Sensitivity of Eisenia andrei (Annelida, Oligochaeta) to a commercial formulation of abamectin in avoidance tests with artificial substrate and natural soil under tropical conditions

Obtaining ecotoxicological data on pesticides in tropical regions is imperative for performing more realistic risk analysis, and avoidance tests have been proposed as a useful, fast and cost-effective tool. Therefore, the present study aimed to evaluate the avoidance behavior of Eisenia andrei to a formulated product, Vertimec(A (R)) 18 EC (a.i abamectin), in tests performed on a reference tropical artificial soil (TAS), to derive ecotoxicological data on tropical conditions, and a natural soil (NS), simulating crop field conditions. In TAS tests an adaptation of the substrate recommended by OECD and ISO protocols was used, with residues of coconut fiber as a source of organic matter. Concentrations of the pesticide on TAS test ranged from 0 to 7 mg abamectin/kg (dry weight-d.w.). In NS tests, earthworms were exposed to samples of soils sprayed in situ with: 0.9 L of Vertimec(A (R)) 18 EC/ha (RD); twice as much this dosage (2RD); and distilled water (Control), respectively, and to 2RD: control dilutions (12.5, 25, 50, 75%). All tests were performed under 25 +/- A 2A degrees C, to simulate tropical conditions, and a 12hL:12hD photoperiod. The organisms avoided contaminated TAS for an EC50,48h = 3.918 mg/kg soil d.w., LOEC = 1.75 mg/kg soil d.w. and NOEC = 0.85 mg/kg soil d.w. No significant avoidance response occurred for any NS test. Abamectin concentrations in NS were rather lower than EC50, 48h and LOEC determined in TAS tests. The results obtained contribute to overcome a lack of ecotoxicological data on pesticides under tropical conditions, but more tests with different soil invertebrates are needed to improve pesticides risk analysis.

Temporary effect of chiseling on the compaction of a Rhodic Hapludox under no-tillage

Mechanical chiseling has been used to alleviate the effects of compaction in soils under no-tillage (NT). However, its effect on the soil physical properties does not seem to have a defined duration period. The purpose of this study was to evaluate the behavior of the bulk density (BD) and degree of compaction (DC) at different soil depths, after chiseling in no-tillage, for one year. The experiment was performed in Ponta Grossa, Paraná State, Brazil, using an Oxisol (Rhodic Hapludox). Bulk density and DC were previously measured in an area under NT for 16 years, then immediately after chiseling (CHI) in May 2009, six months after chiseling (CHI6M) in October 2009 and one year after chiseling (CHI12M) in May 2010. In the layers 0.0-0.10, 0.10-0.20 and 0.20-0.30 m, there was a significant BD reduction CHI and a marked increase CHI6M. The BD values measured CHI12M were similar to those before tillage. Chiseling reduced the DC in the layers 0.0-0.10 m and 0.10-0.20 m, but returned to the initial values one year later. During the evaluation periods CHI, CHI6M and CHI12M, the BD increased in the layer 0.30-0.40 m, compared with NT. The highest DC values were observed six months after chiseling; nevertheless the structural recovery of the soil was considerable, possibly due to the high degree of soil resilience and the influence of the wetting and drying cycles detected in the study period. The chiseling effects, evaluated by BD and DC, lasted less than one year, i.e., the beneficial short-term effects of chiseling on the reduction of the surface BD increased the risk of compaction in deeper soil layers.

Intervalo hídrico ótimo e grau de compactação de um latossolo vermelho após 30 anos sob plantio direto

A qualidade física do solo é um dos fatores determinantes da sustentabilidade agronômica, econômica e ambiental no sistema plantio direto (SPD). A compactação do solo tem sido apontada como um dos fatores de redução da qualidade física em solos sob SPD. Contudo, com a utilização do SPD, pode haver o incremento de matéria orgânica do solo e o desenvolvimento de um sistema poroso contínuo e estável, que atenuam os impactos negativos da compactação. O objetivo deste trabalho foi avaliar a qualidade física de um Latossolo Vermelho distroférrico sob SPD durante 30 anos, utilizando o intervalo hídrico ótimo (IHO) e o grau de compactação do solo (GC). Em uma área comercial com histórico de altas produtividades sob SPD, foram coletadas amostras de solo com estrutura preservada e deformada, para determinação da densidade do solo (Ds), do IHO e do GC. As amostras com estrutura preservada foram obtidas em três posições, relativas às linhas (L), entrelinhas (E) e posição intermediária entre as linhas e entrelinhas (PI) da cultura do milho. Foram determinadas as curvas de retenção de água e resistência do solo à penetração, bem como a Ds. A amostra de solo com estrutura deformada foi usada para obter a curva de compactação, utilizando o teste de Proctor. A Dmax foi obtida a partir da curva de compactação, e o GC foi determinado pela razão entre a Ds e a Dmax. Independentemente dos limites críticos de resistência à penetração (RP), verifica-se redução do IHO com o aumento da Ds. Os maiores valores do IHO foram verificados na posição de amostragem L, e a utilização de RP crítica maior que 2,0 MPa resultou em IHO condizente com a qualidade física desse solo sob SPD de longo tempo. A Dmax foi de 1,52 kg dm-3, e o GC variou de 64 a 87 %, sendo os maiores valores obtidos nas posições E e PI. Os valores de IHO e GC obtidos neste estudo indicam que a qualidade física desse solo não é limitante à produção das culturas após 30 anos de utilização do SPD.

Resiliência física de dois latossolos vermelhos sob plantio direto

A resiliência física de solos é proveniente de processos regenerativos que incluem ciclos de umedecimento e secamento, congelamento e descongelamento, assim como as atividades biológicas. Este estudo testou a hipótese de que as propriedades físicas do solo, como a permeabilidade do solo ao ar, densidade do solo, porosidade de aeração e porosidade total, são indicadores físicos eficientes para quantificar a resiliência de solos de diferentes texturas submetidos ao estresse mecânico (compactação) e após subsequentes ciclos de umedecimento e secamento. O objetivo foi avaliar o comportamento e a resiliência do solo por meio de propriedades físicas de dois Latossolos Vermelhos. Foram retiradas 25 amostras indeformadas (0,00-0,05 m) de dois solos: solo I, com textura argilosa, e solo II, com textura franco-argilo-arenosa, realizando as determinações das propriedades físicas nos tratamentos: antes da compactação (A), depois da compactação (C0) e após ciclos de umedecimento e secamento (C1, C2, C3 e C4). As propriedades densidade do solo e porosidade total não apresentaram recuperação da condição inicial após a compactação nos solos I e II; as propriedades conteúdo volumétrico de água e porosidade de aeração mostraram recuperação parcial apenas no solo I; e a permeabilidade do solo ao ar foi a propriedade que apresentou a melhor recuperação e a maior resiliência. Em relação ao distinto comportamento dos dois solos, observou-se que o solo I foi mais resiliente que o solo II nas propriedades que apresentaram recuperação.

Soil compressibility and least limiting water range of a constructed soil under cover crops after coal mining in Southern Brazil

The use of cover crops affects the support capacity of soil and least limiting water range to crop growth. The objective of this study was to quantify preconsolidation pressure (sigma(p)), compression index (CI) and least limiting water range (LLWR) of a reclaimed coal mining soil under different cover crops, in Candiota, RS, Brazil. In the experiment, with randomized blocks design and four replicates, the following cover crops (treatments) were evaluated: Hemarthria altissima (Poir.) Stapf & C.E. Hubbard, treatment 1 (T1), Paspalum notatum Flugge, treatment 4 (T4), Cynodon dactilon (L) Pers., treatment 5 (T5), control Brachiaria brizantha (Hochst.) Stapf, treatment 7 (T7) and without cover crop treatment 8 (reference treatment, T8). Soil compression and least limiting water range were evaluated with undisturbed samples at a depth of 0.00-0.05 m. In order to evaluate parameters of soil compressibility, the soil samples were saturated with water and subjected to -10 kPa matric potential and then submitted to a uniaxial compression test under the following pressures: 25, 50, 100, 200, 400, 800 and 1600 kPa. Cover crops decreased the preconsolidation pressure of constructed soils after coal mining and the greatest soil reclamation was obtained with the H. altissima cover crop, where the lowest degree of soil compactness and soil load capacity were observed. Soils cultivated under H. altissima or B. brizantha presented the highest least limiting water range and these two cover crops generated similar soil critical bulk density obtained by least limiting water range and soil load support capacity. (C) 2012 Elsevier B.V. All rights reserved.

Phenol biodegradation by a microbial consortium: application of artificial neural network (ANN) modelling

In this study, an effective microbial consortium for the biodegradation of phenol was grown under different operational conditions, and the effects of phosphate concentration (1.4 g L-1, 2.8 g L-1, 4.2 g L-1), temperature (25 degrees C, 30 degrees C, 35 degrees C), agitation (150 rpm, 200 rpm, 250 rpm) and pH (6, 7, 8) on phenol degradation were investigated, whereupon an artificial neural network (ANN) model was developed in order to predict degradation. The learning, recall and generalization characteristics of neural networks were studied using data from the phenol degradation system. The efficiency of the model generated by the ANN was then tested and compared with the experimental results obtained. In both cases, the results corroborate the idea that aeration and temperature are crucial to increasing the efficiency of biodegradation.

Artificial and natural radioactivity in edible mushrooms from Sao Paulo, Brazil

Environmental biomonitoring has demonstrated that organisms such as crustaceans, fish and mushrooms are useful to evaluate and monitor both ecosystem contamination and quality. Particularly, some mushroom species have a high capacity to retain radionuclides and some toxic elements from the soil and the air. The potential of mushrooms to accumulate radionuclides in their fruit-bodies has been well documented. However, there are no studies that determine natural and artificial radionuclide composition in edible mushrooms, in Brazil. Artificial (Cs-137) and natural radioactivity (K-40. Ra-226. Ra-228) were determined in 17 mushroom samples from 3 commercialized edible mushroom species. The edible mushrooms collected were Agaricus sp., Pleurotus sp. and Lentinula sp. species. The activity measurements were carried out by gamma spectrometry. The levels of Cs-137 varied from 1.45 +/- 0.04 to 10.6 +/- 0.3 Bq kg(-1), K-40 levels varied from 461 +/- 2 to 1535 +/- 10 Bq kg(-1), Ra-226 levels varied from 14 +/- 3 to 66 +/- 12 Bq kg(-1) and Ra-228 levels varied from 6.2 +/- 0.2 to 54.2 +/- 1.7 Bq kg(-1). Cs-137 levels in Brazilian mushrooms are in accordance with the radioactive fallout in the Southern Hemisphere. The artificial and natural activities determined in this study were found to be below the maximum permissible levels as established by national legislation. Thus, these mushroom species can be normally consumed by the population without any apparent risks to human health.