Risk assessment of components in tobacco smoke and e-cigarette aerosols: a pragmatic choice of dose metrics

Figures & data

Figure 1. Comparison of the inhaled exposure concentrations of chemical X for different scenarios with the same total dose inhaled daily of 200 mg: smoking (20 cigarettes per day, 10 µg of chemical X/cigarette; a worker (8 hour exposure per day; inhalation rate of 10 m3 per 8 hour); a member of the general population (24 hour exposure per day; inhalation rate: 20 m3 per day). Only the first hour of exposure is shown. See text for additional details about the smoking scenario.

Table 1. Default parameter values for the exposure estimation during smoking.

Parameter	Default value
Puff volume	50 mL
Puff duration	1.5 sec
Puff interval	20 sec
Number of puffs per cigarette	13
Time to smoke one cigarette	6 min
Functional Residual Capacity	2 L
Tidal volume (rest)	500 mL
Breathing rate	12 min^−1
Dead space volume (at rest)	30%

Adapted from Djordjevic et al. (2000) and Snyder et al. (1974).

Table 2. Inhaled concentrations for three scenarios (occupational, general population, smoking) starting from the same total inhaled dose of 200 mg of a fictive chemical X per day.

Exposure scenario	Inhaled dose (mg/day)	Exposure duration (hours/day)	Respiratory volume during exposure (m^3)	Inhaled concentration during exposure (mg/m^3)
Occupational exposure	200	8	10^a	20
Continuous daily exposure	200	24	20^b	10
Smoking	200	2^c	0.143^d	1399

^aA total inhaled volume of 10 m³ per 8-hour shift is assumed.

^bA total inhaled volume of 20 m³ per 24-hour is assumed.

^cThe total duration for smoking 20 cigarettes (assuming 6 min per cigarette, Table 1).

^dPer puff a volume of 50 mL is inhaled combined with 500 mL ambient air (Table 1). The total inhaled volume for 20 cigarettes, assuming 13 puffs per cigarette, then equals (20 × 13 × 0.550 L=) 143 L or 0.143 m³.

Figure 2. Simulations of alveolar air concentrations of a cigarette smoke component during the smoking of one cigarette in two scenarios, one with a substantial alveolar absorption (i.e. 80%) (pink curve) and one with low alveolar absorption (i.e. 15%) (green curve). Alveolar concentrations are expressed relative to the initial alveolar concentration after the first puff.

Figure 3. Stepwise, pragmatic approach for the risk assessment of individual components in tobacco smoke and e-cigarette aerosols.

Table 3. Summary table for MoE calculation and evaluation for glycerol.

	Species	Concentration (mg/m^3)	Hours/day	Day/week	Duration	Result
Calculated MoE
Exposure scenario PoD	Rat	165	6	5	13 weeks	Calculated MoE: 165/46 = 3.6
Exposure estimate smoking	Human	46	2	7	lifetime
Minimal MoE
Quantifiable factors	Interspecies: 2.5 Intraspecies: 10				Duration: 2	Minimal MoE: 50
Remaining factors			Dose rate: ?	Weekly frequency: ?		Expert judgment

Table 4. Summary table for MoE calculation and evaluation for benzene.

	Species	Absorbed dose (mg/kg bw)	Hours/day	Day/week	Duration	Result
Calculated MoE
Exposure scenario PoD	Human	2.1	24	7	lifetime	Calculated MoE: 2.1/0.015 = 140
Exposure estimate smoking	Human	0.015	2	7	lifetime
Minimal MoE
Quantifiable factors	Interspecies: 1 Intraspecies: 10			Weekly frequency: 1	Duration: 1	Minimal MoE: 1000^a
Remaining factors			Dose rate: ?			Expert judgment

^aEFSA (2005) proposes a minimal MoE of 10,000 for a conclusion of low concern for carcinogenic compounds when the PoD is based on an animal estimate. Since the PoD for benzene is based on a human estimate, a minimal MoE of 1000 is considered applicable.

Djordjevic MV, Stellman SD, Zang E. 2000. Doses of nicotine and lung carcinogens delivered to cigarette smokers. J Natl Cancer Inst. 92(2):106–111.

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Snyder WS, Cook MJ, Nasset ES, Karhausen LR, Parry Howells G, Tipton IH. 1974. Report of the task group on reference man. International commission on radiological protection, No. 23. Pergamon Press. p 344.

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