Ecological Role of 6OH-BDE47: Is It a Chemical Offense Molecule Mediated by Enoyl-ACP Reductases?

Although hydroxylated polybrominated diphenyl ethers (OH-BDEs) are among the most abundant natural organobromine compounds, the fundamental biological rationale for marine organisms to produce OH-BDEs remains elusive. Herein, we demonstrated that natural OH-BDEs exerted strong antibacterial activities against Escherichia coli by inhibiting enoyl-[acyl-carrier-protein] reductase (FabI), while anthropogenic OH-BDEs were inactive. Distinct from E. coli, OH-BDE-producing marine γ-proteobacteria including Marinomonas mediterranea MMB-1 (MMB-1) and Pseudoalteromonas luteoviolacea 2ta16 (Pl2ta16) exhibited resistance to 6OH-BDE47. An alternative enoyl-[acyl-carrier-protein] (ACP) reductase, FabV, was detected in all three OH-BDE-producing marine γ-proteobacteria. Thermal stability and protein affinity purification studies revealed that 6OH-BDE47 did not bind to recombinant or endogenous FabV of MMB-1 or Pl2ta16, demonstrating that FabV was the primary mechanism for OH-BDE-producing marine γ-proteobacteria to be resistant to 6OH-BDE47. To further confirm if the laboratory results were evidenced in the field, the 16S rRNA sequencing and metagenomics data from seven field-collected marine sponges were analyzed. Notably, the two Clade 4 sponges containing high concentrations of 6OH-BDE47 exhibited a distinct microbiome community structure compared to the other analyzed clades. Correspondingly, FabV was found to be selectively enriched in the same Clade 4 sponges. The merged evidence from the laboratory experiments and field studies demonstrated that 6OH-BDE47 may act as a chemical offense molecule in marine sponges.

Enhanced Nontarget Screening Algorithm Reveals Highly Abundant Chlorinated Azo Dye Compounds in House Dust.

Humans spend 90% of their time indoors, but the majority of indoor pollutants remain unknown. In this study, a nontarget screening algorithm with reduced false discovery rates was developed to screen indoor pollutants using the Toxic Substances Control Act (TSCA) database. First, a putative lock mass algorithm was developed for post-acquisition calibration of Orbitrap mass spectra to sub-ppm mass accuracy. Then, a one-stop screening algorithm was developed by combining MS1 spectra, isotopic peaks, retention time prediction, and in silico MS2 spectra. A sufficient true positive rate (73%) and false discovery rate (5%) were achieved for the screening of halogenated compounds at a score cutoff of 0.28. Above this cutoff, 427 chemicals were detected from 24 house dust samples, including 39 chlorinated compounds. While some identified halogenated compounds (e.g., triclosan) are well known, 18 previously unrecognized chlorinated azo dyes were detected with high abundance as the largest class of chlorinated compounds. Two chlorinated azo dyes were confirmed with authentic standards, but the two most abundant chlorinated azo dyes were missed by the algorithm due to the limited breadth of the TSCA database. These compounds were annotated as chlorinated analogues of Disperse Blue 373 and Disperse Violet 93 using the DIPIC-Frag method. This study revealed the presence of highly abundant chlorinated azo dyes in house dusts, highlighting their potential health risks in the indoor environment.

Nontarget Screening of Per- and Polyfluoroalkyl Substances Binding to Human Liver Fatty Acid Binding Protein.

More than 1000 per- and polyfluoroalkyl substances (PFASs) have been discovered by nontarget analysis (NTA), but their prioritization for health concerns is challenging. We developed a method by incorporating size-exclusion column co-elution (SECC) and NTA, to screen PFASs binding to human liver fatty acid binding protein (hL-FABP). Of 74 PFASs assessed, 20 were identified as hL-FABP ligands in which eight of them have high binding affinities. Increased PFAS binding affinities correlate with stronger responses in electrospray ionization (ESI-) and longer retention times on a C18 column. This is well explained by a mechanistic model, which revealed that both polar and hydrophobic interactions are crucial for binding affinities. Encouraged by this, we then developed an SECC method to identify hL-FABP ligands, and all eight high-affinity ligands were selectively captured from 74 PFASs. The method was further applied to an aqueous film-forming foam (AFFF) product in which 31 new hL-FABP ligands were identified. Suspect and nontargeted screening revealed these ligands as analogues of perfluorosulfonic acids and homologues of alkyl ether sulfates (C8- and C10/EOn, C8H17(C2H4O)nSO4-, and C10H21(C2H4O)nSO4-). The SECC method was then applied to AFFF-contaminated surface waters. In addition to perfluorooctanesulfonic acid and perfluorohexanesulfonic acid, eight other AFFF chemicals were discovered as novel ligands, including four C14- and C15/EOn. This study implemented a high-throughput method to prioritize PFASs and revealed the existence of many previously unknown hL-FABP ligands.

Widespread presence of chlorinated paraffins in consumer products.

Short-chain chlorinated paraffins (SCCPs) were listed for elimination under the Stockholm Convention in 2017 due to their persistence and toxicity. Although Canada and other Stockholm signatories have prohibited the manufacture, usage and import of SCCPs since 2013, they can still be detected at high concentrations in indoor dust. To identify the sources of the SCCPs in the Canadian indoor environment, short-, medium- and long-chain chlorinated paraffins (SCCPs, MCCPs, LCCPs, respectively) were measured using a sensitive LC-ESI-orbitrap method. SCCPs were detected in 84 of the 96 products purchased in Canada after 2013 (87.5%) including electronic devices, clothing, plastics (toys), and paintings. Concentrations of SCCPs were up to 0.93% (9.34 mg g-1). SCCPs were also detected in newly purchased toys at 0.005-2.02 mg g-1, indicating the potential for children's exposure. Profiles of chlorinated paraffins differed among categories of products. For example, C13-SCCPs were most common in toys, while electronic devices like headphones showed comparable concentrations of SCCPs and MCCPs. Additionally, four new carboxylate derivatives of CPs were detected in an electronic device sample. These are the first data to show the ubiquitous occurrences of SCCPs in a wide range of products currently marketed in Canada, suggesting continuing indoor exposure to SCCPs despite their prohibition.

Screening of Indoor Transformation Products of Organophosphates and Organophosphites with an in Silico Spectral Database.

Numerous transformation products are formed indoors, but they are outside the scope of current chemical databases. In this study, an in silico spectral database was established to screen previously unknown indoor transformation products of organophosphorus compounds (OPCs). An R package was developed that incorporated four indoor reactions to predict the transformation products of 712 seed OPCs. By further predicting MS2 fragments, an in silico spectral database was established consisting of 3509 OPCs and 28,812 MS2 fragments. With this database, 40 OPCs were tentatively detected in 23 indoor dust samples. This is the greatest number of OPCs reported to date indoors, among which two novel phosphonates were validated using standards. Twenty-four of the detected OPCs were predicted transformation products in which oxidation from organophosphites plays a major role. To confirm this, the in silico spectral database was expanded to include organophosphites for suspect screening in five types of preproduction plastics. A broad spectrum of 14 organophosphites was detected, with a particularly high abundance in polyvinyl chloride plastics and indoor end-user goods. This demonstrated the significant contribution of organophosphites to indoor organophosphates via oxidation, highlighting the strength of in silico spectral databases for the screening of unknown indoor transformation products.

Abundances and concentrations of brominated azo dyes detected in indoor dust.

Dust samples were collected from four indoor environments, including childcare facilities, houses, hair salons, and a research facility from the USA and were analyzed for brominated compounds using full scan liquid chromatography high-resolution mass spectrometry. A total of 240 brominated compounds were detected in these dust samples, and elemental formulas were predicted for 120 more abundant ions. In addition to commonly detected brominated flame retardants (BFRs), nitrogen-containing brominated azo dyes (BADs) were among the most frequently detected and abundant. Specifically, greater abundances of BADs were detected in indoor dusts from daycares and salons compared to houses and the research facility. Using authentic standards, a quantitative method was established for two BADs (DB373: Disperse Blue 373 and DV93: Disperse Violet 93) and 2-bromo-4,6-dinitroaniline, a commonly used precursor in azo dye production, in indoor dust. Generally, greater concentrations of DB373 (≤3850 ng/g) and DV93 (≤1190 ng/g) were observed in indoor dust from daycares highlighting children as a susceptible population to potential health risk from exposure to BADs. These data are important because, to date, targeted analysis of brominated compounds in indoor environments has focused mainly on BFRs and appears to underestimate the total amount of brominated compounds.