Kinetics of the metabolic effects, distribution spaces and lipid-bilayer affinities of the organo-chlorinated herbicides 2,4-D and picloram in the liver.

Tordon® is the commercial name of a mixture of two organo-chlorinated herbicides, 2,4-D and picloram. Both compounds affect energy transduction in isolated mitochondria and the present study aimed at characterizing the actions of these two compounds on liver metabolism and their cellular distribution in the isolated perfused rat liver. 2,4-D, but not picloram, increased glycolysis in the range from 10 to 400 µM. The redox potential of the cytosolic NAD+-NADH couple was also increased by 2,4-D. Both compounds inhibited lactate gluconeogenesis. Inhibitions by 2,4-D and picloram were incomplete, reaching maximally 46% and 23%, respectively. Both compounds diminished the cellular ATP levels. No synergism between the actions of 2,4-D and picloram was detected. Biotransformations of 2,4-D and picloram were slow, but their distributions occurred at high rates and were concentrative. Molecular dynamics simulations revealed that 2,4-D presented low affinity for the hydrophobic lipid bilayers, the opposite occurring with picloram. Inhibition of energy metabolism is possibly a relevant component of the toxicity of 2,4-D and of the commercial product Tordon®. Furthermore, the interactions of 2,4-D with the membrane lipid bilayer can be highly destructive and might equally be related to its cellular toxicity at high concentrations.

Persistence of picloram in soil with different vegetation managements.

Herbicides with long residual period may increase the risk of environmental contamination. Adequate management of forage can reduce the half-life of the picloram, one of the most herbicides used in weed control. This study aims to determine the half-life of picloram, using high-performance liquid chromatography in a cultivated soil with Brachiaria brizantha trimmed or not. Brachiaria brizantha was cultivated in 60 pots filled with samples of oxisol, and 30 others were kept uncultivated with this forage. This plant was cut off close to the ground, after 60 days of emergency on 30 vessels. Picloram was applied in all of the plots. Soil samples were collected at 2, 16, 30, 44, 58, 72, 86, 120, 150, and 180 days after the application of this herbicide. These samples were air-dried and stored at - 20 °C. Picloram was extracted by HPLC/UV-Vis detector. Half-life of this herbicide was calculated using kinetics models. The mere presence of roots in treatment with signalgrass cutoff did not reduce the concentrations of this herbicide, except when the emergence of new leaves occurred. The absence of B. brizantha cultivation in areas with application of picloram increases the risk of environmental contamination and successive crops due to the half-life of this herbicide. Brachiaria brizantha reduced half-life picloram and environmental risk in pastures. The validation method is suitable for determining picloram in low concentrations in soil.

Risk of Soil Recontamination Due to Using Eleusine coracana and Panicum maximum Straw After Phytoremediation of Picloram.

This study aimed to evaluate the herbicidal activity of picloram on the biomass of the remediation plants Eleusine coracana and Panicum maximum after cultivation in a soil contaminated with this herbicide. These species were grown in three soils, differentiated based on texture (clayish, middle, and sandy, with 460, 250, and 40 g kg(-1) of the clay, respectively), previously contaminated with picloram (0, 80, and 160 g ha(-1)). After 90 days, the plants were harvested and an extract was produced by maceration of leaves and stems of these plants. It was applied to pots containing washed sand, comprising a bioassay in a growth chamber using soybean as a bioindicator for picloram. Soil and plant samples were analyzed by HPLC. The results showed the presence of picloram or metabolites with herbicidal activity in the shoots of E. coracana and P. maximum at phytotoxic levels with regard to soybean plants, indicating that they work only as phytoextractors and that the presence of straw on the soil surface can promote recontamination within the area. It is not recommended to cultivate species susceptible to picloram in areas where it was reported remediation by E. indica and P. maximum and still present residues of these species.

Evaluating the degradation of the herbicides picloram and 2,4-D in a compartmentalized reactive biobarrier with internal liquid recirculation.

Tordon is a widely used herbicide formulation of 2,4-dichlorophenoxyacetic acid (2,4-D) and 4-amino-3,5,6-trichloropicolinic acid (picloram), and it is considered a toxic herbicide. The purposes of this work were to assess the feasibility of a microbial consortium inoculated in a lab-scale compartmentalized biobarrier, to remove these herbicides, and isolate, identify, and evaluate their predominant microbial constituents. Volumetric loading rates of herbicides ranging from 31.2 to 143.9 g m(-3) day(-1), for 2,4-D, and 12.8 to 59.3 g m(-3) day(-1) for picloram were probed; however, the top operational limit of the biobarrier, detected by a decay in the removal efficiency, was not reached. At the highest loading rates probed, high average removal efficiencies of 2,4-D, 99.56 ± 0.44; picloram, 94.58 ± 2.62; and chemical oxygen demand (COD), 89.42 ± 3.68, were obtained. It was found that the lab-scale biofilm reactor efficiently removed both herbicides at dilution rates ranging from 0.92 to 4.23 day(-1), corresponding to hydraulic retention times from 1.087 to 0.236 days. On the other hand, few microbial strains able to degrade picloram are reported in the literature. In this work, three of the nine bacterial strains isolated cometabolically degrade picloram. They were identified as Hydrocarboniphaga sp., Tsukamurella sp., and Cupriavidus sp.

GH3 expression and IAA-amide synthetase activity in pea (Pisum sativum L.) seedlings are regulated by light, plant hormones and auxinic herbicides.

The formation of auxin conjugates is one of the important regulatory mechanisms for modulating IAA action. Several auxin-responsive GH3 genes encode IAA-amide synthetases that are involved in the maintenance of hormonal homeostasis by conjugating excess IAA to amino acids. Recently, the data have revealed novel regulatory functions of several GH3 proteins in plant growth, organ development, fruit ripening, light signaling, abiotic stress tolerance and plant defense responses. Indole-3-acetyl-aspartate (IAA-Asp) synthetase catalyzing IAA conjugation to aspartic acid in immature seeds of pea (Pisum sativum L.) was purified and characterized during our previous investigations. In this study, we examined the effect of auxin and other plant hormones (ABA, GA, kinetin, JA, MeJA, SA), different light conditions (red, far-red, blue, white light), and auxinic herbicides (2,4-D, Dicamba, Picloram) on the expression of a putative GH3 gene and IAA-amide synthesizing activity in 10-d-old pea seedlings. Quantitative RT-PCR analysis indicated that the PsGH3-5 gene, weakly expressed in control sample, was visibly induced in response to all plant hormones, different light wavelengths and the auxinic herbicides tested. Protein A immunoprecipitation/gel blot analysis using anti-AtGH3.5 antibodies revealed a similar pattern of changes on the protein levels in response to all treatments. IAA-amide synthetase activity determined with aspartate as a substrate, not detectable in control seedlings, was positively affected by a majority of treatments. Based on these results, we suggest that PsGH3-5 may control the growth and development of pea plants in a way similar to the known GH3 genes from other plant species.

Assessment of plant-driven removal of emerging organic pollutants by duckweed.

Constructed treatment wetlands have the potential to reclaim wastewaters through removal of trace concentrations of emerging organic pollutants, including pharmaceuticals, personal care products, and pesticides. Flask-scale assessments incorporating active and inactivated duckweed were used to screen for plant-associated removal of emerging organic pollutants in aquatic plant systems. Removals of four of eight pollutants, specifically atrazine, meta-N,N-diethyl toluamide (DEET), picloram, and clofibric acid, were negligible in all experimental systems, while duckweed actively increased aqueous depletion of fluoxetine, ibuprofen, 2,4-dichlorophenoxyacetic acid, and triclosan. Active plant processes affecting depletion of experimental pollutants included enhancement of microbial degradation of ibuprofen, uptake of fluoxetine, and uptake of degradation products of triclosan and 2,4-dichlorophenoxyacetic acid. Passive plant processes, particularly sorption, also contributed to aqueous depletion of fluoxetine and triclosan. Overall, studies demonstrated that aquatic plants contribute directly and indirectly to the aqueous depletion of emerging organic pollutants in wetland systems through both active and passive processes.

Rapid and complete degradation of the herbicide picloram by Lipomyces kononenkoae.

An enrichment culture approach was used to isolate a pure culture of the yeast Lipomyces kononenkoae, which had the ability to grow on the herbicide picloram. The yeast rapidly and completely degraded 50 microg mL(-1) picloram by 48 h of growth. While L. kononenkoae was found to use both N atoms of picloram as a sole nitrogen source for growth, it failed to mineralize the herbicide or use it as a sole C source. Product analysis done using LC-ESI-MS indicated that biodegradation of picloram by L. kononenkoae proceeds via a didechlorinated, dihydroxylated, pyridinecarboxylic acid derivative. Our results are consistent with the hypothesis that the majority of picloram degradation in the soil is likely due to microbial catabolic processes.

Picloram resistance in transgenic tobacco expressing an anti-picloram scFv antibody is due to reduced translocation.

Picloram resistance exhibited by transgenic tobacco (Nicotiana tabacum) plants expressing an anti-picloram single-chain variable fragment (scFv) antibody was investigated through the study of homozygous lines expressing the antibody. Dose-response bioassays, using foliar application of picloram, showed that these homozygous transgenic plants were resistant to at least 5 g of ai ha-1 picloram and grew normally to produce seed, whereas wild-type plants did not survive. Although these lines had improved resistance compared with those previously reported, significant improvements are still required to achieve field-level resistance. Uptake and translocation studies demonstrated that [14C]picloram translocation from treated leaves to the apical meristem was reduced in transgenic versus wild-type plants. The presence of [14C]picloram visualized by autoradiography and quantified by liquid scintillation spectrometry, demonstrated the distribution of more picloram in the treated leaf and less in the apical meristem of transgenic plants when compared to wild-type plants. No differences between transgenic and wild-type plants were found in the distribution of [14C]clopyralid, a herbicide with structural similarity to picloram as well as the same mechanism of action. No differences were found in the metabolism of [14C]picloram. Taken together, these results suggest that reduced translocation to the site of action is a major mechanism responsible for picloram resistance in tobacco plants expressing this anti-picloram antibody.

Pharmacokinetics of picloram in male volunteers.

The fate of picloram (4-amino-3,5,6-trichloropicolinic acid), an active ingredient in TORDON brand herbicides, was defined in 6 healthy male volunteers following single po doses of 5.0 and 0.5 mg/kg, and a dermal dose of 2.0 mg/kg. Picloram was administered orally as the sodium salt in grape juice. The dermal dose was applied to the volunteers' backs as the free acid dissolved in ethanol. The data indicate picloram was rapidly absorbed from the gastrointestinal tract (t1/2 = 20 min) and rapidly excreted unchanged in the urine. Over 90% of the po dose was recovered as unchanged picloram in the urine excreted through 72 hr; most of the dose (greater than 75%) was excreted within 6 hr and the remainder was excreted with an average half-life of 27 hr. By comparison picloram was slowly absorbed through the skin (t1/2 = 12 hr) and, based on the quantity of picloram excreted in the urine, only a small fraction (0.2%) of the picloram applied to the skin was absorbed. These data indicate that picloram because of its rapid excretion has a low potential to accumulate in man during repeated or prolonged exposures. In addition, picloram was poorly absorbed through human skin and it is unlikely that acutely toxic quantities will be absorbed by this route.

Occupational exposure of herbicide applicators to herbicides used along electric power transmission line right-of-way.

Occupational exposures to herbicides were measured among 12 applicators in 1979 and 24 applicators in 1980, who were applying the three herbicides, 2,4-D, dichloroprop and picloram to electric power transmission rights of ways. In 1979 only urine was analyzed but in 1980 both breathing-zone air samples and urine were analyzed for herbicide residues. Dermal absorption was found to be the major absorption route being up to 50 times greater than exposure by the inhalation route when using a hand gun sprayer. Even with the mist blower herbicide application method, dermal absorption was 4 and 11 times greater than exposure by the inhalation route. Worker education on hazards of skin contact and improved protective equipment significantly reduced the 1980 urine concentrations of herbicide residues. A model is presented to relate the urinary concentrations to equivalent daily exposure levels.