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Epidemiologic Side of Toxicology (6th of 10 Lectures on Toxicologic Epidemiology). Michael H. Dong MPH, DrPA, PhD. readings. Taken in the early ’90s, when desktop computers were still a luxury. Learning Objectives Appreciate the importance of the epidemiologic side of toxicology.
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Epidemiologic Side of Toxicology (6th of 10 Lectures onToxicologic Epidemiology) Michael H. Dong MPH, DrPA, PhD readings
Taken in the early ’90s, when desktop computers were still a luxury.
Learning Objectives • Appreciate the importance of the epidemiologic side of toxicology. • Study the epidemiologic relevance through three historical events. • Learn the impact of epidemiology, which is dynamic, case-dependent, and often tremendous.
Performance Objectives • Able to describe the toxicologic course of the three historical events presented. • To characterize the epidemiologic side of these courses and events. • To outline the purpose as well as the principles of presenting the three toxicologic events.
Three Case Studies for the Epidemiologic Side of Toxicology: 1. Jamaica Ginger Epidemic 2. London Smog of 1952 3. Multistage Model of Carcinogenesis
Ginger Paralysis: Syndrome & Cause • Characterized by ataxia, muscular weakness, unsteady gait, flaccid paralysis of the legs. • Also known as jake leg, wrist drop, and foot drop. • Caused by exposure to TOCP, with delayed onset of 1 to 3 weeks.
Ginger Paralysis: History and Toxicity • The syndrome known for a century; and later, as ginger paralysis due to its first major episode in the USA. • TOCP is the most toxic isomer of TCP; both, like some other OP, can induce delayed neurotoxicity. • The initial effects likely involve the inhibition of neurotoxic esterase.
Ginger Paralysis: The Epidemiologic Side • 20,000 cases reported in the USA in 1930, related to consumption of illegal alcohol contaminated with TOCP. • 10,000 cases reported in Morocco in 1959, related to consumption of food cooked in oil contaminated with TOCP. • The association was initiated by two Oklahoma doctors: Miles and Goldfain.
Ginger Paralysis:The Impact of Epidemiology • It was the first major epidemic that enabled Smith et al. to focus on TOCP as the prime suspect. • A large number of toxicology studies were hence launched, along with U.S. EPA’s development of a regulatory guideline specifically for testing delayed neurotoxicity.
Ginger Paralysis:The Lesson (and Speculation) • Despite the Jamaica ginger episode, there were still numerous outbreaks involving cooking oil contaminated with TOCP. • Delayed neurotoxicity is extremely specific to chemical structure. • It was epidemiologic evidence that advanced the toxicology of TOCP.
London Smog: History & the Epidemic • 4,000 premature deaths, with most being elderly or having preexisting diseases, from breathing heavily polluted air in London in 1952. • Smog is a mixture of smoke and fog, now also involving the equally irritating photochemical air pollution. • Air pollution is predictable, and was recognized back in the Roman period.
London Smog: Toxicity of the Air Pollutants • Sulfur dioxide is an upper airway irritant. • Carbon dioxide is a potent asphyxiant. • Nitrogen dioxide causes severe irritation of the innermost parts of the lungs. • Ozone is a reactive and toxic form of elemental oxygen.
London Smog:Other Pollutants & Newer Problems • Other pollutants: suspended particulate matter (e.g., black smoke); and volatile organic compounds (e.g., petroleum benzene as an exhaust product). • 1.6 million people may now be at risk from poor air quality in urban areas throughout the world. • There are also areas everywhere filled with traffic-generated pollutants.
London Smog: The Impact of Epidemiology • The 1952 incident led to the passage of the British Clean Air Act of 1956. • More epidemiologic studies have since been conducted to cope with air pollution problems and episodes. • Also more studies on long-term toxic effects and on photochemical formation.
London Smog: The Lesson • The older winter smog problem in London and worldwide is now being replaced with summer smogs from photochemical formation. • The adverse health effects of the winter or summer air pollutants cannot be investigated using classic toxicology studies alone.
Multistage Model:The Course of Carcinogenesis • Carcinogenesis is the biochemical process characterizing the progression of normal cells to neoplastic and later into tumor cells. • Multistage model is a quantitative as well as a mechanistic theory used to characterize this biochemical process. • Two of the stages basic to the model are presumably initiation and promotion.
Multistage Model: The Underlying Theories • In addition to being an initiator or a promoter, an agent initially can be a precarcinogen and later be transformed into a harmful ultimate carcinogen. • Initiation is usually irreversible, of short duration, and invisible, whereas promotion has the opposite effects. • As an outgrowth of the challenge to the single stage and the multicell theories.
Multistage Model: The Epidemiologic Side • The single stage model and the multicell model were found to be incompatible with epidemiologic data. • Although the multistage model is based on a single cell theory, its development was driven by epidemiologic data that many cancer incidences increased with the 5th or 6th power of age (that also implicating latency period).
Multistage Model: The Relevance and Impact • Gaining wide acceptance due to the strong evidence that cancer is a single cell in origin. • Useful as a quantitative tool in the cohort analysis of tumors induced by chemicals. • Found for the large part successful in describing many experimental and epidemiologic data.
Multistage Model: The Lesson & Its Utilities • Leading to the use of more proper mitigation measures; and to the adoption by regulatory agencies for cancer risk assessment. • Toxicologists using animal studies, without this epidemiology-based theory, would likely fail to elucidate or make fuller use of the mechanistic process of carcinogenesis.
Overview of Next LecturesHuman Exposure Assessment I & II • Human exposure assessment is one of the key components in the health risk assessment. • Lecture 7 (Assessment I) will cover the direct measurement methods. • Lecture 8 (Assessment II) will focus on the indirect measurement methods.