Risk Assessment

1
Risk Assessment

• PAHs in Binary Mixtures
• Melissa Stafford REU 2003

2
Summary

• A Risk Assessment of PAHs in Binary Mixtures
• PAHs
• Toxicity
• Complex Mixtures
• Ames Assay
• Results and Conclusions

3
Polycyclic Aromatic Hydrocarbons - PAHs

• Potent animal Carcinogens
• Products of artificial and natural processes

Benzo(a)pyrene (BaP)
5-Methylchrysene
Chrysene
4
Natural Sources
Artificial Sources
Grilled Meat
Forest fires
Tobacco Smoke
Car Exhaust
Volcanic Eruptions
5
PAH Metabolism
Aromatic Hydrocarbon Receptor
6
PAH Metabolism
Tyrosine Kinase
7
PAH Metabolism
Cytochrome P450 - CYP1A1 -
BaP
BaP-7,8-diol-9,10epoxide
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Mutations
G to T Transversion
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Research Objectives

• To characterize the interactions of prevalent
  mutagenic PAHs
• Improve our understanding of complex mixtures of
  PAHs in the environment.

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Toxicity Assessments
1 1 2
Additive
EPA
?
Synergistic
Inhibition
1 1 0
1 1 5
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Methods - The Ames Assay
U
Mutagen
Testor Strain
Histidine
Histidine
The more bacteria that live the higher the
mutagenicity!!
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Ames Assay

• What to add
• Salmonella TA98
• Histidine and Biotin
• S9 rat liver
• Minimal Top Agar
• Chemical

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Ames Assay - Results
Positive Control - 2-NitroFlourine -
783 revertants
30 mM Benzo(a)Pyrene (BaP) - With S9 Rat Liver -
Negative Control - BaP without S9 -
337 revertants
37 revertants
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5-MethylChrysene/BaP Mixtures

• 25 reduction in net revertants
• 12.02 standard deviation between trials
• 30 reduction would be considered significant

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Chrysene/BaP Mixtures

• 30 reduction in net revertants
• 96.87 standard deviation between trails
• Discrepancy probably due to degraded Chrysene

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Conclusions

• The data show an overall additive trend
• The inhibition we found is at too insignificant a
  level for the EPA to change current methods.
• Data from this and GJIC will be plugged into QSAR
  for calibration.

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Acknowledgments

• I would like to thank
• Erica Reese for her undying patience and teaching
  ability
• Dr. Autenrieth for her guidance, understanding
  and affection
• Dr. Donnelly for the use of his lab and extensive
  knowledge of the Ames Assay and PAHs.