RISK ASSESSMENT
Mandated by several laws including CERCLA, RCRA, SARA, FIFRA,
TSCA, SDWA
The determination of potential adverse effects of pollutants
is made through the process of risk assessment.
The steps of risk assessment generally include identification
of the hazard through testing, research, and observation; dose-response
assessment, the identification of the relationships between dose
and effect; exposure assessment, estimates of the intensity, frequency,
and duration of human exposure to a toxin; and, risk characterization,
the determination of the total health risk of exposure to a particular
toxin.
Each step in the process of risk assessment involves uncertainty,
extrapolation, and scientific judgments; thus, the results are
tentative and often debatable.
Identification of hazard - based on inherent properties
of substance
Chemical hazards
· Chemical/biochemical characteristics - structure activity
relationships (SAR)
more chlorine, more toxic
more rings in PAHs, more toxic
increasing Kow, more toxic
· Structure
· Solubility
· Vapor pressure
· Bioaccumulation
· Biotransformation
Kow - octanol-water partition coefficient
Koc - organic carbon partition coefficient
Kd - soil-water distribution coefficient
BCF - bioconcentration factor
H - Henry’s Law constant (volatility)
Dose-response assessment
Need to extrapolate data results into area not studied, other
organisms, normal concentrations versus lab concentrations
Problems occur with synergistic and antagonistic effects, sex
and age of population, genetic factors, species variability
Risk - likelihood of exposure
Exposure routes - need to consider magnitude, duration, frequency,
route
· Manufacture
· Use
· Disposal
· Transport in the environment
· Bioconcentration
Receptors
What group or environmental community is likely to be exposed?
Ways to Describe Exposure
• Point-of-Contact Analysis
• Scenario Evaluation
• Dose Reconstruction
• Integrative Assessment
Simplified Dose Calculation:
Calculation of Absorbed Dose From Potential Dose:
Potential Dose = C x IR x ED
AT x BW
Absorbed Dose = Potential Dose x AF
Where:
C = Contaminant Concentration IR = Intake Rate
ED = Exposure Duration AT = Averaging Time
BW = Body Weight AF = Fraction of Potential Dose Absorbed
Concentration (C), intake rate (IR), surface area (SA) and body
weight (BW) vary with time. Absorbed fraction is AF.
Example Problem
Calculate the lifetime average daily potential dose of PCBs that
a person would get from a daily average intake of 30 g of fish
containing 2.5 mg/kg of PCBs for 30 years.
Express potential dose in units of mg/kg-day (concern is cancer
risk).
A reference dose (RfD) is an estimate of daily exposure
to the human population (including sensitive subgroups) that is
likely to be without appreciable risk of deleterious effects during
a lifetime. The ratio of the site-specific dose estimate to the
RfD is called the hazard index (HI).
A reference concentration (RfC) is the estimated concentration
in a particular medium that is likely to be without an appreciable
risk of deleterious effects for the human population (including
sensitive subpopulations) during a lifetime; for RfC, the HI is
the air concentration divided by the RfC
Cancer risk range: Since it’s usually impossible (or
prohibitively expensive) to completely eliminate risk, EPA usually
tries to reduce cancer risks to the 10-4 - 10-6 range.
A slope factor is an upper-bound estimate of the slope
(for low doses) of the carcinogenic dose-response curve …
also known as potency factor
Table 4.1 Hill
Figure 4.2 Hill What does this figure imply? Is it true to end
at zero, zero?
Box 4.3 Hill
pg. 65-66
Exposure Standards and Guidelines Exposure standards and guidelines are developed by governments to protect the public from harmful substances and activities that can cause serious health problems
http://www.epa.gov/safewater/standard/setting.html
How does EPA set standards?
What are MCLs, MCLGs? treatment techniques
What is the difference bewteen primary and secondary standards?
http://www.tnrcc.state.tx.us/permitting/waterperm/pdw/pdw000.html
Texas Water Quality Standards
http://www.epa.gov/safewater/mcl.html
Federal Drinking Water Standards
Risk characterization: Acceptable risk - social statement
Risk management decisions require the integration of scientific
information with technical, legal, political, social, and economic
issues and concerns.
If thresholds exist, then theoretically some of the chemical would
be OK. This affects standard setting. Is any of the chemical acceptable.
What populations are at risk?
A good risk characterization will tell the reader what the
risks are and how important they are and the ideal risk characterization
will be:
Clear
Transparent
Reasonable
Consistent
RBDM/RBCA
Risk-based decision making
Risk-based corrective action
Comparative Risk Analysis
How shall we decide to spend available dollars?
What represents more of a risk?
Read pg: 71 in Hill Reilly's comments
Risk perception
homicide versus suicide
nuclear radiation versus smoking
airplanes versus cancer
Factors Influencing Risk Perception(Fischhoff et al. 1981)
People's perceptions of the magnitude of risk are influenced by
factors other than numerical data.
Risks perceived to be voluntary are more accepted than risks perceived
to be imposed.
Risks perceived to be under an individual's control are more accepted
than risks perceived to be controlled by others.
Risks perceived to be have clear benefits are more accepted than
risks perceived to have little or no benefit.
Risks perceived to be fairly distributed are more accepted than
risks perceived to be unfairly distributed.
Risks perceived to be natural are more accepted than risks perceived
to be manmade.
Risks perceived to be statistical are more accepted than risks
perceived to be catastrophic.
Risks perceived to be generated by a trusted source are more accepted
than risks perceived to be generated by an untrusted source.
Risks perceived to be familiar are more accepted than risks perceived
to be exotic.
Risks perceived to affect adults are more accepted than risks
perceived to affect children.
Table 4.2 Hill
Table 4.3 Hill
Review recommendations to EPA from SAB pg 73-75
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Group C:
Some people have stated that standards are a right to pollute, that no contamination above background should be allowable. What do you think about that? Question 5b on pg 70 asks essentially the same thing.
Due 2/3
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Group A:
Answer question 2 in Hill, p 69.
Due 2/5