PCBs AND ASSOCIATED AROMATICS 901
TABLE 33
North Americans may consume between 189 and 858 times the lifetime limit of PCDDs/PCDFs recommended by the USEPA
during the first year of limitPopulationDaily intake
(pg/Kg/d)First year intake
(pg/Kg)Ratio of first year intake to ADI
uncorr./corr.South Vietnam 908 332,491 EPA 2077 376
(1970) (4377) (1,602,221) (10,013) (1,817)
South Vietnam 88.7 32,389 CDC 20.1 3.6
(1983) (35) (127,612) EPA 202 38
(796) (149)
CDC 2.1 0.4
(8.3) (1.6)North Vietnam 5.1 1,853 EPA 11 2.1
(14.0) (5,113) (31) (5.7)
CDC 0.08 0.03
(0.22) (0.08)Japan 86 31,536 EPA 197 36
(146) (53,144) (332) (60)
CDC 2.0 0.4
(3.3) (0.6)United States 83.1 30,330 EPA 189 27
(337) (137,699) (858) (124)
CDC 1.8 0.27
(8.2) (1.2)the body mass would serve to dilute the contaminant con-
centrations ingested during the first year. It is assumed that
a North American adult grows to 70 Kg and an individual in
Vietnam and Japan grows to about 55 Kg.
The ratio of the first year intake to the recommended
intake values of EPA and CDC are shown in the last two
columns of Table 33. For a cancer risk of 1-6, the 70 year
lifetime recommended intake values for 2,3,7,8-TCDD are
160 and 16000 pg/Kg for the EPA and CDC, respectively.
According to these criteria, a child in North America will
have consumed between 189 and 858 times the lifetime limit
recommended by the EPA. If there is no further ingestion or
excretion of contamination then the adult will have received
27 to 124 times the EPA recommended limit. If one consid-
ers the CDC values instead than a North American child will
have received between 1.8 and 8.2 times the CDC recom-
mended dose or between 0.27 and 1.2 times the CD recom-
mended dose over the person’s lifetime.
There is clearly a substantial difference between the
2,3,7,8-TCDD equivalents found in south Vietnam in 1970
and those found in 1984. The groups tested were different
and reflect the use of Agent Orange for military purposes.
The derived data for the industrial nations of south Vietnam,Japan, and North America are very close and are contrasted
with data for north Vietnam where there is infrequent use of
synthetic industrial and agricultural chemicals.
The “Acceptable Daily Intake” or ADI method for the
determination of health risk from chemicals presupposes
that there is a threshold level below which there is no biolog-
ical response. A safety factor is then applied to account for
variations in individual susceptibility. Current ADI values
for 2,3,7,8-TCDD are predicated on a threshold value of 1
pg/Kg/d derived by Kociba et al. in 1978. Danish authorities
chose a safety factor of 200 to define a “Tolerable Daily
Intake”, or TDI, value of 5 PPq.
A second method of risk assessment is the cancer statis-
tical method which calculates for a given risk level of usu-
ally 10 −6 , the amount of chemical exposure which can occur
over a 70 year lifespan. The model assumes a constant dose
level in a population and an incremental unit risk.
The EPA has estimated that the incremental unit risk
derived from the ingestion of 1 ppq of 2,3,7,8-TCDD in the
body over a lifetime may lead to an additional 156 cancer
incidents per million people exposed.^81 At this point in time
it is not clear what the health risks of the effects of PCDDs
and PCDFs are to humans.C016_003_r03.indd 901C016_003_r03.indd 901 11/18/2005 1:12:38 PM11/18/2005 1:12:38 PM