Silvio César Sampaio

An alternative approach for the use of water solubility of nonionic pesticides in the modeling of the soil sorption coefficients.

The collection of data to study the damage caused by pesticides to the environment and its ecosystems is slowly acquired and costly. Large incentives have been established to encourage research projects aimed at building mathematical models for predicting physical, chemical or biological properties of environmental interest. The organic carbon normalized soil sorption coefficient (K(oc)) is an important physicochemical property used in environmental risk assessments for compounds released into the environment. Many models for predicting logK(oc) that have used the parameters logP or logS as descriptors have been published in recent decades. The strong correlation between these properties (logP and logS) prevents them from being used together in multiple linear regressions. Because the sorption of a chemical compound in soil depends on both its water solubility and its water/organic matter partitioning, we assume that models capable of combining these two properties can generate more realistic results. Therefore, the objective of this study was to propose an alternative approach for modeling logK(oc), using a simple descriptor of solubility, here designated as the logarithm of solubility corrected by octanol/water partitioning (logS(P)). Thus, different models were built with this descriptor and with the conventional descriptors logP and logS, alone or associated with other explanatory variables representing easy-to-interpret physicochemical properties. The obtained models were validated according to current recommendations in the literature, and they were compared with other previously published models. The results showed that the use of logS(p) instead of conventional descriptors led to simple models with greater statistical quality and predictive power than other more complex models found in the literature. Therefore, logS(P) can be a good alternative to consider for the modeling of logK(oc) and other properties that relate to both solubility and water/organic matter partitioning.

The effect of different log P algorithms on the modeling of the soil sorption coefficient of nonionic pesticides

Collecting data on the effects of pesticides on the environment is a slow and costly process. Therefore, significant efforts have been focused on the development of models that predict physical, chemical or biological properties of environmental interest. The soil sorption coefficient normalized to the organic carbon content (Koc) is a key parameter that is used in environmental risk assessments. Thus, several log Koc prediction models that use the hydrophobic parameter log P as a descriptor have been reported in the literature. Often, algorithms are used to calculate the value of log P due to the lack of experimental values for this property. Despite the availability of various algorithms, previous studies fail to describe the procedure used to select the appropriate algorithm. In this study, models that correlate log Koc with log P were developed for a heterogeneous group of nonionic pesticides using different freeware algorithms. The statistical qualities and predictive power of all of the models were evaluated. Thus, this study was conducted to assess the effect of the log P algorithm choice on log Koc modeling. The results clearly demonstrate that the lack of a selection criterion may result in inappropriate prediction models. Seven algorithms were tested, of which only two (ALOGPS and KOWWIN) produced good results. A sensible choice may result in simple models with statistical qualities and predictive power values that are comparable to those of more complex models. Therefore, the selection of the appropriate log P algorithm for modeling log Koc cannot be arbitrary but must be based on the chemical structure of compounds and the characteristics of the available algorithms.

Effects of the organic matter from swine wastewater on the adsorption and desorption of alachlor in soil.

The application of swine wastewater to the soil for agricultural purposes results in the addition of total and dissolved organic matter to the soil, which may interfere with the dynamics of pesticides in the soil. The objective of this study was to evaluate the effects of the application of total and dissolved organic matter from a biodigester and a treatment lagoon of swine wastewater in the adsorption and desorption of alachlor [2-chloro-2,6-diethyl-N(methoxymethyl acetamide)]. The assay was performed by the batch equilibrium method, and the results were fitted to the Freundlich model. The curve comparison test revealed a greater adsorption of alachlor in the soil treated with swine wastewater from the biodigester. The adsorption and desorption of alachlor increased in the soils where swine wastewater was added, and hysteresis was observed in all of the treatments.

Geochemistry of the Upper Paraná River floodplain: study of the Garças Pond and Patos Pond

Abstract The aim of this study was to investigate the temporal evolution of the supply of chemical elements to the Upper Paraná River floodplain and identify trends in the geochemistry of its drainage basin. The primary factor that regulates the supply of chemical elements of the Upper Paraná River floodplain is the flood pulse, which can be magnified by the El Niño—Southern Oscillation. Garças Pond is affected by agriculture, urbanization, discharge of industrial effluents and hydroelectric power production activities. Patos Pond is affected by sugarcane burning, gold mining, agriculture and urbanization.

Physico-chemical properties of common beans under natural and accelerated storage conditions

S.R.M. Coelho, S.H. Prudencio, D. Christ, S.C. Sampaio, and V. Schoeninger. 2013. Physico-chemical characterization of common beans under natural and accelerated storage conditions. Cien. Inv. Agr. 40(3): 629-636. The common bean is an important food in the human diet. Certain storage conditions, high temperatures and high humidity, cause a texture defect that reduces the acceptability of common beans. The present study aimed at evaluating the effect of storage on the physico-chemical properties of common bean grains and the relationship between accelerated aging at 40 °C and 76% RH and storage under natural conditions. Two varieties of common beans (Iapar 81 – carioca variety and Iapar 44 – black variety) were stored at 40 oC and 76% RH for 15, 30, 45, 60 and 75 days to accelerate aging. The same varieties were stored under environmental conditions (natural aging) for 3, 6, 9 and 12 months. For both storage conditions of each variety, fresh beans stored at 5 oC were used as a control group. In all of the samples, hardness, pH, acidity and the soluble protein percentage were analyzed. Both storage processes, in the natural and accelerated conditions, caused an increase in acidity (4.0 to 5.9 and 3.2 to 6.4 g acetic acid kg -1 ) and a decrease in cellular pH (6.65 to 6.45 and 6.65 to 6.45) and protein solubility (77 to 54 and 76 to 38%). The greatest percentage changes in the parameters of acidity, pH and soluble proteins were observed in the beans in the accelerated aging condition. Beans’ hardness during storage has a negative correlation with pH, which shows that it is a good indicator of grain quality. Natural storage for one year is equivalent to accelerated aging for 45 days at 40 °C and 76% RH.

Electrical conductivity of soil irrigated with swine wastewater estimated by time-domain reflectometry¹

A aplicacao de agua residuaria no solo e uma forma alternativa de fertilizacao do solo e de reuso da agua. Entretanto, deve-se dar especial atencao a tecnica, devido ao fato de que sucessivas aplicacoes podem provocar a salinizacao do solo. A reflectometria no dominio do tempo (TDR) permite nao apenas o monitoramento simultâneo e continuo do teor de agua e da condutividade eletrica aparente do solo, como tambem a determinacao indireta da condutividade eletrica de sua solucao. O presente trabalho teve por objetivo avaliar a viabilidade do emprego da TDR na determinacao indireta da condutividade eletrica de um extrato de solo saturado (CEse), empregando-se uma equacao empirica para o equipamento TDR Trase® modelo 6050X1. O experimento foi conduzido utilizando-se amostras deformadas de solo saturadas com agua residuaria da suinocultura nas proporcoes de 0, 0,45, 0,90, 1,80, 2,70 e 3,60 m3 m-3 de solo. As sondas utilizadas eram equipadas com tres hastes de 0,20 cm de comprimento, montadas artesanalmente. O modelo empirico que associou valores da condutividade eletrica mensurado por meio da TDR (CETDR) com CEse propiciou excelente ajuste, indicando a viabilidade da tecnica na determinacao da condutividade eletrica da solucao do solo.

Construction and calibration of TDR probes for volumetric water content estimation in a Distroferric Red Latosol

A determinacao da umidade volumetrica de solos e fator importante no manejo da irrigacao. Dentre os metodos indiretos para a estimativa, a tecnica da reflectometria no dominio do tempo (TDR) vem recebendo significativo enfoque. Como toda tecnica, apresenta vantagens e desvantagens, entre elas a maior desvantagem e a necessidade de calibracao e alto custo de aquisicao. O objetivo principal deste trabalho foi estabelecer um modelo de calibracao para o equipamento de TDR, Trase System Modelo 6050X1 para a estimativa da umidade volumetrica em um Latossolo Vermelho distroferrico tipico. A calibracao foi realizada em condicoes de laboratorio, utilizando amostras deformadas do solo em estudo, acondicionadas em colunas de PVC com volume de 0,0078 m3. As sondas de TDR, fabricadas artesanalmente com tres hastes e 0,20 m de comprimento, foram instaladas verticalmente nas colunas de solo, em um total de cinco sondas por coluna, totalizando dezesseis colunas. Realizaram-se as pesagens com balanca digital e leituras diarias da constante dieletrica com o equipamento TDR. O modelo linear θv =0,0103Ka + 0,1900 para estimativa da umidade volumetrica do solo em estudo apresentou excelente coeficiente de determinacao (0,93), viabilizando o uso das sondas na estimativa indireta da umidade do solo.

Nutrients behavior from the association pig slurry and chemical fertilizers on soybean crop

This study aimed at evaluating the effects of pig slurry application with mineral fertilizer on ions leaching from the soil in soybean crop. The experiment was carried out in 24 drainage lysimeters under protection. The soybean cultivar CD 202/COODETEC was sown in a soil that received 0, 100, 200 and 300 m3ha-1of pig slurry in one cycle, with or without mineral fertilizer. There were three samplings of soil throughout the trial to determine the pH, N, NO3-, K+, Ca2+, Mg2+, Na+, Cu+2, Zn+2, OM, CEC, EC and SAR six times during the crop cycle. The yield was determined in the plants. In soil, pig slurry increased the concentrations of pH, NO3-, K+, Zn+2, OM and CEC, while mineral fertilizer increased P and Zn+2concentrations. The limits observed for the leachate parameters did not present environmental problems according to the Brazilian legislation, but in the intermediate and long term, there special attention should be given to NO3-, P, Na+, EC and SAR. Soybean yield was higher with mineral fertilizer and increased with pig slurry application.

Evaluation of the antioxidant system and neurotoxic effects observed in Rhamdia branneri (Teleostei: Heptapteridae) sampled from streams of the lower Iguazu River basin

The use of multiple biomarkers has been shown to be an efficient method for evaluating environmental contamination. In this work, we evaluate neurotoxic effects and the antioxidant system responses of the R. branneri collected in two streams of lower Iguazu River basin, relating them with different percentage of vegetation coverture, presence of pesticides and fall and winter seasons. The biological samples were collected in March and August of 2015, from two streams that belong to the lower Iguazu River basin (Brazil): the Manoel Gomes River and the Arquimedes Stream. Soil analyses were performed, and the results showed the presence of the following organophosphates in the Manoel Gomes River and the Arquimedes Stream: disulfoton, methyl parathion, and ronnel. The present study detected inhibition of cholinesterase activity in the brain and muscle of fish samples during the fall from the Manoel Gomes River and the Arquimedes Stream. In the Manoel Gomes River, elevated lipoperoxidation was also observed during the fall. It was observed that the increase or decrease of biomarkers was related to temporal variation and, possibly, to the exposure of animals to agrochemicals. Although the Manoel Gomes River and the Arquimedes Stream are located in regions with large areas of vegetation, the soil analyses show that agrochemical residues are able to reach these locations, which suggests that the fauna are in contact with oxidant and anti-cholinesterase agents during the fall, in addition to respond differently during each season.