Spaceflight Maximum Allowable Concentrations for Ethyl Acetate.

INTRODUCTION: Ethyl acetate is a simple organic compound that occurs naturally and is used industrially as a solvent. It has been detected in the ISS atmosphere and is known to off-gas from building materials. As NASA astronauts have been and will be exposed to ethyl acetate during space missions, Spaceflight Maximum Allowable Concentrations (SMACs) were developed following an extensive review of the available literature.METHODS: Toxicological data relevant to SMAC development was collected from electronic databases using principles of systematic review, and from previous assessments and reviews of ethyl acetate.RESULTS: From an initial pool of over 35,000 studies, 10 were identified as studies appropriate to support SMAC development. The toxicological properties of ethyl acetate are relatively straightforward. Ethyl acetate is rapidly absorbed and converted by carboxyesterases to ethanol. At concentrations on the order of 400 ppm for 4-8 h, most volunteers experienced mild irritation but no lasting effects. In subchronic animal studies, mild sedative effects and changes in body weight and weight gain were observed at 750 ppm and above.DISCUSSION: Numerous studies were identified to support the development of both short- and long-duration SMACs. No chronic studies were available, but the high quality of the subchronic studies and the short half-life of ethyl acetate support extrapolation to longer durations.Williams ES, Ryder VE. Spaceflight maximum allowable concentrations for ethyl acetate. Aerosp Med Hum Perform. 2023; 94(1):25-33.

Dynamic ensemble prediction of cognitive performance in spaceflight.

During spaceflight, astronauts face a unique set of stressors, including microgravity, isolation, and confinement, as well as environmental and operational hazards. These factors can negatively impact sleep, alertness, and neurobehavioral performance, all of which are critical to mission success. In this paper, we predict neurobehavioral performance over the course of a 6-month mission aboard the International Space Station (ISS), using ISS environmental data as well as self-reported and cognitive data collected longitudinally from 24 astronauts. Neurobehavioral performance was repeatedly assessed via a 3-min Psychomotor Vigilance Test (PVT-B) that is highly sensitive to the effects of sleep deprivation. To relate PVT-B performance to time-varying and discordantly-measured environmental, operational, and psychological covariates, we propose an ensemble prediction model comprising of linear mixed effects, random forest, and functional concurrent models. An extensive cross-validation procedure reveals that this ensemble outperforms any one of its components alone. We also identify the most important predictors of PVT-B performance, which include an individual's previous PVT-B performance, reported fatigue and stress, and temperature and radiation dose. This method is broadly applicable to settings where the main goal is accurate, individualized prediction of human behavior involving a mixture of person-level traits and irregularly measured time series.

Comparative influences of dermal and inhalational routes of exposure on hazards of cleaning product ingredients among mammalian model organisms.

Health risks resulting from dermal or inhalational exposures are frequently assessed based on rodent oral toxicity information due to a lack of species- or route-specific toxicity data. Default uncertainty factors (UFs; e.g., 10-fold) are also applied during risk assessments to account for variability such as inter-species, intra-species, exposure duration, dose-response, and route-to-route extrapolations. However, whether rodent oral data and a default UF approach can provide adequate protection for other mammalian species under dermal or inhalational exposure scenarios remains understudied, particularly for cleaning product ingredients. Therefore, we collated and examined publicly available median lethal dose (LD50), no-observed-adverse-effect level (NOAEL) and lowest-observed-adverse-effect level (LOAEL) values from different types of standard mammalian toxicity studies for rats (dermal and inhalational), mice, rabbits, guinea pigs, and dogs (oral, dermal and inhalational) using the Cleaning Product Ingredient Safety Initiative (CPISI) database. Probabilistic hazard assessments using chemical toxicity distributions (CTDs) were subsequently conducted, and threshold concentrations (TCs) and 95% confidence intervals (95% CIs) were derived to identify thresholds of toxicological concern (TTCs). Relative sensitivities among or between mammalian species, exposure routes, and chemical classes were also compared based on calculated TC5s and 95% CIs to support future toxicology studies and hazard and risk assessments. We then identified uncertainty factors (UFs) using both CTD comparisons and individual UF probability distributional approaches. Based on available rodent inhalational data, chemical category-specific UFs were derived for ethers. Additionally, we also determined whether default UFs of 10 or 100 would be protective for various distributions of cleaning product ingredients. Our novel observations among these routes of exposure and common mammalian model organisms appear particularly useful for read across and screening-level health hazard and risk assessments when limited data exists for specific chemicals.

Critical review and probabilistic health hazard assessment of cleaning product ingredients in all-purpose cleaners, dish care products, and laundry care products.

Though numerous chemical ingredients are used in cleaning products, empirical mammalian toxicology information is often limited for many substances. Such limited data inherently presents challenges to environmental health practitioners performing hazard and risk assessments. Probabilistic hazard assessment using chemical toxicity distributions (CTDs) is an alternative approach for assessments of chemicals when toxicity information is lacking. The CTD concept allows for derivation of thresholds of toxicological concern (TTCs) to predict adverse effect thresholds for mammalian species. Unfortunately, comparative health hazard assessment of cleaning product ingredients in common use categories such as all-purpose cleaners (APC), dish care products (DCP) and laundry care products (LCP) has not been well studied. However, APC, DCP, and LCP are used routinely for household and industrial applications, resulting in residential and industrial occupational exposures. Therefore, we reviewed and then examined hazard information (median lethal dose (LD50), lowest-observed-adverse-effect level (LOAEL), and no-observed-adverse-effect level (NOAEL)) from different types of standard mammalian toxicity studies for oral toxicity in the rat model from the unique Cleaning Product Ingredient Safety Initiative mammalian toxicology database. Probabilistic distributions (CTDs) were subsequently constructed using LD50, NOAEL and LOAEL data from a specific toxicity study type for all available ingredients in these three use categories. Based on data availability, product type-specific and chemical category-specific CTDs were also generated and compared. For each CTD, threshold concentrations (TCs) and their 95% confidence intervals (95% CIs) at 1st, 5th, 10th, 50th, 90th, 95th and 99th percentiles were calculated using the log-normal model. To test whether the common default uncertainty factor (UF) approach (e.g., 3, 10) in mammalian health risk assessment provides sufficient protection, UFs were also derived for LOAEL-to-NOAEL and exposure duration (e.g., subchronic-to-chronic) extrapolations. Relationships between CTDs of acute LD50s and sublethal LOAELs/NOAELs were also examined for acute-to-chronic ratio calculations, which may be useful in extreme circumstances. Results from our critical review and meta-analysis appear particularly useful for hazard and risk practitioners when identifying TTCs for ingredients in product use categories, and other chemical classes. This approach can also support development of regulatory data dossiers through read across, chemical substitutions and screening-level health risk assessments when limited or no empirical toxicity information exists for industrial chemicals.

Identification of novel uncertainty factors and thresholds of toxicological concern for health hazard and risk assessment: Application to cleaning product ingredients.

Uncertainty factors (UFs) are commonly used during hazard and risk assessments to address uncertainties, including extrapolations among mammals and experimental durations. In risk assessment, default values are routinely used for interspecies extrapolation and interindividual variability. Whether default UFs are sufficient for various chemical uses or specific chemical classes remains understudied, particularly for ingredients in cleaning products. Therefore, we examined publicly available acute median lethal dose (LD50), and reproductive and developmental no-observed-adverse-effect level (NOAEL) and lowest-observed-adverse-effect level (LOAEL) values for the rat model (oral). We employed probabilistic chemical toxicity distributions to identify likelihoods of encountering acute, subacute, subchronic and chronic toxicity thresholds for specific chemical categories and ingredients in cleaning products. We subsequently identified thresholds of toxicological concern (TTC) and then various UFs for: 1) acute (LD50s)-to-chronic (reproductive/developmental NOAELs) ratios (ACRs), 2) exposure duration extrapolations (e.g., subchronic-to-chronic; reproductive/developmental), and 3) LOAEL-to-NOAEL ratios considering subacute/acute developmental responses. These ratios (95% CIs) were calculated from pairwise threshold levels using Monte Carlo simulations to identify UFs for all ingredients in cleaning products. Based on data availability, chemical category-specific UFs were also identified for aliphatic acids and salts, aliphatic alcohols, inorganic acids and salts, and alkyl sulfates. In a number of cases, derived UFs were smaller than default values (e.g., 10) employed by regulatory agencies; however, larger UFs were occasionally identified. Such UFs could be used by assessors instead of relying on default values. These approaches for identifying mammalian TTCs and diverse UFs represent robust alternatives to application of default values for ingredients in cleaning products and other chemical classes. Findings can also support chemical substitutions during alternatives assessment, and data dossier development (e.g., read across), identification of TTCs, and screening-level hazard and risk assessment when toxicity data is unavailable for specific chemicals.

Toward the Design of Less Hazardous Chemicals: Exploring Comparative Oxidative Stress in Two Common Animal Models.

Sustainable molecular design of less hazardous chemicals presents a potentially transformative approach to protect public health and the environment. Relationships between molecular descriptors and toxicity thresholds previously identified the octanol-water distribution coefficient, log D, and the HOMO-LUMO energy gap, ΔE, as two useful properties in the identification of reduced aquatic toxicity. To determine whether these two property-based guidelines are applicable to sublethal oxidative stress (OS) responses, two common aquatic in vivo models, the fathead minnow (Pimephales promelas) and zebrafish (Danio rerio), were employed to examine traditional biochemical biomarkers (lipid peroxidation, DNA damage, and total glutathione) and antioxidant gene activation following exposure to eight structurally diverse industrial chemicals (bisphenol A, cumene hydroperoxide, dinoseb, hydroquinone, indene, perfluorooctanoic acid, R-(-)-carvone, and tert-butyl hydroperoxide). Bisphenol A, cumene hydroperoxide, dinoseb, and hydroquinone were consistent inducers of OS. Glutathione was the most consistently affected biomarker, suggesting its utility as a sensitivity response to support the design of less hazardous chemicals. Antioxidant gene expression (changes in nrf2, gclc, gst, and sod) was most significantly (p < 0.05) altered by R-(-)-carvone, cumene hydroperoxide, and bisphenol A. Results from the present study indicate that metabolism of parent chemicals and the role of their metabolites in molecular initiating events should be considered during the design of less hazardous chemicals. Current empirical and computational findings identify the need for future derivation of sustainable molecular design guidelines for electrophilic reactive chemicals (e.g., SN2 nucleophilic substitution and Michael addition reactivity) to reduce OS related adverse outcomes in vivo.

Global Assessment of Bisphenol A in the Environment: Review and Analysis of Its Occurrence and Bioaccumulation.

Because bisphenol A (BPA) is a high production volume chemical, we examined over 500 peer-reviewed studies to understand its global distribution in effluent discharges, surface waters, sewage sludge, biosolids, sediments, soils, air, wildlife, and humans. Bisphenol A was largely reported from urban ecosystems in Asia, Europe, and North America; unfortunately, information was lacking from large geographic areas, megacities, and developing countries. When sufficient data were available, probabilistic hazard assessments were performed to understand global environmental quality concerns. Exceedances of Canadian Predicted No Effect Concentrations for aquatic life were >50% for effluents in Asia, Europe, and North America but as high as 80% for surface water reports from Asia. Similarly, maximum concentrations of BPA in sediments from Asia were higher than Europe. Concentrations of BPA in wildlife, mostly for fish, ranged from 0.2 to 13 000 ng/g. We observed 60% and 40% exceedences of median levels by the US Centers for Disease Control and Prevention's National Health and Nutrition Examination Survey in Europe and Asia, respectively. These findings highlight the utility of coordinating global sensing of environmental contaminants efforts through integration of environmental monitoring and specimen banking to identify regions for implementation of more robust environmental assessment and management programs.

Street dust: implications for stormwater and air quality, and environmental through street sweeping.

Street dust represents a source of dual potential risk to stormwater and air quality. It has been well documented that street dust washes into local watersheds and can degrade water quality. Research has also demonstrated that ambient particulate matter (PM10) , which is associated with adverse health outcomes, can arise from resuspension of accumulated street dust. Furthermore, many contaminants, including metals, are present at higher concentrations in the smallest available particles, which are more likely to be resuspended in air and stormwater runoff. Although street cleaning is listed as a best management practice for storm water quality by the EPA, data are limited on the critical parameters (technology, environment, usage), which determine the effectiveness of any street cleaning program, particularly in the peer-reviewed literature. The purpose of the present study was to develop a comprehensive understanding of the efficacy of various street cleaning technologies and practices to protect both water quality and public health. Few studies have compared the effectiveness of street sweeping technologies to remove street dust. Unfortunately, the dearth of comprehensive data on exposure, contaminant concentrations, and efficacy of various sweeping technologies and strategies precludes developing quantitative estimates for potential risk to humans and the environment. Based on the few studies available, regenerative air street sweepers appear to provide the most benefit with regard to collection of small particles and prevention of re-entrainment. It is also clear from the available data that local conditions, climate, and specific needs are critical determinants of the ideal street sweeping strategy (technology, frequency, speed, targeted areas, etc.). Given the critical need for protection of water and air quality in rapidly expanding urban regions (e.g., megacities), further research is necessary to develop best practices for street dust management. Herein, we provide a framework for future experimental studies to support risk-based assessments of street cleaning technologies.

Development and application of a novel method for high-throughput determination of PCDD/Fs and PCBs in sediments.

A selective pressurized liquid extraction technique was developed for the simultaneous extraction of polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (dl-PCBs) from contaminated sediments. The final method incorporated cleanup adsorbents (Florisil, alumina, and silica) into the extraction cell in a 1:1 ratio of matrix to individual adsorbent (w/w). Sulfur, a common interference found in sediments, was successfully removed by placing activated copper in the extraction bottle prior to extraction. No additional postextraction cleanup was required, and sample throughput was reduced to 2.5 h per sample. Target analytes were quantified using high-resolution gas chromatography/electron-capture negative ionization mass spectrometry and verified by high-resolution gas chromatography/high-resolution mass spectrometry. Though mean analyte recoveries (n = 3) of PCDD/Fs and dl-PCBs were 84 ± 5.8% and 70 ± 8.4%, respectively, mean surrogate recoveries for all PCDD/Fs using this novel method were greatly improved compared with US Environmental Protection Agency (USEPA) method 1613 (∼25-155%) and USEPA method 8290a (40-135%). After development, the method was used to examine surficial sediment samples from the San Jacinto River waste pits, a Superfund site in Houston, Texas, USA. In all samples, PCDD/Fs and dl-PCBs were detected, and the contaminant concentrations ranged over 5 orders of magnitude.

Selective pressurized liquid extraction technique capable of analyzing dioxins, furans, and PCBs in clams and crab tissue.

A selective pressurized liquid extraction technique (SPLE) was developed for the analysis of polychlorodibenzo-p-dioxins, polychlorodibenzofurans (PCDD/Fs) and dioxin-like polychlorobiphenyls (dl-PCBs) in clam and crab tissue. The SPLE incorporated multiple cleanup adsorbents (alumina, florisil, silica gel, celite, and carbopack) within the extraction cell. Tissue extracts were analyzed by high resolution gas chromatography coupled with electron capture negative ionization mass spectrometry. Mean recovery (n = 3) and percent relative standard deviation for PCDD/Fs and dl-PCBs in clam and crabs was 89 ± 2.3 and 85 ± 4.0, respectively. The SPLE method was applied to clams and crabs collected from the San Jacinto River Waste Pits, a Superfund site in Houston, TX. The dl-PCBs concentrations in clams and crabs ranged from 50 to 2,450 and 5 to 800 ng/g ww, respectively. Sample preparation time and solvents were reduced by 92 % and 65 %, respectively, as compared to USEPA method 1613.

Cancer risk from incidental ingestion exposures to PAHs associated with coal-tar-sealed pavement.

Recent (2009-10) studies documented significantly higher concentrations of polycyclic aromatic hydrocarbons (PAHs) in settled house dust in living spaces and soil adjacent to parking lots sealed with coal-tar-based products. To date, no studies have examined the potential human health effects of PAHs from these products in dust and soil. Here we present the results of an analysis of potential cancer risk associated with incidental ingestion exposures to PAHs in settings near coal-tar-sealed pavement. Exposures to benzo[a]pyrene equivalents were characterized across five scenarios. The central tendency estimate of excess cancer risk resulting from lifetime exposures to soil and dust from nondietary ingestion in these settings exceeded 1 × 10(-4), as determined using deterministic and probabilistic methods. Soil was the primary driver of risk, but according to probabilistic calculations, reasonable maximum exposure to affected house dust in the first 6 years of life was sufficient to generate an estimated excess lifetime cancer risk of 6 × 10(-5). Our results indicate that the presence of coal-tar-based pavement sealants is associated with significant increases in estimated excess lifetime cancer risk for nearby residents. Much of this calculated excess risk arises from exposures to PAHs in early childhood (i.e., 0-6 years of age).

NF-κB and matrix-dependent regulation of osteopontin promoter activity in allylamine-activated vascular smooth muscle cells.

Repeated cycles of oxidative injury by allylamine in vivo induce a proliferative rat vascular (aortic) smooth muscle cell (vSMC) phenotype characterized by matrix-dependent enhancement of mitogenic sensitivity, changes in cell surface integrin expression, and osteopontin (opn) overexpression. Here, we show that constitutive and mitogen-stimulated NF-κB DNA binding activity is enhanced in allylamine vSMCs. Matrix-specific changes in cellular Rel protein expression were observed in allylamine vSMCs. The NF-κB DNA binding element located at -1943 in the 5'-UTR strongly inhibited opn promoter activity in allylamine vSMCs, and this response was regulated by the extracellular matrix. Constitutive increases in opn promoter activity were only seen when allylamine cells were seeded on a fibronectin substrate, and this response was independent of the NF-κB DNA binding sequence within the regulatory region. Thus, NF-κB functions as a critical regulator of the allylamine-induced proliferative phenotype in vSMCs.

Coal-tar-based pavement sealcoat and PAHs: implications for the environment, human health, and stormwater management.

Coal-tar-based sealcoat products, widely used in the central and eastern U.S. on parking lots, driveways, and even playgrounds, are typically 20-35% coal-tar pitch, a known human carcinogen that contains about 200 polycyclic aromatic hydrocarbon (PAH) compounds. Research continues to identify environmental compartments-including stormwater runoff, lake sediment, soil, house dust, and most recently, air-contaminated by PAHs from coal-tar-based sealcoat and to demonstrate potential risks to biological communities and human health. In many cases, the levels of contamination associated with sealed pavement are striking relative to levels near unsealed pavement: PAH concentrations in air over pavement with freshly applied coal-tar-based sealcoat, for example, were hundreds to thousands of times higher than those in air over unsealed pavement. Even a small amount of sealcoated pavement can be the dominant source of PAHs to sediment in stormwater-retention ponds; proper disposal of such PAH-contaminated sediment can be extremely costly. Several local governments, the District of Columbia, and the State of Washington have banned use of these products, and several national and regional hardware and home-improvement retailers have voluntarily ceased selling them.

Application of chemical toxicity distributions to ecotoxicology data requirements under REACH.

The European Union's REACH regulation has further highlighted the lack of ecotoxicological data for substances in the marketplace. The mandates under REACH (registration, evaluation, authorization, and restriction of chemicals) to produce data and minimize testing on vertebrates present an impetus for advanced hazard assessment techniques using read-across. Research in our group has recently focused on probabilistic ecotoxicological hazard assessment approaches using chemical toxicity distributions (CTDs). Using available data for chemicals with similar modes of action or within a chemical class may allow for selection of a screening point value (SPV) for development of environmental safety values, based on a probabilistic distribution of toxicity values for a specific endpoint in an ecological receptor. Ecotoxicity data for acetylcholinesterase inhibitors and surfactants in Daphnia magna and Pimephales promelas were gathered from several data sources, including the U.S. Environmental Protection Agency's ECOTOX and Pesticides Ecotoxicity databases, the peer-reviewed literature, and the Human and Environmental Risk Assessment (HERA) project. Chemical toxicity distributions were subsequently developed, and the first and fifth centiles were used as SPVs for the development of screening-predicted no-effect concentrations (sPNECs). The first and fifth centiles of these distributions were divided by an assessment factor of 1,000, as recommended by REACH guidance. Use of screening values created using these techniques could support the processes of data dossier development and environmental exposure assessment, allowing for rigorous prioritization in testing and monitoring to fill data gaps.

An initial probabilistic hazard assessment of oil dispersants approved by the United States National Contingency Plan.

Dispersants are commonly applied during oil spill mitigation efforts; however, these industrial chemicals may present risks to aquatic organisms individually and when mixed with oil. Fourteen dispersants are listed on the U.S. Environmental Protection Agency (U.S. EPA) National Oil and Hazardous Substances Pollution Contingency Plan (NCP). Availability of environmental effects information for such agents is limited, and individual components of dispersants are largely proprietary. Probabilistic hazard assessment approaches including Chemical Toxicity Distributions (CTDs) may be useful as an initial step toward prioritizing environmental hazards from the use of dispersants. In the present study, we applied the CTD approach to two acute toxicity datasets: NCP (the contingency plan dataset) and DHOS (a subset of NCP listed dispersants reevaluated subsequent to the Deepwater Horizon oil spill). These datasets contained median lethal concentration (LC50) values for dispersants alone and dispersant:oil mixtures, in two standard marine test species, Menidia beryllina and Mysidopsis bahia. These CTDs suggest that dispersants alone are generally less toxic than oil. In contrast, most dispersant:oil mixtures are more toxic than oil alone. For the two datasets (treated separately because of differing methodologies), CTDs would predict 95% of dispersant:oil mixtures to have acute toxicity values above 0.32 and 0.76 mg/L for Mysidopsis and 0.33 mg/L and 1.06 mg/L for Menidia (for DHOS and NCP, respectively). These findings demonstrate the utility of CTDs as a means to evaluate the comparative ecotoxicity of dispersants alone and in mixture with different oil types. The approaches presented here also provide valuable tools for prioritizing prospective and retrospective environmental assessments of oil dispersants.

The European Union's REACH regulation: a review of its history and requirements.

In 2006, the European Union (EU) promulgated a monumental regulatory initiative for the Registration, Evaluation, Authorization, and Restriction of Chemicals (REACH). To date, several thousand pages of text have been needed to describe the expectations of this regulation. There were numerous reasons for the promulgation of REACH, but, by and large, it is an extension of the global desire to produce fewer industrial chemicals, to understand the possible human and ecological hazards of those that are produced, and to insure that any major threat is anticipated, as well as prevented. Most industry-related groups consider it the most wide-ranging and costly regulatory initiatives related to health risk assessment ever to be promulgated. This review presents a description of REACH that should inform scientists, managers, and others about its objectives and the means to satisfy them. Registration is required for all chemicals manufactured or imported into the EU, unless specifically exempted. Registration is expected to be a collaborative process among companies, which will generate a dossier containing data on physicochemical characteristics, as well as toxicological and ecotoxicological properties. Though the magnitude of the gaps in the data required for registration is uncertain at this point, it is clear that basic toxicology testing will have to be conducted for many chemical substances that have not undergone formal review up to this point. For many chemicals, an examination of hazards and risks arising from the use of these substances will also be required in the form of a chemical safety report (CSR). Beginning with the dual processes of dossier and substance evaluation, the European Chemicals Agency (ECHA), the Member States of the EU, and the European Commission will identify chemicals that may pose unacceptable hazards to human health and/or the environment, and will curtail or restrict their usage. The implementation of REACH will expand and deepen the fields of applied toxicology and exposure assessment by spurring activity and innovation in sampling and analysis, toxicology testing, exposure modeling, alternative toxicity testing, and risk assessment practices.

The transgenic mouse assay as an alternative test method for regulatory carcinogenicity studies--implications for REACH.

REACH, an EU regulation that requires the submission of safety data in support of the protection of human and environmental health, mandates that registration should be achieved with the minimum amount of animal testing possible. Under REACH, a two-year carcinogenicity assay may be required for certain chemicals produced at >1000 metric tonnes per year. In addition, some chemicals that are found to be genotoxic will also require testing. Alternative methods have been explored in an attempt to improve the predictivity of this bioassay as well as to reduce the number of animals used for such testing. This research has focused on the use of transgenic/knockout mouse models. Study results from selected models indicate that they are useful in hazard identification, even if they are not entirely suitable for risk assessment on their own. Carcinogenic hazard assessment can be greatly enhanced and animal use reduced if the traditional two-year rat bioassay is combined with a well conducted transgenic mouse assay. Importantly, the use of transgenic animals to supplement a traditional two-year carcinogenicity study may help reduce the number of false negatives, one of the unstated goals of REACH via the precautionary principle.

Levels of polychlorinated dibenzo-p-dioxins, dibenzofurans, and biphenyls in southern Mississippi catfish and estimation of potential health risks.

Fish consumption has been classified as one of the primary pathways of exposure to polychlorinated dibenzo-p-dioxins, dibenzofurans (PCDD/Fs) and biphenyls (PCBs). In this study, we evaluated tissue levels of the 17 laterally substituted PCDD/Fs, 12 dioxin-like PCBs, and 97 non-dioxin-like PCBs in a number of wild-caught and farm-raised catfish collected throughout southern Mississippi. Total lipid-adjusted TEQ and non-dioxin-like PCB concentrations in wild-caught catfish fillets were significantly higher than concentrations in farm-raised fillet samples. The percent contribution of PCDDs, PCDFs, and dioxin-like PCBs to mean total TEQ varied between wild-caught and farm-raised samples as well as by collection site for wild-caught catfish. The non-dioxin-like PCBs that contributed the most to total PCB concentrations also differed between wild-caught and farm-raised samples. Regardless of whether samples were farm-raised or wild-caught, estimated cancer risks associated with consumption of these catfish were less than 27.0E-06. Overall, results of this study indicate that levels of dioxin-like compounds and PCBs in Mississippi catfish are similar to those measured in more recent studies in the US and that levels of these compounds appear to be decreasing in this food source.