Dissipation and risk assessment of forchlorfenuron and its major metabolites in oriental melon under greenhouse cultivation.

Forchlorfenuron is a widely used plant growth regulator. The uptake of forchlorfenuron and its major metabolites poses a potential risk for human health. However, little is known about the dissipation of forchlorfenuron and its major metabolites in agricultural food. In this study, the metabolite 4-hydroxyphenyl-forchlorfenuron was first identified in oriental melon, which exhibited the highest level of residues of 4.42-5.12 µg/kg on the 4-7th days after application. Forchlorfenuron was found to be dissipated rapidly in melon at the recommended application rates, with half-lives ranging from 1.20 to 1.33 days. The rate of dissipation of 4-hydroxyphenyl-forchlorfenuron was greater than that of metabolism from forchlorfenuron in the oriental melon. However, the other metabolite, 3-hydroxyphenyl-forchlorfenuron, was not detected in oriental melon. The risk assessment showed that the acute and chronic dietary exposure risks of forchlorfenuron in oriental melon were 0.0011-0.0037% and 0.06-0.12%, respectively, suggesting little health risk to Chinese consumers.

Phytotoxicity assessment of isoproturon on growth and physiology of non-targeted aquatic plant Lemna minor L. - A comparison of continuous and pulsed exposure with equivalent time-averaged concentrations.

Phenylurea herbicides are often present in the aquatic ecosystems and may be accumulated by the non-targeted organisms and impose a negative effect on the organism and the community. This study aims to investigate and compare the effects of two different isoproturon (IPU) pulse exposure scenarios on the non-targeted aquatic plant Lemna minor with effects observed in the standard test with continuous exposure. The obtained results showed that continuous IPU treatment causes significant reduction of photosynthetic pigment concentration and proteins as well as inhibition of L. minor growth. The activities of CAT, G-POX, and APX were significantly induced to diminish the accumulation of ROS under IPU treatment, but the induction of antioxidant enzymes was not sufficient to protect the plants from herbicide-induced oxidative stress. The growth of L. minor under pulse exposure to IPU recovers fast, but pulse treatment results in significant physiological changes in treated plants. The accumulation of H2O2 and lipid peroxidation products, alongside the reduced concentration of proteins and photosynthetic pigments in pulse treatment after a recovery period, indicates that IPU causes prolonged oxidative stress in L. minor plants. The recovery potential of L. minor plants after treatment with herbicides may have an important role in maintaining the population of essential primary producers in aquatic ecosystems, but IPU-induced physiological changes could potentially have a significant role in modulating the response of the plants to the next exposure event.

Ecotoxicological assessment of Fluazuron: effects on Folsomia candida and Eisenia andrei.

The cattle production in Brazil has increased considerably in the last years, mainly due to the control of parasite infestation of the animals, which cause loss of productivity to the sector. Fluazuron is an active ingredient (a.i.) of the benzoylurea class used to control ticks in cattle. As this a.i. has been found unchanged in animal feces, which may present a risk to edaphic organisms, this study aimed to assess the effects of fluazuron on survival, reproduction, and behavior of the soil invertebrates Folsomia candida and Eisenia andrei, through ecotoxicological assays. We carried out bioassays in a tropical artificial soil (TAS) spiked with increasing doses of the insecticide. Earthworm mortality was found only at the highest tested fluazuron concentration (LOEC = 160 mg a.i. kg-1 dry soil and NOEC = 80 mg kg-1), while the reproduction of F. candida and E. andrei was reduced at lower fluazuron concentrations (EC50 = 4.48 mg kg-1 and EC50 = 20.8 mg kg-1, respectively). Avoidance behavior was detected for both species at lower concentrations than those that caused impacts on reproduction, indicating that the substance may affect the soil habitat function. Since the possible adverse effects of fluazuron on edaphic fauna are still unknown or neglected, this study also warns about the possible harmful effect of veterinary pharmaceutical products on edaphic fauna.

Identification, Synthesis, and Safety Assessment of Thidiazuron [1-Phenyl-3-(1,2,3-thidiazol-5-yl)urea] and Its Metabolites in Kiwifruits.

The quality of kiwifruit became worse as a result of the abuse of plant growth regulators (PGRs). The safety of the fruits treated with PGRs also worried consumers. Therefore, the present study analyzed the structure of thidiazuron [TDZ, (1-phenyl-3-(1,2,3-thidiazol-5-yl)-urea)] (1) and its metabolites of biotransformation in kiwifruits using liquid chromatography hybrid ion trap time-of-flight mass spectrometry (LC-IT-TOF-MS). Standard compounds were also synthesized and used for structural identification of those metabolites. In addition, cytotoxicity of TDZ and its metabolites was tested through sulforhodamine B assays against normal Chinese hamster ovary (CHO) cells. Four metabolites were identified. They were 4-hydroxy-thidiazuron (2), 3-hydroxy-thidiazuron (3), thidiazuron-4-O-ß-d-glucoside (4), and thidiazuron-3-O-ß-d-glucoside (5). Values of IC50 of compounds 1, 2, and 3 to CHO cells were 18.3 ± 1.8, 37.56 ± 1.5, and 23.36 ± 1.59 µM, respectively. Compounds 4 and 5 had no effect on CHO cells.

Assessment of toxicity thresholds in aquatic environments: does benthic growth of diatoms affect their exposure and sensitivity to herbicides?

Benthic diatoms evolved in a biofilm structure, at the interface between water and substrata. Biofilms can adsorb toxicants, such as herbicides, but little is known about the exposure of biofilm organisms, such as benthic diatoms, to these adsorbed herbicides. We assessed the sensitivity of 11 benthic diatoms species to 6 herbicides under both planktonic and benthic conditions using single-species bioassays. The concentration that reduced the growth rate of the population by 10% (EC10) and 50% (EC50), respectively, varied depending on the species, the herbicides, and the growth forms involved. As a general trend, the more hydrophobic the herbicide, the more species were found to be sensitive under benthic growth conditions. Statistical differences (alpha<5%) were observed between the sensitivities under planktonic and benthic growth conditions for many hydrophobic herbicides. A protective effect of the biofilm against herbicides was observed, and this tended to decrease (at both the EC10 and EC50 levels) with increasing hydrophobicity. The biofilm matrix appeared to control exposure to herbicides, and consequently their toxicity towards benthic diatoms. For metolachlor, terbutryn and irgarol, benthic thresholds derived from species sensitivity distributions were more protective than planktonic thresholds. For hydrophobic herbicides, deriving sensitivity thresholds from data obtained under benthic growth seems to offer a promising alternative.

Assessment of the potentiality of TDZ on multiple shoot induction in Bauhinia tomentosa L., a woody legume.

An efficient and reproducible protocol for in vitro multiplication of Bauhinia tomentosa L. was developed. Multiple shoots were regenerated from cotyledonary node and stem nodal segments excised from in vitro raised seedlings on Murashige and Skoog (MS) medium supplemented with different concentrations (0.1, 0.3, 0.5, 0.8 and 1.0 µM) of thidiazuron (TDZ). The maximum response (62.6%) was recorded on MS medium amended with 0.8 µM TDZ. A long exposure to TDZ for 8 weeks showed abnormalities such as fasciation and compact shoots formation. To avoid adverse effects of prolonged exposure to TDZ in long-term establishment, the culture were transferred to TDZ free MS medium for further multiplication and elongation. The highest number of shoots and shoot length were recorded at the end of fourth subculture passage. Ex vitro rooting was achieved when the basal cut end of regenerated shoots were dipped in 200 µM indole-3-butyric acid (IBA) for half an hour followed by their transplantation in plastic pots filled with sterile Soilrite™ where 60% plantlets grew well and all expressed normal development.

A laboratory assessment of the toxic attributes of six 'reduced risk insecticides' on Galendromus occidentalis (Acari: Phytoseiidae).

The modified excised leaf disc method was used to measure the effects of six insecticides on eggs, larvae, adults, and female fecundity of Galendromus occidentalis (Nesbitt) in a 'worst case laboratory exposure'. This study identified insecticides that would be recommended for tier II field evaluations for an integrated pest management program. Commercially formulated insecticides were applied with a thin-layer chromatography sprayer adjusted to 10.34 kPa (1.5 psi), at the recommended label concentrations in Canada. LC(50) values were estimated from aliquots above and below that concentration. Spinetoram and spirotetramat were toxic at label concentrations. The label concentration for spinetoram was 34.3-fold the LC(50) estimate (0.006 gL(-1)) and for spirotetramat the label concentration was 7.7-fold the LC(50) estimate (0.03 gL(-1)). Clothianidin was considerably less toxic and the label concentration was 0.15-fold the LC(50) estimate (2.29 gL(-1)). Estimates of LC(50) for novaluron and chlorantraniliprole could not be established. Both materials showed slight toxicity to at least one growth stage of the predator. Novaluron, clothianidin and chlorantraniliprole should be evaluated in the field for compatibility in IPM programs. Flubendiamide was harmless to all growth stages and it is recommended for inclusion in IPM programs without additional tier II field evaluations. Field evaluations with spinetoram and spirotetramat should be pursued only if alternatives are unavailable.

Community-level microalgal toxicity assessment by multiwavelength-excitation PAM fluorometry.

In ecotoxicological studies involving community-level investigations, rapid and multiparametric fluorescence-based methods may provide substantial advantages over traditional methods used for structural and functional community analysis. Therefore, multiwavelength-excitation pulse-amplitude modulated (PAM) fluorometry was applied in this study to assess long-term changes in periphyton community structure, short-term effects on periphyton functioning (photosynthesis) and pollution induced community tolerance (PICT). For inter-calibration, periphyton structure was evaluated by chemotaxonomic analysis of accessory pigments and a four-wavelength-excitation PAM fluorometer. Short-term effects of herbicides were evaluated by fluorescence quenching analysis and (14)C-incorporation as a proxy of primary production. Subsequently, the method was applied to assess structural and functional changes in periphyton communities after isoproturon exposure for 14 and 26 days, respectively. Results showed good correlation of the PAM fluorescence-based measurements with traditional methods for biofilms in the initial colonisation phase for structural and functional parameters. However, for biofilms older than 9 weeks PAM fluorescence may underestimate biomass. Multiwavelength-excitation PAM fluorometry showed good correlation with marker pigment concentrations indicating that this method provides a reliable estimate of the community structure. PAM fluorometry was able to quantify changes of biomass and follow relative shifts in class composition of biofilms under exposure of isoproturon. Short-term tests based on the quantification of the inhibition of the effective quantum yield revealed a concentration-dependent increase of PICT. The observation of two succession phases of the biofilms after 14 and 26 days of growth, respectively, revealed that sensitivity of biofilms decreased with increasing age and biomass, respectively, but PICT remained a characteristic parameter of exposed communities in a concentration-dependent relationship. In conclusion, multiwavelength-excitation PAM fluorometry has considerable potentials in multispecies and multiparameter assessment of toxic effects on community level in terms of (1) a combined and rapid evaluation of structural and functional parameters in parallel, (2) screening of trends over time, (3) observing effects in replication and (4) being non-destructive. The approach therefore provides a perspective for a better understanding of community-level effects as species interactions in terms of PICT and therefore a higher ecological realism in risk assessment of toxicants.