Question

Naphthalene is a volatile organic compound (VOC) as well as the lightest polycyclic aromatic hydrocarbon (PAH). Inhalation of naphthalene may cause respiratory and neurological effects among humans. It is classified as a possible human carcinogen. A recent monitoring program shows that the average concentration of naphthalene in air is 4.5 µg/m3 in indoor air. Assess the non-cancer hazard and cancer risk assuming people continuously inhale naphthalene at this concentration. Toxicological information of naphthalene: RfC = 3 µg/m3 Unit risk = 3.4 × 10-5/ (µg/m3)

Questions:

(1) Calculate the hazard quotient, and interpret the result

(2) Calculate the cancer risk, and interpret the result

(3) Discuss at least 4 uncertainties in the above analyses

Answer 1

A hazard quotient is the ratio of the potential exposure to a substance and the level at which no adverse effects are expected. It is primarily used by US EPA to assess the health risks of air toxics.

exposure concetration =  4.5 µg/m3

RfC = 3 µg/m3

HAZARD QUOTIENT (HQ)= exposure concetration/ RfC

=4.5/ 3

HQ > 1 MEANS HAZARDOUS

The cancer unit risk describes the excess cancer risk associated with an inhalation exposure to a concentration of 1 µg/m3 of a given chemical; the cancer potency factor describes the excess cancer risk associated with exposure to 1 mg of a given chemical per 9 kilogram of body weight.

3)Using the draft estimate of the cancer URE, and assuming that an individual's long term exposure is equal to the median concentration (0.89 µg m−3) in the four cities, the lifetime excess cancer risk is 9 × 10−5. The 90th percentile concentration (6.57 µg m−3) gives a risk estimate of 7 × 10−4. Homes with measurements in the 100 µg m−3 range represent cancer risks in the 10−2 range, which places naphthalene among the top environmental risks.

the cancer risk estimates are based on a draft and controversial assessment of naphthalene's carcinogenic potential, which depends heavily on a study in male rats. However, naphthalene exposure remains of concern using the old URE, and the frequency and extent of exceedences over the non-cancer chronic RfC and WHO guideline also remain problematic.

Study emphasized high-end concentrations, which not infrequently reached high levels that are commensurate with risks that exceed health-based guidelines and other benchmarks.

naphthalene was not measured in large exposure studies, nor has it been measured in studies using biomarkers or personal samples that can better account for multiple exposure compartments.

A draft estimate for naphthalene's carcinogenic potential (URE) was used, although the earlier URE would not dramatically change conclusions.

While several factors associated with high naphthalene concentrations are identified, and preliminary apportionments of indoor sources are made, the assessment is semiquantitative due to large differences in the building characteristics and unmeasured covariates, e.g., naphthalene application rates. Measure particulate phase naphthalene, although nearly all naphthalene is expected to be in the vapor phase had not been included