Relationships Between Aquatic Toxicity, Chemical Hydrophobicity, and Mode of Action: Log Kow Revisited.

Relationships between toxicity and chemical hydrophobicity have been known for nearly 100 years in mammals and fish, typically using the log of the octanol:water partition coefficient (Kow). The current study reassessed the influence of mode of action (MOA) on acute aquatic toxicity-log Kow relationships using a comprehensive database of 617 organic chemicals with curated and standardized acute toxicity data that did not exceed solubility limits, their consensus log Kow values, and weight of evidence-based MOA classifications (including 6 broad and 26 specific MOAs). A total of 166 significant (p < 0.05) log Kow-toxicity models were developed across six taxa groups that included QSARs for 5 of the broad and 13 of the specific MOAs. In this study, we demonstrate that QSARs based on MOAs can significantly increase LC50 prediction accuracy for specific acting chemicals. Prediction accuracy increases when QSARs are built based on highly specific MOAs, rather than broad MOA classifications. Additionally, we demonstrate that building QSAR models with chemicals in specific MOA groupings, rather than broader MOA groups leads to significantly better estimates. We also evaluated the differences between models developed from mass-based (µg/L) and mole-based (µmol/L) toxicity data and demonstrate that both are suitable for QSAR development with no clear trend in greater model accuracy. Overall, the results reveal that, despite high variance in all taxa and MOA groups, specific MOA-based models can improve the accuracy of aquatic toxicity predictions over more general groupings.Please check and confirm that the authors and their respective affiliations have been correctly identified and amend if necessary.The affiliations are correct.

Assessment of a New Approach Method for Grouped Chemical Hazard Estimation: The Toxicity-Normalized Species Sensitivity Distribution (SSDn).

New approach methods are being developed to address the challenges of reducing animal testing and assessing risks to the diversity of species in aquatic environments for the multitude of chemicals with minimal toxicity data. The toxicity-normalized species sensitivity distribution (SSDn) approach is a novel method for developing compound-specific hazard concentrations using data for toxicologically similar chemicals. This approach first develops an SSDn composed of acute toxicity values for multiple related chemicals that have been normalized by the sensitivity of a common species tested with each compound. A toxicity-normalized hazard concentration (HC5n) is then computed from the fifth percentile of the SSDn. Chemical-specific HC5 values are determined by back-calculating the HC5n using the chemical-specific sensitivity of the normalization species. A comparison of the SSDn approach with the single-chemical SSD method was conducted by using data for nine transition metals to generate and compare HC5 values between the two methods. We identified several guiding principles for this method that, when applied, resulted in accurate HC5 values based on comparisons with results from single-metal SSDs. The SSDn approach shows promise for developing statistically robust hazard concentrations when adequate taxonomic representation is not available for a single chemical.

Dimensions of Sexual Health Conversations among U.S. Black Heterosexual Couples.

Sexual health communication is an important feature of healthy intimate relationships; however, some couples may avoid discussing difficult matters (e.g., HIV/STI testing, sexual satisfaction) to minimize interpersonal conflict. From October 2018 to May 2019 in New York State, we conducted a multi-method descriptive pilot study to characterize Black heterosexual couples' (N = 28) sexual health conversations. Partners individually completed an online sexual health/relationship survey before engaging in-person for a joint dyadic qualitative in-depth interview. Quantitative descriptive statistics demonstrated that most absolute score differences among couple's preferences for sexual health outcomes, communal coping and sexual relationship power were mainly small, but greatest regarding extra-dyadic sexual behaviors. A qualitative descriptive approach discerned, motivation and norms for sexual health conversations, and communication patterns. Thematic and content analysis revealed two central themes: initiating and sustaining sexual health conversations, and leveraging features of the couples to promote sexual health. Integrated findings indicate that couples possess varied communication patterns that operate with motivations for sexual health conversations toward subsequent sexual health promotion. Equitable and skewed communication patterns emerged as relationship assets that can be leveraged to optimize sexual health. There is also opportunity for future work to address communication regarding extra-dyadic behavior and preferences. Asset-based considerations are discussed.

Potential for Interspecies Toxicity Estimation in Soil Invertebrates.

Interspecies correlation estimation (ICE) models are linear regressions that predict toxicity to a species with few data using a known toxicity value in a surrogate species. ICE models are well established for estimating toxicity to fish and aquatic invertebrates but have not been generally developed or applied to soil organisms. To facilitate the development of ICE models for soil invertebrates, a database of single chemical toxicity values was compiled from knowledgebases and reports that included 853 records encompassing 192 chemicals and 12 species. Most toxicity data for single chemicals tested in soil media were for species of earthworms, with only limited data for other species and taxa. ICE models were developed for eleven separate species pairs as least squares log-linear regressions of acute toxicity values of the same chemicals tested in both the surrogate and predicted species of soil organisms. Model uncertainty was assessed using leave one out cross-validation as the fold difference between a predicted and measured toxicity value. ICE models showed high accuracy within order (e.g., earthworm to earthworm), but less prediction accuracy in the two across-taxa models (Arthropoda to Annelida and the inverse). This study provides a proof-of-concept demonstration that ICE models can be developed for soil invertebrates.

The Toxicogenome of Hyalella azteca: A Model for Sediment Ecotoxicology and Evolutionary Toxicology.

Hyalella azteca is a cryptic species complex of epibenthic amphipods of interest to ecotoxicology and evolutionary biology. It is the primary crustacean used in North America for sediment toxicity testing and an emerging model for molecular ecotoxicology. To provide molecular resources for sediment quality assessments and evolutionary studies, we sequenced, assembled, and annotated the genome of the H. azteca U.S. Lab Strain. The genome quality and completeness is comparable with other ecotoxicological model species. Through targeted investigation and use of gene expression data sets of H. azteca exposed to pesticides, metals, and other emerging contaminants, we annotated and characterized the major gene families involved in sequestration, detoxification, oxidative stress, and toxicant response. Our results revealed gene loss related to light sensing, but a large expansion in chemoreceptors, likely underlying sensory shifts necessary in their low light habitats. Gene family expansions were also noted for cytochrome P450 genes, cuticle proteins, ion transporters, and include recent gene duplications in the metal sequestration protein, metallothionein. Mapping of differentially expressed transcripts to the genome significantly increased the ability to functionally annotate toxicant responsive genes. The H. azteca genome will greatly facilitate development of genomic tools for environmental assessments and promote an understanding of how evolution shapes toxicological pathways with implications for environmental and human health.

The physiological stress response of the Atlantic stingray (Hypanus sabinus) to aerial exposure.

Although secondary stress physiology of elasmobranchs is fairly well studied, gaps remain in our understanding of species differences, including stress recovery. We examined the physiological stress response to air exposure in Atlantic stingrays (Hypanus sabinus) using a serial sampling method requiring minimal handling. Many elasmobranch stress studies exclusively quantify glucose, although there is evidence that elasmobranchs are unusually reliant on ketone bodies. Therefore, we also tested the hypothesis that ketone bodies play a significant role in the elasmobranch stress response by examining plasma ß-hydroxybutyrate. Plasma osmolality, urea, trimethylamine-N-oxide, and a suite of ions were also measured to characterize departures from homeostasis due to air exposure. H. sabinus were exposed to air for 30 min and serially sampled at 0, 15, and 30 min, as well as 48 h after the stressor to assess the extent of recovery. Blood lactate and acidosis increased significantly during the stressor and returned to basal levels by 48 h. Glucose values were significantly affected, with the highest values observed at 48 h, suggesting that animals were not fully recovered as initially indicated by other metrics. Average plasma ß-hydroxybutyrate was unaffected by the stressor. This suggests that ketone bodies may not be a major fuel source used during acute stress, at least in the timeframe examined.

Na⁺/K⁺-ATPase α1 mRNA expression in the gill and rectal gland of the Atlantic stingray, Dasyatis sabina, following acclimation to increased salinity.

BACKGROUND: The salt-secreting rectal gland plays a major role in elasmobranch osmoregulation, facilitating ion balance in hyperosmotic environments in a manner analogous to the teleost gill. Several studies have examined the central role of the sodium pump Na(+)/K(+)-ATPase in osmoregulatory tissues of euryhaline elasmobranch species, including regulation of Na(+)/K(+)-ATPase activity and abundance in response to salinity acclimation. However, while the transcriptional regulation of Na(+)/K(+)-ATPase in the teleost gill has been well documented the potential for mRNA regulation to facilitate rectal gland plasticity during salinity acclimation in elasmobranchs has not been examined. Therefore, in this study we acclimated Atlantic stingrays, Dasyatis sabina (Lesueur) from 11 to 34 ppt salinity over 3 days, and examined changes in plasma components as well as gill and rectal gland Na(+)/K(+)-ATPase α1 (atp1a1) mRNA expression. RESULTS: Acclimation to increased salinity did not affect hematocrit but resulted in significant increases in plasma osmolality, chloride and urea. Rectal gland atp1a1 mRNA expression was higher in 34 ppt-acclimated D. sabina vs. CONTROLS: There was no significant change in gill atp1a1 mRNA expression, however mRNA expression of this gene in the gill and rectal gland were negatively correlated. CONCLUSIONS: This study demonstrates regulation of atp1a1 in the elasmobranch salt-secreting gland in response to salinity acclimation and a negative relationship between rectal gland and gill atp1a1 expression. These results support the hypothesis that the gill and rectal gland play opposing roles in ion balance with the gill potentially facilitating ion uptake in hypoosmotic environments. Future studies should further examine this possibility as well as potential differences in the regulation of Na(+)/K(+)-ATPase gene expression between euryhaline and stenohaline elasmobranch species.