Aflatoxin Risk Assessment

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Aflatoxin Risk Assessment Red Book Model
Exercise

• Charles Yoe, Ph.D.
• College of Notre Dame of Maryland

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Risk Analysis

Risk Management
Risk Assessment
Risk Communication
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Risk Assessment

• What can go wrong?
• How can it happen?
• How likely is it?
• What is the magnitude of the effect?

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What are the steps?

• CODEX
• Hazard identification
• Hazard characterization
• Exposure assessment
• Risk characterization

• NAS
• Hazard identification
• Dose-response assessment
• Exposure assessment
• Risk characterization

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Risk Assessment CODEX

• Hazard Identification
• The identification of known or potential health
  effects associated with a particular agent.
• Hazard Characterization
• The qualitative and/or quantitative evaluation of
  the nature of the adverse effects associated with
  biological, chemical, and physical agents which
  may be present in food. Dose-response
  assessments should be performed if the data are
  available.

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Risk Assessment CODEX

• Exposure Assessment
• The qualitative and/or quantitative evaluation of
  the degree of intake likely to occur.
• Risk Characterization
• Integration of hazard identification, hazard
  characterization and exposure assessment into an
  estimation of the adverse effects likely to occur
  in a given population, including attendant
  uncertainties.

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Risk Assessment NAS

• Hazard Identification
• Determine if exposure to an agent causes an
  increased incidence of an adverse health effect.
• Dose-Response Assessment
• Characterize the relationship between exposure
  (at different levels or doses) and the incidence
  of the adverse health effect.

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Risk Assessment NAS

• Exposure Assessment
• Measure or estimate the intensity, frequency, and
  duration of actual or hypothetical exposures of
  humans to the identified agent
• Risk Characterization
• estimate the probability of specific harm to an
  exposed individual or population based on
  information from dose-response and exposure
  assessments.

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Turkey X Disease

• 1960 1000s turkey poults died in England
• Major investigation
• Turkeys poisoned by agent in peanut meal
  component of their feed
• Agent found in peanuts contaminated with certain
  mold
• Mold, Aspergillus flavus, not responsible for
  poisoning

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Turkey X Disease

• 1965 MIT team solved mystery of turkey X
• Aflatoxin discovered

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Mycotoxins

• No awareness of mold-related disease before 1960s
• Imported peanut meal killed 1000s of turkeys in
  England 1960s
• The mold Aspergillus flavus produced toxins that
  fluoresced under analysis
• aflatoxin blue (AFB)
• aflatoxin green (AFG)
• Over 100 mycotoxins identified since aflatoxin

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Molds and Mycotoxins

• Considerable worldwide significance
• Public health
• Agriculture
• Economics
• Aflatoxin cost 20M to US peanut crop 1989
• Foods that are ground present particular problems

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What do we know about aflatoxin?
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Aflatoxin

• Mixture of 4 closely related chemicals
• Two emit blue fluorescence B1 B2
• Two emit green fluorescence G1 G2
• Research showed them regularly
• peanuts some peanut products
• corn
• nuts
• Fed to animals can show up in derived food
  products

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Aflatoxin

• Experimental studies showed
• potent liver poison
• malignant tumors in rats, ferrets, guinea pigs,
  mice, monkeys, sheep, ducks, trout
• Results reported 1961-1976
• Low level but not infrequent contaminant of some
  human foods

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Some Questions About Aflatoxin

• What is to be done?
• Are aflatoxins a threat to public health?
• How many cancers can be attributed to them?
• Why is there no clear link to human cancers?
• If a menace, how can we control it?
• How much of our resources is this worth?

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Aflatoxicosis

• Poisoning from mold-produced metabolites
• Affects all tested species and humans
• Occurs when food supplies are limited and people
  ate moldy grains
• Flabby heart, edema, abdominal pain, liver
  necrosis, palpable liver
• Chronic ingestion--liver tumors

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FDA and Aflatoxin

• Decided limits were in order, based on what could
  be detected
• 1968 gt30 ppb in peanut products unfit
• Lowered to 20 ppb soon after
• No completely safe level can be established for
  cancer causing chemicals
• Does this mean as science gets better food
  becomes less safe?

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FDA and Aflatoxin

• Meeting 20 ppb not too great a burden on peanut
  butter industry
• discolored peanuts could be eliminated by sorting
  machines
• required substantial new quality control measures
• Did this make scientific sense?
• If aflatoxin can be detected it is unacceptable
  if it cannot it is acceptable

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Yes

• Potent cancer causing agent in animals
• Do not wait for human data to control it
• Animal tests are reliable indicators of human
  risk
• Risky at any level of intake
• Eliminate human exposure or reduce it to lowest
  possible level

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No

• Animal cancers occur at levels well above FDA
  limit
• Provide some safety to humans but 20 ppb is too
  low
• Policy of no safe level is not supported by
  science
• Animals not proven reliable indicators of human
  risk
• Carcinogenic potency highly variable among
  species
• No evidence of cancer in humans

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FDA and Aflatoxin

• Easy to detect 5ppb in some labs
• 1 ppb almost routine in some labs
• FDA did not call for these lower limits
• Large fraction of peanut butter would fail 1 ppb
  standard
• Economic impact of 1ppb could be very large

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Detection

• Analytical chemists can now measure levels
  toxicologists are unable to evaluate for
  biological significance
• 1 ppm is like a second in 11.6 days
• 1 ppb is a second in 32 years
• 1 ppt is a second in 3,169 years

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ppb

• Weight of contaminant divided by weight of food
• In kg of peanut butter, 20 ppb is 20 micrograms

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Aflatoxin Occurrence 1989
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A Few More Points

• Corn responsible for most human exposure
• Peanuts and peanut butter in US
• Drought and other damage encourage mold
• Heat not enough to destroy mycotoxin
• Processing not effective in destroying mycotoxins
• Preventing formation is crucial

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Aflatoxin and Peanuts

• Average concentration in peanuts and peanut
  butter is 2 ppb
• FDA defect action level (DAL) to seize peanuts is
  20 ppb
• In practice anything over 15 ppb is rejected
• Average daily intake estimate is 0.005 ppb from
  peanuts

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Science and Economics

• Just how certain is our science on matters like
  this?
• Size of economic consequence should not influence
  scientific thinking, but it influences scientists
  and policy makers when there are scientific
  uncertainties

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Aflatoxin Management Options

• Constant testing
• more in drought years
• Seize contaminated crops
• Destroy contaminated crop residues
• Agricultural techniques
• forced air drying of crops
• controlled storage conditions
• Minimize exposure to moldy foods

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Lets look at a CODEX/NAS risk assessment
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Hazard Identification

• Evolving understanding
• Turkey X
• JECFA 1987
• JECFA 1997

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JECFA 1987

• Evaluated at 31st meeting of JECFA 1987
• Considered potential human carcinogen
• Insufficient information to set tolerable intake
  level
• Urge reduction to lowest practicable level

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JECFA 1997

• One of most potent mutagenic and carcinogenic
  substances known
• Liver cancer in most species
• Some evidence humans are at lower risk than other
  species
• Epidemiological studies show no detectable
  independent risk
• Ongoing studies--Shanghai, Thailand, Qidong

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JECFA 1997

• Hepatitis B virus may increase liver cancer risk
• Estimated 50 to 100 of liver cancers are
  associated with Hepatitis B

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What is the hazard?
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Hazard Identification

• The Committee considered that the weight of
  scientific evidence, which includes
  epidemiological data, laboratory animal studies
  in vivo and in vitro metabolism studies, supports
  a conclusion that aflatoxins should be treated as
  carcinogenic food contaminants, the intake of
  which should be reduced to levels as low as
  reasonably achievable
• Source JECFA 1997

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Hazard Characterization

• We will use a simple dose-response analysis
• This makes the two models, CODEX and NAS
  essentially equivalent

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Aflatoxin Toxicity

• B1 (AFB1) most common, most studied, most toxic
• Toxicity varies by species
• LD50 .5 mg/kg for duckling
• LD50 60 mg/kg for mouse
• Binds to nucleic acids in some species
• Difficult to assess for humans
• Death usually from liver damage

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Dose-Response Analysis

• Limitations of available aflatoxin data
• Confounded by concurrent Hepatitis B
• Reliability precision of aflatoxin exposure in
  study population are unknown
• Shape of dose-response relationship unknown

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Sources of Information

• Animal bioassays
• Human feeding trials
• Epidemiological data
• Cell lines (tissue cultures)
• Animal studies most common for cancers

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Animal Studies

• Relatively high dose to relatively few animals
• Absence of data in low dose region
• Which mathematical model best approximates
  dose-response in low dose region
• Fit data that exists
• Linear extrapolation to zero from fitted curve or
  95 confidence interval

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Dose Response Linear Interpolation
Upper Confidence Limit
Actual Data
Excess Tumor Rate
Alternative Extrapolations
Estimated Dose Response
Linear Extrapolation
Dosage
Experimental Range
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Low Dose Response

• Threshold/No threshold assumption is
  significant
• Many mathematical models possible
• Determines potency estimate
• Does not rely on safety factors

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Dose-Response

• Potential biases in potency
• Only studies with association were used
• Historical levels ignored in favor of current
  levels of intake
• Hepatitis B prevalence systematically
  underestimated in early studies
• Non-primary liver cancers may have been included
• Interpolation method

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Dose-Response

• Population risks
• Vary from population to population
• Geographically
• Culturally--diet
• Susceptibility--base health

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Dose Response Factors

• Diet also affects toxicity
• Human response variable
• males and children more susceptible
• Hepatitis B increases cancer risk

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Potency Values

• HbsAg
• 0.3 cancers/year per 100,000 population per ng
  aflatoxin/kg bw per day
• Uncertainty range 0.05 to 0.5

• HBsAg-
• 0.01 cancers/year per 100,000 population per ng
  aflatoxin/kg bw per day
• Uncertainty range 0.002 to 0.03

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Exposure Assessment

• Estimating frequency and intensity of exposure to
  agent
• Magnitude, duration, schedule and route of
  exposure
• Size, nature and class of exposed population
• Detailing associated uncertainties

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Aflatoxin Exposure Assessment

• Contamination levels data appear biased
• Studies focus on commodity lots thought
  contaminated
• Contamination levels must be used with caution
  for patterns of importance not exact
  contamination estimates

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CDF Aflatoxin in US Maize
Contamination (µg/kg)
Cumulative density
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Hypothetical Standards

• Assume 20 µg/kg rejection level
• 4 maize crop rejected
• mean aflatoxin level of 0.91 µg/kg
• Assume 10 µg/kg rejection level
• 6.2 maize crop rejected
• mean aflatoxin level of 0.58 µg/kg
• Standards remove most highly contaminated ,
  reducing average

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Risk Characterization

• Combine dose-response and exposure assessments
• Describe risk in meaningful and useful fashion

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Cancer Incidence

• Combine
• Aflatoxin potency estimates (risk per unit dose)
• Dose response
• Estimates of aflatoxin intake (dose per person)
• Exposure
• What are the uncertainties in these analyses?

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Lets do a simple risk assessment.
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Sample Data and Assumptions

• Assume
• Low contamination of food
• Small prevalence of hepatitis B (1 carriers)
• Potency .3 with HBSAG
• Potency .01 with HBSAG-
• European diet intake 19 ng/person per day
• Adult human weighs 60 kg
• Population of 30 million

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Aflatoxin Risk Assessment

• 1) Calculate estimated population potency
• a) What is potency for HBSAG?
• b) What is of HBSAG?
• c) What is potency for HBSAG-?
• d) What is of HBSAG-?
• e) ab cd population potency

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Aflatoxin Risk Assessment

• 2) Calculate intake per kg bw
• a) What is intake per person?
• b) What is weight of a person?
• c) a/b
• 3) Calculate increased cancer rate due to
  aflatoxin
• a) 1e x 2c

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Aflatoxin Risk Assessment

• 4) Calculate increased number of cancers
• a) What is cancer rate?
• b) What is population
• c) ab
• 5) Repeat calculations for uncertain range of
  potency

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Calculate Cancers per Year

• 0.01 x 99 0.03 x 1 0.013 cancers/year per
  100,000 population per ng aflatoxin/kg bw per day
• Range in cancer deaths is 0.002 to 0.035
• 19 ng/person per day ? 60 kg bw per person
  .317 ng/kg bw per day
• .317 ng/kg bw per day x 0.013 cancers/year per
  100,000 population per ng aflatoxin/kg bw per day
  0.0041 cancers/year per 100,000 people

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Calculate Cancers per Year

• 30,000,000 people x 0.0041 cancers/year per
  100,000 people 1.23 cancers/year

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Risk Assessment Model

• Which steps were hazard identification?
• Which steps were dose-response assessment?
• Which steps were exposure assessment?
• Which steps were risk characterization?

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Model Comparison

• Food safety vs... CODEX/NAS Model
• Did food safety have four steps?
• What were major differences?
• What were similarities?
• Which was easier? Why?
• Which do you prefer? Why?

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Lets see how we can address the uncertainty in a
model like this.
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Whats Next?

• Once the risk has been assessed
• Risk management decides what to do about it
• Risk Communication
• The risk is described to others
• Management options are explained

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The End