The impact of precursors on aquatic exposure assessment for PFAS: Insights from bioaccumulation modeling.

Risk assessment for per- and polyfluoroalkyl substances (PFAS) is complicated by the fact that PFAS include several thousand compounds. Although new analytical methods have increased the number that can be identified in environmental samples, a significant fraction of them remain uncharacterized. Perfluorooctane sulfonate (PFOS) is the PFAS compound of primary interest when evaluating risks to humans and wildlife owing to the consumption of aquatic organisms. The exposure assessment for PFOS is complicated by the presence of PFOS precursors and their transformation, which can occur both in the environment and within organisms. Thus, the PFOS to which wildlife or people are exposed may consist of PFOS that was discharged directly into the environment and/or other PFOS precursors that were transformed into PFOS. This means that exposure assessment and the development of remedial strategies may depend on the relative concentrations and properties not only of PFOS but also of other PFAS that are transformed into PFOS. A bioaccumulation model was developed to explore these issues. The model embeds toxicokinetic and bioenergetic components within a larger food web calculation that accounts for uptake from both food and water, as well as predator-prey interactions. Multiple chemicals are modeled, including parent-daughter reactions. A series of illustrative simulations explores how chemical properties can influence exposure assessment and remedial decision making. Integr Environ Assess Manag 2021;17:705-715. © 2021 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Dehalococcoides mccartyi strain JNA dechlorinates multiple chlorinated phenols including pentachlorophenol and harbors at least 19 reductive dehalogenase homologous genes.

Pentachlorophenol and other chlorinated phenols are highly toxic ubiquitous environmental pollutants. Using gas chromatographic analysis we determined that Dehalococcoides mccartyi strain JNA in pure culture dechlorinated pentachlorophenol to 3,5-dichlorophenol (DCP) via removal of the ortho and para chlorines in all of the three possible pathways. In addition, JNA dechlorinated 2,3,4,6-tetrachlorophenol via 2,4,6-trichlorophenol (TCP) and 2,4,5-TCP to 2,4-DCP and 3,4-DCP, respectively, and dechlorinated 2,3,6-TCP to 3-chlorophenol (CP) via 2,5-DCP. JNA converted 2,3,4-TCP to 3,4-DCP and 2,4-DCP by ortho and meta dechlorination, respectively. 2,3-DCP was dechlorinated to 3-CP, and, because cultures using it could be transferred with a low inoculum (0.5 to 1.5% vol/vol), it may act as an electron acceptor to support growth. Using PCR amplification with targeted and degenerate primers followed by cloning and sequencing, we determined that JNA harbors at least 19 reductive dehalogenase homologous (rdh) genes including orthologs of pcbA4 and pcbA5, pceA, and mbrA, but not tceA or vcrA. Many of these genes are shared with D. mccartyi strains CBDB1, DCMB5, GT, and CG5. Strain JNA has previously been shown to extensively dechlorinate the commercial polychlorinated biphenyl (PCB) mixture Aroclor 1260. Collectively the data suggest that strain JNA may be well adapted to survive in sites contaminated with chlorinated aromatics and may be useful for in situ bioremediation.

Dehalococcoides mccartyi strain JNA in pure culture extensively dechlorinates Aroclor 1260 according to polychlorinated biphenyl (PCB) dechlorination Process N.

We isolated Dehalococcoides mccartyi strain JNA from the JN mixed culture which was enriched and maintained using the highly chlorinated commercial PCB mixture Aroclor 1260 for organohalide respiration. For isolation we grew the culture in minimal liquid medium with 2,2',3,3',6,6'-hexachlorobiphenyl (236-236-CB)(20 µM) as respiratory electron acceptor. We repeatedly carried out serial dilutions to extinction and recovered dechlorination activity from transfers of 10(-7) and 10(-8) dilutions. Fluorescence microscopy, DGGE and RFLP analysis of PCR amplified16S rRNA genes, and multilocus sequence typing of three housekeeping genes confirmed culture purity. No growth occurred on complex media. JNA dechlorinated most hexa- and heptachlorobiphenyls in Aroclor 1260 (50 µg/mL) leading to losses of 51% and 20%, respectively. Dechlorination was predominantly from flanked meta positions of 34-, 234-, 235-, 236-, 245-, 2345-, 2346-, and 2356-chlorophenyl rings, as indicated by the underscores. The major products were 24-24-CB, 24-26-CB, 24-25-CB, and 25-26-CB. We identified 85 distinct PCB dechlorination reactions and 56 different PCB dechlorination pathways catalyzed by JNA. Dechlorination pathways were confirmed by mass balance of substrates and products. This dechlorination pattern matches PCB Dechlorination Process N. JNA is the first pure culture demonstrated to carry out this extensive and environmentally relevant PCB dechlorination pattern.

Complete genome sequence of the metabolically versatile plant growth-promoting endophyte Variovorax paradoxus S110.

Variovorax paradoxus is a microorganism of special interest due to its diverse metabolic capabilities, including the biodegradation of both biogenic compounds and anthropogenic contaminants. V. paradoxus also engages in mutually beneficial interactions with both bacteria and plants. The complete genome sequence of V. paradoxus S110 is composed of 6,754,997 bp with 6,279 predicted protein-coding sequences within two circular chromosomes. Genomic analysis has revealed multiple metabolic features for autotrophic and heterotrophic lifestyles. These metabolic diversities enable independent survival, as well as a symbiotic lifestyle. Consequently, S110 appears to have evolved into a superbly adaptable microorganism that is able to survive in ever-changing environmental conditions. Based on our findings, we suggest V. paradoxus S110 as a potential candidate for agrobiotechnological applications, such as biofertilizer and biopesticide. Because it has many associations with other biota, it is also suited to serve as an additional model system for studies of microbe-plant and microbe-microbe interactions.