Lect 6 Organics - ENSC

Lecture Title and Instructor

  • ENSC 201: Environmental Toxicology and Chemical Risks Lecture 6: Organic Compounds

  • Instructor: Louise M. Winn, Ph.D.

  • Contact: winnl@queensu.ca

Outline of the Lecture

  • Major organic chemicals of interest:

    • Persistent organic pollutants (POPs)

    • Other important environmental toxicant classes

  • Review of key aspects of contaminants:

    • Sources and uses – relates to exposure

    • Importance for environmental toxicology

    • Human concern aspects

  • Future lectures will cover:

    • Oil contamination

    • Pesticides

    • Drinking water

Organic Contaminants Overview

  • Over 40,000+ industrial chemicals alongside many natural chemicals in toxicology.

  • Importance in Environmental Toxicology is linked to exposure and hazards related to chemical properties.

Persistent Organic Pollutants (POPs)

  • Defined as significant environmental problems including 12 priority compounds per the Stockholm convention (1972).

  • Categorized based on release method:

    • Compounds purposely made and released

    • Compounds made unintentionally and released

    • Compounds accidentally produced and released

Key Characteristics of Organic Contaminants - PBT

  • Persistent, Bioaccumulative, and Toxic (PBT) are key properties.

  • All the “dirty dozen” POPs exhibit PBT properties.

Persistence

  • Defined as the residence time of contaminants in environmental compartments (e.g. soil, water, etc.).

  • Measured through average time or half-life; may require complex modeling.

Bioaccumulation

  • Accumulates in food webs and organisms over time.

  • Relation to previous lectures on bioconcentration and biomagnification.

Toxicity

  • Relative toxicity indicated through values such as LC50 or LD50.

  • Exposure levels can result in toxicity at unexpectedly low doses due to bioaccumulation.

  • Relationship: (P + B) → Exposure; (Exposure + T) → Risk.

Regulation of Contaminants

  • Need research to determine concentrations or doses where effects commence.

  • Regulative actions usually target threshold toxicity values with safety factors, primarily a safety factor of at least 100 to account for inter-species differences.

Case Study: DDT

  • Compound para-dichlorodiphenyldichloroethylene (DDT):

    • Subject of Rachel Carson’s book "Silent Spring" (1962).

    • Detection in human tissue led to regulatory actions.

    • Main decay product is DDE, a metabolite noted for its toxicity on par with DDT.

    • Regulatory nuances considering its importance in disease control in the developing world.

Organic Contaminants - PCBs

  • Polychlorinated Biphenyls (PCBs): major known POPs.

  • Characteristics:

    • Stable, non-volatile, persistent, and produced for various industrial uses like electrical insulation.

  • Mixtures known as "Aroclor" provided by Monsanto.

Toxicity of PCBs

  • High tendency for bioaccumulation, similar to DDT.

  • Acute and chronic toxicity may appear low at permissible levels but significant developmental impacts are observed.

  • Increased emphasis on early life stages in chronic exposure studies.

Organic Contaminants - Dioxins and Furans

  • Among the most toxic POPs, produced unintentionally through combustion processes.

  • Toxicity mechanisms involve binding to Aryl Hydrocarbon Receptors (AhR).

  • Diverse sources, including herbicides (2,4,5-T), incineration, and bleaching processes.

Emerging Contaminants

  • Emerging contaminants like brominated compounds and EDCs are being identified for adverse environmental impacts.

  • Concerns related to bioaccumulation and chronic toxicity potential.

  • Continuous monitoring required for their emerging presence in ecosystems.

Summary

  • Ongoing research is crucial to identify and regulate new compounds effectively.

  • Future regulations need to be grounded in robust scientific evidence to address these critical environmental concerns.