Garret L. Hart

Lead bullet fragments in venison from rifle-killed deer: potential for human dietary exposure.

Human consumers of wildlife killed with lead ammunition may be exposed to health risks associated with lead ingestion. This hypothesis is based on published studies showing elevated blood lead concentrations in subsistence hunter populations, retention of ammunition residues in the tissues of hunter-killed animals, and systemic, cognitive, and behavioral disorders associated with human lead body burdens once considered safe. Our objective was to determine the incidence and bioavailability of lead bullet fragments in hunter-killed venison, a widely-eaten food among hunters and their families. We radiographed 30 eviscerated carcasses of White-tailed Deer (Odocoileus virginianus) shot by hunters with standard lead-core, copper-jacketed bullets under normal hunting conditions. All carcasses showed metal fragments (geometric mean = 136 fragments, range = 15–409) and widespread fragment dispersion. We took each carcass to a separate meat processor and fluoroscopically scanned the resulting meat packages; fluoroscopy revealed metal fragments in the ground meat packages of 24 (80%) of the 30 deer; 32% of 234 ground meat packages contained at least one fragment. Fragments were identified as lead by ICP in 93% of 27 samples. Isotope ratios of lead in meat matched the ratios of bullets, and differed from background lead in bone. We fed fragment-containing venison to four pigs to test bioavailability; four controls received venison without fragments from the same deer. Mean blood lead concentrations in pigs peaked at 2.29 µg/dL (maximum 3.8 µg/dL) 2 days following ingestion of fragment-containing venison, significantly higher than the 0.63 µg/dL averaged by controls. We conclude that people risk exposure to bioavailable lead from bullet fragments when they eat venison from deer killed with standard lead-based rifle bullets and processed under normal procedures. At risk in the U.S. are some ten million hunters, their families, and low-income beneficiaries of venison donations.

Osmium isotope constraints on lower crustal recycling and pluton preservation at Lassen Volcanic Center, CA

Osmium isotope compositions of intermediate- to silicic-composition calc-alkaline volcanic rocks from the Lassen volcanic region of the Cascade arc are significantly more radiogenic (QOs = +23 to +224) than typical mantle. These evolved arc rocks in the Lassen region have unradiogenic Sr, Nd, and Pb isotope compositions which overlap with those of contemporaneous mafic lavas. Crystal fractionation of mafic- to intermediate-composition magmas produces Re/Os ratios that are high enough to evolve to very radiogenic Os isotope compositions in only a few million years, providing a potential fingerprint for detecting the involvement of such young, relatively mafic crust in magmatic systems. However, the Sr, Nd, and Pb isotope compositions will remain constant over such short time intervals due to relatively low parent/daughter enrichment during magmatic evolution. The radiogenic Os isotope compositions in typically evolved Lassen rocks are interpreted to reflect significant interaction with lower crustal material that has radiogenic Os isotope compositions. Beneath this section of the Cascade arc, large amounts of such high-QOs lower crust may have formed and been isolated from MASH zone mixing and homogenization processes during the Pliocene or Late Miocene. The results from this study indicate that Os isotopes may provide a unique glimpse into lower crustal processes, such as recycling, in primitive orogenic arcs. 9 2002 Elsevier Science B.V. All rights reserved.

New osmium isotope evidence for intracrustal recycling of crustal domains with discrete ages

New 187Os/188Os ratios of Quaternary Mount Adams volcanic rocks from the Cascade arc in southern Washington vary by .300% ( 187 Os/ 188 Os 5 0.165-0.564) and fall into high (.0.319) and low (0.166 to 0.281) groups of 187 Os/ 188 Os ratios that are sub- stantially more radiogenic than mantle values. These Os isotope compositions and groupings are interpreted to reflect recycling of discrete intracrustal domains with high 187Os/188Os ratios but dif- fering ages, thus recording the process of crustal hybridization and homogenization. Os isotope compositions provide new constraints on amounts of intracrustal recycling in young subduction-zone en- vironments that reflect the magmatic history of the arc. Sr, Nd, Hf, and Pb isotope variations in this young, mafic arc complex are too small to allow such constraints.

A reassessment of Mojavia and a new Cheyenne Belt alignment in the eastern Great Basin

A separate basement terrane, Mojavia or the Mojave province with characteristic 2.0–2.3 Ga model ages, has been proposed to underlie much of the western U.S. Its existence, posited on patterns of Pb and Nd isotope data, has been propagated in the literature for more than two decades. New and compiled U/Pb geochronology shows there is no direct evidence of >2.0 Ga juvenile basement rocks exposed within Mojavia of the eastern Great Basin. Pb and Nd model ages, by contrast, vary from Archean to Neoproterozoic with large variations exhibited, commonly within small regions. Archean ages are concentrated northward, suggesting the influence of sediment shed southward from the Wyoming province onto Paleoproterozoic basement terranes. In places, including the Farmington Canyon complex, sediment has been tectonically reprocessed and now is preserved as high-grade metamorphic rock in accretionary melanges. There is no strong evidence that Mojavian basement exists outside of the Mojave Desert region proper. A statistical evaluation of common Pb and Sr isotopes in Phanerozoic igneous rocks shows distinct differences north and south of one proposed boundary between Mojavia and the Yavapai province. However, close examination suggests that variation in these parameters could be produced by the influence of Archean material shed from the Wyoming province rather than representing a distinct difference in the age and isotopic character of the basement. Statistical discrimination of candidate terranes and terrane boundaries may be valuable for their recognition, but such differences alone do not prove their existence. The northern boundary of Mojavia with the Wyoming province in the eastern Great Basin has been given the same name, the Cheyenne Belt, as the exposed suture be tween Paleoproterozoic and Archean basement in southern Wyoming. We reassess the location of this boundary in the Great Basin. New age controls on key basement outcrops in the Uinta Mountains and Farmington Canyon complex that were previously considered Archean indicate that these rocks are Paleoproterozoic in age (∼1.7 Ga). Thus, the Cheyenne Belt has traditionally been placed too far south; it must lie in a poorly defined location north of these localities.