Module 6 -ENCI 481

Risk

The probability of an adverse effect occurring within a given time period

Difference between risk and hazard

Hazard is the potential to cause harm risk combines probability and consequence

Risk perception

How individuals subjectively view risk often differing from scientific assessment

Factors influencing risk perception

Voluntariness control familiarity dread visibility and knowledge

Acceptable risk level

A commonly accepted benchmark of approximately 1 in 1 million per year

De minimis risk

Very small risk generally considered negligible typically 10^-6

Exposure

Contact between a chemical and a receptor

Dose

Amount of a chemical that actually enters the body and reaches target organs

Exposure vs dose

Exposure is encountered amount dose is absorbed amount

Acute health effects

Short term effects from brief exposure

Chronic health effects

Long term effects from prolonged exposure

Sub chronic effects

Effects from intermediate duration exposure

Main components of human health risk assessment

Hazard assessment exposure assessment and risk characterization

Hazard assessment

Evaluation of the toxic properties of a chemical

Exposure assessment

Estimation of how much of a chemical reaches a receptor

Risk characterization

Integration of hazard and exposure to estimate risk

Carcinogens

Chemicals assumed to have no safe exposure threshold

Non carcinogens

Chemicals assumed to have a safe exposure threshold

Cancer slope factor SF

Parameter used to estimate cancer risk per unit intake

Reference dose RfD

Estimated daily exposure likely to be without appreciable risk over a lifetime

NOAEL

No observed adverse effect level

LOAEL

Lowest observed adverse effect level

RfD calculation

RfD equals NOAEL divided by uncertainty and modifying factors

Uncertainty factor UF

Factor accounting for variability and uncertainty in toxicity data

Exposure intake equation

Intake equals C times IR times EF times ED divided by BW times AT

C in intake equation

Chemical concentration

IR in intake equation

Ingestion rate

EF in intake equation

Exposure frequency

ED in intake equation

Exposure duration

BW in intake equation

Body weight

AT in intake equation

Averaging time

Averaging time for non carcinogens

Exposure duration times 365 days

Averaging time for carcinogens

70 years times 365 days

Hazard quotient HQ

HQ equals intake divided by RfD

Acceptable non carcinogenic risk

HQ less than 1

Hazard index HI

Sum of hazard quotients for multiple non carcinogenic chemicals

Acceptable hazard index

HI less than 1

Lifetime average daily dose LADD

Average daily intake over a lifetime used for cancer risk

Cancer risk equation

Cancer risk equals LADD times slope factor

Individual excess lifetime cancer risk IELCR

Probability of developing cancer due to exposure

Total cancer risk CTR

Sum of cancer risks from multiple carcinogens

Acceptable cancer risk range

Between 10^-6 and 10^-4

Risk based screening level RBSL

Maximum allowable concentration for a target risk

How RBSL is calculated

By rearranging the intake equation for concentration

Key difference carcinogenic vs non carcinogenic risk

Carcinogens use slope factors non carcinogens use RfDs

Key decision criteria for water acceptability

HQ less than 1 and cancer risk within acceptable range

Why risk assessment focuses on extremes

Protects sensitive populations and worst case exposures

Why risk perception matters

Public acceptance influences policy and project approval