Chemical Modeling in Aqueous Systems - ACS Publications

8 Chemical Speciation of Copper i n River Water Effect of Total Copper, p H , Carbonate, and Dissolved Organic Matter

WILLIAM G. SUNDA and PETER J. HANSON

Downloaded by FUDAN UNIV on February 17, 2017 | http://pubs.acs.org Publication Date: March 19, 1979 | doi: 10.1021/bk-1979-0093.ch008

National Marine Fisheries Service, Southeast Fisheries Center, Beaufort Laboratory, Beaufort, NC 28516 There i s i n c r e a s i n g evidence that the a v a i l a b i l i t y of a q u e o u s t r a c e m e t a l s t o a number o f o r g a n i s m s i s d e t e r m i n e d by f r e e metal i o n a c t i v i t y r a t h e r than t h e t o t a l c o n c e n t r a t i o n o f metal i n s o l u t i o n (]_-6j. The c h e m i c a l a s s o c i a t i o n s o f t r a c e metals with inorganic and organic ligands a r e major f a c t o r s that c o n t r o l metal i o n a c t i v i t i e s and thus bioavailability. I n t h i s s t u d y , we i n v e s t i g a t e t h e c o m p l e x a t i o n o f c o p p e r b y i n o r g a n i c and o r g a n i c l i g a n d s i n t h e water o f two r i v e r s i n coastal North C a r o l i n a . An i o n - s e l e c t i v e e l e c t r o d e was used t o d i f f e r e n t i a t e between f r e e a n d bound c u p r i c i o n i n t i t r a t i o n s o f r i v e r w a t e r s a n d model s o l u t i o n s . S t a b i l i t y c o n s t a n t s were determined i n chemically defined solutions f o r complexation of c o p p e r by h y d r o x i d e and c a r b o n a t e i o n s , t h e two m a j o r i n o r g a n i c c o p p e r c o m p l e x i n g l i g a n d s i n most n a t u r a l waters ( 7 ) . From t h e s e r e s u l t s , t o t a l c o p p e r i n t h e r i v e r w a t e r was p a r t i t i o n e d into o r g a n i c and i n o r g a n i c forms and s t a b i l i t y constants f o r complexa t i o n o f c o p p e r by n a t u r a l o r g a n i c l i g a n d s were c a l c u l a t e d . F i n a l l y , models were c a l c u l a t e d which p r e d i c t t h e v a r i a t i o n s i n chemical s p e c i a t i o n o f copper r e s u l t i n g from changes i n t h e c h e m i cal parameters: pH, carbonate a l k a l i n i t y , concentration of d i s s o l v e d o r g a n i c m a t t e r , and c o n c e n t r a t i o n o f t o t a l d i s s o l v e d copper. The r i v e r s s a m p l e d were t h e N e w p o r t a n d N e u s e . The Newport R i v e r i s a s m a l l c o a s t a l p l a i n r i v e r (mean d i s c h a r g e a p p r o x i m a t e l y 0 . 4 t o 11.2 m 3 s e c " 1 ) w i t h a w a t e r s h e d o f a p p r o x i m a t e l y 3 4 0 k m ? . T h e N e u s e R i v e r , i n c o n t r a s t , i s a l a r g e r r i v e r (mean d i s c h a r g e a p p r o x i m a t e l y 130 m 3 s e c - 1 ) , o r i g i n a t i n g i n t h e piedmont r e g i o n w i t h a d r a i n a g e b a s i n o f a p p r o x i m a t e l y 1.1 χ 10^ k m 2 . The Newport R i v e r w a t e r u s e d i n t h i s i n v e s t i g a t i o n i s c h a r a c t e r i z e d by a h i g h c o n c e n t r a t i o n o f d i s s o l v e d o r g a n i c c a r b o n ( 1 5 mgC l o w pH ( 6 . 0 ) , l o w c a r b o n a t e a l k a l i n i t y ( 0 . 0 6 mM) a n d r e l a t i v e l y l o w c o n c e n t r a t i o n s o f a l k a l i n e e a r t h c a t i o n s T Ï Ï . 1 4 mM C a a n d 0 . 0 3 mM M g ) . The Neuse w a t e r h a d an a p p r e c i a b l y l o w e r c o n c e n t r a t i o n o f d i s s o l v e d o r g a n i c c a r b o n ( 3 . 0 mgC £ - ' ) , h i g h e r pH ( 6 . 8 ) , h i g h e r

American Chemical ^^(M^/EîlifSr^3"14^08'50/0 c

r

s

e

This fr|Pte /^ WJ Çf *Λ^·5· copyright P u b l i s l M P ¥ 9 # Î B n » i c & C h e m i c a l Society

Washington, D. C.

20035

Jenne; Chemical Modeling in Aqueous Systems ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

CHEMICAL MODELING IN AQUEOUS SYSTEMS

148

c a r b o n a t e a l k a l i n i t y ( 0 . 1 5 mM), and a b o u t t h e o f c a l c i u m a n d m a g n e s i u m ( 0 . 1 3 mM C a a n d 0 . 0 4 Materials

and

Water

same c o n c e n t r a t i o n s mM M g ) .

Methods

samples were

c o l l e c t e d from

the

Newport

River

upstream


f r o m N e w p o r t , N o r t h C a r o l i n a and from t h e Neuse R i v e r s e v e r a l m i l e s downstream from K i n s t o n , North C a r o l i n a . Standard procedures f o r h a n d l i n g water samples were adopted to m i n i m i z e changes in the natural s t a t e of the samples during sampling P o r t i o n s o f the samples were f i l t e r e d through g l a s s (Gelman A-E) w i t h i n 24 h r o f c o l l e c t i o n . A portion t e r e d r i v e r w a t e r was e x p o s e d t o h i g h i n t e n s i t y u l t r a t i o n ( L a J o l l a S c i e n t i f i c Model PO-14 Photooxidation

and s t o r a g e . fiber filters of the f i l aviolet radiUnit) to

photooxidize organic matter (8). C a l c i u m and magnesium c o n c e n t r a t i o n s were d e t e r m i n e d i n f i l t e r e d s a m p l e s by f l a m e a t o m i c absorption spectrophotometry (Perkin Elmer 403). D i s s o l v e d o r g a n i c c a r b o n w a s d e t e r m i n e d u s i n g a CHN a n a l y s e r ( F a n d M 1 8 5 ) o n t h e r e s i d u e l e f t a f t e r f r e e z e d r y i n g samples of a c i d i f i e d , filtered r i v e r water. Carbonate a l k a l i n i t y s a m p l e s w a s c a l c u l a t e d f r o m pH a n d librated with a i r . The

chemical

speciation

of

o f f i l t e r e d and U V - t r e a t e d PQQ2 d a t a f o r s a m p l e s e q u i -

copper

in

river

water

and

model

s o l u t i o n s was i n v e s t i g a t e d by a t i t r a t i o n t e c h n i q u e i n w h i c h c u p r i c i o n a c t i v i t i e s w e r e m e a s u r e d a t c o n s t a n t pH a s t h e t o t a l c o p p e r c o n c e n t r a t i o n ( [ C U J Q J ] ) w a s v a r i e d by i n c r e m e n t a l a d d i t i o n s o f CUSO4. p C u ( - l o g c u p r i c i o n a c t i v i t y ) was m e a s u r e d w i t h a c u p r i c i o n - s e l e c t i v e e l e c t r o d e ( O r i o n 9 4 - 2 9 ) a n d pH w i t h a g l a s s e l e c t r o d e (Beckman 39301) b o t h c o u p l e d t o a s i n g l e j u n c t i o n Ag/AgCl reference e l e c t r o d e (Orion 90-01) i n a temperature c o n t r o l l e d (25 + 0 . 5 ° C ) w a t e r b a t h . Total copper concentrations in t h e t i t r a t e d s o l u t i o n s were d e t e r m i n e d d i r e c t l y by a t o m i c a b s o r p tion spectrophotometry ( P e r k i n Elmer 603) u s i n g a g r a p h i t e furnace (Perkin Elmer 2200). Measurement of t o t a l copper c o n c e n t r a t i o n s i s necessary because of a d s o r p t i v e l o s s of copper from s o l u t i o n onto

container

The tions at

and/or

electrode

surfaces.

f o l l o w i n g p r o c e d u r e was f o l l o w e d 2 5 ° C and c o n s t a n t pH. The t h r e e

f o r a l l copper t i t r a e l e c t r o d e s were f i r s t

p r e c o n d i t i o n e d f o r 3 0 m i n i n a s o l u t i o n a t pH 8 c o n t a i n i n g 0 . 1 M T r i s b a s e , 0 . 0 5 M HC1 a n d s u f f i c i e n t C U S O 4 t o a c h i e v e a p C u o f 13.0 to 13.5. The e l e c t r o d e s w e r e t h e n r i n s e d s e v e r a l t i m e s w i t h d i s t i l l e d w a t e r and p l a c e d f o r 30 min i n a p o r t i o n o f t h e s o l u t i o n t o be t i t r a t e d . T h e e l e c t r o d e s w e r e t h e n p l a c e d i n a f r e s h 7 0 m& p o r t i o n o f t h e same s o l u t i o n c o n t a i n e d i n a 1 0 0 m i l b o r o s i l i c a t e g l a s s b e a k e r and t i t r a t e d w i t h CUSO4. S u f f i c i e n t t i m e was a l l o w e d f o r the e l e c t r o d e s to r e a c h steady s t a t e p o t e n t i a l s a f t e r each copper a d d i t i o n . A t no c o p p e r a d d i t i o n , 6 0 m i n w a s a l l o w e d . For c o p p e r c o n c e n t r a t i o n s 2 χ 1 0 " 5 M) i t w a s n e c e s s a r y t o a d d s u f f i c i e n t q u a n t i t i e s o f NaOH t o n e u t r a l i z e h y d r o g e n i o n s r e l e a s e d by t h e c o m p l e x a t i o n o f weak a c i d f u n c t i o n a l groups. T i t r a t i o n s w e r e p e r f o r m e d on u n t r e a t e d , f i l t e r e d , a n d UVt r e a t e d f i l t e r e d r i v e r w a t e r s a m p l e s a t i n s i t u a n d a d j u s t e d pH values. T h e e f f e c t o f pH o n c o p p e r s p e c i a t i o n w a s i n v e s t i g a t e d by t i t r a t i o n o f f i l t e r e d N e w p o r t R i v e r w a t e r a t pH 7 . 0 a n d f i l t e r e d N e w p o r t a n d N e u s e w a t e r s a t pH 8 . 0 . Newport R i v e r water w a s a d j u s t e d t o pH 7 . 0 b y d e c r e a s i n g t h e p a r t i a l p r e s s u r e o f CO? f r o m t h e i n i t i a l a m b i e n t v a l u e o f a b o u t 10 t i m e s t h e a t m o s p h e r i c level. To a d j u s t t h e pH t o 8 . 0 , s o d i u m b i c a r b o n a t e w a s a d d e d t o b r i n g t h e r i v e r w a t e r s a m p l e s t o a c o n c e n t r a t i o n o f 0 . 5 mM w i t h s u b s e q u e n t a d j u s t m e n t o f Ρ(χ)2· T i t r a t i o n s were a l s o c o n d u c t e d a t pH 7 . 0 i n m o d e l s o l u t i o n s c o n s i s t i n g o f 0 . 0 1 M KNO3 a n c l 0 e l !0Îi NaHC03 w i t h a n d w i t h o u t t h e a d d i t i o n o f 0 . 7 5 μΜ h i s t i d i n e t o t e s t e l e c t r o d e b e h a v i o r i n s o l u t i o n s o f known c h e m i s t r y . S t a b i l i t y c o n s t a n t s f o r t h e c o m p l e x a t i o n o f c o p p e r by h y d r o x i d e i o n (Cu h y d r o l y s i s ) were d e t e r m i n e d f r o m m e a s u r e m e n t s o f pCu a n d P L C U J O J ] a s a f u n c t i o n o f pH i n s o l u t i o n s c o n t a i n i n g 0 . 0 1 M KNO3 a n d ! - 0 a n d 2 · 5 μ Μ C U S O 4 . These s o l u t i o n s were f i r s t p u r g e d w i t h n i t r o g e n a t pH < 6 t o r e m o v e CO2 a n d t h e n c l o s e d t o the atmosphere. M e a s u r e m e n t s w e r e made u n d e r a n i t r o g e n a t m o s p h e r e a s t h e s o l u t i o n s w e r e t i t r a t e d w i t h s m a l l q u a n t i t i e s ( < 2 5 \ii per a d d i t i o n ) of a concentrated s o l u t i o n of Κ0Η. For the d e t e r mination of s t a b i l i t y constants f o r carbonate complexes, measure a s a m e n t s o f pCu a n d P [ C U J Q T ] *e f u n c t i o n o f pH i n a s o l u t i o n c o n t a i n i n g 0 . 0 1 M NaHC03 a n d 5 μΜ CUSO4. T h e pH a n d t h u s t h e c a r b o n a t e i o n a c t i v i t y was v a r i e d by a d j u s t i n g P c 0 2 W

E

R

E

m(

C u p r i c i o n a c t i v i t i e s and c u p r i c i o n c o n c e n t r a t i o n s were determined using the Nernst equation from the d i f f e r e n c e s i n p o t e n t i a l between t h e t e s t s o l u t i o n s and a s t a n d a r d s o l u t i o n c o n s i s t i n g o f Ι Ο " 5 M CUSO4 a n d 0 . 0 1 M KNO3 a t pH 5 . 4 + 0 . 3 . V a l u e s o f c u p r i c i o n a c t i v i t y i n t e s t s o l u t i o n s w e r e b a s e d on a c u p r i c ion a c t i v i t y c o e f f i c i e n t of 0 . 6 8 in the standard s o l u t i o n as c a l c u l a t e d from the extended Debye-Huckel equation. For measure m e n t s i n d e f i n e d s o l u t i o n s c o n t a i n i n g 0 . 0 1 M KNO3 o r 0 . 0 1 M NaHC03 c u p r i c i o n c o n c e n t r a t i o n s c o u l d be d i r e c t l y c o m p u t e d v i a t h e N e r n s t e q u a t i o n b e c a u s e a c t i v i t y c o e f f i c i e n t s w e r e t h e same in both t e s t and s t a n d a r d s o l u t i o n s . Total copper c o n c e n t r a t i o n s i n a l i q u o t samples o f the t i t r a t i o n s o l u t i o n s w e r e m e a s u r e d by e l e c t r o t h e r m a l a t o m i c a b s o r p t i o n u s i n g d i r e c t i n j e c t i o n o f t h e a c i d i f i e d (HNO3) s a m p l e i n t o t h e graphite furnace. S t a n d a r d s w e r e p r e p a r e d a t t h e same a c i d s t r e n g t h a s t h e s a m p l e s and c o p p e r v a l u e s were o b t a i n e d by t h e comparator method. Copper c o n c e n t r a t i o n s i n f i l t e r e d (Gelman A E) N e w p o r t a n d Neuse w a t e r s w e r e 0 . 0 1 1 μΜ and 0 . 0 2 5 μ Μ , r e s p e c t i v e l y , and were w e l l w i t h i n a n a l y t i c a l c a p a b i l i t y . T h u s , no



150

s a m p l e p r e c o n c e n t r a t i o n was r e q u i r e d . The p r e c i s i o n a s e s t i m a t e d by r e p l i c a t e a n a l y s e s was a b o u t + 0 . 0 0 0 6 2 μ Μ , ( r e p o r t e d a s one s t a n d a r d d e v i a t i o n ) w h i c h i s e q u i v a l e n t t o a 1% r e l a t i v e standard d e v i a t i o n a t the midrange of the standards. Computation of S t a b i l i t y Constants f o r Hydroxo and Carbonato Complexes. S t a b i l i t y c o n s t a n t s f o r the f o r m a t i o n o f hydroxo com p l e x e s w e r e c o m p u t e d by l i n e a r r e g r e s s i o n f r o m t h e f o l l o w i n g equation: [Cu

T 0 T

]

-

[Cu2+] =

0H"


a

3

Cu(0H)9

[Cu2+]

a

0H"

+

K

Cu0H+

(

1

)

2

2+ where [CUJOJ] and [Cu ] a r e the measured c o n c e n t r a t i o n s o f t o t a l d i s s o l v e d c o p p e r and c u p r i c i o n r e s p e c t i v e l y and aoH~ i s t h e a c t i v i t y o f h y d r o x i d e i o n ^ s c o m p u t e d ^ f r o m t h e m e a s u r e d pH a n d t h e ion product of water. Kcu0H+ and 3Cu(0H)2 a r e s t a b i l i t y constants f o r t h e f o r m a t i o n o f mono a n d d i h y d r o x o c o m p l e x e s a s d e f i n e d b y the equations: [Cu0H+]

[Cu(0H)2]

(3)

Mass

balance

[Cu

Equation and 4 . The ([Cu a

2 +

0H"-

],

]

T Q T

1

for

total

= [Cu2+]

+

i s derived

left

term

of

[CUTQT]* P h )

soluble

copper

[Cu0H+]

+ [Cu(0H)2]

by a l g e b r a i c equation a

The y - i n t e r c e p t

n

d

t

h

e

i s expressed

by t h e

.

combination

1 was c o m p u t e d

(4)

of

equations

f o r each data

regressed as a l i n e a r

n

and t h e s l o p e

of

equation:

2, set

function

the regression

line

3

of

are

Cu0H+ a n d 3cu(0H)2' respectively. A s i m i l a r l i n e a r r e g r e s s i o n p r o c e d u r e was u s e d f o r t h e determination of carbonato s t a b i l i t y constants. Here t h e e q u a t i o n regressed was: 2 K

([Cu

T 0 T

]

-

([Cu2+]

+ [Οι

2 +

a j

]Σ 1

e

Cu(C03)|-

a

C0§"

+

K

CuC03

H

. β*))/ [Cu2+]

a

C Q

2

-

=

3

.


(

'

8.

1

Ο

The

term

[Cu2+]

a

Σ

151

Copper in River Water

SUNDA A N D HANSON

Q H

* _ $.

represents

the concentration

of

mono


p l u s d i h y d r o x o complexes as comptued from s t a b i l i t y c o n s t a n t s ( T a b l e I ) . The a c t i v i t y o f c a r b o n a t e i o n was computed f r o m t h e c o n c e n t r a t i o n o f a d d e d NaHCU3 ( 0 . 0 1 M) a n d c a r b o n a t e a c i d i t y c o n s t a n t s a t i n f i n i t e d i l u t i o n a n d 2 5 ° C r e p o r t e d i n Stumm a n d Morgan ( 9 J . The s t a b i l i t y c o n s t a n t s o b t a i n e d f r o m t h e s l o p e a n d y - i n t e r c e p t of the r e g r e s s i o n of equation 6 a r e d e f i n e d i n terms a n d t h e of t h e c o n c e n t r a t i o n s o f C u 2 + , CUCO3, and Cu(003)2 a c t i v i t y of carbonate i o n . S t a b i l i t y c o n s t a n t s f o r hydroxo and c a r b o n a t o complexes were c o r r e c t e d t o i n f i n i t e d i l u t i o n u s i n g a c t i v i t y c o e f f i c i e n t s c a l c u l a t e d from the extended Debye-Huckel equation. Scatchard plots. S t a b i l i t y c o n s t a n t s f o r t h e b i n d i n g o f Cu by a m o d e l l i g a n d ( h i s t i d i n e ) a n d by n a t u r a l o r g a n i c l i g a n d s i n r i v e r w a t e r were computed u s i n g S c a t c h a r d p l o t diagrams as d e s c r i b e d p r e v i o u s l y by M a n t o u r a a n d R i l e y ( 1 0 ) . The g e n e r a l equation f o r t h i s analysis was: [CuL.] - — — [Cu2+]

=

Κ [L c ι

lui

]

-

Κ [CuL ] c ι

(1

where LCuL-i] and [LJ_JQT] a r e t h e c o n c e n t r a t i o n s o f copper l i g a n d complex and t o t a l l i g a n d . Κς i s a c o n d i t i o n a l s t a b i l i t y c o n s t a n t v a l i d f o r a given set of chemical c o n d i t i o n s of pH, i o n i c strength and c o n c e n t r a t i o n o f c o m p e t i n g metal i o n s ( C a , M g , e t c ) :

K

c

-

^ [Cu

]

([L.]

(7,

+ Σ [H L] + Σ N

[MeL])

Σ [HnL] i s t h e c o n c e n t r a t i o n o f a l l p r o t o n a t e d f o r m s o f a weak a c i d l i g a n d a n d Σ [ M e L ] i s t h e sum o f a l l c o m p l e x e s o f t h e l i g a n d w i t h m e t a l s o t h e r t h a n c o p p e r , p a r t i c u l a r l y Ca a n d M g . The c o n c e n t r a t i o n o f o r g a n i c a l l y bound c o p p e r was c o m p u t e d t o be e q u a l to the t o t a l measured c o n c e n t r a t i o n of copper i n s o l u t i o n minus the computed c o n c e n t r a t i o n s of i n o r g a n i c s p e c i e s : C u 2 + , CuOH+, C u ( 0 H ) 2 , CUCO3 a n d C u ( C 0 3 ) £ ~ . C o n c e n t r a t i o n s o f t h e s e s p e c i e s were c a l c u l a t e d from hydroxo and carbonato s t a b i l i t y c o n s t a n t s determined i n t h i s study (Table I ) . A c t i v i t y c o e f f i c i e n t s used i n t h e s e c a l c u l a t i o n s were computed from t h e extended DebyeHuckel e q u a t i o n u s i n g e s t i m a t e s o f i o n i c s t r e n g t h based on t h e measured c o n c e n t r a t i o n s of C a 2 + , M g 2 + , carbonate a l k a l i n i t y a n d ,


152


where of

applicable The

Scatchard

histidine one

is

complex

[CuL] plots

of

plot

straight formed.

should

tration

at

pH

be

linear

histidine

derived

from

8.0)

curves

different

stripping

the

added

sites)

and

a

was

concentration

copper is

the

to

for

-Kc.

river

presence to

likely

stability

a

equal

of

a

to

the

showed

several

estimate groups

total

of

one-to-

function

However,

Here an

of

single

as

water

constants.

adopted

titration

only

[CuL]/[Cu2+]

equal

data

(more

conditional

of

slope

stability

ligands

the there

an x - i n t e r c e p t

indicating

procedure

individual

plot

with

and

for

since

titration

non-linear with

analyses

forward Here a

sites of


(titrations

NaHC03.

of

concen Scatchard markedly

binding iterative

concentration

ligands

or

binding

constants.

Chemical S p e c i a t i o n Models. Using the s t a b i l i t y constants d e r i v e d by us f o r c o p p e r c o m p l e x e s w i t h h y d r o x o and c a r b o n a t o l i g a n d s ( T a b l e I) and f o r n a t u r a l o r g a n i c l i g a n d s ( T a b l e II), t h e Newport and Neuse R i v e r s were modeled f o r c o p p e r s p e c i a t i o n as a f u n c t i o n o f p H , t o t a l c o p p e r , c a r b o n a t e a l k a l i n i t y and t o t a l dissolved organic the equation: [Cu

T Q T

]

=

matter.

[Cu2+]

+

Speciation

[CuOH+]

[Cu(C03)2~]

+

+

[CuL

models

were

[Cu(0H)2]

T Q T

+

calculated

[CuC03]

+

]

(8)

where

[CuOH+]

[Cu(0H)2]

[CuC03]

a

Cu

2 +

1

a

Cu

2 +

a

0H"

K

CuOH+

a

Cu

2 +

a

0H-

3

Cu(0H)2

a

Cu

2 +

a

C02"

Y

Cu

2 +

K

1

Y

CuC03

1

/

CuOH+

Y

Y

Cu(0H)2

C

U

C

0

3

2

[Cu(C03)2-] a

Cu2+

a

Cu

a

C0

3

2

"

3

Cu(C03)2"

1

Y

Cu(C03)2"

Ν 2 +

I

CLi-T0T]

from

K

c - i '


8.

Κ and

3 denote

conditional tion

of

ion

the

for

ith

corrected

their

were

not

valid

153

constants,

under

the

[L-J-T0T] i s

ligand

group

(ligand

by

Scatchard

coefficient. considered

Κς_η·

same

determination,

resolved

activity

stability

constants

organic

ligands

complexes in

as

the

Ν total

single

zero

stability

conditions of


SUNDA A N D HANSON

or

the

significant

concentra

binding

analyses,

Polynuclear

are

chemical site)

and

γ

and m i x e d

and,

thus,

is

the

ligand

not

included

model.

Results

and

Discussion 2+


Hydroxo measured

as

containing Ι.ΟμΜ some o f

0.01

the

be

carbonato

functions

a

PrCu2+j

decrease

accounted

adsorption

of

M KNO3

CUSO4.

could in

and

pH n

in

the by

1).

a

range

approximately

above

this

from

was is

first

plot

separate fold is

(Figure

of

titrations

pH

(Figure

indicative

and

excludes

cupric

of

or

for

the

p[Cu

indicated

the whose

value

the

of

(1θ6·48) (106·

dilution

10

Values 10

1 4

·

in

siderable species error can

constant 11.80) and

U

of

)

at

the

9

natural for

(log

who

of

32

also

of

that

the

range and

constant

at

copper or

pH

was

electrode

found

as

that

the

pH

adsorption

copper

of

of

the

[CU

are

for of

of

the

2 +

species in

a

species in

free

Cu(0H)£

7.7

to

(Cu0H+ Table

monohydroxo

of

10.8 and

I.

Our

complex

previously

published

strength

approaching

ionic

at

]/[CUJOJ]

Analysis

range

given

five

reduction

complexes. pH

three

to

hydrolysis

observed

the

for

up

concentration

ratio

precipitation in

pH

despite

values infinite

U ) .

T4,

constant

are

V5). as

to

waters.

quite

This the

of

this

11.78)

at

importance and

25°C

reported

used

a cupric data

the

(J4)

of

dihydroxo ranging has

and by

Our

Paulson

dilution (J4)

adsorptive

loss

of

con

of

procedures

dihydroxo

infinite

1θ"Ό·7 in

dihydroxo

discusses sources

(log

ion-selective electrode

for

complex

from

resulted

copper

computational

variability.

that

his

for

variable

variability

Paulson

with

corrected

curve

hydrolysis

constant

25°C

a function

the

by pH

experimental =

were

mononuclear

constants

stability

much

to pH

containers

indicating

polynuclear

two

literature ]Z_

onto

dissolved

caused

of

13,

9

the

agreement

also

been

as

behavior

formation

within 6 6

due

increasing

dissolved

adsorption

single

P[CUJQT] and

previous

account

close

·

copper

remained

the

decreased

possibility

uncertainty

in

in

6

(1J_,

3

This

stability

Ql_,

reported

measured

stability

falls

to

0

for

a

in

presence

Cu(0H)2)

on

2).

],

but

and

least

1).

formation 2 +

adsorption

then

fall

have

9.0

μΜ

concentration

dissolved

increased with

92% o f

]/[CUJOT])

2 +

the

the

i o n may

(solid) data

to

P([CU

differences

given

to

values

i n c r e a s e d and

reversible A

due

Consistent

At

ion

were

solutions 2.5

in

to

p[Cujpj] of of

cupric

to

and

i n c r e a s i n g pH.

decrease

Up

J

titrations

measured

7.0

range.

solution

KOH

concentrations

Adsorption

the

lost

the

initial

d

values

surfaces.

for

p[Cu

increased with

for

(Figure

constants.

that

stability is

in

32

=

technique

copper.




154

pH Figure 1. Loss of copper by surface adsorption as a function of pH for solutions containing lOmM KNO ; (M) and (\J) 10 Μ CuSO, , and (Ο) 2.5 Μ CwS0 ; (U) increasing pH and decreasing pH. pH varied by addition of concentrated KOH and HCl. s

μ

t

μ


4

Jenne; Chemical Modeling in Aqueous Systems ACS Symposium Series; American Chemical Society: Washington, DC, 1979. 4

s

^

h

)

μ

/[C-TOTJJ

[Cu2

h

Figure 2. Titration data for complexation of copper by hydroxide. All solutions contained lOmM KNO ; (Α) Ι.ΟμΜ CuSO (Ο) 2.5 Μ CuSO (first run), and (•) 2.5μΜ C w S 0 (second run). Curve calculated according to hydroxo constants determined in this work (Table I).

Ρ

Ρ( V


156

CHEMICAL MODELING IN AQUEOUS

Table

I.

Stability C032",

Ligand

Ionic

OH" 2C 0

3

Histidine


and

constants

for

reaction

h i s t i d i n e at

strength

of

copper

with

SYSTEMS OH",

25°C.

log

log

0

corr.

6.48

11.78

0

corr.

6.74

10.24

0.01

10.45*

0.01

10.55

18.80

References

e2

This

work

II

II

II

II

S i l l en

& Martel 1,

(12)

*

C a l c u l a t e d from a c o n d i t i o n a l s t a b i l i t y constant at 100.21 ( F i g u r e 5) and f i r s t and second hydrogen i o n t i o n c o n s t a n t s of 1 0 9 · 2 0 and 1 0 6 · 0 0 (12.).

pH 7 . 0 0 of associa-

A n a l y s i s o f d a t a f o r pLCu^"1"], P [ C U T Q T ] a n d pH f o r t h e s o l u t i o n c o n t a i n i n g 0 . 0 1 M N a H C Û 3 a n d 5 μ Μ tubOq a r e c o n s i s t a n t w i t h t h e p r e s e n c e o f b o t h mono a n d d i c a r b o n a t o c o m p l e x e s ( F i g u r e 3 ) . C o n s t a n t s f o r t h e s e complexes computed from t i t r a t i o n data a r e g i v e n i n Table I and a r e i n good agreement w i t h p r e v i o u s l y pub l i s h e d v a l u e s a s r e p o r t e d i n S i l l e n a n d M a r t e l (21), S u n d a (13) and B i l i n s k i e t a K (7J. A d s o r p t i o n o f c o p p e r i n the 0.01 M b i c a r b o n a t e s o l u t i o n s was n o t a s g r e a t (maximum a d s o r p t i o n 50%) as t h a t w h i c h o c c u r e d i n t h e a b s e n c e o f c a r b o n a t e i o n , s u g g e s t i n g t h a t carbonato complexes of copper a r e not as r e a d i l y adsorbed as c u p r i c ion and/or copper hydroxo s p e c i e s . M o d e l s o l u t i o n s : T i t r a t i o n s a t c o n s t a n t pH a n d a v a r i a b l e p[CuTnï\T D a t a f o r t h e Cu t i t r a t i o n o f a m o d e l s o l u t i o n c o n t a i n i n g 0 . 7 5 μ Μ h i s t i d i n e , 0 . 1 mM N a H C 0 3 a n d 0 . 0 1 M KNO3 a t pH 7.0 ( F i g u r e 4T~was a n a l y z e d by l i n e a r r e g r e s s i o n u s i n g a S c a t c h a r d p l o t diagram (Figure 5). This analysis yielded a s t a b i l i t y con s t a n t i n good agreement w i t h p r e v i o u s l y p u b l i s h e d v a l u e s (Table I). A t h e o r e t i c a l c u r v e c a l c u l a t e d f r o m t h i s c o n s t a n t was i n g o o d a g r e e m e n t w i t h t h e m e a s u r e d pCu a n d P [ C U J O T ] d a t a throughout t h e t i t r a t i o n r a n g e o f p [ C u j O T ] ( F i g u r e 4) i n d i c a t i n g good e l e c t r o d e b e h a v i o r e v e n a t c o n c e n t r a t i o n s o f CUJQT a s l o w as 1 0 " 8 · 2 M. pCu a n d PECUJQT] d a t a d i d n o t a g r e e as c l o s e l y w i t h t h e t h e o r e t i c a l l y c a l c u l a t e d curve for a t i t r a t i o n of a s i m i l a r s o l u t i o n c o n t a i n i n g no a d d e d c h e l a t o r . The m e a s u r e d pCu v a l u e s w e r e i n good agreement w i t h v a l u e s c a l c u l a t e d on the b a s i s of i n o r g a n i c c o m p l e x a t i o n f o r t o t a l c o p p e r c o n c e n t r a t i o n s >_ 1 0 " ? M , b u t d e v i ated from p r e d i c t e d values below t h i s c o n c e n t r a t i o n ^ F i g u r e 4 ) . A maximum d i f f e r e n c e b e t w e e n m e a s u r e d a n d c a l c u l a t e d pCu v a l u e s



II.

Acid

3.0 5.0

8.00

8.00

6.78

8.00

3

3

...

iî

L

&

L

& 2.7 2.9

2.1 1.9 3.0

1.2 1.1 1.2

8.7 8.6 1.6

7.00

&

5.0 1.8 1.0

Ligand

for

E-6

E-7

Copper

8 8 D . (J 8.0 3.3 4.0

E-4* E-3* E-3* E-3* 2.4 2.4

1.1

Schnitzer II

&

II

II

&

II

g

II

of

II

Khan,(18)

II

Riley,(10)

II II

II

II

II II

II

II II

II

II

II

II II

II

II

II

II

II II

II

II

II

II

II

paper

II

This

Mantoura II

Ligands

Reference

Organic

b i n d i n g s i t e s per on d a t a i n ( 1 8 ) ) .

8.3

4.8

11.2

9.5 7.3 4.9

Κ

E-5 E-4

E-5 E-4 E-3

10.9 8.8 6.9

9.7 7.8 5.6

E-5 E-4 E-2 E-5 E-4 E-3

9.0 6.2 4.6

log

Natural

E-5 E-3 E-3

by

8.9 9.6

7.0 6.4 9.9

8.0 7.5 8.2

E-6 E-5 E-4 E-7 E-6 E-5

5.8 5.7 1.0

3.3 1.2 6.7

E-7 E-6 E-4

E-7 E-5 E-4

of

M o l e s o f Cu Binding Sites g organic carbon

Complexation

Ligand Concentration M

Constants

5.95

pH

Stability

Data c o n v e r t e d f r o m number o f b i n d i n g s i t e s p e r g o f o r g a n i c m a t t e r t o o r g a n i c c a r b o n a s s u m i n g n a t u r a l f u l v i c a c i d s c o n t a i n 46% c a r b o n ( b a s e d

Fulvic

Soil

River

Water

*

Water

Conditional

River

Lake

Neuse

Newport

Natural

Table


158


1

Τ

SYSTEMS

1


/

/ :

/

3

3

or

o /

•

-

1

pH Figure 3. Titration data for complexation of copper by carbonate. Solution con tained lOmU NaHCOs and 5μΜ CuSOj,. pH varied by adjusting P Curve calculated according to hydroxo and carbonato stability constants determined in this work (Table I). C O r


Copper


SUNDA AND HANSON

in River

P[

C U

Water

TOT]

Figure 4. Copper titrations of model solutions at 25°C and pH 7.00. (•) Solu tion contained 0.01M KN0 and O.lmM NaHC0 in distilled water. (O) Solution contained 0.75μΜ histidine, 0.01M KN0 , and O.lmM NaHC0 . Solid lines through data points are theoretical curves calculated according to constants given in Table I. Dark solid line represents p C w = p[Cu T7· 3

3

3

3

T0


160



Figure

5.

Scatchard

plot for histidine model solution. for the data is shown.

The linear regression


line

8.

SUNDA AND HANSON

Copper

in River

Water

161


T h l s ( 0 . 4 pCu u n i t s ) o c c u r e d a t P [ C U J Q T ] 8 · ° · deviation from i d e a l b e h a v i o r i s a p p a r e n t l y due t o a d i s e q u i l i b r i u m between t h e s o l u t i o n t i t r a t e d a n d t h e membrane s u r f a c e o f t h e c u p r i c i o n selective electrode. Our e x p e r i e n c e h a s shown t h a t 1 0 " ^ M t o t a l copper i s often the lower l i m i t f o r accurate determination of cupric ion activity. However, the exact l i m i t of d e t e c t i o n i s de t e r m i n e d by a v a r i e t y o f f a c t o r s : c o m p l e x i n g c h a r a c t e r i s t i c s o f the s o l u t i o n i n c l u d i n g k i n e t i c s of the complexation r e a c t i o n s , p r e c o n d i t i o n i n g o f the e l e c t r o d e s u r f a c e , and time a l l o w e d t o establish equilibrium. The c u p r i c i o n e l e c t r o d e shows b e s t b e h a v i o r i n w e l l b u f f e r e d s o l u t i o n s i n which the k i n e t i c s of com p l e x a t i o n r e a c t i o n s are f a s t , such as i n the h i s t i d i n e s o l u t i o n .

Copper t i t r a t i o n s o f r i v e r w a t e r . Copper t i t r a t i o n data i n d i c a t e s t h a t c o p p e r i s h i g h l y bound i n both Newport and Neuse River water (Figures 6 and 7 ) . A g e n e r a l l y c l o s e agreement between t i t r a t i o n c u r v e s o f f i l t e r e d and u n f i l t e r e d samples i s c o n s i s t a n t w i t h m i n o r t o n e g l i g i b l e b i n d i n g by p a r t i c u l a t e m a t t e r r e t a i n e d by g l a s s f i b e r f i l t e r s ( t h e mean r e t e n t i o n s i z e o f g l a s s f i b e r f i l t e r s i s a p p r o x i m a t e l y 0 . 7 t o 0 . 9 ym ( ] J o ) . Close agreement between measurements o f background t o t a l dissolved c o p p e r i n u n t r e a t e d Neuse R i v e r w a t e r ( 0 . 0 2 9 μΜ) and f i l t e r e d Neuse R i v e r w a t e r ( 0 . 0 2 5 μΜ) a l s o i n d i c a t e s t h a t o n l y a m i n o r f r a c t i o n o f c o p p e r was a s s o c i a t e d w i t h p a r t i c u l a t e m a t t e r . Non-ideal behavior of the cupric ion electrode occurs at PECUJOJ] > 7 i n t h e t i t r a t i o n s o f both f i l t e r e d and u n f i l t e r e d N e w p o r t R i v e r w a t e r a t pH 5 . 9 5 a n d f i l t e r e d w a t e r a t pH 7 . 0 a n d 8.0. A t l o w t o t a l c o p p e r c o n c e n t r a t i o n s , m e a s u r e d pCu v a l u e s approach a constant value independent of the t o t a l copper i n solution. S i m i l a r b e h a v i o r was o b s e r v e d f o r f i l t e r e d Neuse River w a t e r a t pH 8 . 0 , b u t n o t a t pH 6 . 7 8 . As i n d i c a t e d by t i t r a t i o n d a t a ( F i g u r e s 6 a n d 7 ) , b i n d i n g o f c o p p e r i n b o t h Neuse a n d Newport R i v e r w a t e r d e c r e a s e s w i t h i n c r e a s i n g t o t a l c o p p e r i n a manner c o n s i s t a n t w i t h a s t e p w i s e t i t r a t i o n o f a number o f d i f f e r e n t l i g a n d s a n d / o r b i n d i n g s i t e s . B i n d i n g o f c o p p e r i n c r e a s e s w i t h i n c r e a s i n g pH c o n s i s t a n t w i t h r e a c t i o n s w i t h p r o t o n a t e d weak a c i d s . C o m p a r i s o n s o f Cu t i t r a t i o n s o f n a t u r a l f i l t e r e d r i v e r w a t e r and U V - i r r a d i a t e d f i l t e r e d r i v e r w a t e r show a l a r g e d e c r e a s e i n binding of copper a f t e r photooxidation of organic matter. UVt r e a t m e n t r e s u l t e d i n > 97% d e s t r u c t i o n o f d i s s o l v e d o r g a n i c m a t t e r i n b o t h Neuse a n d Newport R i v e r w a t e r s , b a s e d on l i g h t a b s o r p t i o n m e a s u r e m e n t s i n t h e w a v e l e n g t h r a n g e 3 0 0 - 5 0 0 nm a n d measurements of d i s s o l v e d o r g a n i c c a r b o n . M e a s u r e d pCu v a l u e s i n n a t u r a l f i l t e r e d N e w p o r t R i v e r w a t e r a t pH 5 . 9 5 a r e a p p r e c i a b l y higher than p r e d i c t e d f o r complexation t o i n o r g a n i c l i g a n d s (CO*}" a n d 0 H _ ) a l o n e b y v a l u e s r a n g i n g f r o m 0 . 7 a t P [ C U J Q T ] 4 . 2 t o 2 . 4 a t P[CUJOT] 6 . 9 . From c a l c u l a t i o n s a t PECUJOT] 6 · 9 ο η 1 Υ 0 · 4 % of t h e copper i n s o l u t i o n i s present as i n o r g a n i c s p e c i e s , p r i m a r i l y C u 2 + , w i t h t h e r e m a i n i n g 99% a p p a r e n t l y bound t o o r g a n i c




162

Figure 6. Copper titrations of Neuse River water at 25°C. (Φ) Untreated water at in situ pH 6.78; (\J) glass-fiber filtered water at pH 6.78; (A) glass-fiber filtered water at pH 8.00; (0 ) UV-treated glass-fiber filtered water at 6.78; ( • ) twice filtered UV-treated water at pH 6.78, first filtration by glass-fiber prior to UVirradiation, second filtration by membrane (0.2 ™ nuclepore) after irradiation. Model curves through data points were calculated according to stability constants determined in this work (Tables I and II). Dotted lines indicate limits on data used for calculation of conditional stability constants for organic binding. μ




SUNDA AND HANSON

Figure 7. Copper titration of Newport River water at 25°C. (Φ) Untreated water at in situ pH 5.95; ([J) glass-fiber filtered water at pH 5.95; (O) ghss-fiber filtered water at pH 7.00; (A) glass-fiber filtered water at pH 8.00; (0) UV-treated glass-fiber filtered water at pH 5.95. Model curves through data points were calculated according to stability constants determined in this work (Tables I and II). Dotted lines indicate limits on data used for calculation of conditional sta bility constants.


164



ligands. The p r e d o m i n a n c e o f b i n d i n g by o r g a n i c l i g a n d s i s c o n f i r m e d by an a l m o s t c o m p l e t e d e s t r u c t i o n o f b i n d i n g c a p a b i l i t y after UV-photooxidation ( F i g u r e 7 ) . In t h e U V - t r e a t e d Newport R i v e r w a t e r a t pH 5 . 9 5 , m e a s u r e d p C u v a l u e s w e r e i n g o o d a g r e e m e n t w i t h those c a l c u l a t e d from i n o r g a n i c complexation i n the range of P [ C U J O T ] 7 t o 4. A s l i g h t i n c r e a s e i n m e a s u r e d p C u o f u p t o 0.4 u n i t s was o b s e r v e d r e l a t i v e t o t h a t p r e d i c t e d f r o m i n o r g a n i c c o m p l e x a t i o n a t P L C U J Q T ] > 7. T h i s d e v i a t i o n f r o m pCu v a l u e s c a l c u l a t e d from c o n s i d e r a t i o n of i n o r g a n i c complexation a t p [ C u j g y ] > 7 i s s i m i l a r to t h a t o b s e r v e d i n t h e model s o l u t i o n c o n t a i n i n g 0.01 M KNO3 a n d 0.1 mM N a H C Û 3 a t pH 7 ( F i g u r e 4 ) a n d t h u s , may a l s o be d u e t o n o n - i d e a l e l e c t r o d e b e h a v i o r a t l o w t o t a l copper concentrations. U V - t r e a t m e n t o f f i l t e r e d Neuse R i v e r w a t e r a l s o c a u s e d a l a r g e d e c r e a s e i n t h e b i n d i n g o f c o p p e r a t pH 6 . 7 8 a n d p [ C u j o j ] 1_ 7 c o n s i s t a n t w i t h p r e d o m i n a n c e o f b i n d i n g o f c o p p e r b y o r g a n i c ligands in the natural f i l t e r e d r i v e r water. However, at values o f PLCUTQJ] > 7 i n t h e p h o t o o x i d i z e d f i l t e r e d Neuse R i v e r w a t e r (pH 6 . 7 8 ; 9 t h e m e a s u r e d pCu v a l u e s b e h a v e a s i f c o p p e r was h i g h l y bound by a s i t e p r e s e n t a t a l o w c o n c e n t r a t i o n 10 7· M) w i t h a r e l a t i v e l y h i g h s t a b i l i t y c o n s t a n t , a l t h o u g h we r e c o g n i z e t h a t t h e c u p r i c i o n e l e c t r o d e may b e e x h i b i t i n g s o m e d e g r e e o f non-ideal behavior. F i l t r a t i o n of the UV-treated r i v e r water t h r o u g h a 0.2 ym f i l t e r ( N u c l e p o r e ) r e d u c e d t h e b a c k g r o u n d c o n c e n t r a t i o n o f c o p p e r i n t h e w a t e r f r o m 0 . 0 2 5 μΜ t o b e l o w t h e d e t e c t i o n l i m i t o f t o t a l c o p p e r a n a l y s i s (0.001 μ Μ ) i n d i c a t i n g t h a t t h e b a c k g r o u n d c o p p e r was e i t h e r a d s o r b e d t o o r i n c o r p o r a t e d into f i l t r a b l e particles. T i t r a t i o n of t h i s r e f i l t e r e d water a l s o g a v e a c u r v e f o r m e a s u r e d pCu v s P E C U J Q T ] Ί η a g r e e m e n t w i t h a reduced level of copper b i n d i n g . The n a t u r e o f t h e p a r t i c l e s t h a t c o p p e r was a p p a r e n t l y a s s o c i a t e d w i t h i s unknown a s i s t h e nature of the chemical a s s o c i a t i o n . T h e p a r t i c l e s may h a v e b e e n hydrous metal oxides or a small f r a c t i o n of organic matter r é s i s t e n t t o p h o t o o x i d a t i o n . We d o n o t k n o w w h e t h e r t h e p a r t i c l e s were i n i t i a l l y p r e s e n t i n the r i v e r w a t e r o r were formed d u r i n g p h o t o o x i d a t i o n , o r w h e t h e r c o p p e r was a d s o r b e d t o t h e s u r f a c e o f the p a r t i c l e s or incorporated i n t o the p a r t i c l e m a t r i x . All of these p o s s i b i l i t i e s are completely c o n s i s t a n t with the observed data. However, s i n c e the apparent degree of a s s o c i a t i o n of copper with the p a r t i c l e s present in UV-treated water i s small at p [ C u j o j ] 1 7, o u r c o n c l u s i o n t h a t c o p p e r i n t h e n a t u r a l river w a t e r i s p r i m a r i l y b o u n d by o r g a n i c m a t t e r a t P E C U J O T ] 7 i s not affected significantly. _

5

Analysis of Organic Binding. Scatchard p l o t s for the binding o f c o p p e r i n f i l t e r e d r i v e r w a t e r showed n o n - l i n e a r i t y i n d i c a t i v e of the presence of binding s i t e s having d i f f e r e n t s t a b i l i t y cons t a n t s ( F i g u r e 8 ) . S i m i l a r n o n - l i n e a r b e h a v i o r has a l s o been o b s e r v e d i n S c a t c h a r d p l o t s f o r c o p p e r b i n d i n g by n a t u r a l organic



1E-6

E[cuLi] , M

4E-6

u

3

1.27E-5

7 E-6 { 1.67E-5

Figure 8. Scatchard plot for glass-fiber filtered Neuse River water at in situ pH 6.78 and 25°C. Linear segments shown for three resolved binding sites, L L,, and L . Model curve through data points was calculated from resolved stability constants and total concentrations for the three binding sites.

5E2



166 ligands (JO). was

from

lake water

Scatchard conducted

plot

and

analysis

soil of

as measured data

for

by

river

gel water

chromatography titrations


T h i s was d o n e because o f a p p a r e n t n o n - i d e a l e l e c t r o d e b e h a v i o r a t [CUJOT] < 1 0 " 7 M. Data a t the h i g h e s t c o n c e n t r a t i o n s o f t o t a l copper i n N e w p o r t R i v e r w a t e r a t pH 7 . 0 a n d pH 8 . 0 w e r e a l s o e x c l u d e d b e c a u s e pCu v a l u e s a p p r o a c h t h o s e p r e d i c t e d f o r t h e f o r m a t i o n of s o l i d c o p p e r h y d r o x i d e , i . e . , p C u 6 . 7 a t pH 8 . 0 a n d 4 . 7 a t pH 7.0. I n o u r a n a l y s i s , we m o d e l e d t h e d a t a f o r b i n d i n g o f c o p p e r b y o r g a n i c m a t t e r i n a c c o r d a n c e w i t h t h e f e w e s t number o f binding s i t e s required to account f o r the observed copper t i t r a t i o n data. T h e t i t r a t i o n d a t a f o r e a c h r i v e r a n d pH w e r e a n a l y z e d separately by r e s o l v i n g t h e S c a t c h a r d p l o t s i n t o p o s t u l a t e d o n e , t w o , three and f o u r b i n d i n g s i t e models. The f o u r p o s s i b l e m o d e l s f o r e a c h r i v e r a n d pH w e r e t e s t e d a g a i n s t t h e d a t a u s i n g a r u n s t e s t a n d F - t e s t (17) t o d e t e c t and t e s t t h e s i g n i f i c a n c e o f s y s t e m a t i c d e viations. F r o m t h e s e t e s t s we c o n c l u d e t h a t a t l e a s t t h r e e s e p a r a t e b i n d i n g s i t e s a r e r e q u i r e d t o model t h e Newport t i t r a t i o n d a t a a t pH 5 . 9 5 , 7 . 0 a n d 8 . 0 a n d t h e N e u s e d a t a a t pH 6.78 ( F i g u r e s 6 and 7 ) . Two b i n d i n g s i t e s a r e r e q u i r e d f o r t h e Neuse a t pH 8 . 0 w h i c h i s c o n s i s t e n t w i t h t h e r e s t r i c t e d r a n g e o f the t i t r a t i o n data. T h e a c t u a l n u m b e r o f b i n d i n g s i t e s may b e g r e a t e r t h a n t h e number r e s o l v e d , s i n c e s i t e s h a v i n g s i m i l a r s t a b i l i t y c o n s t a n t s c a n n o t be r e s o l v e d by t h e p r e s e n t t e c h n i q u e . Values for t o t a l c o n c e n t r a t i o n o f b i n d i n g s i t e s and c o n d i t i o n a l stability constants are given in Table II. In g e n e r a l , a c o n s i s t a n t s e t o f c o n d i t i o n a l s t a b i l i t y c o n s t a n t s was o b t a i n e d f o r t h e two r i v e r s i n w h i c h t h e c o n s t a n t s i n c r e a s e w i t h pH a n d d e c r e a s e w i t h t h e r a t i o o f m o l e s o f b i n d i n g s i t e s p e r gram o r g a n i c c a r b o n ( F i g u r e 9 ) . The r e l a t i o n s h i p b e t w e e n s t a b i l i t y c o n s t a n t s a n d pH i s s i m i l a r f o r a l l t h r e e p r o p o s e d b i n d i n g s i t e s i n e a c h r i v e r w i t h v a l u e s o f Δ l o g K c / Δ pH i n t h e t h e range 1.0 to 1 . 3 . M e a n v a l u e s f o r [ί ·_χοτ] " f ° r e a c h ° f i = l , 2 or 3 types of b i n d i n g s i t e s are h i g h e r i n the Newport R i v e r w a t e r r e l a t i v e t o t h o s e f o r t h e Neuse by f a c t o r s r a n g i n g f r o m 4 to 5. T o t a l l i g a n d c o n c e n t r a t i o n Σ [L-J-TOT]» i . e . , t o t a l binding c a p a c i t y , i s h i g h e r i n t h e Newport by a f a c t o r o f 5 w h i c h i s i n agreement w i t h the f i v e f o l d d i f f e r e n c e i n d i s s o l v e d o r g a n i c carbon (DOC): 1 5 mgC i H f o r t h e N e w p o r t a n d 3 . 0 mgC i H f o r the Neuse. T h u s , the g e n e r a l p i c t u r e t h a t emerges i s t h a t the b i n d i n g c h a r a c t e r i s t i c s of the o r g a n i c m a t t e r i n the Newport R i v e r water i s s i m i l a r t o t h a t i n t h e Neuse w i t h t h e m a j o r d i f f e r e n c e b e i n g t h e q u a n t i t y o f b i n d i n g s i t e s p r e s e n t a s i n d i c a t e d by t h e dif f e r e n c e i n the q u a n t i t y of d i s s o l v e d o r g a n i c c a r b o n . Ί

It i s l i k e l y t h a t most i f not a l l of the observed b i n d i n g of copper to o r g a n i c matter r e s u l t s from complexation to f u l v i c or humic a c i d s . Newport R i v e r w a t e r has a p r o n o u n c e d y e l l o w i s h brown c o l o r and shows c o n t i n u o u s l y i n c r e a s i n g l i g h t a b s o r p t i o n w i t h d e c r e a s i n g w a v e l e n g t h (1_3) c o n s i s t e n t w i t h t h e p r e s e n c e o f


8.

these

substances.

carbon gH

ratios

From u n p u b l i s h e d

(0.02 gN g C ~ ' ) ,

g C " l ) and c a r b o x y l

the to

dissolved those

of

Similarly, organic United able

The binding copper

complex

plain

mixtures

of

functional binding

of

of

to

1.3.

in binding

A

Binding primarily

with

effects

of metals

to

by c h e l a t i o n

an a d j a c e n t composed

(phthalate

of

( 1 3 mmol

consistent indicates

(18). mmol

there

the observed

binding to

the

pH r a n g e

6 to

1.3

copper

of

9),

since

pH v a l u e s to

whereas

Therefore, humic

binding

show

copper

t h e pH a t w h i c h the t i t r a t i o n that

conditional organic

which

acids

these

often

vary

(Δ l o g in

in

which

group

protonated

be m o s t l y for

at

de-

copper

consistent

with

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are highly

c a n be

for

dependent

and the

Published

considerably

differences

and

account

reactions

was c o n d u c t e d

was e x a m i n e d .

apparent

to

sites

stability

ligands

less

is

slopes

mechanisms

a r e most

Newport

organic

a phenolic will

with

rings

binding

be p r i m a r i l y

groups

group

and/or

groups

groups

from

chelation

the measurement

curve

for fulvic

reported

that

This

ion from

our data

by n a t u r a l

of

slightly

data).

In a d d i t i o n ,

will

type

only

by c a r b o x y l

the proposed

salicylate

on

constants

of

in

a n d 8.0 a n d

River

for a l l three

carboxyl

η

occur

on a r o m a t i c

Newport

primarily

groups

compounds,

to

results of

these

sites)

pH 7.0

carboxyl

copper.

observed

type

pH 6 . 8 a r e for

to

a carboxyl

capacities for

unpublished

8 may r e s u l t

of has

at

i o n d i s p l a c e s a hydrogen

Our binding

1.0

of

the ob

the surface

i s thought

gC"l) at

groups of

values

i s that

an i n c r e a s e

or

groups

binding

are sufficient

Δ pH)

pro tona t e d .

of

important.

carboxyl

gC"1)

the binding

Κς/

(equation

copper

indicate

from

(salicylate

Copper

carboxyl

for

of

of

c o n s i s t i n g of

+ 1 mmol

g C " 1 ; Sunda,

with that

of

9)

compounds

sites

two a d j a c e n t

(11+1

the content

copper

compounds

the reaction

molecules

may be

group

matter~Tl0

t h e Neuse

binding

iden

of

(20) a n d / o r

possibility

pH r e s u l t s

humic

with

phenolic

groups)

organic

neutral

and f u l v i c

For

(Figure

Both

copper

sites

groups

HnL,

second

(21_).

a

binding

(9)

Δ l o g Κ ς / Δ pH

1.0

increase

matter

southeastern indistinguish

= C u L + nH

colloids

than

humic

(18).

dissolved

the

individual

site

on p o l y e l e c t r o l y t i c

for

of

for

similar

soils

the

pH i s t y p i c a l

charge

River

are

properties

groups.

negative

sites

river

Postulated

i n l o g Κς w i t h

acid

slopes

the range

and

from

that

on p o l y e l e c t r o l y t i c m o l e c u l e s

a protonated

+ HnL

observed

extracted

has c h e m i c a l

acids.

water

to

(0.11

( 1 3 meq g C " ' )

River

reported

nitrogen

ratios

particles.

t o weak

Cu

acids have

that

carbon

ratios

i n Newport

coastal

fulvic

sites

increase

with

served

of

carbon

167

we know

to

1_2> a n d L 3 m a y r e p r e s e n t

within

colloidal

in

i n another

those

different

and f u l v i c

et_ a l _ . ( 1 9 )

data

hydrogen

to

matter

the S a t i l l a ,

as L ] ,

molecules or

humic Beck

matter

from

group

organic

States,

tified



SUNDA A N D HANSON

portion

stability

a n d Cheam

(22)

reasonably




168

Log([Lj. oT]/9C) T

Figure 9. Rehtionship between the log of the conditional stability constant and the log of the binding site concentration per gram dissolved organic carbon for individual binding sites. Newport River pH 8.00; (U) Neuse River pH 8.00; (O) Newport River pH 7.00; (%) Neuse River pH 6.78; (A) Newport River pH 5.95; (£) lake water (10).



8.

SUNDA AND HANSON

Copper

in River

Water

169

a c c o u n t e d f o r b y d i f f e r e n c e s i n pH a n d t h e r a t i o o f [ C u T o i J / g r a m organic matter. O u r c o n d i t i o n a l c o n s t a n t s a t pH 8 . 0 f o r t h a t p o r t i o n o f t h e b i n d i n g s i t e s d e s i g n e d a s L_2 a r e i n g o o d agreement w i t h s t a b i l i t y c o n s t a n t s m e a s u r e d by M a n t o u r a a n d R i l e y (10) f o r b i n d i n g o f c o p p e r by o r g a n i c m a t t e r f r o m l a k e w a t e r a t t h e same pH a n d s i m i l a r r a t i o o f m o l e s o f b i n d i n g s i t e s p e r g r a m o r g a n i c carbon (Figure 9 ) . M a n t o u r a a n d R i l e y , who u s e d a g e l f i l t r a t i o n t e c h n i q u e to measure s t a b i l i t y c o n s t a n t s , found t h e i r data c o n s i s t e n t w i t h t h e p r e s e n c e o f two s e p a r a t e b i n d i n g s i t e s . To m o d e l o u r t i t r a t i o n d a t a we u s u a l l y h a d t o p o s t u l a t e t h e e x i s t e n c e o f no f e w e r t h a n t h r e e s e p a r a t e o r g a n i c b i n d i n g s i t e s . The a p p a r e n t d i f f e r e n c e b e t w e e n r e s u l t s o f t h e t w o s t u d i e s c a n be r e s o l v e d i f we n o t e t h a t o u r t i t r a t i o n s u s u a l l y c o v e r e d 2 t o 3 o r d e r s o f m a g n i t u d e change i n bound c o p p e r c o n c e n t r a t i o n w h e r e a s , the e x p e r i m e n t s o f Mantoura and R i l e y (10J c o v e r e d o n l y s l i g h t l y g r e a t e r than one o r d e r o f m a g n i t u d e . T h u s , i t was i m p o s s i b l e f o r these i n v e s t i g a t o r s to determine the c h a r a c t e r i s t i c s of copper binding outside of t h e i r experimental range. C h e m i c a l S p e c i a t i o n Models f o r t h e Neuse and Newport R i v e r Waters. Copper s p e c i a t i o n m o d e l s f o r f i l t e r e d Newport a n d Neuse R i v e r waters as a f u n c t i o n o f t o t a l copper c o n c e n t r a t i o n a t i n s i t u pH v a l u e s ( F i g u r e s 1 0 a a n d 1 1 a ) i n d i c a t e t h a t s o l u b l e c o p p e r i s g r e a t e r t h a n 98% bound t o o r g a n i c l i g a n d s i n t h e r a n g e o f t o t a l copper concentration normally encountered i n r i v e r water, i.e., p [ C u j o j ] — 7. At these c o n c e n t r a t i o n s , copper i s p r i m a r i l y c o m p l e x e d by o r g a n i c b i n d i n g s i t e L ] , a s i t e r e p r e s e n t i n g l i g a n d s present a t low concentrations with high s t a b i l i t y constants. S i t e L-| a c c o u n t s f o r a b o u t 1% o f t h e t o t a l b i n d i n g c a p a c i t y b u t >90% o f t h e b o u n d c o p p e r a t P [ C U J O T ] ϋ 7 . Only a t extremely high c o n c e n t r a t i o n s o f t o t a l c o p p e r , i . e . , PECUTQTJ 1 3 . 7 i n t h e Newport and £ 4 . 5 i n t h e Neuse, would i n o r g a n i c s p e c i e s o f copper become d o m i n a n t . I n c r e a s i n g t h e pH o f t h e N e w p o r t f r o m 5 . 9 5 t o 7 . 0 ( F i g u r e s 10a a n d 10b) w i t h o u t c h a n g i n g c a r b o n a t e a l k a l i n i t y does n o t a l t e r t h e o r d e r o f dominance o f copper s p e c i e s . However, in the n a t u r a l range of t o t a l copper c o n c e n t r a t i o n s (i.e., P L C U T Q J ] ^ 7 ) i n c r e a s i n g pH t o 7 . 0 d o e s i n c r e a s e t h e e x t e n t o f t o t a l organic binding r e l a t i v e to inorganic species. This r e s u l t s f r o m t h e s t r o n g pH d e p e n d e n c e o f c o n d i t i o n a l s t a b i l i t y c o n s t a n t s f o r copper complexes w i t h n a t u r a l o r g a n i c l i g a n d s as d i s cussed previously. A t i n s i t u pH a n d i n s i t u c o n c e n t r a t i o n s o f d i s s o l v e d c o p p e r i n t h e Neusë~TÔ.025 μ Μ ) a n d t h e N e w p o r t ( 0 . 0 1 1 μ Μ ) , t h e m o d e l s p r e d i c t s i m i l a r pCu v a l u e s f o r t h e t w o r i v e r s ( 1 0 . 4 a n d 1 0 . 6 f o r t h e Neuse and N e w p o r t ) . Thus i n c o n s i d e r a t i o n o f t h e m a j o r f a c t o r s c o n t r o l l i n g pCu v a l u e s i n t h e two r i v e r s , t h e h i g h e r c o n c e n t r a t i o n o f o r g a n i c b i n d i n g s i t e s and lower t o t a l dissolved c o p p e r i n t h e Newport a r e a l m o s t e x a c t l y c o m p e n s a t e d f o r by t h e h i g h e r pH o f t h e N e u s e . 1



Figure 10. Chemical speciation model for dissolved copper in the Newport River at 25°C as a function of total copper concentration, (a) In situ pH 5.95, [Alk] = O.OSmM and I = 0.0005M; (b) pH 1.00, [Alk] = 0.05mU and I = 0.005M; and (c) pH 8.00, [Alk] = 0.55mM and I = 0.001U. D0C^15mgCLK

TOT

p[Cu ]


Copper

in River

Water


SUNDA AND HANSON

Figure 11. Chemical speciation model for dissolved copper in the Neuse River at 25°C as a function of total copper concentration, (a) In situ pH 6.78, [Alk] = 0.15mM and I = 0.0005M; and (h) pH 8.00, [Alk] = 0.65mM and I = 0.001U. DOC = 3 mgCL . 1



172


SYSTEMS

Models f o r copper s p e c i a t i o n as a f u n c t i o n of t o t a l c o n c e n t r a t i o n o f o r g a n i c s i t e s p[Ljoj] ( F i g u r e s 12 a n d 1 3 ) w e r e c a l c u l a t e d a t PCCUJQT] 7 w l t h t h e a s s u m p t i o n t h a t t o t a l o r g a n i c m a t t e r was v a r i e d w i t h o u t a l t e r a t i o n o f t h e r e l a t i v e c o n c e n t r a t i o n s of i n d i v i d u a l binding s i t e s w i t h r e s p e c t to the t o t a l . Copper s p e c i e s a r e a l s o shown v e r s u s d i s s o l v e d o r a a n i c c a r b o n (DOC) u s i n g m e a s u r e d v a l u e s o f 15 a n d 3 . 0 mgC f o r the Newport and Neuse, r e s p e c t i v e l y . A t i n s i t u pH ( F i g u r e s 1 2 a a n d 1 3 a ) , the d o m i n a n c e o f o r g a n i c bound s p e c i e s i s a g a i n d e m o n s t r a t e d by t h e o b s e r v a t i o n t h a t DOC w o u l d h a v e t o d r o p b e l o w a p p r o x i m a t e l y 0.4 a n d 0 . 2 mgC i H f o r t h e Newport and Neuse r e s p e c t i v e l y , before i n o r g a n i c s p e c i e s of copper would dominate. T h e e f f e c t o f pH o n o r g a n i c c o m p l e x a t i o n i s a l s o e v i d e n t a s DOC i n t h e N e w p o r t w o u l d h a v e t o b e r e d u c e d t o a p p r o x i m a t e l y 0 . 1 mgC i H a t pH 7 . 0 a n d 0 . 0 8 mgC i H a t pH 8 . 0 b e f o r e i n o r g a n i c s p e c i e s w o u l d dominate over organic species. S i m i l a r l y , DOC f o r t h e N e u s e w o u l d h a v e t o b e r e d u c e d t o 0 . 1 mgC J T 1 a t pH 8 . 0 . I n a r e c e n t r e v i e w , D u c e a n d D u u r s m a (23) c o n c l u d e t h a t o u r knowledge of d i s s o l v e d o r g a n i c carbon i n the w o r l d ' s r i v e r s i s limited. From a v a i l a b l e d a t a f o r s u c h r i v e r s as t h e A m a z o n , Hudson, M i s s i s s i p p i , M a c K e n z i e and o t h e r s , d i s s o l v e d o r g a n i c c a r b o n w a s f o u n d t o r a n g e f r o m 2 t o 5 mgC £ _ 1 . These v a l u e s are c o m p a r a b l e t o t h a t f o u n d i n t h e N e u s e ( 3 . 0 mgC £ _ 1 ) , b u t l o w e r t h a n i n t h e N e w p o r t ( 1 5 mgC £ _ 1 ) . Comparing t h i s range of DOC c o n c e n t r a t i o n w i t h the r e s u l t s of o u r work and assuming t h a t the complexing c h a r a c t e r i s t i c s of the organic matter remains a p p r o x i m a t e l y t h e s a m e a m o n g w a t e r s h e d s , we w o u l d e x p e c t c o p p e r c h e m i s t r y i n t h e w o r l d ' s r i v e r s t o be d o m i n a t e d b y c o p p e r - o r g a n i c interactions. This c o n c l u s i o n agrees w i t h t h a t of Mantoura et a l . ( 2 4 ) a s b a s e d on t h e i r c o p p e r s p e c i a t i o n model f o r r i v e r water. C o p p e r s p e c i a t i o n i n t h e N e w p o r t and Neuse R i v e r s was c a l c u l a t e d a s a f u n c t i o n o f c a r b o n a t e a l k a l i n i t y a t s e v e r a l pH v a l u e s f o r p [ C u j o j ] 7 and the n a t u r a l s u i t e o f o r g a n i c l i g a n d s d e t e r m i n e d p r e v i o u s l y ( F i g u r e s 14 a n d 1 5 ) . The a l k a l i n i t y r a n g e was s e l e c t e d to r e f l e c t that expected i n the w o r l d ' s r i v e r s . From the data of L i v i n g s t o n e (25), the a l k a l i n i t y of the w o r l d ' s a v e r a g e r i v e r w a s c a l c u l a t e d t o b e a p p r o x i m a t e l y 0 . 9 6 mM. Stumm and Morgan (9J p r e s e n t data t h a t s u g g e s t c a r b o n a t e a l k a l i n i t i e s in the w o r l d ' s freshwater would f a l l i n the approximate range 0.1 t o 8 mM. _1 I n t h e N e w p o r t R i v e r w i t h a DOC o f 15 mgC l~ , o r g a n i c copper s p e c i e s c l e a r l y dominate over the f u l l range of alkalinit i e s ( p [ A l k ] 5 t o 2 ) a t pH 5 . 9 5 , 7 . 0 a n d 8 . 0 . A t P[CU QT] 7 and P[LJQT] 3 . 7 t o 3 . 9 , t h e o r g a n i c b i n d i n g s i t e c o n c e n t r a t i o n s and s t a b i l i t y constants are s u f f i c i e n t l y large for organic matter to s u c c e s s f u l l y outcompete i n o r g a n i c l i g a n d s . Thus, the copper complexes with i n d i v i d u a l f r a c t i o n s of organic binding s i t e s are e s s e n t i a l l y invariant with a l k a l i n i t y (Figures 14a-c). A s pH i s i n c r e a s e d the r e l a t i v e amounts o f i n o r g a n i c s p e c i e s of c o p p e r d e c l i n e e s p e c i a l l y a t low a l k a l i n i t i e s . As a l k a l i n i t y i n c r e a s e s T



Figure 12. Chemical speciation model for dissolved copper in the Newport River at 25°C as a function of total organic binding site concentration, (a) In situ pH 5.95, [Alk] = O.OSmM and I = 0.0005M; (b) pH 7.00, [Alk] = 0.05m\l and I = 0.0005M; and (c) pH 8.00, [Alk] = 0.55mM and I = 0.001M.


00


174

NEUSE RIVER pH 8.00

NEUSE RIVER pH 6.78

Log DOC (mgC-!" )

Log DOC (mgC'!" )

1

1

-1

0

1

2

0

1

2

3


-2

Figure 13. Chemical speciation model for dissolved copper in the Neuse River at 25°C as a function of total organic binding site concentration, (a) In situ pH 6.78, [Alk] = 0.15mM and I = 0.0005M; and (b) pH 8.00, [Alk] = 0.65mM and I = 0.001M.



Figure

14.

T0T

Chemical speciation model for dissolved copper in the Newport a function of carbonate alkalinity at v[Cu ] 7.

p[Alk] River


at 25°C

as

ι—· οι


176

pH 6.78


NEUSE RIVER

NEUSE RIVER

pH 8.00

p[Alk] Figure

15.

Chemical speciation at 25°C as a function

model for dissolved copper in the Neuse of carbonate alkalinity at tp[Cu t] 7 TO


River

8.

the

relative

dominate

importance

the

> 10"3·

14b)

and

5.95

(Figure

[A1K]

species at

For general

the

pattern

8.0.

The

lower

allows

stronger

the

situ

competes

the

In

are

associated these

natural

L3

may

ligands

Newport

River

addition

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at

a

P[CUTQJ]

organicj)

to

data).

ing

ionic

an

(6.0)

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an

addition

to

a value

by

less

of

-3.42).

same

of of

than

2.7 0.2

the

value

Since

the

calcium (9j,

the our

that as

pH

omission

of

waters. be

total

value

increasing

electrode

slight

log

at

the

of

(Sunda,

the

calcium

initial same a

the

value

of

to

-3.56

of

increase

to

a

had

mM

value

0.94

by

from

mM c a u s e d

only

0.2

units.

have c o n c e n t r a t i o n s ranges

changing

have

0.26

organic]")

conditions,

of

concentration

should

of

Mg(NÛ3)2 addition

concentration waters

contain

([Cu2+]/[Cu

experimental by

unpub

concentration

log

an

M

]/[Cu-

p[Cujoj]

values

of

10"1 2 +

water

same

ionic

KNO3

([Cu

River

effect

the

by

concentration

influence

ions

a

backgound

concentration

within

copper

a value

of

to also

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water

units

M KNO3)

magnesium

Increasing

M to

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River

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^

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of

At

out-

assumption

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0.3

mM t o

copper.

c a l c i u m and

to

the

and

Neuse

concentrations

only

of

investigated

a minor

of

influence

models.

general

organic

river ing

majority

dissolved

solved

0.04

of

copper

of

(from

or

6.78

complexing

would

w h i c h may

(LCu2+]/[Cu-organic])

binding

This

0.2

a

pH

for

same

of

CUCO3 c o m p l e x

sample

from

under

and magnesium

The

only

magnesium of

the

conditional

Newport

caused

(7.7),

and magnesium

calcium on

log

7.7

buffer

units

in

strongly

strength

of

mM d e c r e a s e d

Likewise

with

organic

value

Ca(N03)2

background of

that

using

ionic

same

pH

matter ligands

Increased

filtered

by

strength

increasing values

pH

the

at

the

least

Previous

by

initial

In

the

by

of

increase

2)

alkalinity.

water

copper

and

ini

in

15a).

strength

that

sample

6.0

lished

10~2-8

but

(24).

in

of

inorganic >

compete

binding

of

At

the

5 to

increased a l k a l i n i t y

ionic

strength

(p[Alk]

assumed of

matter.

binding

by

clear

organic

(Figure

organic

the

of

[ΑΙ Κ]

increased

on

b)

increased concentrations

however,

14c). dominant

follows

to

shown,

the

dominance

binding have

is

speciation

have

cations

organic in

(Figure

ion

to

7.0

with

concentrated

because

with two

8.0

pH

copper

independent

valid

pH

increases

t

a

and

and

site

at

complex

> 10"3.2

cupric

9

alkalinities

o u r m o d e l s , we

strictly

result

most

[Alk]

15a

competition 6.78

for

the

concentration

binding

constants

and

pH

177

alkalinities.

River, all

Water

monocarbonato

free

(Figures

species for

organic

14a)

all

Neuse

ganic

in

the

species

(Figure pH

of

in River

inorganic

situ

organic


Copper

SUNDA AND HANSON

and

the

principal

copper

to

range

alkalinity

concentration

copper

the

predicted

occur

of

and

concentration.

in

total

values

variables

s p e c i a t i o n models copper,

is

principally pH,

encountered

disin

world

controlling organic

bind-

composition In

rivers

of

organic

c a s e s where

the

matter, toxicity



178 of

dissolved

activity, crease

copper

we w o u l d

with

to organisms predict

decreasing

i s determined

toxicity

dissolved

of

by f r e e

dissolved

organic

matter

copper

cupric to

ion

i n -

and d e c r e a s i n g

pH.

Acknowledgements

Lewis

The a u t h o r s wish to thank L i l l i a n A. Flanagan f o r t h e i r able assistance in the laboratory.

a n d J o Ann M. We t h a n k


D a v i d R. C o l b y f o r h e l p f u l d i s c u s s i o n s d u r i n g t h e p r e p a r a t i o n of t h i s paper. The r e s e a r c h on w h i c h t h i s m a n u s c r i p t i s b a s e d was s u p p o r t e d by a n i n t e r a g e n c y a g r e e m e n t b e t w e e n t h e D e p a r t m e n t o f Energy and the N a t i o n a l Marine F i s h e r i e s S e r v i c e . This manuscript i s c o n t r i b u t i o n number 7 8 - 5 3 B , S o u t h e a s t F i s h e r i e s C e n t e r , N a t i o n a l M a r i n e F i s h e r i e s S e r v i c e , NOAA, B e a u f o r t , N . C . , USA. R e f e r e n c e t o t r a d e names d o e s n o t i m p l y e n d o r s e m e n t by t h e N a t i o n a l Marine Fisheries Service,

Abstract The complexation of copper by organic and inorganic ligands was investigated in the Neuse and Newport Rivers, two North Carolina rivers that have widely different concentrations of dissolved organic carbon (3 and 15 mgC l ). Potentiometric titrations with a cupric ion electrode were used to measure complexation of copper by organic and inorganic ligands in river waters and chemically defined solutions. Stability constants for complexation of copper by OH and CO , the dominant inorganic ligands for copper in natural waters, were determined. Constants at infinite dilution for CuOH , CUCO , and Cu(CO )2-2 (10 · , 106.74, and 10 · , respectively) agree favorably with previously published values. However, our constant for Cu(OH) (10 · ) is ~ 2 orders of magnitude lower than values that have been widely used in equilibrium calculations of copper speciation in natural waters. As a result many published equilibrium models for copper appear to have overestimated the importance of the copper dihydroxo species resulting in some cases in an appreciable over-estimation of the total level of copper complexation. Copper was highly complexed by dissolved materials in Neuse and Newport river waters. A marked reduction in complexation following UV-phocoxidation of organic matter indicated that copper was bound predominantly to organic ligands. Binding characteristics of the organic matter in the two rivers was similar and a pronounced increase in binding with pH suggested complexation of copper by protonated weak acids. Scatchard plot analysis of the Cu binding data indicated the presence of at least three organic binding sites in each river whose conditional stability constants increased with increasing pH and decreasing ratio of binding site concentration per gram organic carbon. Copper speciation models were computed for the range of pH, organic matter concentration, alkalinity and total copper typically found in rivers. These -1

-

2-

3

+

6 48

3

3

10 24

11 78

2


8.

SUNDA AND HANSON


179


models predicted that the speciation of copper in the world's rivers will be dominated by complexes with natural organic ligands. Binding of copper by organic ligands should have a marked in fluence on biological and geochemical reactivity of copper in rivers, affecting important processes and phenomena such as toxicity and nutritional availability to organisms, adsorption onto surfaces, precipitation, and solid solution. Computational models for the chemical speciation of copper in natural waters that ignore organic complexation may inaccurately describe the chemistry of copper in terrestrial waters and perhaps marine waters as well. Literature Cited 1. 2. 3.

4. 5.

6.

7.

8.

9. 10.

Sunda, W.G., and Guillard, R.R.L. The relationship between cupric ion activity and the toxicity of copper to phyto plankton. J. Mar. Res. 34, 511-529 (1976). Anderson, D.M. and Morel, F.M.M. Copper sensitivity of Gonyaulax tamarensis. Limnol. Oceanog. 23, 283-295 (1978). Sunda, W.G., Engel, D.W. and Thuotte, R.M. Effect of chemi cal speciation on toxicity of cadmium to grass shrimp, Palaemonetes pugio: importance of free cadmium ion. Environ. Sci. Tech. 12, 409-413 (1978). Andrew, R.W., Biesinger, K.E. and Glass, G.E. Effects of inorganic complexing on the toxicity of copper to Daphnia magna. Water Res. 11, 309-315 (1977). Jackson, G.A. and Morgan, J . J . Trace metal-chelator inter actions and phytoplankton growth in seawater media: Theoretical analysis and comparison with reported observations. Limnol. Oceanog. 23, 268-282 (1978). Sunda, W.G., and Lewis, J.M. Effect of complexation of natural organic ligands on the toxicity of copper to a unicellular alga, Monochrysis lutheri. Limnol. Oceanogr. (in press). Bilinski, Η., Huston, R. and Stumm, W. Determination of the stability constants of some hydroxo and carbonato complexes of Pb(II), Cu(II), Cd(II) and Zn(II) in dilute solutions by anodic stripping voltammetry and differential pulse polarography. Anal. Chim. Acta 84, 157-164 (1976). Armstrong, F . A . J . , Williams, P.M. and Strickland, J.D.H. Photo-oxidation of organic matter in seawater by ultraviolet radiation, analytical and other applications. Nature 211, 481-483 (1966). Stumm, W. and Morgan, J . J . "Aquatic Chemistry," 583 p. Wiley Interscience, New York. 1970. Mantoura, R.F.C. and Riley, J.P. The use of gel filtration in the study of metal binding by humic acids and related compounds. Anal. Chim. Acta 78, 193-200 (1975).


180

11. 12. 13. 14.


15. 16. 17. 18. 19.

20. 21. 22. 23. 24. 25.


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November 16,

1978.


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