1

Date: July 16, 2012

From: Centers for Disease Control and Prevention / Agency for Toxic 

Substances and Disease Registry

Subject: Comments on EPA’s Toxicological Review of Benzo[a]pyrene

To: Environmental Protection Agency

General comments: 

Overall, the toxicological review of benzo[a]pyrene is quite comprehensive. We feel the 

review does a good job of outlining the process used to arrive at each reference value. 

EPA has lowered the oral cancer slope factor from 7.3 to 1 (mg/kg/day)-1and determined 

that benzo[a]pyrene is “carcinogenic to humans. In addition, the review developed several new 

values including oral reference dose, reference concentration, inhalation unit risk and dermal 

cancer slope factor. These additions and changes will allow ATSDR to conduct more accurate 

and complete evaluations of exposure pathways involving benzo[a]pyrene.

It would be helpful to include a table that outlines the strengths and weaknesses of each 

of the studies presented and discussed throughout the document. 

The review includes a detailed examination of benzo[a]pyrene DNA adducts and the 

work conducted in this area. However, benzo[a]pyrene also forms adducts with proteins 

such hemoglobin and serum albumin. Exposure to PAHs has been assessed by protein 

adduct dosimetry using benzo[a]pyrene as a model compound due to its well-known 

carcinogenic properties. There is a fair amount of research work that has been conducted 

in this area, but the authors fail to mention any of this work in the review. Proteins and 

DNA adducts are both considered useful biomarkers to assess exposure to 

benzo[a]pyrene in molecular and/or epidemiology studies. Perhaps the authors should 

consider whether an evaluation and discussion of benzo[a]pyrene protein adducts fit 

within the scope of this toxicological review. 

It would also be helpful to clarify the setting and population of interest for both the 

chronic (oral) Rfd based on the 7-day exposure model by Chen et al (2012) and the 

chronic (inhalational) RfC based on the 10-day exposure model by Archibong et al 

(2002).

Other Comments:

Page XXX Line 9 “Evidence for specific DNA adducts” 

Since the reactive intermediate benzo[a]pyrene diol expoxide (BPDE) can bind to 

guanine and adenine residues in DNA, language should be included to define/clarify what 

is meant by specific DNA adducts. Benzo[a]pyrene DNA adducts are formed when 

reactive metabolites of B(a)P, e.g., BPDE, bind to DNA. BPDE binds specifically with 

exocyclic amino groups of deoxyguanine (dG) and deoxyadenine (dA) residues. 
However, the bulky DNA adducts that are primarily formed are the guanine adducts 

(10α-(deoxyguanosin-N

2

-yl)-7α,8β,9β-trihydroxy-7,8,9,10-tetrahydrobenzo(a)pyrene or 

dG-N

2

-BPDE)

Page 1-33 Line 32 Table 1-8

The work conducted by Matiasovic et al “Effects of Postnatal Exposure of 

Benzo[a]pyrene on the Immunity of Immature Rats” (2008) was not included in the table. 

In this work, Matiasovic et al determined the effect of benzo[a]pyrene on the developing 

immune system of immature rats. 

Design: Newborn rats received different concentrations (0.1, 1.0 and 10.0 mg/kg/day) of 

benzo[a]pyrene in the first 14 days after birth. 

Results: T cells in the spleen and mitogenic activity increased, decrease in expression of 

IL-4 and IFN-gamma was observed, spleenocytes were dose dependent, erythrocytes 

decreased in a dose dependent manner

Page 1-4, 1-11-12

Would suggest using birth cohort and not pregnancy cohort

Page 1-15 line 21 “the analytical methods were similar in the two studies”

Since the exposure measures have been shown to be method dependent, the method 

similarities and differences among the two studies should be detailed. It would be 

interesting to know how the limit of detection (LOD) compared between the two 

methods. 

Page 1-19 Table 1-5

We suggest changing the column headers to Reference and Study Design 

Page 1-30 Section 1.1.3. Line 15 “limited number of occupational studies particularly in 

coke oven workers”

Need to provide references for the limited number of studies involving coke oven 

workers. Also, there is no discussion of work conducted by Ming-Tsang Wu et al. 

“Relationship of Exposure to Coke Oven Emissions and Urinary Metabolites of 

Benzo[a]pyrene and Pyrene in Coke-Oven Workers (2002)

Page 1-59 Line 5 Summary of Metabolic Activation Pathways

Benzo[a]pyrene also forms adducts with proteins such hemoglobin and serum albumin. 

The protein adduct metabolic activation pathway has been well described in published 

manuscripts. It would be interesting to show both the DNA and the protein adduct 

pathway. Also, the stereochemistry of the reactive diolepoxide intermediate will 

determine the type of mutation that occurs. The (+) anti-diol expoxide intermediate is 

reportedly more carcinogenic than the (-) syn-diol epoxide intermediate. A more robust 

discussion of the mechanism of action as it relates to endpoints such as developmental 

and reproductive effects should be discussed and would help to strengthen this section.