A model to evaluate past exposure to 2,3,7,8-TCDD

Area of Science:

• Environmental Science
• Toxicology
• Biostatistics

Background:

• Dioxin concentrations in the environment rose from the 1930s to the 1960s/70s, followed by a decline.
• Human exposure to dioxins primarily occurs through the food supply, but the link between environmental deposition and food concentrations is complex.
• Understanding historical human exposure trends to dioxins, particularly 2,3,7,8-TCDD (TCDD), is crucial for public health.

Purpose of the Study:

• To statistically reconstruct past human exposure patterns to 2,3,7,8-TCDD (TCDD).
• To assess the temporal trends of TCDD exposure using a pharmacokinetic model fitted to body burden data.

Main Methods:

• A simple pharmacokinetic (PK) model incorporating a time-varying TCDD exposure dose was developed.
• The PK model was fitted to TCDD body burden data from five U.S. studies (1972-1987) using a Bayesian statistical approach.
• Model parameters, excluding exposure, were based on existing knowledge or estimations.

Main Results:

• A time-varying exposure dose provided a significantly better fit to body burden data than a constant dose, indicating historical fluctuations in TCDD exposure.
• Peak TCDD exposure was estimated in the late 1960s, aligning with sediment core data.
• Average peak exposure doses were estimated at 1.4-1.9 pg TCDD/kg-day, decreasing to <0.10 pg TCDD/kg-day by the late 1980s.

Conclusions:

• Human exposure to TCDD has varied significantly throughout the 20th century, peaking in the late 1960s.
• The modeled decline in TCDD exposure aligns with environmental trends and recent exposure estimates.
• The study highlights the utility of pharmacokinetic modeling for reconstructing historical toxicant exposure.