Lead acetate ecotoxicity in tropical soils

Lead acetate (AcPb) is an important raw material used in chemical industries worldwide. The potential toxicity of AcPb is generally attributed to the presence of Pb. However, the effect of AcPb on the environment as a whole is still poorly known. This study aimed to evaluate AcPb toxicity on three standard species of soil invertebrates and two plant species using ecotoxicology tests. Three tropical soils (Oxisol, Inceptisol, and Tropical Artificial Soil (TAS)) were contaminated with different concentrations of AcPb and one dose of K-acetate (positive control). These soils were used in tests with Eisenia andrei (earthworm), Folsomia candida (springtail), Enchytraeus crypticus (enchytraeid), Zea mays (maize), and Phaseolus vulgaris (common bean). Dose-response curves obtained in the laboratory tests were used to estimate the EC₅₀ values for each species. Among invertebrates, the highest sensitivity to AcPb was observed for E. crypticus in the TAS (EC₅₀ = 29.8 mg AcPb kg^-1), whereas for E. andrei and F. candida the highest sensitivity was observed in the Oxisol (EC₅₀ = 141.9 and 1835 mg AcPb kg^-1, respectively). Folsomia candida was the least sensitive invertebrate species to AcPb in all soils. Among plant species, Z. mays was less sensitive (EC₅₀ = 1527.5 mg AcPb kg^-1) than P. vulgaris (EC₅₀ = 560.5 mg AcPb kg^-1) in the Oxisol. The present study evidenced that the toxicity of AcPb should not be attributed uniquely to the presence of Pb, as the treatment containing uniquely Ac provoked the same toxicity as the highest dose of AcPb.

A new hypothesis for the origin of Amazonian Dark Earths

Amazonian Dark Earths (ADEs) are unusually fertile soils characterised by elevated concentrations of microscopic charcoal particles, which confer their distinctive colouration. Frequent occurrences of pre-Columbian artefacts at ADE sites led to their ubiquitous classification as Anthrosols (soils of anthropic origin). However, it remains unclear how indigenous peoples created areas of high fertility in one of the most nutrient-impoverished environments on Earth. Here, we report new data from a well-studied ADE site in the Brazilian Amazon, which compel us to reconsider its anthropic origin. The amounts of phosphorus and calcium-two of the least abundant macronutrients in the region-are orders of magnitude higher in ADE profiles than in the surrounding soil. The elevated levels of phosphorus and calcium, which are often interpreted as evidence of human activity at other sites, correlate spatially with trace elements that indicate exogenous mineral sources rather than in situ deposition. Stable isotope ratios of neodymium, strontium, and radiocarbon activity of microcharcoal particles also indicate exogenous inputs from alluvial deposition of carbon and mineral elements to ADE profiles,  beginning several thousands of years before the earliest evidence of soil management for plant cultivation in the region. Our data suggest that indigenous peoples harnessed natural processes of landscape formation, which led to the unique properties of ADEs, but were not responsible for their genesis. If corroborated elsewhere, this hypothesis would transform our understanding of human influence in Amazonia, opening new frontiers for the sustainable use of tropical landscapes going forward.

Critical mercury concentration in tropical soils: Impact on plants and soil biological attributes

Mercury is a toxic element that becomes a problem when present at high concentrations in soils. Mercury toxicity in soils varies depending on chemical species, concentration, exposure routes, and organism vulnerability. There is little information regarding the toxicity of Hg in tropical soils, especially for establishing safe levels of this pollutant. The purpose of this study was to investigate Hg concentrations in two tropical soils and their effect on oats and common beans, as well as on soil biological attributes. The experiment was carried out in a greenhouse, following ISO 11.269-2 and OECD-208 guidelines. Oat and common bean were cultivated in a Typic Hapludox (TyHpx) and Rhodic Acrudox (RhAcx) contaminated with HgCl₂ at the following concentrations: 0, 2.5, 5.0, 10.0, 20.0, 40.0, and 80.0 mg of Hg kg^-1 of dry soil. The biological variables analyzed were seedling emergence, vegetative growth, chlorophyll content (SPAD index), gas exchange (photosynthetic rate, internal CO₂ concentration, transpiration rate, and stomatal conductance), and Hg concentration and accumulation in shoot dry matter. Microbial biomass carbon, soil basal respiration, and metabolic quotient (qCO₂) were also analyzed. Due to the sorptive characteristics of TyHpx, it had higher Hg concentrations than RhAcx. Mercury showed toxic effects on both oat and common bean species. However, common bean was affected only at concentrations higher than 20 mg kg^-1. The microbial community showed high sensitivity to soil Hg concentrations, but external factors, such as the plant species cultivated, influenced the sensitivity of the community. The microbiota was most sensitive in pots with common bean, and this effect was more pronounced at low clay and low organic matter contents (TyHpx). In this study, the concentration of 0.36 mg kg^-1 was critical for Hg in these soils, based on its deleterious effects on oat and common bean and on biological soil attributes.

Efficacy of and effect on tooth sensitivity of in-office bleaching gel concentrations: a randomized clinical trial

With the aim of reducing the side effects of in-office bleaching agents, less-concentrated hydrogen peroxide (HP) gels have been released by manufacturers. We evaluated the tooth sensitivity (TS) and bleaching efficacy (BE) of two HP concentrations in this study. Gels containing 35% and 20% HP (HP35 and HP20, respectively) were applied on teeth of 60 caries-free patients. Color was recorded at baseline and one week after the first and second bleaching sessions using the Vita Classical shade guide. TS was recorded on a 0-4 scale. BE at each weekly recall was evaluated by Kruskall-Wallis and Mann-Whitney tests (α=0.05). Absolute risk of TS and its intensity was evaluated by Fisher exact and Mann-Whitney tests, respectively (α=0.05). After two bleaching sessions, color change of approximately eight tabs was obtained with HP35; whereas, with HP20 it was six tabs (p<0.05). Only 26.7% (HP35) and 16.7% (HP20) of the participants reported TS, and no statistical differences were detected among them. Both in-office bleaching gels showed similar TS intensity, but the 35% HP agent produced faster bleaching.

[Influence of nutrition on hormone secretion. II. Study in Ribeirão, Pernambuco, Brazil (author's transl)]

1. Ten children from Ribeirão of both sexes, aged 1 to 6 years, suffering from 2nd and 3rd degree malnutrition were studied. The mean circulating growth hormone levels were significantly higher in both groups before dietary therapy, but the highest values were found in children with 3rd degree malnutrition. It was demonstrated that serum growth hormone levels were significantly related to the severity of malnutrition. A positive correlation was found between the nutritional status and the growth hormone levels. 2. The mean circulating insulin levels were lower before dietary therapy, but a significant correlation was not noted between the nutritional status and the insulin levels. 3. After the dietary therapy the hormone levels progressively returned to normal. These children showed a better recovery than those of the previous study, Agua Preta. This observation may be due to the active participation of the mothers in the nutritional recuperation of their children.

[Influence of nutrition on hormone secretion. I. Study in Agua Preta (author's transl)]

A positive correlation between the circulating growth hormone levels and the nutritional status was reported in 9 children of both sexes, aged 1 to 6 years, suffering from 2nd degree malnutrition. The mean serum insulin levels, the mean urinary 17-KS and 17-OHCS levels were low before the dietary therapy. No significant correlation between the levels of these hormones and the nutritional status was found. The hormone levels gradually returned to normal after the dietary therapy and the nutritional status of the children improved, according to the observed biochemical, clinical and anthropometric data.