Recommendations for advancing media preparation methods used to assess aquatic hazards of oils and spill response agents.

Laboratory preparation of aqueous test media is a critical step in developing toxicity information needed for oil spill response decision-making. Multiple methods have been used to prepare physically and chemically dispersed oils which influence test outcome, interpretation, and utility for hazard assessment and modeling. This paper aims to review media preparation strategies, highlight advantages and limitations, provide recommendations for improvement, and promote the standardization of methods to better inform assessment and modeling. A benefit of media preparation methods for oil that rely on low to moderate mixing energy coupled with a variable dilution design is that the dissolved oil composition of the water accommodation fraction (WAF) stock is consistent across diluted treatments.  Further, analyses that support exposure confirmation maybe reduced and reflect dissolved oil exposures that are bioavailable and amenable to toxicity modeling.  Variable loading tests provide a range of dissolved oil compositions that require analytical verification at each oil loading. Regardless of test design, a preliminary study is recommended to optimize WAF mixing and settling times to achieve equilibrium between oil and test media. Variable dilution tests involving chemical dispersants (CEWAF) or high energy mixing (HEWAF) can increase dissolved oil exposures in treatment dilutions due to droplet dissolution when compared to WAFs. In contrast, HEWAF/CEWAFs generated using variable oil loadings are expected to provide dissolved oil exposures more comparable to WAFs. Preparation methods that provide droplet oil exposures should be environmentally relevant and informed by oil droplet concentrations, compositions, sizes, and exposure durations characteristic of field spill scenarios. Oil droplet generators and passive dosing techniques offer advantages for delivering controlled constant or dynamic dissolved exposures and larger volumes of test media for toxicity testing. Adoption of proposed guidance for improving media preparation methods will provide greater comparability and utility of toxicity testing in oil spill response and assessment.

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).

Assessing toxicity of hydrophobic aliphatic and monoaromatic hydrocarbons at the solubility limit using novel dosing methods.

Reliable delineation of aquatic toxicity cut-offs for poorly soluble hydrocarbons is lacking. In this study, vapor and passive dosing methods were applied in limit tests with algae and daphnids to evaluate the presence or absence of chronic effects at exposures corresponding to the water solubility for representative hydrocarbons from five structural classes: branched alkanes, mono, di, and polynaphthenic (cyclic) alkanes and monoaromatic naphthenic hydrocarbons (MANHs). Algal growth rate and daphnid immobilization, growth and reproduction served as the chronic endpoints investigated. Results indicated that the dosing methods applied were effective for maintaining mean measured exposure concentrations within a factor of two or higher of the measured water solubility of the substances investigated. Chronic effects were not observed for hydrocarbons with an aqueous solubility below approximately 5 µg/L. This solubility cut-off corresponds to structures consisting of 13-14 carbons for branched and cyclic alkanes and 16-18 carbons for MANHs. These data support reliable hazard and risk evaluation of hydrocarbon classes that comprise petroleum substances and the methods described have broad applicability for establishing empirical solubility cut-offs for other classes of hydrophobic substances. Future work is needed to understand the role of biotransformation on the observed presence or absence of toxicity in chronic tests.

Chronic toxicity of selected polycyclic aromatic hydrocarbons to algae and crustaceans using passive dosing.

Because of the large number of possible aromatic hydrocarbon structures, predictive toxicity models are needed to support substance hazard and risk assessments. Calibration and evaluation of such models requires toxicity data with well-defined exposures. The present study has applied a passive dosing method to generate reliable chronic effects data for 8 polycyclic aromatic hydrocarbons (PAHs) on the green algae Pseudokirchneriella subcapitata and the crustacean Ceriodaphnia dubia. The observed toxicity of these substances on algal growth rate and neonate production were then compared with available literature toxicity data for these species, as well as target lipid model and chemical activity-based model predictions. The use of passive dosing provided well-controlled exposures that yielded more consistent data sets than attained by past literature studies. Results from the present study, which were designed to exclude the complicating influence of ultraviolet light, were found to be well described by both target lipid model and chemical activity effect models. The present study also found that the lack of chronic effects for high molecular weight PAHs was consistent with the limited chemical activity that could be achieved for these compounds in the aqueous test media. Findings from this analysis highlight that variability in past literature toxicity data for PAHs may be complicated by both poorly controlled exposures and photochemical processes that can modulate both exposure and toxicity. Environ Toxicol Chem 2016;35:2948-2957. © 2016 SETAC.

A novel passive dosing system for determining the toxicity of phenanthrene to early life stages of zebrafish.

Reliable experimental early life stage chronic toxicity data for fish are limited and further data are needed for polyaromatic hydrocarbons to establish environmental quality objectives and compare with toxicity model predictions. Efforts are underway to develop a zebrafish embryo toxicity test guideline to reduce, refine and replace the use of vertebrates in animal testing. An adaptation of this method which includes embryo lethal and sub-lethal developmental endpoints after a 5-day exposure as well as larval survival and growth endpoints during a subsequent 25-day test period is described using phenanthrene as a model test substance. To deliver well controlled exposure concentrations, a passive dosing system consisting of silicone coated vials and silicone O-rings was employed. Acute results indicated that edema and spinal curvature were the most sensitive sub-lethal effects observed and in many cases preceded observed mortality. The 30-day LC/EC10 for larval survival and growth was 40 and 67 µg/L respectively. Concentrations shown to cause adverse effects in this study are in the range of previous studies that have investigated the chronic effects of phenanthrene on fish. Further, results indicate that predicted water quality objectives for phenanthrene derived using the target lipid model are protective of early life stage effects on zebrafish. Based on these results the predicted water quality objectives for phenanthrene derived using the target lipid model (10 µg/L) would be protective of early life stage effects on zebrafish.