Toxicology LOs

Define “Toxicology” according to SOT (Society of Toxicology):

Toxicology is defined by SOT as the study of the adverse effects of chemical, physical, or biological agents on living organisms and the ecosystem, including the prevention and treatment of such adverse effects.

Understand how toxins can affect human systems:

Toxins can affect the human body in multiple ways depending on:

• Type of toxin (e.g., neurotoxins, carcinogens, teratogens, immune system depressants).

• Dose – “The dose makes the poison” (Paracelsus).

• Route of exposure – Inhalation, ingestion, dermal contact.

• Bioaccumulation – Toxins build up in tissues over time.

• Biomagnification – Toxins become more concentrated as they move up the food chain.

• Persistence – Some chemicals like PCBs and DDT have long biological half-lives, causing prolonged exposure.

Be familiar with ATSDR’s top toxic substances and their sources:

According to the Agency for Toxic Substances & Disease Registry (ATSDR):

• Their Substance Priority List is updated every 2 years.

• Top toxic offenders include:

  • Metals (e.g., arsenic, lead, mercury).

  • Untreated wood.

  • Mercury amalgam fillings.

  • Industrial chemicals like benzene.

  • Persistent organic pollutants (e.g., PCBs, DDT).

Appraise the use of animal models in measuring toxicity:

Animal models (e.g., mice) are widely used due to cost, time, and ethical constraints.

Limitations include:

Evolutionary distance: Humans and mice are separated by ~80 million years, so results may not always translate directly.

Difficult to compare toxicity across species or between unrelated chemicals.

Interpret Ames test results:

Purpose: Tests if a substance is mutagenic (can cause genetic mutations).

• Uses His⁻ Salmonella (can't grow on histidine-free media unless a mutation restores the gene).

• A revertant regains the ability to synthesize histidine (i.e., becomes wild-type).

• Interpretation:

  • Plate with few colonies (~5) = Negative control (no mutagenicity).

  • Plate with many colonies (~300) = Positive result; chemical is likely mutagenic.

Interpret dose-response curves and LD50 values:

• Dose-response curve shows how the magnitude of exposure relates to the severity of toxic effects.

• LD₅₀ (Lethal Dose for 50%): The dose at which 50% of test subjects die.

  • Lower LD₅₀ = Higher toxicity.

  • Used for comparing acute toxicity.

Compare voluntary and involuntary risks:

• Voluntary risks: Risks we choose to take (e.g., smoking, skydiving).

• Involuntary risks: Risks we are exposed to without consent (e.g., pollution, secondhand smoke).

• Risk perception differs: People are less tolerant of involuntary risks, even if the actual risk is lower.

Interpret lifetime odds of death tables:

• These tables show the probability of dying from various causes (e.g., heart disease, car accidents).

• Helps contextualize risk.

• Important in public health decision-making and risk communication.

Classify reasons for the emergence of emerging infectious diseases globally:

Emerging infectious diseases arise due to:

• Globalization and travel.

• Urbanization and overcrowding.

• Climate change.

• Disruption of ecosystems.

• Antibiotic misuse.

• Zoonotic transmission (e.g., SARS, Ebola).

Identify the causative agent, vector (when relevant), transmission, and epidemiology of selected emerging infectious diseases:

• Zika Virus

  • Agent: Zika virus

  • Vector: Aedes mosquito

  • Transmission: Mosquito bite, sexual contact, mother-to-child

  • Epidemiology: Outbreaks in South America, Caribbean

• Ebola Virus

  • Agent: Ebola virus

  • Vector: Bats (reservoir); no true arthropod vector

  • Transmission: Body fluids

  • Epidemiology: West Africa outbreaks, high mortality

• COVID-19 (SARS-CoV-2)

  • Agent: Coronavirus SARS-CoV-2

  • Transmission: Airborne droplets, surface contact

  • Epidemiology: Global pandemic starting in 2019

Show two mechanisms for the acquisition of antibiotic resistance genes in bacteria:

• Conjugation – Transfer of plasmids carrying resistance genes via direct contact.

• Transformation – Uptake of free DNA fragments from the environment.

• (Bonus) Transduction – Transfer of genes via bacteriophages (viruses that infect bacteria).