Chronic aquatic toxicity of perfluorooctane sulfonic acid (PFOS) to Ceriodaphnia dubia, Chironomus dilutus, Danio rerio, and Hyalella azteca.

Perfluorooctane sulfonic acid (PFOS) is a ubiquitous and persistent contaminant in aquatic ecosystems. Chronic toxicity information for aquatic organisms is limited, therefore we conducted chronic PFOS toxicity tests for four model organisms commonly used for freshwater toxicology assays: Chironomus dilutus (midge), Ceriodaphnia dubia (water flea), Hyalella azteca (amphipod) and Danio rerio (zebrafish). The 16-day survival test with C. dilutus resulted in the lowest PFOS exposure concentrations to cause significant impacts, with reduced survival at 1 µg/L, a LC50 of 7.5 µg/L, and a growth EC10 of 1.5 µg/L. D. rerio was the next most sensitive species, with a 30-day LC50 of 490 µg/L and reduced growth at 260 µg/L. Effects for C. dubia and H. azteca occurred at concentrations a thousand-fold higher than for C. dilutus. H. azteca had a 42-day LC50 of 15 mg/L, an EC50 of 3.8 mg/L for reproduction (neonates per female) and an EC50 of 4.7 mg/L for growth. C. dubia was similarly tolerant of PFOS, with a 6-day LC50 of 20 mg/L for survival and an EC50 of 7 mg/L for reproduction (neonates per adult). H. azteca, C. dubia, and, to a lesser extent, D. rerio, appear tolerant of PFOS concentrations typically found in the environment. However, in agreement with previous studies, C. dilutus was particularly sensitive to PFOS exposure, with lethal and sublethal effects occurring at concentration levels present at highly contaminated sites.

Mode of action evaluation for reduced reproduction in Daphnia pulex exposed to the insensitive munition, 1-methyl-3-nitro-1-nitroguanidine (MeNQ).

The US Department of Defense (DOD) is developing insensitive munitions (IMs) that are resistant to unintended detonation to protect warfighters. To enable material life-cycle analysis for the IM, 1-methyl-3-nitro-1-nitroguanidine (MeNQ), ecotoxicological impacts assessment was required. A previous investigation of MeNQ exposures in Daphnia pulex revealed concentration-responsive decreases in reproduction relative to controls (0 mg/L) across a 174, 346, 709, 1385, and 2286 mg/L exposure range. The present study used those exposures to conduct global transcriptomic expression analyses to establish hypothetical mode(s) of action underlying inhibited reproduction. The number of significantly affected transcripts and the magnitude of fold-change differences relative to controls tended to increase with increasing MeNQ concentration where hierarchical clustering analysis identified separation among the "low" (174 and 346 mg/L) and "high" (709, 1385, and 2286 mg/L) exposures. Vitellogenin is critical to Daphnia reproductive processes and MeNQ exposures significantly decreased transcriptional expression for vitellogenin-1 precursor at the lowest exposure level (174 mg/L) with benchmark dose (BMD) levels closely tracking concentrations that caused inhibited reproduction. Additionally, juvenile hormone-inducible protein, chorion peroxidase, and high choriolytic enzyme transcriptional expression were impacted by MeNQ exposure having potential implications for egg production / maturation and overall fecundity. In concert with these effects on specific genes involved in Daphnia reproductive physiology, MeNQ exposures caused significant enrichment of several canonical-pathways responsible for metabolism of cellular energy substrates where BMD levels for transcriptional expression were observed at ≤100 mg/L. These observations imply possible effects on whole-organism energy budgets that may also incur indirect costs on reproduction.