Risk Assessment Document
p-Dichlorobenzene (1,4-dichlorobenzene; CAS Registry No. 106-46-7,
hereafter referred to as pDCB) was first produced commercially
in the U.S.A. in 1915 (IARC, 1982). It has long been used
as a moth repellent and as a space deodorant; it is also used
industrially as an intermediate in organic syntheses.
The pDCB that is found in indoor air originates mainly from
moth repellents used to protect clothing and from deodorants
that are used in the household.
The pDCB that is existing indoor, while providing benefits
such as moth control and deodorizing effects, raise some concerns
regarding potential risks to human health. We focused our
risk assessment on human exposure through inhalation of pDCB
in indoor air because pDCB is mainly used as a moth repellent
to protect clothing,.
Our primary objective was to estimate the magnitude of risks
from the present uses of pDCB by examining and analyzing knowledge
regarding exposures and potential hazards.
Our secondary objective was, in the event of a significant
risk being identified, to suggest possible actions that might
be adopted, taking into account the risk–benefit tradeoff.
In estimating the risks, we investigated whether hazards observed
in animal experiments were likely to occur in humans, and
we estimated the distributions of mid- to long-term exposure
concentrations from monitoring data, which were derived from
This document contains a comprehensive review of hazard-assessment
information, including oral exposures, and summarizes its
rationale in the reference concentration, for chronic inhalation
hazards, which was determined by Research Center for Chemical
Risk Management, National Institute for Advanced Industrial
Science and Technology (CRM, AIST).
The endpoint of the assessment of the toxicity hazard of chronic
exposure to pDCB was hepatotoxicity. Hepatotoxity was observed
in test animals exposed to pDCB by both oral and inhalation
routes; increases in liver weight, increases in leakage of
enzymes in the liver, and histopathological changes were also
After results of some chronic inhalation studies were examined
in detail, a high-quality two-year study in mice was chosen
as the study on which to base the reference concentration.
Non-neoplastic changes observed in the livers of mice in this
study were defined as an endpoint, and the no observed adverse
effect level (NOAEL) was calculated to be 80 mg/m3 by converting
the study result of 75 ppm into an equivalent concentration
at a continuous exposure of 24 hours/day.
The reference concentration was determined to be 800ƒÊg/m3;
this value was obtained from the value of the NOAEL (80 mg/m3)
divided by an uncertainty factor (100).
In this document, the amount of the pDCB emitted to the envirionment,
pDCB concentrations in indoor air and outdoor air, and pDCB
concentrations in the environment re summarized. In order
to obatining the distributions of pDCB concentrations of indoor
air, raw data from "Nationwide Survey on Volatile Organic
Compounds in Indoor Air" (Ministry of Health and Welfare 1999)
From the result of this analysis, the proportion of households
using pDCB-based moth repellents/fumigants was determined
to be 0.9 and the proportion of households not using it was
0.1 (this group of households was called "households with
no indoor usage" (abbreviated as N)).
Furthermore, according to the histogram for concentrations
contributed by indoor sources of emission ([indoor concentration]
– [outdoor concentration]), households using pDCB-based
moth repellents/fumigants could be classified into “households
with higher indoor usage” and “households with lower indoor
usage” (ratio 0.61:0.39).
By assuming that each group has a lognormal distribution,
a geometric mean (GM) and a geometric standard deviation (GSD)
were obtained followed by goodness-of-fit test to the histogram.
Thus, distributions of concentrations contributed by indoor
emission sources in "living spaces" were obtained for each
of the three groups "households with higher indoor usage"
as H), "households with lower indoor usage"
L), and "households with no indoor usage" (N).
The GM (ƒÊg/m3) values were 60.7, 2.1, and 0, respectively,
and the GSD values were 5.1, 3.2, and 1, respectively; the
ratio of the three types of household groups was 0.55:0.35:0.10.
Next, distributions of concentrations (arising from indoor
sources of emission) throughout indoor spaces, including bedrooms,
were estimated under the assumption that concentration of
a bedroom is an average of two times as a living room at the
Thus, the average concentration within a house was calculated,
taking into account the time that individual family members
spent indoors. If the total indoor concentrations should be
obtained, Outdoor concentrations were added to these concentrations.
Human exposure to pDCB was evaluated on the basis of indoor
concentrations and outdoor concentrations, taking into consideration
the time spent in each situation.
The exposed population was divided into two groups according
to their patterns of life spent. One group consisted of housewives,
babies and preschool children, and elderly persons (abbreviated
LT, see Table 3); the other group consisted of working people
and students (ST).
The exposed population was also divided into three groups
depending on the amount of pDCB used in the household. These
groups were "households with higher indoor usage" (H),
with lower indoor usage" (L), and "households with no indoor
usage" (N). As a result, the population as a whole was classified
into a total of six groups, i.e. LT & H, LT & L, LT
& N, ST & H, ST & L, and ST & N. By using
this distribution together with the outdoor concentrations
obtained in Chapter V, inhalation exposure levels were estimated
for the above six groups, and rates of exposure exceeding
the reference concentration were identified.
The proportion of the population for which the exposure concentration
exceeded the reference value of 800ƒÊg/m3 was 5.4%
for the group with the highest exposure (the group LT &
H, Table 5).
The ratio for the population as a whole was calculated to
be 2.4%, half of which belonged to the group LT & H; the
other half belonged to the group ST & H (Table 6). People
in these groups need to take some measures to reduce their
exposure to indoor concentrations of pDCB.