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THE RISE OF THE FINELY-ADVANCED TRANSBOUNDARY
ENVIRONMENTAL MODEL (FATE): A STATE-OF-THE-ART MODEL
PREDICTION OF THE GLOBAL SINK OF PERSISTENT ORGANIC
POLLUTANTS
Kawai, T.1, Handoh, I.C.1, and Takahashi, S.1
1 Centre for Marine Environmental Studies (CMES), Ehime University, Matsuyama, Japan
Abstract
The Finely-Advanced Transboundary Environmental model (FATE) was developed to better understand and
quantify the non-steady dynamics of Persistent Organic Pollutants (POPs) in the global environment. FATE
is a simulator that encodes POPs dynamics in the five environmental compartments (atmosphere, oceans,
cryosphere, soil, and vegetation), such as atmospheric advection and diffusion processes, and
bioconcentration processes in the vegetation and marine phytoplankton. We demonstrate the
FATE-predictions of the polychlorinated biphenyls (PCBs) #28 and #153, for the period of 1931-2100. Our
focus here is on the global sinks (degradations, and the removal to the deep oceans) of PCBs. The fractions of
annual global sinks in the environmental compartments varied significantly with the chlorination level of the
selected PCBs: The primary sinks in the past 80 years appeared to be degradations in the atmosphere and soil
for PCB#28 (58%) and PCB#153 (47%), respectively. PCB#153 removal to the deep ocean was a secondary
sink (21%), while this was not the case for PCB#28 (less than 1%).
Introduction
Modelling the dynamics of Persistent Organic Pollutants (POPs) is an important issue for 21st century
science. A rapid progress has been made in the development of numerical models for POPs dynamics, and
these models are capable of quantifying the long-range transport potential and the overall persistency of
POPs in the environment (See review of Fenner et al., 2005 1). However, high-resolution global models that
predict non-steady dynamics of POPs are yet to be developed (e.g., Malanichev et al., 2004 2; Leip and
Lammel, 2004 3). Model predictions of the POPs fate, such as environmental sinks on centennial timescales,
have not been reported even for well-known legacy POPs.
Considering above, we have developed a space-resolving, time-dependent, multi-compartment model to
predict the fate and transport of POPs, called the Finely-Advanced Transboundary Environmental model
(FATE). Our model is capable of quantifying the long-range transboundary transports, source-receptor
relationships, and persistent sinks of POPs, and may well be applicable to environmental risk assessments of
Vol. 71, 2009 / Organohalogen Compounds page 001599
POPs. We stress that the FATE incorporates oceanic biogeochemical processes, and thus quantifies POPs
removal to the deep oceans which are associated with phytoplankton detritus settling (Daches et al., 1999 4).
In this study, we outline the FATE and major physicochemical parameters and input/forcing data used in
the model runs that generate centennial predictions of two selected polychlorinated biphenyls (PCB #28 and
#153), and assess the global sinks.
Materials and methods
The FATE represents non-steady POPs dynamics within and across five environmental compartments:
atmosphere, ocean, cryosphere, soil, and vegetation
(Figure 1). The horizontal resolution is 2.5°×2.5°.
In the follow- ings, we briefly describe the
framework of, and integral input/forcing data of the
FATE.
Figure 1. Schematic diagram of the Finely-Advanced Transboundary Environmental model (FATE)
ATMOSPHERE: The model atmosphere, from the mean sea-level surface to the tropopause (100 hPa), is
divided into 10 sigma layers (σ = 0.95, 0.88, 0.76, 0.58, 0.43, 0.3, 0.19, 0.11, 0.05, and 0). The model solves
3D advection and diffusion, degradation, and gas/particle partitioning processes of POPs. Dry and wet
deposition and gaseous exchange with the underlying surfaces are calculated in the lowest atmospheric layer.
The degradation process of POPs in the atmosphere obeys a second-order equation of the POPs and OH
radical concentrations. Dry and wet deposition are parameterized by the methods of Tsyro and Erdman
(2000) 5, and Atlas and Jurado et al. (2005) 6, respectively. Gaseous exchange between the reference height in
the atmosphere ( 995.0=σ ) and the underlying compartments are formulated by a network of resistances for
the molecular and turbulent diffusions. The integrated mass transfer coefficients are estimated by the
Monin-Obukhov similarity theory.
OCEANS: The current version of the ocean compartment does not include both horizontal and vertical
transports of POPs. Instead, the model ocean consists of a large number of boxes, each of which has a height
equal to the depth of the mixed layer. Within each box, POPs partitioning between dissolved and
sorbed/adsorbed in/on marine phytoplankton4, degradation, and removal to the deep ocean associated with
σ = 0.76
σ = 0.58
σ = 0.43
σ = 0.30
σ = 0.19
σ = 0.11
σ = 0.05
CRYOSPHERE OCEAN SOIL
Grass land Broadleaf
forest
Coniferous
forest
σ = 0.90
σ = 0.99
Tropopause (100 hPa)ATMOSPHERE
VEGETATION
Emission
Degradation3D advection
and diffusion
Cgas Cparticle
MIXED LAYER
DEEP OCEANCRYOSPHERE
Cdissolved
DegradationDegradation
σ = 0.995Gaseous exchange
Dry/wet depositions
Detritus settling
VEGETATION
Cgas Cliquid
Csolid CDOC
Cleaf
Gaseous exchange Bioconcentration
Dry/wet depositions
Gaseous exchange
Degradation
Degradation
σ = 0.995
DefoliationDry deposition
SOILDiffusion
Vol. 71, 2009 / Organohalogen Compounds page 001600
Table 1. Physicochemical parameters for PCB#28
and #153 that are used in the model (Malanichev et
al., 2004 2
). R and T are the universal gas
constant and the ambient temperature, respectively.
0T is 283.15 K. All variables are non-
dimensional, except for the degradation rate
constant for the atmosphere which has unit,
113 −− smoleccm
Table 2. Input/forcing data used in FATE
phytoplankton detritus settling are determined. The degradation process of POPs is governed by a first-order
equation of POPs concentration. We have assumed that the turnover time of phytoplankton biomass through
the growth and motality is 66.7 days 4
.
CRYOSPHERE: The model assumes no POPs emission from the cryosphere to the atmosphere (Wania and
Mackay, 1995 7
). However, POPs deposited to the cryosphere from the atmosphere by dry/wet deposition
degrade at the same degradation rate as that used for the oceans.
SOIL: The soil compartment consists of 10 uniform vertical layers that range from the soil top to a depth of
30 cm; each layer is 3 cm deep. 1-D (vertical)
molecular diffusion, degradation, and partitioning
between gaseous, solid, dissolved phases, and
sorbed on dissolved organic matter are calculated.
The degradation of POPs is described by a first
order equation with a degradation rate constant
specific for POPs.
VEGETATION: The vegetation is classified into
five plant functional types, evergreen broad-leaved
and needle-leaved forests, deciduous broad-leaved
and needle-leaved forests, and grassland. The
intake of POPs into the vegetation compartment is
governed by dry/wet deposition and gaseous
exchange with the atmosphere. The
bioconcentration factor is parameterized for each
plant functional type as an exponential function of
the octanol-air partition coefficient (Mclachlan and
Horstmann, 1998 8
). The transport of POPs from
vegetation (leaf layer) to the vegetation soil, is
described by defoliation.
PHYSICOCHEMICAL PARAMETERS: The main
physicochemical parameters, partitioning
coefficients and degradation rate constants, are
summarized in Table 1. It is generally accepted that
the partitioning coefficients depend on the ambient
temperature. This temperature dependency is taken
species Values/equations
PCB#28
PCB#153
PCB#28
PCB#153
PCB#28
PCB#153
PCB#28
PCB#153
PCB#28
PCB#153
PCB#28
PCB#153Soil
Octanol/air
Degradation rate constants
Atmosphere
Ocean
Parameters
Partition coefficients
Air/water
Octanol/water
( )[ ]0/1/17430exp/642.7 TTRT −−
( )[ ]0/1/18347exp/146.4 TTRT −−51031.6 ×61094.7 ×
( )[ ]0
8/1/18731exp1078.5 TT −×
( )[ ]0
10/1/110811exp1064.3 TT −×
( )RT/13720exp107.2 10−×
( )RT/15380exp1012.8 11−×
71033.1 −×
91060.1 −×
9104.7 −×
91017.1 −×
Sources/references
Breivik et al., 2007 9
Wind velocity
Temperature
Precipitation rate
Mixed layer depth World Ocean Atlas 1994 11
Primary production SeaWIFS and VGPM 12
GLC2000 13
and USGS glcc v2 14
Soil organic carbon
contentsISRIC-WISE
15
Terrestrial data
Variables
Emission
Climate data
NCEP/NCAR reanalysis 1 10
Land cover
Vol. 71, 2009 / Organohalogen Compounds page 001601
into account in air/water and octanol/air partitioning coefficients.
INPUT/FORCING DATA: The input/forcing data used in the FATE are summarized in Table 2 with
corresponding data sources and/or references. Each data are interpolated onto 2.5°×2.5° horizontal grids.
Yearly, 6-hourly, and monthly data were used for emission, meteorology, and oceanography, respectively. The
emission data, which was provided by Breivik et al. (2007) 9, has a significant uncertainty in the estimate. For
simplicity, we have adopted the high emission scenario. FATE runs were all forced with 6-hourly and
monthly mean climatologies, and yearly emission data sets, thus explicitly resolving the seasonal and
interannual variability in all instances.
Results and discussion
The FATE-predicted global sinks/contents in each of the five environmental compartments were divided into
the following four periods: i) 1931-1970, ii) 1971-2008, iii) 2009-2050, and iv) 2051-2100 (Table 3).
Figure 2 shows the geographical distribution of global sinks for the year 1970 (the peak of the PCBs
emission).
The soil was shown to be the dominant reservoir of both PCB#28 and #153. The fraction of PCB#28
contents in the oceans tend to be significantly larger than that of PCB#153. In the light of the chronology, the
global sinks of PCB#28 and #153 exhibit distinct differences: In the past 80 years, degradation in the
atmosphere was the largest sink of PCB#28 (58%), while degradation in soil dominated PCB#153 (47%).
Removal to the deep oceans was found to be secondary sink of PCB#153 (21%), while this was not the case
for PCB#28 (less than 1%). These differences could be explained in part by those of physicochemical
properties of PCB#28 and #153 (see Table 1): The relatively large Henry's law constant and degradation rate
constant of PCB#28 for the atmosphere appeared to enhanced the oceanic content and atmospheric sink of
PCB#28. Similarly, the relatively small octanol/water partitioning coefficients of PCB#28 suppressed the
removal to the deep oceans.
It should, however, be stressed that the current development of the FATE contained some oversimplified
processes. The key issues to be addressed are summarized as follows: 1) The FATE did not incorporate any
key terrestrial hydrological processes, such as infiltration and/or surface runoff. Mclachlan et al. (2002) 16
pointed out that the vertical transports of dissolved-phase POPs significantly modify the vertical distribution
of POPs within the soil. Since the soil is always a dominant reservoir of PCBs (Table 2), removal of PCBs
from the surface soil by infiltration and/or surface runoff are unlikely to be trivial. 2) There were no POPs
transports processes in the modelled oceans. Lohmann et al. (2006) 17
suggested that the dynamic deep water
formation could be more effective sink of PCBs more than the biogeochemical settling associated with
organic carbon. This implies the needs for incorporation of 3-D oceanic advection and diffusion processes
that profile the global thermohaline circulation. 3) In the oceanic biogeochemistry of the FATE, we assumed
Vol. 71, 2009 / Organohalogen Compounds page 001602
constant growth and detritus rates that were extrapolated from studies on natural lakes, which was not
realistic. These rates could critically depend on phytoplankton functional types and the ambient temperature.
We have developed the state-of-the-art model, FATE, in order to better understand and quantify the
dynamics of POPs in the global environment. The FATE-predicted global sinks of PCB#28 and #153 could
provide new insights into our current understanding of the fate and transport of POPs. Nevertheless, the
FATE is of necessarily limited value in addressing full dynamics of POPs, owing to uncertainties in the input
data sets (especially the emission data) and the paucity of model validation. In order to surmount this
difficulty, we have now devoted much effort to 1) evaluate the FATE by extensive observation, and to 2)
combining the FATE predictions and Bayesian uncertainty analysis.
Table 3. Summary of the FATE-predicted global contents and sinks of PCB#28 and #153.
Global sinks (contents) (%) Total
sink
(ton) Atmosphere Ocean Soil Vegetation Cryosphere
Removal to the
deep ocean
[1931-1970]
PCB#28 58.26 (2.99) 11.78 (2.77) 15.58 (65.90) 13.38 (28.29) 0.25 (0.06) 0.75 (-) 3494.2
PCB#153 18.85 (0.62) 0.43 (0.70) 35.34 (78.57) 17.33 (19.27) 0.52 (0.84) 27.54 (-) 306.2
[1971-2008]
PCB#28 57.14 (2.77) 10.85 (2.26) 19.64 (73.45) 11.48 (21.46) 0.29 (0.06) 0.60 (-) 6625.8
PCB#153 16.56 (0.44) 0.36 (0.45) 50.18 (86.82) 12.35 (10.68) 1.27 (1.60) 19.29 (-) 1176.8
[2009-2050]
PCB#28 50.73 (1.49) 7.84 (1.23) 28.16 (79.38) 12.69 (17.89) 0.02 (0.00) 0.55 (-) 383.8
PCB#153 5.05 (0.08) 0.07 (0.06) 83.28 (95.68) 4.35 (2.50) 1.99 (1.67) 5.25 (-) 366.7
[2051-2100]
PCB#28 7.35 (0.08) 0.95 (0.06) 89.08 (98.45) 2.56 (1.41) 0.00 (0.00) 0.06 (-) 0.3
PCB#153 0.42 (0.01) 0.00 (0.00) 97.39 (98.75) 0.51 (0.26) 1.33 (0.98) 0.35 (-) 72.6
Figure 2. FATE-predicted geographical distributions of annual sinks of the year, 1970. Upper and lower
panels are the results of PCB#28 and #153, respectively.
(ng/yr)
(ng/yr)
Atmospheric sink (PCB#28) Terrestrial sink (PCB#28) Oceanic sink (PCB#28) Removal to the deep ocean (PCB#28)
Atmospheric sink (PCB#153) Terrestrial sink (PCB#153) Oceanic sink (PCB#153) Removal to the deep ocean (PCB#153)
Vol. 71, 2009 / Organohalogen Compounds page 001603
Acknowledgements
This work was supported by the Ehime University Global COE “Interdisciplinary Studies on Environmental
Chemistry” Programme under the Ministry of Education, Culture, Sports, Science and Technology, the
Government of Japan, and by Japan Society for the Promotion of Science Grant-in-Aid for Young Scientists
(B) (21710033).
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