Environmental Health, Safety, and Risk Assessment
Core concepts
Risk assessment has four steps: hazard identification, dose–response, exposure assessment, and risk characterization. For noncarcinogens, compare chronic daily intake (CDI) with the reference dose (RfD) to get hazard quotient; HQ > 1 signals concern. For carcinogens, multiply CDI by the slope factor (SF) or unit risk; acceptable risk is often 10^-6 to 10^-4. Know exposure factors (body weight, intake rate, exposure frequency/duration, averaging time), units (mg/kg-day), and routes (ingestion, inhalation, dermal). Occupational health adds OSHA PELs (8-hr TWA), STELs, ceilings, NIOSH RELs, IDLH, and controls: elimination/substitution, engineering, administrative, PPE. Safety topics include confined spaces, LOTO, HAZWOPER, respiratory protection, noise, heat stress, and emergency response. Toxicology concepts include LD50/LC50, uncertainty factors, and bioaccumulation. Document assumptions and use conservative default factors when site-specific data are lacking. Risk is not the same as hazard.
Worked example
C = 0.01 mg/L, IR = 2 L/day, EF = 350 d/yr, ED = 30 yr, BW = 70 kg, AT = 70×365 d. CDI = (0.01×2×350×30)/(70×25,550) = 1.17×10^-4 mg/kg-day. With SF = 1.5 (mg/kg-day)^-1, cancer risk = 1.76×10^-4. Trap: use lifetime averaging for carcinogens but exposure-period averaging for noncarcinogens.
Rule of thumb
For a quick screen, risk ≈ intake × potency; HQ ≈ intake ÷ RfD. If either exceeds its target, refine assumptions before concluding.