Sediment Characteristics and Phase Association andMobility of Fe, Mn, Zn, Cu, Pb and Cd in Core Sedimentsfrom Lake Edku

J.K.A.U:: Mar. Sci., Vol. 4, pp. 19-35 (1413 A:H./1993 A.D.

Sediment Characteristics and Phase Association and Mobility of Fe, Mn, Zn, Cu, Pb and Cd in Core Sediments

from Lake Edku

MOHAMED A. EL-SA YED

Faculty of Marine Science, King Abdulaziz University, Jeddah, Saudi Arabia

ABSTMCf. The acid soluble and total concentrations of Fe, Mn, Cu, Zn, Pb and Cd were measured in sediment cores from Lake Edku; one of the Nile Delta coastal lagoons, southern Mediterranean Sea. The proportions of sand, silt and clay and the contents of CaCO3 and organic carbon were also determined.

The results show that the average total concentrations of Fe, Mn, Zn, Cu, Pb and Cd are 57787 :!: 19447,943:!: 395,81 :!: 19,55 :!: 21,42:!: 10 and 3.4 :!: 0.7 IJog g-l respectively. The percentage of the acid leachable fraction of these metals in the given order are: 18, 64, 30, 52, 61 and 30.

The importance of the different binding substrates was inferred from the statistical relationships. The results indicate two groups of metal associa- tions: Fe, Zn and Cu are preferentially associated with clay and to lesser ex- tent with silt; calcareous shells are the favorite sites for the second group comprising Mn, Pb and Cd. The statistical relationships between the acid leachable metal phases and the different substrates maintain the same trend but with more specific and improved correlations.

The geochemical mobility of metals was inferred using a relative condi- tional measure referred as Lability Index. The studied metals showed a gen- eral mobility decrease with depth in cores.

Introduction

The study of trace metals geochemistry in lake sediments offers valuable information for understanding the historical development of the basin. Hakanson and Jansson

19

I/R;

1/0!~

L/'\

b

m

:J oX

"C lJ.J

OJ

-a

I QJ

:-=:

;:7 /

0

QJ U)

C 0

QJ C

0l- I-

QJ -0

~

QJ

<\]<7

~

QD

~

J

o~ /iI'\

m~

N.

c1

~~

(T'I.

~

e

i'-

"

,',

~'

'", ,,.:

~

E

...,.

o~' 10

(Y"\~

0

Ii:

.,;~

.g~

.9.OJ CIl)

.5-a.

E

(U'"

"0

~

(U>,

-g~

0 (U

<

OJ

Sediment Characteristics and Phase Association ,23

TABLE 1. Total trace metals concentrations (lJ-g g- and % of sand, silt, clay, TOC and CaCOJ1

Silt I Gay I TOC I CaCO

Zn Co Pb Cd Sand

Fe Mn

26

2.

22 28

24

3.0 3.1 3.6 4.3 3.5

73 67 66 53 65

17 20 18 19 19

10 13 16 28 16

5.3 6.5 4.2 1.7 4.5 0-4

4-10 10-20 20-38

51612 52728 53965 76478 58696

1780 1219 913 ill6 1257

97 98 74 97 91

43 47 48 67 51

44 33 31 50 40 1

2 3 4 Mean

2.9 4.1 4.0 3.4 2.8 3.4

76 73 74

0.0 9

46 15 17 13 22 18 17

9 10 13 78 73 37

44 40 38 4 11 27

23938 29648 30763 95165 66159 49135

1194 979 680 475 387 743

48 50 46 103 91 68

29 28 26 100

70 51

42 40 39 42 26 38

0-5 5-10 10-18 18-39 39-41

1.4 0.8 0.3 0.5 0.8 2

3 4 5 Mean

53 24 19 18 18 35 25

0.0

240 25 46 36 36 38 26 23 30 33

22 30 45 46 44 39 52 70 43

2.6 2.0 2.1 2.1 2.5 2.1 2.2 2.8 2.4

46 26 26 27 33 28 24 11 28 43817

70372 70770 72524 67948 58699 83723 56381 65529

1228 949 815 820 737 344 1388 351 829

65 84 88 91 81 95 99 70 84

46 63 62 63 58 96 63 55 63

58 35 45 42 43 40 68 51 48

4.0

2.8 2.8 3.2 3.6 2.4 5.0 3.6 3.4 0-

2- 4- 6.

8.

10.

15- 25- 2 3 4 5 {,

7 II Mean Lake

average 57787 943 81 55 42 3.4 45 23 32 2.6 27

precipitation (Berner 1971) or to the formation of Fe- III humate complexes (Stumm and Morgan 1981). The dotted appearance of the sediment could be resulted from differential flocculation. The whole sediment in these layers is made up of silty clay and showed a sharp decline in sand, carbonates and organic carbon (Fig. 2). Obvi- ously, organic matter accumulation was inhibited by highly oxic conditions.

The sediments of core 3 showed the highest percentage of fine materials. The aver- age silt and clay content is 76% of the total sediment. The upper most layers showed the maximum concentrations of sand and carbonates and the lowest clay contents, whereas, at the bottom of the core the opposite trend was observed (Fig. 2).

Trace Metals Iron

Generally, the sediments of lake Edku are iron-rich, the average of the total iron content in the three cores is 5.8% and may reach values as high as 7-9.5% particularly in the lower core intervals (20-40 cm).

The data indicate that more than 80':;0 of the iron occur in the non-reactive residual fraction (Table 2). The correlation analysis suggests that about 70% of the residual

.1

.4 -6 .8

-10 -15 -20 -40

Lake averafe Mean Mean Me,,!) Cnre

12345678 1234~ 123^II

419)/\ I 9Rf1t1 Sample I ~~ FeliMn

(L) "/oL (r)

0.460.320.430.30ns0.450.430.62nsns100 Fe 18426 5512 23

2341.8 6230 2125588 5175 17

72317 22848 24

573W 8769 13

'1947~ 97117 :JI) 39912 11700 23

43831 8897 17

43491 10474 19

67974 8504 11

4f1J11)? QR94 1~

TABLE 3. Correlation analysis. 8 -

Mn Cu Cu Pb Cd,- (L) %L (r) (L) "toL (r) (L) --~ (r) ,,"toL (r) I , ---

296 1484 83 54. 43 44 20 23 53 13 32 11 1.7 1.3 43384 835 69 61 38 38 21 26 56 8,5 25 75 2.1 1.0 33

364 549 60 49 25 34 17 31 64 9,5 21 70 2.8 0,8 22

711 405 36 79 18 18 45 22 35 28 22 44 3.2 U 25

4:19 R1R 62 60 :11 34 2li 2li 52 15 25 65 2.5 U 31

.'\,71 Sediment Characteristics and Phase Association

Mn0.73ns

-0.790.560.440.770.77

-0.540.341.00 127 1!Ki7 89 30 18 37 18 II 38 0.5 41 99 1.2 1.7 ~

192 787 80 32 18 37 14 14 50 1.6 39 96 2.8 1.3 32

52 628 92 33 13 29 14 13 48 3.8 36 90 2.6 1.4 35227 248 52 78 25 25 42 58 58 29 13 32 2.8 0.6 17

247 140 36 73 19 20 32 38 54 14 11 44 2.2 0.6 21

1/iQ ~74 7n 49 19 ~ 24 27 4R 10 211 70 2.3 1.1 33 -Zn

35511 831Xi 19 230 9I.K) 81 46 18 28 15 31 67 2059108 11264 16 329 620 65 64 20 24 25 38 61 14

58240 12530 18 256 559 69 64 24 27 22 39 64 2459289 13235 18 261 559 68 68 23 26 26 37 59 21

55016 12932 19 234 503 68 58 22 28 23 35 60 26

49014 9685 17 58 286 83 79 16 17 72 24 25 15

77125 6598 8 1255 133 10 82 18 18 35 27 44 48

51088 5293 9 265 86 25 35 34 49 22 34 61 415554Q 99R/1 11) '11;1 4h7 ,Q ~7 7.7 ')] lI1 l6 " 26

7~nsnsns0.510.75nsns0.30100 -Zn:4 I 30 127 129 152 117 '1.1

:.- 0.860.540.83

-0.69ns

-0.80

-0.81

JcOO Cu TABLE 2. Residual (r) and leachable (L) trace metal concentrations (lI.g g-1 and percentage of the leach.able fraction of the total concentration.

Co(L)

0.830.400.850.87ns0.96

1."00 "h

.

Pb Cd %L

(L) (L)

2516

0.84-0.52

-0.820.82ns].00 rJi 1 38 65 2.5 1.5 3721 61 2.0 0.8 2821 48 2.0 0.8 2821 50 2.5 0.7 2018 41 2.9 0.7 1825 62 1.5 0.9 3820 29 4.3 0.7 1410 20 3.1 0.5 1422 47 26 /l,R 2~

1.0130 25

A -acid leachable fraction.B -residual fraction.

(A) (I

Sediment Characteristics and Phase Association 27

/--" ~

~~ ~

0 .D-0

Q.oN

~~~~

';"01

0 010:J'-

U-o:JO .-"' ~ ~

o-'O-~--

I I I I

0 N

~

FIG. 3. Distribution of acid leachable and residual trace metals in sediment cores.

highest average concentration for labile and residual copper ,indicating probably the influence of the source area.

Lead

The greatest part of lead was found in the HClleached fraction, it forms on the av- erage about 60% of the total metal (Table 2), nevertheless, values as high as 99% do occur. These high values are shown to be specific to carbonate substrate. The corre- lation analysis suggests that the acid .leachable lead holding substrates are carbonates and manganese phases (Table 3). Therefore, highest lead concentrations are found in the upper sediment layers, being enriched with carbonates and/or manganese oxides. High surface lead concentrations could also be partly attributed to atmos- pheric input of urban dust enriched in lead (Forstner and Wittmann 1981).

On the contrary, the highest concentrations of residual lead were found associated with se;diments of the lower core intervals having the highest clay and residual iron contents (Fig. 1 & 2).

Cadmium

Cadmium was found in relatively high concentrations. Surprisingly most of it was found in the residual form (Table 2). Yet, similar values were also reported by Pre- mazzi et al. (1986) for 13 Italian lakes and by Forstner and Wittnam (1981) for Wis- konsin lake.

The sediments of lake Edku were originally derived from agricultural lands which coUld have been enriched with cadmium through digenetic processes. The use of phosphat~ fertilizers which are known to contain significant cadmium concentrations (Table 4) may enhance this process. Helios-Rybica and Forstner (1986) suggested that cadmium may substitute for major cations in the octahedral units of clay miner- als. They mentioned that the relatively open structure of mixed layer minerals in par- ticular, can offer diffusion-'type sorption sites, in which potentially toxic heavy met- als may become semi-reversibly incorporated during sediment digeneses.

Mineralogical studies of lake Edku sediments (Moussa andSaad; in prep.) showed that the fine silt and clay minerals are composed entirely of mixed iayer illite-smictite and subordinate kaolinite.

The labile cadmium was found associated with the same substrates as the l,abile lead, i.e., the carbonates and manganese oxides, with increasing concentrations in the surface layers, which may suggest its anthropogenic origin.

Judgement of Result\'

The average concentration values of trace metals were inspected by comparing them with the metal concentrations in the standard shales and related sediment types (Table 4).

The enrichment factors indicate that the lake sediments are particularly enriched with lead and cadmium. The labile forms of these two metals seem to be mainly con-

Sediment Characteristics and Phase Association 31

TABLE 5. Distribution of lability index in the core samples.

Interval

(crn) Fe Mn Zn Cu Pb Cd

Core 1 5.01

2.17 1.51 0.57

0.79 0.62 0.50 0.22

1.14 1.25 1.79 0.50

2.44 2.94 2.25 0.77

0.76

O.~0.34 0.34 0-4

4-10 10-20 20-28

0.29 0.20 0.24 0.13

Core 2

82.60 42.20 9.40 0.50 0.80

1..42 0;46 0..54 0..21 0..27

0-5 5-10 10'-18 18-~9 39-41

0.30 0.27 0.20 0.32 0.15

8.40 4.10 12.10

1.10 0.57

0.59 0.58

Q4Q

0,32

Q26

0.61 0.99 0.90 1.36 1.17 Core 3

2.02 1,55l.m

1.42 1.48 0.34 0.77 1;55

1.89 1.54 0.91

1.02 0.69 1.63 0.41 0.25

0.50 0.40 0.40 0.28 0.24 0.60 0.16 0.16

o~

2.

4- 6- 8-10.

15- 25.

0.23 0.19 0.22 0.22 0.24 0.20 0.09 0.1

4.30 1.88 2.18 2.14 2.15 4.93 0.11

0.32

0.40 0.31 0.37 0.33 0.38 0.21 0.22 0.98

index of cadmium and, to some extent lead, can be correlated with that of manganese which showed the higflest index and therefore, seems the most reactiye metal.

Considering the lability index as a reliable measure for the metal mobility, man:

ganese, lead and copper appear more reactive than zinc, cadmium and iron.

Conclusion

The concentrations of Fe, Mn, Zn and Cu demonstrate that .the sediments of lake Edku are nonpolluted with respect to these metals. The measured concentrations rather reflect the lithological influence of the catchment area as well astheenhanced geochemical activity. Therefore, the mean con,centrations of .these metals can be re- garded as the background values.

On .the other hand, the concentrations of Pb and Cd indicate some enrichment with these two metals. Atmospheric precipitation is probably the main factor which is responsible for Pb enrichment, whereas, Cd seems to originate from the drainage of the soil of the catchment area.

.2 -4 .6 .8 .10 .15 .20 .40

In the context of the relative importance of the different substrates, it is revealed that the inorganic carbon plays a major role in the elimination of some trace metals.

The build up process of calcareous shells results probably in the inco~oration of Pb, Cd and Mn in the shells. On the other hand, manganese hydrous oxides were found to be important sinks for lead and cadmium. Copper is shown to be particularly sequestrated by a discrete iron hydrous oxide phase in addition to adso~tion onto clay mineral surfaces. Zinc was lJlainly assQCiated with the organic matter.

The mobility of the studied metals as revealed from the postulated Lability Index generally decreases with increasing depth in core. Manganese, copper and lead ap- peared more mobile than zinc and cadmium; iron was the least reactive.

Acknowledgement

The author is greatly indebted to Dr. Mahmoud Kh. El-Sayed and Dr. Atef A Mousa for the critical reading of the manuscript.

References

Berner, R.A. (1971) Principles of Chemical Sedimentology. McGraw-Hill, Inc., New York, 240 p.

Carignan, R. and Nriagu, J.O. (1985) Trace metal deposition and mobility in the sediments of two lakes near Sudbury, Ontario. Geochem. Cosmochem. Acta 49: 1753-1764.

Dowidar, N.M., Morcos, M.A., Saad, M.A. and El-Samra, M.E. (1976) Hydrographic observations o~

pollution in Abu Qir Bay, Alexandria, Egypt. Acta Adriatica 18: 381-396.

Eckert, J.M. and Sholkovitz, E.R. (1976) The flocculation of iron, aluminium and humates from river water by electrolytes. Geochem. Cosmochem. Acta 40: 847-848.

Forstner, U. (1977) Metal concentrations in recent lacustrine sediments. Arch. Hydrobiol. 80: 172-191.

Forstner, U. and Wittmann,G. T.W. (1981) Metal Pollution in the Aquatic Environment. Springer-Verlag, Berlin, 486 p.

Hakanson, L. and Jansson, M. (eds.) (1983) Principles of Lake Sedimentology. Springer-Verlag, Berlin, 416p.

Helios-Rybica, E. and Forstner, U.(1986) Effectofoxyhydratecoatingson the binding energy of metals by clay minerals. In: Sly, P.G. (Ed.), Sediments and Water Interactions. Springer-Verlag, New York, pp.381-385.

Jenne, E.A. {1977) Trace elements sorption by sediments and soils; sites and processes. In: Chappell, W.R.and Petersen, K.K. (Ed;), Molybdenum in the Environment. Marcel Dekker Inc., New York, pp.425-553.

Khamis, M., Geochemistry of Phosphorus in Lake Edku. M.Sc. Thesis, Alexandria University, (in prep:)..

Martin, J.M., Nirel, P. and Thomas, A.J. (1987) Sequential extraction techniques: Promises and prob- lems. Mar. Chem. 22: 313-341.

MQussa, A.A. and Saad, N.A., Mineral Composition of Lake Edku Sediments. (in prep.).

Patterson, C.C. and Settle, D.M, (1987) Review of data on eolian fluxes of industrial and natural lead to the 1ands and seas in remote regions on a global scale. Mar. Chem. 22: 137-162.

Pickering, W.F. (1980) Zinc inte,action with soil and sediments.Jn: Nriagu, J.O. (Ed.), Zinc in the Envi- ronment, part 1, Willey Inter. Pub., New York, pp. 72-107.

Premazzi, G., Provini, A., Gagginoi, G.F. and Parise, G. (1986) Geochemical trends in sediments from 13 Italian subalpine lakes. In: Sly,P.G. (Ed.), Sediments and Water Interactions. Springer-Verlag, New York, pp. 157-165.

Rashid, M.A., Buckley, D.E. and Robertson, K.R. (1982) Interactions of marine humic acid with clay min- erals and natural sediment. Geoderma 8: 11-27.

Sediment Characteristics and Phase Association. 35

If ~ I., ~ jJ I., ;:..:.~ I., ~ JJ-I ~ ~.J ~ \; J..t-P.J I..;-'"' I., ..,J I ~ !.,.->

~ .) 1 ~ I..;-'"' I., J 0 ~ t ~ i.,.-:.o.) t.s:J I., ~ l.p ) I.,

Jo:-JI ~l3-1 ¥ ~

:r.:,..j\ J..:&- ~\ ~\:o:- ~ )~\ ~p ~

~~~\ ~.~\ ~\ ~ OJ.-.:l:o

~JJ..I .:r' ~ ~ ...,;...~ ;-""-\_:"~_c.1IIJSJ ~1.;..,1.j=S;.J1 .;..,).1i .~\

0..\>-1., ..,.J..,5.)1 ~ ,-;-,,1.,) o.l..s.f ~ ~., )ls:J1., ,-""L.,.,)I., Ior"L :J1., 1!.1;:}1., ~I.,

,-;-,,1.,)1 ..;...l;~J ~I .)!.,ll., .;..,l;J'..;>J1 ~ ~ I.S ' J::Jll:.I.).;..,~.:r'

.JL.oo1.,..JI., .:J'.;.JI., J-)I .:r'

\J"6..:JiJ l!..l;)iJ ~iJ ~J.J.-I .:.,.0 JS:J ~I ..:.olj.5jJl .la...p .:,1 Jl i!!l:;.:J1 ~ ,. , t -t Y -00 -A' -~ t,. -oV'\A V) ~!p1 Js;. I./' i.'=""~\5:!iJ ,-""l ,-!iJ j:S;J1 Jl ~I ~l:I-4 ~I ".;:I:~ j:Sj ~":";\SJ (il~/ il~J~

.("/."',,1'\' -I.OY-(.'" -"/.'\t -"/.'A)I./'~LJI'":o-:'jJl~.)S:J1 4Ai1y" ;~ ~ ~~-' .f"'~1 CJ"" ~~ ,)~-' j&o ~L.,...:... ~I .;..,li~1 ..:oJ,) Jl.,...L..aJ1 ~ J.,ioif ~ ,:,;;\,:. .;)-'l-:J1., .!li)1., ~.1.:I..1 : ~I...JI ';"'I:...:.;'il ~

~~I~~ J.,4Al1 ~)I ~I JS~I ~ ~ ..:J'.;JI ~ Jif~-, CJ"" .jJ;.1 j&o ~L.,...:... ~\ .;..,~L..l1 ~-' .r~,)t.s:J1., -"""L..,)I., p>;.:il CJ"" 4;.,sJ.1

.~.,...;-,;sf o;~-' o~'-)'II.iA is{,; iA.;.l1 ...,..:a.LJ..~ ~I ..,...~I J)~ ~ if';:" IJ"loA.. ilJ>.;.,.4.;.pL;...lJ ~~~I ~~I ~L~~.I

~ ",:-,~)I ~y\$'J.:,-J1 .~~;.. 4.-\$' ~ ~ .;.pl:.J1 ~ ~.,f 4' Ji" ' 4",...l::l1 .~JJ..~ i~~ls:J~ .!.1.;)1 ~ -""" .:r' ;Sf 1J"l-:J~ 1J""L...)t, ~\ ~ -""" .:..;15