Dopaminergic and anti-estrogenic responses in juvenile steelhead (Oncorhynchus mykiss) exposed to bifenthrin.

The frequency of detection and concentrations of bifenthrin, a pyrethroid insecticide, in the waterways inhabited by the endangered species, steelhead trout (Oncorhynchus mykiss), has become a significant concern for regulatory agencies. Endocrine disruption has been observed with estrogenic and anti-estrogenic responses in fish species at different life stages. Since several studies have indicated alterations in dopaminergic signaling associated with endocrine responses, juvenile steelhead were exposed to environmentally relevant concentrations of 60 or 120 ng/L bifenthrin for two weeks. Fish brains were assessed for dopamine levels and the expression of genes involved in dopaminergic and estrogenic processes, such as catechol-o-methyltransferase (comt) and monoamine oxidase (mao). Vitellogenin (vtg) and estrogenic receptors (ERα1, ERß1, and ERß2) were also evaluated in livers of the animals. Dopamine concentrations were significantly higher in fish brains following bifenthrin exposure. Consistent with a reduction in dopamine clearance, there was a significant decrease in the mRNA expression of comt with increased bifenthrin concentration. Hepatic expression of ERα1 and ERß2 mRNA was significantly decreased with increased bifenthrin concentration. These data support the possible mechanism of bifenthrin altering the dopaminergic pathway at low ng/L concentrations, in juvenile steelhead, which could interfere with endocrine feedback loops. These findings support the need for and importance of identifying species and life stage differences in pesticide modes of action to reduce uncertainties in risk assessments.

Methylation and Demethylation of Emerging Contaminants in Plants.

Many contaminants of emerging concern (CECs) have reactive functional groups and may readily undergo biotransformations, such as methylation and demethylation. These transformations have been reported to occur during human metabolism and wastewater treatment, leading to the propagation of CECs. When treated wastewater and biosolids are used in agriculture, CECs and their transformation products (TPs) are introduced into soil-plant systems. However, little is known about whether transformation cycles, such as methylation and demethylation, take place in higher plants and hence affect the fate of CECs in terrestrial ecosystems. In this study, we explored the interconversion between four common CECs (acetaminophen, diazepam, methylparaben, and naproxen) and their methylated or demethylated TPs in Arabidopsis thaliana cells and whole wheat seedlings. The methylation-demethylation cycle occurred in both plant models with demethylation generally taking place at a greater degree than methylation. The transformation rate of demethylation or methylation was dependent on the bond strength of R-CH3, with demethylation of methylparaben or methylation of acetaminophen being more pronounced. Although not explored in this study, these interconversions may exert influences on the behavior and biological activity of CECs, particularly in terrestrial ecosystems. The study findings demonstrated the prevalence of transformation cycles between CECs and their methylated or demethylated TPs in higher plants, contributing to a more complete understanding of risks of CECs in the human-wastewater-soil-plant continuum.

Removal of neonicotinoid insecticides in a large-scale constructed wetland system.

Neonicotinoid insecticides are among the most used insecticides and their residues are frequently found in surface water due to their persistence and mobility. Neonicotinoid insecticides exhibit toxicity to a wide range of aquatic invertebrates at environmentally relevant levels, and therefore their contamination in surface water is of significant concern. In this study, we investigated the spatiotemporal distribution of six neonicotinoids in a large wetland system, the Prado Wetlands, in Southern California, and further evaluated the wetlands' efficiency at removing these insecticides. Total neonicotinoid concentrations in water ranged from 3.17 to 46.9 ng L-1 at different locations within the wetlands, with imidacloprid and dinotefuran among the most detected. Removal was calculated based on concentrations as well as mass flux. The concentration-based removal values for a shallow pond (vegetation-free), moderately vegetated cells, densely vegetated cells, and the entire wetland train were 16.9%, 34.2%, 90.2%, and 61.3%, respectively. Principal component analysis revealed that pH and temperature were the primary factors affecting neonicotinoids removal. Results from this study demonstrated the ubiquitous presence of neonicotinoids in surface water impacted by urban runoff and wastewater effluent and highlighted the efficiency of wetlands in removing these trace contaminants due to concerted effects of uptake by wetland plants, photolysis, and microbial degradation.

Distribution of pyrethroid insecticides in urban storm drain structures: Catch basins, open channels, and outfalls.

Surface water runoff can transport contaminants offsite to downstream aquatic ecosystems. The prevalence of impervious surfaces in urban areas enhances surface runoff and contributes to contamination of urban surface streams. Urban areas have complex drainage systems for the conveyance of drainage water, however, there is a dearth of information on the distribution of contaminants within storm drain system structures. Pyrethroid insecticides are among the most used insecticides in urban areas, and trace levels of pyrethroids are known to exert toxicity to aquatic invertebrates. To investigate pyrethroid occurrence and distribution throughout an urban drainage system, samples of water, sediment, algae, and biofilm were collected from catch basins, open channels, and outfalls in Los Angeles County, California, during the dry season. From 3 catch basins, 7 open channels, and 7 outfalls, a total of 28 water samples, 4 sediment samples, 8 algae samples, and 4 biofilm samples were collected and analyzed. Pyrethroid concentrations above the reporting limit were detected in 89% of water samples and all sediment, algae, and biofilm samples, with bifenthrin and cyfluthrin being the most frequently detected compounds. The median total pyrethroid concentrations in water, sediments, algae, and biofilms were 27 ng/L, 88 ng/g, 356 ng/g, and 3556 ng/g, respectively. Bifenthrin concentrations in catch basins were found to be significantly higher than those in open channels or outfalls. Significant correlations were found for various metrics, including between pyrethroid partitioning in water samples and total suspended solids. These findings highlight the role of underground catch basins as a sink as well as a secondary source for contaminants such as pyrethroid insecticides. Prevention of the input of these urban originated contaminants to catch basins is crucial for protecting the water quality of urban surface waters.

Influence of methylation and demethylation on plant uptake of emerging contaminants.

Contaminants of emerging concern (CECs) as well as their transformation products (TPs) are often found in treated wastewater and biosolids, raising concerns about their environmental risks. Small changes in chemical structure, such as the addition or loss of a methyl group, as the result of methylation or demethylation reaction, may significantly alter a chemical's physicochemical properties. In this study, we evaluated the difference in accumulation and translocation between four CECs and their respective methylated or demethylated derivatives in plant models. Suspended Arabidopsis thaliana cell culture and wheat seedlings were cultivated in nutrient solutions containing individual compounds at 1 mg/L. The methylated counterparts were generally more hydrophobic and showed comparative or greater accumulation in both plant models. For example, after 1 h incubation, methylparaben was found in A. thaliana cells at levels two orders of magnitude greater than demethylated methylparaben. In contrast, the demethylated counterparts, especially those with the addition of a hydroxyl group after demethylation, showed decreased plant uptake and limited translocation. For example, acetaminophen and demethylated naproxen were not detected in the shoots of wheat seedlings after hydroponic exposure. Results from this study suggest that common transformations such as methylation and demethylation may affect the environmental fate of CECs, and should be considered to obtain a more comprehensive understanding of risks of CECs in the environment.

Pyrethroid insecticides in urban catch basins: A potential secondary contamination source for urban aquatic systems.

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.

The Use of Non-targeted Lipidomics and Histopathology to Characterize the Neurotoxicity of Bifenthrin to Juvenile Rainbow Trout (Oncorhynchus mykiss).

Due to the detection frequencies and measured concentrations in surface water, the type I pyrethroid insecticide, bifenthrin, has been of particular concern within the Sacramento-San Joaquin Delta in California. Concentrations have been detected above levels previously reported to impair neuroendocrine function and induce neurotoxicity to several species of salmonids. Metabolomic and transcriptomic studies indicated impairment of cellular signaling within the brain of exposed animals and potential alteration of lipid metabolism. To better understand the potential impacts of bifenthrin on brain lipids, juvenile rainbow trout (Oncorhynchus mykiss) were exposed to mean bifenthrin concentrations of 28 or 48 ng/L for 14 days, and non-targeted lipidomic profiling in the brain was conducted. Brain tissue sections were also assessed for histopathological insult following bifenthrin treatment. Bifenthrin-exposed trout had a concentration-dependent decrease in the relative abundance of triglycerides (TGs) with levels of phosphatidylcholines (PCs) and phosphatidylethanolamines (PEs) significantly altered following 48 ng/L bifenthrin exposure. An increased incidence of histopathological lesions, such as focal hemorrhages and congestion of blood vessels, was noted in the brains of bifenthrin-treated animals, suggesting an association between altered lipid metabolism and neuronal cell structure and integrity.

Contaminants of emerging concerns in recycled water: Fate and risks in agroecosystems.

Recycled water (RW) has been increasingly recognized as a valuable source of water for alleviating the global water crisis. When RW is used for agricultural irrigation, many contaminants of emerging concern (CECs) are introduced into the agroecosystem. The ubiquity of CECs in field soil, combined with the toxic, carcinogenic, or endocrine-disrupting nature of some CECs, raises significant concerns over their potential risks to the environment and human health. Understanding such risks and delineating the fate processes of CECs in the water-soil-plant continuum contributes to the safe reuse of RW in agriculture. This review summarizes recent findings and provides an overview of CECs in the water-soil-plant continuum, including their occurrence in RW and irrigated soil, fate processes in agricultural soil, offsite transport including runoff and leaching, and plant uptake, metabolism, and accumulation. The potential ecological and human health risks of CECs are also discussed. Studies to date have shown limited accumulation of CECs in irrigated soils and plants, which may be attributed to multiple attenuation processes in the rhizosphere and plant, suggesting minimal health risks from RW-fed food crops. However, our collective understanding of CECs is rather limited and knowledge of their offsite movement and plant accumulation is particularly scarce for field conditions. Given a large number of CECs and their occurrence at trace levels, it is urgent to develop strategies to prioritize CECs so that future research efforts are focused on CECs with elevated risks for offsite contamination or plant accumulation. Irrigating specific crops such as feed crops and fruit trees may be a viable option to further minimize potential plant accumulation under field conditions. To promote the beneficial reuse of RW in agriculture, it is essential to understand the human health and ecological risks imposed by CEC mixtures and metabolites.

Effects of chemical and natural ageing on the release of potentially toxic metal additives in commercial PVC microplastics.

Various chemical substances, such as potentially toxic trace metals, are used as plastic additives to improve the performance of polymers and extend the service life of plastic products. However, these added trace metals are likely released from plastic into the environment when the plastic becomes a pollutant, although the process is poorly understood. In this study, chemical ageing of commercial polyvinyl chloride (PVC) microplastics using hydrogen peroxide (H2O2) and natural ageing of PVC that had been added to an alkaline paddy soil were undertaken to evaluate the potential release of trace metals from PVC. Enhanced release of trace metals from PVC with the increasing H2O2 concentrations was observed, in which the released Pb was 1-2 orders of magnitude higher than other metals (p < 0.01). The released Cr, Ni, Pb, Cu, Zn, Cd and Mn accounted for 87.37%, 79.27%, 22.02%, 20.93%, 17.06%, 15.11%, and 11.02% of their total concentrations (0.28 ± 0.03, 0.08 ± 0.01, 13.67 ± 0.18, 1.07 ± 0.02, 2.20 ± 0.18, 0.05 ± 0.00 and 1.26 ± 0.08 mmol kg-1) in PVC after ageing with 30% H2O2, respectively. Compared with the control treatment without PVC addition, the concentrations of CaCl2-extractable Cu, Mn, Ni, Pb, and Zn in the soil treated with 5% PVC are significantly increased after incubation for 60 days (p < 0.01). In conclusion, chemical and natural ageing have the potential to lead to the release of Cu, Mn, Ni, Pb, and Zn from the commercial PVC into aquatic and terrestrial environments.

When vector control and organic farming intersect: Pesticide residues on rice plants from aerial mosquito sprays.

Conflicts often exist between the use of pesticides for public health protection and organic farming. A prominent example is the use of insecticides for mosquito control in rice fields designated for organic farming. Rice fields, with static water and other conducive conditions, are favorable mosquito habitats. Best management practices are urgently needed to ensure the integrity of organic farming while addressing the need for public health protection. In this study, we evaluated aerial ultra-low-volume (ULV) applications of two classes of mosquito adulticides, pyrethrins and organophosphates, and their deposition and residues on rice plants throughout an active growing season in the Sacramento Valley of California. Frequent applications of pyrethrin synergized with piperonyl butoxide (PBO) and rotating applications of synergized pyrethrins and naled, an organophosphate, were carried out on two large blocks of rice fields. Aerial ULV application of either synergized pyrethrins or naled was able to generate uniform droplets above the fields with high efficacy for mosquito control. Rice leaf samples were collected before and after a subset of applications, and rice grains were sampled at harvest. Frequent applications of synergized pyrethrins resulted in some accumulation of the synergist PBO on rice leaves, but pyrethrins and naled dissipated rapidly from the leaves after each application with no noticeable accumulation over repeated applications. At harvest, no detectable residues of the pesticides or PBO were found in the rice grains. The absence of pesticide residues in the rice grains at harvest suggested that the ULV aerial application led to deposition of only very low levels of residues on rice plants during the growing season. When coupled with the short persistence and/or poor mobility of the insecticides, such applications resulted in negligible pesticide residues in rice grains.

Conjugation of Di-n-butyl Phthalate Metabolites in Arabidopsis thaliana and Potential Deconjugation in Human Microsomes.

Plasticizers, due to the widespread use of plastics, occur ubiquitously in the environment. The reuse of waste resources (e.g., treated wastewater, biosolids, animal waste) and other practices (e.g., plastic mulching) introduce phthalates into agroecosystems. As a detoxification mechanism, plants are known to convert phthalates to polar monophthalates after uptake, which are followed by further transformations, including conjugation with endogenous biomolecules. The objective of this study was 2-fold: to obtain a complete metabolic picture of the widely used di-n-butyl phthalate (DnBP) by using a suite of complementary techniques, including stable isotope labeling, 14C tracing, and high-resolution mass spectrometry, and to determine if conjugates are deconjugated in human microsomes to release bioactive metabolites. In Arabidopsis thaliana cells, the primary initial metabolite of DnBP was mono-n-butyl phthalate (MnBP), and MnBP was rapidly metabolized via hydroxylation, carboxylation, glycosylation, and malonylation to seven transformation products. One of the conjugates, MnBP-acyl-ß-d-glucoside (MnBP-Glu), was incubated in human liver (HLM) and intestinal (HIM) microsomes and was found to undergo rapid transformations. Approximately 15% and 10% of MnBP-Glu were deconjugated to the free form MnBP in HIM and HLM, respectively. These findings highlight that phthalates, as diesters, are susceptible to hydrolysis to form monoesters that can be readily conjugated via a phase II metabolism in plants. Conjugates may be deconjugated to release bioactive compounds after human ingestion. Therefore, an accurate assessment of the dietary exposure of phthalates and other contaminants must consider plant metabolites, especially including conjugates, to better predict their potential environmental and human health risks.

Metabolism of mono-(2-ethylhexyl) phthalate in Arabidopsis thaliana: Exploration of metabolic pathways by deuterium labeling.

Mono-(2-ethylhexyl) phthalate (MEHP) is the primary monoester transformation product of the commonly used plasticizer, di-2-ethylhexyl phthalate (DEHP), and has been frequently detected in various environmental compartments (e.g., soil, biosolids, plants). Plants growing in contaminated soils can take up MEHP, and consumption of the contaminated plants may result in unintended exposure for humans and other organisms. The metabolism of MEHP in plants is poorly understood, but critical for evaluating the potential human and environmental health risks. The present study represents the first attempt to explore the metabolic fate of MEHP in plants. We used Arabidopsis thaliana cells as a plant model and explored metabolic pathways of MEHP using deuterium stable isotope labelling (SIL) coupled with time-of-flight high resolution mass spectrometer (TOF-HRMS). A. thaliana rapidly took up MEHP from the culture medium and mediated extensive metabolism of MEHP. Combining SIL with TOF-HRMS analysis was proved as a powerful method for identification of unknown MEHP metabolites. Four phase Ⅰ and three phase Ⅱ metabolites were confirmed or tentatively identified. Based on the detected transformation products, hydroxylation, oxidation, and malonylation are proposed as the potential MEHP metabolism pathways. In cells, the maximum fraction of each transformation product accounted for 2.8-56.5% of the total amount of metabolites during the incubation. For individual metabolites, up to 2.9-100% was found in the culture medium, suggesting plant excretion. The results in the cell culture experiments were further confirmed in cabbage and A. thaliana seedlings. The findings suggest active metabolism of MEHP in plants and highlight the need to include metabolites in refining environmental risk assessment of plasticizers in the agro-food systems.