Jeffrey L. Howard

Sequential extraction analysis of heavy metals using a chelating agent (NTA) to counteract resorption

The geochemical partitioning of Pb, Ni and Zn in contaminated quartz-rich sediment and soil samples was characterized by sequential extraction analysis in the presence and absence of nitrilotriacetic acid (NTA). With NTA, levels of metals recovered are higher in the earlier steps and lower in the later steps of the procedure. This suggests that post-extraction resorption is effectively counteracted by chelation, thereby improving the accuracy of the method. An NTA concentration of 200 mg liter(-1) appears to be sufficient for counteracting resorption without causing significant dissolution of non-targeted phases in the samples studied. However, experiments using reference materials spiked with solutions containing Pb, Ni, Cu and Zn suggest that resorption will remain a problem when large amounts of strong sorbents such as organic matter are present. The results also show that although post-extraction resorption does occur in the absence of NTA, the magnitude of resorption is small (<20 to 30% of the summed total of metal present in the sample) in quartz-rich sediments.

Sequential extraction analysis of heavy metals in sediments of variable composition using nitrilotriacetic acid to counteract resorption

Artificial sediments were made that contained variable amounts (up to 20% by weight) of feldspar, calcite, Fe-oxide or organic matter. Analysis of samples spiked with Pb and Zn in the presence and absence of nitrilotriacetic acid (NTA) showed that 400 mg l(-1) of chelating agent greatly reduced or eliminated sorption in each case. Further study showed that this NTA concentration did not cause significant mineral dissolution. Resorption during sequential extraction analysis of artificial sediments is indicated by the fact that with NTA, levels of metals are higher in the first step and lower during subsequent steps, compared with levels obtained without NTA. However, the addition of 400 mg l(-1) of NTA to each extracting solution in the sequence appears to be effective for counteracting resorption in feldspathic, calcareous, ferruginous and carbonaceous sediments.

Sequential extraction analysis of lead in Michigan roadside soils: Mobilization in the vadose zone by deicing salts?

Abstract Sequential extraction analysis was used to characterize the geochemical partitioning of Pb in roadside soils of the Detroit, MI area. Four soil profiles (10, 30, 60, and 100 m from road) w...

Pedogenesis, geochemical forms of heavy metals, and artifact weathering in an urban soil chronosequence, Detroit, Michigan

An urban soil chronosequence in downtown Detroit, MI was studied to determine the effects of time on pedogenesis and heavy metal sequestration. The soils developed in fill derived from mixed sandy and clayey diamicton parent materials on a level late Pleistocene lakebed plain under grass vegetation in a humid-temperate (mesic) climate. The chronosequence is comprised of soils in vacant lots (12 and 44 years old) and parks (96 and 120 years old), all located within 100 m of a roadway. An A-horizon 16 cm thick with 2% organic matter has developed after only 12 years of pedogenesis. The 12 year-old soil shows accelerated weathering of iron (e.g. nails) and cement artifacts attributed to corrosion by excess soluble salts of uncertain origin. Carbonate and Fe-oxide are immobilizing agents for heavy metals, hence it is recommended that drywall, plaster, cement and iron artifacts be left in soils at brownfield sites for their ameliorating effects.

Micromorphology and dissolution of quartz sand in some exceptionally ancient soils

Abstract Scanning electron microscopy (SEM) was used to study the effect of prolonged weathering on the micromorphology of quartz sand. Three soil chronosequences in the southeastern United States (Virginia), with weathering profiles ranging in age from ∼ 90 ka to ∼ 10 Ma, were studied. Detrital sand grains from soil B horizons show that dissolution features are crystallographically controlled and develop progressively over time from smaller to larger etch pits, then to an interconnected network of grooves and crevasses, and finally to bulk grain decomposition. SEM also shows that disintegrating quartzite clasts in the oldest gravelly soils have been preferentially leached of silica cement, possibly due to selective weathering along ‘dust lines’ and spalling-off of quartz overgrowths. Severely etched quartz, usually attributed to tropical weathering, is an unreliable paleoclimate indicator because similar features can form as a result of prolonged weathering under a temperate climate. However, the well-defined relationship between quartz micromorphology and duration of weathering suggests that SEM is a useful tool for soil correlation and geomorphic analysis.

Artifact weathering, anthropogenic microparticles and lead contamination in urban soils at former demolition sites, Detroit, Michigan

A chronological sequence of urban soils 3-92 years old was studied to determine the effects of time on morphogenesis, artifact weathering, and the geochemical partitioning of Pb. Key chronofunctions determined are an increase in ˆA horizon Development Index (defined herein based on soil color) and water-soluble Pb, and a decrease in pH and C/N, with increasing soil age. Key artifact weathering reactions are: 1) portlandite in mortar altered to calcite, 2) ferrite in wrought-iron altered to ferrihydrite and goethite, and 3) carbonaceous materials altered to water-soluble organic substances. Mortar and wrought-iron were found to be Pb-bearing, but weather to produce immobilizing agents. Hence, they are both a source and a sink for Pb. The origin and mobilization of water-soluble Pb is complex and probably includes microbial extracellular polymeric substances, biodegraded soil organic matter, and solubilized organic substances derived from carbonaceous anthropogenic microparticles (soot, char and coal-related wastes).

Provenance of quartzite clasts in the Eocene–Oligocene Sespe Formation: Paleogeographic implications for southern California and the ancestral Colorado River

Quartzite clasts in fluvial Sespe Formation conglomerates of the Santa Monica Mountains were compared petrographically with potential source rocks in the Basin and Range and Transition Zone provinces to determine their provenance. Modal analysis indicates that Sespe orthoquartzite clasts are mainly quartzofeldspathic and derived from source rocks with craton-interior provenance. Such clasts were probably derived from Stirling Quartzite and Wood Canyon Formation sources in the northern Mojave Desert. The Mazatzal Peak Quartzite of central Arizona is the probable source of quartzolithic orthoquartzite clasts containing abundant detrital jasper grains. Sespe metaquartzite clasts are mainly from sources in the southern Mojave Desert, but some may be from the Yavapai terrane of central Arizona. The dual provenance of orthoquartzite clasts suggests that the Sespe paleoriver was a bifurcating system tapping both Mojave Desert and Sonora Desert sources. After compensating for Neogene displacement along the San Andreas fault, a paleogeographic reconstruction shows that there is a general spatial coincidence between Sespe (and other Cenozoic) paleodelta deposits around Los Angeles that contain exotic clasts, and the inferred location of the mouth of the Colorado River (assuming that it existed during the Eocene). Thus, the Colorado River may be much older than previously thought (as old as late Paleocene), and perhaps was once part of an ancient fluvial connection with the Mojave Desert interior.

Paleocene to Holocene paleodeltas of ancestral Colorado River offset by the San Andreas fault system, southern California

Upper Paleocene to middle Miocene fluvial-deltaic rocks in the Los Angeles and Ventura basins were deposited by a Colorado paleoriver prior to 300 km of dextral displacement on the San Andreas fault. During the late Miocene, movement on the fault and associated rifting in the Salton trough rerouted the paleoriver into the proto–Gulf of California. Since the Pliocene, translation of a moving Colorado deltaic depocenter along the fault has filled the Salton trough progressively southeastward. The postulated Colorado paleoriver extended north approximately along the lower course of the present river where it joined with Gila and Amargosa paleotributaries. Late Cenozoic tectonism disrupted the Amargosa paleoriver, and the modern course of the Colorado River through the lower Grand Canyon was developed.

The Quartzite Problem Revisited

A review of past terminology and previous petrological studies suggests that quartzite should be classified descriptively as both a sedimentary and a metamorphic rock. Quartzite is identified in the field as a quartz‐rich rock (exclusive of chert and vein quartz) that is exceptionally hard and, when broken by a rock hammer, fractures irregularly through both grains and cement (where present) to form an irregular or conchoidal fracture surface. Quartzite is differentiated from quartzose sandstone (arenite), which is softer and fractures around individual grains, and from chert and vein quartz by a bright vitreous luster. Quartzite is classified further on the basis of microscopic features into orthoquartzite and metaquartzite by the presence of clastic and metamorphic microtextures, respectively. Low‐grade, medium‐grade, and high‐grade subtypes of metaquartzite are differentiated by mortar, foam, and porphyroblastic microtextures, respectively. Composition is not used as a criterion for classification; hence, quartzite may contain a significant proportion (>10%) of nonquartz minerals. As defined here, quartzite is readily identified by megascopic features in outcrop, and subtypes of quartzite can be distinguished microscopically, even when the geologic context of the sample is unknown.

Geochemical behavior of lead in an alfisol and an ultisol at high levels of contamination

Abstract The behavior of Pb in the A and B horizons of an Alfisol from Michigan and an Ultisol from Virginia was studied to determine the effects of “shock”; loading. Combined sequential extraction‐sorption isotherm analysis (CSSA), a relatively new and little tested method, was used in the study. After spiking to simulate severe contamination (∼3000 to 60,000 mg/kg), CSSA revealed unexpectedly high levels of exchangeable Pb in the A horizon of the Alfisol and in both horizons of the Ultisol, and showed that the sorption capacities of the phases commonly responsible for fixation of Pb at low to moderate levels of contamination were exceeded. Carbonate sorbed the bulk of the Pb in the Alfisol B horizon and has a high sorption capacity in both soils, despite the presence of other phases with a strong affinity for Pb. Thus, when shock loading occurs (e.g., at a shooting range or dump sites), the highly contaminated A horizons of both soils are expected to pose a serious toxic hazard to humans, and groundwate...