Aflatoxin Risk Assessment “Red Book” Model Exercise

1. Aflatoxin Risk Assessment “Red Book” Model Exercise Charles Yoe, Ph.D. College of Notre Dame of Maryland

2. Risk Analysis Risk Management Risk Assessment Risk Communication

3. Risk Assessment • What can go wrong? • How can it happen? • How likely is it? • What is the magnitude of the effect?

4. CODEX Hazard identification Hazard characterization Exposure assessment Risk characterization NAS Hazard identification Dose-response assessment Exposure assessment Risk characterization What are the steps?

5. 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.

6. 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.

7. 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.

8. 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.

9. Turkey X Disease • 1960 1000’s 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

10. Turkey X Disease • 1965 MIT team solved mystery of turkey X • Aflatoxin discovered

11. 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

12. 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

13. What do we know about aflatoxin?

14. 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

15. 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

16. 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?

17. 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

18. FDA and Aflatoxin • Decided limits were in order, based on what could be detected • 1968 >30 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?

19. 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

20. 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

21. 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

22. 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

23. 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

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

25. Aflatoxin Occurrence 1989

26. 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

27. 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

28. 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

29. 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

30. Let’s look at a CODEX/NAS risk assessment

31. Hazard Identification • Evolving understanding • Turkey X • JECFA 1987 • JECFA 1997

32. 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

33. 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

34. JECFA 1997 • Hepatitis B virus may increase liver cancer risk • Estimated 50 to 100% of liver cancers are associated with Hepatitis B

35. What is the hazard?

36. 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

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

38. 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

39. 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

40. Sources of Information • Animal bioassays • Human feeding trials • Epidemiological data • Cell lines (tissue cultures) • Animal studies most common for cancers

41. 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

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

43. Low Dose Response • “Threshold/No threshold” assumption is significant • Many mathematical models possible • Determines potency estimate • Does not rely on safety factors

44. 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

45. Dose-Response • Population risks • Vary from population to population • Geographically • Culturally--diet • Susceptibility--base health

46. Dose Response Factors • Diet also affects toxicity • Human response variable • males and children more susceptible • Hepatitis B increases cancer risk

47. 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 Potency Values

48. 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

49. 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

50. CDF Aflatoxin in US Maize Contamination (µg/kg) Cumulative density