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Volatility of TCDD and PCB from soil
C h e m o s p h e r e , V o l . 1 6 , No.4, P r i n t e d in G r e a t B r i t a i n
pp
907-920,
1987
0045-6535/87 $ 3 . 0 0 + .OO P e r g a m o n J o u r n a l s Ltd.
VOLAfILITY OF 1CDD AND PCB FROH SOIL
6 Eduljee RechemInternational Limited C h a r l e s t ~ l Road, Hardley, llythe Southampton 504 6ZA, U.K. ABSIRACT
V o l a t i l i s a t i r ~ , Fluxes o f 2 , 3 , 7 , 8 - t e t r 8 c h l o r o d i b e n z o d i o x i n and Aroclors 12~2, 1254 nnd 126(I were e s t i m a t e d from t i m model o f .]ury e t . a l . , developed f o r compounds w l t h s i m i l a r p h y s i c a l properties, lira i n f l u e i m e o f s o i l water c o . L e n t , s o i l o r g a n i c m a t t e r and water e v a p o r a t i o . was i o v e s t i g a t e d .
Increasing soil
orgmde matter decreased tim volsLilisation
flux nf all
four chemicals. Water e v s p o r s t i ~ l was accompanied by increased f l u x e s , implyi=~ t i r o l tim cl~m,icsls were susceptible to wicking, lira trends observed were in qualitative agreeme, t with field and laboratory studies. ]Ira predicted fluxes serve as a basis For comparing limit volakilisation behaviour against pesticides s,d other homologues, and For the construction of models describing the environmental Fate o f these compounds. INIRUOUCIION
P o l y c h l o r i n a t e d d i o x i n s and p o l y c h l o r i n a t e d biphenyls (PCBs) are c h a r a c t e r i s e d by low vapour pressures
and aquel,us solubilities, and high hydrophobicity, suggesting that these compounds
strongly sorb to soil, and that their moSility in a terrestrial environment is low. for example, describes 2,3,7,8-tetrachlorodibenzodioxin in relation to leaching by rainfall or irrigation.
llellir,g,
(]CDD) as "immobile" in soil Z~I,2 3
Measurements in the field have, however,
identified perpetration o£ boll, TCDD and PCBs into soil, albeit at a very slow rate.
Freema,i
and 5chroy ~" 5 _7 found that TCDD had dispersed 10 cm in 12 years at [g]in Air force Base. Movement detected, sites.
was
attributed
to the existence
but did not quantify,
of temperature
]CDD dissipation
gradients.
Young et.al.
L" 4 .7
in soil at two pheno×y herbicide storage
McClure ~" 5 .7 measured PCB fluxes at ta Jolla, California,
ai~d found that the PCB
concentration
in soil at a depth of 10 cm was typically 0.2 to 0.8 of the concentration at
the surface.
Other leaching experiments on PCB ace reviewed by 5trek and Weber Z" 6_7 and
Pal et.al. I-7_7. In order
to balance
the
concentrations
of ]CDD and PCB at
907
the soil/sir
interface
908
w i t h d e p o s i t i o n and removal Fluxes, we need t o understand the processes which a f f e c t chemicals i n the e n v i r o n m e n t . soi]
due t o h y d r a u l i c a c t i o n ,
deplete
the c o n c e n t r a t i o n
deposition
and m i x i n g
Apart
these p o l l u t a n t s dust
at
from d i f f e r e n t
the s u r f a c e sources,
PCBs Z~ B,9 _7 and TCDD ~- 10,11 7 removal mechanism.
have e s t a b l i s h e d
that
of
the s o i l ;
resuspension
p h o t o c h e m i c a l d e g r a d a t i o n , b i o d e g r a d a t i o n and e v a p o r a t i o n . significant
o f ICDD and PCB i n t o the
t h e r e are a number o f o t h e r p h y s i c o c h e m i c a l p r o c e s s e s t h a t can
of
with
From downward t r a n s p o r t a t i o n
these
of
for dust
example,
particles,
S t u d i e s on the p h o t o c h e m i s t r y o f photo-oxidation
can c o n s t i t u t e
a
B i o d e g r a d a t i o n i s not c o n s i d e r e d t o be a major removal p a t h -
way f o r these chemicals ~ ' 1 2 , 1 ~ 7 . lhibodcaux Z-14.7 thP. major
route
suggested t h a t for
offsite
v a p o u r i s a t i o n o f TCDD from c o n t a m i n a t e d s o i l
transport
from a h e r b i c i d e
Nash and B e a l l E 1 5 _ 7 d e t e c t e d ICDD v o l a t i l i s a t i o n 2,4-D.
Hackay and Wolkoff Z-16_7 and Hackay
aEion f l u x e s o f PCB From water b o d i e s . surface.
Hurphy e t . a l .
trations
above hazardous waste l a n d f i l l
Clearly,
volati]isation
of
plots
these compou,~ds i n t o
measured h i g h atmospheric PCB concen-
sites.
the atmosphere, under c e r t a i n
Z-21-7
have p o i n t e d
surfm'es
is very difficult,
out,
volatilJs-
Z-18_7 measured l o s s o f PCB From a sand
Z-20J
o f TCDD and PCB could be a s i g n i f i c a n t
Philippi
Facility.
t r e a t e d w i t h S i l v e x and
Z-17-7 c a l c u l a t e d s i g n i f i c a n t
Haque e t . a l .
C 1 9 - 7 and Lewis e t . a l .
p r o d u c t i o n and d i s p o s a l
from f i e l d
et.al.
s u r f a c e s wa,J
a theoretical
r o u t e f o r secondary emissions
conditions.
treatment
of
However, as I l u t t e r votatilisation
fro,,
owing to the c o m p l e x i t y and interdependence o f f a c t o r s
o r g a n i c carbon c o n t e n t , c a p i l l a r y
movement, o f s o i l
arid soil
such as
w a t e r , t e m p e r a t u r e and h u m i d i t y .
VULAI ILISAIll)N Information Podo]l air flux.
orl the
eL.al.
diffusion
influerlce
E 22_7
of
soil
speculated
properties
that
or w a t e r - m e d i a t e d e v a p o r a t i o n ( w i c k i n g ) ,
V a p o u r i s a t i o n Flux was noL q u a n t i f i e d .
Kearney e t . a l . distilling
E 23_7
considered
with water,
and P h i l i p p i
on TCDD v o l a t i l i s a t i o n
IEDD would not
lhis
that
be expected t o
is
by s o i l -
and i n c r e a s e d m o i s t u r e would lower the
Thibodeaux E 1 4 J
]CDD would behave l i k e
has r e p o r t e d o p p o s i t e v i e w s . DDI and v o l a t i l i s e
pherlomena has been q u e s t i o n e d by Igue e t . a l .
Z-21 .7 estimaLed the v o l a t i l i s a t i o n
i~consisterlt.
volatilise
Flux from wet s o i l
by co-
E24.7.
tlutter
t o be 2 - 3 ng/cm2/h,
about 75% t h a t o f DD]. The i n f o r m a t i o n
on PCB v o l a t i l i s a t i o n
demonstrated t h a t
From s o i l
evaporation of Aroclor
is also inconclusive.
Ilaque e t . a l .
1254 was much slower from Woodburn s o i l
Z-18_7
that
Ottawa sand, presumably because o f the h i g h e r o r g a n i c m a t t e r c o n t e n t o f the former. workers a l s o i d e n t i f i e d soil.
enhanced e v a p o r a t i o n due t o w i c k i n g ,
Fluxes were not measured.
]oss from e x p e r i m e n t a l s o i l Scharpenseel e t . under s t e r i l e
al.
L-27 7
conditions,
Hoza e t . a l .
systems,
/'25.7
measured l a r g e PCB losses
whereas Krogmann e t .
al.
From sand but not from Woodburn
and Iwata e t . a l .
to v o l a t i l i s a t i o n ,
From These
~'26.7 attributed
but again f l u x e s w e r e n o t
PCB
quantified.
from an e x p e r i m e n t a l p l o t m a i n t a i n e d
L~ 2B_7 found t h a t PCB removal from s o i l
was v e r y low. In the absence o f detailed experimental data on the influence o f s o i l v o l a t i l i s a t i o n o f ICDD and PCBs, i t
would be oF i n t e r e s t to e l i c i t
properties on the
t h i s information through
the application oF t h e o r e t i c a l models which have been developed for pesticides, compounds
909
a p p r o x i m a t e TCDD and PCBs in t h e i r
which most c l o s e l y
the work o f Jury e t . a l . 1260
in
order
to
/-29,30,31,32_7 will
predict
vapourisation
physical properties.
In t h i s p n l m [ .
be a p p l i e d to ICDD and A r o c l o r s 1242, 1254 and fluxes
under
various
environmental
conditions.
V O L A I I L I S A I I O N MODEL
1he v o l a t i l i s a t i o n diffusion
rate
of
a surface-applied
by a d s o r p t i o n t o the s o i l . addition
chemical w i l l
through the a i r boundary l a y e r and i t s ]tie v o l a t i l i s a t i o n
be determined by i t s
r a t e For a s o i l - i n c o r p o r a t e d
to the above, depend on tile r a t e o f d e s o r p t i o n from the s o i l
the s u r f a c e . diffusion,
rate
nf
vapour pressure or vapour d e n s i t y , m o d i f i e d chemical w i l ] , i n
and upward movement (o
1wo mechanisms f o r upward movemenL can o p e r a t e , i n d e p e n d e n t l y or s i m u l t a n e o u s l y ;
and mass t r a n s f e r .
Diffusion
i n v o l v e s movement o f the chemical L h r o u q h a q r n d i e n t ,
caused e i t h e r by a depleLed s u r f a c e c o n c e n t r a t i o n due to e v a p o r a L i o n , or L e m p e r a t u r e q r a d i e n t . q as suggested by Freeman and Schroy f o r
1CDD ~ - 3 .7.
temperature,
adsorption,
waLer.
and by v a r i a b l e s
Diffusion
Hans t r a n s f e r
through s o i l
of
a chemical
chemical i n s o l u t i o n , as w i t t i n g
affecting
1he d i f f u s i o n such as s o i l
is
controlled
hy
and s o i l
can occur i n both vapour and s o l u t i o n phases Z-33_7. is
effected
by the upward movement o f
t o r e p l a c e e v a p o r a t i v e water l o s s a t tile s o i l
L-3a 7 .
rate
organic matter
waLer,
containing
the
s u r f a c e , a process known
]he r a t e o f movement~ determined by the r a t e o f water e v a p o r a t i o n ,
dependent on the r e l a t i v e
h u m i d i t y o f the a i r ,
wind speed, tile degree o f s o l u b i l i t y
and to s o i l
adsorption.
Jury e t . a l .
,_/"29,38,31,32 7 i n c o r p o r a t e d these f a c t o r s i n t o a mathematical model d e s c r i b i n g
the
transport
of
assumes l i n e a r , first
Wicking g e n e r a l l y a c c e l e r a t e s tile v o l a t i l i s a L i o n
is
in water,
chemicals
through
equilibrium
order loss,
soil,
partitioning
and loss
at
the s o i l - a i r
between l i q u i d ,
rate of a chemical.
interface.
!he model
vapour and adsorbed phases,
net
a stagnant a i r boundary l a y e r , and steady s t a t e water flow upwards (wickJnq)
or downwards ( l e a c h i n g ) . Diffusion
Coefficients
lhe s o i l - g a s
diffusion
DG :
coefficient
i s g i v e n by
(a10/3 / f12 ) D~ir
where DGait i s the a i r - g a s d i f f u s i o n
(l)
c o e f f i c i e n t , _ a i s the v o l u m e t r i c a i r c o n t e n t o f the s o i l ,
and ~ i s tile s o i l p o r o s i t y . lhe s o i l - l i q u i d
diffusion
DL
coefficient,
/
:
~2
[ 810/3 /
where t) ~water L i s the w a t e r - l i q u i d
DL i s
_water ] UL
diffusiou coefficient,
(2) and fl tile v o l u m e t r i c wa/er c o n t e n t ,
(~ - a). lhe e f f e c t i v e effects
diffusion
coefficient,
o f a d s o r p t i o n and p a r t i t i o n i n g DE
=
(DG/RG)
+
DE, i s the sum o f DG end DL, each c o r r e c t e d f o r the between gaseous and l i q u i d
(DL/RLI
phases.
Thus, (3)
where RG = P K D / K | t RL
= /DKD
+
+ 8
8/K H +
aK H
+
a
(~) (5)
?:.©
P
being the bulk density of the soil, K D the soil-liquid partition coefficient and KII ,
llEnry 's constant. Volatilisation
Flux
The effective solute convection velocity is given by VE :
JW/ RL
(6)
where 3W is the water flux;
upward ( - ) , downward (+) or zero.
At the soil surface, the
effective transport velocity across tile stagnant air boundary layer of thickness d is given by ~air. HE = uG / (dR G)
(7)
For a uniform incorporation of H (kg/m2) of chemical to a depth of L (m)below tile surface, the v o l a t i l i s a t i o n Flux at the surface is written as JV
[
o
[(L + VEt) I )
VEt
{
+ (2HE + VE) exp [HE(HE+VE)L/DE] { exp(HEL/DE)erFc
-erfc
[
(L + (2HE + VE)t) J4DEL ]
(2HE + VE)t /4DEt ]II
(8)
where C is tile uniform i n i t i a l concenLration oF tile applied chemical, p is the firsLo order degradation (loss) rate constant given by t is time, erfc (x) tile comple-
(0.693/t½),
mentary error function and t½ the volatiiisation h a l f - l i f e . Eqn. (8) permits tile calculation of v o l a t i l i s a t i o n flux as a function of soil parameters such as moisture, density,
porosity,
organic
temperature (i.e.
carbon
fraction
(incorporated
into KD;
see below),
bulk
change i n KH) and o t h e r f a c t o r s such as w a t e r e v a p o r a t i o n r a t e mid
the amount o f chemical a p p l i e d .
Ihe model has been t e s t e d on a wide range o f chemicals Z-32~7. ]NPU[ PARAI~IERS
lhere is considerable uncertainity fluxes
ca|culated
From Eqn.
(8)
o v e r many o f the i n p u t parameters. should o n l y
For t h i s
be regarded as q u a l i t a t i v e
reason, tile
estimates,
and an
indication of trends. Diffusion
coefficients
D Gair
=
For a i r - g a s
and w a t e r - l i q u i d
transport
are assigned v a l u e s o f ~ 2 9 7
0.43 m2/d
Dwater L =
4.3 x 10 -5
(9) m=/d
(10)
The soil-liquid partition coefficient, KD, is obtained From the equation ~D
=
Koc foc
(11)
where foc is the fraction of organic carbon in the soil, and KociS its partition coefficient, obtained from the octanol-water partition coefficient, Kow , with log K
oc
=
1.029 log K
ow
-
0.18
Z~ 2 9 J (12)
911
K D is expressed in 51 units of m~/kg.
The dimensionless Henry's constant, KII, is given by
tile ratio of tile concentration of the chemical in the soil air and liquid phases.
Applyin 9
tile ideal gas law to the former, we get /-35_7 KH
=
16.04 PH/(IS)
(13)
where M is the molecular weight of the solute, P its vapour pressure (rot, of Hg) and 5 its
s o l u b i l i t y in water (mg/l), both at tlle temperature I . While Kow and Kllare uniquely defined For ]CDD, t h i s is not the case For Aroclors 1242, 1254 and 1260, considered in t h i s paper.
Doskey and Andren
/-36.7
Bad Mackay e t . a l . L-17_7 have
noted that the calculation of K H requires that the vapour pressure and aqueous s o l u b i l i l y must r e f e r
to
t h e same s t a t e
temperature,
the Aroclors
of matter;
are viscous
whereas individual
liquids.
PCB i s o m e r s a r e s o l i d s
Aroclors
in the environment
at ambient
partition as
individual isomers, as can be seen from the adsorption experiments of lwata et.al. Z-26_7 and therefore, a rigorous examination of their behaviour should also be on this basis L-37,38_7. Heasurements standard:
of
PCBs
in
the
environment
have
invariably
been
referenced
to
an
Aroclor
the importance of isomer-specific data has only been appreciated in recent work
/-39,40_7.
For tt~e p r e s e n t c a l c u l a t i o n s , from 5chroy e t . a l . Hackay
et.al.
/-41_7.
E 17 7
vapour, p r e s s u r e ,
solubility
and K
OW
data f o r
1CDD were taken
For the A r o e l o r s , d a t a on 1242 and 1254 were taken from
w i t h mean l o g Kow v a l u e s o f 5.0 and 6.4 r e s p e c t i v e l y .
I n f o r m a t i o n on
Aroclor 1260 was obtained From Rapaport and Eisenreich Z-42..7, with a mean log K
of 6.B. ow
Karickhoff and Morris 2-43-7 and Girvan et.al. /-44.7 have suggested that reported partition
c o e f f i c i e n t data may be too low by a factor of two of three.
At present there is i n s u f f i c i e n t
information to establish whether t h i s is indeed the case. lhe d e g r a d a t i o n h a l f - l i f e , experimentation.
t½, i s a n o t h e r parameter t h a t has not been u n e q u i v o c a l l y d e f i n e d by
Heasured d e g r a d a t i o n g e n e r a l l y accounts For a l l
Forms or l o s s ,
b i o d e g r a d a t i o n , l e a c h i n g , photochemical r e a c t i o n and e v a p o r a t i o n . has not been q u a n t i f i e d ,
except from the s u r f a c e s o f pure l i q u i d s .
found t h a t 2% o f ICDD had v o l a t i l i s e d
from a glass s u r f a c e , a f t e r
C 23-7 s t u d i e d the p e r s i s t e n c e o f ICDD i n two s o i l the a p p l i e d amount p e r s i s t e d a f t e r from 5eveso. half-life soil.
one y e a r .
]sensec two days.
including l o s s per se
and Jones / - 4 5 _ ] Kearney e t . a l ,
types at t h r e e r a t e s o f a p p l i c a t i o n .
]his half-life
di Domenico and co-workers L" 4 6 , 4 7 7
Italf
is consistent with early reports
and Kimbrough e t . a ] .
L-48_7 e s t i m a t e the
o f ICDD to be i n the r e g i o n o f 10 - 12 years f o r ICDD t h a t had been mixed i n t o the Freeman a~d 5chroy [
remained
in
the
soil
towards the s u r f a c e . application applied unshaded McClure
Volatilisation
after
3 _7 Found t h a t 12 y e a r s ,
plots / - 5_7
the ICDD a p p l i e d at a deptll o f 11 cm had there
From the g r a d i e n t o f the d i f f u s e d
would have r e s u l t e d
2,4-D
all
although
in
breakthrough
contaminated
with
1CDD, onto
experienced
loss
of
calculated
a half-life
ICDD, of
to
was evidence o f front,
PCB i n
the
to top
movement
is evident that a shallower
the s u r f a c e .
experimental
equivalent
it
diffusive
grass
Nash and B e a l l plots.
a half-life 10 cm o f
soil,
Both of
about
~ 15 -7
shaded and one y e a r .
of 6 years,
this
included both leaching and emissions i n t o the atmosphere. Wallnoffer e t . a l . E49.7 measured losses of about 50% of Aroclor 1254 when applied to three s o i l types, during a 2 to 4 month period.
Moza e t . a l .
~ ' 2 5 , 5 0 . 7 l o s t 79% o f a d i c h l o r o b i p h e n y l ,
67% o f a t r i c h l o r o b i p h e n y l
an(~
~ J.J-
42% o f a p e n t a c h l o r o b i p h e n y l ff18_7
from the t o p 1 cm o f a sandy loam d u r i n g one y e a r . Hague e t . a l .
a p p l i e d A r o e l o r 1254 to Ottawa sand and Woodburn s o i l .
sand f o r
tetra-,
penta-,
and h e x a - c h l o r o b i p h e n y l s
was greater from wet sand than from dry sand. from Woodburn s o i l .
Volatilisation
half-lives
from
were 10, 25 and 4D days r e s p e c t i v e l y ,
lo~s
lhese workers did not detect v o l a t i l i s a t i o n
lwata et. al. [ 26_} applied Aroclor 1254 to six Californian s o i l s ,
incorporated to a depth o f 15 cm.
50% o f the lower chlorinated isomers
was
lost
in
two
months, whereas oniy 18% of the heptachlorobiphenyls was lost in 8 months, froma loamy sand. toss after I year from soils containing 10% to 19% of organic matter amounted to 5~ for all chlorinated species. Scharpenseel et.a]. [ 2 7 ~
investigated the movement of a triehlorobiphenyl in soil.
the administered quantity remained after a period of 9 months. applied amount
remained after 9 months,
rather than evaporation.
12% of
In a sandy soil, 8% of the
but most of the loss was attributed
to leachinq
PCB loss was experienced under both sterile and biotic conditions.
llaque and Sehmedding ~ 5 1 ~
and Kilzer et.al. ~ 5 2 ] have also established that PCBs volatilise
from soil surfaces - the latter workers measured volatilisation rates for a tri- and pentachIorobiphenyl uuder conditions of wicking, From
the experimental
evidence,
HcClure's
Aroelors would appear to be too high, lwata et.al,
and Seharpenseel et.al,
from wet soils,
as a function of water loss.
estimation of a half-life of 6 years
[or tlle
faking into account the work of Moza et.al., referred to above, we ascribe tentative half-lives of
0.5, 1.0 and 2.0 years for Aroclors 1242, 1254 and 1260 respectively.
For ICDD we assume
a
half-life of 10 years, under soil-incorporated conditions. A list of these n,,d other input parameters used in the simulation is presented in fable I. Factors such as water content, organic 6arbon fraction and water evaporation rate were varied to assess their influence on vapourisation
flux.
RESULTS
Diffusion c o e f f i c i e n t s (DG/RG), (DL/RL) and DE are l i s t e d in fable 2, and i l l u s t r a t e d in Figure
1.
Volatilisation
Fluxes f o r
nominal
P = 1550 kg/m ~ and ~ = 0.5 are shown i n and Jw = ( - ) Eqn.
5 ram/day, a t
volumetric
soil
lables
soil
properties
3 and 4 f o r
water contents
of f : 0.O125, L : 0.O1 m, oc two e v a p o r a t i o n r a t e s ; JW = U
o f O.1,
(7) was a s s i g n e d a v a l u e o f 4.75 x 10 -3 m For no e v n p o r a t i o n ,
evaporation
rate
of
1 kg/m ~ t o f a c i l i t a t e
5 ram/day ~ 31_7.
Co,
the i n i t i a l
0.3 and 0.5 m3/m ~
concentration,
easy c o n v e r s i o n For o t h e r a p p l i c a t i o n
rates
d in
and 2.38 x 10 -3 m f o r an is
nominally
set
(H kg/m' t o a d e p t h o f
at
L m).
DISCUSSION ICDO Exmmination of fable 2 and Figure la shows that diffusion of TCDO in s o i l is vapour-dominated up to a volumetric water content of 0.3 m3/m ~, and then liquid-dominated to saturation, implies
that
movement
to
the
surface,
and
therefore
vapourisation
into
the
air,
lhis would
initially decrease as the pore spaces are filled with water, and then increase as liquid diffusion predominates.
Vapourisation fluxes listed in Table 5 confirm this trend.
Fluxes
913
1ABLE 1 - INPUT PARAI4EIERS r o e EQN. 8
Aroclors
Property
Units
Soil
P
kg/m ~
1350
T
K
ICDD
1242
1254
1260
1140
86
2600
6500
0.5 298 O.01
m
L
O.O125
f'oc m~/kg
Koc
7.9 E-5
KH
t%
IABLE 2 -
O.114
0.023
3650
days
365
183
0.29t 73(1
DIFFUSION COEFFICIENIS FOR I C ~ ) AND AROCLORS 1242, 1254 AND 1260 AS A FIINCTION OF SOIL WAIER CONIEN!
Diffusion coefficients, m'/d 8
DG/R G
DL/R L
DE
DG/R G
TCDD
0 O.1 0.2 0.3 0.4 0.5
7.02 3.33 1.27 3.33 3.00
E-13 E-13 E-13 E-14 E-15 O
0 4.15 4.18 1.62 4.22 8.89
E-15 E-14 E-13 E~13 E~13
4.43 2.10 8.05 2.08 2.08
E-07 E-B7 E-08 E-O8 E-09 0
0 1.82 1,83 7.09 1.85 3.89
E-12 E-11 E-11 E-10 E-IO
DE
A r o c l o r 1242 7.82 3.37 1.69 1.95 4.25 8.89
E-13 E-13 E-13 E-13 E-13 E-13
3.06 1.45 5.55 1.44 1.44
4.43 2.10 8.05 2.O9 2.26 3.89
E-07 E-07 E-O8 E-08 E-O9 E-IO
4.53 2.10 8.20 2.12 2.03
E-06 E-O6 E-07 E-07 E-08 0
0 6.22 6.27 2.42 6.23 I . 33
E-11 E-IU E-09 E-09 E-08
3.06 I .45 5.56 I .46 2.06 I .33
t -(16 E-06 E-U7 E-D7 E-[18 E-O8
4.53 2.11 8.2U 2.12 2.11 1.55
E-U7 [-07 E-01] E-UB E-09 E-IO
A r o c l o r 1260
Aroclor 1254 0 O.1 0.2 0.3 0.4 0.5
DL/R L
E-07 E-O7 E-O8 E-U8 E-09 0
0
7.25 7.32 2.83 7.37 1.55
E-13 E-12 E-II [-11 E-IO
9!Z
'.0 '.0 O O I
I
c3 cM
I
I
I
I
I
W
L.~J tuJ
r~
¢x% ¢c~
i~u'%
u",, ,,O
~dO LZ'I OC)
WW
~S
I
o, ~, o,
O
L~LdW
W
$
I
•
°
q
I
!
WL.~J O-. ,r--
I
El
bJ W
•
w
°
i
IN
§
,
I
hi
1
o ~P, ",O
I.~2
t.~J La.I
T
•
•
~-.I c-J
•
°
N
t~l L/
Lr~
=,~o,
s, s, s, bJ
l
LJW
"
I ' ~ N •
t.~l w
~ O i
L~
N °
°
I
WL¢.I
W
R~
',D r - -
°
•
fa')
!-- A
°
~-J
,-: ,-: ,Z
~8 t~,
i.i
N
E3
°
CD
!
O0
•
•
t-
r.
C~
d-
~ o ¢~0 i~ .
o~o
I.i.
~Jw~J C O o
(:3 !
•
,
,
I
I
X
~.1
~o-, C )
~,~o,
"4:) ~:) r",.
•,L} "-Q
w
W
L~.J b J
...l I.~ Z
P-. r ~ I
I
C3 I
O !
-e-
(/1 xo ~•
.
c)
I
k~.l I M
"'w
.
i
ll W
f'-- O~ •
•
°
I
I
i,i
I
I.i
L~
.
.
!
I
I~J t . J L~J ,.,/
,~,=, La.J W
t.iJ
',D r,'~ Ii
II
'.0 r - -
I
3 •
°
f " - "43
,...I
I
q-- ...1"
L~L~ OxOx f-~ m7
~.4
=~o w
w
t.a.I
La.J W
t~.l
(~', "4~ o', •
°
•
•
°
w w
F~W •
•
°
•
o
915
FIGURE
1 - DIFFUSION
a -
1EDD
COEFFICIENTS
b - AffOCLOfl 1242
AS A F U N E I I O N
OF S O I L WAIER EONIENI
c - AROCLOR 1254
'DE
"DL/RL
d - AROCLOR 1260 ....
'DG/R G
10 -5 10 - 1 2
-
(a)
°L
% G
~
\
10 -13
",/ \ \
Z
~ 1 0 -14
/
•
/
\,
\
10-71 -
, /"
\
\, \
/ lO -15
~
I
[I
I
II .1
io-11l /
I ~
0.3
I
0.5
I
t
0.1
',
I
0.3
0.5
6
i
(c)
(d)
i
1U-6 i
10 - ]
% G 10 -5
10 - 8
I I,I
~°
x
{J
\
z t,-,,
~ 1 0 -10
/
t
I
/
I
l
/
I
I I
I
I
o.1
0.3 B
I
t
/-
10 -11
I
/
10 -12
I
/
/
I
o.5
10 -1~
L !
/
/
I I
I o.1
I
I
I I
0.3
0.5
916
increase
with
to w i c k i n g . [qn.
(8)
water evaporation rate;
the model t h e r e f o r e
This i s c o n t r a r y to the views o f P o d o l l e t . a l .
is
suitable
for
predicting
volatilisation
a d d i t i o n s o f TCDD, such as the r e l e a s e o f 5eveso. incident
is
likely
t o be h i g h , s i n c e N ( 9 ) o f
(C° = M/L) i s t h e r e f o r e l a r g e . by m u l t i p l y i n g fraction
the f l u x
by t ,
o f the i n i t i a l
predicts
fluxes
as a consequence o f
The i n i t i a l
flux
resulting
The c u m u l a t i v e v o l a t i l i s a t i o n
after
all
discrete
from such an
t i m e t can be c a l c u l a t e d
distribution
as a p e r c e n t a g e or
The depth o f i n c o r p o r a t i o n i n f l u e n c e s the h a l f - l i f e
5inca f o r T£DD the f a c t o r s ~ - 6 E t and (2HE+V E) I(t +(2ttE+VE)t ] exp (HEL/D E) e r f e ---
to z e r o f o r
subject
]CDD i s d i s p e r s e d t o a v e r y s h a l l o w d e p t h , and
chemical Jn the s o i l .
tends
ICDD i s
~-22_7.
and e x p r e s s i n g the r e s u l t i n g
l o a d i n g , H.
that
but the s m a l l e s t
v a l u e s o f L.
of a
<< L,
]he v a r i a t i o n
in
f l u x w i t h depth o f
i n c o r p o r a t i o n can t h e r e f o r e be approximated to a p r o - r a t a change i n CO. |he p r e d i c t i o n s Z" 53 _7 f o r
from Eqn. (8) may be compared w i t h f l u x e s c a l c u l a t e d by ]hibodeaux and L i p s k y
TCDD v o l a t i l i s a t i o n
from t h i n
dust
O.037 ng/m=/y ( t h e e s t i m a t e d s u r f a c e - l a y e r New York, s i t e )
[qn.
i s 104 days.
life,
b u i l d u p and TCDD d e p o s i t i o n r a t e rc~r a B r o o k | y n , o f 0.035 ng/m = in one year wJ~l~
]he q u a n t i t y Of ]CDD r e m a i n i n g i s t h e r e f o r e 0.004 ng/m 2. The r e s u ] t J n 9
computed from the e q u a t i o n t j~
deeper
Taking L as a 0.00004 m and H as
(8) p r e d i c t s a c u m u l a t i v e v o l a t i l i s a t i o n
no water e v a p o r a t i o n . half-life,
layers.
=
0.693t/lo
(M(t)/H(0))
Thibodeaux and L i p s k y e s t i m a t e an e v a p o r a t i o n h a l f - l i f e
incorporati.~n
of
TCDD o f
a few m i l l i m e t r e s
o f 190 days at 25°C.
would d r a m a t i c a l l y
s i n c e movement to the s u r f a c e i s 'then c o n t r o l l e d
increase
its
A
hair-
by the v e r y slow r a t e o f d i f f u s i o ~
through the s o i l . lhe p e r c e n t a g e o f o r g a n i c m a t t e r i n the s o i l 2 shows the i n f l u e n c e o f f
affects
the v o l a t i l i s a t i o n
f l u x o f ]CDD.
l e v e l s o f 0.002, 0.0125 and 0 . 0 5 on the v o l a t i l i t y
oc no w a t e r e v a p o r a t i o n i s o c c u r r i n g . and depresses the v o l a t i l i s a t i o n
Figure
o f TCDD, when
I n c r e a s i n g o r g a n i c c o n t e n t r e t a r d s the movement o f ICDD
flux.
~B
Diffusion coefficients dominated.
listed in Table 2 show that transport
An interesting
is almost entirely qas-phase
feature of the values for Aroclors 1254 and 1260 is that since
KH, Koc and R L vary by the same amounts, the diffusion coefficients, R G and hence JV as given by Eqn.
(8) are
Computational
virtually
limitations
identical,
for soil
in ca]culating
water
contents
of leas
than 0.5 m]/m ~.
the complementary error function of large numbers
precluded Lhe evaluation of volatilisation flux of Aroclor 1260 for B = 0.5, and of Aroclor 1242
for t =
following
the
30 days.
In qualitative
downward t r e n d
with
terms,
respect
to
the
fluxes at these values are very
increased
saturation
and i n c r e a s e d
low, time,
respectively. Calculated fluxes is taking place,
f o r a water e v a p o r a t i o n r a t e o f 5 mm/day are l a r g e r t h a n w h e n n o e v a p o r a t i o v ~ s u p p o r t i n g the o b s e r v a t i o n s o f Haque e t . a l .
small increase with increase in soil
~18_7.
F l u x e s appear t o show a
water c o n t e n t , but decrease a g a i n as the s o i l
approaches
FIGURE 2 - VOLAIILISATION FLUX AS A F~IIUN OF ORGANIC CARBON FRACIION 13 ....
= O.]m'/m'; f
OC
:
Omm/d;
=
JW
0.002
113- 5
-
CO f
OC
1 kg/m J ;
= 0.0125
L
--
~
f
13.01 m =
OC
0.05
I
112110
113- 6
e-3
113- 7
113- 8
I
I
I fJO0
2UUU
3IIDLI
Days
10 - 3
10 - 3 ~
ARUCLOR 1 2 4 2
\
10 - 4
AROCL13R 1 2 5 4
.
10 - 4 -
• \
o
10 -5
10 - 5 -
~
v
10 -6
10 -;7
|
0
10-71
,, |
10
20
Days
30
0
I
,
#
10
20 Days
30
~aturation.
This trend
is compatible
with reported recoveries of PCB from air-dried and
saturated soils E 5 4 . 7 . Figure
2 shows
tile change
in volatilisation
matter,
for Aroclors
differs
for the two Aroclors,
fractions, results
but
in
decrease
a
1242 and 1254.
tenfold
decrease 1242.
or
increase
being more pronounced
less so at higher
for Aroclor
flux with increasing
]he effect
fractions.
levels of soil organic soil
organic
fraction
for Aroclor 1242 at low soil organic
A change
in volntilisation
Extrapolation
in
from foc
flux
= 0.0125 ~o foe
for Aroclor
of the curves
1254,
for Aroclor
and
-- 0.05
a twofold
1242 to 30 days and
comparison with Aroelor 1254, suggests that differences between the two fluxes diminish with if~crease i n
foc
and t i m e .
Iwata e t . a l .
/ - 2 6 _ 7 found t h a t
in
loamy
sand
(f
:
0.0(}1),
oc
almu.';t a l l In a silt
of loam
the t e t r a - c h l o r i n a t e d (r
= 0.2)
OC
isomers i n A r o c l o r
no preferential
losses
were
1254 had v a p o u r i s e d detected
over
this
in
12 months.
period.
lhe Flux for Aroclor 1242 shows marked differences against those of Aroclors 1254 and 1260, with increase in time.
For 8 -- 0.1 and 0.3, the three Aroclors have similar fluxes at the
initial stages but the flux of Aroclor 1242 then decreases at a faster rate.
the reason for
this behaviour is not known - presumably increasingly tenacious adsorption forces operate on Aroclor 1242, resulting in a significant lowering or volatilisation rate with time. An approximate comparison or predicted volatilisation L" 52 .7 can be made. 2,4,6,2'
flux with the study of Kilzer et.al.
These workers measured v o l a t i l i s a t i o n
,4 ' - p e n t a c h l o r o b i p h e n y ]
from wet s o i l s ,
w a t e r e v a p o r a t e d o v e r one and two hours at 25°C.
rates for a 2,5,4'
e x p r e s s e d as a f u n c t i o n
of
trichloro the
and
volume o f
The e x p e r i m e n t c o n s i s t e d o f i m p r e g n a t i n g a
bed of soil, I c,n d~'ep, with PEB to a concentration of 50 ppb, in a
jar
or 8 cm diameter.
The observed volatilisation rate of the pentachloro isomer after one and two hours was (].49% and 0.26,% or the original concentration per ml of evaporated water.
Since evaporation rate
was about I ml/hr, this corresponds to a decrease of 0.4?°~/hr, over two hours. Converting theinitial concentration of 50 ppb into units compatible with Eqn.(8), 30ppb (w/w) of PEB corresponds to C O = 6.8 x 10 -5 kg/m ~ of soil, assuming a soil density o£ 1350 kg/m ~. The initial
loading,
H(O),
is 3.4 x 10 -9 kg over 5.02 x 10 -] m ~, or 6.7 x 10 -7 kg/m 2.
Assuming a flux (Co = I) of 2 x 10 -4 kg/m2/d, the corresponding flux for C O = 5.B x 10-5kg/m ~ is 5.8 x 10 -10 kg/m=/hr, or 5.8 x 10 -10 kg/m ~ in one hour. therefore
(5.8 x 10-10/6.7 x 10 -7 ) x 100, or 0.09,~.
modelled
rate
corresponds by Kilzer
of
water
evaporation
under
conditions
Percentage
loss
in one hour is
The observed value was 0.49%. or
wicking
(5 mm
the
evaporation/day)
to a volumetric evaporation rate that is much smaller than the I ml/hr measured et.a};
the assumed
Despite these uncertainties,
flux is therefore
likely to be lower than its true value.
the agreement with Kilzer's experimental result is encouraging,
and suggests that .the predicted values are within an order or magnitude of actual volatilisation rates.
CONCLUSIONS Volatiliaation fluxes for ICDD and Aroclors 1242, 1254 and 1260, calculated from the model or Jury et.al, are in qualitative agreement with observations from field and laboratory experiments.
The model
predicts
that both
]CDD and tile Aroclors are subject to wicking.
The
97.9
u n c e r t a i n t y in many o f the i n p u t parameters to the model precludes the use of the c a l c u l a t e d Fluxes i n d e t a i l e d q u a n t i t a t i v e c a l c u l a t i o n s - r a t h e r , they should be regarded as q u a l i t a t i v e estimates,
until
sufficient
e x p e r i m e n t a l evidence i s a v a i l a b l e
to v e r i f y
the values,
lhe
model serves as a basis f o r comparing the behaviour o f these compounds against o t h e r homologucs, or s o l v e n t s such as 2 , 4 , 5 - 1 o r m i n e r a l o i l
in which they are o f t e n encountered,
lhe Fluxes
may be used to develop models c h a r a c t e r i s i n g the f a t e o r s p i l l a g e s or o f stack emissions,
l,
t h i s r e s p e c t , the present work complements the study o f lhibodeaux and Lipsky Z'53_7 on the Fate o f ICDD i n t h i n dust l a y e r s . has been published C 5 5 ~ ,
A p r e l i m i n a r y n o t i c e of- recent f i e l d
experiments w i t h I['DD
but d e t a i l e d r e s u l t s are not a v a i l a b l e For comparison. REFERENCES
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I u i n s t r a , L., in Proc. PCB Seminar, lhe Hague (1983).
40.
MackayD., Shin, W.Y., B i l l i n g t o n , J. and tluang J. in "Physical Behaviour of PgBs in Lhe Great Lakes", Ann. Arbor Science, (1983).
41.
5chroy, J.H., ttileman, F.D., and Cheng, S.C., £hemosphere,
42.
Rapaport, R.A., and Eisenreieh, 5.J., Environ. Sci. leehnol. 1B, 163 (1984).
43.
Karickhoff, 5.W. and Morris, K.R., Environ. 5ci. lechnol. 19, 51 (1985).
44.
Girvan, D.C., 5klarew, D.S., and Ainsworth, C.C., PCB Seminar, EPR], £S/EA/EL-4480, Seattle (1985).
45.
Isensee, A.R. and Jones, G.E., J. Agric. Food Chem. 19, 1210 (1971).
46.
di Domenico, A., Viviano, G., and Zapponi, G., in "Chlorinated Dioxins and Related Compounds : Impact on the Environment", (Ed) O. Hutzinger, Ro Frei, E. Merian and F. Pocchiari, Pergamon Press (1982).
47.
di Domenico, A., 5ilano, V., Viviano, G. and Zapponi, G., Ecotoxical. [nviro,. Safety, 4, 339 (1980).
48.
Kimbrough, R.D., Falk, H., Stehr, P. and Fries, G., J. 1oxicol. Environ. 11eath 14, 47 (1984).
Farmer, W.J., J. Environ. Quality 12, 558 (1983).
6/7,
877 (19B5).
49.
Wallnoffer, P.R., Koniger, M. and Engelhardt, G., Z. Pflanz. PFlanzeosehutz B2, 91 (1975).
50.
M o z a , P., Weisgerber, I. and Klein, W., J. Agric. Food Chem. 24, 881 (1976).
51.
Haque, R. and 5chmedding, D.W., J. Environ. Sci. Health (B), 11, 129 (1976).
52.
K i l z e r , L., 5eheunert, I . , Geyer, H., Klein, W. andKorte, F., Chemosphere,8, 751 (1979).
53.
[hibodeaux, L.J. and Lipsky, D., tlaz. Waste & Haz. Mat. 2, 225 (1985).
54.
Gauger, G.A., Smith, G.A., and Sullivan, J.M., PCB Seminar, EPRI, C5/EA/EL - 4480, Seattle (1985).
55.
Freeman,R.A., ttileman, F.D. and Schroy, J.M., Abstracts of Papers, 191st AC5 National Heeting, New York, 1986.
(Received
in UK 30 O c t o b e r
1986)
pp
907-920,
1987
0045-6535/87 $ 3 . 0 0 + .OO P e r g a m o n J o u r n a l s Ltd.
VOLAfILITY OF 1CDD AND PCB FROH SOIL
6 Eduljee RechemInternational Limited C h a r l e s t ~ l Road, Hardley, llythe Southampton 504 6ZA, U.K. ABSIRACT
V o l a t i l i s a t i r ~ , Fluxes o f 2 , 3 , 7 , 8 - t e t r 8 c h l o r o d i b e n z o d i o x i n and Aroclors 12~2, 1254 nnd 126(I were e s t i m a t e d from t i m model o f .]ury e t . a l . , developed f o r compounds w l t h s i m i l a r p h y s i c a l properties, lira i n f l u e i m e o f s o i l water c o . L e n t , s o i l o r g a n i c m a t t e r and water e v a p o r a t i o . was i o v e s t i g a t e d .
Increasing soil
orgmde matter decreased tim volsLilisation
flux nf all
four chemicals. Water e v s p o r s t i ~ l was accompanied by increased f l u x e s , implyi=~ t i r o l tim cl~m,icsls were susceptible to wicking, lira trends observed were in qualitative agreeme, t with field and laboratory studies. ]Ira predicted fluxes serve as a basis For comparing limit volakilisation behaviour against pesticides s,d other homologues, and For the construction of models describing the environmental Fate o f these compounds. INIRUOUCIION
P o l y c h l o r i n a t e d d i o x i n s and p o l y c h l o r i n a t e d biphenyls (PCBs) are c h a r a c t e r i s e d by low vapour pressures
and aquel,us solubilities, and high hydrophobicity, suggesting that these compounds
strongly sorb to soil, and that their moSility in a terrestrial environment is low. for example, describes 2,3,7,8-tetrachlorodibenzodioxin in relation to leaching by rainfall or irrigation.
llellir,g,
(]CDD) as "immobile" in soil Z~I,2 3
Measurements in the field have, however,
identified perpetration o£ boll, TCDD and PCBs into soil, albeit at a very slow rate.
Freema,i
and 5chroy ~" 5 _7 found that TCDD had dispersed 10 cm in 12 years at [g]in Air force Base. Movement detected, sites.
was
attributed
to the existence
but did not quantify,
of temperature
]CDD dissipation
gradients.
Young et.al.
L" 4 .7
in soil at two pheno×y herbicide storage
McClure ~" 5 .7 measured PCB fluxes at ta Jolla, California,
ai~d found that the PCB
concentration
in soil at a depth of 10 cm was typically 0.2 to 0.8 of the concentration at
the surface.
Other leaching experiments on PCB ace reviewed by 5trek and Weber Z" 6_7 and
Pal et.al. I-7_7. In order
to balance
the
concentrations
of ]CDD and PCB at
907
the soil/sir
interface
908
w i t h d e p o s i t i o n and removal Fluxes, we need t o understand the processes which a f f e c t chemicals i n the e n v i r o n m e n t . soi]
due t o h y d r a u l i c a c t i o n ,
deplete
the c o n c e n t r a t i o n
deposition
and m i x i n g
Apart
these p o l l u t a n t s dust
at
from d i f f e r e n t
the s u r f a c e sources,
PCBs Z~ B,9 _7 and TCDD ~- 10,11 7 removal mechanism.
have e s t a b l i s h e d
that
of
the s o i l ;
resuspension
p h o t o c h e m i c a l d e g r a d a t i o n , b i o d e g r a d a t i o n and e v a p o r a t i o n . significant
o f ICDD and PCB i n t o the
t h e r e are a number o f o t h e r p h y s i c o c h e m i c a l p r o c e s s e s t h a t can
of
with
From downward t r a n s p o r t a t i o n
these
of
for dust
example,
particles,
S t u d i e s on the p h o t o c h e m i s t r y o f photo-oxidation
can c o n s t i t u t e
a
B i o d e g r a d a t i o n i s not c o n s i d e r e d t o be a major removal p a t h -
way f o r these chemicals ~ ' 1 2 , 1 ~ 7 . lhibodcaux Z-14.7 thP. major
route
suggested t h a t for
offsite
v a p o u r i s a t i o n o f TCDD from c o n t a m i n a t e d s o i l
transport
from a h e r b i c i d e
Nash and B e a l l E 1 5 _ 7 d e t e c t e d ICDD v o l a t i l i s a t i o n 2,4-D.
Hackay and Wolkoff Z-16_7 and Hackay
aEion f l u x e s o f PCB From water b o d i e s . surface.
Hurphy e t . a l .
trations
above hazardous waste l a n d f i l l
Clearly,
volati]isation
of
plots
these compou,~ds i n t o
measured h i g h atmospheric PCB concen-
sites.
the atmosphere, under c e r t a i n
Z-21-7
have p o i n t e d
surfm'es
is very difficult,
out,
volatilJs-
Z-18_7 measured l o s s o f PCB From a sand
Z-20J
o f TCDD and PCB could be a s i g n i f i c a n t
Philippi
Facility.
t r e a t e d w i t h S i l v e x and
Z-17-7 c a l c u l a t e d s i g n i f i c a n t
Haque e t . a l .
C 1 9 - 7 and Lewis e t . a l .
p r o d u c t i o n and d i s p o s a l
from f i e l d
et.al.
s u r f a c e s wa,J
a theoretical
r o u t e f o r secondary emissions
conditions.
treatment
of
However, as I l u t t e r votatilisation
fro,,
owing to the c o m p l e x i t y and interdependence o f f a c t o r s
o r g a n i c carbon c o n t e n t , c a p i l l a r y
movement, o f s o i l
arid soil
such as
w a t e r , t e m p e r a t u r e and h u m i d i t y .
VULAI ILISAIll)N Information Podo]l air flux.
orl the
eL.al.
diffusion
influerlce
E 22_7
of
soil
speculated
properties
that
or w a t e r - m e d i a t e d e v a p o r a t i o n ( w i c k i n g ) ,
V a p o u r i s a t i o n Flux was noL q u a n t i f i e d .
Kearney e t . a l . distilling
E 23_7
considered
with water,
and P h i l i p p i
on TCDD v o l a t i l i s a t i o n
IEDD would not
lhis
that
be expected t o
is
by s o i l -
and i n c r e a s e d m o i s t u r e would lower the
Thibodeaux E 1 4 J
]CDD would behave l i k e
has r e p o r t e d o p p o s i t e v i e w s . DDI and v o l a t i l i s e
pherlomena has been q u e s t i o n e d by Igue e t . a l .
Z-21 .7 estimaLed the v o l a t i l i s a t i o n
i~consisterlt.
volatilise
Flux from wet s o i l
by co-
E24.7.
tlutter
t o be 2 - 3 ng/cm2/h,
about 75% t h a t o f DD]. The i n f o r m a t i o n
on PCB v o l a t i l i s a t i o n
demonstrated t h a t
From s o i l
evaporation of Aroclor
is also inconclusive.
Ilaque e t . a l .
1254 was much slower from Woodburn s o i l
Z-18_7
that
Ottawa sand, presumably because o f the h i g h e r o r g a n i c m a t t e r c o n t e n t o f the former. workers a l s o i d e n t i f i e d soil.
enhanced e v a p o r a t i o n due t o w i c k i n g ,
Fluxes were not measured.
]oss from e x p e r i m e n t a l s o i l Scharpenseel e t . under s t e r i l e
al.
L-27 7
conditions,
Hoza e t . a l .
systems,
/'25.7
measured l a r g e PCB losses
whereas Krogmann e t .
al.
From sand but not from Woodburn
and Iwata e t . a l .
to v o l a t i l i s a t i o n ,
From These
~'26.7 attributed
but again f l u x e s w e r e n o t
PCB
quantified.
from an e x p e r i m e n t a l p l o t m a i n t a i n e d
L~ 2B_7 found t h a t PCB removal from s o i l
was v e r y low. In the absence o f detailed experimental data on the influence o f s o i l v o l a t i l i s a t i o n o f ICDD and PCBs, i t
would be oF i n t e r e s t to e l i c i t
properties on the
t h i s information through
the application oF t h e o r e t i c a l models which have been developed for pesticides, compounds
909
a p p r o x i m a t e TCDD and PCBs in t h e i r
which most c l o s e l y
the work o f Jury e t . a l . 1260
in
order
to
/-29,30,31,32_7 will
predict
vapourisation
physical properties.
In t h i s p n l m [ .
be a p p l i e d to ICDD and A r o c l o r s 1242, 1254 and fluxes
under
various
environmental
conditions.
V O L A I I L I S A I I O N MODEL
1he v o l a t i l i s a t i o n diffusion
rate
of
a surface-applied
by a d s o r p t i o n t o the s o i l . addition
chemical w i l l
through the a i r boundary l a y e r and i t s ]tie v o l a t i l i s a t i o n
be determined by i t s
r a t e For a s o i l - i n c o r p o r a t e d
to the above, depend on tile r a t e o f d e s o r p t i o n from the s o i l
the s u r f a c e . diffusion,
rate
nf
vapour pressure or vapour d e n s i t y , m o d i f i e d chemical w i l ] , i n
and upward movement (o
1wo mechanisms f o r upward movemenL can o p e r a t e , i n d e p e n d e n t l y or s i m u l t a n e o u s l y ;
and mass t r a n s f e r .
Diffusion
i n v o l v e s movement o f the chemical L h r o u q h a q r n d i e n t ,
caused e i t h e r by a depleLed s u r f a c e c o n c e n t r a t i o n due to e v a p o r a L i o n , or L e m p e r a t u r e q r a d i e n t . q as suggested by Freeman and Schroy f o r
1CDD ~ - 3 .7.
temperature,
adsorption,
waLer.
and by v a r i a b l e s
Diffusion
Hans t r a n s f e r
through s o i l
of
a chemical
chemical i n s o l u t i o n , as w i t t i n g
affecting
1he d i f f u s i o n such as s o i l
is
controlled
hy
and s o i l
can occur i n both vapour and s o l u t i o n phases Z-33_7. is
effected
by the upward movement o f
t o r e p l a c e e v a p o r a t i v e water l o s s a t tile s o i l
L-3a 7 .
rate
organic matter
waLer,
containing
the
s u r f a c e , a process known
]he r a t e o f movement~ determined by the r a t e o f water e v a p o r a t i o n ,
dependent on the r e l a t i v e
h u m i d i t y o f the a i r ,
wind speed, tile degree o f s o l u b i l i t y
and to s o i l
adsorption.
Jury e t . a l .
,_/"29,38,31,32 7 i n c o r p o r a t e d these f a c t o r s i n t o a mathematical model d e s c r i b i n g
the
transport
of
assumes l i n e a r , first
Wicking g e n e r a l l y a c c e l e r a t e s tile v o l a t i l i s a L i o n
is
in water,
chemicals
through
equilibrium
order loss,
soil,
partitioning
and loss
at
the s o i l - a i r
between l i q u i d ,
rate of a chemical.
interface.
!he model
vapour and adsorbed phases,
net
a stagnant a i r boundary l a y e r , and steady s t a t e water flow upwards (wickJnq)
or downwards ( l e a c h i n g ) . Diffusion
Coefficients
lhe s o i l - g a s
diffusion
DG :
coefficient
i s g i v e n by
(a10/3 / f12 ) D~ir
where DGait i s the a i r - g a s d i f f u s i o n
(l)
c o e f f i c i e n t , _ a i s the v o l u m e t r i c a i r c o n t e n t o f the s o i l ,
and ~ i s tile s o i l p o r o s i t y . lhe s o i l - l i q u i d
diffusion
DL
coefficient,
/
:
~2
[ 810/3 /
where t) ~water L i s the w a t e r - l i q u i d
DL i s
_water ] UL
diffusiou coefficient,
(2) and fl tile v o l u m e t r i c wa/er c o n t e n t ,
(~ - a). lhe e f f e c t i v e effects
diffusion
coefficient,
o f a d s o r p t i o n and p a r t i t i o n i n g DE
=
(DG/RG)
+
DE, i s the sum o f DG end DL, each c o r r e c t e d f o r the between gaseous and l i q u i d
(DL/RLI
phases.
Thus, (3)
where RG = P K D / K | t RL
= /DKD
+
+ 8
8/K H +
aK H
+
a
(~) (5)
?:.©
P
being the bulk density of the soil, K D the soil-liquid partition coefficient and KII ,
llEnry 's constant. Volatilisation
Flux
The effective solute convection velocity is given by VE :
JW/ RL
(6)
where 3W is the water flux;
upward ( - ) , downward (+) or zero.
At the soil surface, the
effective transport velocity across tile stagnant air boundary layer of thickness d is given by ~air. HE = uG / (dR G)
(7)
For a uniform incorporation of H (kg/m2) of chemical to a depth of L (m)below tile surface, the v o l a t i l i s a t i o n Flux at the surface is written as JV
[
o
[(L + VEt) I )
VEt
{
+ (2HE + VE) exp [HE(HE+VE)L/DE] { exp(HEL/DE)erFc
-erfc
[
(L + (2HE + VE)t) J4DEL ]
(2HE + VE)t /4DEt ]II
(8)
where C is tile uniform i n i t i a l concenLration oF tile applied chemical, p is the firsLo order degradation (loss) rate constant given by t is time, erfc (x) tile comple-
(0.693/t½),
mentary error function and t½ the volatiiisation h a l f - l i f e . Eqn. (8) permits tile calculation of v o l a t i l i s a t i o n flux as a function of soil parameters such as moisture, density,
porosity,
organic
temperature (i.e.
carbon
fraction
(incorporated
into KD;
see below),
bulk
change i n KH) and o t h e r f a c t o r s such as w a t e r e v a p o r a t i o n r a t e mid
the amount o f chemical a p p l i e d .
Ihe model has been t e s t e d on a wide range o f chemicals Z-32~7. ]NPU[ PARAI~IERS
lhere is considerable uncertainity fluxes
ca|culated
From Eqn.
(8)
o v e r many o f the i n p u t parameters. should o n l y
For t h i s
be regarded as q u a l i t a t i v e
reason, tile
estimates,
and an
indication of trends. Diffusion
coefficients
D Gair
=
For a i r - g a s
and w a t e r - l i q u i d
transport
are assigned v a l u e s o f ~ 2 9 7
0.43 m2/d
Dwater L =
4.3 x 10 -5
(9) m=/d
(10)
The soil-liquid partition coefficient, KD, is obtained From the equation ~D
=
Koc foc
(11)
where foc is the fraction of organic carbon in the soil, and KociS its partition coefficient, obtained from the octanol-water partition coefficient, Kow , with log K
oc
=
1.029 log K
ow
-
0.18
Z~ 2 9 J (12)
911
K D is expressed in 51 units of m~/kg.
The dimensionless Henry's constant, KII, is given by
tile ratio of tile concentration of the chemical in the soil air and liquid phases.
Applyin 9
tile ideal gas law to the former, we get /-35_7 KH
=
16.04 PH/(IS)
(13)
where M is the molecular weight of the solute, P its vapour pressure (rot, of Hg) and 5 its
s o l u b i l i t y in water (mg/l), both at tlle temperature I . While Kow and Kllare uniquely defined For ]CDD, t h i s is not the case For Aroclors 1242, 1254 and 1260, considered in t h i s paper.
Doskey and Andren
/-36.7
Bad Mackay e t . a l . L-17_7 have
noted that the calculation of K H requires that the vapour pressure and aqueous s o l u b i l i l y must r e f e r
to
t h e same s t a t e
temperature,
the Aroclors
of matter;
are viscous
whereas individual
liquids.
PCB i s o m e r s a r e s o l i d s
Aroclors
in the environment
at ambient
partition as
individual isomers, as can be seen from the adsorption experiments of lwata et.al. Z-26_7 and therefore, a rigorous examination of their behaviour should also be on this basis L-37,38_7. Heasurements standard:
of
PCBs
in
the
environment
have
invariably
been
referenced
to
an
Aroclor
the importance of isomer-specific data has only been appreciated in recent work
/-39,40_7.
For tt~e p r e s e n t c a l c u l a t i o n s , from 5chroy e t . a l . Hackay
et.al.
/-41_7.
E 17 7
vapour, p r e s s u r e ,
solubility
and K
OW
data f o r
1CDD were taken
For the A r o e l o r s , d a t a on 1242 and 1254 were taken from
w i t h mean l o g Kow v a l u e s o f 5.0 and 6.4 r e s p e c t i v e l y .
I n f o r m a t i o n on
Aroclor 1260 was obtained From Rapaport and Eisenreich Z-42..7, with a mean log K
of 6.B. ow
Karickhoff and Morris 2-43-7 and Girvan et.al. /-44.7 have suggested that reported partition
c o e f f i c i e n t data may be too low by a factor of two of three.
At present there is i n s u f f i c i e n t
information to establish whether t h i s is indeed the case. lhe d e g r a d a t i o n h a l f - l i f e , experimentation.
t½, i s a n o t h e r parameter t h a t has not been u n e q u i v o c a l l y d e f i n e d by
Heasured d e g r a d a t i o n g e n e r a l l y accounts For a l l
Forms or l o s s ,
b i o d e g r a d a t i o n , l e a c h i n g , photochemical r e a c t i o n and e v a p o r a t i o n . has not been q u a n t i f i e d ,
except from the s u r f a c e s o f pure l i q u i d s .
found t h a t 2% o f ICDD had v o l a t i l i s e d
from a glass s u r f a c e , a f t e r
C 23-7 s t u d i e d the p e r s i s t e n c e o f ICDD i n two s o i l the a p p l i e d amount p e r s i s t e d a f t e r from 5eveso. half-life soil.
one y e a r .
]sensec two days.
including l o s s per se
and Jones / - 4 5 _ ] Kearney e t . a l ,
types at t h r e e r a t e s o f a p p l i c a t i o n .
]his half-life
di Domenico and co-workers L" 4 6 , 4 7 7
Italf
is consistent with early reports
and Kimbrough e t . a ] .
L-48_7 e s t i m a t e the
o f ICDD to be i n the r e g i o n o f 10 - 12 years f o r ICDD t h a t had been mixed i n t o the Freeman a~d 5chroy [
remained
in
the
soil
towards the s u r f a c e . application applied unshaded McClure
Volatilisation
after
3 _7 Found t h a t 12 y e a r s ,
plots / - 5_7
the ICDD a p p l i e d at a deptll o f 11 cm had there
From the g r a d i e n t o f the d i f f u s e d
would have r e s u l t e d
2,4-D
all
although
in
breakthrough
contaminated
with
1CDD, onto
experienced
loss
of
calculated
a half-life
ICDD, of
to
was evidence o f front,
PCB i n
the
to top
movement
is evident that a shallower
the s u r f a c e .
experimental
equivalent
it
diffusive
grass
Nash and B e a l l plots.
a half-life 10 cm o f
soil,
Both of
about
~ 15 -7
shaded and one y e a r .
of 6 years,
this
included both leaching and emissions i n t o the atmosphere. Wallnoffer e t . a l . E49.7 measured losses of about 50% of Aroclor 1254 when applied to three s o i l types, during a 2 to 4 month period.
Moza e t . a l .
~ ' 2 5 , 5 0 . 7 l o s t 79% o f a d i c h l o r o b i p h e n y l ,
67% o f a t r i c h l o r o b i p h e n y l
an(~
~ J.J-
42% o f a p e n t a c h l o r o b i p h e n y l ff18_7
from the t o p 1 cm o f a sandy loam d u r i n g one y e a r . Hague e t . a l .
a p p l i e d A r o e l o r 1254 to Ottawa sand and Woodburn s o i l .
sand f o r
tetra-,
penta-,
and h e x a - c h l o r o b i p h e n y l s
was greater from wet sand than from dry sand. from Woodburn s o i l .
Volatilisation
half-lives
from
were 10, 25 and 4D days r e s p e c t i v e l y ,
lo~s
lhese workers did not detect v o l a t i l i s a t i o n
lwata et. al. [ 26_} applied Aroclor 1254 to six Californian s o i l s ,
incorporated to a depth o f 15 cm.
50% o f the lower chlorinated isomers
was
lost
in
two
months, whereas oniy 18% of the heptachlorobiphenyls was lost in 8 months, froma loamy sand. toss after I year from soils containing 10% to 19% of organic matter amounted to 5~ for all chlorinated species. Scharpenseel et.a]. [ 2 7 ~
investigated the movement of a triehlorobiphenyl in soil.
the administered quantity remained after a period of 9 months. applied amount
remained after 9 months,
rather than evaporation.
12% of
In a sandy soil, 8% of the
but most of the loss was attributed
to leachinq
PCB loss was experienced under both sterile and biotic conditions.
llaque and Sehmedding ~ 5 1 ~
and Kilzer et.al. ~ 5 2 ] have also established that PCBs volatilise
from soil surfaces - the latter workers measured volatilisation rates for a tri- and pentachIorobiphenyl uuder conditions of wicking, From
the experimental
evidence,
HcClure's
Aroelors would appear to be too high, lwata et.al,
and Seharpenseel et.al,
from wet soils,
as a function of water loss.
estimation of a half-life of 6 years
[or tlle
faking into account the work of Moza et.al., referred to above, we ascribe tentative half-lives of
0.5, 1.0 and 2.0 years for Aroclors 1242, 1254 and 1260 respectively.
For ICDD we assume
a
half-life of 10 years, under soil-incorporated conditions. A list of these n,,d other input parameters used in the simulation is presented in fable I. Factors such as water content, organic 6arbon fraction and water evaporation rate were varied to assess their influence on vapourisation
flux.
RESULTS
Diffusion c o e f f i c i e n t s (DG/RG), (DL/RL) and DE are l i s t e d in fable 2, and i l l u s t r a t e d in Figure
1.
Volatilisation
Fluxes f o r
nominal
P = 1550 kg/m ~ and ~ = 0.5 are shown i n and Jw = ( - ) Eqn.
5 ram/day, a t
volumetric
soil
lables
soil
properties
3 and 4 f o r
water contents
of f : 0.O125, L : 0.O1 m, oc two e v a p o r a t i o n r a t e s ; JW = U
o f O.1,
(7) was a s s i g n e d a v a l u e o f 4.75 x 10 -3 m For no e v n p o r a t i o n ,
evaporation
rate
of
1 kg/m ~ t o f a c i l i t a t e
5 ram/day ~ 31_7.
Co,
the i n i t i a l
0.3 and 0.5 m3/m ~
concentration,
easy c o n v e r s i o n For o t h e r a p p l i c a t i o n
rates
d in
and 2.38 x 10 -3 m f o r an is
nominally
set
(H kg/m' t o a d e p t h o f
at
L m).
DISCUSSION ICDO Exmmination of fable 2 and Figure la shows that diffusion of TCDO in s o i l is vapour-dominated up to a volumetric water content of 0.3 m3/m ~, and then liquid-dominated to saturation, implies
that
movement
to
the
surface,
and
therefore
vapourisation
into
the
air,
lhis would
initially decrease as the pore spaces are filled with water, and then increase as liquid diffusion predominates.
Vapourisation fluxes listed in Table 5 confirm this trend.
Fluxes
913
1ABLE 1 - INPUT PARAI4EIERS r o e EQN. 8
Aroclors
Property
Units
Soil
P
kg/m ~
1350
T
K
ICDD
1242
1254
1260
1140
86
2600
6500
0.5 298 O.01
m
L
O.O125
f'oc m~/kg
Koc
7.9 E-5
KH
t%
IABLE 2 -
O.114
0.023
3650
days
365
183
0.29t 73(1
DIFFUSION COEFFICIENIS FOR I C ~ ) AND AROCLORS 1242, 1254 AND 1260 AS A FIINCTION OF SOIL WAIER CONIEN!
Diffusion coefficients, m'/d 8
DG/R G
DL/R L
DE
DG/R G
TCDD
0 O.1 0.2 0.3 0.4 0.5
7.02 3.33 1.27 3.33 3.00
E-13 E-13 E-13 E-14 E-15 O
0 4.15 4.18 1.62 4.22 8.89
E-15 E-14 E-13 E~13 E~13
4.43 2.10 8.05 2.08 2.08
E-07 E-B7 E-08 E-O8 E-09 0
0 1.82 1,83 7.09 1.85 3.89
E-12 E-11 E-11 E-10 E-IO
DE
A r o c l o r 1242 7.82 3.37 1.69 1.95 4.25 8.89
E-13 E-13 E-13 E-13 E-13 E-13
3.06 1.45 5.55 1.44 1.44
4.43 2.10 8.05 2.O9 2.26 3.89
E-07 E-07 E-O8 E-08 E-O9 E-IO
4.53 2.10 8.20 2.12 2.03
E-06 E-O6 E-07 E-07 E-08 0
0 6.22 6.27 2.42 6.23 I . 33
E-11 E-IU E-09 E-09 E-08
3.06 I .45 5.56 I .46 2.06 I .33
t -(16 E-06 E-U7 E-D7 E-[18 E-O8
4.53 2.11 8.2U 2.12 2.11 1.55
E-U7 [-07 E-01] E-UB E-09 E-IO
A r o c l o r 1260
Aroclor 1254 0 O.1 0.2 0.3 0.4 0.5
DL/R L
E-07 E-O7 E-O8 E-U8 E-09 0
0
7.25 7.32 2.83 7.37 1.55
E-13 E-12 E-II [-11 E-IO
9!Z
'.0 '.0 O O I
I
c3 cM
I
I
I
I
I
W
L.~J tuJ
r~
¢x% ¢c~
i~u'%
u",, ,,O
~dO LZ'I OC)
WW
~S
I
o, ~, o,
O
L~LdW
W
$
I
•
°
q
I
!
WL.~J O-. ,r--
I
El
bJ W
•
w
°
i
IN
§
,
I
hi
1
o ~P, ",O
I.~2
t.~J La.I
T
•
•
~-.I c-J
•
°
N
t~l L/
Lr~
=,~o,
s, s, s, bJ
l
LJW
"
I ' ~ N •
t.~l w
~ O i
L~
N °
°
I
WL¢.I
W
R~
',D r - -
°
•
fa')
!-- A
°
~-J
,-: ,-: ,Z
~8 t~,
i.i
N
E3
°
CD
!
O0
•
•
t-
r.
C~
d-
~ o ¢~0 i~ .
o~o
I.i.
~Jw~J C O o
(:3 !
•
,
,
I
I
X
~.1
~o-, C )
~,~o,
"4:) ~:) r",.
•,L} "-Q
w
W
L~.J b J
...l I.~ Z
P-. r ~ I
I
C3 I
O !
-e-
(/1 xo ~•
.
c)
I
k~.l I M
"'w
.
i
ll W
f'-- O~ •
•
°
I
I
i,i
I
I.i
L~
.
.
!
I
I~J t . J L~J ,.,/
,~,=, La.J W
t.iJ
',D r,'~ Ii
II
'.0 r - -
I
3 •
°
f " - "43
,...I
I
q-- ...1"
L~L~ OxOx f-~ m7
~.4
=~o w
w
t.a.I
La.J W
t~.l
(~', "4~ o', •
°
•
•
°
w w
F~W •
•
°
•
o
915
FIGURE
1 - DIFFUSION
a -
1EDD
COEFFICIENTS
b - AffOCLOfl 1242
AS A F U N E I I O N
OF S O I L WAIER EONIENI
c - AROCLOR 1254
'DE
"DL/RL
d - AROCLOR 1260 ....
'DG/R G
10 -5 10 - 1 2
-
(a)
°L
% G
~
\
10 -13
",/ \ \
Z
~ 1 0 -14
/
•
/
\,
\
10-71 -
, /"
\
\, \
/ lO -15
~
I
[I
I
II .1
io-11l /
I ~
0.3
I
0.5
I
t
0.1
',
I
0.3
0.5
6
i
(c)
(d)
i
1U-6 i
10 - ]
% G 10 -5
10 - 8
I I,I
~°
x
{J
\
z t,-,,
~ 1 0 -10
/
t
I
/
I
l
/
I
I I
I
I
o.1
0.3 B
I
t
/-
10 -11
I
/
10 -12
I
/
/
I
o.5
10 -1~
L !
/
/
I I
I o.1
I
I
I I
0.3
0.5
916
increase
with
to w i c k i n g . [qn.
(8)
water evaporation rate;
the model t h e r e f o r e
This i s c o n t r a r y to the views o f P o d o l l e t . a l .
is
suitable
for
predicting
volatilisation
a d d i t i o n s o f TCDD, such as the r e l e a s e o f 5eveso. incident
is
likely
t o be h i g h , s i n c e N ( 9 ) o f
(C° = M/L) i s t h e r e f o r e l a r g e . by m u l t i p l y i n g fraction
the f l u x
by t ,
o f the i n i t i a l
predicts
fluxes
as a consequence o f
The i n i t i a l
flux
resulting
The c u m u l a t i v e v o l a t i l i s a t i o n
after
all
discrete
from such an
t i m e t can be c a l c u l a t e d
distribution
as a p e r c e n t a g e or
The depth o f i n c o r p o r a t i o n i n f l u e n c e s the h a l f - l i f e
5inca f o r T£DD the f a c t o r s ~ - 6 E t and (2HE+V E) I(t +(2ttE+VE)t ] exp (HEL/D E) e r f e ---
to z e r o f o r
subject
]CDD i s d i s p e r s e d t o a v e r y s h a l l o w d e p t h , and
chemical Jn the s o i l .
tends
ICDD i s
~-22_7.
and e x p r e s s i n g the r e s u l t i n g
l o a d i n g , H.
that
but the s m a l l e s t
v a l u e s o f L.
of a
<< L,
]he v a r i a t i o n
in
f l u x w i t h depth o f
i n c o r p o r a t i o n can t h e r e f o r e be approximated to a p r o - r a t a change i n CO. |he p r e d i c t i o n s Z" 53 _7 f o r
from Eqn. (8) may be compared w i t h f l u x e s c a l c u l a t e d by ]hibodeaux and L i p s k y
TCDD v o l a t i l i s a t i o n
from t h i n
dust
O.037 ng/m=/y ( t h e e s t i m a t e d s u r f a c e - l a y e r New York, s i t e )
[qn.
i s 104 days.
life,
b u i l d u p and TCDD d e p o s i t i o n r a t e rc~r a B r o o k | y n , o f 0.035 ng/m = in one year wJ~l~
]he q u a n t i t y Of ]CDD r e m a i n i n g i s t h e r e f o r e 0.004 ng/m 2. The r e s u ] t J n 9
computed from the e q u a t i o n t j~
deeper
Taking L as a 0.00004 m and H as
(8) p r e d i c t s a c u m u l a t i v e v o l a t i l i s a t i o n
no water e v a p o r a t i o n . half-life,
layers.
=
0.693t/lo
(M(t)/H(0))
Thibodeaux and L i p s k y e s t i m a t e an e v a p o r a t i o n h a l f - l i f e
incorporati.~n
of
TCDD o f
a few m i l l i m e t r e s
o f 190 days at 25°C.
would d r a m a t i c a l l y
s i n c e movement to the s u r f a c e i s 'then c o n t r o l l e d
increase
its
A
hair-
by the v e r y slow r a t e o f d i f f u s i o ~
through the s o i l . lhe p e r c e n t a g e o f o r g a n i c m a t t e r i n the s o i l 2 shows the i n f l u e n c e o f f
affects
the v o l a t i l i s a t i o n
f l u x o f ]CDD.
l e v e l s o f 0.002, 0.0125 and 0 . 0 5 on the v o l a t i l i t y
oc no w a t e r e v a p o r a t i o n i s o c c u r r i n g . and depresses the v o l a t i l i s a t i o n
Figure
o f TCDD, when
I n c r e a s i n g o r g a n i c c o n t e n t r e t a r d s the movement o f ICDD
flux.
~B
Diffusion coefficients dominated.
listed in Table 2 show that transport
An interesting
is almost entirely qas-phase
feature of the values for Aroclors 1254 and 1260 is that since
KH, Koc and R L vary by the same amounts, the diffusion coefficients, R G and hence JV as given by Eqn.
(8) are
Computational
virtually
limitations
identical,
for soil
in ca]culating
water
contents
of leas
than 0.5 m]/m ~.
the complementary error function of large numbers
precluded Lhe evaluation of volatilisation flux of Aroclor 1260 for B = 0.5, and of Aroclor 1242
for t =
following
the
30 days.
In qualitative
downward t r e n d
with
terms,
respect
to
the
fluxes at these values are very
increased
saturation
and i n c r e a s e d
low, time,
respectively. Calculated fluxes is taking place,
f o r a water e v a p o r a t i o n r a t e o f 5 mm/day are l a r g e r t h a n w h e n n o e v a p o r a t i o v ~ s u p p o r t i n g the o b s e r v a t i o n s o f Haque e t . a l .
small increase with increase in soil
~18_7.
F l u x e s appear t o show a
water c o n t e n t , but decrease a g a i n as the s o i l
approaches
FIGURE 2 - VOLAIILISATION FLUX AS A F~IIUN OF ORGANIC CARBON FRACIION 13 ....
= O.]m'/m'; f
OC
:
Omm/d;
=
JW
0.002
113- 5
-
CO f
OC
1 kg/m J ;
= 0.0125
L
--
~
f
13.01 m =
OC
0.05
I
112110
113- 6
e-3
113- 7
113- 8
I
I
I fJO0
2UUU
3IIDLI
Days
10 - 3
10 - 3 ~
ARUCLOR 1 2 4 2
\
10 - 4
AROCL13R 1 2 5 4
.
10 - 4 -
• \
o
10 -5
10 - 5 -
~
v
10 -6
10 -;7
|
0
10-71
,, |
10
20
Days
30
0
I
,
#
10
20 Days
30
~aturation.
This trend
is compatible
with reported recoveries of PCB from air-dried and
saturated soils E 5 4 . 7 . Figure
2 shows
tile change
in volatilisation
matter,
for Aroclors
differs
for the two Aroclors,
fractions, results
but
in
decrease
a
1242 and 1254.
tenfold
decrease 1242.
or
increase
being more pronounced
less so at higher
for Aroclor
flux with increasing
]he effect
fractions.
levels of soil organic soil
organic
fraction
for Aroclor 1242 at low soil organic
A change
in volntilisation
Extrapolation
in
from foc
flux
= 0.0125 ~o foe
for Aroclor
of the curves
1254,
for Aroclor
and
-- 0.05
a twofold
1242 to 30 days and
comparison with Aroelor 1254, suggests that differences between the two fluxes diminish with if~crease i n
foc
and t i m e .
Iwata e t . a l .
/ - 2 6 _ 7 found t h a t
in
loamy
sand
(f
:
0.0(}1),
oc
almu.';t a l l In a silt
of loam
the t e t r a - c h l o r i n a t e d (r
= 0.2)
OC
isomers i n A r o c l o r
no preferential
losses
were
1254 had v a p o u r i s e d detected
over
this
in
12 months.
period.
lhe Flux for Aroclor 1242 shows marked differences against those of Aroclors 1254 and 1260, with increase in time.
For 8 -- 0.1 and 0.3, the three Aroclors have similar fluxes at the
initial stages but the flux of Aroclor 1242 then decreases at a faster rate.
the reason for
this behaviour is not known - presumably increasingly tenacious adsorption forces operate on Aroclor 1242, resulting in a significant lowering or volatilisation rate with time. An approximate comparison or predicted volatilisation L" 52 .7 can be made. 2,4,6,2'
flux with the study of Kilzer et.al.
These workers measured v o l a t i l i s a t i o n
,4 ' - p e n t a c h l o r o b i p h e n y ]
from wet s o i l s ,
w a t e r e v a p o r a t e d o v e r one and two hours at 25°C.
rates for a 2,5,4'
e x p r e s s e d as a f u n c t i o n
of
trichloro the
and
volume o f
The e x p e r i m e n t c o n s i s t e d o f i m p r e g n a t i n g a
bed of soil, I c,n d~'ep, with PEB to a concentration of 50 ppb, in a
jar
or 8 cm diameter.
The observed volatilisation rate of the pentachloro isomer after one and two hours was (].49% and 0.26,% or the original concentration per ml of evaporated water.
Since evaporation rate
was about I ml/hr, this corresponds to a decrease of 0.4?°~/hr, over two hours. Converting theinitial concentration of 50 ppb into units compatible with Eqn.(8), 30ppb (w/w) of PEB corresponds to C O = 6.8 x 10 -5 kg/m ~ of soil, assuming a soil density o£ 1350 kg/m ~. The initial
loading,
H(O),
is 3.4 x 10 -9 kg over 5.02 x 10 -] m ~, or 6.7 x 10 -7 kg/m 2.
Assuming a flux (Co = I) of 2 x 10 -4 kg/m2/d, the corresponding flux for C O = 5.B x 10-5kg/m ~ is 5.8 x 10 -10 kg/m=/hr, or 5.8 x 10 -10 kg/m ~ in one hour. therefore
(5.8 x 10-10/6.7 x 10 -7 ) x 100, or 0.09,~.
modelled
rate
corresponds by Kilzer
of
water
evaporation
under
conditions
Percentage
loss
in one hour is
The observed value was 0.49%. or
wicking
(5 mm
the
evaporation/day)
to a volumetric evaporation rate that is much smaller than the I ml/hr measured et.a};
the assumed
Despite these uncertainties,
flux is therefore
likely to be lower than its true value.
the agreement with Kilzer's experimental result is encouraging,
and suggests that .the predicted values are within an order or magnitude of actual volatilisation rates.
CONCLUSIONS Volatiliaation fluxes for ICDD and Aroclors 1242, 1254 and 1260, calculated from the model or Jury et.al, are in qualitative agreement with observations from field and laboratory experiments.
The model
predicts
that both
]CDD and tile Aroclors are subject to wicking.
The
97.9
u n c e r t a i n t y in many o f the i n p u t parameters to the model precludes the use of the c a l c u l a t e d Fluxes i n d e t a i l e d q u a n t i t a t i v e c a l c u l a t i o n s - r a t h e r , they should be regarded as q u a l i t a t i v e estimates,
until
sufficient
e x p e r i m e n t a l evidence i s a v a i l a b l e
to v e r i f y
the values,
lhe
model serves as a basis f o r comparing the behaviour o f these compounds against o t h e r homologucs, or s o l v e n t s such as 2 , 4 , 5 - 1 o r m i n e r a l o i l
in which they are o f t e n encountered,
lhe Fluxes
may be used to develop models c h a r a c t e r i s i n g the f a t e o r s p i l l a g e s or o f stack emissions,
l,
t h i s r e s p e c t , the present work complements the study o f lhibodeaux and Lipsky Z'53_7 on the Fate o f ICDD i n t h i n dust l a y e r s . has been published C 5 5 ~ ,
A p r e l i m i n a r y n o t i c e of- recent f i e l d
experiments w i t h I['DD
but d e t a i l e d r e s u l t s are not a v a i l a b l e For comparison. REFERENCES
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