The photodegradation of 2,3,7,8-, 1,3,6,8-, and
1,2,3,4-tetrachlorodibenzo-p-dioxins (TCDDs) under
xenon lamp irradiation results in only reductive
dechlorination. From 2,3,7,8-TCDD, 2,3,7-
trichlorodibenzo-p-dioxin (2,3,7-TrDCC), 2,7- and 2,8-
dichlorodibenzo-p-dioxins (2,7- and 2,8-DCDD), 2-
monochlorodibenzo-p-dioxin (2-MCDD), and dibenzo-
p-dioxin (DD) are identified. From 1,3,6,8-TCDD, the
six degradation products 1,3,6-TrCDD, 1,3-DCDD, 1,6-
DCDD, 1-MCDD, 2-MCDD, and DD are identified,
while the nine degradation products 1,2,3-TrCDD, 1,2,4-TrCDD, 1,2-DCDD, 1,3-DCDD, 1,4-DCDD, 2,3-
DCDD, 1-MCDD, 2-MCDD, and DD are detected from
1,2,3,4-TCDD. In the photodegradation reaction,
chlorine atoms in the 2-, 3-, 7- and/or 8-positions are
dechlorinated more rapidly than those in the other
positions.
