Anaerobic biodegradation of phenanthrene and pyrene by sulfate-reducing cultures enriched from contaminated freshwater lake sediments.

Our current understanding of the susceptibility of hazardous polycyclic aromatic hydrocarbons (PAHs) to anaerobic microbial degradation is very limited. In the present study, we obtained phenanthrene- and pyrene-degrading strictly anaerobic sulfate-reducing enrichments using contaminated freshwater lake sediments as the source material. The highly enriched phenanthrene-degrading culture, MMKS23, was dominated (98%) by a sulfate-reducing bacterium belonging to the genus Desulfovibrio. While Desulfovibrio sp. was also predominant (79%) in the pyrene-degrading enrichment culture, MMKS44, an anoxygenic purple non-sulfur bacterium, Rhodopseudomonas sp., constituted a significant fraction (18%) of the total microbial community. Phenanthrene or pyrene biodegradation by the enrichment cultures was coupled with sulfate reduction, as evident from near stoichiometric consumption of sulfate and accumulation of sulfide. Also, there was almost complete inhibition of substrate degradation in the presence of an inhibitor of sulfate reduction, i.e., 20 mM MoO42-, in the culture medium. After 180 days of incubation, about 79.40 µM phenanthrene was degraded in the MMKS23 culture, resulting in the consumption of 806.80 µM sulfate and accumulation of 625.80 µM sulfide. Anaerobic pyrene biodegradation by the MMKS44 culture was relatively slow. About 22.30 µM of the substrate was degraded after 180 days resulting in the depletion of 239 µM sulfate and accumulation of 196.90 µM sulfide. Biodegradation of phenanthrene by the enrichment yielded a metabolite, phenanthrene-2-carboxylic acid, suggesting that carboxylation could be a widespread initial step of phenanthrene activation under sulfate-reducing conditions. Overall, this novel study demonstrates the ability of sulfate-reducing bacteria (SRB), dwelling in contaminated freshwater sediments to anaerobically biodegrade three-ringed phenanthrene and highly recalcitrant four-ringed pyrene. Our findings suggest that SRB could play a crucial role in the natural attenuation of PAHs in anoxic freshwater sediments.

Perfluorooctane sulfonate (PFOS) induces several behavioural defects in Caenorhabditis elegans that can also be transferred to the next generations.

Perfluorooctane sulfonate (PFOS) is a well-known global persistent organic pollutant of grave concern to ecological and human health. Toxicity of PFOS to animals and humans are well studied. Although few studies have reported the behavioral effect of PFOS on nematode Caenorhabditis elegans, it's transgenerational effects were seldom studied. Therefore, we investigated the toxicity of PFOS on several behavioral responses besides bioaccumulation and transgenerational effects in C. elegans. In contrast to the several published studies, we used lower concentrations (0.5-1000 µg/L or 0.001-2.0 µM) that are environmentally relevant and reported to occur close to the contaminated areas. The 48 h median lethal concentration of PFOS was found to be 3.15 µM (1575 µg/L). PFOS (≥0.01 µM) caused severe toxicity to locomotion, and this effect was even transferred to progeny. However, after a few generations, the defect was rectified in the progeny of single-time exposed parent nematodes. Whereas, continuous exposure at 0.001 µM PFOS, no visible defects were observed in the progeny. PFOS (≥0.01 µM) also significantly decreased the brood size in a concentration-dependent manner. Besides, lifespan was affected by the higher concentration of PFOS (≥1.0 µM). These two behavioral endpoints, lifespan and reproduction defects, became less severe in the progeny. Chemotaxis plasticity was also significantly retarded by ≥ 1.0 µM PFOS compared to the control group. Results indicate that PFOS can exert severe neurobehavioral defects that can be transferred from parents to their offspring. The findings of this study have significant implications for the risk assessment of perfluorinated substances in the environment.

Acute Toxicity and Transgenerational Effects of Perfluorobutane Sulfonate on Caenorhabditis elegans.

Perfluorobutane sulfonate (PFBS), due to its increasing use as an alternative to perfluooctane sulfonate (PFOS), is widely detected in humans and the environment, necessitating the evaluation of its potential ecotoxicological risk. We assessed the toxicity and bioaccumulation potential of PFBS in Caenorhabditis elegans, using lethality, locomotion, reproduction, life span, growth, and chemotactic behavior as the effect parameters. In addition, a total of 6 generations of exposed parent animals were monitored for locomotion, brood, and life span behaviors. Life span and brood size were significantly reduced in parent nematodes (P0) following exposure to ≥0.1 mM PFBS, but these negative effects did not transfer to the progeny. Although there was no remarkable effect on reproduction and life span in parent worms exposed to ≤0.01 mM PFBS, multigenerational exposure at 0.0005 mM significantly affected the F4 and F5 progeny. Furthermore, 0.01 to 2.0 mM of PFBS substantially retarded the locomotion behavior of P0 worms. At higher concentrations such as 1.0 mM, this negative effect on locomotion was transferred to the next generation (F1) but later recovered from F2 progeny onward. Our findings demonstrate for the first time that chronic exposure to PFBS at higher concentrations can cause behavioral toxicity and could be transferred to the progeny. These findings have significant implications for the environmental risk assessment of PFBS. Environ Toxicol Chem 2021;40:1973-1982. © 2021 SETAC.