Aquatic organisms are usually exposed to various co-existing pollutants. However, toxic effects of pesticide mixtures on aquatic organisms and its potential underlying mechanism still remain unclear. The joint effects of fenpropathrin (FEN) and paclobutrazol (PAC) on zebrafish (Danio rerio) using diverse toxicological endpoints were investigated in the current work. Our data exhibited that the 96-h LC₅₀ values of FEN to zebrafish at multiple life phases ranged from 0.0029 (0.0013–0.0042) to 0.16 (0.082–0.23) mg a.i. L⁻¹, which were lower by comparison to PAC ranging from 13.16 (8.564–21.03) to 23.43 (17.94–29.91) mg a.i. L⁻¹. Combination of FEN and PAC displayed synergistic effect on embryonic zebrafish. Activities of T-SOD, Cu/Zn-SOD and CYP450 were remarkably changed in the majority of single and mixture treatments by comparison to the untreated group. The mRNA levels of 17 genes related to oxidative stress, cellular apoptosis, immune system and endocrine system were assessed, and the data suggested that embryonic zebrafish were affected by both single pesticides and their mixtures. Five genes (P53, tsh, ERα, crh and cxcl-clc) showed greater alterations when exposed to pesticide mixtures by comparison to their individual chemicals. Therefore, it is urgently necessary to conduct more studies on mixture toxicities of different pesticides to explore the chemical mixtures with synergistic interactions.

Pesticide contamination is a threat to many aquatic habitats, and runoff from residential homes is a major contributor of these chemicals in urban surface streams and estuaries. Improved understanding of their fate and transport can help identify areas of concern for monitoring and management. In many urban areas, runoff water congregates in numerous underground catch basins before draining into the open environment; however, at present essentially no information is available on pesticide presence in these systems. In this study, we collected water samples from a large number of underground urban catch basins in different regions of California during the active pest management season to determine the occurrence and profile of the widely used pyrethroid insecticides. Detectable levels of pyrethroids were found in 98% of the samples, and the detection frequency of individual pyrethroids ranged from no detection for fenpropathrin to 97% for bifenthrin. In the aqueous phase, total pyrethroid concentrations ranged from 3 to 726 ng/L, with a median value of 32 ng/L. Pyrethroids were found to be enriched on suspended solids, with total concentrations ranging from 42 to 93,600 ng/g and a median value of 2,350 ng/g. In approximately 89% of the samples, whole water concentrations of bifenthrin were predicted to have toxic units >1 for sensitive aquatic invertebrates. The high detection frequency of bifenthrin and overall pyrethroid concentrations, especially for particle-bound residues, suggest that underground urban catch basins constitute an important secondary source for extended and widespread contamination of downstream surface waters by pesticides such as pyrethroids in urban regions.

Numerous natural preparations in traditional Chinese medicine are prepared as decoctions. Processing factors (PFs) comparing the levels of pesticide residues in decoctions to those in the corresponding unprocessed products should be considered in exposure assessments. Thus, this study determined the residue levels of six pesticides (chlorpyrifos, phoxim, imidacloprid, thiamethoxam, fenpropathrin, and emamectin benzoate), as well as 3,5,6-trichloropyridinol, the primary metabolite of chlorpyrifos, and clothianidin, the main metabolite of thiamethoxam in Baishao, Paeoniae radix lactiflora (Fam. Ranunculaceae). The results showed that significant time-response effects were present for the release of pesticides from P. radix. The PFs calculated were < 1, indicating a significant reduction in pesticide residues after TCM processing. The water solubility and partition coefficient values of the pesticides may have played a basic role in the dissipation of the residues during the TCM decocting process. A risk assessment based on the hazard quotient with PFs revealed that exposure to pesticide residues in P. radix was far below the levels that might pose a health risk. In conclusion, the results presented here are of theoretical and practical value for the safety evaluation of TCMs.

The concentration levels of some important pesticides were evaluated in soil samples from different areas of the North of Iran (Golestan province) and to indicate the possible sources and risks of contamination. A multiresidue analytical procedure using the QuEChERS approach was developed to extract and measure 12 pesticide residues from ten different classes in 145 soil samples including agricultural, garden, forestal, and residential areas. The analysis was performed using reversed-phase liquid chromatography equipped with an ESI mass spectrometry instrument by multiple reaction monitoring (MRM) in positive-ion modes. Retention times and occurrence of two conventional transitions were used as identification criteria. Three pesticide residues including malathion, propargite, and butachlor were observed in soil samples. Malathion residue was found in ˃ 51% of soil samples, and its levels in approximately 35% of the cases were more than the residue limit (50 μg kg⁻¹). Propargite residue was observed in 49% of the samples and its levels in 11% of the cases were more than the residue limit. The most frequently observed levels of malathion and propargite were found in forestal and residential areas. The amount of butachlor residue in one of the residential soil samples was at least 10 times more than the residue limit. Some of the pesticides including imidacloprid, cyproconazole, diazinon, and chlorpyrifos displayed residue levels below 50 μg kg⁻¹. The other pesticides, namely carbaryl, thiophanate-methyl, fenpropathrin, krezoxim-methyl, and pinoxaden, were not detected in any soil samples. These findings might be useful for implementing programs to monitor the presence of pesticides in soils and the related crops, to carry out more precise risk assessment studies.

The photodegradation processes of fenpropathrin and λ-cyhalothrin were studied in hexane, methanol/water (1:1, v/v), and acetone in both ultraviolet light and simulated sunlight. Intermediates in the photodegradation process were identified using gas chromatography/mass spectrometry (GC/MS), and the analysis of intermediates was used to speculate on possible photodegradation pathways. The photodegradation processes of fenpropathrin and λ-cyhalothrin followed pseudo first-order kinetics. The photodegradation rates varied according to the solvent in decreasing order: hexane > methanol/water (1:1, v/v) > acetone. The effects of substances coexisting in the environment on the photodegradation of pyrethroids were also investigated in the research. Acetone, humic acid, and riboflavin increased photodegradation rates while L-ascorbic acid slowed the process. This study provides a theoretical basis for the removal of pyrethroid pollution from the natural environment.

Pseudomonas aeruginosa strain GF31, isolated from a contaminated soil, can effectively degrade β-cypermethrin (β-CP), as well as fenpropathrin, fenvalerate, and cyhalothrin. The highest level of degradation (81.2 %) was achieved with the addition of peptone. Surprisingly, the enzyme responsible for degradation was mainly localized to the extracellular areas of the bacteria, in contrast to the other known pyrethroid-degrading enzymes, which are intracellular. Although intact bacterial cells function at about 30 °C for biodegradation, similar to other degrading strains, the crude extracellular extract of strain GF31 remained biologically active at 60 °C. Moreover, the extract fraction showed good storage stability, maintaining >50 % of its initial activity following storage at 25 °C for at least 20 days. Significant differences in the characteristics of the crude GF31 extracellular extract compared with the known pyrethroid-degrading enzymes indicate the presence of a novel pyrethroid-degrading enzyme. Furthermore, the identification of 3-phenoxybenzoic acid and 2,2-dimethylcyclopropanecarboxylate from the degradation products suggests the possibility that β-CP degradation by both the strain and the crude extracellular fraction is achieved through a hydrolysis pathway. Further degradation of these two metabolites may lead to the development of an efficient method for the mineralization of these types of pollutants.