Modeling demonstrates minimal ecological risks of cuttings discharges associated to oil and gas drilling with deep water wells.

To assess the impacts of drill cutting discharges in the Gulf of Mexico, a particle dispersion modeling study was conducted on hypothetical drilling scenarios. The goal was to assess cumulative seabed deposition, and potential hydrocarbon loading from non-aqueous drilling fluids (NADF). Cuttings drilled with NADF showed to have minimal impact on local fauna at the deep-water well simulated. A hypothetical drill site was modeled under 3 different seasonally representative met-ocean conditions. The site is located approximately 260 km from the coast in water roughly 3500 meters (m) deep. Cumulative deposition was assessed for all materials released, whereas hydrocarbon loading was assessed based on the potential for NADF fluids to be retained on cuttings. Smothering effects on the benthic community are not anticipated. Hydrocarbon deposition was also very limited, ≤165 ppm of TPH. Overall, the cuttings drilled with NADF are predicted to have minimal impact on local fauna.

Using weight of evidence to assess degradation potential of UVCB hydrocarbon solvents.

Hydrocarbon solvents are a diverse group of petrochemical substances that are identified as unknown or variable composition, complex reaction products, or biological materials (UVCBs) and may contain tens of thousands of individual chemical constituents. As such, it is generally not possible to analytically resolve every chemical constituent in a hydrocarbon solvent. This, along with the low water solubility and/or high vapor pressure of constituents, precludes the use of many standardized tests designed to determine biodegradation in the environment (e.g., Organization for Economic Co-operation and Development [OECD] 309). A weight of evidence approach may be needed to reduce uncertainty to an acceptable level such that a determination on the biodegradation of the substance can be drawn. Based on the OECD 2019 weight of evidence guidance, we present a framework using various lines of evidence that can be used to evaluate the biodegradation of a UVCB solvent in a weight of evidence approach. The lines of evidence include whole substance testing, data on representative constituents, quantitative structure activity relationship (QSAR) models, and biological plausibility. Using these lines of evidence, "Hydrocarbon, C11-C14, normal alkane, isoalkane, cyclic, <2% aromatics" (EC# 926-141-6) was evaluated in a case study. Data from three whole substance tests, 43 constituents (representing 152 data points), three QSAR models and evidence of microbial degradation pathways were evaluated. Based on the available data, it is concluded that the solvent for the case study is not expected to persist in the environment. This framework sets out a real-world example of how the weight of evidence can be used to evaluate hydrocarbon solvents. While focused on persistence, similar approaches can be used to evaluate other endpoints such as bioaccumulation and toxicity. Integr Environ Assess Manag 2023;19:1120-1130. © 2023 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Effects of bioturbation on environmental DNA migration through soil media.

Extracting and identifying genetic material from environmental media (i.e. water and soil) presents a unique opportunity for researchers to assess biotic diversity and ecosystem health with increased speed and decreased cost as compared to traditional methods (e.g. trapping). The heterogeneity of soil mineralogy, spatial and temporal variations however present unique challenges to sampling and interpreting results. Specifically, fate/transport of genetic material in the terrestrial environment represents a substantial data gap. Here we investigate to what degree, benthic fauna transport genetic material through soil. Using the red worm (Eisenia fetida), we investigate how natural movement through artificial soil affect the transport of genetic material. All experiments were run in Frabill® Habitat® II worm systems with approximately 5 cm depth of artificial soil. We selected an "exotic" source of DNA not expected to be present in soil, zebrafish (Danio rerio) tissue. Experiment groups contained homogenized zebrafish tissue placed in a defined location combined with a varying number of worms (10, 30 or 50 worms per experimental group). Experimental groups comprised two controls and three treatment groups (representing different worm biomass) in triplicate. A total of 210 soil samples were randomly collected over the course of 15 days to investigate the degree of genetic transfer, and the rate of detection. Positive detections were identified in 14% - 38% of samples across treatment groups, with an overall detection rate of 25%. These findings highlight two important issues when utilizing environmental DNA for biologic assessments. First, benthic fauna are capable of redistributing genetic material through a soil matrix. Second, despite a defined sample container and abundance of worm biomass, as many as 86% of the samples were negative. This has substantial implications for researchers and managers who wish to interpret environmental DNA results from terrestrial systems. Studies such as these will aid in future study protocol design and sample collection methodology.

Multistressor interactions in the zebrafish (Danio rerio): Concurrent phenanthrene exposure and Mycobacterium marinum infection.

The simultaneous exposure of organisms to toxicants and disease causing agents poses a serious risk to important stocks. Worldwide, aquatic animal disease outbreaks have been increasing in both frequency and severity, and many have been associated with anthropogenic environmental change. Little is known about the complex interactions of the immune system and biotransformational pathways of vertebrates; however, urbanization and coastal development create a scenario in which a wide range of species are exposed to chemical pollutants in conjunction with a wide spectrum of ubiquitous, opportunistic pathogens. These interactions can severely compromise organismal health. Potential effects include decreased fitness, increased predation, decreased fecundity, reduced metabolic activity, suppressed immune function and mortality. Recent attention has been paid to immunomodulation in toxicant exposed fishes. In our current study we investigated the effects of the common polycyclic aromatic hydrocarbon phenanthrene in conjunction with Mycobacterium marinum infection in the zebrafish, Danio rerio. The goal of our study was to elucidate the interactions between stressors in the host organism. Fish were exposed to either a high or low dose of phenanthrene, infected with M. marinum or received a combination exposure of toxicant and bacteria. Results of our study were evaluated using survivorship analysis, toxicant body burden, and histology. Our data show an interaction between M. marinum infection and exposure to a high dose of phenanthrene in the zebrafish. Survivorship was significantly reduced for animals only exposed to the high dose of phenanthrene as compared to all other experimental groups. The increased survivorship for fish exposed to both Mycobacterium and a high dose of phenanthrene suggests an antagonistic interaction between stressors. Body burden data, which show significant differences in the ratio of phenanthrene:metabolites between experimental groups, suggests a disruption of the biotransformational pathway. We postulate that the inflammatory response, initiated by bacterial infection, is impeding the ability of the zebrafish to completely metabolize phenanthrene. In addition, the correlation between reduced metabolite production and increased survival indicates that phenanthrene metabolites are more toxic than the parent compound. Our study underscores the importance of investigating multiple stressor interactions as a way to better understand complex environmental interactions.