Particularly Polycyclic Aromatic Hydrocarbons Research Articles

A web-based scoping review assessing the influence of smoking and smoking cessation on antidiabetic drug meabolism: implications for medication efficacy.

Currently 1.3 billion individuals globally engage in smoking, leading to significant morbidity and mortality, particularly among diabetic patients. There is urgent need for a better understanding of how smoking influences antidiabetic treatment efficacy. The review underscores the role of cigarette smoke, particularly polycyclic aromatic hydrocarbons (PAHs), in modulating the metabolic pathways of antidiabetic drugs, primarily through the induction of cytochrome P450 (CYP450) enzymes and uridine diphosphate (UDP)-glucuronosyltransferases (UGTs), thus impacting drug pharmacokinetics and therapeutic outcomes. Furthermore, the review addresses the relatively uncharted territory of how smoking cessation influences diabetes treatment, noting that cessation can lead to significant changes in drug metabolism, necessitating dosage adjustments. Special attention is given to the interaction between smoking cessation aids and antidiabetic medications, a critical area for patient safety and effective diabetes management. This scoping review aims to provide healthcare professionals with the knowledge to better support diabetic patients who smoke or are attempting to quit, ensuring tailored and effective treatment strategies. It also identifies gaps in current research, advocating for more studies to fill these voids, thereby enhancing patient care and treatment outcomes for this at-risk population.

Distribution, sources, ecological risk and microbial response of polycyclic aromatic hydrocarbons in Qingdao bays, China

Bay ecosystem has garnered significant attention due to the severe threat posed by organic pollutants, particularly polycyclic aromatic hydrocarbons (PAHs). However, there is a dearth of information regarding the extent of PAHs pollutant risk and its impact on microbial communities and metabolism within this environment. In this study, the distribution, sources, ecological risk, and microbial community and metabolic response of PAHs in Jiaozhou Bay, Aoshan Bay, and Lingshan Bay in Qingdao, China were investigated. The results showed that the average concentration of ∑PAHs ranged from 120 to 614 ng/L across three bays, with Jiaozhou and Aoshan Bay exhibiting a higher risk than Lingshan Bay due to an increased concentration of high-molecular-weight PAHs. Further analysis revealed a negative correlation between dissolved organic carbon concentration and ∑PAHs concentration in water. Metagenomic analysis demonstrated that higher levels of PAHs can lead to decreased microbial diversity, while the abundance of PAHs-degrading bacteria is enhanced. Additionally, the Erythrobacter, Jannaschia and Ruegeria genera were found to have a significant correlation with low-molecular-weight PAH concentrations. In terms of microbial metabolism, higher PAH concentrations were beneficial for carbohydrate metabolic pathway but unfavorable for amino acid metabolic pathways and membrane transport pathways in natural bay environments. These findings provide a foundation for controlling PAHs pollution and offer insights into the impact of PAHs on bacterial communities and metabolism in natural bay environments.

A new steady-state gas–particle partitioning model of polycyclic aromatic hydrocarbons: implication for the influence of the particulate proportion in emissions

Abstract. Gas–particle (G–P) partitioning is a crucial atmospheric process for semi-volatile organic compounds (SVOCs), particularly polycyclic aromatic hydrocarbons (PAHs). However, accurately predicting the G–P partitioning of PAHs has remained a challenge. In this study, we established a new steady-state G–P partitioning model based on the level-III multimedia fugacity model, with a particular focus on the particulate proportion (ϕ0) of PAHs in emissions. Similar to previous steady-state models, our new model divided the G–P partitioning behavior into three domains based on the threshold values of log KOA (octanol–air partitioning coefficient), with slopes of 1, from 1 to 0, and 0 for the three domains. However, our model differed significantly from previous models in different domains. We found that deviations from the equilibrium-state G–P partitioning models were caused by both gaseous interference and particulate interference, with ϕ0 determining the influence of this interference. Different forms of the new steady-state model were observed under different values of ϕ0, highlighting its significant impact on the G–P partitioning of PAHs. Comparison of the G–P partitioning of PAHs between the prediction results of our new steady-state model and monitored results from 11 cities in China suggested varying prediction performances under different values of ϕ0, with the lowest root mean square error observed when ϕ0 was set to 0.9 or 0.99. The results indicated that the ϕ0 was a crucial factor for the G–P partitioning of PAHs. Furthermore, our new steady-state model also demonstrated excellent performance in predicting the G–P partitioning of PAHs with entirely gaseous emission and polybrominated diphenyl ethers with entirely particulate emission. Therefore, we concluded that the ϕ0 should be considered in the study of G–P partitioning of PAHs, which also provided a new insight into other SVOCs.

Skin microbiome differentiates into distinct cutotypes with unique metabolic functions upon exposure to polycyclic aromatic hydrocarbons

BackgroundThe effects of air pollutants, particularly polycyclic aromatic hydrocarbons (PAHs), on the skin microbiome remain poorly understood. Thus, to better understand the interplay between air pollutants, microbiomes, and skin conditions, we applied metagenomics and metabolomics to analyze the effects of PAHs in air pollution on the skin microbiomes of over 120 subjects residing in two cities in China with different levels of air pollution.ResultsThe skin microbiomes differentiated into two cutotypes (termed 1 and 2) with distinct taxonomic, functional, resistome, and metabolite compositions as well as skin phenotypes that transcended geography and host factors. High PAH exposure was linked to dry skin and cutotype 2, which was enriched with species with potential biodegradation functions and had reduced correlation network structure integrity. The positive correlations identified between dominant taxa, key functional genes, and metabolites in the arginine biosynthesis pathway in cutotype 1 suggest that arginine from bacteria contributes to the synthesis of filaggrin-derived natural moisturizing factors (NMFs), which provide hydration for the skin, and could explain the normal skin phenotype observed. In contrast, no correlation with the arginine biosynthesis pathway was observed in cutotype 2, which indicates the limited hydration functions of NMFs and explains the observed dry skin phenotype. In addition to dryness, skin associated with cutotype 2 appeared prone to other adverse conditions such as inflammation.ConclusionsThis study revealed the roles of PAHs in driving skin microbiome differentiation into cutotypes that vary extensively in taxonomy and metabolic functions and may subsequently lead to variations in skin–microbe interactions that affect host skin health. An improved understanding of the roles of microbiomes on skin exposed to air pollutants can aid the development of strategies that harness microbes to prevent undesirable skin conditions.BrPedpW9L_z6DnVXNf3dTwVideo

Prospects of emerging PAH sources and remediation technologies: insights from Africa.

Remediation of polluted environmental media is critical to realization of the goals of the United Nations Decade on Ecosystem Restoration (UNDER) project. Many natural-resource dependent economies in Africa are characterized by numerous contaminated sites resulting from conventional and artisanal natural-resource mining. Alongside these extractive activities, there are refining, processing, and power plant operations, agriculture, urban, and infrastructure developments that contribute to increased discharges of toxins into the environment, particularly polycyclic aromatic hydrocarbons (PAHs), which are carcinogenic in nature. As a result, human and environmental receptors (i.e., air, water, soil, and biota) face increasing risk of exposure to higher concentrations of PAH. Evidence exists of widespread PAH contamination and in some instances where corrective action has been taken, residual contaminant levels exceeding regulatory thresholds remain in the environment due to the use of inappropriate and unsustainable remedial methods. Considering the long-term harmful effects of PAH on human and ecosystem health, land use, and the complexity of Africa's environmental deterioration, it is essential to explore remediation strategies that benefit both the environment and the economy. This review examined the status, opportunities, and challenges related to the application of emerging green technologies to remediate PAH-contaminated sites in five African countries (South Africa, Nigeria, Angola, Egypt, and Kenya). This paper concludes that bioremediation presents a sustainable option, considering its low net emissions and environmental footprints, and its low economic cost to Africa's poor communities and overburdened economy. However, an integration of biological and physico-chemical approaches could address various compounds and concentrations of PAH contamination.

Impact of wildfire on water quality in Caramulo Mountain ridge (Central Portugal)

Fire is a major ecosystem process affecting forests and wooded areas in the Mediterranean basin. In recent years, a clear increase in wildfires in Portugal has taken place with strong impacts on ecosystems. The destruction of vegetation cover and the change in soil properties lead to modifications in the hydrological regime, due to the contribution of each component of the hydrological cycle, and qualitative aspect, with the mobilization of substances that are forwarded to water bodies by overland flow and infiltration. This study evaluates the impact of a large wildfire on groundwater and surface water quality by various constituents of concern, particularly polycyclic aromatic hydrocarbons (PAHs) in Caramulo Mountain (Central Portugal). Water samples from burnt and unburnt areas were collected in eight sampling points, over five campaigns, during 19 months, to evaluate the influence of precipitation and the time elapsed since the wildfire on the magnitude of pollutant loads entering the reservoirs as well as the impact attenuation. Fourteen of the 16 priority PAHs were found, especially naphthalene and benzo(ghi)perylene. The concentration of PAHs followed the precipitation profile, proving the influence of overland flow and infiltration on the input of these pollutants into surface water and groundwater. The behavior of nutrients and other trace elements was also evaluated, revealing similar fluctuations for several major ions (Mg+, Cl− and SO42−) and metallic elements (Fe, Mn and Pb). The research results have contributed to improve the understanding of fundamental physical and biogeochemical processes controlling the formation and transport of PAHs in hydrological systems, and the role of natural remediation processes.

A multi-year study of hepatic biomarkers in coastal fishes from the Gulf of Mexico after the Deepwater Horizon Oil Spill

Following the 2010 Gulf of Mexico oil spill, concerns were raised regarding exposure of fish to crude oil components, particularly polycyclic aromatic hydrocarbons (PAHs). This three year study examined hepatic enzymes in post-mitochondrial supernatant fractions from red snapper (Lutjanus campechanus) and gray triggerfish (Balistes capriscus) collected in the north central Gulf of Mexico between 2011 and 2014. Biomarker activities evaluated included benzo(a)pyrene hydroxylase (AHH), ethoxyresorufin O-deethylase (EROD), glutathione transferase (GST), and glutathione peroxidase (GPx). Mean EROD activity was higher in gray triggerfish (12.97 ± 7.15 pmol/min/mg protein [mean ± SD], n = 115) than red snapper (2.75 ± 1.92 pmol/min/mg protein, n = 194), p < 0.0001. In both species, EROD declined over time between 2011 and 2014. Declines in GST and GPx activities were also noted over this time period for both species. Gray triggerfish liver was fatty, and heptane extracts of the liver fat contained fluorescent substances with properties similar to known PAHs, however the origin of these PAHs is unknown.

Evidence of colloidal transport of PAHs during column experiments run with contaminated soil samples.

Brownfield soils may contain high levels of organic pollutants particularly polycyclic aromatic hydrocarbons (PAHs). It is essential to predict their migration and fate and to evaluate the risk of transfer to sensitive targets, such as water resources, ecosystems and human health. In this study, soil samples have been taken from an experimental contaminated site of former steel activities located at Homecourt (Lorraine, France). These samples have been lixiviated in laboratory column in water-saturated condition at room temperature. The effluent has been collected by fraction and analysed by a standard method giving total concentration of each of 16 PAHs. The breakthrough curves of 16 PAHs significantly evolve in the same way according to the volume of effluent and tend to vanish to 12-15 pore volumes. If several PAHs remain at a concentration below the solubility, others clearly exceed this threshold. Material balance sheets show that only a very small fraction of PAHs is mobilised. These results are interpreted by postulating that PAHs are transported by the solution not only in the dissolved state but also by associations with particulate or dissolved organic matter.

An Integrated Simulation-based Process Control and Operation Planning (IS-PCOP) System for Marine Oily Wastewater Management

The chronic discharge of oily wastewater, mainly including bilge water, offshore produced water and ballast water, has been referred to as a major contributor to marine oil pollution. Although gravity-based treatment techniques have been widely used to separate oil from wastewater, many dissolved toxic organics, particularly Polycyclic Aromatic Hydrocarbons (PAHs), are not likely to be effectively removed and may cause severe environmental problems. Further treatment has therefore become necessary for the shipping and offshore oil and gas industries, particularly in the harsh environments (e.g., the Arctic Ocean) where ecosystems are extremely vulnerable. Among many chemical and biological treatment techniques, ultraviolet (UV) irradiation and advanced oxidation techniques have been recently regarded as promising solutions to the removal of PAHs. Such advanced treatment systems, as compared to the traditional ones, are usually lack of in-depth understanding of reaction mechanisms and kinetics, process control requirements, and long-term planning strategies. More particularly, the integration of process control and operation planning has been proven in the literature to greatly reduce process cost and improve system performance. However, such integration is usually complicated by many factors such as the multi-scale nature of decisions, the lack of knowledge of process dynamics and control, and uncertainty. These deficiencies can drastically hinder the widespread application of these advanced treatment systems in the shipping and offshore industries. In response to these knowledge and technique gaps, this research proposes an integrated process control and operation planning system to aid marine oily wastewater management based on experimental study, process modeling, process control, operation planning and their coupling.

Steam reforming of α-methylnaphthalene as a model tar compound over olivine and olivine supported nickel

At high temperature, biomass steam gasification generates tars and more particularly Polycyclic Aromatic Hydrocarbons (PAHs). To assess the ability of olivine-based catalyst to eliminate the tars by steam reforming, α-methylnaphthalene (MNP) was chosen as model compound. The Ni/olivine has shown a good ability to reform the MNP, much better than olivine alone. Moreover, catalyst water pre-treatment has proven its efficiency. Thereby, this investigation has emphasized secondary reactions such as water gas shift reaction, and an overall mechanism has been proposed, taking into consideration the important role of adsorbed oxygen species coming from water catalytic dissociation over nickel metal.In addition, catalyst activity and stability have been discussed on the basis of X-ray diffraction (XRD) and scanning electron microscopy (SEM) coupled with EDX analysis, carried out on the samples before and after experiments. On the prepared fresh catalysts, we have shown the presence of NiO–MgO solid solution, formed on the surface of olivine support. Then, after the experiment, both Ni metal (Ni0) and Ni–Fe alloys have been observed.

Quantifying the concentration of crude oil microdroplets in oil–water preparations

Dissolved constituents of crude oil, particularly polycyclic aromatic hydrocarbons (PAHs), can contribute substantially to the toxicity of aquatic organisms. Measured aqueous concentrations of high-molecular weight PAHs (e.g., chrysenes, benzo[a]pyrene) as well as long-chain aliphatic hydrocarbons can exceed the theoretical solubility of these sparingly soluble compounds. This is attributed to the presence of a "microdroplet" or colloidal oil phase. It is important to be able to quantify the dissolved fraction of these compounds in oil-in-water preparations that are commonly used in toxicity assays because the interpretation of test results often assumes that the compounds are dissolved. A method is presented to determine the microdroplet contribution in crude oil-in-water preparations using a comparison of predicted and measured aqueous concentrations. Measured concentrations are reproduced in the model by including both microdroplets and dissolved constituents of petroleum hydrocarbons. Microdroplets were found in all oil-water preparation data sets analyzed. Estimated microdroplet oil concentrations typically ranged from 10 to 700 µg oil/L water. The fraction of dissolved individual petroleum hydrocarbons ranges from 1.0 for highly soluble compounds (e.g., benzene, toluene, ethylbenzene, and xylene) to far less than 0.1 for sparingly soluble compounds (e.g., chrysenes) depending on the microdroplet oil concentration. The presence of these microdroplets complicates the interpretation of toxicity test data because they may exert an additional toxic effect due to a change in the exposure profile. The implications of the droplet model on toxicity are also discussed in terms of both dissolved hydrocarbons and microdroplets.

Detection of organic contamination in sediments by double-shoot pyrolysis–GC/MS

Pyrolysis coupled with gas chromatography–mass spectrometry (Py–GC–MS) has been previously proved to be an appropriate tool for the screening of organic contaminants in sediments. In this work the double-shoot pyrolysis technique has been applied to assess the contamination degree of sediment samples from Castro Marim Natural Park (South Portugal) and the Ria of Huelva (SW Spain). Compounds released both by thermodesorption at sub-pyrolysis temperatures (250–280°C) and subsequent pyrolysis (300–500°C) revealed information on the origin of the sedimentary organic matter and the occurrence of organic contamination in the sediments. Thermal desorption was found to be effective in releasing organic contaminants from spiked samples. However, in real sediments samples, higher pyrolysis temperatures (>300°C) were necessary to detect the occurrence of organic contaminants. Particularly polycyclic aromatic hydrocarbons (PAHs) and linear alkylbenzenes (LABs) were detected in variable proportions in most sediment samples.

PAHs from the Inside Out: Birth Outcomes Vary among Ethnic Groups in NYC

In humans, the developmental hazards associated with exposure to urban ambient air pollution, particularly polycyclic aromatic hydrocarbons (PAHs), continue to be debated. PAHs are formed during the incomplete burning of fossil fuels, wood, and tobacco products, with high levels found in automobile exhaust and industrial emissions. This month, researchers at Columbia University report that prenatal exposure to PAHs affects birth outcomes differently in pregnant African-American and Dominican women [EHP 116:658–665; Choi et al.]. Previously the same group showed that approximately 40% of the children studied had in utero DNA damage as a result of exposure to air pollution from fossil fuel combustion. The same group has also examined the link between prenatal exposure to airborne PAHs and intrauterine growth restriction, a condition in which the fetus is smaller than expected for the length of pregnancy, and has shown a relationship between prenatal exposure to PAHs and reduced birth weight in African Americans in New York City and whites in Krakow, Poland. In the current prospective study, the team recruited women from local prenatal care clinics in New York City. The women lived in three neighborhoods served by Columbia’s Mailman School of Public Health. The target population was limited to women aged 18–35 who did not use tobacco products or illicit drugs; did not have diabetes, hypertension, or known HIV; and had started prenatal care by the twentieth week of pregnancy. The researchers interviewed each woman in the last trimester of pregnancy, in her home, to obtain information on health, lifestyle, and exposure history. They also gave each woman a small backpack containing an air monitor for measuring PAH exposure. The personal air monitor operated continuously over a 48-hour period at 4 L per minute to simulate normal lung capacity, collecting particulate and semivolatile vapor and aerosol PAHs. Filters were replaced every 48 hours and analyzed for pyrene and carcinogenic PAHs, including benzo[a]pyrene (BaP), which has been associated with adverse reproductive and developmental effects in laboratory animals and humans. The investigators collected birth outcome information from medical records, including gestational age, which was estimated by attending clinicians and validated by sonogram. The analysis included 616 mother–child pairs. The results showed universal and variable personal exposure to PAHs, with a mean exposure to BaP (0.368 ng/m3) consistent with the ambient BaP level in New York City. Among African Americans, prenatal PAH exposure increased the risk of preterm delivery and the likelihood of infants being born small for gestational age (SGA; meaning birth weight is below the tenth percentile of babies of the same gestational age). As prenatal PAH exposure increased, so did cephalization index, a ratio of head circumference to birth weight that can presage developmental problems later in childhood. Among Dominicans, there was no association between airborne PAH exposure and significant increase in risk of SGA, reduced birth weight ratio, increased cephalization index, or preterm delivery. This could reflect healthful cultural practices among recent Dominican immigrants such as more nutritious diets and more supportive social networks. The possible health-protective effects of the Dominicans’ cultural habits and the specific factors underlying the greater vulnerability of the African-American subjects warrant further study.

Application and evaluation of the neutral red retention (NRR) assay for lysosomal stability in mussel populations along the Iberian Mediterranean coast

The neutral red retention (NRR) assay to determine lysosomal membrane stability (LMS) was applied to wild mussels (Mytilus galloprovincialis) sampled from fourteen sites with different degrees of chemical pollution along the Iberian Mediterranean coast in 2002 and 2003. Total body burdens for a range of contaminants were measured in pooled samples (n = 50) of whole soft tissues in order to explore possible causality. Mean LMS values (n = 15) were significantly greater in mussels from one of the selected two reference sites (San Diego) than in chemically well-characterized hotspot sites. Mean LMS values were inversely correlated with contaminant concentrations in mussel tissues (except for Zn). The multidimensional scaling ordination technique classified the sampling sites into three groups according to their chemical-physical-biological similarities and the results were statistically confirmed using ANOSIM analysis. The results show that lysosomal stability is an effective indicator of health status in mussels along the Iberian Mediterranean coast and that it is related to body burden of contaminants, particularly polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs).

Factors affecting quantitative analysis in laser desorption/laser ionization mass spectrometry.

Microprobe laser desorption/laser ionization mass spectrometry (microL(2)MS) is a sensitive and selective technique that has proven useful in the qualitative and semiquantitative detection of trace organic compounds, particularly polycyclic aromatic hydrocarbons (PAHs). Recent efforts have focused on developing microL(2)MS as a quantitative method, often by measuring the ratio of signal strength of an analyte to an internal standard. Here, we present evidence of factors that affect these ratios and thus create uncertainty and irreproducibility in quantification. The power and wavelength of the desorption laser, the delay time between the desorption and ionization steps, the power of the ionization laser, and the ionization laser alignment are all shown to change PAH ratios, in some cases by up to a factor of 24. Although changes in the desorption laser parameters and the delay time cause the largest effects, the ionization laser power and alignment are the most difficult parameters to control and thus provide the most practical limitations for quantitative microL(2)MS. Variation in ratios is seen in both synthetic poly(vinyl chloride) membranes and in "real-life" samples of Murchison meteorite powder. Ratios between similar PAHs vary less than those between PAHs that differ greatly in mass and structure. This finding indicates that multiple internal standards may be needed for quantification of samples containing diverse PAHs.

Mise en évidence et validation de biomarqueurs écotoxicologiques dans la population d’anguilles d’un étang de la Réserve Naturelle Nationale de Camargue, le Vaccarès, exposée à des polluants organiques persistants

Though located in a rather remote area free from neighbouring industrial activities, the French National Nature Reserve of Camargue is however exposed to a non point source contamination by a number of persistant organic pollutants, particularly polycyclic aromatic hydrocarbons (PAH) and organochlorine compounds (OC) . Due to the nature of this contamination, investigations about validation of biomarkers in the eels of the Vaccarès lagoon have proven to be of the utmost importance. They have been focused on the characterization and validation of biomarkers related to metabolic responses including, not only the detoxification mechanisms (biotransformation, antioxidant process) and the energy requirements, but also some unspecific metabolic processes. These last ones are enzymatic membrane markers implicated either in the neuronal conduction (acetylcholinesterase, AChE) or in the osmoregulation and the energy metabolism (ATPases). The experimental results have been screened by the way of a multivariate analysis. It may be concluded that the rate of tissue glycogen seems to be a sensitive biomarker as well as three hepatic activities involved in the protection against oxyradicals : catalase, glutathion peroxidase (SeGPx) and superoxide dismutases (SOD). The muscle and gill ATPases as well as the muscle and brain AChE show more significant results in term of biomarkers than the biotransformation enzymes : ethoxyresorufine-O-deethylase (EROD) and uridine diphospho-glucuronyl transferase (UDPGT). However most of these enzymatic activities depend on a number of abiotic factors. This study brings some conclusive elements for the validation of the biomarkers use from data obtained in laboratory studies to their application in field ecotoxicology. It also raises the question about the tissue location of the contaminant in fish, in relationship to their age or their mode of contamination, and its influence on the biomarkers response. As a conclusion, if the validation of membrane indicators is confirmed, this study, by its innovative approach, provides the first statement on the extent of the ecotoxicological threat for the aquatic species in a protected area, stemming from the occurrence of persistent organic pollutants (POP) in the cell membranes.

Anaerobic Biotransformation of Aromatic and Polycyclic Aromatic Hydrocarbons in Soil Microcosms: A Review

Industrial activities introduce a wide variety of xenobiotic aromatic compounds into the biosphere. These aromatic and polycyclic aromatic compounds find their way into anaerobic marine and freshwater sediments, saturated aquifers, and waterlogged soils where neither their impact on carbon flow nor their propensity to persist is clearly understood. Although some halogenated aromatic compounds are degraded via anaerobic pathways, anaerobic transformation of aromatics remains limited to a small range of chemicals. This paper reviews anaerobic transformation processes for aromatic compounds, particularly polycyclic aromatic hydrocarbons (PAHs) in soil microcosms. A simplified pathway of PAH biotransformation and a conceptual pathway of PAH degradation under different redox-conditions are presented.

Are aromatic hydrocarbons the primary determinant of petroleum toxicity to aquatic organisms?

Aromatic components of oil, particularly polycyclic aromatic hydrocarbons (PAHs), are generally assumed to be the toxic fraction of spilled petroleum. We evaluated this assumption by analyzing the chemistry and toxicity of water accommodated fractions (WAFs) prepared from three environmentally weathered middle distillate oils differing in aromatic content. Oil toxicity was determined in short-term growth and survival tests with the mysid shrimp, Mysidopsis bahia. Median lethal concentrations (LC50s) ranged from 0.9 to 1.5 mg l −1 total petroleum hydrocarbons (TPH), and growth-inhibiting concentrations (EC20s) ranged from 0.13 to 1.1 mg l −1 TPH. Toxicity of the three oils expressed as μg l −1 ∑PAH (sum of 40 PAH analytes; parent and alkyl homologues) ranged from 2.2 to 9.2 μg l −1 (LC50s) and from 0.32 to 5.7 μg l −1 (EC20s). The test oil with the lowest aromatic content, expressed as either μg l −1 PAH or μg l −1 naphthalenes in WAF had the greatest toxicity. The test oil WAF with the lowest total PAH concentration also had the lowest concentrations of single PAH analytes measured at concentrations greater than the detection limit. The results of this study demonstrated that low aromatic content oil can be highly toxic and that PAHs were not the major determinant of the toxicity of the three weathered middle distillate oils.