Surface active phenomenaby humic substances of aquatic origin

Revue trancaisc dcs SGIEIGES llE L'EAU, | (19821 285 - 296

Surface active phenomena

by humic substances of aquatic origin

P h 6 n o m d n e s d e te n s i o n s u p e r f i c i e l l e

p a r l e s s u b s t a n c e s h u m i q u e s d ' o r i g i n e a q u a t i q u e

S . A . V l S S E R

R 6 s u m 6

L a t e n s i o n s u p e r f i c i e L L e d e s o t u t i o n s d ' a c i d e s f u t v i q u e s e t h u m i q u e s d ' o r i g i n e a q u a t i q u e o u o b t e n u s d e s u b s t r a t s m i c r o b i e n s a 6 t 6 6 t u d i 6 e d a n s t e b u t d r 6 t a b L i r d e q u e [ [ e f a g o n [ a v a t e u r d e c e L l . e - c i d 6 p e n d d e [ ' o l i g i n e , d u p o i d s m o I e c u I a i r e , d e s g r o u p e m e n t s f o n c t i o n n e I s e t d e [ ' e t a t d r h u m i f i c a t i o n d u m a t 6 r i e [ - L a f o r m e m o t e c u I a i r e d e s s u b s - t a n c e s h u m i q u e s a a u s s i 6 t 6 6 t u d i e e i p a r t i r d e L a t e n s i o n s u p e r f i - c i e [ [ e . L o r s q u e p o s s i b I e , l e s r 6 s u L t a t s o b t e n u s s u r L ' h u m u s a q u a t i - q u e o n t 6 t 6 c o m p a 1 6 s a v e c c e u x p n o v e n a n t d e s s u b s t a n c e s h u m i q u e s d ' o r i g i n e t e r r e s t r e .

I L a p p a r a i t q u e , n o r m a l e m e n t , t e s p r o d u i t s h u m i q u e s d ' o r i g i n e a q u a - t i q u e s o n t p L u s t e n s i o - a c t ' i f s q u e I e s s u b s t a n c e s h u m j q u e s o b t e n u e s d u m i L i e u t e r r e s t r e . A d e s c o n c e n t r a t i o n s t e t L e s q u e c e t t e s r e n c o n - t r 6 e s d a n s [ e m i L i e u n a t u r e L , I e s a c i d e s h u m i q u e s ( h u m a t e s ) a q u a t i - q u e s b a i s s e n t [ a t e n s i o n s u p e r f i c i e [ [ e d e s e a u x d a v a n t a g e q u e L e s a c i d e s f u I v i q u e s ( f u t v a t e s ) . 0 n a d e m o n t 1 6 g u e I a t e n s i o - a c t i v i t e d e t r h u m u s a u g m e n t e a v e c s o n p o i d s m o t e c u t a i r e e t q u ' e t t e a t e n d a n - c e d d i m i n u e r l o r s d u p r o c e s s u s d , h u m i f i c a t i o n d u m a t 6 r i e t -

S u m m a n y

T h e s u r f a c e a c t i v i t y o f f u l v i c a n d h u m i c m a t t e r o f a q u a t i c o r i g i n a n d f r o m m i c r o b i a I s u b s t r a t e s w a s s t u d i e d i n o r d e r t o e s t a b l i s h h o h , ' i t c o u L d c h a n g e w i t h o r i g i n , m o t e c u t a r w e i g h t / f u n c t i o n a I g r o u p c o n t e n t a n d s t a t e o f h u m i f i c a t i o n o f t h e h u m i c m a t e r i a t . I t w a s a L s o u s e d t o o b t a i n i n f o r m a t i o n o n t h e m o t e c u [ a r s i z e a n d s h a p e o f t h e s u b s t a n c e s i n v e s t i g a t e d . l l h e r e v e r p o s s i b t e , t h e r e s u t t s w e r e c o m p a - r e d w i t h t h o s e o b t a i n e d o n h u m i c s u b s t a n c e s f r o m t e r r e s t r i a L e n v i - r o n m e n t s .

D e p a r t m e n t o f S o i l S c i e n c e , L a v a l l J n i v e r s i t y , C i t 6 U n i v e r s i t a i r e , Q u e b e c , C a n a d a G t K 7 P 4

2 8 6 S c i e n c e s d e L ' e a u 7 , n o s

I t v J a s s h o w n t h a t t h e a q u a t i c f u L v i c a n d h u m i c a c i d s w e r e g e n e r a L t y m o r e s u r f a c e a c t i v e t h a n h u m i c m a t t e r f r o m s o i L s . T h e s u r f a c e a c t i - v i t y i n c r e a s e d w i t h r i s i n g m o L e c u L a r v i e i g h t a n d n o r m a I t y d e c r e a s e d w i t h p r o g r e s s i v e h u m i f i c a t i o n o f t h e m a t e r i a t - A t n a t u r a I c o n c e n t r a - t i o n s a q u a t i c h u m i c a c i d s w e r e n o r m a t [ y m o r e s u r f a c e a c t i v e t h a n f u t v i c a c i d s .

I rurRopucr r oru

The phenonenon of surface

metrical- amphophilic organic

( T S C H A P E K e t a L . , 1 9 7 8 ) . T h e h u m a t e s s u g g e s t s , t h e r e f o r e , n o n - p o l a r p a r t s .

a c t i v i t y i s , i n g e n e r a l , i n h e r e n t t o a s y m - m o l e c u l e s o f m e d i u m m o l e c u l a r w e i g h t e x i s t e n c e o f s u r f a c e a c t i v i t y b y a l k a l i t h a t t h e m o l e c u l e s c o n t a i n p o l a r a s w e l l - a s

S u r f a c e a c t i v e s u b s t a n c e s c a n p l a y a n i m p o r t a n t r o l e i n b i o l o g i c a l

phenomena in the aquatic environment by affeeting : the permeability and

s t r u c t u r e o f c e l f u l a r m e m b r a n e s ( a n d t h e r e f o r e t h e u p t a k e a n d r e l e a s e o f c e r t a i n m e t a b o l i t e s ) ; t h e s t r u c t u r e o f s o n r e m a c r o r n o l e c u l e s s u c h a s p r o - t e i n s ( a f f e c t i n g i n t h i s w a y f o r i n s t a n c e t h e a c t i v i t y o f e n z y m e s ) r the p r o c e s s o f r e s p i r a t i o n ; t h e s o l u b i l i s a t i o n o f n u t r i e n t s o r t o x i n s i n t h e e n v i r o n m e n t ( r e s u l t i n q i n t h e s t i n u l a t i o n o r i n h i b i t i o n o f v i t a f p r o c e s s e s ) .

T h e s u r f a c e t e n s i o n o f s o i f f u l v i c a c i d ( F A ) and humic acid ( H A ) so-

lutions has been reported to be pH dependent (CHEN and SCHNITZER, 797e) ,

w h i c h w o u l d b e t h e r e s u l t o f t h e i o n i z a t i o n o f a c i d i c f u n c t i o n a l g r o u p s

such as COOH and phenolic OH. At high pH values these groups will form

hydrophilic sites thus increasing the amphophilic character and there-

f o r e a L s o t h e s u r f a c e a c i t i v i t v o f t h e h u m i c s o l - u t e s .

I n t h e p r e s e n t i n v e s t i g a t i o n t h e s u r f a c e a c t i v i t y o f f u l v i c a n d h u m i c r n a t t e r m o l e c u l a r w e i g h t ( m w ) fractions o f v a r i o u s a q u a t i c o r i g i n s w a s

i n v e s t i g a t e d . I n o r d e r t o e x a m i n e t h e e f f e c t o f h u m i f i c a t i o n o n t h e s u r - f a c e a c t i v e p r o p e r t i e s o f h u m u s , a l s o f u l v i c a n d h u m i c a c i d s o b t a i n e d f r o m m i c r o b i a l s u b s t r a t e s a n d s u b j e c t e d t o d i f f e r e n t i n c u b a t i o n p e r i o d s w e r e s t u d i e d . W i t h t h e o b t a i n e d r e s u l - t s s e v e r a L o t h e r p h y s i c o - c h e m i c a l - c h a r a c t e r i s t i c s o f h u m i c m o l e c u f e s c o u l d f u r t h e r b e i n v e s t i q a t e d .

ExprR t I\TENTAL

O r i g i n o f m a t e r i a l

A q u a t i c h l r m i c m a t t e r o f n a t u r a l o r i g i n w a s s a m p l e s c o l l - e c t e d d u r i n g S e p t e m b e r 1 9 7 4 f r o m a

o b t a i n e d f r o m 1 5 0 f . v / a t e r r i v e r ( C h i c o u t i m i R i v e r )

Surface actittities of aquatie humic substances 2 8 7

and a swamp, situated in the Laurentide Park in the precambrian Shield

r e g i o n o f t h e p r o v i n c e o f Quebec, Canada.

H u m i c m a t e r i a l o f m i c r o b i a l o r i g i n w a s o b t a i n e d f r o m a g l u c o s e - ] ' e a s t e x t r a c t n e d i u m ( g l u c o s e : o . 1 t ; Difco yeast extract : 0 . 1 % ) i n o c u -

lated with an actinomycete obtained from a Quebec forest soil, and incur

b a t e d u n d e r c o n s t a n t c o n d i t i o n s o f a e r a t i o n , t e m p e r a t u r e ( 2 5 o C ) and pH ( 7 . 0 ) . S a m p l e s $ r e r e c o l - l - e c t e d f o r r e c o v e r y o f F A , s a n d H A ' s a f t e r 1 4 , 6 0 a n d 1 8 0 d a y s o f i n c u b a t i o n .

F o r s a m p l e s o f b o t h n a t u r a l a n d m i c r o b i a l o r i g i n s , f r a c t i o n a t i o n p r o - c e d . u r e s w e r e s t a r t e d w i t h i n o n e d a v o f c o l l e c t i - o n .

b . F r a c t i o n a t i o n p r o c e d u r e

A f t e r t h e a d j u s t m e n t o f t h e s a m p l e s t o 8 . 4 , t h e y w e r e c e n t r i f u g e d a t 2 8 . 0 0 0 g i n a S o r v a l u l t r a c e n t r i f u g e f i t t e d w i t h a c o n t i n u o u s - f l o w

head in order to remove any particulate organj_c and inorganic matter.

T h e s u p e r n a t a n t w a s n e x t f i l t e r e d c o n s e c u t i v e l y o v e r D i a p o r * f i l t e r s n o . D P O 6 , D P O 4 5 a n d D P O 2 b r i t h respective p o r e s i z e s o f 0 . 6 , 0 . 4 5 a n d 0 . 2 }tn.

Very Large volumes, such as was the case of samples coll_ected from

n a t u r a f e n v i r o n m e n t s ( 1 5 0 r.) w e r e r e d u c e d b y c o n c e n t r a t i n g t h e o r g a n i c m a t t e r b y m e a n s o f a D i a f i b e r * m e m b r a n e c a r t r i d g e f i r t e r n o . H l o p l o u n t i l the el-uate became coloured.

T h e H A f r a c t i o n w a s p r e c i p i t a t e d b y a c l j u s t i n g t h e p H t o 1 . 5 a f t e r

which the above-mentioned centrifugation and Diafiber filtration proce-

d . u r e s w e r e r e p e a t e d . T h e f i n a L s o r u t j - o n ( c o n t a i n i n g t h e f u l v i c f r a c t i o n )

was then reduced in volume by ultrafiltration using a Diafl-o* uMo5 ultra-

f i l t e r .

T h e H A r s w e r e p u r i f i e d b y r e p e a t i n g a c y c l e o f p r e c i p i t a t i o n a t p H 1 . 5 f o l l - o w e d b y d i s s o l u t i o n a t p H 8 . 0 u n t i l t h e s u p e r n a t a n t a t p H 1 . 5 r e m a i n e d v i r t u a l l v c o l _ o u r l e s s .

I n t h e c a s e o f t h e F A ' s , t h e c o n c e n t r a t e , a f t e r a d j u s t m e n t t o p H 1 . 5 , w a s p a s s e d o v e r A m b e r l i t e r e s i n + X A D - 2 , p r e v i o u s l y p u r i f i e d a n d a c t i v a -

ted by refluxing it in a Soxhlet apparutus with methanol for a period of

t w o d a y s . T h e a b s o r b e d f u l v i c m a t t e r w a s p a r t i a l l y e l u t e d ( u p to 90 ?) u s j - n g a T R I S b u f f e r ( p H 8 . 4 , I = 0 . 1 5 ) , a f t e r w h i c h t h e e ] u a t e w a s c o n c e n t r a t e d o v e r a D i a f l o U M O 5 u l t r a - f i l t r a t i o n m e m b r a n e _

Sqne residual brown-coloured materi_al obtained from the XAD-2 resin

by washing it subsequently with methanol appeared to contain a high per-

c e n t a g e o f l y p o p h i l i c m a t e r i a l , T h i s f r a c t i o n w h i c h a m o u n t e d t o a p p r o x . 1 0 I o f t h e t o t a l F A c o n t e n t o f t h e o r i g i n a l s a m p l e , w a s n o t f u r t h e r

investigated in this study.

Both fulvic and humic acids were next suspended in a TRIS buffer

( p H 8 - 4 , I = 0 . 1 5 ) , a n d b y u s i n g D i a f l o u l t r a f i l t r a t i o n m e m b r a n e s , f i t t e d i n t o c o n t i n u o u s l y - s t i r r e d u l t r a f i - t - t r a t i o n c e 1 I s , w e r e f r a c t i o n a t e d i n t o f o u r f r a c t i o n s w i t h a v e r a g e m w o f r e s p e c t i v e l y 7 5 0 , 5 5 0 0 , 2 5 0 0 0 a n d 2 0 0 0 0 0 d a l t o n s . B y a p p l y i n g t h e p r e s c r i b e d p r e s s u r e d u r i n g t h e u l t r a f i l -

x A m i c o n C o r p o r a t i o n , L e x i n g t o n , l v l A . U . S , 4 .

* B D H C h e m i c a l s , T o r o n t o , C a n a d a

2 8 8

tration procedure and by maj.ntaining the pH and ionic strength of the

s o l u t i o n s a t t h e i n d i c a t e d l e v e f s , t h e a v e r a g e p a r t i c l e s i z e o f t h e h u m i c m a t t e r f r a c t i - o n s i n t h e u l t r a f i l t r a t e s w a s f o u n d t o m a t c h r e a s o n - a b l y w e l l w i t h t h e a v e r a g e m o l e c u l a r s i z e s o f t h e h u m i c c o m p o u n d s a s i n d i c a t e d b y u l t r a c e n t r i f u g a t i o r r .

After fractionation the concentrates were thoroughly washed with TRIS

b u f f e r u n t i l t h e u l t r a f i l t r a t e r e m a i n e d c o n p l e t e l y c o l o u r l e s s . T h e b u f - f e r u n t i l w a s f i n a l f y r e m o v e d b y w a s h i n g t h e h u n i c f r a c t i o n s ( p r e s e n t i n t h e f o r m o f t h e i r K s a l t s ) w i t h d i s t i l l e d w a t e r u n t i l t h e f i f t r a t e h a d a p H o f 7 . 0 a n d w a s c o m p l e t e l y c h l o r i d e f r e e . T h e c o n c e n t r a t i o n o f t h e h u m i c f r a c t i o n s v / a s t h e n a d j u s t e d t o 0 . 5 t , a f t e r w h i c h t h e d r y m a t e r i a l w a s o b t a i n e d b y f r e e z e - d r y i n g .

c . M e a s u r e m e n t o f s u r f a c e a c t i v i t y

T h e s u r f a c e t e n s i o n m e a s u r e m e n t s h r e r e c a r r i e d o u t a t 2 5 o C a n d p H 7 . 0 b y t h e d u N o u y m e t h o d ( C e n c o s u r f a c e t e n s i o m e t e r n o . 7 0 5 3 5 , C e n t r a l S c i e n t i f i c C o m p a n y , C h i c a g o ) . T h e c o n c e n t r a t i o n r a n g e o f t h e p o t a s s i u m f u l v a t e s a n d h u m a t e s i n v e s t i g a t e d w a s b e t w e e n 1 0 a n C 1 0 " U9 1-'and t h e a c c u r a c y o f t h e m e a s u r e m e n t s w a s O . 0 5 d y n e c m - ' .

T h e o b t a i n e d s u r f a c e t e n s i o n s Y w e r e p l o t t e d v e r s u s t h e l o g v a l u e s o f t h e c o n c e n t r a t i o n s o f t h e h u m i c m a t e r i a l a n d f r o m t h e s t e e p e s t s l o p e

of the curves,(dy,/dlogC)p3xr the maximum surface adsorptj-on f *.* was

c a l c u l a t e d a c c o r d i n g t o c i b b s ' e q u a t i o n ( T S C H A P E K and VIASOWSKI, 1916) :

f = - I d Y , - 2

, R E ' ( d r " c ) T m o l e c m o r f = - r . ? ' 1 5 x t o - "

E * ;

"

m o l e c m - 2 ,

i n w h i c h Y represents t h e s u r f a c e t e n s i o n i n d y n e s c m - r , a n d C t h e c o n c e n t r a t i o n o f s o l u t e i n p e r c e n t .

According to the results obtained by TSCHAPEK et aL. (1980) use of

t h e a b o v e e q u a t i o n w a s j u s t i f i e d a s t h e c o n c e n t r a t i o n s o f t h e h u m i c m a t t e r u s e d f o r t h e d e t l r r n i n a t i o n

" t ( - * \ " n a ) o . * r . t " r e x c e e d e d 3 x l O - a U S 1 - : a n d w e r e t h e r e f o r e w e l l b e l - o w t h e t h r e s h o f d v a l u e o f 6 x 1 O - " U S l - ' .

From the | .r" value the rninimum cross-sectional area Amin per mole-

cule waq calcul-ated using the foltowing equation (TSCHAPEK and WASOWSKI,

79'76) :

m 1 n

in which N represents m o l e - l ) , h e n c - e ,

l a - r l l a -

. ^ - 8

A l . b b X ] U p t l

mrn = -_;-- A- molecure- -

t 1

| . N

max

t h e n u m b e r o f A v o g a d r o ( 6 . 0 2 x 1023 mol-ecules

Surface actit;ities of aquatlc humic substances 2 8 9

R E s r i l t s A N D D r s c u s s r o N

T h e s u r f a c e t e n s i o n v e r s u s c o n c e n t r a t i o n p l o t s ( f j - g u r e 1 ) s h o w t h e c h a r a c t e r i s t i c s h a p e s o f a d s o r p t i o n c u r v e s . C H E N a n d S C E N I T Z E R ( 1 9 ? g ) r e p o r t e d t h a t f o r F A ' s t h e s e p l o t s h a d a h y p e r b o l i c s h a p e , w h e r e a s f o r E A r s t h e y w e r e l i n e a r . T h i s c o u l d n o t b e c o n f i r m e d f o r F A ' s a n d H A ' s o f

aquatic origin or from microbial- cultures for which only sigmoid-shaped

c u r v e s w e r e o b t a i n e d .

H i g h e s t s u r f a c e t e n s i o n d e p r e s s i o n s ( 7 2 - y ) w e r e o b s e r v e d f o r F A ' s o f t h e a q u a t i c e n v i r o n m e n t s a n d t h e m a x i m u m d e p r e s s i o n o b t a i n e d ( 3 5 . 1 r 0 . 7 d y n e c m - I ) w a s f o r t h e F A ' s f r o m t h e s w a m p . H A ' s o f a q u a t i c o r i g i n a n d m i c r o b i a l F A ' s a n d H A ' s g a v e v e r y s i m i f a r m a x i m u m - d e p r e s s i o n s o f r e s p . 2 8 . O r 2 . 4 ; 2 6 . 6 * 6 . 2 a n d 2 7 . 4 * , 3 . 6 d y n e c r n - ' . C t t E N a n d S C H N I T Z E R ( 1 9 7 8 ) r e p o i t e d f o r 0 . 6 % F A a n d H A s o l u t i o n s ( p H 7), prepared f r o m m a t e r i a l s o f w i d e l y d i f f e r e n t o r i g i n , s u r f a c e t e n s i o n d e p r e s s i o n s r a n g ' i n g f r o m 2 . 8 t o 2 7 . O d y n e c m - ' . T h e h i g h e s t d e p r e s s i o n m e a s u r e C b y

us and obtained on an aguatic FA was approximately 8 units larger than

t h e h i g h e s t d e p r e s s i o n o b t a i n e d b y C H E N a n d S C H N I T Z E R ( 1 9 7 8 ) , w h i c h w a s o n a F A f r o m a p o d s o l . F o r t h e a q u a t i c H A ' s t h e a v e r a g e d e p r e s s i o n o b t a i - n e d b y u s ( 2 8 . 0 d y n e c m - ' ) w a s a p p r o x i m a t e l y 5 u n i t s l a r g e r t h a n t h e a v e r a g e m a x i m u m d e p r e s s i o n r e p o r t e d s o f a r f o r H A ' s o f t e r r e s t r i a l o r i g i n

( C H E N and SCHNTTZER, 1978, TSCHAPEK, e t a L . , l 9 8 O ) .

Although maximum depressions in surface activity, are often higher

f o r F A ' s t h a n H A ' s , f o r t h e l a t t e r t h e y a r e g e n e r a l l y o b s e r v e d a t l _ o w e r c o n c e n t r a t i o n s ( f i g u r e 1 ) . I t a p p e a r s , t h e r e f o r e , t h a t a t a l o w c o n c e n - t r a t i o n r a n g e ( 1 - 5 mgl-1) HA's often s h o w a h i - g h e r s u r f a c e a c t i v i t y l h a n F A ' s . T h e l a t t e r , t h o u g h , a r e n o r m a ] I y t h e m o r e p o w e r f u l s u r f a c e t e n s i o n d e p r e s s o r s a t h i g h e r c o n c e n t r a t i o n s r a n g e s ( > 25 mgl-,) A s , h o w e v e r ,

the average fulvic and humic acid concentration in the natural waters

i n v e s t i g a t e d w a s r e s p . 1 . 8 a n d 0 . 3 m g I - l ( V I S S E R , u n p u b l i s h e d r e s u l t s ) , i t c a n b e a s s u m e d t h a t i n t h e s e w a t e r s H A ' s w e r e t h e m o r e i m p o r t a n t s u r - f a c e a c t i v e s u b s t a n c e s .

The average value of the maximum slope of the y versus 1og C plot

( t a b l e 1 ) w a s h i g h e r f o r a q u a t i c F A ' s a n d H A r s t h a n f o r m a t e r i a l f r o r n t h e m i c r o b i a l c u l t u r e s o r f o r t h e s o i l h u m i c p r o d u c t s ( F A : -9.70, H A : - 23.14) as investigated b y C H E N a n d S C H N I T Z E R ( 1 9 7 8 ) . T h i s w o u l d i m p l y t h a t a m o n g s t t h e d i f f e r e n t t y p e s o f h u r n i c m a t t e r i n v e s t i g a t e d , m a t e r i a l

of aquatic origin normally has the highest maximum surface adsorption

f *.* and, as shown in table 2, the lowest minimum cross-sectional a r e a

per molecule. Humic molecules of aquatic origin wouLd therefore appear

t o b e l e s s c o n d e n s e d t h a n t h o s e g f o t h e r o r i g i n s . A s i m i l l _ a r c o n c l u s i o n

was reached from a study of the-$ ratio of different types of humic

m a t t e r ( V I S S E R , unpublished r e s u l t s ) . T h e h i g h e r m i n i m a l - c r o s s - s e c t i o n a l a r e a s o f t h e F A ' s a s c o m p a r e d t o H A ' s w o u l d a l s o indicate t h a t H A ' s p o s - s e s s a m o r e c o n d e n s e d s t r u c t u r e t h a n F A ' s .

With respect to the effect of environmental origin of humic compounds

on their surface active properties, table 3 shows that huric matter from

the swarnp environment gave higher surface tension depressions than mate-

rial from the river water. Humic substances from the swamp had also

lower minimum average cross-sectional areas per molecule than humic pro-

ducts obtained from the river water.

s^o

IJ ai

\) \

AJ q

q) t)

^a^6-,.6 t^ ^.'A '(noa

wo++oil sp?oe c?umll pup o?a?'n!

suoVqoo,{ ]o

q4bVan .rp7noa7ow ,tot

saa,tnc uo?+Da+uacuoc se uo'Lsua+

aoD!,tns

L aar$?,d

1Ol 1Ol

o8 t oo oo ? og E otft oooo l r o3oa I

ot l ot ' l

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YN

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.t)^r. oooooE r ooofE rr^|r :! of!, rr^rr rr^rt oocs

xt ot lo

YL af

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t.

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l fl 00 3 vr .r I otl asvnt .

rr^rr OOOOOI

? E O9 OO r ^r rt

rr^rr oots r rr^rr ogz

ta to tt

al o

Y!

c

zg

o2

t.

o8 t oo oo I! ol t t og oo@s l l o8o8 I l os l o8 I

()9 ()0()009 ! o0 () 00 9t 0()9s ()9

I l os 09

, oo oo P og E gf og oooo t t

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to,lllfir.r' t*

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(Fraal xotrvuxttraot

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z

:

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,t

Surface actioities of aquatic humic substanees

Table L

Values of the mar. slopes in surface tension os Log conc. cut'ttes of hunrLc matter fz,aetions fz,om different sources

f r a c t i o n o r i g i n hurnification a v e r a g e m w o f f r a c t i o n ( d a l t o n s ) period

or source

'150 5 5 0 0 2 5 0 0 0 2 0 0 0 0 0

r A microbial

aquatic

microbial aquatic

4 days 60 days 180 days river swanp 180 days river swamP

- 1 5 . 4 7

- L J - Z Z

- 1 5 . 2 2 - L 6 . 6 7 - 2 3 . 8 8 - 2 9 . 5 8

- z z - t o

- 2 9 . 1 0

- 1 7 . 9 2 - t 7 . 2 A - 1 5 .6 4 - L 6 . 1 6 - 2 4 . 2 7

- 2 4 . 4 7 - 2 9 . t o

- 1 3 . 4 3 - L o . 5 2 - 7 3 . 5 2 - 1 5 . 6 9 - 2 L . 7 0 - 1 8 . 8 8 - 1 8 . 6 5 - 2 5 . 6 9

- 1 0 . 4 3 - 1 2 . 9 6

- L Z . L >

- 1 5 . 3 2 - L 6 . 7 9

- t o . r 9 - J J . f , 5 HA

Tahle 2

Minirnan cross-seetioltaL a?eas per moLecule (A-",-) for hrnnic matter of

di f ferent Zrisin 1 a' mot. edi)tlJ- t-)

orrgln f r a c t i o n

F A H A

rnicrobi.al 5 8 . 0 i . 1 2 . 3 4 2 . 1 * , 4 . 2

aquatic terrestrial

5 0 . ? i 1 0 . 7 9 6 . 5 ( a t P I t 2 ) r ) 3 8 . 0 i 8 . 8 4 0 . 4 t , 3 9 2

1 ) C H E N a n d S C H N I T Z E R ( 1 9 7 8 I . 2 l T S C H A P E K e t e l . ( 1 9 8 0 1 .

TabLe 3 Atserage nnn. surface tensLon depression

ev,oss-sect. axea pe? mol. (A^4n)

(72 -"y) ,o, and min for aEtat. HM

s o u r c e I ' F

(dyne crn-r)

r r t

(A2 molecule-r)

HA HA FA

FA

sv/amP

3 1 . 9 - 1 . 9 3 5 . 1 - 0 . ?

2 6 . 4 - 2 . 3 2 9 . 6 - L . 2

5 s . 7 - 2 . 1 4 2 . 4 - 9 . 6

4 3 . 8 - 8 . 9 3 2 . 2 - 3 . 5

* I : m a x . I I : m i n .

s u r f a c e t e n s i o n d e p r e s s i o n ,

c r o s s - s e c t i o n a l a r e a l m o l .

292 Scienees de Lteatt 1, no7

] n t h e l o w e r m w r a n g e ( ( 5 500 daltons), m i c r o b i a l l y - p r o d u c e d F A ' s

are highly surface active substances which gradually lose part of their

s u r f a c e a c t i v i t y w i t h p r o g r e s s i n g h u m i f i c a t i o n ( f i g u r e 2 ) H i g h e r m w

FA's () 25 O0O claltons) are shown to give l-ower surface tension depres-

sions, but their surface active properties increase slightly as humifi-

c a t i . o n p r o c e e d s . A s V I S S E R ( u n p u b l i s h e d r e s u f t s ) c a l c u l a t e d t h a t t h e s e

FArs maintained an alrnost constant average mw of 2 657 t 165 daltons

during the humification period under investigation, it can be assumed

that the average surface activity decreased as the material beca-

m e m o r e h u m i f i e d . F o r H A ' s e x t r a c t e d f r o m a t r o p i c a l s w a m P V I S S E R ( 1 9 6 4 ) a l s o n o t i c e d a n o v e r a l l d e c r e a s e i n s u r f a c e a c t i v i t y w i t h p r o g r e s s i v e h u m i f i c a t i o n .

E

t

! oB

.;

o 40

!

.E 6

a

U

. :

change,s in suz,face tension O"Or"*#i"rlr, ,oononssing hunification by molecular ueight fz,actions of microbially produeed- fulonb acid.s.

A s t a b l e 4 ( c o l u m n 1 ) i n d i c a t e s , s i g n i f i c a n t n e g a t i v e c o r r e l a t i o n s

existed betvreen the mw of humic substances of aquatic and microbial ori-

gin and the maximum obtainable surface tension depressions in their

soLutions. Lower mw fractions of these humic materials cause therefore

h i g h e r s u r f a c e t e n s i o n d e p r e s s i o n s t h a n l a r g e r m w f r a c t i o n s . G i v e n t h e

positive correlation between the maximum surface tension depression and

t h e t o t a l a c i d i t y o f h u m i c m a t t e r ( T a b l e 4 , column 3), it is likely t h a t

Surface actit;i,ties of aqttatic hwnic substances

the reason why lower molecular weight fractions show a higher maximum

s u r f a c e t e n s i o n d e p r e s s i o n t h a n f r a c t i o n s w i t h a l a r g e r m o l e c u l a r w e i g h t

is the higher cooH and phenolic oH functional group content of the former

( V I S S E R , 1 9 8 2 ) . I n T a b l e 4 ( c o l u m n 5 ) i t i s s h o w n t h a t t h e m a x i m u m s u r -

face tension depression is more significantly correlated with the cooH

content for humic compounds from microbial cultures than for those from

t h e n a t u r a l w a t e r s . I t i s p o s s i b l e t h a t i n a q u a t i c h u m i c m a t t e r o t h e r

groups besides cooH play an important role in surface active phenomena.

Tahle 4

Relations bek'teen the moLecular ueight and uarious forms of aciditg of

dLfferent tgpes of htanLc nateriaLs and the marLtm,m surfaee tension

depz,ession of theiz, solutions

correlation cef f icients

fraction or-i gin w/ (72-.(\ N,/tot. (12-"{\ /tot. ('12-\) /OH

r ),/cooH

( a l

r

J ) ( 2 )

t x

FA nicrobial

aquatic river

swmp microbial

aquatic river

swmP

- o . 8 1 * + * - 0 . 6 5 + - 0 . 9 3 * * - 0 . 9 1 * * - 0 . 8 2 i - o . 7 9 - 0 . 8 6 * - O . 8 2 * - O . 9 5 * * - 0 . 8 3 * _ 0 . 9 8 * * * _ 0 . 7 5

0 . 6 5 x 0 . 9 1 * * o . 7 9 o . 8 2 * 0 . 8 3 * 0 . 7 5

- o . 1 2 0 . 8 5 r * + 0 . 9 6 * * 0 . 9 5 * *

d a q d r i q

O . 9 7 * * 1 . O O * * * 0 . 8 8 * 0 . 8 4 r o . 9 o * 0 . 8 8 *

I n m a n y i n s t a n c e s a v e r y s i g n i f i c a n t n e g a t i v e c o r r e l a t i o n w a s d e t e c -

ted between the minimurn cross-sectional- area per molecule and the maxi-

m u m s u r f a c e t e n s i o n d e p r e s s i o n , i n p a r t i c u l a r i n t h e c a s e o f t h e F A r s ( r = 0 . 7 4 , p 1 0 . 0 0 1 ) , w h i c h i s i n s u p p o r t o f o u r f i n d i n g s t h a t m o l e -

cul-es in the lower molecular weight range are the most surface active

( p . 2 8 9 ) . T h e n o r m a l - l y h i g h e r A m i n v a l - u e s f o r F A r s t h a n f o r H A r s o f t h e

sErme mw could be the result of the presence in the former of more ioni-

zed functional groups such as COOI{ and phenolic OH. This is also

s u g g e s t e d b y t h e s i g n i f i c a n t n e g a t i v e c o r r e l a t i o n c o e f f i c i e n t s w h i c h

were found to exist for FA's with respect to 4nin versus COOH or total

a c i d i t y ( r e s p . r = - 0 . 6 3 w i t h p < 0 . 0 1 a n d r = - 0 . 6 2 w i t h p ( 0 . 0 1 ) .

Comparison between the data of Table 4 (cofumn 3-5) and those pres-

e n t e d b y C H E N a n d S C H N I T Z E R ( 1 9 7 8 ) , w h o f o u n d i n t h e c a s e o f F A ' s f r o m a p o d s o l t h " t t y T a o a a l

a c i d i t y = - 0 . 6 1 2 ( p < 0.01), a n d a h " a t y , r " o o n

= - 0 . 3 5 6 , w o u l d i n d i c a t e t h a t t h e s u r f a c e a c t i v i t y o f F A r s o f a q u a t i c

origin and from microbial cuftures depends more on the presence of acidic

groups than do the surface active properties of soil humic matter. In

t h i s c o n t e x t . i t i s i n t e r e s t i n g t o n o t e i n T a b l e 4 ( c o l u m n 3 - 5 ) f o r F A r s

from the swamp, environment resembling closest that of a soil, the absen-

ce of any significant correl-ation between acidic groups and maximum sur-

f a c e d e p r e s s i o n -

2 9 4 Sc'Lences de Lteau L, no7

The mi-nimum cross-sectionaL areas of the FA and HA molecules can be

used to calcufate their minimum moiecular weight :

*r.i., = surface

"...*ir x height x density x N (Avogadro).

Assuming for the molecules a height of approximately 2 x their diameter

( T S C H A P E K et aL., 1 9 8 0 ) . t h e f o r m u l a c a n b e r e w r i t t e n a s : m w = A x 1 0 - 1 6 x 2

ml_n mln x 1 . 4 x 6 x 7 0 2 3 ,

o r : m w . = 1 . 8 9 6 x A x

mrn ml_n

The according to this formula carcuLated minimum'molecular weight varues

of the FA and HA fractions of aquatic origin and from microbial cultures

are shown in Table 5 - It is evident that for the lohrer mw samples

( m ^ r - 7 5 0 daltons) t h e m w , a s o b t a i n e d b y u l t r a f i l t r a t i o n , i s o f t h e s a m e

order of magnitude as that caLculated from surface activitv data.

TabLe 5

Calculated minirnnn moLeculaz, ueighi; oalues fz,om surface actiuity measzuements on fuLuic and Vrunic aeid solutions

' 4 x A

x 1 0 - 1 6

; mrn

v n. mrn

f r a c t i o n o r i q i n source

average mw based on AMICoN

u l t r a f j - L t r a t i o n ( d a l t o n s )

? q n

5 5 0 0 2 5 0 0 0 2 0 0 0 0 0

F A m i c r o b i a l

aquatic r].ver

swamp

9 7 4

+ o f ,

337 5 0 0

J q o

6 1 6 O J f ,

3 6 1 470 346

L O92

6 t 5 a 5 t

6 6 2

o I 4

4t7

1 . 2 7 5 9 0 5

I 6 Y

o z J

7 0 2 280

aquatic river

swamP

The discrepancy between the sets of data for the higher mw fractions can

be correctect by apptying a different height/diameter factor. By assuming

t h e m w o f t h e f r a c t i o n s o b t a i n e d b y t h e u l t r a f i l t r a t i o n t e c h n i q u e ( p . 2 8 8 ) t o b e c o r r e c t , t h i s f a c t o r w a s c a l c u l a t e d u s i n g t h e f o l l o w i n g f o r m u l a :

mw

n

h

d

O . 9 7 5 x A ^ E - -

mJ-n v -hin

Surface actittities of aquatic humic subatances

T h e r e s u l t i n g d a t a , e n l i s t e d i n T a b l e 6 , w o u l d s u g g e s t t h a t i n s o l u t i o n t h e h u m i c m o l e c u l e s o f l o w m w ( - 7 5 0 d a l t o n s ) a r e m o s t l i k e l y e l l i p t i c a l

in shape (the FA and HA molecules having at the air,/water interface ave-

r a g e h e i g h t , / d i a m e t e r r a t i o s o f b e t w e e n 1 . 6 a n d 4 . 4 ) , w h e r e a s t h e h i g h e r

mw molecules would possess a more threadlike shape. Although the above

figures should be used with great caution as they are derived from values

which express only a lower limit of the surface of the molecules at the

interface area, they nevertheless all indicate an asymmetrical shape for

t h e h u r n i c m o l e c u l e s , i n p a r t i c u l a r f o r t h e H A r s . E l o n g a t e d e l l i p s o i d a l s h a p e s h a v e a l s o b e e n r e p o r t e d f o r h u m i c c o m p o u n d s . b y P I R E T e t a L . ( 1 9 6 0 ) , w h o f o r p e a t H A f o u n d a n a x i a l r a t i o o f a r o u n d l I , b y O P S J O V e t a L . ( 7 9 7 1 ) ,

who for soif HArs arrived at ratios from 6-12. and by CHEN and SCHNITZER

( t 9 7 6 ) , w h o c a l c u l a t e d f o r s o i l F A ' s a n d H A ' s a x i a l r a t i o s o f b e t w e e n r e s p e c t i v e l y 8 . 8 - 1 1 . 9 a n d 1 3 - 1 6 .

TabLe 6 Calculated nattrntn

"atios

of height/dLameter of fuluic and hwnic ac'Ld

moleeuLes p?esent qt the aLr/uater interfaee

average mw (daltons)

f r a c t i o n origin

source

T ) U 5 5 0 0 2 5 0 0 0

FA

H A

microbial aquatic

microbial aquatic

swamp

rl-ver swamp

L Z . ) U I J . I O

3 0 .3 0

2 3 - 2 6

3 1 .2 5

5 Z - Z O

4 5 . 4 2 5 7 .2 ' 7

Y J . I f ,

5 7 .6 0 7 4 . 2 3 1 2 0 . 0 0

1 . 8 8 3 . 2 3 4 . 4 4

? n ?

4 . 3 5

Cottclus t ot't

B Of the humic matter of different origins investigated, that frqn natu-

ral waters appeared to possess the least condensed structure.

tr Ihe surface activity of aquatic humus increases l^tith rising mw of the

m a t e r i a l .

tr Whereas at low concentrations (( 5 mg 1-I) aquatic HArs nonnal-ly were

more surface active than the FA's, the latter generally showeil a higher

surface activity than the ltrArs when present at higher concentrations

( ) 2 5 m s 1 - ' ) .

o Aquatic fulvic and humic acids were normally found to be more surface

active than their terrestrial counterparts.

a Acidic groups appeared to play a more important role in the surface

activity of FA's of aquatic origin than in that of their terrestrial

counterparts.

2 9 6 S c i e n c e s d e L ' e a u 7 , n o 7

tr For microbially-formed humus it was noticed that with progressive humi-

fication the surface activity of the low mw I'A fraction diminished,

whereas that of the hiqh mv, fraction increased.

o Aquatj-c FA molecules would appear to have a more open structure and

to be more voh:rninous than HArs of similar origin and rnolecular weight.

D Indications were obtained that, whereas low mw aquatic compounils would

have an elliptical form when in solution, higher mw fractions are pro-

bahly more threadlike in shape.

R e r e R e r u c e s

CHBiI Y., SCHNITZER M., Viscosity measu-

rements on soil hwic substa ces . Soi.L S c i . S o c . A t n . J . , 1 9 7 6 , 4 0 , e 6 6 - 8 7 2 . CHEN Y., SCHNI?ZER M., Ttle surface ten- sion of aqueous solutions of soil hwic s u b s t i l c e s . S o i L S c i . , L 9 ' 7 e , n 5 , 7 - 1 5 . O L M R B . c . , W S S ' E R S . A . , C h l o r o f o m

production frm the clorination of aqua-

tic hmic material : the effect of mole- cular peight , enviroment ad season.

W a t e ! R e s , , 1 9 8 0 , L A t L 1 3 7 - 7 L 4 1 .

O R L O V D . S . , A M M O S O V A Y a . M . , G L E B O V A G . I . , G O R S H K O V A Y e . 1 . . r l r l n N . P . , K O L E S N I K O V M . P . , M o l e c u l a r w e i g h t s , s i z e s a d c o n - figuration of hmic acid particles. Sots.

Soi.L Sci. (EngL. h'ansL. Pochuouedenie), L97t , 3, 673-687 .

P I R E T 8 . L . , V T H I T E R . c . , W A L T E R H . C . ,

MADDEN A.J., Sme physico-chmical pro-

perties of peat huic acids. Sci, Proc.

R . D u b l i n S o c . S e r ' . 4 . , 1 9 6 0 , 6 9 - ? 9 ,

TSCHAPEK M., WASOVISKI C., The surface actj.vity of hmic acid. Geochin. Cosrc- c h i m . A c t a , t 9 i 6 , 4 0 , 1 3 4 3 - 1 3 4 5 . T S C H A P E K M . , S C O P P A C . O . , ! { A S O W S K I C . , On the surface activity of hmic acid.

Z. Pflanzenernaehr. Bodenkde, L9'1a, f4f, 2 0 3 - 2 0 1 .

T S C H A P E K M . , W A S O W S K T C . , S C O p p A C . O . , TORRES SANCHEZ R.ln., On the surface acti-

vity of hmic acid. Agrochimtca, 1980,

u , 3 O - 3 A .

VISSER S.A., Oxidation-reduction poten-

tials ad capillary activitj,es of hmic acids. triafi;ne (tond), 1964, 2O4. 581 V I S S E R s . A . , A c i d i c f u n c t i o n a l g r o u p content of aquatic hwic matter : its

dependence upon origin, moleculd weight

and ilegree of hwification of the mate- r i a l . J . E n u . S c . H e a L t h , 1 9 8 2 , ( i n p r e s s ) .