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Childhood lead poisoning in the U.S. continues to be a major unresolved child public health issue. One barrier to solving the problem of lead poisoning concerns current child blood lead level (BLL) monitoring practices. In most states, one or two BLL tests administered in early childhood are used to rule out lead exposure. Current knowledge, however, regarding the multiple, complex biological mechanisms that underlie lead absorption and distribution during development suggests that child BLLs should be assumed to be an informative but necessarily fluctuating metric of current child lead exposure. We review some key mechanisms and pathways that influence lead absorption, lead distribution, and the stability of lead in red blood cells. We also consider how each of these factors and their development are likely to drive fluctuations in child BLLs over time. The goal of this special report is to provide a starting point for change in current child BLL testing practices. Solving the problem of child lead exposure will require new approaches to child BLL testing that take into account likely fluctuations in child BLLs., Introduction Lead poisoning in U.S. children continues at staggering rates in selected sectors, particularly among those living in under-resourced communities where older unrenovated housing and lead paint are still major [...]

Soils with strong texture-contrast between A and B horizons dominate the agricultural zones of the west and south of Australia. The B horizon is often sodic and of much finer texture than the A (or E) horizon above, and can have a bulk density as high as 2 g [cm.sup.-3]. When dry, these B horizons may severely impede the root growth of annual cereal crops. The objective of this study was to characterise the mineralogy and chemistry of fine pores at the interface of an E and a sodic B horizon of an Alfisol (Sodosol). Micro-X-ray fluorescence spectroscopy (μ-XRF) was used to locate the distribution of calcium (Ca), manganese (Mn), iron (Fe), zinc (Zn), and copper (Cu), and μ-X-ray absorption near edge structure (μ-XANES) spectroscopy or μ-X-ray absorption fine structure (μ-XAFS) spectroscopy to investigate speciation of Fe, Mn, Zn, and Cu around a pore. Both natural aggregates and thin sections were employed but measurements from thin sections were more useful because of the smaller thickness of the sample. The distribution maps showed that Ca was present in the pores but the other elements were not. Copper, Mn, and Zn were concentrated around the micropore. Manganese was always well correlated with Fe. Manganese was found in reduced form, i.e. Mn(II), and associated with phosphates, whereas Fe was in oxidised form and mostly associated with oxides. Zinc was mostly associated with carbonates (C[O.sub.3]), sulfates (S[O.sub.4]), and silicates (Si[O.sub.4]). The results were then compared with measurements by laser ablation inductively coupled plasmamass spectrometry (LA-ICP-MS). Only some of the observations made by μ-XRF were confirmed by LA-ICP-MS, most probably because of the superior detection limits of synchrotron-based μ-XRF., Introduction Soils with strong texture-contrast between surface and B horizons, called duplex soils in Australia, dominate the agricultural zones of the west and south of Australia. The A and E [...]

The potential availability (E) and partitioning ([K.sub.d]) of Se added to three soils as elemental Se ([Se.sup.0]), sodium selenite ([MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]), and sodium selenate ([MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]) were measured by isotopic dilution using either [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]. The soils were kept either submerged or at 80% water-holding capacity for either 15 or 60 d. Both [K.sub.d] and E values were controlled by the type of Se, soil moisture content, and time after application. The [K.sub.d] values for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] were largely controlled by soil type, with the soil having the lowest pH and highest concentrations ofoxalate-extractable Al and Fe having the highest [K.sub.d] values. The [K.sub.d] values for [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], on the other hand, were largely influenced by the incubation period, and to a lesser extent soil type and moisture conditions. Selenate [K.sub.d] values decreased with incubation and were higher under submerged conditions. The availability of [Se.sup.0] as measured by concentrations of labile Se species was low due to limited oxidation to [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]. Elemental Se is therefore not suitable for preplant Se fertilization of lowland rice (O*Tza satit,a L.) because it is not readily oxidized. In the submerged soils, concentrations of labile [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] and [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] were also low, with >80% of the Se added as either [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] or [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] being fixed into nonlabile pools, probably through reduction to [Se.sup.0]. Rates of oxidation of [Se.sup.0] will play a critical role in determining whether reduced [Se.sup.0] formed in submerged soils after fertilization will contribute to plant Se uptake through oxidation either during field drainage before harvest or in the rice rhizosphere. doi: 10.2136/sssaj2009.0416

In Australia a class of soils known as duplex soils covers approximately 20% of the continent. Their defining characteristic is a sharp texture contrast between the A (or E) and B horizon. The upper B horizon at the point of contact with the E horizon is often highly sodic and of such a high strength that root growth and proliferation, water conductivity, aeration, water storage, and water uptake are restricted. Roots growing in these soils rely on channels created by previous roots or cracks arising from shrink-swell forces associated with seasonal wetting and drying. Although the characteristics of rhizospheres compared with the soil matrix are well documented there is a paucity of knowledge about how long these changes persist after roots decay. This knowledge is fundamental to our understanding of root growth in duplex soils in which plants rely on pore networks formed by previous plants to proliferate in the subsoil. In this study we investigated the heterogeneous chemistry of micropores in situ using synchrotron-based [mu]-x-ray fluorescence spectroscopy (XRF), [mu]-x-ray absorption near edge structure spectroscopy (XANES), and extended [mu]-x-ray absorption fine structure spectroscopy (EXAFS). The distribution maps of Ca, Mn, Fe, Cu, and Zn at micrometer resolution were collected using [mu]-XRF. Subsequently, specific locations with higher concentrations (hot spots) of Mn, Fe, Cu, or Zn were selected and XANES and EXAFS spectra were collected to study the speciation of these elements around the micropore compared with the soil matrix. The [mu]-XRF maps showed that Mn was depleted around one of the micropores studied but accumulated around another micropore. Copper and Zn accumulated around the micropores, whereas Ca was predominantly inside micropores. There was no difference between matrix and micropore surface with respect to the distribution of Fe. Around micropores Mn was present in reduced form (Mn II) and Fe was in its oxidized form (Fe III). Manganese and Cu were present in the form of phosphates, Fe as Fe oxides, and Zn as Zn phosphates and adsorbed Zn. Abbreviations: APS, Advanced Photon Source; EDXA, Energy Dispersive x-ray analysis; EXAFS, extended x-ray absorption fine structure; LCF, Linear combination fitting; SEM, scanning electron microscope; XANES, x-ray absorption near edge structure; XRF, x-ray fluorescence.

The benefits of Mn and Zn fluid fertilizers over conventional granular products in calcareous sandy loam soils have been agronomicalty demonstrated. We hypothesized that the differences in the effectiveness between granular and fluid Mn and Zn fertilizers is due to different Mn and Zn reaction processes in and around fertilizer granules and fluid fertilizer bands. We used a combination of several synchrotron-based x-ray techniques, namely, spatially resolved micro-x-ray fluorescence (p-XRF), micro-x-ray absorption near edge structure spectroscopy (p-XANES), and bulk-XANES and -extended x-ray absorption fine structure (EXAFS) spectroscopy, along with several laboratory-based x-ray techniques to speciate different fertilizerderived Mn and Zn species in highly calcareous soils to understand the chemistry underlying the observed differential behavior of fluid and granular micronutrient forms. Micro-XRF mapping of soil-fertilizer reactions zones indicated that the mobility of Mn and Zn from liquid fertilizer was greater than that observed for equivalent granular sources of these micronutrients in soil. After application of these micronutrient fertilizers to soil, Mn and Zn from liquid fertilizers were found to remain in comparatively more soluble solid forms, such as hydrated Mn phosphate-like, Mn calcite-like, adsorbed Zn-like, and Zn silicate-like phases, whereas Mn and Zn from equivalent granular sources tended to transform into comparatively less soluble solid forms such as Mn oxide-like, Mn carbonate-like, and Zn phosphate-like phases. Abbreviations: EDAX, energy dispersive x-ray analysis; EXAFS, extended x-ray absorption fine structure; LCF, linear combination fitting; MAP, monoammonium phosphate; SEM, scanning electron microscopy; TGMAP, technical-grade monoammonium phosphate; XANES, x-ray absorption near-edge structure; XAS, x-ray absorption spectroscopy; XRD, x-ray diffraction; XRF, x-ray fluorescence.

We employed x-ray computed microtomography (X-ray CT) to observe differences in moisture around fertilizer P granules (monoammonium phosphate, MAP) versus injection zones of fluid P fertilizer (technical grade monoammonium phosphate, TG MAP) in a calcareous soil over time. X-ray CT allows nondestructive visualization of small columns containing soils and fertilizers. We were able to visualize the increase in density around the highly hygroscopic fertilizer granule over time. It appeared that both water flow toward the granule and precipitation of P could be responsible for the development of about 1 mm thick high density zone immediately adjacent to the granule. The mass flow of water toward the granule may have slowed or restricted the diffusion of fertilizer P from the granule, thus increasing the chances for P fixation through precipitation reactions. Also, the granule became less dense with time indicating the progress of granule dissolution. In contrast, injection of fluid fertilizer (TG-MAP) in soil did not result in moisture changes over time as evidenced by a lack of X-ray CT detectable density differences in the soil column. These data support previous findings that, when P is supplied in granular form, P diffusion and isotopic lability in calcareous soils are reduced compared with equivalent liquid fertilizer formulations, probably due to precipitation reactions induced by osmotically induced flow of soil moisture into the fertilizer granule.