Study Guide for Environmental Toxicology (ENVT302)

Course Overview of Environmental Toxicology (ENVT302)

  • Foundations of Environmental Toxicology
  • Ecotoxicology: Principles and Processes
  • Persistent Organic Pollutants (POPs)
    • PFAS (Per- and polyfluoroalkyl substances)
  • Impact of Dioxins and Furans on Reproduction
  • Endocrine Disrupting Chemicals (EDCs)
  • Pesticides and the Environment
  • Environmental Exposure Assessment & Ecological Risk Assessment (ERA)

Course Synopsis

  • Environmental Toxicology (EnTox) introduces core concepts, frameworks, and tools to understand and manage environmental contaminants.
    • Emphasis on the link between sources, fate, transport in media, exposure pathways, and adverse outcomes.
    • Units focus on priority contaminant classes: POPs, dioxins/furans, EDCs, pesticides, and more.
    • Comparison to earlier course on ecological risk assessment (ERA) principles:
    • Evidence → Risk characterization → Decision-making and environmental management.

Housekeeping Issues

  • Assessment methods:
    • In-class tests, presentations, practicum, mid-semester, and final exams with percentage allocations of 10%, 20%, and 60%.
  • Core module integral to environmental management; potential inspiration for research topics.
  • Assumed prerequisite knowledge in Environmental Chemistry, Ecology, Toxicology, Public/Environmental Health, and Health Impact Risk Assessment (HIRA).

What is Environmental Toxicology (EnTox)?

  • Definition:
    • Systematic investigation of xenobiotic substances (now referred to as environmental contaminants or stressors) across environmental compartments (atmosphere, hydrosphere, lithosphere, biosphere).
  • Focus on studying sources, fate, transport, transformation, exposure, and adverse effects of various agents, particularly chemical, physical, and biological stressors.
  • The field is multidisciplinary, drawing from toxicology, analytical chemistry, biochemistry, genetics, ecology, pathology, etc.

Environmental Toxicology vs. Ecotoxicology

  • EnTox employs selected typical species or laboratory test organisms to examine responses to chemicals as a method to extrapolate data to the ecosystem level.
  • Ecotoxicology is often used interchangeably with Environmental Toxicology, with distinctions in focus:
    • EnTox includes human health endpoints, while Ecotoxicology focuses solely on ecological endpoints.

Key Focus Areas in Environmental Toxicology (EnTox)

  • Point Source:
    • Defined as a discrete source where pollutants enter the environment from a specific point, easier to monitor and regulate (e.g., industrial effluent pipe).
  • Diffuse Source:
    • Pollution from many small, scattered sources; harder to control, often preventive and land-management based (e.g., agricultural runoff).
  • Persistence:
    • Length of time a chemical remains in the environment without degradation.
  • Bioaccumulation:
    • The accumulation of substances, such as pesticides, in the tissues of living organisms.
  • Biomagnification:
    • Increased concentration of substances in organisms at each successive level of the food chain.
  • Environmental Fate & Transport:
    • How contaminants move and transform in the environment.
  • Exposure Assessment:
    • Assessment of exposure pathways (e.g., inhalation, ingestion).

Evolution of Environmental Toxicology (EnTox)

  • Mid-1940s industrialization spurred a rapid increase in synthetic chemical and waste streams in agriculture, mining, and manufacturing.
  • Initial assumptions of "dilution as solution" were proven inadequate; increased evidence of chronic low-dose effects.

Historical Context

  • 1962: Rachel Carson's Silent Spring published revealing impacts of synthetic pesticides (DDT) on ecosystems.
  • 1970s: Love Canal disaster leads to the establishment of the EPA, heightened awareness of regulatory toxicology.
  • 1980s: Bhopal disaster; Chernobyl accident highlights the threats of industrial chemical and radiological contamination.
  • 1990s-2000s: Introduction of endocrine disruption paradigm; persistent organic pollutants (POPs) highlighted.
  • Presently: Focus on emerging contaminants like microplastics, pharmaceuticals, and PFAS, plus climate-toxicology interactions.

The DPSIR Framework

  • DPSIR: Drivers, Pressures, State, Impact, Response helps to analyze environmental problems.
    • Drivers: Human needs (energy, food, transport).
    • Pressures: Direct stressors from drivers (chemical emissions, waste).
  • State: Environmental condition changes (contaminant levels).
  • Impact: Effects on human or ecosystem health (toxicity, biodiversity loss).
  • Response: Actions taken (regulation, remediation).
  • EnTox focuses on the Pressures, State, and Impacts parts of the chain.

Application of DPSIR Framework

  • Relevant examples include:
    • Urban air pollution, land degradation, water resource management, biodiversity reduction, tourism, and climate change impacts (e.g., in the Okavango Delta).

Source-Pathway-Receptor (SPR) Model

  • Overview: A cause-effect model focusing on the contaminant's source, exposure route, and biological responses.
    • All three components must be connected for a risk to exist.
    • Breaking any link in this chain eliminates the risk.
  • Components:
    1. SOURCE: The origin of the chemical stressor (e.g., industries, agricultural runoff).
    2. PATHWAY: The route of exposure (e.g., air, water, soil).
    3. RECEPTOR: The entity that is impacted.

Source Characterization

  • Understanding chemical release dynamics is essential for modeling contamination.
  • Chemical Speciation: Form and physical state affect toxicity (e.g., Cr(III) vs Cr(VI)).
  • Release Rate: Steady streams vs spills creates differing environmental impacts.

Exposure Pathways

  • Complete pathways consist of:
    • Contaminant source -> environmental medium -> point of exposure -> route of entry -> receptor population.

Mechanisms of Transport and Transformation

  • Transport Mechanisms:
    • Advection: Bulk flow movement carried by water or wind.
    • Molecular Diffusion: Movement from high to low concentration.
    • Sorption/Desorption: Attachment or detachment of contaminants to/from soil or particles.
  • Transformation Processes:
    • Degradation via hydrolysis, oxidation, photolysis, and microbial degradation affecting toxicity.

Contaminants and their Characteristics

  • Water Solubility & Vapour Pressure:
    • Solubility affects transport abilities and mobility.
    • High vapour pressure leads to greater volatility (e.g., TCE, PCE).
  • Octanol-Water Partition Coefficient (Kow):
    • Describes the distribution of chemicals between organic solvents and water, indicating potential for bioaccumulation.
  • High Kow values are associated with greater bioaccumulation in organisms. Examples: PCBs, DDT.

Receptors in Environmental Toxicology

  • Receptors are biological entities exposed to stressors with measurable adverse effects.
    • Levels of organization include individual organisms, populations, communities, and entire ecosystems.
    • Adverse effects could be mortality, reduced reproduction, or population declines.

Sensitive Receptors and Sentinel Species

  • Sensitive receptors indicate environmental health, e.g., amphibians signal ecosystem changes.
  • Sentinel Species: Organisms like amphibians that demonstrate early signs of environmental stress due to their high sensitivity to pollutants.
  • Examples: Lichens, bees, and coral reefs are additional indicators for specific environmental concerns.

Keystone Species and Ecological Impact

  • Keystone species have large effects on ecosystem structure; their removal can trigger dramatic shifts.
  • Example: Sea otters maintaining balance in kelp forest ecosystems.

Indicator Species

  • Indicator species inform on environmental condition based on narrow tolerance ranges (e.g., mayflies indicating clean water).

Dose-Response Relationships

  • Dose-response relationships characterize effects based on exposure levels and target organ response; important for risk assessments.

Environmental Persistence and Chemical Characteristics

  • Environmental persistence relates to how long contaminants remain active within environments without degradation, characterized by half-life measurements.
    • Non-persistent (

Environmental Regulations and Implications

  • Chemicals with high persistence and bioaccumulation potential raise red flags, guiding regulatory frameworks.