Persistence of the biocide activity of atrazine in soils of the southeast of Buenos Aires Province

Atrazine persistence in soils of the southeast of Buenos Aires Province, was studied by an oat bioassay. Atrazine doses of 0.58, 1.16, and 2.32 mg.g-1 dry soil weight (DSW) were applied to pots containing soils from Balcaree, A. Gonzáles Chaves and San Cayetano sites, whose organic matter (OM) content of soils were 5.70, 5.15, and 3,84%, respectively. Avena sativa cv. Millauquén plants were grownth in the pots under greenhouse conditions at different times after atrazine application. Shoots were evenly cut above the soil and dry weight determined as a measure of plant growth. Plants grown in non-sprayed soil were used as controls. Relative dry weight (RDW) of shoots was calculated as percentage of control. Atrazine phytotoxicity was expressed in terms of 50 % plant growth reduction (GR50) in the soils under study. Herbicide persistence was expressed in terms of days after treatment (DAT) needed for the plant to achieve 80% of RDW. Atrazine GR50 values of 0.30, 0.64, and 0.90 mg.g-1 DSW in soils from San Cayetano, Balcare and A.G. Chaves, were respectively obtained at 42 DAT. Herbicide persistences at the recommended dose (1.16 mg.g-1) were 100, 143, and 221 DAT for A.G. Chaves, Balcarce and San Cayetano soils, respectively. San Cayetano soil had both the lowest OM content and cation exchange capacity (CEC), as well as the highest pH, of all the soil studied here. These results were consistent with both the lowest GR50 and the highest persistence abtained for atrazine in this soil.

Carryover effect of fomesafen, applied on edible bean, on sucessional maize

Carryove reffects of fomesafen on successional maize were studied in clay soil. Fomesafen was applied as postemergence at Five rate s (0; 0.12 5: 0.25 ; 0.37 5, and 0.5 kg/ha-1) to edible beans. Maize was planted 198 and 65 days after fomesafen application in 1992 and 212 and 65 days after fomesafen application in 1993. Fomesafen residues were detected in soils up to 20cm depth but residue concentration was higher in 0-10 cm soil depth. Fomesafen residues reduced leaf chlrophyll content and root volume of 10 days old maize when planted 65 days after application but were not affected when planted 212 days after application. However, the decreases in leaf chlorophyll and root volume did not affect the maize yield.

Imidazolinone Degradation in Soil in Response to Application History

Accelerated herbicide degradation consists in its faster degradation in areas where it has been previously applied, due to the adaptation of microbial population to that particular compound. Accelerated degradation can reduce herbicide persistence and reduce its efficacy in soil. The objective of this study was to investigate if imidazolinone herbicides have enhanced microbial degradation in rice paddy soils. A laboratory experiment was conducted, evaluating the CO2 evolution rate from soils with and without history of herbicide application (imazapyr + imazapic and imazethapyr + imazapic), incubated with imidazolinone herbicides: imazethapyr, imazapyr, imazapic, imazamethabenz, imazamox and an untreated check. The amount of CO2 released from the soil was measured. As a result, the prior application of imidazolinones does not stimulate microbial degradation of herbicides from the same chemical group.

PERSISTENCE OF ATRAZINE, METRIBUZIN AND SIMAZINE HERBICIDES IN TWO SOILS

An oat bioassay was conducted in pots under greenhouse conditions to determine the persistence of atrazine, metribuzin and simazine herbicides in soils of the southeast of Buenos Aires Province, Argentina. Atrazine rates of 0, 0.58, 1.16 and 2.32 mug g-1 of active ingredient (a.i.), metribuzin rates of 0, 0.14, 0.28 and 0.56 mug g-1 of a.i., and simazine rates of 0, 0.72, 1.45 and 2.9 mug g-1 of a.i. dry soil weight were applied to pots containing soils from Balcarce and San Cayetano sites. Organic matter (OM) content and pH of Balcarce soil were 5.5% and 5.8%, while for San Cayetano soil were 2.9% and 6.7%, respectively. Relative dry weight (RDW) of oat shoots was calculated as percentage of control. Considering a 20% RDW reduction of oat shoots, persistences of recommended rates for the region were: atrazine (1.16 mug g-1 of a.i.), 78 and 130 days after treatment (DAT) for Balcarce and San Cayetano soil, respectively; metribuzin (0.28 mug-1 of a.i.), 63 and 77 DAT for Balcarce and San Cayetano soil, respectively; simazine (1.45 mug g-1 of a.i.), 81 and 156 DAT for Balcarce and San Cayetano soil, respectively. Results show that persistence of atrazine, metribuzin and simazine in soil increased with high rates, low OM content and high pH.

Influence of repeated applications of glyphosate on its persistence and soil bioactivity

Pesticide degradation studies are essential to evaluate its impact in the environment and on non-target organisms. The effect of repeated soil applications of the herbicide glyphosate on its dissipation and on soil microorganisms was studied by radiometric and microbial techniques. Results indicated fast dissipation of the [14C]-glyphosate or [14C]metabolites extractable residues (half-life of 0.92±0.29 month), but increasing half-lives of total mineralization ranging from 2.2 to 3.4 months as the number of applications increased from 1 to 4. No significant correlation was found between 14CO2 production and dehydrogenase activity.

Atrazine persistence applied as commercial and xerogel formulations in oxisol

The intensive use of pesticides have contaminated the soil and groundwater. The application of herbicides as controlled release formulations may reduce the environmental damage related to their use because it may optimize the efficiency of the active ingredient and reducing thus the recommended dose. The objective of this study was to evaluate the persistence of the herbicide atrazine applied as commercial formulation (COM) and as controlled release formulation (xerogel - XER) in Oxisol. The experimental design used was split-plot randomized-blocks with four replications, in a (2 x 6) + 1 arrangement. The two formulations (COM and XER) were assigned to main plots and different atrazine concentrations (0, 3.200, 3.600, 4.200, 5.400 and 8.000 g atrazine ha-1) were assigned to sub-plots. Persistence was determined by means of dissipation kinetics and bioavailability tests. The methodology of bioassays to assess the atrazine availability is efficient and enables to distinguish the tested formulations. The availability of atrazine XER is higher than the commercial in two different periods: up to 5 days after herbicide application and at the 35th day after application. The XER formulation tends to be more persistent in relation to COM formulation.

Soil Persistence of Chlorimuron-Ethyl and Metsulfuron-Methyl and Phytotoxicity to Corn Seeded as a Succeeding Crop

Two experiments were carried out to evaluate soil persistence of chlorimuron-ethyl and metsulfuron-methyl and phytotoxicity to corn seeded as a succeeding crop. One experiment was conducted with chlorimuron-ethyl applied at 20 g ha-1, and one with metsulfuron-methyl applied at 3.96 g ha-1. Treatments were arranged in a factorial design with two types of soil (sandy and clay), three irrigation regimes (daily, weekly and no irrigation) and four application timings (90, 60 and 30 days before corn seeding, as well as untreated plots). Soil persistence of the herbicides was influenced by water availability, molecule water solubility (leaching potential) and application timings prior to corn seeding. In sandy soil, with adequate water availability, leaching probably had the greatest influence, reducing the persistence of the products, and consequently allowing less time between product application and corn seeding. In clay soil, microbial degradation was probably more important, because it was assumed that the lesser time available for microorganism activity, the lesser the damage was observed for corn, as long as the crop had enough water availability. Metsulfuron-methyl was the least phytotoxic herbicide, possibly as a result of the properties of its molecule and its higher leaching potential.

The Intrahippocampal Infusion Of Crotamine From Crotalus Durissus Terrificus Venom Enhances Memory Persistence In Rats.

Previous research has shown that crotamine, a toxin isolated from the venom of Crotalus durissus terrificus, induces the release of acetylcholine and dopamine in the central nervous system of rats. Particularly, these neurotransmitters are important modulators of memory processes. Therefore, in this study we investigated the effects of crotamine infusion on persistence of memory in rats. We verified that the intrahippocampal infusion of crotamine (1 μg/μl; 1 μl/side) improved the persistence of object recognition and aversive memory. By other side, the intrahippocampal infusion of the toxin did not alter locomotor and exploratory activities, anxiety or pain threshold. These results demonstrate a future prospect of using crotamine as potential pharmacological tool to treat diseases involving memory impairment, although it is still necessary more researches to better elucidate the crotamine effects on hippocampus and memory.

Chitosan/tripolyphosphate Nanoparticles Loaded With Paraquat Herbicide: An Environmentally Safer Alternative For Weed Control.

Paraquat is a fast acting nonselective contact herbicide that is extensively used worldwide. However, the aqueous solubility and soil sorption of this compound can cause problems of toxicity in nontarget organisms. This work investigates the preparation and characterization of nanoparticles composed of chitosan and sodium tripolyphosphate (TPP) to produce an efficient herbicidal formulation that was less toxic and could be used for safer control of weeds in agriculture. The toxicities of the formulations were evaluated using cell culture viability assays and the Allium cepa chromosome aberration test. The herbicidal activity was investigated in cultivations of maize (Zea mays) and mustard (Brassica sp.), and soil sorption of the nanoencapsulated herbicide was measured. The efficiency association of paraquat with the nanoparticles was 62.6 ± 0.7%. Encapsulation of the herbicide resulted in changes in its diffusion and release as well as its sorption by soil. Cytotoxicity and genotoxicity assays showed that the nanoencapsulated herbicide was less toxic than the pure compound, indicating its potential to control weeds while at the same time reducing environmental impacts. Measurements of herbicidal activity showed that the effectiveness of paraquat was preserved after encapsulation. It was concluded that the encapsulation of paraquat in nanoparticles can provide a useful means of reducing adverse impacts on human health and the environment, and that the formulation therefore has potential for use in agriculture.

Removal Of Glyphosate Herbicide From Water Using Biopolymer Membranes.

Enormous amounts of pesticides are manufactured and used worldwide, some of which reach soils and aquatic systems. Glyphosate is a non-selective herbicide that is effective against all types of weeds and has been used for many years. It can therefore be found as a contaminant in water, and procedures are required for its removal. This work investigates the use of biopolymeric membranes prepared with chitosan (CS), alginate (AG), and a chitosan/alginate combination (CS/AG) for the adsorption of glyphosate present in water samples. The adsorption of glyphosate by the different membranes was investigated using the pseudo-first order and pseudo-second order kinetic models, as well as the Langmuir and Freundlich isotherm models. The membranes were characterized regarding membrane solubility, swelling, mechanical, chemical and morphological properties. The results of kinetics experiments showed that adsorption equilibrium was reached within 4 h and that the CS membrane presented the best adsorption (10.88 mg of glyphosate/g of membrane), followed by the CS/AG bilayer (8.70 mg of glyphosate/g of membrane). The AG membrane did not show any adsorption capacity for this herbicide. The pseudo-second order model provided good fits to the glyphosate adsorption data on CS and CS/AG membranes, with high correlation coefficient values. Glyphosate adsorption by the membranes could be fitted by the Freundlich isotherm model. There was a high affinity between glyphosate and the CS membrane and moderate affinity in the case of the CS/AG membrane. Physico-chemical characterization of the membranes showed low values of solubility in water, indicating that the membranes are stable and not soluble in water. The SEM and AFM analysis showed evidence of the presence of glyphosate on CS membranes and on chitosan face on CS/AG membranes. The results showed that the glyphosate herbicide can be adsorbed by chitosan membranes and the proposed membrane-based methodology was successfully used to treat a water sample contaminated with glyphosate. Biopolymer membranes therefore potentially offer a versatile method to eliminate agricultural chemicals from water supplies.

Chitosan Nanoparticles Loaded The Herbicide Paraquat: The Influence Of The Aquatic Humic Substances On The Colloidal Stability And Toxicity.

Polymeric nanoparticles have been developed for several applications, among them as carrier system of pesticides. However, few studies have investigated the fate of these materials in the environment in relation to colloidal stability and toxicity. In nature, humic substances are the main agents responsible for complexation with metals and organic compounds, as well as responsible for the dynamics of these nanoparticles in aquatic and terrestrial environments. In this context, the evaluation of the influence of aquatic humic substances (AHS) on the colloidal stability and toxicity of polymeric nanoparticles of chitosan/tripolyphosphate with or without paraquat was performed. In this study, the nanoparticles were prepared by the ionic gelation method and characterized by size distribution measurements (DLS and NTA), zeta potential, infrared and fluorescence spectroscopy. Allium cepa genotoxicity studies and ecotoxicity assays with the alga Pseudokirchneriella subcapitata were used to investigate the effect of aquatic humic substances (AHS) on the toxicity of this delivery system. No changes were observed in the physical-chemical stability of the nanoparticles due to the presence of AHS using DLS and NTA techniques. However some evidence of interaction between the nanoparticles and AHS was observed by infrared and fluorescence spectroscopies. The ecotoxicity and genotoxicity assays showed that humic substances can decrease the toxic effects of nanoparticles containing paraquat. These results are interesting because they are important for understanding the interaction of these nanostructured carrier systems with species present in aquatic ecosystems such as humic substances, and in this way, opening new perspectives for studies on the dynamics of these carrier systems in the ecosystem.

Anomalous diffusion in non-Markovian walks having amnestically induced persistence

We report numerically and analytically estimated values for the Hurst exponent for a recently proposed non-Markovian walk characterized by amnestically induced persistence. These results are consistent with earlier studies showing that log-periodic oscillations arise only for large memory losses of the recent past. We also report numerical estimates of the Hurst exponent for non-Markovian walks with diluted memory. Finally, we study walks with a fractal memory of the past for a Thue-Morse and Fibonacci memory patterns. These results are interpreted and discussed in the context of the necessary and sufficient conditions for the central limit theorem to hold.

Spontaneous symmetry breaking in amnestically induced persistence

We investigate a recently proposed non-Markovian random walk model characterized by loss of memories of the recent past and amnestically induced persistence. We report numerical and analytical results showing the complete phase diagram, consisting of four phases, for this system: (i) classical nonpersistence, (ii) classical persistence, (iii) log-periodic nonpersistence, and (iv) log-periodic persistence driven by negative feedback. The first two phases possess continuous scale invariance symmetry, however, log-periodicity breaks this symmetry. Instead, log-periodic motion satisfies discrete scale invariance symmetry, with complex rather than real fractal dimensions. We find for log-periodic persistence evidence not only of statistical but also of geometric self-similarity.

Frequency of LCT-13910C > T single nucleotide polymorphism associated with adult-type hypolactasia/lactase persistence among Brazilians of different ethnic groups

Background: Adult-type hypolactasia, the physiological decline of lactase some time after weaning, was previously associated with the LCT -13910C>T polymorphism worldwide except in Africa. Lactase non-persistence is the most common phenotype in humans, except in northwestern Europe with its long history of pastoralism and milking. We had previously shown association of LCT -13910C>T polymorphism with adult-type hypolactasia in Brazilians; thus, we assessed its frequency among different Brazilian ethnic groups. Methods: We investigated the ethnicity-related frequency of this polymorphism in 567 Brazilians [mean age, 42.1 +/- 16.8 years; 157 (27.7%) men]; 399 (70.4%) White, 50 (8.8%) Black, 65 (11.5%) Brown, and 53 (9.3%) Japanese-Brazilian. DNA was extracted from leukocytes; LCT -13910C>T polymorphism was analyzed by PCR-restriction fragment length polymorphism. Results: Prevalence of the CC genotype associated with hypolactasia was similar (57%) among White and Brown groups; however, prevalence was higher among Blacks (80%) and those of Japanese descent (100%). Only 2 (4%) Blacks had TT genotype, and 8 (16%) had the CT genotype. Assuming an association between CC genotype and hypolactasia, and CT and TT genotypes with lactase persistence, 356 (62.8%) individuals had hypolactasia and 211 (37.2%) had lactase persistence. The White and Brown groups had the same hypolactasia prevalence (similar to 57%); nevertheless, was 80% among Black individuals and 100% among Japanese-Brazilians (P < 0.01). Conclusion: The lactase persistence allele, LCT -13910T, was found in about 43% of both White and Brown and 20% of the Black Brazilians, but was absent among all Japanese Brazilians studied.

Photoinduced Degradation of the Herbicide Clomazone Model Reactions for Natural and Technical Systems

The photodegradation of the herbicide clomazone in the presence of S(2)O(8)(2-) or of humic substances of different origin was investigated. A value of (9.4 +/- 0.4) x 10(8) m(-1) s(-1) was measured for the bimolecular rate constant for the reaction of sulfate radicals with clomazone in flash-photolysis experiments. Steady state photolysis of peroxydisulfate, leading to the formation of the sulfate radicals, in the presence of clomazone was shown to be an efficient photodegradation method of the herbicide. This is a relevant result regarding the in situ chemical oxidation procedures involving peroxydisulfate as the oxidant. The main reaction products are 2-chlorobenzylalcohol and 2-chlorobenzaldehyde. The degradation kinetics of clomazone was also studied under steady state conditions induced by photolysis of Aldrich humic acid or a vermicompost extract (VCE). The results indicate that singlet oxygen is the main species responsible for clomazone degradation. The quantum yield of O(2)(a(1)Delta(g)) generation (lambda = 400 nm) for the VCE in D(2)O, Phi(Delta) = (1.3 +/- 0.1) x 10(-3), was determined by measuring the O(2)(a(1)Delta(g)) phosphorescence at 1270 nm. The value of the overall quenching constant of O(2)(a(1)Delta(g)) by clomazone was found to be (5.7 +/- 0.3) x 10(7) m(-1) s(-1) in D(2)O. The bimolecular rate constant for the reaction of clomazone with singlet oxygen was k(r) = (5.4 +/- 0.1) x 10(7) m(-1) s(-1), which means that the quenching process is mainly reactive.