Risk Assessment II
Dec 9, 2009
Is there a “safe” dose ?
For effects other than cancer:
Dose-Response
Dose
Increasing Response
0Threshold
Non-carcinogensNo
Observed
Adverse
Effects
Level
NOAEL
ACCEPTABLE DAILY INTAKE (ADI) or TOLERABLE DAILY INTAKE (TDI)
The amount of a substance that can be ingested over a lifetime without significant health risk
ADI = NOAEL Safety Factor(s)
Poor quality of data
Safety Factor = 10 x 10 [x 10] [x 10]Inter-speciesAnimal-to-human Intra-species Particularly
inter-individual severe effectvariability
Units: mg/kg/dayBased on most sensitive species and most sensitive end-point
Extrapolations
• From short-term studies to lifetime exposure
• From high doses in animal studies to low doses in environmental exposure
• From animals to humans
Scale from animal to human
• Scale according to body weight (BW)• Scale according to surface area – (BW)2/3
• Scale according to relative metabolic rates – (BW)3/4
• Biological modeling – physiologically-based (PBPK)
Variability • Inter-individual
variation in – Exposure– Metabolism– Repair capacity– Sensitivity– …
Uncertainty: Factors that we do not know or understand fully (yet)
• True magnitude of– Exposure– Metabolism– Repair capacity– Sensitivity
• How to extrapolate from test animals to humans, high to low doses…
• How to combine risks
Carcinogens: There exists a “measurable” risk from any exposure,
eg 4.1 x 10 -6 cancer risk for exposure to 1 μg/m3 of CH2Cl2 for a lifetime
Non-carcinogens: A “safe” dose can be determined
Pathogens: An “infectious dose” can be determined- ID50, , - Dose that produces 1 in 104 risk of infection
Each is considered in isolation
Approach has been chemical by chemical.Multiple chemical exposure requires combined risk assessment approach. Multiple sources of exposure need to be accounted for.
Combinations
• Binary mixtures• Ternary mixtures• Four- , five-component mixtures• Six, seven, eight….• ...• Complex mixtures
The Risk Cup• Food Quality Protection Act (1996)
– Amendment to Food Drugs and Cosmetics Act (1906, 1938)
• “Assess the risk of the pesticide chemical residue [to infants and children] based on…available information concerning the cumulative effects on infants and children of such residues and other substances that have a common mechanism of toxicity”
Interactions
• Additivity• Synergism• Potentiation• Antagonism
Interactions can be expected between chemicals that
• Act by binding to the same receptor• Act through the same mechanism• Require the same enzyme for
activation/detoxication
Additivity
• Chemicals A, B, C…N are all toxic• Potency of mixture = Sum of potencies *
concentrations of constituents
• Effecttotal = PotencyA * DoseA + PotencyB * DoseB + PotencyC * DoseC +…..+PotencyN * DoseN
Synergism
• The whole is greater than the sum of the individual constituents
Effecttotal >> PotencyA* DoseA + PotencyB* DoseB… +… + PotencyN* DoseN
Potentiation
• One constituent A is toxic, the other B is not.
• Effect of the combination A + B is greater than the effect of the active constituent
Effecttotal >> PotencyA* DoseA
where PotencyB = 0
Antagonism
• Effect of the whole is less than the sum of the effects of the individual components
Effecttotal << PotencyA* DoseA + PotencyB* DoseB… +… + PotencyN* DoseN
• Competing risks
Drinking water disinfectant by-products
↔ infectious diseases
Comparison of RisksDisabilityAdjustedLifeYears
One DALY = 1 lost year of healthy lifeDisability is weighted by a factor that reflects the severity of the disease on a scale from 0 (perfect health) to 1 (equivalent to death). WHO Global Burden of Disease analysis http://www.who.int/healthinfo/global_burden_disease/en/index.html
Some examples of weighing factors
• Asthma -- 0.043• Blindness – 0.600• Cancer: Liver – 0.20• Cancer: Trachea, bronchus and lung 0.15
– Metastatic 0.75• Cirrhosis of the liver - 0.330• Cleft palate - Cases 0.103• Diarrheal diseases - 0.105• Malaria - 0.191
USA, Both sexes, National Center for Health Statistics
Life expectancy at birth
Year of birth
Age at death
Year of birth
Age at death
1900 47.3 1980 73.71950 68.2 1990 75.4
1960 69.7 2000 77.0
1970 70.8 2005 77.82007 77.9