Lect 3 Principles and Methods - ENSC

Lecture Overview

• Course: ENSC 201: Environmental Toxicology and Chemical Risks

• Speaker: Louise M. Winn, Ph.D.

• Location: Botterell Hall RM 557

• Contact: winnl@queensu.ca

Introduction to Toxicity

• Toxic effects initiate from a reaction between a chemical and living tissue.

• Key concepts:

  • Hazard: Inherent capacity of a chemical to cause harm.

  • Toxicity: The capacity to produce adverse effects upon exposure.

• Fundamental principle: No exposure means no effect.

Definitions of Toxicants

• Toxicant: Harmful substance when introduced into an organism.

• Toxin: A toxicant produced by living organisms (e.g., aflatoxins, botulinum toxin).

• Xenobiotic: Substances foreign to a biological system.

• Anthropogenic: Human-made substances.

Principles of Toxicity

• Quote by Paracelsus: "All things are poisons, for there is nothing without poisonous qualities. It is only the dose which makes a thing poisonous."

Assessing Toxicity

• Laboratory testing involves:

  • Exposing organisms to various doses/concentrations over time.

  • Recording physiological responses under controlled conditions.

• Assesses the quantitative relationship between exposure and damage to organisms.

Dose-Response Relationship

• Assumptions:

  1. Response is due to the toxicant.

  2. Response relates to the exposure amount (dose/concentration).

Standardized Testing Methods

• Variability in species sensitivity warrants standardized tests.

• Commonly used surrogate species (e.g., mice/rats) for human toxicity extrapolation.

• Environment and Climate Change Canada supports biological test methods.

Components of Toxicity Tests

• Key elements of testing include:

  • Receptor: Organism exposed to the toxicant.

  • Route of exposure: Inhalation, ingestion, dermal exposure, injection.

  • Dose vs. Concentration: Amount taken up vs. amount in the environment.

  • Duration: Acute (<96 hours) vs. chronic exposure.

Measuring Response in Toxicity Tests

• Types of responses:

  • Lethal vs. Sublethal responses.

  • Categorization of data:

    • Quantal response (all-or-none, e.g., death).

    • Graded response (variable, e.g., heart rate).

  • Endpoints: Quantifiable responses related to exposure.

Nutrient and Non-Nutrient Toxicity

• Definitions:

  • Nutrient: Necessary for growth.

  • NOEC: No observed effect concentration.

  • LOEC: Lowest observed effect concentration.

Endpoint Assessment

• Metrics:

  • LD50: Dose killing 50% at time t.

  • LC50: Concentration killing 50% at time t.

  • ED50: Dose causing a response in 50%.

  • EC50: Concentration causing a response in 50%.

• Importance of duration of exposure noted (e.g., 96 h LC50 = 32 mg/L).

Toxicity Measurement Example

• Assessment of effluent toxicity using rainbow trout:

  • Exposure to different dilutions of effluent over time.

  • Measure responses at various concentrations.

Visualization Techniques in Toxicity Testing

• Plotting Methods:

  1. Time-based Plot: Shows responses over time at a single concentration.

  2. Concentration-based Plot: Response across various concentrations at a fixed time.

Toxicity Testing Objectives

• Standardized assessments conveying:

  • Monitoring effluent and environmental quality.

  • Data for establishing environmental guidelines.

  • Predictive capabilities of ecological responses.

Complexities of Laboratory-based Testing

• Realistic conditions complicate toxicity testing.

• Valuable data can still be sourced from well-designed studies.

Ecosystem Models in Testing

• Types:

  • Microcosms: Small replication of ecosystems.

  • Mesocosms: Intermediate size studies or experiments.

  • Experimental ponds for larger scale studies.

Techniques Utilized in Environmental Toxicology

• Key disciplines include:

  • Analytic Chemistry, Biology, Biochemistry, Physiology, Ecology, Toxicology.

Biological Monitoring

• Utilizing biological indicators to assess environmental changes.

• Indicator organisms: Sensitive to environmental factors like acidity or pollution.

• Trends from changes in organism populations can be observed.

Biomarkers in Toxicology

• Biochemical markers: Indications of organism's subcellular responses to substances.

• Examples include heat shock proteins, cytochrome P450, and metallothionein.

Challenges in Animal Testing

• Issues include:

  • Costs and ethics of testing numerous substances.

  • Alternatives: Tissue cultures, predictive models, and epidemiology.

Conclusion of Toxicity Testing

• The significance of defining dose-response relationships.

• Communicating hazards to both public and regulators.

• Introduction of new terminology for clarity in communication.