Guilherme Lopes

Subproduto da indústria de alumínio como amenizante de solos contaminados com cádmio e chumbo

Soil pollution with trace elements has been of great concern in the last years due to the increase in contaminated areas, which calls for a better understanding of trace element availability and environmental remediation. This study evaluated the performance of an aluminum industry by-product as soil amendment in Cd- and Pb-contaminated soils. Samples of a sandy (50 g kg-1 clay) and a clayey (540 g kg-1 clay) soil were mixed with polluted soil (15 %) with high Cd and Pb concentrations and then treated with increasing doses: 0, 0.25, 0.50, 1.00, and 2.00 % (dry weight basis) - of an Al industry by-product. Additional treatments for comparison purposes consisted of: lime, a silicate by-product and turf, at rates of 0.25, 0.50, and 2.00 % respectively, as well as the non-contaminated soils. Plant and soil parameters were evaluated as follows: i) root and shoot dry matter production of Brachiaria decumbens and the respective Cd and Pb concentrations; and, ii) soil Cd and Pb concentrations, as well as the pH and the electrolytic conductivity (EC) of soil leachates. Cadmium and lead concentrations were measured in both unfiltered and 0.45 µm- filtered leachates, and Cd and Pb amounts in the plant roots and shoots were measured after nitric-perchloric digestion. Metal analysis were performed by either flame or graphite furnace atomic absorption spectrophotometry. Increasing the application rates of the Al industry by-product caused an increase in pH of the leachates and yielded higher EC values in the sandy than in the clayey soil. Unlike Cd, the Pb concentration differed between filtered and non-filtered soil leachates. The Al industry by-product favored the root and shoot dry matter production of B. decumbens and reduced Cd concentrations in the latter (mg kg-1) while the Pb concentration was not significantly altered.

Caracterização de subproduto da indústria de alumínio e seu uso na retenção de cádmio e chumbo em sistemas monoelementares

The present work aimed to characterize an aluminum industry by-product in natura (L.A. nat) and after phosphate and thermal pretreatments; evaluate the adsorption/desorption capacity of Cd and Pb by this L.A. nat form and after the aforementioned pretreatments, comparing them with an in natura iron mining by-product (L.F. nat). The L.A. nat presented a high pH as well as a high Na concentration and also an oxide-rich mineralogy. Pretreatment of the by-product had no significant effect upon Cd and Pd adsorption/desorption. The L.A. nat performed better than the L.F. nat as an Cd and Pb adsorbent.

A New Approach to Sampling Intact Fe Plaque Reveals Si-Induced Changes in Fe Mineral Composition and Shoot As in Rice

The Fe (oxyhydr)oxide rind, or Fe plaque, that forms on aquatic plant roots is an important sorbent of metal(loid)s and plays a role in the attenuation of metal(loid) uptake into higher plants. However, the mineral composition of Fe plaque and thus its potential to sorb metal(loid)s is affected by solution chemistry. The predominant strategy to characterize Fe plaque using dithionite-citrate-bicarbonate (DCB) extraction and elemental analysis reveals total Fe quantity but misses the mineral structure of the Fe (oxyhydr)oxide. Here, we developed a new technique using gentle sonication to sample intact Fe plaque from the root system and concentrate it for subsequent mineralogical characterization using synchrotron-based X-ray diffraction and X-ray absorption spectroscopy. We then coupled that data with conventional DCB extraction. The sample preparation method was effective at concentrating As-bound Fe plaque minerals in a uniform coating onto membranes that could easily be analyzed with X-ray techniques. Using these methods, we show that the percentage of poorly ordered Fe minerals in Fe plaque increases with increasing pore-water Si in flooded rice paddy soils. These findings have implications for understanding mineral controls on As cycling in the soil-rice nexus, and the sampling approach can be adopted for other aquatic plant systems.

Fitorremediação de solos contaminados com arsênio (As) utilizando braquiária

Conduziu-se este trabalho, com o objetivo de avaliar o potencial fitoextrator de arsenio (As) da Brachiaria decumbens Stapf., cultivada em casa de vegetacao, utilizando-se seis solos: Latossolo Amarelo Distrofico (LAd), Latossolo Vermelho Distrofico (LVd), Neossolo Fluvico (RU), Neossolo Quartzarenico (RQ), Gleissolo Haplico (GX) e Gleissolo Melânico (GM). O As foi adicionado aos solos na forma de arsenato de sodio heptahidratado nas doses 0, 25, 50, 200 e 800 mg kg-1. As plantas foram coletadas 55 dias apos a semeadura, separadas em parte aerea e raiz e, apos secagem do material em estufa, o mesmo foi digerido segundo o metodo 3051 da USEPA, sendo o teor de As determinado por espectrofotometria de absorcao atomica (EEA) com forno de grafite. Observou-se reducao no desenvolvimento da braquiaria de forma diferenciada nas seis classes de solo. Houve baixa translocacao do As, da raiz para a parte aerea, sendo essa especie considerada tolerante ao elemento e nao hiperacumuladora, podendo ser utilizada em programas de revegetacao de areas contaminadas pelo elemento.

PHOSPHORUS FRACTIONS AND AVAILABILITY IN A HAPLIC PLINTHOSOL UNDER NO-TILLAGE SYSTEM IN THE BRAZILIAN CERRADO

Soil use and fertilizer management as well as cropping systems influence phosphorus (P) availability in the soil. This study evaluated P fractions and availability in a chronosequence of anthropic influence in a Haplic Plinthosol, in sites under no-till for different time periods: seven (NT7), eleven (NT11), and sixteen (NT16) years. Labile P concentrations in the soil accounted for 10%, 8%, and 9% of the total P for treatments NT7, NT11, and NT16, respectively. The labile P values ranged between 99 and 122 mg dm-3andindicatied no time in no-tillage influence on labile P under in the studied Plinthosol. However, moderately labile P contents increased with time: NT7 < NT11 < NT16 (237, 341, and 375 mg dm-3, respectively). This increased followed the elevation in iron oxide contents, indicating a relationship between mineralogy and P accumulation. Regardless of no-tillage period, P contents extracted by Mehlich-1 were lower, underestimating the available P content, when compared with the extraction using a P selective resin. The stocks of labile P were sufficient to maintain high crop yields, according to the recommendations for the Cerrado region. Even if labile P contents are reduced, when adopting no-till system, the contents and stocks of P in the soil after several years were high enough to provide for adequate crop yields.

Selenium behavior in the soil environment and its implication for human health

O selenio (Se) e um elemento importante que foi descoberto em 1817 e reconhecido como elemento essencial para os humanos e animais desde os anos 60. Esse elemento apresenta, dentre outras funcoes, papel relevante no sistema antioxidante dos mamiferos. Niveis inadequados de Se no corpo humano tem sido uma preocupacao bem conhecida em muitas regioes do mundo. Esse problema de desnutricao com Se ocorre frequentemente devido a dietas pobres nesse elemento, o que provavelmente tem relacao com a baixa disponibilidade de Se nos solos onde as culturas agricolas estao sendo cultivadas. Atualmente, sabe-se que, alem da quantidade de Se contida nos alimentos, sua forma (e.g., inorgânica ou orgânica) e importante para a nutricao humana. Apesar da deficiencia de Se ser um problema em alguns locais, algumas regioes do mundo apresentam niveis altos de Se nos solos, causando varias desordens e doencas nas pessoas que moram nestas areas consideradas seleniferas. Sendo um elemento essencial, o Se deve ser suprido em quantidades adequadas para evitar efeitos prejudiciais. Assim, levando-se em consideracao a importância dos solos como um meio para garantir o suprimento adequado de Se para a populacao, esta revisao tem abordado o comportamento do Se no ambiente do solo (e.g., formas de Se e reacoes de adsorcao e dessorcao) e sua relevância para a saude humana. Como mensagem final, a compreensao do comportamento de Se em solos visando prever sua disponibilidade para as culturas agricolas em diferentes sistemas sera uma abordagem significativa em estudos futuros para estabelecer formas e doses seguras de Se para serem adicionadas em fertilizantes. A biofortificacao agronomica, aliada a biofortificacao genetica, de culturas basicas com Se tem sido sugerida como importante ferramenta para melhorar a ingestao de Se pela populacao que vive em locais onde os solos sao pobres em Se.

Soil management and ionic strength on selenite retention in oxidic soils

Sorption of selenium (Se) on soils may be influenced by factors that are changed though agricultural practices usually performed for crop production, such as soil pH, competing anion and organic matter contents, among others. This study aimed to evaluate the influence of soil management and ionic strength (IS) on Se retention in Brazilian soils, which is important to predict Se availability in both systems, native and cultivated soils. For that, adsorption and desorption reactions of Se were evaluated in 16 soil samples (eight from cultivated soils and eight from native soils), using solutions containing 100 and 500 μg L-1 Se in the form of sodium selenate and in two IS, 15 and 150 mM. Se adsorption varied as a function of IS for most soils, which may indicate that the adsorption mechanism by outer-sphere complex is important for selenate retention in the studied soils, but future studies involving other techniques, such as spectroscopic studies, are needed to more clearly confirm the adsorption mechanism. In general, adsorption varied in relation to soil characteristics, and native soils adsorbed larger Se amounts than the cultivated soils. In terms of desorption, soils which had larger Se adsorbed amounts also presented larger desorbed amounts. Finally, IS and soil management influenced the availability of selenate in the studied soils.