What is Risk ?
Risk = f(hazard, exposure)
Risk can be removed or reduced by one of the two parameters above.
It is better to remove risk by removing hazard.
However, it is not always possible and therefore, we need to manage the risk by managing exposure.
It is better to remove risk by removing hazard.
However, it is not always possible and therefore, we need to manage the risk by managing exposure.
Risk assessment is a process used to evaluate the potential health risks posed by exposure to hazardous substances, including both carcinogens (substances that can cause cancer) and non-carcinogens (substances that cause harm other than cancer). The process typically involves several steps: hazard identification, dose-response assessment, exposure assessment, and risk characterization. Here's how risk assessment differs between carcinogens and non-carcinogens:
Risk Assessment for Carcinogens
Risk Assessment for Carcinogens
- Hazard Identification: Identifies if a substance is potentially carcinogenic based on epidemiological studies, animal studies, and other relevant data.
- Dose-Response Assessment: For carcinogens, the assessment often assumes that there is no safe threshold, meaning any exposure could potentially lead to an increased risk of cancer. This approach is based on the linear no-threshold (LNT) model, which posits that the risk of cancer increases linearly with the dose of the carcinogen.
- Exposure Assessment: Estimates the magnitude, duration, and frequency of human exposures to the carcinogen.
- Risk Characterization: Combines the dose-response and exposure assessments to estimate the incremental risk of cancer from exposure to the carcinogen. This is often expressed as an excess lifetime cancer risk (ELCR), which represents the additional risk of developing cancer over a lifetime due to exposure.
- Hazard Identification: Determines whether a substance has the potential to cause harm other than cancer, such as neurotoxicity, liver damage, reproductive effects, etc.
- Dose-Response Assessment: For non-carcinogens, a threshold level is often identified below which no adverse effects are expected to occur. This leads to the establishment of reference doses (RfD) for oral exposure or reference concentrations (RfC) for inhalation, representing daily exposure levels that are unlikely to cause adverse health effects over a lifetime.
- Exposure Assessment: As with carcinogens, this step involves estimating the magnitude, duration, and frequency of human exposures to the non-carcinogen.
- Risk Characterization: Evaluates the potential for adverse health effects by comparing the estimated exposure level to the reference dose or concentration. This step often involves calculating a hazard quotient (HQ) or a hazard index (HI) for mixtures of substances, where an HQ or HI greater than 1 indicates a potential concern for health effects.
- Dose-Response Relationship: Carcinogens are often assessed with the assumption that no safe level of exposure exists (LNT model), while non-carcinogens are evaluated based on the presence of a threshold level below which no adverse effects are expected.
- Risk Characterization: For carcinogens, risk is typically quantified as an increased probability of cancer over a lifetime, while for non-carcinogens, risk assessment focuses on whether exposure levels are below safety thresholds to prevent non-cancer adverse health effects.
Chronic Daily Intake (CDI)
The CDI is a measure of the amount of a substance that a person is exposed to per day over an extended period, typically assumed to be a lifetime. The formula for calculating CDI depends on the route of exposure, such as ingestion, inhalation, or dermal absorption.
- Ingestion: CDIingest=C×IR×EF×ED/(BW×AT) Where:
- C = Concentration of the substance in water or food (mg/kg or mg/L)
- IR = Ingestion rate (kg/day for food, L/day for water)
- EF = Exposure frequency (days/year)
- ED = Exposure duration (years)
- BW = Body weight (kg)
- AT = Averaging time (days); for non-carcinogens, it's typically ED × 365, and for carcinogens, it's a lifetime (e.g., 75 years × 365 days/year)
- Inhalation: CDIinhale=C×IR×EF×ED/(BW×AT)
- C = Concentration in air (mg/m³)
- IR = Inhalation rate (m³/day)
- Dermal: CDIdermal=C×SA×AF×EF×ED/(BW×AT)
- C = Concentration on the skin surface (mg/cm² or mg/kg)
- SA = Skin surface area available for contact (cm²)
- AF = Absorption factor (unitless)
- For Carcinogens: Risk=CDI×SF
- SF = Slope factor (mg/kg/day)⁻¹; represents the probability of cancer per unit of exposure
- For Non-Carcinogens: HQ=CDI/RfD
- HQ = Hazard Quotient
- RfD = Reference Dose (mg/kg/day)
Incorporating these formulas and standard values into risk assessment processes allows for a more precise evaluation of potential health risks from exposure to carcinogenic and non-carcinogenic substances.
