Toxicology and Risk of Nitrate and Nitrite

1. Historical Aspects of the Toxicology and
Risk Assessment of Nitrate and Nitrite
James R. Coughlin, PhD CFS
President, Coughlin & Associates
Aliso Viejo, California USA
jrcoughlin@cox.net
www.linkedin.com/in/jamescoughlin
Symposium: Is It Time to Change the
Paradigm for Food Toxicology?
Nitrate as a Case Study
IFT Annual Meeting, Chicago
July 17, 2018

2. Presentation Outline
 Nitrite / Nitrate and Methemoglobenimia (1940’s - )
 Carcinogenicity -
 N-nitroso compounds (1956 - )
 Nitrite per se (1979 - )
 IARC Classifications –
 Ingested Nitrate and Nitrite (June 2006, 2010)
 Nitrite-processed Meat (October 2015, 2018)
 U.S. National Toxicology Program – NTP Report on Carcinogens (Sept 2016 - )
 California Proposition 65 Battles over Nitrite (1998 - )
 WCRF / AICR – Processed Meat and Human Colorectal Cancer (2007, 2018)
 Introduction to “Benefit-Risk” Evaluation & Acceptable Daily Intake (ADI)
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3. Safety and Regulatory History of Nitrite / Nitrate -
Methemoglobenimia (MHG)
 Mechanism:
 ~ 5% of ingested nitrate is converted to nitrite in vivo
 Nitrite can bind to ferrous (Fe++) hemoglobin to form ferric (Fe+++)
hemoglobin (methemoglobin) and nitric oxide
 Because methemoglobin cannot transport oxygen, normal oxygen
transport can be altered, resulting in toxicity
 Data from the 1940’s-1950’s document that high doses of nitrate, usually in
contaminated well water, were associated with occurrence of MHG in infants
& very young children
 More recent studies have lessened this concern, because the earlier
studies were confounded by gastroenteritis and altered
pharmacokinetics in infants
 Studies support the absence of MHG in older children and adults, but
some sensitive infants may still be of concern.
ATSDR, 2015
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4. N-Nitrosamine Carcinogenicity Concerns
Began with Rodents in 1956
~
My PhD/Post-doc research on N-Nitrosamines
formed in the “Maillard Browning Reaction”
began in 1974 at UC Davis
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8. National Academy of Sciences’ Expert Reviews
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11. International Agency for Research on Cancer (IARC)
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Evaluation of “Ingested Nitrate and Nitrite” - June 2006
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Evaluation of Red and Processed Meat - October 2015
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12. IARC Monograph No. 94 (2010) on “Ingested Nitrate and
Nitrite”
[Meeting held in June 2006, I served as Observer for American Meat Institute]
Conclusions:
 Inadequate evidence in humans for the carcinogenicity of nitrate in
food and drinking water.
 Limited evidence in humans for the carcinogenicity of nitrite in food
[stomach cancer endpoint based on epidemiology].
 Limited evidence in experimental animals for the carcinogenicity of
nitrite per se [totally unfounded after NTP bioassay conclusions!].
 Overall Evaluation - Group 2A - “Ingested nitrate or nitrite under
conditions that result in endogenous nitrosation is probably
carcinogenic to humans.”
Note: IARC Monograph Director desperately fought for processed meat
to be classified in this meeting, but the Working Group did not agree.
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15. IARC: Red & Processed Meat Decisions (Oct. 2015)
 22 invited scientists on Working Group; 8 global meat industry Observers were
silenced!; 8 days of deliberations; 18 meat industry written submissions not shared
with WG; conclusions published two weeks later in Lancet Oncology (Oct. 2015)
 RED MEAT: [No “Sufficient Evidence” = No Calif. Prop 65 listing is expected]
 Group 2A, “Probable Human Carcinogen”
 “Limited Evidence” in humans, colorectal cancer only
 “Inadequate Evidence” in animals
 Mechanistic considerations worsened classification from Group 3 to Group 2A
 PROCESSED MEAT: [Will eventually be listed by Calif. Prop 65]
 Group 1, “Human Carcinogen”
 “Sufficient Evidence” in humans for colorectal cancer only;
Relative Risk =1.18; but barely statistically significant, fuller published meta-
analysis showed no increased risk; IARC excluded some epi studies
 “Inadequate Evidence” in animals
 Mechanistic considerations worsened classification from Group 2B to Group 1.
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17. NTP’s Report on Carcinogens Considers Listing of
Red & Processed Meats (September 2016)
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18. California Proposition 65
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Nitrite “Battles” raging since 1998 on…
- Reproductive / Developmental Toxicity
- Carcinogenicity
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19. Proposition 65 - Sodium Nitrite Reprotox Listing Challenge
 April - June 1998 – OEHHA requested information on 15 chemicals,
including nitrite, for potential listing as developmental toxicants under the
AB mechanism, based on EPA’s Toxic Release Inventory; American Meat
Institute (AMI) submitted written comments to OEHHA
 December 1998 – OEHHA published “Notice of Intent to List” Nitrite
 February - May 1999 – AMI coalition submitted comments objecting to
nitrite’s listing on scientific grounds, and OEHHA agreed that the
scientific criteria for listing had not been met; but OEHHA passed the
listing decision to the DART Identification Committee (8 scientists)
 July - Sept 1999 – AMI coalition submitted written comments to DART
Committee objecting to listing
 June 2000 – DART Committee voted NOT to list sodium nitrite as a
reproductive or developmental toxicant
 Listing could have meant birth defects warnings on packages of bacon,
ham, hot dogs, etc.
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20. “Nitrite in Combination with Amines or Amides” –
Proposition 65 Carcinogen Listing Challenge
 IARC Monograph No. 94 (2010) on “Ingested Nitrite and Nitrate”
classified as Group 2A “probably carcinogenic” due to Endogenous
Nitrosation
 “Nitrite in Combination with Amines or Amides” – the only
“sufficient evidence” finding
 American Meat Institute and Grocery Manufacturers Association
submitted comments objecting to this “Authoritative Bodies” (AB)
listing in May 2014
 After consideration of our comments, the state determined that the
regulatory criteria for automatic AB listing had not been met
 But the state notified us in May 2015 that they would ask the
Carcinogen Identification Committee (CIC) to consider this for listing
 The CIC voted unanimously November 2016 not to list, agreeing with
our industry comments, another victory.
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21. American Institute for Cancer Research / World Cancer
Research Foundation – Processed Meats and Colorectal Cancer
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23. Acceptable Daily Intake for Nitrate (ADI)
WHO/FAO JECFA -
 ADI of 0-3.7 mg nitrate/kg bw for nitrate set in 1974, reconfirmed in
1995 & 2002, based on studies of sodium nitrate fed orally to rats &
dogs; no carcinogenic effects
 Concluded that public health risk is negligible when intake is below
this ADI
 ADI is equivalent to ~ 222 mg nitrate ion/day for a 60 kg individual
U.S. EPA Reference Dose (RfD) – similar to an ADI -
 EPA chose a different data set to estimate their RfD
 Used very old human case studies of methemoglobinemia in infants
and young children; poor anecdotal studies, confounders like
gastritis
 In 1991, established chronic oral RfD for noncarcinogenic effects =
1.6 mg nitrate-nitrogen/kg bw-day, or 7 mg nitrate/kg bw-day, and
has not revised the RfD since, but it is now under review.
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24. Summary and Conclusions
 Potential hazards of Nitrite and Nitrate exposure have been extensively
evaluated by many regulatory agencies and public health bodies for decades
 Nitrate is not a carcinogen and is associated with an overall low level of
toxicity…it’s been Nitrite that has gotten all the attention
 Nitrite per se is not a carcinogen in animals or man
 Yes, nitrite does react to form carcinogenic N-nitroso compounds in foods and
in the human body, but at levels much too low to induce cancer risk in humans
 Processed meats have been tortured with barely-statistically significant
epidemiologic findings [colorectal cancer only] and unproven mechanistic
hypotheses
Must use Benefit-Risk Evaluation…can we consider previously
“toxic” substances to be beneficial to human health under a
New Paradigm?
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25. Thank You!
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Questions?
James R. Coughlin, PhD CFS
jrcoughlin@cox.net
949-916-6217