Project description:Purpose: The goals of this study are to investigate developmental toxicity and hazard potential of a short-chain PFAS homologous series in zebrafish, specifically interrogating the impact of different functional head groups. Developmental toxicity findings were supplemented with investigations into transcriptom-wide effects of body burdens following PFAS exposures. Methods: For developmental toxicity assessments, dechorionated embryonic zebrafish were statically exposed at 8 hours post fertilization (hpf) to either vehicle control (0.5% methanol) or to FBSA, PFBS, PFPeA, or 4:2 FTS across a range of concentrations (1-100 µM, normalized to 0.5% methanol) in 96-well plate format. Morphological and Behavior endpoints were assessed at 24 and 120 hpf. For investigations into transcriptomic effects and body burdens, embryos were exposed to vehicle control or 47 µM of each PFAS and then sampled at 48 hpf, before morphological effects were observable. Transcriptomic effects of FBSA exposure were phenotypically anchored to abnormal morphology at 120 hpf as 47 µM was the concentration at which morphological effects were observed in 80% of the exposure group. At 48 hpf, 10 embryos were pooled per replicate, euthanized via ice bath, and total RNA extracted using a Zymo Research Direct-zol RNA MiniPrep kit and then sequenced on the BGISEQ-500 platform (Beijing Genomics Institute; BGI) for the transcriptomic investigation. Data analysis and visualization was conducted by BGI and their Dr. Tom platform. Briefly, sequencing data was filtered using SOAPnukes to remove adaptor sequences, N content greater than 5%, and low-quality reads. Clean reads were mapped to the reference genome (Danio rerio GRCz11) using HISAT2. Gene fusions and differential splicing were detected using Ericscript and rMATS, clean read alignments using Bowtie2 and expression level calculations using RSEM. Differential expression analysis was performed using DESEq2 (q-value ≤ 0.05), followed by gene ontology enrichment analysis using Phyper and transcription factor enrichment analysis using MetaCore. For body burden measurments, 4 replicates of 40 embryos were pooled per exposure group, euthanized on ice, homogenized, and analyzed by high pressure liquid chromatography and triple quadrupole mass spectrometry. Results: Across the 4-fluorinated carbon short-chain PFAS series, all chemicals induced larval behavior effects, but only FBSA caused morphological, behavioral and large-scale transcriptomic disruptions (specifically at 47 µM). Notably, exposures at concentrations shown to induce only behavior effects resulted in a small number of differentially expressed genes. Biological processes enriched following FBSA exposure at 47 µM were related to lipid metabolism and biosynthesis, cellular homeostasis, brain and nervous system development, and immune processes. The bioaccumulative potential of the series at 47 µM was FBSA > PFBS > 4:2 FTS > PFPeA.

Project description:Traditional toxicity testing has been unable to keep pace with the introduction of new chemicals into commerce. Consequently, there are limited or no toxicity data upon which to base a risk assessment for many chemicals to which fish and wildlife may be exposed. Per- and polyfluoroalkyl substances (PFAS) are emblematic of this issue in that most the ecological hazards of most PFAS remain uncharacterized. The present study employed a high throughput assay to identify the concentration at which 20 PFAS, with diverse properties, elicited a concerted gene expression response in larval fathead minnows (Pimephales promelas, 5-6 days post-fertilization) exposed for 24 h. Based on a reduced transcriptome approach that measured whole body expression of 1832 genes, the median transcriptomic point of departure (tPOD) for the 20 PFAS tested was 10 µM. Longer chain carboxylic acids (12-13 C-F) and an eight C-F di-alcohol, N-alkyl sulfonamide, and telomer sulfonic acid were among the most potent PFAS, eliciting gene expression responses at concentrations below 1 µM. With a few exceptions, larval fathead minnow tPODs were concordant with those based on whole transcriptome response in human cell lines. However, larval fathead minnow tPODs were often greater than those for Daphnia magna exposed to the same PFAS. The tPODs overlapped concentrations at which other sub-lethal effects have been reported in fish (available for 10 PFAS; including a range of species, life stages, and study designs). Nonetheless, fathead minnow tPODs were all orders of magnitude higher than aqueous PFAS concentrations detected in tributaries of the North American Great Lakes suggesting a substantial margin of safety in those systems, even for PFAS with significant potential for bioaccumulation. Overall, results broadly support the use of a fathead minnow larval transcriptomics assay to derive screening level potency estimates for use in ecological risk-based prioritization. Traditional toxicity testing has been unable to keep pace with the introduction of new chemicals into commerce. Consequently, there are limited or no toxicity data upon which to base a risk assessment for many chemicals to which fish and wildlife may be exposed. Per- and polyfluoroalkyl substances (PFAS) are emblematic of this issue in that most the ecological hazards of most PFAS remain uncharacterized. The present study employed a high throughput assay to identify the concentration at which 20 PFAS, with diverse properties, elicited a concerted gene expression response in larval fathead minnows (Pimephales promelas, 5-6 days post-fertilization) exposed for 24 h. Based on a reduced transcriptome approach that measured whole body expression of 1832 genes, the median transcriptomic point of departure (tPOD) for the 20 PFAS tested was 10 µM. Longer chain carboxylic acids (12-13 C-F) and an eight C-F di-alcohol, N-alkyl sulfonamide, and telomer sulfonic acid were among the most potent PFAS, eliciting gene expression responses at concentrations below 1 µM. With a few exceptions, larval fathead minnow tPODs were concordant with those based on whole transcriptome response in human cell lines. However, larval fathead minnow tPODs were often greater than those for Daphnia magna exposed to the same PFAS. The tPODs overlapped concentrations at which other sub-lethal effects have been reported in fish (available for 10 PFAS; including a range of species, life stages, and study designs). Nonetheless, fathead minnow tPODs were all orders of magnitude higher than aqueous PFAS concentrations detected in tributaries of the North American Great Lakes suggesting a substantial margin of safety in those systems, even for PFAS with significant potential for bioaccumulation. Overall, results broadly support the use of a fathead minnow larval transcriptomics assay to derive screening level potency estimates for use in ecological risk-based prioritization.

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Sulfonamide functional head group drives developmental toxicity of short-chain per- and polyfluorolkyl substances

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