Slides: Pesticides & Other Organic Chemicals

Introduction to Environmental Health

  • Course: PHS 3014

  • Week: 9 (Pesticides & Other Organic Chemicals)

  • Date: 20 October 2025

  • Instructor: Prof. Ryan Calder, Virginia Tech

  • Slides from: Prof. A. Cohen, Department of Public Health Sciences.

In the News 20 October 2025

Key Article Topic

  • Headline: Trump links autism and Tylenol: Is there any truth to it?

    • President Trump cautioned against taking Tylenol, suggesting a risk of autism.

    • Strong scientific evidence supporting a link between acetaminophen and autism is lacking.

    • Article by Helen Pearson & Heidi Ledford.

Health & Safety Related to Acetaminophen

  • Research Findings: 27 studies explored the correlation of acetaminophen usage with autism.

    • Results: Positive correlation found in 67%, no correlation in 23%, negative correlation in 10%.

  • Study Reflection: Prada et al. (2025) indicated reliance on midwives for structured interviews, leading to a reported 7.5% acetaminophen usage among pregnant individuals, contrasting globally accepted stats (~50%).

Developmental Concerns of Acetaminophen

Risk Factors Identified

  • Acetaminophen use

  • Chronic stress/inflammation during fetal development

  • Maternal characteristics and demographics

Possible Outcomes

  • Associated with autism in children; suggests necessity for precautions in pregnant populations.

Congenital Anomalies Related to Acetaminophen Exposure

  • Anencephaly/Craniorachischisis: Fatal neural tube defects from improper closure during fetal development.

  • Encephalocele: Brain tissue protrudes through the skull.

  • Anotia/Microtia: Absence or underdevelopment of external ear parts; often leads to hearing issues.

  • Cleft Lip/Palate: Facial deformities affecting feeding and dental health.

  • Gastroschisis: Abdominal defects where intestines protrude; requires surgical repair.

Questions Raised in Discussions

  • Can we accurately state “no evidence” exists for maternal acetaminophen usage and autism?

  • Is the current evidence adequate for informed decision-making?

  • Do the potential risks overshadow the benefits?

Learning Objectives for Pesticides & Organic Chemicals

  • Definition of organic chemicals and pesticides.

  • Familiarity with common pesticide classes:

    • Insecticides, herbicides

    • Ecological and health implications, particularly in carcinogenic and endocrine-disruption contexts.

    • Understanding controversies surrounding chlorpyrifos and atrazine.

Overview of Organic Chemicals

  • Composition: Mainly consists of carbon (C), hydrogen (H), nitrogen (N), oxygen (O).

  • Characteristics: Carbon's ability to form four covalent bonds allows creation of stable compounds like amino acids, fatty acids, carbohydrates, etc.

Naturally Occurring Organic Hazards

  • Hazardous natural compounds:

    • Aflatoxins

    • Mycotoxins

    • Dioxins (increased through industrial activity).

Anthropogenic Organic Exposures

  • Characteristics:

    • Often persist long-term in the environment (e.g., PCBs).

    • Designed to inflict harm (pesticides/herbicides) applied to food systems.

    • Occupational exposures stemming from manufacturing and application processes.

Health Risks Associated with Organic Chemical Exposure

  • Volatization increases respiratory risks (e.g., benzene, toluene).

  • Many are flammable (hydrocarbons) and have toxic effects based on solubility (lipid vs. water).

  • Predictive Challenges: Risks associated with chemical exposure can often be unpredictable (carcinogenic, neurotoxic).

Mechanistic Toxicology

  • Field focused on understanding variability in toxicity among different chemicals.

Types of Organic Compounds

Aromatic Compounds

  • Organic molecules with a benzene ring (examples include benzene and toluene).

Hydrocarbons

  • Organic compounds containing only carbon and hydrogen (e.g., acetylene, benzene).

Volatile Organic Compounds (VOCs)

  • Characteristics: Organic compounds that evaporate easily (e.g., benzene, methylene chloride).

Persistent Organic Pollutants (POPs)

  • Definition: Toxic chemicals causing adverse health effects globally, transportable via air/water.

  • Examples: DDT, polycyclic aromatic hydrocarbons (PAHs).

Definition and Overview of Pesticides

  • Definition: Substances used to kill, repel, or control pest species.

  • Classes of Pesticides:

    • Disinfectants, fungicides, herbicides, insecticides, repellents, rodenticides.

Informative Historical Context

  • Interactions between mining and agriculture in California’s history influenced chemical development for pest control.

Regulatory Environment and Health Risks of Pesticides

  • Pesticide usage has been widespread without complete understanding of human/ecological risks.

  • Older pesticides like DDT remain prevalent in environment with noted acute and chronic health effects.

Pesticide Exposure Risks

Populations at Risk

  • Agricultural workers

  • Pets

  • Children

  • Livestock

  • Sensitive groups (e.g., pregnant women)

Classes of Pesticides

Common Classes and their Mechanisms

  • Organophosphates: Inhibit acetylcholinesterase.

  • Carbamates: Reversible acetylcholinesterase inhibitors.

  • Organochlorines: Persistent in environment, bioaccumulates—associated with immune suppression and cancer.

  • Pyrethroids: Derived from chrysanthemum, paralyze insects.

  • Neonicotinoids: Affect nicotinic acetylcholine receptors.

Regulatory Status and Toxicity Concerns

  • Increasing regulations due to potential threats to human health/pollinators.

Historical Timeline of Chlorpyrifos

  • 1965: Approval by U.S. EPA; 2000: Residential ban; 2017: Reversal of ban; 2021: All food tolerances revoked; 2023: Tolerances reinstated.

Specific Chemical Case Studies: Atrazine

Atrazine Overview

  • Use: Widely applied herbicide to control weeds; Resilience against degradation in waterways.

  • Regulatory Classification: Restricted use; monitored due to potential carcinogenic effects and environmental altercations.

Atrazine Usage Timeline

  • 1958 to 2023: Developed, broad usage initiated, affected by lawsuits, scientific reevaluation regarding reproductive impacts; current status involves restrictions.

Conclusion: Understanding Pesticides and Public Health

  • The EPA is tasked with monitoring pesticide applications, focusing on the prevention of harmful exposures and promoting integrated pest management (IPM). This comprehensive overview of pesticides highlights historical concerns, health risks, and evolving regulatory landscapes to effectively inform public health initiatives.