Benzo[a]pyrene (BaP) is formed by incomplete combustion of organic materials (petroleum, coal, tobacco, etc.). BaP is designated by the International Agency for Research on Cancer as a group 1 known human carcinogen; a classification supported by numerous studies in preclinical models and epidemiology studies of exposed populations. Risk assessment relies on toxicokinetic and cancer studies in rodents at doses 5–6 orders of magnitude greater than average human uptake. Using a dose-response design at environmentally relevant concentrations, this study follows uptake, metabolism, and elimination of [¹⁴C]-BaP in human plasma by employing UPLC - accelerator mass spectrometry (UPLC-AMS). Volunteers were administered 25, 50, 100, and 250 ng (2.7–27 nCi) of [¹⁴C]-BaP (with interceding minimum 3-week washout periods) with quantification of parent [¹⁴C]-BaP and metabolites in plasma measured over 48 hours. [¹⁴C]-BaP median T_max was 30 minutes with C_max and area under the curve (AUC) approximating dose-dependency. Marked inter-individual variability in plasma pharmacokinetics following a 250 ng dose was seen with 7 volunteers as measured by the C_max (8.99 ± 7.08 ng × mL⁻¹) and AUC_0–48hr (68.6 ± 64.0 fg × hr⁻¹ × mL⁻¹). Approximately 3–6% of the [¹⁴C] recovered (AUC_{0–48 hr}) was parent compound, demonstrating extensive metabolism following oral dosing. Metabolite profiles showed that, even at the earliest time-point (30 min), a substantial percentage of [¹⁴C] in plasma was polar BaP metabolites. The best fit modeling approach identified non-compartmental apparent volume of distribution of BaP as significantly increasing as a function of dose (p=0.004). Bay region tetrols and dihydrodiols predominated, suggesting not only was there extensive first pass metabolism but also potentially bioactivation. AMS enables the study of environmental carcinogens in humans with de minimus risk, allowing for important testing and validation of physiologically based pharmacokinetic models derived from animal data, risk assessment, and the interpretation of data from high-risk occupationally exposed populations.

One of the most significant challenges in human health risk assessment is to evaluate hazards from exposure to environmental chemical mixtures. Polycyclic aromatic hydrocarbons (PAHs) are a class of ubiquitous contaminants typically found as mixtures in gaseous and particulate phases in ambient air pollution associated with petrochemicals from Superfund sites and the burning of fossil fuels. However, little is understood about how PAHs in mixtures contribute to toxicity in lung cells. To investigate mixture interactions and component additivity from environmentally relevant PAHs, two synthetic mixtures were created from PAHs identified in passive air samplers at a legacy creosote site impacted by wildfires. The primary human bronchial epithelial cells differentiated at the air–liquid interface were treated with PAH mixtures at environmentally relevant proportions and evaluated for the differential expression of transcriptional biomarkers related to xenobiotic metabolism, oxidative stress response, barrier integrity, and DNA damage response. Component additivity was evaluated across all endpoints using two independent action (IA) models with and without the scaling of components by toxic equivalence factors. Both IA models exhibited trends that were unlike the observed mixture response and generally underestimated the toxicity across dose suggesting the potential for non-additive interactions of components. Overall, this study provides an example of the usefulness of mixture toxicity assessment with the currently available methods while demonstrating the need for more complex yet interpretable mixture response evaluation methods for environmental samples.

The development of new approach methodologies that include human cells differentiated into organotypic formats is of high interest due to their structural and functional similarities to tissues in vivo, enabling mechanistic understanding and translation to adverse health outcomes in humans. However, these systems often fail to capture complex intercellular signaling required for processes such as pulmonary inflammation induced by polycyclic aromatic hydrocarbons (PAHs). To investigate airway epithelial–macrophage interactions in response to benzo[a]pyrene and a PAH mixture (Tox Mix), co-culture models utilizing primary human bronchial epithelial cells (HBECs) differentiated at the air–liquid interface were cultured with THP-1 macrophages either directly or indirectly, alongside HBECs alone. After 24 h of exposure, cytokine expression (IL1B, IL6, CXCL8, TNF) as well as PAH biomarkers previously identified for chemical metabolism (CYP1A1, CYP1B1), oxidative stress (ALDH3A1, HMOX1, NQO1), and barrier integrity (TJP2) were evaluated. Cytotoxicity and barrier integrity were also assessed. HBECs alone and direct co-cultures exhibited similar responses after PAH treatment, while indirect co-cultures showed lower sensitivity to induction of inflammatory cytokines and CYP1A1 and CYP1B1 biomarker expression following exposure to PAHs. The expression of other biomarkers, including ALDH3A1, HMOX1, and NQO1, remained largely consistent across all models after treatment. Overall, these findings suggest that direct co-culture systems may provide a more physiologically relevant platform for studies of PAH-induced toxicity and demonstrate that the configuration of co-culture systems can influence cellular responses to chemical exposure.