EHPLE Public Health cheat sheet

Exposure = concentration × contact time; dose is the amount reaching a target organ after absorption, and internal dose is estimated by biomonitoring (blood, urine, hair, nails).

Exposure pathways: inhalation, ingestion, dermal absorption, and injection; the pathway with the highest medium-specific concentration and contact rate usually dominates total exposure.

Exposure factors (US EPA Exposure Factors Handbook): adult inhalation rate ≈ 13–16 m³/day, water ingestion ≈ 2 L/day, soil ingestion ≈ 50–100 mg/day for adults, higher for children.

Hazard quotient HQ = exposure dose ÷ reference dose (RfD); HQ > 1 indicates the exposure exceeds the RfD and warrants risk management review.

Cancer risk = dose × slope factor (SF) or inhalation unit risk (IUR); acceptable risk range commonly 1×10⁻⁶ to 1×10⁻⁴, with 1×10⁻⁶ as the point of departure for remediation decisions.

Bioaccumulation factor (BAF) = concentration in organism ÷ concentration in surrounding medium at steady state; biomagnification is the increase in tissue concentration across trophic levels.

Half-life governs persistence: t½ = ln(2)/k, where k is the first-order elimination or degradation rate constant; a chemical with t½ > 60 days is generally considered persistent.

Sensitivity analysis identifies which exposure variable (e.g., ingestion rate, exposure duration, concentration) drives most of the variance in the risk estimate; Monte Carlo simulation propagates distributions through the exposure model.

Reference dose (RfD) = NOAEL or BMDL divided by uncertainty factors (typically 10 for interspecies, 10 for intraspecies, plus database and LOAEL-to-NOAEL factors).

Incidence proportion = new cases ÷ population at risk during a period; incidence rate = new cases ÷ person-time at risk.

Prevalence = incidence × average duration of disease (when disease is in steady state); prevalence increases with longer survival even if incidence is unchanged.

Relative risk (RR) = incidence in exposed ÷ incidence in unexposed; attributable risk = incidence in exposed − incidence in unexposed; population attributable fraction = (incidence total − incidence unexposed) ÷ incidence total.

Odds ratio (OR) approximates RR when the disease is rare (<10% cumulative incidence); OR is the standard measure in case-control studies.

Surveillance types: passive (routine reporting by providers), active (health department solicits cases), sentinel (selected providers or sites), syndromic (pre-diagnostic symptom clusters) and laboratory-based.

Notifiable disease reporting timelines vary by jurisdiction; immediately reportable conditions (e.g., anthrax, botulism, cholera) require notification within hours, while others allow 1–7 days.

Outbreak investigation steps: verify diagnosis and establish case definition, confirm existence of outbreak, characterize by person/place/time, generate hypotheses, test hypotheses, implement control, communicate.

Sensitivity = true positives ÷ all diseased; specificity = true negatives ÷ all non-diseased; positive predictive value depends on prevalence and falls as prevalence falls.

Age adjustment (direct method) applies age-specific rates from the study population to a standard population; the standardized mortality ratio (SMR) = observed deaths ÷ expected deaths × 100.

Major US statutes: Clean Air Act (CAA), Clean Water Act (CWA), Safe Drinking Water Act (SDWA), Resource Conservation and Recovery Act (RCRA), Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA/Superfund), Toxic Substances Control Act (TSCA), Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), and Food Quality Protection Act (FQPA).

CAA National Ambient Air Quality Standards (NAAQS) cover six criteria pollutants: ozone, particulate matter, carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead; primary standards protect health, secondary standards protect welfare.

CWA regulates discharges to surface waters through National Pollutant Discharge Elimination System (NPDES) permits and sets technology-based effluent limits plus water quality-based limits where needed.

SDWA authorizes EPA to set National Primary Drinking Water Regulations (NPDWRs) as maximum contaminant levels (MCLs) or treatment techniques; states may be primacy agencies and may adopt stricter standards.

CERCLA establishes liability for release of hazardous substances and created the Superfund; the National Oil and Hazardous Substances Pollution Contingency Plan (NCP) governs response actions and the National Priorities List (NPL) ranks sites.

RCRA Subtitle C governs hazardous waste from cradle to grave (generation, transport, treatment, storage, disposal); Subtitle D governs non-hazardous solid waste.

FQPA of 1996 amended FIFRA and the Federal Food, Drug, and Cosmetic Act (FFDCA), requiring an additional 10× safety factor to protect infants and children and aggregate and cumulative risk assessments for pesticides with a common mechanism of toxicity.

TSCA regulates industrial chemicals; the 2016 Frank R. Lautenberg Chemical Safety for the 21st Century Act requires EPA to evaluate existing chemicals and makes safety findings without considering cost.

Regulatory takings and preemption: federal environmental statutes generally set floors, not ceilings, allowing states to impose more stringent requirements, except where Congress expressly preempts state law.

HACCP has seven principles: hazard analysis, determine critical control points (CCPs), establish critical limits, monitor CCPs, establish corrective actions, verify, and maintain records.

A critical control point is a step where control can be applied and is essential to prevent, eliminate, or reduce a food safety hazard to an acceptable level; critical limits must be measurable (e.g., 71.1°C for 15 seconds for poultry).

Biological hazards dominate foodborne illness: norovirus, nontyphoidal Salmonella, Clostridium perfringens, Campylobacter, and Staphylococcus aureus; STEC O157:H7 and Listeria monocytogenes cause severe outcomes.

Temperature danger zone is 4°C to 60°C (40°F to 140°F); perishable food should not remain in this range for more than 2 hours (1 hour when ambient temperature exceeds 32°C/90°F).

Dangerous bacterial toxins: botulinum toxin is heat-labile (destroyed by boiling ≥10 minutes), while Staphylococcus aureus enterotoxin and Bacillus cereus emetic toxin are heat-stable.

FATTOM summarizes microbial growth requirements: Food, Acidity (pH), Temperature, Time, Oxygen, and Moisture (water activity, aw); most bacteria require aw > 0.85 and pH near neutral.

Food defense and traceability: the US FDA Food Traceability Rule (FSMA 204) requires lot-level records for foods on the Food Traceability List; one-up/one-down traceability supports rapid recall.

Allergen control focuses on the nine major US allergens (milk, eggs, fish, crustacean shellfish, tree nuts, peanuts, wheat, soybeans, sesame) and requires cleaning validation to prevent cross-contact.

Wastewater treatment train: preliminary (screening, grit removal) → primary (settling, removes ~60% TSS) → secondary (biological, activated sludge or trickling filter, removes BOD and TSS) → tertiary (nutrient removal, filtration, disinfection).

BOD5 measures oxygen consumed by microorganisms over 5 days at 20°C; COD measures chemical oxidation and is always ≥ BOD; the BOD/COD ratio > 0.5 indicates readily biodegradable wastewater.

Typical secondary effluent limits: BOD5 and TSS 20–30 mg/L; disinfection by chlorination followed by dechlorination to protect aquatic life from residual chlorine.

Drinking water treatment: coagulation, flocculation, sedimentation, filtration, and disinfection; the multiple-barrier concept and the surface water treatment rule require 99.9% (3-log) Giardia and 99.99% (4-log) virus removal/inactivation.

Disinfection CT concept: CT = disinfectant residual concentration (mg/L) × contact time (minutes); required CT depends on disinfectant, pH, temperature, and target organism.

Disinfection byproducts (DBPs) such as trihalomethanes (THMs) and haloacetic acids (HAAs) form when chlorine reacts with natural organic matter; precursor removal before chlorination reduces DBP formation.

Eutrophication is driven by nitrogen and phosphorus; total phosphorus above roughly 0.02–0.05 mg/L in lakes often triggers algal blooms; wastewater nutrient limits are increasingly stringent.

Waterborne pathogens of concern include Cryptosporidium (chlorine-resistant, requires UV or ozone), Giardia, Legionella, and enteric viruses; coliforms and E. coli serve as indicator organisms.

Combined sewer overflows (CSOs) and sanitary sewer overflows (SSOs) discharge untreated sewage during wet weather; green infrastructure and storage reduce overflow volume.

PM2.5 penetrates deep into the alveoli and is the air pollutant most consistently associated with cardiopulmonary mortality; there is no established safe threshold.

Ozone forms photochemically from NOx and volatile organic compounds (VOCs) in sunlight; peak ozone occurs on hot, sunny afternoons downwind of emission sources.

Air Quality Index (AQI) categories: 0–50 good, 51–100 moderate, 101–150 unhealthy for sensitive groups, 151–200 unhealthy, 201–300 very unhealthy, 301–500 hazardous, based on the pollutant with the highest sub-index.

Indoor air pollutants include radon (second leading cause of lung cancer in the US after smoking), environmental tobacco smoke, combustion products (CO, NO2), volatile organic compounds, mold, and asbestos.

Radon action level is 4 pCi/L in the US; mitigation (sub-slab depressurization) is recommended at or above that level.

Carbon monoxide binds hemoglobin with ~200–250 times the affinity of oxygen, forming carboxyhemoglobin; symptoms include headache, dizziness, and nausea, and CO is odorless and colorless.

Risk assessment paradigm (NRC 1983): hazard identification, dose-response assessment, exposure assessment, and risk characterization; risk management and risk communication are separate steps.

Dose-response models: linearized multistage or benchmark dose for carcinogens, and threshold models with uncertainty factors for noncancer effects; the inhalation unit risk is expressed per µg/m³.

Air dispersion modeling (e.g., AERMOD) uses emission rates, meteorology, terrain, and stack parameters to estimate downwind concentrations for comparison with NAAQS and permit limits.

Core public health functions: assessment, policy development, and assurance; essential services include monitoring health status, diagnosing and investigating hazards, and enforcing laws.

Program planning frameworks: the 10 Essential Public Health Services, CDC's Program Evaluation Framework (engage stakeholders, describe the program, focus the evaluation, gather credible evidence, justify conclusions, ensure use), and logic models linking inputs, activities, outputs, outcomes.

SMART objectives are Specific, Measurable, Achievable, Relevant, and Time-bound; outcome objectives describe health status change while process objectives describe program activities.

Performance measures commonly include reach (proportion of target population served), fidelity, efficiency (cost per service), and equity (differences across subgroups).

Risk communication principles: be first, be right, be credible; acknowledge uncertainty; use plain language; tailor messages to audience risk perception and numeracy.

Outbreak or emergency incident command uses ICS with sections for operations, planning, logistics, and finance/administration; the incident action plan is updated each operational period.

Cost-effectiveness analysis compares cost per health outcome (e.g., cost per QALY or per case averted); a lower incremental cost-effectiveness ratio (ICER) indicates better value.

Quality improvement models (PDSA: Plan-Do-Study-Act) test small changes before scaling; accreditation (e.g., PHAB) uses standards and measures to document capacity and performance.

Ethics in environmental health practice include transparency, protection of vulnerable populations, community engagement, and avoidance of conflicts of interest in advisory and regulatory decisions.