Evaluation of the phototoxicity of unsubstituted and alkylated polycyclic aromatic hydrocarbons to mysid shrimp (Americamysis bahia): Validation of predictive models

Photoreactivity of polycyclic aromatic hydrocarbons (PAHs) and their mechanisms of phototoxicity against human immortalized keratinocytes (HaCaT)

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous organic compounds in the environment. They are produced by many anthropogenic sources of different origins and are known for their toxicity, carcinogenicity, and mutagenicity. Sixteen PAHs have been identified as Priority Pollutants by the US EPA, which are often associated with particulate matter, facilitating their dispersion through air and water. When human skin is exposed to PAHs, it might occur simultaneously with solar radiation, potentially leading to phototoxic effects. Phototoxic mechanisms involve the generation of singlet oxygen and reactive oxygen species, DNA damage under specific light wavelengths, and the formation of charge transfer complexes. Despite predictions of phototoxic properties for some PAHs, there remains a paucity of experimental data. This study examined the photoreactive and phototoxic properties of the 16 PAHs enlisted in the Priority Pollutants list. Examined PAHs efficiently photogenerated singlet oxygen and superoxide anion in simple solutions. Furthermore, singlet oxygen phosphorescence was detected in PAH-loaded HaCaT cells. Phototoxicity against human keratinocytes was evaluated using various assays. At 5 nM concentration, examined PAHs significantly reduced viability and mitochondrial membrane potential of HaCaT cells following the exposure to solar simulated light. Analyzed compounds induced a substantial peroxidation of cellular proteins after light treatment. The results revealed that a majority of the examined PAHs exhibited substantial reactive oxygen species photoproduction under UVA and violet-blue light, with their phototoxicity corresponding to their photoreactive properties. These findings improve our comprehension of the interactions between PAHs and human skin cells under environmental conditions, particularly when exposed to solar radiation.

Effects of aromatic hydrocarbons and evaluation of oil toxicity modelling for larvae of a tropical coral

Application of oil toxicity modelling for assessing the risk of spills to coral reefs remains uncertain due to a lack of data for key tropical species and environmental conditions. In this study, larvae of the coral Acropora millepora were exposed to six aromatic hydrocarbons individually to generate critical target lipid body burdens (CTLBBs). Larval metamorphosis was inhibited by all six aromatic hydrocarbons, while larval survival was only affected at concentrations >2000 μg L-1. The derived metamorphosis CTLBB of 9.7 μmol g-1 octanol indicates larvae are more sensitive than adult corals, and places A. millepora larvae among the most sensitive organisms in the target lipid model (TLM) databases. Larvae were also more sensitive to anthracene and pyrene when co-exposed to ecologically relevant levels of ultraviolet radiation. The results suggest that the application of the phototoxic TLM would be protective of A. millepora larvae, provided adequate chemical and light data are available.

New Insights into the Phototoxicity of Anthracene-Based Chromophores: The Chloride Salt Effect†

Unraveling the causes underlying polycyclic aromatic hydrocarbon phototoxicity is an essential step in understanding the harmful effects of these compounds in nature. Toward this end, we have studied the DNA interactions and photochemistry of N1-(anthracen-9-ylmethyl)ethane-1,2-diaminium dichloride in the presence and absence of NaF, KF, NaCl, KCl, NaBr, KBr, NaI, and KI (350 nm hν, pH 7.0). Exposing pUC19 plasmid to UV light in solutions containing 400 mM KCl formed significantly more direct strand breaks in DNA compared to no-salt control reactions. In contrast, NaCl increased DNA damage moderately, while the sodium(I) and potassium(I) fluoride, bromide, and iodide salts generally inhibited cleavage (I- > Br- > F-). A halide anion-induced heavy-atom effect was indicated by monitoring anthracene photodegradation and by employing the hydroxyl radical (•OH) probe hydroxyphenyl fluorescein (HPF). These studies revealed that among no-salt controls and the eight halide salts, only NaCl and KCl enabled the anthracene to photosensitize the production of high levels of DNA-damaging reactive oxygen species (ROS). Pre-irradiation of N1-(anthracen-9-ylmethyl)ethane-1,2-diaminium dichloride at 350 nm increased the amounts of chloride salt-induced •OH detected by HPF in subsequent anthracene photoactivation experiments. Taking into consideration that •OH and other highly reactive ROS are extremely short-lived, this result suggests that the pre-irradiation step might lead to the formation of oxidized anthracene photoproducts that are exceedingly redox-active. The fluorometric probes HPF and Singlet Oxygen Sensor Green revealed that KCl concentrations ranging from 150 to 400 mM and from 100 to 400 mM, respectively, enhanced N1-(anthracen-9-ylmethyl)ethane-1,2-diaminium dichloride photosensitized •OH and singlet oxygen (1O2) production over no-salt controls. Considering the relatively high levels of Na+, K+, and Cl- ions that exist in the environment and in living organisms, our findings may be relevant to the phototoxic effects exhibited by anthracenes and other polycyclic hydrocarbons in vivo.

A review of the order mysida in marine ecosystems: What we know what is yet to be known

Mysids have a high ecological importance, particularly by their role in marine food chains as a link between the benthic and pelagic realms. Here we describe the relevant taxonomy, ecological aspects such as distribution and production, and their potential as ideal test organisms for environmental research. We also highlight their importance in estuarine communities, trophic webs, and their life history, while demonstrating their potential in addressing emergent problems. This review emphasizes the importance of mysids in understanding the impacts of climate change and their role in the ecology of estuarine communities. Although there is a dearth of research in genomic studies, this review emphasizes the relevance of mysids and their potential as a model organism in environmental assessment studies of prospective or retrospective nature and highlights the need for further research to enhance our understanding of this group's ecological significance.

Recommendations for advancing test protocols examining the photo-induced toxicity of petroleum and polycyclic aromatic compounds

Photo-induced toxicity of petroleum products and polycyclic aromatic compounds (PACs) is the enhanced toxicity caused by their interaction with ultraviolet radiation and occurs by two distinct mechanisms: photosensitization and photomodification. Laboratory approaches for designing, conducting, and reporting of photo-induced toxicity studies are reviewed and recommended to enhance the original Chemical Response to Oil Spills: Ecological Research Forum (CROSERF) protocols which did not address photo-induced toxicity. Guidance is provided on conducting photo-induced toxicity tests, including test species, endpoints, experimental design and dosing, light sources, irradiance measurement, chemical characterization, and data reporting. Because of distinct mechanisms, aspects of photosensitization (change in compound energy state) and photomodification (change in compound structure) are addressed separately, and practical applications in laboratory and field studies and advances in predictive modeling are discussed. One goal for developing standardized testing protocols is to support lab-to-field extrapolations, which in the case of petroleum substances often requires a modeling framework to account for differential physicochemical properties of the constituents. Recommendations are provided to promote greater standardization of laboratory studies on photo-induced toxicity, thus facilitating comparisons across studies and generating data needed to improve models used in oil spill science.

Co-exposure to UV radiation and crude oil increases acute embryotoxicity and sublethal malformations in the early life stages of Atlantic haddock (Melanogrammus aeglefinus)

Crude oil causes severe abnormalities in developing fish. Photomodification of constituents in crude oil increases its toxicity several fold. We report on the effect of crude oil, in combination with ultraviolet (UV) radiation, on Atlantic haddock (Melanogrammus aeglefinus) embryos. Accumulation of crude oil on the eggshell makes haddock embryos particularly susceptible to exposure. At high latitudes, they can be exposed to UV radiation many hours a day. Haddock embryos were exposed to crude oil (5-300 μg oil/L nominal loading concentrations) for three days in the presence and absence of UV radiation (290-400 nm). UV radiation partly degraded the eggs' outer membrane resulting in less accumulation of oil droplets in the treatment with highest oil concentration (300 μg oil/L). The co-exposure treatments resulted in acute toxicity, manifested by massive tissue necrosis and subsequent mortality, reducing LC50 at hatching stage by 60 % to 0.24 μg totPAH/L compared to 0.62 μg totPAH/L in crude oil only. In the treatment with nominal low oil concentrations (5-30 μg oil/L), only co-exposure to UV led to sublethal morphological heart defects. Including phototoxicity as a parameter in risk assessments of accidental oil spills is recommended.

Counter-historical study of alternative dispersant use in the Deepwater Horizon oil spill response

Recent completion of oil fate modeling and a mass budget of the Deepwater Horizon (DWH) oil spill allows for a counter-historical study using quantitative Comparative Risk Assessment (CRA) methodology. Novel application of subsea dispersant injection (SSDI) during the response reduced surfacing oil, volatile organic carbon emissions, and oil on shorelines. The effectiveness of that application, and potential alternatives had dispersant not been used or been used more aggressively, were evaluated by modifying and comparing the validated oil fate model under different SSDI strategies. A comparison of mass balance results, exposure metrics, and CRA scoring for Valued Ecological Components (VECs) shows the value of SSDI in achieving risk reduction and tradeoffs that were made. Actual SSDI applied during the DWH oil spill reduced exposures to varying degrees for different VECs. Exposures and relative risks across the ecosystem would have been substantially reduced with more effective SSDI.

A review on polycyclic aromatic hydrocarbons distribution in freshwater ecosystems and their toxicity to benthic fauna

Polycyclic aromatic hydrocarbons (PAHs) are a group of organic compounds, found ubiquitously in all environmental compartments. PAHs are considered hazardous pollutants, being of concern to both the environmental and human health. In the aquatic environment, PAHs tend to accumulate in the sediment due to their high hydrophobicity, and thus sediments can be considered their ultimate sink. Concurrently, sediments comprise important habitats for benthic species. This raises concern over the toxic effects of PAHs to benthic communities. Despite PAHs have been the subject of several reviews, their toxicity to freshwater benthic species has not been comprehensively discussed. This review aimed to provide an overview on PAHs distribution in freshwater environments and on their toxicity to benthic fauna species. The distribution of PAHs between sediments and the overlying water column, given by the sediment-water partition coefficient, revealed that PAHs concentrations were 2 to 4 orders of magnitude higher in sediments than in water. The sediment-water partition coefficient was positively correlated to PAHs hydrophobicity. Toxicity of PAHs to benthic fauna was addressed through Species Sensitivity Distributions. The derived hazardous concentration for 5% of the species (HC₅) decreased as follows: NAP (376 μg L^-1) > PHE > PYR > FLT > ANT (0.854 μg L^-1), varying by 3 orders of magnitude. The hazardous concentrations (HC₅) to benthic species were inversely correlated to the hydrophobicity of the individual PAHs. These findings are pertinent for environmental risk assessment of these compounds. This review also identified future challenges regarding the environmental toxicity of PAHs to freshwater benthic communities, namely the need for updating the PAHs priority list and the importance of comprehensively and more realistically assess the toxicity of PAHs in combination with other stressors, both chemical and climate-related.

Lethal, behavioral, growth and developmental toxicities of alkyl-PAHs and non-alkyl PAHs to early-life stage of brine shrimp, Artemia parthenogenetica

Alkyl-PAHs are the predominant form of PAHs in crude oils which are supposed to demonstrate different toxicities compared to non-alkyl PAHs. Little information is available about the toxicity of alkyl-PAHs on marine Artemia. This study addressed and compared the lethal, behavioral, growth and developmental toxicities of three alkyl-PAHs, namely 3-methyl phenanthrene (3-mPhe), retene (Ret) and 2-methyl anthracene (2-mAnt), to their non-alkyl forms, phenanthrene (Phe) and anthracene (Ant) using Artemia parthenogenetica (nauplii, <24 h) as test organism following a 48 h and a 7 d of exposure, respectively. Benzo-a-pyrene (Bap) was selected as a reference toxicant for the comparison with the above alkyl-PAHs and non-alkyl PAHs. Results showed that for all tested endpoints, A. parthenogenetica nauplii had the highest sensitivity to Bap while Ant had no significant effect on nauplii survival or development within given concentrations. Considering the aqueous freely dissolved PAH concentrations, the 48 h-LC₅₀ (survival), 48 h-EC₅₀ (immobility) and 7 d-LC₁₀ (survival) of Bap were calculated as 0.321, 0.285 and 0.027 μg/L, respectively, which were twofold to fivefold lower than those of Phe, 3-mPhe, Ret, Ant and 2-mAnt. A higher acute toxicity of alkyl-PAHs (3-mPhe and 2-mAnt) than their non-alkyl forms (Phe and Ant) was observed. Not limited to Phe, the common non-polar narcotic mode of action was also observed for Bap, 3-mPhe, Ret and 2-mAnt, which was evident by the inhibited mobility of nauplii. The decreased body lengths were found for all PAH treatments compared to the solvent control, whereas instar retardations were only found in nauplii exposed to Bap, Phe and Ret. Our findings emphasized the sensitivity differences of A. parthenogenetica nauplii to selected alkyl PAHs and non-alkyl PAHs and confirmed the application of lethal, behavioral and growth indicators in the toxicity evaluation of selected PAHs other than Ant. However, the distinct toxicities of these PAHs suggested other toxic modes of action may play more important roles apart from narcotic mode of action and need to be elucidated in future studies. In addition, a strong correlation between the body length and the instar of A. parthenogenetica nauplii was observed for each PAH exposure, suggesting that body length can be representative for both growth and developmental indicators during biological monitoring of PAH pollution in marine environment.

A review of human and animals exposure to polycyclic aromatic hydrocarbons: Health risk and adverse effects, photo-induced toxicity and regulating effect of microplastics

Polycyclic aromatic hydrocarbons (PAHs) are one of the most widely distributed persistent organic pollutants (POPs) in the environmental media. PAHs have been widely concerned due to their significant health risk and adverse effects to human and animals. Currently, the main sources of PAHs in the environment are the incomplete combustion of fossil fuels, as well as municipal waste incineration and agricultural non-surface source emissions. In this work, the scope of our attention includes 16 typical PAHs themselves without involving their metabolites and industrial by-products. Exposure of human and animals to PAHs can lead to a variety of adverse effects, including carcinogenicity and teratogenicity, genotoxicity, reproductive- and endocrine-disrupting effects, immunotoxicity and neurotoxicity, the type and severity of which depend on a variety of factors. On the other hand, the regulatory effect of microplastics (MPs) on the bio-toxicity and bioaccumulation capacity of PAHs has now gradually attracted attention. We critically reviewed the adsorption capacity and mechanisms of MPs on PAHs as well as the effects of MPs on PAHs toxicity, thus highlighting the importance of paying attention to the joint bio-toxicity caused by PAHs-MPs interactions. In addition, due to the extensive nature of the common exposure pathway of PAHs and ultraviolet ray, an accurate understanding of biological processes exposed to both PAHs and UV light is necessary to develop effective protective strategies. Finally, based on the above critical review, we highlighted the research gaps and pointed out the priority of further studies.

Polycyclic aromatic compounds (PACs) in the Canadian environment: The challenges of ecological risk assessments

Ecological risk assessments (ERAs) of polycyclic aromatic compounds (PACs), as single congeners or in mixtures, present technical challenges that raise concerns about their accuracy and validity for Canadian environments. Of more than 100,000 possible PAC structures, the toxicity of fewer than 1% have been tested as individual compounds, limiting the assessment of complex mixtures. Because of the diversity in modes of PAC action, the additivity of mixtures cannot be assumed, and mixture compositions change rapidly with weathering. In vertebrates, PACs are rapidly oxygenated by cytochrome P450 enzymes, often to metabolites that are more toxic than the parent compound. The ability to predict the ecological fate, distribution and effects of PACs is limited by toxicity data derived from tests of a few responses with a limited array of test species, under optimal laboratory conditions. Although several models are available to predict PAC toxicity and rank species sensitivity, they were developed with data biased by test methods, and the reported toxicities of many PACs exceed their solubility limits. As a result, Canadian Environmental Quality Guidelines for a few individual PACs provide little support for ERAs of complex mixtures in emissions and at contaminated sites. These issues are illustrated by reviews of three case studies of PAC-contaminated sites relevant to Canadian ecosystems. Interactions among ecosystem characteristics, the behaviour, fate and distribution of PACs, and non-chemical stresses on PAC-exposed species prevented clear associations between cause and effect. The uncertainties of ERAs can only be reduced by estimating the toxicity of a wider array of PACs to species typical of Canada's diverse geography and environmental conditions. Improvements are needed to models that predict toxicity, and more field studies of contaminated sites in Canada are needed to understand the ecological effects of PAC mixtures.

The effects of ultraviolet radiation and climate on oil toxicity to coral reef organisms - A review

Oil pollution remains a significant local threat to shallow tropical coral reef environments, but the environmental conditions typical of coral reefs are rarely considered in oil toxicity testing and risk assessments. Here we review the effects of three environmental co-factors on petroleum oil toxicity towards coral reef organisms, and show that the impacts of oil pollution on coral reef taxa can be exacerbated by environmental conditions commonly encountered in tropical reef environments. Shallow reefs are routinely exposed to high levels of ultraviolet radiation (UVR), which can substantially increase the toxicity of some oil components through phototoxicity. Exposure to UVR represents the most likely and harmful environmental co-factor reviewed here, leading to an average toxicity increase of 7.2-fold across all tests reviewed. The clear relevance of UVR co-exposure and its strong influence on tropical reef oil toxicity highlights the need to account for UVR as a standard practice in future oil toxicity studies. Indeed, quantifying the influence of UVR on toxic thresholds of oil to coral reef species is essential to develop credible oil spill risk models required for oil extraction developments, shipping management and spill responses in the tropics. The few studies available indicate that co-exposure to elevated temperature and low pH, both within the range of current daily and seasonal fluctuations and/or projected under continued climate change, can increase oil toxicity on average by 3.0- and 1.3-fold, respectively. While all three of the reviewed environmental co-factors have the potential to substantially increase the impacts of oil pollution in shallow reef environments, their simultaneous effects have not been investigated. Assessments of the combined effects of oil pollution, UVR, temperature and low pH will become increasingly important to identify realistic hazard thresholds suitable for future risk assessments over the coming century.

Sensitivity of modeled oil fate and exposure from a subsea blowout to oil droplet sizes, depth, dispersant use, and degradation rates

As part of a Comparative Risk Assessment (CRA) developed and reported previously, oil spill modeling of a hypothetical blowout at 1400 m in the northeastern Gulf of Mexico was performed to evaluate changes in oil exposures with alternative response options, i.e., combinations of mechanical recovery, in-situ burning, surface dispersant application and subsea dispersant injection (SSDI). To assess if conclusions from this study could be extended to other spill scenarios, sensitivities of the predicted oil fate and exposure metrics to location, release depth, oil and gas flow rate, gas content, orifice size, oil droplet size distribution, and biodegradation rates were examined. Results show that the fraction of oil surfacing is highly sensitive to oil droplet size distribution and depth of release. Across the simulations performed, SSDI use reduced oil droplet sizes released, thereby mitigating surface and shoreline oiling, volatile hydrocarbon exposures, and potential surface water column exposures.

Interactive Effects of Mixtures of Phototoxic PAHs

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in the environment as components in complex mixtures derived from petroleum based products. PAHs are unique in their ability to absorb UV light, resulting in significant increases in acute toxicity. The objective of this study was to determine if mixtures of the phototoxic PAHs fluoranthene, pyrene, and anthracene conform to the additive model of toxicity. Median lethal concentrations (LC50) were calculated for mysid shrimp (Americamysis bahia) and inland silverside (Menidia beryllina) exposed to individual, binary, and ternary mixtures of the selected PAHs. Mixtures were evaluated on a toxic unit basis to account for potency differences and toxicity data was analyzed using the concentration-addition and independent-action models. Data indicated that the model of additivity is sufficient in describing the toxicity of mixtures of phototoxic PAHs; therefore predictive models should consider an additivity model for assessing the toxicity of hydrocarbon mixtures.

Predicting phototoxicity of alkylated PAHs, mixtures of PAHs, and water accommodated fractions (WAF) of neat and weathered petroleum with the phototoxic target lipid model

The toxicity of petroleum can increase considerably after exposure to solar radiation, during which certain components in the mixture, including polycyclic aromatic hydrocarbons (PAHs), absorb light in ultraviolet and visible portions of the solar radiation spectrum. A phototoxic target lipid model (PTLM), previously developed to predict the phototoxicity of single PAHs, is validated for 4 species (Americamysis bahia, Rhepoxynius abronius, Daphnia magna, and Pimephales promelas) exposed to 12 compounds that are components of petroleum, including alkylated PAHs and dibenzothiophene. The PTLM is also used to predict the phototoxicity of binary and ternary mixtures of 3 PAHs, pyrene, anthracene, and fluoranthene, to A. bahia and Menidia beryllina. Finally, it is used to predict the toxicity of water accommodated fractions of neat and naturally weathered Macondo crude oil samples from the Deepwater Horizon oil spill sites. The Gulf of Mexico species, including A. bahia, M. beryllina, Cyprinodon variegatus, and Fundulus grandis were exposed to the oil samples under natural and simulated solar radiation. The results support the applicability of the PTLM for predicting the phototoxicity of petroleum. Environ Toxicol Chem 2018;37:2165-2174. © 2018 SETAC.

Comparative risk assessment of oil spill response options for a deepwater oil well blowout: Part II. Relative risk methodology

Subsea dispersant injection (SSDI) was a new oil spill response (OSR) technology deployed during the Deepwater Horizon accident. To integrate SSDI into future OSR decisions, a hypothetical deepwater oil spill to the Gulf of Mexico was simulated and a comparative risk assessment (CRA) tool applied to contrast three response strategies: (1) no intervention; (2) mechanical recovery, in-situ burning, and surface dispersants; and, (3) SSDI in addition to responses in (2). A comparative ecological risk assessment (CRA) was applied to multiple valued ecosystem components (VECs) inhabiting different environmental compartments (ECs) using EC-specific exposure and relative VEC population density and recovery time indices. Results demonstrated the added benefit of SSDI since relative risks to shoreline, surface wildlife and most aquatic life VECs were reduced. Sensitivity of results to different assumptions was also tested to illustrate flexibility of the CRA tool in addressing different stakeholder priorities for mitigating the impacts of a deepwater blowout.

Comparative Risk Assessment of spill response options for a deepwater oil well blowout: Part 1. Oil spill modeling

Oil spill model simulations of a deepwater blowout in the Gulf of Mexico De Soto Canyon, assuming no intervention and various response options (i.e., subsea dispersant injection SSDI, in addition to mechanical recovery, in-situ burning, and surface dispersant application) were compared. Predicted oil fate, amount and area of surfaced oil, and exposure concentrations in the water column above potential effects thresholds were used as inputs to a Comparative Risk Assessment to identify response strategies that minimize long-term impacts. SSDI reduced human and wildlife exposure to volatile organic compounds; dispersed oil into a large water volume at depth; enhanced biodegradation; and reduced surface water, nearshore and shoreline exposure to floating oil and entrained/dissolved oil in the upper water column. Tradeoffs included increased oil exposures at depth. However, since organisms are less abundant below 200 m, results indicate that overall exposure of valued ecosystem components was minimized by use of SSDI.

Polycyclic aromatic hydrocarbons (PAHs) in sediments from a typical urban impacted river: application of a comprehensive risk assessment

Soweto and Lenasia, the most densely populated area of South Africa, is simultaneously a thriving metropolis, with a fair share of people still living in squalor conditions directly dependant on the natural resources. Because of industrialisation the populace and environment in this urban area are exposed to various pollutants. The aquatic environment was selected as a proxy to study the effect of industrial pollution in this area. The concentrations, source identification, and various environmental risks of polycyclic aromatic hydrocarbons (PAHs) were determined in sediments of the upper reaches of the Klip River. Composite sediment samples collected in low-flow conditions in 2013 and 2014 ranged from 270-5400 ng/g. The PAHs in this aquatic ecosystem were dominated by 4-ring congeners and could be attributed to combustion of organic fuels by chemical mass balance. Heavy traffic and industrial complexes in the northern part of the study area were responsible for the PAH fingerprints. Probable adverse effects such as toxicity to benthic biota were proven after comparison with international sediment quality guidelines (SQG) both survey years. Toxic equivalence quotients (TEQs) calculated for the sediments using fish potency factors (FPFs) were up to 30 times greater than the Canadian guideline for dioxin-like compounds, indicating high probability of carcinogenic effect to fish mediated through the aryl-hydrocarbon receptor. Finally, sediments in the area posed moderate to high ecological risk, which corroborates the other toxicity assessments. The advantage of investigating multiple risk endpoints, is the comprehensive results obtained that allows for a more realistic representation of the study area. Consequently more aspects are kept into account that results in better conclusions.