In-situ treatment of herbicide-contaminated groundwater-Feasibility study for the cases atrazine and bromacil using two novel nanoremediation-type materials.

Two injectable reactive and sorption-active particle types were evaluated for their applicability in permeable reaction zones for in-situ removal of herbicides ("nanoremediation"). As model substances, atrazine and bromacil were used, two herbicides frequently occurring in groundwater. In order to provide recommendations for best use, particle performance was assessed regarding herbicide degradation and detoxification. For chemical reduction, Carbo-Iron® was studied, a composite material consisting of zerovalent iron and colloidal activated carbon. Carbo-Iron reduced bromacil with increased activity compared to nanoscale zerovalent iron (nZVI). The sole reaction product, 3-sec-butyl-6-methyluracil, showed 500-fold increase in half-maximal-effect concentration (EC50) towards the chlorophyte Scendesmus vacuolatus compared to the parent compound. The detoxification based on dehalogenation confirmed the dependency of the specific mode-of-action on the carbon-halide bond. For atrazine, neither nZVI nor Carbo-Iron showed significant degradation under the conditions applied. As novel subsurface treatment option, Trap-Ox® zeolite FeBEA35 was studied for generation of in-situ permeable oxidation barriers. Both adsorbed atrazine and bromacil underwent fast unselective oxidation. The transformation products of the Fenton-like reaction were identified, and oxidation pathways derived. For atrazine, a 300-fold increase in EC50 for S. vacuolatus was found over the duration of the reaction, and a loss of phytotoxicity to non-detectable levels for bromacil.

Influence of Three Citrus Herbicides on Potential Production of Sorghum bicolor 'Topper 76-6' as a Bioenergy Crop.

Planting bioenergy crops on land previously used for citrus production may offer an alternative source of revenue for growers looking for alternative-to-citrus crops. However, residual herbicides used in citrus production may adversely affect alternative crops. This study evaluated effects of three herbicides (bromacil, norflurazon, and simazine) commonly used in citrus production on the bioenergy crop Sorghum bicolor 'Topper 76-6'. Plants were exposed to herbicides in soil for 1-5 weeks and observations of effects on photosynthetic quantum yield, leaf greenness, height, and biomass were made. Results indicate that concentrations of bromacil and norflurazon greater than 0.09 and 0.07 mg/kg and simazine >0.46 mg/kg will impair growth and development in similar soils. Concentrations below these may also be toxic.

Phytotoxicity of chiral herbicide bromacil: Enantioselectivity of photosynthesis in Arabidopsis thaliana.

With the wide application of chiral herbicides and the frequent detection of photosystem II (PSII) herbicides, it is of great importance to assess the direct effects of PSII herbicides on photosynthesis in an enantiomeric level. In the present study, the enantioselective phytotoxicity of bromacil (BRO), typical photosynthesis inhibition herbicide, on Arabidopsis thaliana was investigated. The results showed that S-BRO exhibited a greater inhibition of electron transmission in photosystem I (PSI) of A. thaliana than R-BRO by inhibiting the transcription of fnr 1. S-BRO also changed the chlorophyll fluorescence parameters Y (II), Y (NO), and Y (NPQ) to a greater extent than R-Bro. Transcription of genes psbO2, Lhcb3 and Lhcb6 was down-regulated in an enantioselective rhythm and S-BRO caused more serious influence, indicating that S-BRO did worse damage to the photosystem II (PSII) of A. thaliana than R-BRO. This study suggested that S-BRO disturbed the photosynthesis of plants to a larger extent than R-BRO and provided a new sight to evaluate the phytotoxicity of chiral herbicides.

Photo-catalysis of bromacil under simulated solar light using Au/TiO2: evaluation of main degradation products and toxicity implications.

Bromacil (5-bromo-3-sec-butyl-6-methyluracil) is a substituted uracil herbicide used worldwide. It is not readily biodegradable and has the potential to contaminate different types of water bodies with possible impact on diverse non-target species. In this work, degradation of bromacil in aqueous Au/TiO2 suspension under simulated sunlight allowed fourteen degradation products to be identified. The photodegradation of bromacil followed (pseudo) first order kinetics in the presence of 0.2 g L(-1) of Au/TiO2 with a half-life of 25.66 ± 1.60 min and a rate constant of 0.0271 ± 0.0023 min(-1). Transformation routes of the photo-catalytic degradation of bromacil were then proposed. Complementary toxicity assessment of the treated bromacil solution revealed a marked decrease in toxicity, thereby confirming that by-products formed would be less harmful from an environmental point of view. Photo-catalytic degradation of bromacil thus appears to hold promise as a cost-effective treatment technology to diminish the presence of this herbicide in aquatic systems.

Combined toxicity of pesticide mixtures on green algae and photobacteria.

Different organisms have diverse responses to the same chemicals or mixtures. In this paper, we selected the green algae Chlorella pyrenoidosa (C. pyrenoidosa) and photobacteria Vibrio qinghaiensis sp.-Q67 (V. qinghaiensis) as target organisms and determined the toxicities of six pesticides, including three herbicides (simetryn, bromacil and hexazinone), two fungicides (dodine and metalaxyl) and one insecticide (propoxur), and their mixtures by using the microplate toxicity analysis. The toxicities of three herbicides to C. pyrenoidosa are much higher than those to V. qinghaiensis, and the toxicities of metalaxyl and propoxur to V. qinghaiensis are higher than those to C. pyrenoidosa, while the toxicity of dodine to C. pyrenoidosa is similar to those to V. qinghaiensis. Using the concentration addition as an additive reference model, the binary pesticide mixtures exhibited different toxicity interactions, i.e., displayed antagonism to C. pyrenoidosa but synergism to V. qinghaiensis. However, the toxicities of the multi-component mixtures of more than two components are additive and can be predicted by the concentration addition model.

Toxicity of the herbicides bromacil and simazine to the aquatic macrophyte, Vallisneria americana Michx.

Vallisneria americana Michx. (tapegrass) is an ecologically important submersed, vascular aquatic plant that provides food and shelter for many aquatic and waterfowl species. This plant often occurs close to land areas where herbicides are used. Nontarget exposure of these plants to herbicides may compromise ecological structure and function. The objective of the present study was to evaluate the suitability of several endpoint measurements for determining no-observable-adverse effect concentrations (NOAECs), lowest-observable-adverse effect concentrations (LOAECs), and median effective concentration values (EC50s) for tapegrass exposed to the herbicides bromacil (0-0.092 mg/L) and simazine (0-0.592 mg/L) following a 13-d single-pulse exposure and 15-d (bromacil) or 14-d (simazine) postexposure periods. The NOAEC/LOAEC/EC50 for fresh weight gains, new leaf production, and total leaf growth after 13-d exposure to bromacil were 0.020/0.036/0.032, 0.036/0.054/0.036, and 0.036/0.054/0.043 mg/L, respectively. The same respective NOAEC/LOAEC/EC50s for simazine were <0.058/0.058/0.067, 0.229/0.344/0.154, and 0.058/0.116/0.081 mg/L. Reductions in quantity and fresh weight of daughter plants produced and stolon fresh weights occurred at bromacil concentrations > or = 77, 0.020, and 0.036 mg/L, respectively; and simazine concentrations > or = 0.344, >0.592, and > or = 0.116 mg/L, respectively. Neither herbicide affected leaf greenness, total chlorophyll concentrations, or carbohydrate allocation. Although toxicity was shown for many endpoints, most EC50 values were greater than aquatic life benchmark values for algae used by the U.S. Environmental Protection Agency (U.S. EPA), but less than for aquatic plants, indicating that V. americana would likely be protected by use of the algal benchmark criteria.

Combined photobacterium toxicity of herbicide mixtures containing one insecticide.

To test whether the dose-addition (DA) model can predict the combined toxicity of the mixtures of herbicides that coexisted with insecticide(s), we selected five herbicides (simetryn, prometon, bromacil, velpar, and diquat) and one organophosphorus insecticide (dichlorvos) as the test components. The inhibition toxicities of the six pesticides as well as those of their mixtures to Vibrio qinghaiensis sp.-Q67 were determined by using the microplate toxicity test procedure. The dose-response curves (DRCs) between the observed inhibition toxicities and the doses of the pesticides or the mixtures were modeled by using the nonlinear least square fitting. It was shown that all dose-response relationships were effectively described by the Weibull function. To fully explore the combined toxicities of mixtures including various concentration compositions, we designed three equivalent-effect concentration ratio (EECR) mixtures and six uniform design concentration ratio (UDCR) mixtures. The combined toxicity of a mixture is identified by inspecting whether the DRC predicted by the dose addition (DA) or independent action (IA) locates in the 95% confidence interval of the DRC of the mixture. Furthermore, the possible reason for the three mixtures to depart from the DA action was the very high concentration ratio of diquat in the mixtures.

Herbicide impact on Hormosira banksii gametes measured by fluorescence and germination bioassays.

The innovative bioassay described here involves chlorophyll a fluorescence measurements of gametes from the macroalgae, Hormosira banksii, where gametes (eggs) were exposed to Diuron, Irgarol and Bromacil. Response was assessed as percent inhibition from control of effective quantum yield (DeltaF/Fm') of photosystem II, herein referred to as % PSII Inhibition. This was measured with the dual-channelled pulse amplitude modulated (PAM) fluorometer, ToxY-PAM. The fluorescence bioassay was run simultaneously with an established H. banksii germination bioassay to compare sensitivity, precision, and time-to-result. The fluorescence bioassay gave highly sensitive results evidenced by EC(50)s (% PSII Inhibition) for Diuron, Irgarol and Bromacil being three, four and three orders of magnitude (respectively) lower than EC50s generated from the germination bioassays. Precision of the fluorescence bioassay was demonstrated with low coefficient of variations (<30%) for all three toxicants. With regard to time, the fluorescence bioassay gave results within 6h, as opposed to more than 50h for the germination bioassay.

Suicidal inactivation of human dihydropyrimidine dehydrogenase by (E)-5-(2-bromovinyl)uracil derived from the antiviral, sorivudine.

An enzymatic study was performed to clarify the mechanism of 18 acute deaths in patients who had received the new oral antiviral drug, sorivudine (SRV), during anticancer chemotherapy with 5-fluorouracil (5-FU) prodrugs. Human dihydropyrimidine dehydrogenase (hDPD), playing a key role in the liver as the rate-limiting enzyme in catabolism of 5-FU, was expressed in E. coli, purified and incubated in the presence of NADPH with SRV or (E)-5-(2-bromovinyl)uracil (BVU), a metabolite of SRV produced by human gut flora. hDPD was rapidly and irreversibly inactivated by BVU, but not by SRV. Radioactivity of [14C]BVU was incorporated into hDPD in the presence of NADPH in a manner reciprocal to the enzyme inactivation. In the absence of NADPH, hDPD was not inactivated by BVU, nor radiolabeled with [14C]BVU. Thus, as we demonstrated previously with studies using the rat, the acute deaths were strongly suggested to be attributable to markedly elevated tissue 5-FU levels which were responsible for irreversible inhibition of hDPD by covalent binding of a reduced form of BVU as a suicide inactivator.

Mutagenicity of 5-bromouracil and N6-hydroxyadenine studied by yeast oligonucleotide transformation assay.

The mutagenicity of 5-bromouracil (BrU) and N6-hydroxyadenine (HA) was tested by means of the yeast oligonucleotide transformation procedure. BrU-containing oligonucleotide was not mutagenic; although two mutants (per 200 micrograms oligonucleotide) were obtained, they were attributed to base insertion or base substitution at positions different from BrU. This result supports the view that BrU mutagenesis is dependent on intracellular nucleotide pool imbalance. In contrast, HA-containing oligonucleotide was highly mutagenic; 56 mutants (per 140 micrograms oligonucleotide) were obtained. Of 21 induced mutants examined, 20 had G and one had C at the HA position, a result indicating that HA-->G changes took place. To provide back-up evidence, we carried out a general reversion assay for base HA using a set of yeast tester strains, and the results showed that HA induces exclusively AT-to-GC and GC-to-AT transitions. We conclude that in S. cerevisiae HA is a classic base analog mutagen, causing AT-to-GC and GC-to-AT transitions by ambiguous base pairing. The present work has clearly demonstrated the usefulness of the oligonucleotide transformation procedure for elucidating mutagenicity of modified bases.

Mouse strain differences in induction of micronuclei by base analogues and nucleosides.

The frequency of induced micronucleated polychromatic erythrocytes (MNPCEs) was compared in BALB/c, C57BL/6, and DBA/2 mice after intraperitoneal (i.p.) injection of 5-bromodeoxyuridine (BUdR), 5-fluorodeoxyuridine (FUdR), cytosine arabinoside (Ara-C), 6-mercaptopurine (6-MP), 5-bromouracil (5-BU), thymidine (TdR), uridine (UdR), adenosine (AdR) and guanosine (GdR). The experimental procedure was a single i.p. injection followed by harvest at 30 h. The frequency of MNPCEs was significantly increased in all strains by treatment with BUdR, FUdR, Ara-C and 6-MP compared to vehicle control. TdR and UdR induced MNPCEs slightly in BALB/c mice but showed no effect on C57BL/6 and DBA/2 mice. 5-BU, AdR, and GdR did not increase the frequency of MNPCEs in any mouse strain used. These results suggest that BALB/c mice are more susceptible to induction of MNPCEs by clastogenic base analogues and nucleosides than are C57BL/6 or DBA/2 mice.

Potent anti-viral 5-(2-bromovinyl) uracil nucleosides are inactive at inducing gene mutations in Salmonella typhimurium and V79 Chinese hamster cells and unscheduled DNA synthesis in primary rat hepatocytes.

(E)-5-(2-bromovinyl)-2'-deoxyuridine (BDVU), one of the most potent and selective anti-herpes agents described to date, and its close congeners (E)-5-(2-bromovinyl)-1-beta-D-arabinofuranosyluracil (BVaraU) and (E)-5-(2-bromovinyl)uracil (BVU), as well as the reference compounds 5-iodo-2'-deoxyuridine (IDU) and 5-trifluoro-2'-deoxythymidine (TFT) were examined for their genotoxic potential. With the exception of a weak activity of TFT in the newly developed strain TA 102, none of the compounds was active in a bacterial cell mutagenesis (Salmonella/microsome) assay. Nor did they induce DNA repair (unscheduled DNA synthesis) in primary rat hepatocytes. In a mammalian cell mutagenesis assay using V79 Chinese hamster cells, the reference compounds IDU and TFT proved highly cytotoxic and mutagenic, whereas BVDU, BVaraU and BVU were neither cytotoxic nor mutagenic.

Induction of SOS functions in Escherichia coli by lesions resulting from incorporation of 5-bromouracil into DNA.

Lesions induced by 5-bromouracil (BU), after its incorporation into DNA, led to effective induction of prophage lambda and W reactivation (or BU reactivation). Prophage induction due to incorporated BU occurred only with the wild-type prophage, and not for the lambda c1857 mutant with a thermosensitive repressor. Antipain, a protease inhibitor, inhibited wild-type prophage induction 70-90%. This indicates that BU-induced lesions may induce the SOS repair system. The finding that such lesions provoke BU reactivation permits the inference that BU-induced mutagenesis also proceeds via involvement of the error-prone repair system, and not directly as a result of base-pairing errors. Genetic evidence suggests that induction of the SOS repair system as a result of incorporation of BU into DNA is linked to the subsequent appearance of uracil residues and apyrimidinic sites, resulting from dehalogenation of incorporated BU. Apyrimidinic sites appear to be more effective than uracil residues in induction of the SOS system.