Photo-transformation of 2,3,7,8-TCDD in presence of
natural organic matter studied by in vitro bioassay
P.
a
Macíková ,
J.P.
b,c,d,e
Giesy
,
M.
a
Bittner , Luděk
a
Bláha
Research Centre for Toxic Compounds in the Environment (RECETOX), Faculty of Science, Masaryk University, Kamenice 3,
62500 Brno, Czech Republic
b Department of Biomedical Veterinary Science and Toxicology Centre, Univ. of Saskatchewan, Canada
c Zoology Department and Center for Integrative Toxicology, Michigan State University, East Lansing, USA
d Biology and Chemistry Department, City University of Hong Kong, Kowloon, Hong Kong, SAR, China
e School of Biological Sciences, University of Hong Kong, Hong Kong, SAR, China
a
 Mainly manmade organic compounds resistant to
environmental degradation with ability to
bioaccumulate in organisms, and cause adverse health
effects.
 Compounds such as polychlorinated dibenzo-p-dioxins
(e.g. 2,3,7,8-TCDD), polychlorinated biphenyls, or
polycyclic aromatic hydrocarbons.
 Toxicity of TCDD is mediated via interaction with
cytosolic arylhydrocarbon receptor - AhR (so called
AhR-mediated toxicity or „dioxin-like“ toxicity).
Natural Organic Matter (NOM)
 Ubiquitous product of decomposition of dead organic
matter; mainly contains humic and fulvic acids.
 Usually up to 50 mg/L in freshwaters.
 HA and FA exert indirect and direct biological effects.
 Photochemically active compounds, that absorb solar
radiation and subsequently release reactive oxygen
species (ROS) or mediate degradation of other
compounds present in water via photosensitization [1].
Methods
 Irradiation of TCDD and TCDD+NOM solutions were
done in sealed quartz tubes by the direct sun light.
 The initial concentration of TCDD was 16–19 pg/L as
determined by HRGC/HRMS analysis
 Suwannee River NOM was obtained from International
Humic Substances Society, and used in experiments in
concentration range 0.5 to 150 mg/L.
 TCDD+NOM were irradiated for 72h when sample
aliquots were taken in 0, 1, 3, 6, 24, 72 h. Irradiation
was carried out in two technical replicates. Initial pH of
solutions was set to 7.3 - 7.6.
 AhR-mediated activity of samples was evaluated using
in vitro bioassay based on H4IIE-luc cell line - rat
hepatoma cells transfected with luciferase gene under
control of Ah-receptor (Fig. 3).
TCDD + NOM
Freshwater natural organic matter (NOM) can accelerate photochemical
degradation of persistent organic pollutant 2,3,7,8-TCDD in water.
RESULTS
150
TCDD pure
TCDD+NOM5
TCDD+NOM10
TCDD+NOM50
TCDD+NOM150
100
50
0
0
40
20
60
Fig. 1 AhR-mediated activity of irradiated TCDD and TCDD+NOM samples
 Suwannee River NOM was shown not to be able to mediate AhR-dependent response itself.
 AhR-mediated activity of irradiated samples of pure TCDD and mixtures TCDD+NOM (except
NOM150, i.e. 150 mg/L) decreased rapidly upon first hours of irradiation with average half-life 2
hours of sun irradiation
 TCDD in the mixture with NOM in concentration 150 mg.L-1 (TCDD+NOM150 at Fig. 1 and 2) has
photodegraded more slowly with half-life nearly 40 hours
DISCUSSION
 TCDD undergo photodegradation both in
absence or presence of NOM, but no
significant enhancement of photodegradation
rate (by possible formation of ROS) was
observed.
 Slower photodegradation of TCDD sample
irradiated in presence of NOM150 was caused
probably by absorption of effective
wavelength by NOM (so called „filter effect“
[2]), because only this concentrated NOM
solution exert more violent brown colour.
Nevertheless, this level is not environmentally
relevant.
50
40
30
20
10
0
Fig. 2 Half-lives of photodegradation of TCDD in
mixture with various NOM levels
CONCLUSIONS
Fig. 3 Experimental design of photodegradation studies
80
Time (hours)
t1/2 (hours)
Hydrophobic Organic Compounds (HOCs)
HYPOTHESIS
Luminescence induction
(normalized %)
BACKGROUND
c
d
e
 Hypothesis that photodegradation of TCDD can be accelerated in the presence of NOM was not confirmed.
 In-vitro bioassay was proven to be suitable method for photodegradation studies of biologically active
compounds (AhR active compounds in this case).
Acknowledgement: Supported by project CETOCOEN project from the European Regional Development Fund (Z.1.05/2.1.00/01.0001)
References: 1 - Steinberg C. E. W. Ecology of Humic Substances in Freshwaters , Springer:, 2003. 2 - Boreen A. L. et al. (2004). Environ. Sci. Technol., 38, pp. 3933-3940.