The toxicokinetics and risk assessment of pyrethroids pesticide in tilapia (Oreochromis mossambicus) upon short-term water exposure

Long-term exposure to dimefluthrin inhibits the growth of Acrossocheilus fasciatus

Dimefluthrin (DIM) is a synthetic pyrethroid insecticide commonly used for the control of pests, particularly for mosquitoes and other flying insects. However, the effects of DIM on non-target aquatic organisms are not known. In this study, we evaluated the long-term effects of DIM on juvenile Acrossocheilus fasciatus (a species of teleost fish) by exposing them to two different concentrations (0.8 μg/L and 4 μg/L) for 60 days. After 60 d of exposure, DIM induced a significant decrease in body weight and irregular, diffused villi in the intestines of A. fasciatus, accompanied by alterations in the expression of immune-related genes. Furthermore, Gene Ontology (GO) enrichment analysis revealed that among the differentially expressed genes (DEGs), all downregulated genes were enriched in processes such as small molecule/cellular amino acid metabolism, generation of precursor metabolites and energy, and phosphatase activity. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis revealed that the downregulated genes were associated with processes such as cytokine-cytokine receptor interaction, chemokine signaling pathway, JAK-STAT signaling pathway, intestinal immune network for IgA production, natural killer cell-mediated cytotoxicity, and antigen processing and presentation. In contrast, upregulated DEGs were linked to processes such as necroptosis, phototransduction, and Hippo signaling pathway. These results demonstrate the potential toxicity of DIM to non-target aquatic organisms, indicating the broader ecological implications of its use.

Uptake, tissue distribution, and biotransformation pattern of triclosan in tilapia exposed to environmentally-relevant concentrations

Although triclosan has been ubiquitously detected in aquatic environment and is known to have various adverse effects to fish, details on its uptake, bioconcentration, and elimination in fish tissues are still limited. This study investigated the uptake and elimination toxicokinetics, bioconcentration, and biotransformation potential of triclosan in Nile tilapia (Oreochromis niloticus) exposed to environmentally-relevant concentrations under semi-static regimes for 7 days. For toxicokinetics, triclosan reached a plateau concentration within 5-days of exposure, and decreased to stable concentration within 5 days of elimination. Approximately 50 % of triclosan was excreted by fish through feces, and up to 29 % of triclosan was excreted through the biliary excretion. For fish exposed to 200 ng·L-1, 2000 ng·L-1, and 20,000 ng·L-1, the bioconcentration factors (log BCFs) of triclosan in fish tissues obeyed similar order: bile ≈ intestine > gonad ≈ stomach > liver > kidney ≈ gill > skin ≈ plasma > brain > muscle. The log BCFs of triclosan in fish tissues are approximately maintained constants, no matter what triclosan concentrations in exposure water. Seven biotransformation products of triclosan, involved in both phase I and phase II metabolism, were identified in this study, which were produced through hydroxylation, bond cleavages, dichlorination, and sulfation pathways. Metabolite of triclosan-O-sulfate was detected in all tissues of tilapia, and more toxic product of 2,4-dichlorophenol was also found in intestine, gonad, and bile of tilapia. Meanwhile, two metabolites of 2,4-dichlorophenol-O-sulfate and monohydroxy-triclosan-O-sulfate were firstly discovered in the skin, liver, gill, intestine, gonad, and bile of tilapia in this study. These findings highlight the importance of considering triclosan biotransformation products in ecological assessment. They also provide a scientific basis for health risk evaluation of triclosan to humans, who are associated with dietary exposure through ingesting fish.

Occurrence, distribution, and health risk assessment of pyrethroid and neonicotinoid insecticides in aquatic products of China

Synthetic pyrethroid insecticides (SPIs) and neonicotinoid insecticides (NEOs), now dominant in the insecticide market, are increasingly found in aquatic environments. This study focused on six SPIs and five NEOs in aquatic products from four Chinese provinces (Shandong, Hubei, Shanxi and Zhejiang) and the risk assessment of the safety for the residents was conducted. It revealed significantly higher residues of Σ6SPIs (6.27-117.19 μg/kg) compared to Σ5NEOs (0.30-14.05 μg/kg), with SPIs more prevalent in fish and NEOs in shellfish. Carnivorous fish showed higher pesticide levels. Residues of these two types of pesticides were higher in carnivorous fish than in fish with other feeding habits. In the four regions investigated, the hazard quotient and hazard index of SPIs and NEOs were all <1, indicating no immediate health risk to human from single and compound contamination of the two types of pesticides in aquatic products. The present study provides valuable information for aquaculture management, pollution control and safeguarding human health.

Curcumin protects against fenvalerate-induced neurotoxicity in zebrafish (Danio rerio) larvae through inhibition of oxidative stress

Fenvalerate (FEN), a typical type II pyrethroid pesticide, is widely used in agriculture. FEN has been detected in the environment and human body. However, the neurotoxicity of FEN has not been well elucidated. This study aimed to explore the mechanisms underlying FEN-induced neurotoxicity using the zebrafish (Danio rerio) model. We also investigated whether curcumin (CUR), a polyphenol antioxidant that exhibits neuroprotective properties, can prevent FEN-induced neurotoxicity. Here, zebrafish embryos were exposed to 0, 3.5, 7 and 14 μg/L of FEN from 4 to 96 h post fertilization (hpf) and neurotoxicity was assessed. Our results showed that FEN decreased the survival rate, heart rate, body length and spontaneous movement, and increased malformation rate. FEN caused neurobehavioral alterations, including decreased swimming distance and velocity, movement time and clockwise rotation times. FEN also suppressed neurogenesis in transgenic HuC:egfp zebrafish, reduced cholinesterase activity and downregulated the expression of neurodevelopment related genes (elavl3, gfap, gap43 and mbp). In addition, FEN enhanced oxidative stress via excessive reactive oxygen species and antioxidant enzyme inhibition, then triggered apoptosis by upregulation of apoptotic genes (p53, bcl-2, bax and caspase 3). These adverse outcomes were alleviated by CUR, indicating that CUR mitigated FEN-induced neurotoxicity by inhibiting oxidative stress. Overall, this study revealed that CUR ameliorated FEN-induced neurotoxicity via its antioxidant, indicating a promising protection of CUR against environmental pollutant-induced developmental anomalies.

Concepts on Accumulation of Pesticides and Veterinary Drugs in Fish: A Review with Emphasis in Tilapia

The quality of the aquatic environment can be compromised by the practice of intensive use of pesticides in agriculture and by the misuse of veterinary drugs. Therefore, organisms that live in aquatic ecosystems may be affected due to the presence of these chemicals, through runoff, leaching and other processes. Exposure of aquatic organisms to these xenobiotics could pose health risks. Consequently, there is a growing interest in predicting the bioaccumulation of these substances in aquatic biota from experiments conducted under laboratory conditions. Studies on fish have been performed due to its importance as human food and their wide distribution in most of the aquatic environment. Thus, this article reviews the concepts on determining the accumulation of pesticides and veterinary drugs in fish. The risk regarding the consumption of fish containing residues of these chemical agents, the acceptable daily intake, the testing protocols and the analytical techniques used to determine the residues of these substances in fish tissues are discussed. An emphasis on studies involving tilapia as the test organism was included because, according to Food and Agricultural Organization (FAO), this species is one of the most cultivated in the world.

Efficiency of hematological, enzymological and oxidative stress biomarkers of Cyprinus carpio to an emerging organic compound (alphamethrin) toxicity

Alphamethrin is one of the extensively used pyrethroids. Its non-specific mode-of-action might affect the non-target-organisms. Its toxicity data on aquatic organisms are lacking. We determined the toxicity (35 days) of alphamethrin (0.6µg/L and 1.2µg/L) on non-target-organisms by evaluating the efficiency of hematological, enzymological and antioxidants biomarkers of Cyprinus carpio. Compared with the control group, the efficiency of the biomarkers studied was significantly (p<0.05) impaired in the alphamethrin groups. Alphamethrin-toxicity altered hematology, transaminases and the potency of LDH of fish. ACP and ALP activity and biomarkers of oxidative stress in the gills, liver and muscle tissues were affected. IBRv2 index reveals that the biomarkers were inhibited. The observed impairments were the toxicity effects of alphamethrin with respect to concentration and time. The effectiveness of biomarkers for alphamethrin toxicity was like the toxicity data available on other banned insecticides. Alphamethrin could cause multiorgan toxicity on aquatic organisms at µg/L level.

Exposure to cypermethrin pesticide disturbs the microbiome and disseminates antibiotic resistance genes in soil and the gut of Enchytraeus crypticus

Worldwide, pyrethroids, such as cypermethrin, are the second most applied group of insecticides, however, their effects on the soil microbiome and non-target soil fauna remain largely unknown. Herein, we assessed the change of bacterial communities and antibiotic resistance genes (ARGs) of soil and in the gut of the model soil species Enchytraeus crypticus using a combination of 16S rRNA gene amplicon sequencing, and high-throughput qPCR of ARGs. Results indicate that cypermethrin exposure enriches potential pathogens (e.g. Bacillus anthracis) in the soil and gut microbiome of E. crypticus, heavily disrupting the latter's microbiome structure, and even disrupts activities of the E. crypticus immune system. The co-occurrence of potential pathogens (e.g. Acinetobacter baumannii), ARGs, and mobile genetic elements (MGEs) revealed the increased risk of pathogenicity as well as antibiotic resistance in potential pathogens. Moreover, structural equation modeling demonstrated that the dissemination of ARGs was not only promoted by MGEs, but also by the ratio of the core to non-core bacterial abundance. Collectively, these results provide an in-depth view of the previously unappreciated environmental risk of cypermethrin on the dissemination of ARGs in the soil and non-target soil fauna.

In vitro study of deltamethrin-induced extracellular traps in hemocytes of Ruditapes philippinarum

Deltamethrin (DLM), a broad-spectrum pesticide, has been proven to have toxic effects on aquatic organisms. Here, we detected the formation of extracellular traps (ETosis) formation in Manila clam (Ruditapes philippinarum) hemocytes stimulated by three concentrations of DLM (0.01, 0.1 and 1 μg/mL) in vitro, and explored the underlying mechanisms induced by this pesticide. Extracellular DNA structure observation and quantitative results indicated that DLM exposure could obviously induce hemocytes ETosis, especially under high concentration of DLM induction. Moreover, DLM increased the levels of myeloperoxidase (MPO) and reactive oxygen species (ROS) in a dose-dependent manner, and enhanced the mRNA expression of several ROS-related genes. DPI (NADPH oxidase inhibitor) and ABAH (MPO inhibitor) could substantially inhibit DLM-induced extracellular traps (ETs), suggesting that the induced ETs release was caused by the induction of the ROS burst and MPO production. In addition, three concentrations of DLM-induced ETs were also accompanied by mitochondrial dysfunction, such as increasing the production of mitochondrial ROS, leading to a decrease in mitochondrial membrane potential (MMP) and activation of mitochondrial permeability transition pore (MPTP). Taken together, these results will shed new light on the immunotoxicity of DLM in clams and perhaps lays the foundation for health assessment in bivalves.

Computer-aided toxicity prediction and potential risk assessment of two novel neonicotinoids, paichongding and cycloxaprid, to hydrobionts

Paichongding (IPP) and cycloxaprid (CYC) have been effectively used as the alternative products of imidacloprid (IMI) against IMI-resistant insects and exhibit a great market potential. However, risk assessment of IPP and CYC for non-target organisms, especially ecological risk assessment for non-target aquatic organisms, is still lacking. Here, we predicted the toxicity and potential risks of IPP, CYC, and their transformation products (TPs) to hydrobionts. The results indicated that IPP and CYC could generate 428 and 113 TPs, respectively, via aerobic microbial transformation. Nearly half of the IPP TPs and nearly 41 % of the CYC TPs exhibited high or moderate toxicity to Daphnia or fish. Moreover, we found that IPP, CYC, and 80 TPs of them posed potential risks to aquatic ecosystems. Almost all harmful TPs contained a 6-chloropyridine ring structure, suggesting that this structure may be associated with the strong toxicity of these TPs to aquatic organisms, and these TPs (IPP-TP2 or CYC-TP2, IPP-TP197 or CYC-TP71, IPP-TP198 or CYC-TP72, and IPP-TP212 or CYC-TP80) may appear in aquatic environments as final products. The risks posed by these TPs to aquatic ecosystems require more attention. This study provides insights into the toxicity and ecological risks of IPP and CYC.