Fate of Cd in Agricultural Soils: A Stable Isotope Approach to Anthropogenic Impact, Soil Formation, and Soil-Plant Cycling.

The application of mineral phosphate (P) fertilizers leads to an unintended Cd input into agricultural systems, which might affect soil fertility and quality of crops. The Cd fluxes at three arable sites in Switzerland were determined by a detailed analysis of all inputs (atmospheric deposition, mineral P fertilizers, manure, and weathering) and outputs (seepage water, wheat and barley harvest) during one hydrological year. The most important inputs were mineral P fertilizers (0.49 to 0.57 g Cd ha-1 yr-1) and manure (0.20 to 0.91 g Cd ha-1 yr-1). Mass balances revealed net Cd losses for cultivation of wheat (-0.01 to -0.49 g Cd ha-1 yr-1) but net accumulations for that of barley (+0.18 to +0.71 g Cd ha-1 yr-1). To trace Cd sources and redistribution processes in the soils, we used natural variations in the Cd stable isotope compositions. Cadmium in seepage water (δ114/110Cd = 0.39 to 0.79‰) and plant harvest (0.27 to 0.94‰) was isotopically heavier than in soil (-0.21 to 0.14‰). Consequently, parent material weathering shifted bulk soil isotope compositions to lighter signals following a Rayleigh fractionation process (ε ≈ 0.16). Furthermore, soil-plant cycling extracted isotopically heavy Cd from the subsoil and moved it to the topsoil. These long-term processes and not anthropogenic inputs determined the Cd distribution in our soils.

Developing a Medical School Curriculum on Racism: Multidisciplinary, Multiracial Conversations Informed by Public Health Critical Race Praxis (PHCRP).

Background: To fight racism and its potential influence on health, health care professionals must recognize, name, understand and talk about racism. These conversations are difficult, particularly when stakes feel high-in the workplace and in interracial groups. We convened a multidisciplinary, multi-racial group of professionals in two phases of this exploratory project to develop and pilot an intervention to promote effective dialogues on racism for first year medical students at the University of Minnesota Medical School. Methods: Informed by a Public Health Critical Race Praxis (PHCRP) methodology in Phase I, initial content was developed by a group of seven women primarily from racial and ethnic minority groups. In a later phase, they joined with five White (primarily male) colleagues to discuss racism and race. Participants met monthly for 12 months from Jan 2016-Dec 2016. All participants were recruited by study PI. An inductive approach was used to analyze meeting notes and post intervention reflections to describe lessons learned from the process of employing a PHCRP methodology to develop the aforementioned curriculum with a multidisciplinary and multi-racial group of professionals dedicated to advancing conversations on racial equity. Results: Participants from Phase I described the early meetings as "powerful," allowing them to "bring their full selves" to a project that convened individuals who are often marginalized in their professional environments. In Phase II, which included White colleagues, the dynamics shifted: "…the voices from Phase I became quieter…"; "I had to put on my armor and fight in those later meetings…". Conclusions: The process of employing PHCRP in the development of an intervention about racism led to new insights on what it means to discuss racism among those marginalized and those with privilege. Conversations in each phase yielded new insights and strategies to advance a conversation about racism in health care.

Improvements in Cd stable isotope analysis achieved through use of liquid-liquid extraction to remove organic residues from Cd separates obtained by extraction chromatography.

Organic compounds released from resins that are commonly employed for trace element separations are known to have a detrimental impact on the quality of isotopic analyses by MC-ICP-MS. A recent study highlighted that such effects can be particularly problematic for Cd stable isotope measurements (M. Gault-Ringold and C. H. Stirling, J. Anal. At. Spectrom., 2012, 27, 449-459). In this case, the final stage of sample purification commonly applies extraction chromatography with Eichrom TRU resin, which employs particles coated with octylphenyl-N,N-di-isobutyl carbamoylphosphine oxide (CMPO) dissolved in tri-n-butyl phosphate (TBP). During chromatography, it appears that some of these compounds are eluted alongside Cd and cannot be removed by evaporation due to their high boiling points. When aliquots of the zero-ε reference material were processed through the purification procedure, refluxed in concentrated HNO3 and analyzed at minimum dilution (in 1 ml 0.1 M HNO3), they yielded Cd isotopic compositions (ε114/110Cd = 4.6 ± 3.4, 2SD, n = 4) that differed significantly from the expected value, despite the use of a double spike technique to correct for instrumental mass fractionation. This result was accompanied by a 35% reduction in instrumental sensitivity for Cd. With increasing dilution of the organic resin residue, both of these effects are reduced and they are insignificant when the eluted Cd is dissolved in ≥3 ml 0.1 M HNO3. Our results, furthermore, indicate that the isotopic artefacts are most likely related to anomalous mass bias behavior. Previous studies have shown that perchloric acid can be effective at avoiding such effects (Gault-Ringold and Stirling, 2012; K. C. Crocket, M. Lambelet, T. van de Flierdt, M. Rehkämper and L. F. Robinson, Chem. Geol., 2014, 374-375, 128-140), presumably by oxidizing the resin-derived organics, but there are numerous disadvantages to its use. Here we show that liquid-liquid extraction with n-heptane removes the organic compounds, dramatically improving quality of the Cd isotope data for samples that are analyzed at or close to minimum dilution factors. This technique is quick, simple and may be of use prior to analysis of other isotope systems where similar resins are employed.

Cadmium Isotope Fractionation in Soil-Wheat Systems.

Analyses of stable metal isotope ratios constitute a novel tool in order to improve our understanding of biogeochemical processes in soil-plant systems. In this study, we used such measurements to assess Cd uptake and transport in wheat grown on three agricultural soils under controlled conditions. Isotope ratios of Cd were determined in the bulk C and A horizons, in the Ca(NO3)2-extractable Cd soil pool, and in roots, straw, and grains. The Ca(NO3)2-extractable Cd was isotopically heavier than the Cd in the bulk A horizon (Δ(114/110)Cdextract-Ahorizon = 0.16 to 0.45‰). The wheat plants were slightly enriched in light isotopes relative to the Ca(NO3)2-extractable Cd or showed no significant difference (Δ(114/110)Cdwheat-extract = -0.21 to 0.03‰). Among the plant parts, Cd isotopes were markedly fractionated: straw was isotopically heavier than roots (Δ(114/110)Cdstraw-root = 0.21 to 0.41‰), and grains were heavier than straw (Δ(114/110)Cdgrain-straw = 0.10 to 0.51‰). We suggest that the enrichment of heavy isotopes in the wheat grains was caused by mechanisms avoiding the accumulation of Cd in grains, such as the chelation of light Cd isotopes by thiol-containing peptides in roots and straw. These results demonstrate that Cd isotopes are significantly and systematically fractionated in soil-wheat systems, and the fractionation patterns provide information on the biogeochemical processes in these systems.

Decline of anthropogenic lead in South Atlantic Ocean surface waters from 1990 to 2011: New constraints from concentration and isotope data.

Anthropogenic emissions have severely perturbed the marine biogeochemical cycle of lead (Pb). Here, we present new Pb concentration and isotope data for surface seawater from GEOTRACES section GA02, sampled in the western South Atlantic in 2011. The South Atlantic is divided into three hydrographic zones: equatorial (0-20°S), subtropical (20-40°S), and subantarctic (40-60°S). The equatorial zone is dominated by previously deposited Pb transported by surface currents. The subtropical zone largely reflects anthropogenic Pb emissions from South America, whilst the subantarctic zone presents a mixture of South American anthropogenic Pb and natural Pb from Patagonian dust. The mean Pb concentration of 16.7 ± 3.8 pmol/kg is 34 % lower than in the 1990s, mostly driven by changes in the subtropical zone, with the fraction of natural Pb increasing from 24 % to 36 % between 1996 and 2011. Although anthropogenic Pb remains predominant, these findings demonstrate the effectiveness of policies that banned leaded gasoline.

Towards an understanding of the Cd isotope fractionation during transfer from the soil to the cereal grain.

Cd in soils might be taken up by plants, enter the food chain and endanger human health. This study investigates the isotopic fractionation of major processes during the Cd transfer from soils to cereal grains. Thereto, soil, soil solution, wheat and barley plants (roots, straw and grains) were sampled in the field at three study sites during two vegetation periods. Cd concentrations and δ114/110Cd values were determined in all samples. The composition of the soil solution was analyzed and the speciation of the dissolved Cd was modelled. Isotopic fractionation between soils and soil solutions (Δ114/110Cd20-50cm-soil solution = -0.61 to -0.68‰) was nearly constant among the three soils. Cd isotope compositions in plants were heavier than in soils (Δ114/110Cd0-20cm-plants = -0.55 to -0.31‰) but lighter than in soil solutions (Δ114/110Cdsoil solution-plants = 0.06-0.36‰) and these differences correlated with Cd plant-uptake rates. In a conceptual model, desorption from soil, soil solution speciation, adsorption on root surfaces, diffusion, and plant uptake were identified as the responsible processes for the Cd isotope fractionation between soil, soil solution and plants whereas the first two processes dominated over the last three processes. Within plants, compartments with lower Cd concentrations were enriched in light isotopes which might be a consequence of Cd retention mechanisms, following a Rayleigh fractionation, in which barley cultivars were more efficient than wheat cultivars.

Naming Institutionalized Racism in the Public Health Literature: A Systematic Literature Review.

OBJECTIVES: Although a range of factors shapes health and well-being, institutionalized racism (societal allocation of privilege based on race) plays an important role in generating inequities by race. The goal of this analysis was to review the contemporary peer-reviewed public health literature from 2002-2015 to determine whether the concept of institutionalized racism was named (ie, explicitly mentioned) and whether it was a core concept in the article. METHODS: We used a systematic literature review methodology to find articles from the top 50 highest-impact journals in each of 6 categories (249 journals in total) that most closely represented the public health field, were published during 2002-2015, were US focused, were indexed in PubMed/MEDLINE and/or Ovid/MEDLINE, and mentioned terms relating to institutionalized racism in their titles or abstracts. We analyzed the content of these articles for the use of related terms and concepts. RESULTS: We found only 25 articles that named institutionalized racism in the title or abstract among all articles published in the public health literature during 2002-2015 in the 50 highest-impact journals and 6 categories representing the public health field in the United States. Institutionalized racism was a core concept in 16 of the 25 articles. CONCLUSIONS: Although institutionalized racism is recognized as a fundamental cause of health inequities, it was not often explicitly named in the titles or abstracts of articles published in the public health literature during 2002-2015. Our results highlight the need to explicitly name institutionalized racism in articles in the public health literature and to make it a central concept in inequities research. More public health research on institutionalized racism could help efforts to overcome its substantial, longstanding effects on health and well-being.