Background and Reference Values of Metals in Soils from Paraíba State, Brazil

ABSTRACT Soil contamination by heavy metals threatens ecosystems and human health. Environmental monitoring bodies need reference values for these contaminants to assess the impacts of anthropogenic activities on soil contamination. Quality reference values (QRVs) reflect the natural concentrations of heavy metals in soils without anthropic interference and must be regionally established. The aim of this study was to determine the natural concentrations and quality reference values for the metals Ag, Ba, Cd, Co, Cu, Cr, Mo, Ni, Pb, Sb and Zn in soils of Paraíba state, Brazil. Soil samples were collected from 94 locations across the state in areas of native vegetation or with minimal anthropic interference. The quality reference values (QRVs) were (mg kg-1): Ag (<0.53), Ba (117.41), Cd (0.08), Co (13.14), Cu (20.82), Cr (48.35), Mo (0.43), Ni (14.44), Sb (0.61), Pb (14.62) and Zn (33.65). Principal component analysis grouped the metals Cd, Cr, Cu, Ni, Pb and Sb (PC1); Ag (PC2); and Ba, Co, Fe, Mn and Zn (PC3). These values were made official by Paraíba state through Normativa Resolution 3602/2014.

Determination of the critical period of weed control in corn using a thermal basis

Field studies were conducted over 3 years in southeast Buenos Aires, Argentina, to determine the critical period of weed control in maize (Zea mays L.). The treatments consisted of two different periods of weed interference, a critical weed-free period, and a critical time of weed removal. The Gompertz and logistic equations were fitted to relative yields representing the critical weed-free and the critical time of weed removal, respectively. Accumulated thermal units were used to describe each period of weed-free or weed removal. The critical weed-free period and the critical time of weed removal ranged from 222 to 416 and 128 to 261 accumulated thermal units respectively, to prevent yield losses of 2.5%. Weed biomass proved to be inverse to the crop yield for all the years studied. When weeds competed with the crop from emergence, a large increase in weed biomass was achieved 10 days after crop emergence. However, few weed seedlings emerged and prospered after the 5-6 leaf maize stage (10-20 days after emergence).

Effect of soil interacting herbicides on soybean nodulation in Balcarce, Argentina

Two trials were performed in Balcarce, Argentina (37° 45' LS; 58° 18' LW) during 1993-94, to assess the effect of eight herbicides applied individually or in tank mixtures, on nodule number, nodule dry weight, seed yield and N percent in seed in soybean Asgrow 3205, inoculated with Bradyrhizobium japonicum CB 1809. Individual herbicides and doses in kg ha-1 of a.i. were metribuzin (0.48), acetochlor (0.90), metolachlor (1), flumioxazin (0.075), trifluralin (0.96), imazaquin (0.20), imazethapyr (0.10) and chlorimuron ethyl (0.0125). The mixtures were metribuzin+acetochlor (0.48+0.9), flumioxazin+acetochlor (0.075+0.9), imazaquin+acetochlor (0.2+0.9), metribuzin+metolachlor (0.48+1.92), and flumioxazin+ metolachlor (0.075+1.92). A control treatment without herbicides was included. Both trials were laid out as randomized complete blocks with four replicates, on a loam illitic thermic petrocalcic Paleudoll, 5.7% organic matter (OM), 25% clay, 30.4 cmol kg-1 CEC. Nodules were sampled at V2 (second node), V6 (sixth node) and R5 (beginning seed) growth stages. Herbicides did not significantly affect the beginning of nodulation or nodule number and mass at R5, not either grain yield or N accumulation. This indicates lack of interference between soil interacting herbicides and N fixation in the high organic matter, loam soils of SE Buenos Aires province, even though a tendency in less number and dry weight of nodules was evident at the two latter growth stages.

Inter and intra-guild interactions in egg parasitoid species of the soybean stink bug complex

The objective of this research was to evaluate the parasitism behavior of Telenomus podisi Ashmead, Trissolcus basalis (Wollaston) e Trissolcus urichi Crawford (Hymenoptera: Scelionidae) on eggs of Nezara viridula L., Euschistus heros F., Piezodorus guildinii Westwood and Acrosternum aseadum Rolston (Heteroptera: Pentatomidae), in no choice and multiple choice experiments. For all parasitoid species, the results demonstrated the existence of a main host species that maximizes the reproductive success. The competitive interactions among the parasitoid species were investigated in experiments of sequential and simultaneous release of different combinations of parasitoid pairs on the hosts N. viridula, E. heros and A. aseadum. Exploitative competition was observed for egg batches at the genus level (Telenomus vs. Trissolcus) and interference competition at the species level (T. basalis vs. T. urichi). Trissolcus urichi was the most aggressive species, interfering with the parasitism of T. basalis. Generally, T. basalis showed an opportunistic behavior trying to parasitise eggs after T. urichi had abandoned the egg batch. The selection of parasitoid species for use in augmentative biological control programs should take into account the diversity of pentatomids present in soybean in addition to the interactions among the different species of parasitoids.

Sugarcane crop efficiency in two growing seasons in São Paulo State, Brazil

A conceptual framework for crop production efficiency was derived using thermodynamic efficiency concept, in order to generate a tool for performance evaluation of agricultural systems and to quantify the interference of determining factors on this performance. In Thermodynamics, efficiency is the ratio between the output and input of energy. To establish this relationship in agricultural systems, it was assumed that the input energy is represented by the attainable crop yield, as predicted through simulation models based on environmental variables. The method of FAO's agroecological zones was applied to the assessment of the attainable sugarcane yield, while Instituto Brasileiro de Geografia e Estatística (IBGE) data were used as observed yield. Sugarcane efficiency production in São Paulo state was evaluated in two growing seasons, and its correlation with some physical factors that regulate production was calculated. A strong relationship was identified between crop production efficiency and soil aptitude. This allowed inferring the effect of agribusiness factors on crop production efficiency. The relationships between production efficiency and climatic variables were also quantified and indicated that solar radiation, annual rainfall, water deficiency, and maximum air temperature are the main factors affecting the sugarcane production efficiency.

Methodological adaptation for nematodes extration in forest soils of the southern Mata Atlântica

The objective of this work was to clarify whether the method to extract nematodes from European soils is suitable for forest soils and litter in the eastern of Paraná state, Brazil, and whether nematode abundance differs between sites with different ecosystems and levels of human interference. The study sites were situated in the coastal area of the Serra do Mar, near the town of Antonina, in Eastern Paraná, Brazil. Cobb's sieving and decanting method was more appropriate than ISO method, since extraction efficiency was higher and intra-sample variability was significantly lower. In order to achieve an extraction efficiency higher than 90%, Cobb's method was modified. For the extraction of nematodes from litter, the Baermann funnel, with an extraction time of 48 hours, yielded an extraction efficiency higher than 90%. Nematode abundance in litter was higher than in soil. The mean number of individuals extracted from the litter increased with the age stage of the forest sites sampled, and there was no difference in the number of individuals in the soil of the four forest sites. Mean nematode abundance in soil in banana plantations was about twice as high compared to the banana-palmito mixed stands and to the forest sites.

Procedures for evaluating the tolerance of cassava genotypes to postharvest physiological deterioration

Abstract: The objective of this work was to define procedures to assess the tolerance of cassava genotypes to postharvest physiological deterioration (PPD) and to microbial deterioration (MD). Roots of six cassava genotypes were evaluated in two experiments, during storage under different environmental conditions: high temperature and low soil moisture; or low temperature and high soil moisture. Roots were treated or not with fungicide (carbendazim) before storage. Genotype reactions to MD and PPD were evaluated at 0, 2, 5, 10, 15, 20, and 30 days after harvest (DAH), in the proximal, medial, and distal parts of the roots. A diagrammatic scale was proposed to evaluate nonperipheral symptoms of PPD. Fungicide treatment and root position did not influence PPD expression; however, all factors had significant effect on MD severity. Genotypes differed as to their tolerance to PPD and MD. Both deterioration types were more pronounced during periods of higher humidity and lower temperatures. The fungicide treatment increased root shelf life by reducing MD severity up to 10 DAH. Whole roots showed low MD severity and high PPD expression up to 10 DAH, which enabled the assessment of PPD without significant interference of MD symptoms during this period.

Análise potenciométrica de redissolução com ultramicroeletrodos: fundamentos e aplicações na determinação de metais traços

The Potentiometric Stripping Analysis (PSA) is described with emphasis on ultramicroelectrode applications with a laboratory developed computer based instrumentation. The technique potentialities as compared with the voltammetric approach are pointed out based on the current literature. Some results of trace metals analysis including zinc, cadmium, lead and copper in vinegar and canned food samples are presented. The mainly advantage found in our laboratory was the technique capability to analyse natural samples with minimum matrix interference and the low level of noise found in our determinations.

Alternativas quimiométricas para a resolução de problemas analíticos clássicos: determinação espectrofotométrica de misturas de zircônio e háfnio

The determination of zirconium-hafnium mixtures is one of the most critical problem of the analytical chemistry, on account of the close similarity of their chemical properties. The spectrophotometric determination proposed by Yagodin et al. show not many practical applications due to the significant spectral interference on the 200-220 nm region. In this work we propound the use of a multivariate calibration method called partial least squares ( PLS ) for colorimetric determination of these mixtures. By using PLS and 16 calibration mixtures we obtained a model which permits determination of zirconium and hafnium with accuracy of about 1-2% and 10-20%, respectively. Using conventional univariate calibration the inaccuracy of the determination is about 10-25% for zirconium and above 57% for hafnium.

Filmes de óxidos anódicos de nióbio: efeito eletrocrômico e cinética da reação de eletro-intercalação

The aim of this work is to study the electrochromism and the reaction kinetics of lithium electrointercalation in anodic niobium oxide films. The oxide grown in an acid environment by application of an alternating potential shows interference colour (iridescence) and when reduced in lithium perclorate/PC solution, the intercalation of Li+ ions and electrons causes a reversible colour change (electrochromism), characterized here by electrochemical and optical measurements. A model where the reaction kinetics is dominated by diffusion of ionic pairs (Li+, e-) in the oxide film permitted the reproduction of current and absorbance temporal dependence, confirming the relationship between the electrochromic and electrochemical reactions. From the results obtained, a relation was established where the colour change is associated to the reduction of Nb+5 to Nb+4 ions with simultaneous cations injection.

X-ray fluorescence determination of adsorbed copper on activated charcoal after glycerin complexation

X-This work shows an alternative method to copper determination by X-Ray Fluorescence (XRF). Since copper concentration in natural waters is not enough to reach XRF detection limit, a liquid-solid preconcentration procedure was proposed. Glycerin was used to complex the metal increasing its adsorption on activated charcoal. The solid phase was used to XRF determination. Several parameters were evaluated, such as, the complexation pH, the charcoal adsorption limit and the glycerin concentration. The interferences are lead and bismuth and the sensitivities decreased in the order Cu2+, Bi3+ and Pb2+. The advantages of the method are its simplicity, low cost and low spectral interference.

Determinação permanganimétrica de íons Fe3+ com o uso de zinco metálico como redutor - uma contribuição ao ensino de química analítica

The classical volumetric titration of Fe2+ with MnO4-, used in some routine analysis as well as in undergraduate courses was improved. SnCl2 (to reduce Fe3+ to Fe2+) and HgCl2 (to oxidize excess SnCl2) were substituted by metallic zinc in boiling solutions, thus avoiding the toxic HgCl2 and Hg2Cl2; nitrate ions do not interfere in the improved methodology (it is an interference in the classical one) and the reproducibility of the determinations is increased by using metallic zinc. Determinations by students of undergraduate courses are discussed.

Determinação de carbaril utilizando testes ELISA (Enzyme-linked immunosorbent assay) e CLAE com detecção por arranjo de diodos

ELISAs have been applied to pesticide residue analysis due to their high sensitivity and selectivity. However, some ELISAs performance may be affected by matrix components. In this work, ELISA for carbaryl in water samples was checked for interference by naturally occurring fulvic acids. The results suggested that the high fulvic acid concentration (ž³30 mg L-1) and acidic pH conditions (pH 4.0) interfere with the signal detection decreasing the method sensitivity. A dilution of the samples and adjust to pH 8.0 are appropriate to minimize the matrix interferences in the ELISA method. Good correlation between ELISA and HPLC-DAD results was observed.

Adsorção de zinco e cádmio em colunas de turfa

The aim of this work was to evaluate the adsorption conditions of zinc and cadmium ions from aqueous solutions using a comercially available peat from Balneário Arroio do Silva, Santa Catarina State, Brazil. Adsorption studies were carried out in column experiments using radiotracers of the studied metals (65Zn and 115Cd). The pH influence and the interference of other ions, such as Na+, Ca2+, Fe3+ and Al3+on the adsorption process were investigated. The results showed that peat columns are able to retain more than 99% of metal ions in solution in a range of pH from 3,7 to 6,5. Ca2+ and Al3+ ions were the main interferent on adsorption of Zn and Cd ions in solution.

Deposição eletrolítica catódica e anódica simultâneas para minimizar interferências de cobre e chumbo na determinação espectrofotométrica de cádmio em água e alimentos via reação com Verde de Malaquita e iodeto

Simultaneous electrolytic deposition is proposed for minimization of Cu2+ and Pb2+ interferences on automated determination of Cd2+ by the Malachite Green-iodide reaction. During electrolysis of sample in a cell with two Pt electrodes and a medium adjusted to 5% (v/v) HNO3 + 0.1% (v/v) H2SO4 + 0.5 mol L-1 NaCl, Cu2+ is deposited as Cu on the cathode, Pb2+ is deposited as PbO2 on the anode while Cd2+ is kept in solution. With 60 s electrolysis time and 0.25 A current, Pb2+ and Cu2+ levels up to 50 and 250 mg L-1 respectively, can be tolerated without interference. With on-line extraction of Cd2+ in anionic resin minicolumn, calibration graph in the 5.00 - 50.0 µg Cd L-1 range is obtained, corresponding to twenty measurements per hour, 0.7 mg Malachite Green and 500 mg KI and 5 mL sample consumed per determination. Results of the determination of Cd in certified reference materials, vegetables and tap water were in agreement with certified values and with those obtained by GFAAS at 95% confidence level. The detection limit is 0.23 µg Cd L-1 and the RSD for typical samples containing 13.0 µg Cd L-1 was 3.85 % (n= 12).