Environmental Health
Exam focus
Links between environmental exposures and human health, disease pathways, toxicology basics and health-based standards.
Core rules
- Waterborne diseases: cholera (Vibrio cholerae), typhoid (Salmonella typhi), hepatitis A and dysentery; indicators include E. coli and coliforms.
- Vector-borne diseases: malaria (Anopheles), dengue and chikungunya (Aedes aegypti); control targets breeding sites and the vector.
- Air pollution: PM₂.₅ penetrates alveoli and enters the blood; it is linked to asthma, COPD and cardiovascular disease. CO binds haemoglobin.
- Bioaccumulation is build-up within an organism; biomagnification is increasing concentration along a food chain. Fat-soluble, persistent substances such as DDT and methylmercury magnify.
- Toxicology: dose-response, LD₅₀ (lower means more toxic), threshold effects, carcinogens and endocrine disruptors.
- Occupational exposure limits and WHO air quality guidelines are health-based.
Worked example
Water contains 0.001 mg/L of a pesticide. Algae concentrate it 100× to 0.1 mg/kg. Small fish concentrate 10× to 1 mg/kg. Large fish concentrate 10× to 10 mg/kg. A human eating the large fish receives 10 mg/kg. Biomagnification multiplies at each trophic step for persistent lipophilic chemicals.
Traps
- Confusing bioaccumulation with biomagnification.
- Saying dengue is waterborne; it is vector-borne.
- Assuming all pollutants biomagnify; only persistent, fat-soluble ones do.
- Treating LD₅₀ as the safe dose rather than a lethality statistic.