Environmental Health and Toxicology
Core concepts
Understand exposure pathways (ingestion, inhalation, dermal) and the dose-response relationship. Know toxicokinetics (absorption, distribution, metabolism, excretion) and the role of biotransformation-some agents are bioactivated (e.g., organophosphates require metabolic activation). Distinguish acute vs chronic toxicity and local vs systemic effects.
Know major toxicant classes: organophosphates/carbamates (cholinesterase inhibition), anticoagulant rodenticides (vitamin K antagonism), lead (neuro/hematologic), arsenic, mycotoxins (aflatoxin-hepatotoxic/carcinogenic; ergot; fumonisin), nitrate/nitrite (methemoglobinemia), cyanide, salt, and ionophores. Understand environmental fate (persistence, bioaccumulation, biomagnification) and risk assessment (hazard identification, dose-response, exposure assessment, risk characterization).
Traps
- Confusing bioaccumulation (within an organism) with biomagnification (up a food chain).
- Assuming a low-dose exposure is always safe-some agents are carcinogens without threshold assumptions.
- Mixing methemoglobinemia (nitrate/nitrite, chlorate) with cholinesterase inhibition.
- Forgetting species differences in metabolism (e.g., cats' limited glucuronidation).
Worked rule of thumb
Use the exposure equation: Risk ≈ (Hazard × Exposure). A highly toxic agent with no exposure poses no risk; a low-toxicity agent with high exposure can. For diagnostics, match clinical syndrome to likely toxicant: hemolysis/methemoglobinemia → nitrate; bleeding → anticoagulants; SLUDGE signs → organophosphates; neurologic signs → lead or organochlorines.
Example: Cattle grazing nitrate-accumulating forage develop methemoglobinemia; treat with methylene blue and reduce exposure.