mean responses were similar among basins. The field necropsy and histopathological examination determined that MRB fish were generally in poorer health than those from the other basins, primarily due to parasitic infestations. Tumors were found in few fish (n=5; 0.01%); ovarian tumors of smooth muscle origin were found in two ARB carp from the same site. Intersex gonads were identified in 47 male bass (42%) representing 12 sites and may indicate exposure to potential endocrine disrupting compounds. Comparatively high vitellogenin concentrations (>0.35 mg/mL) in male fish from the MRB, SRB, and PRB indicate exposure to estrogenic or anti-androgenic chemicals.

Environmental contaminants in fish and their associated risk to piscivorous wildlife in the Yukon River Basin, Alaska.

Organochlorine chemical residues and elemental contaminants were measured in northern pike (Esox lucius), longnose sucker (Catostomus catostomus), and burbot (Lota lota) from 10 sites in the Yukon River Basin (YRB) during 2002. Contaminant concentrations were compared to historical YRB data and to toxicity thresholds for fish and piscivorous wildlife from the scientific literature. A risk analysis was conducted to screen for potential hazards to piscivorous wildlife for contaminants that exceeded literature-based toxicity thresholds. Concentrations of total DDT (sum of p,p'-homologs; 1.09-13.6 ng/g), total chlordane (0.67-7.5 ng/g), dieldrin (<0.16-0.6 ng/g), toxaphene (<11-34 ng/g), total PCBs (<20-87 ng/g), TCDD-EQ (