1. The role of sunlight and organic matter in the degradation of aquatic pollutants
Kim Foster / Rachel McCarthy / Douglas Latch
Department of Chemistry, Seattle University, Seattle, WA 98122
4. Summary and Ongoing Work
3. Results and Discussion1. Background
A. Singlet Oxygen Reactions
A. Background and perspective
B. Selected Aquatic Pollutants and Calculated
Reaction Rates
5. Acknowledgements We would like to thank our PI Doug Latch, as well as Joe Arguinchona and Stephan Ledger for their
help with this project. We would also like to thank our collaborator Bill Arnold and his team at the
University of Minnesota.
• Phenols, bisphenols and various pharmaceutical pollutants are susceptible to photodegradation by singlet oxygen through indirect photolysis.
• Rate of reaction between the pollutant and the singlet oxygen is pH dependent.
• Composition of natural water samples affects rate at which a pollutant can degrade. Wastewater effluents seem to degrade pollutants at higher rates.
• Further studies will focus on:
• Developing methods to measure rate constants for the indirect photolysis of pharmaceuticals using singlet oxygen.
• Determining the concentrations of singlet oxygen in various effluent waters as well as their reactivities with pollutants.
• Determining degradation products of the bisphenols.
• Comparing experimentally determined rate constants, to rate constants which have been computed by collaborators.
Above: Schematic illustrating sunlight induced transformation
of aquatic pollutants downstream from wastewater treatment
plants.
2. Aquatic Photochemistry
A. Photochemistry in natural waters and
the role of organic matter (OM)
Above: Schematic representation of the role of
organic matter (OM) in direct and indirect
photochemical processes, including acting as
an antioxidant.
Above: The potential for wastewater to dictate the composition
of organic matter in rivers. Natural waters are dominated by
allochthonous (terrestrial; white arrow) NOM, while EfOM is
primarily autochthonous (microbial; solid red arrow) in origin.
The relative sizes (and fill/shading) of the arrows indicate the
proportion of flow derived from natural stream flow and
wastewater effluent. In many effluent dominated rivers, the flow
is essentially 100% wastewater. For effluent impacted rivers,
the relative importance of the effluent may be seasonally
dependent.
minimally impacted effluent impacted effluent dominated
B. Potential influence of effluent organic matter
(EfOM) on aquatic processes
Wastewater treatment plants (WWTPs) contribute to
surface water quality in multiple ways. First, they
remove most contaminants from waste streams.
Second, they discharge organic matter that may be
involved in the solar degradation of contaminants
that elude removal at the WWTPs. This “effluent
organic matter” (EfOM) has recently been identified
as a potential major contributor to contaminant fate.
The focus of this work is to quantify production of
photochemically produced reactive intermediates
(PPRIs) from EfOM and to measure how rapidly the
PPRIs break down contaminants of concern. Current
work is focused on acquiring rate constants for the
reaction of 1O2 or carbonate radicals with select
contaminants, as well as measuring PPRI’s in sunlit
waters.
Above: Pseudo first order reaction of pollutant 3-chlorophenol reacting with 1O2, where slopes of
the line give kobs. Rate constant of the FFA + perinaphthenone reaction used to calculate kpollutant.
-3.5
-3
-2.5
-2
-1.5
-1
-0.5
0
0.5
0 1 2 3 4 5 6 7 8 9
ln(At/A0)
Time (s)
-0.35
-0.3
-0.25
-0.2
-0.15
-0.1
-0.05
0
0.05
0 100 200 300 400
ln(At/A0)
Time (s)
pH 6
pH 7
pH 8
pH 9
pH 10
[S]
[S]
obsk
dt
d

t
[S]
[S]
obsdk
d

 
tt
dk
d
0
obs
0
t
[S]
[S]
t
[S]
[S]
ln obs
0
t
k





rearrange:
integrate:
Analysis of Photochemical Kinetics
3. Direct vs. Indirect Photolysis of Pentachlorophenol
-0.45
-0.4
-0.35
-0.3
-0.25
-0.2
-0.15
-0.1
-0.05
0
0 2000 4000 6000 8000 10000 12000 14000 16000
ln(At/A0)
Time (s)
Metro Waste
S. Anna
S.Cruz Green
S.Cruz N. Tucson
S.Cruz Rio Rico
S.Cruz Tucson
Left: pH dependency of BPAF degradation by perinaphthenone generated singlet oxygen.
Right: Indirect photolysis of BPAP by PPRI’s generated in different natural waters obtained from
various locations in southwest regions of United States.
Above: Reaction scheme for the generation of 1O2 by perinaphthenone , and the pathways in
which excited state perinaphthenone can react.
Chemical
CAS
Number Common Use
Calculated krxn
(M-1 s-1)
pH 6 pH 10
Other Wastewater Related Compounds
pentachlorophenol 87-86-5 Pesticide 2.73x107 4.12x107
p-chloro-m-cresol 59-50-7 Preservative 1.31X107 1.76x108
m-cresol 108-39-4 Disinfectant,
Preservative
9.17x106 1.03x108
p-cresol 106-44-5 Industrial
Intermediate
1.79x108 1.05x108
4-chlorophenol 106-48-9 Industrial
Intermediate
2.58x106 4.97x107
3-chlorophenol 108-43-0 Industrial
Intermediate
3.22x106 4.77x107
2-nitrophenol 88-75-5 Fungicide 9.30x106 3.32x107
2-chlorophenol 95-57-8 Pesticide 2.91x106 8.66x107
3-nitrophenol 554-84-7 Fungicide 1.85x106 4.16x107
2,6-dimethylphenol 576-26-1 Adhesive 1.42x108 1.64x108
2,4,6-
trichlorophenol
88-06-2 Pesticide 3.26x107 5.49x107
2,3,5-
trichlorophenol
933-78-8 Pesticide 3.13x107 4.49x107
BPAF 135876-30-1 Plasticizer - 1.31x107
BPAP 1571-75-1 Plasticizer 4.73x106 3.21x107
BPF 620-92-8 Plasticizer 3.67x107 3.71x107
BPS 80-09-1 Plasticizer - 1.84x107
BPZ 843-55-0 Plasticizer 1.36x107 2.84x107
Table 1:Selected Aquatic Pollutants and a Summary of Calculated Reaction Rates
Above: Rates were calculated from the experimental kobs using
the equation 𝑘 𝑟𝑥𝑛 =
𝑘 𝑜𝑏𝑠
[1
𝑂2
] 𝑠𝑠
, where [1O2]ss is experimentally
determined through an FFA experiment under identical conditions.
Left: (a) Direct vs. indirect photolysis at pH 6.
The slope of these lines gives the value of
kobs which is 7.4x10-4 s-1 for direct photolysis
and 2.6x10-3 s-1, giving an adjusted kobs of
1.9x10-3 s-1. ♦= Direct photolysis, or ■=
Indirect photolysis. (b) Indirect photolysis of at
various pH. ♦ = pH 6, ■ = pH 10. For pH 6
kobs is 2.6x10-3 s-1 and for pH 10 it is 3.9x10-3
s-1 prior to adjustment for direct photolysis
a b