Total suspended matter and particulate lead speciation in the heavily polluted Western Harbour of Alexandria Egypt

 

M.A.H.Saad1, A.I.Beltagy2, M.A.Fahmy2, M.R.Abdel-Moati1 and W.M.Mahmoud2

 

1. Oceanography Department, Faculty of Science, Alexandria University, Moharam Bay, Alexandria,

     Egypt.

2. Institute of Oceanography and Fisheries, Anfoushi, Alexandria, Egypt.

E-Mail of corresponding author : Saad @ internetalex.com

 

ABSTRACT

The Western Harbour (WH) receives untreated pollutants affecting dramatically its compartments.  Surface and bottom water samples were collected bimonthly from the WH for investigating the distribution of total suspended matter (TSM) and particulate lead (PPb) species.  The increase in TSM with depth coincided with vertical diffusion of the WH sediments by wave action and water currents.  High TSM values were found at locations directly influenced by contaminated discharges.  Because the environmental impact of lead species may be more important than the total metal concentration, lead partitioning pattern was investigated in the WH to determine the metal sources, geochemistry, associations and availability for biota.  The order of abundance of the different lead fractions was F5 > F3 > F4 > F2 > F1, constituting 41.34 > 31.08 > 22.96 >3.20 >1.42% of the total PPb.  The insignificant correlations between F1 and the environmental conditions illustrate that they were not effective in controlling its distribution.  The spatial distribution of F2 recorded a maximum at a location characterized by high carbonate content.  The stepwise regression model between F2 and F4 in the surface water shows that the increase in F2 was governed mainly by the organic fraction of the phytoplankton.  The annual mean F3 values for the surface and bottom waters were almost close, reflecting the enrichment of TSM in both water layers with Fe/Mn content, which is a substrate for Pb capture.  From F5 and chlorophyll-a association, a significant portion of F5 was of biogenic origin rather than lithogenous alumino silicate material.

 

INTRODUCTION

Lead is one of the oldest metals known to man.  Its emission into the atmosphere has much increased during the last century. Its anthropogenic inputs greatly exceed those from natural sources.  The atmospheric fallout of lead constitutes its most important source in the aquatic environments (Moore & Ramamoorthy,1984).  Although lead is a nonessential element, it is present in all tissues and organs of mammals causing hazardous effects as it is a commulative poison.

 

Until recently, the majority of environmental researches on trace metals were based on an assessment of the total metal concentration.  It has become increasingly evident that the environmental impact of a particular metal species may be more important than the total metal concentration (Sibley & Morgan,1975).

 

Only a few studies were carried out on lead in the Egyptian coastal marine regions.  Abdel-Moati (1990a) studied the behaviour and fluxes of copper and lead in the Nile River Estuary.  An input/output flux for lead in a coastal Bay off Alexandria Region was also studied by Abdel-Moati (1991). Abou El-Dahab (1985) investigated the chemical cycle of inorganic pollutants including Pb in an ecosystem west of Alexandria.  Levels of some heavy metals, including Pb in El-Mex were examined by Abdel-Moneim et al., (1994).

 

A research project has been undertaken to study the geochemical behaviour of lead in the WH of Alexandria.  As this ecosystem is complicated, due to the influence of several factors on its physical, chemical and biological characteristics, some hydrochemical parameters were investigated for understanding their effects on altering the discrete forms of lead and their levels in the WH.  The spatial distribution of lead in the dissolved and particulate forms was determined.  Also, the distribution of dissolved and particulate lead species in the water column and bottom sediments was investigated.  The present study, a part of this project, deals with local and monthly variations of total suspended matter (TSM) and particulate lead speciation in the heavily polluted WH.

 

The WH receives the vast majority of the Egyptian external trade. It is considered as one of the most important and biggest harbours of the Mediterranean Sea.  It has a length of 7 km and a maximum width of 2 km.  Its depth varies from 5.5-14.0 m.  It is divided into the inner and outer harbours, having areas of 200 and 600 acres, respectively.  The WH opens to the sea by       EL-Boughaz and is protected by two water breaks.  The WH is heavily polluted, receiving several external and internal pollutants from different sources.

 

MATERIAL AND METHODS

Sampling was carried out every two months from October 1989 to August 1990 at 8 locations selected to cover different regions in the WH.  Surface water samples were collected in polyethylene bottles at 30 cm below the water surface to avoid floating matter.  The bottom samples were collected by a Niskin PVC sampler at 50 cm above the sediments to avoid their disturbance.

 

Before filtration of the samples, special standards of cleanliness were adhered to the laboratory.  TSM was determined gravimetrically, using Millipore membrane filter paper (0.45mm).  The sequential extraction procedure for the speciation of particulate lead in TSM was carried out according to the method described by Tessier et al., (1979).  The five lead fractions determined were exchangeable (F1), bound to carbonate (F2), bound to Fe-Mn oxides (F3), bound to organic matter and sulphides (F4) and residual (F5).

 

 For testing the precision of the procedure, the total lead concentration (5:1 HF/HClO4) was determined.  Comparison of the total metal concentration with the sum of the concentrations of the five fractions showed a good agreement.  The accuracy of the procedure was also tested by using five replicates of the standard reference material (SRM) 1645 from the National Bureau of Standards.  The coefficient of variations gave 3.25%. 

 

RESULTS AND DISCUSSION

Total suspended matter (TSM)

The WH receives TSM from different sources.  The values of TSM showed an increase with depth in some months at some stations, reflecting the vertical diffusion of the bottom sediments from wave actions and water currents.  However the high TSM values occasionally found in surface water possibly originated from the air-borne dust, plankton productivity and wastes discharged from ships and land-based sources.

 

The highest regional average TSM value of 59.60 ± 6.95 mg/l at station VI reflects the position of this station opposite to the Noubaria Canal, which supplied the outer harbour with more than 90000m3/day of drainage waters contaminated with untreated sewage wastes.  However, the lowest regional average TSM value at station IV (42.09 ±  3.71 mg/l) reflects the position of this station at the Boughaz far away from the direct effects of pollution (Table 1).

 

The highest monthly average TSM value of 65.49 ±  3.04 mg/l and 69.38 ±  23.63 mg/l in December and February, respectively (Table 2) coincided with  stirring up of the bottom sediments by strong wind prevailing in winter, increasing the  turbulece of the water column.  However, the lowest monthly average of 38.40 ±   7.30 mg/l in October (Table 2) could be related to the stability of the water column (Abdel-Moati,1981).

 

Particulate lead speciation

The lead partitioning pattern in the WH was studied to determine the metal sources geochemistry, associations and availability for the biota.  The order of abundance of the different lead fractions was F5 > F3 > F4 > F2 > F1, constituting 41.34 > 31.08 >  22.96 > 3.20 > 1.42% of the total particulate lead.

 

Exchangeable fraction (F1)

In the WH, lead was less partitioned towards this fraction, giving an annual mean concentration of 2.35 ± 0.64 mg/g.  This may be due to its loosely bound character, as it is considered more soluble than the other associations depending on the changes in environmental parameters±

 

The vertical distribution of F1 indicates noticeable decrease in the surface, possibly reflecting the obvious variations of the environmental conditions in the surface layer, such as pH and dissolved oxygen.

 

The regional variations of F1 showed its highest level of 4.19 ± 2.52 mg/g (Table 1) at station I, a sheltered area offering favourable conditions for precipitation and adsorption of this fraction.  However, the lowest regional average concentration of 1.17 ± 0.06 mg/g was found at station VIII, despite its position in the inner port and its characterization by the high TSM content of 51.94 ± 0.78 mg/l (Table 1).  This might be due to the lowest concentration of dissolved oxygen at this station, which accelerated the release of lead.

 

The minimum monthly average F1 value of 1.09 ± 0.36 mg/g in December (Table 2) coincided with the strong turbulence processes in winter in changing the establishment of chemical equilibrium between adsorption/desorption processes and also resulted from the increase in the rate of release of this easily solubilized fraction by strong water agitation. The insignificant relationships between F1 and the environmental conditions illustrate that these parameters were not effective in controlling the distribution of F1 in the WH and the prevailing winds seemed to be the responsible factor.  This significant direct relationship between F1 and F2 reveals that the exchangeable lead was mainly associated with carbonate fraction of suspended particulate materials in the WH.

 

Carbonate fraction (F2)

This fraction recorded only an annual mean of 5.28 ± 0.79 mg/g, as the WH was affected mainly by internal and external organic pollution sources.

 

The spatial distribution of F2 recorded a maximum average of 7.97±  0.47 mg/g at station I (Table 1), where the carbonate content was relatively high.  However, the lowest regional average F2 concentration of 3.93 ± 1.77 mg/g (Table 1) at station VI reflects dilution of the inorganic carbonate by  Noubaria discharges.

 

F2 was poor in October and enriched in June, as shown from the lowest and highest seasonal averages of 1.87 ± 0.40 and 11.24 ± 0.52 mg/g, respectively (Table 2), possibly reflecting  the increase in phytoplankton density and other algal vegetation during warm season accompanied by the decrease in CO2 content, leading to precipitation of carbonates from the bicarbonates.                 A similar observation was also found by Badr (1993) on the carbonate fraction of copper in the Eastern Harbour of Alexandria.

 

Statistical analysis shows that the effect of environmental conditions was insignificant and F4 followed by F3 were the main factors influencing the distribution of F2 in the bottom water of the WH.

 

Reducible (Fe/Mn oxides) fraction (F3)

The annual mean values of F3 in the surface (50.60 mg/g) and bottom (51.93 mg/g) waters were almost close, reflecting the enrichment of TSM in both water layers with Fe/Mn content, which is considered as a substrate for Pb capture.  Abdel-Moati      & El-Nady (1991) reported that the correlations of Zn, Cu and Pb of TSM with its Al, Fe and Mn contents were positively high      (p < 0.001), indicating that sorption Al, Fe, and Mn particulate phase plays an important role in controlling the abundance and distribution of these metals in the southeastern Mediterranean waters.

 

The regional distribution of F3 in the WH showed a maximum of 63.46±  4.75 mg/g at station I, an area affected by shipyard wastes.

 

Monthly variations of F3 showed highest averages of 75.65 ± 7.94 and 71.59 ± 22.61 mg/g in June and August and lowest of 34.66 ± 11.35 and 34.60 ± 0.91 mg/g in December and February (Table 2).  This reflects the influence of biological activities, which increased the consumption of iron and manganese from seawater in warm season converting them into organo-metallic complexes, representing an important scavenging substrate of lead.

 

Organic/sulphide fraction (F4)

F4 gave an annual average value of 37.87 ± 1.66 mg/g.  The WH was exposed to huge amounts of discharges, mainly from anchoring vessels and external sources especially in front of station VIII, located in a stagnant area in the inner port giving  a lowest average  salinity value  due to these  discharges.   F4 gave the highest regional average value of 48.23 ± 9.77  mg/g at this station (Table 1), due to the huge amounts of organic wastes and the highest average concentration of chlorophyll-a.  However, the lowest regional average value of 28.99±  14.59 mg/g at station V (Table 1) was matched with the low content of F4 in the sediments of the same location, which was sandy and gravelly sandy poor in its organic content (Rifaat,1982).

 

The highest monthly average value of F4 calculated in June (73.57±  4.28 mg/g) and the lowest of (16.17 ± 3.44 mg/g) in October (Table 2) coincided mainly with the relationship between living organisms and the organic lead.

 

The stepwise regression models relating F4 with the other variables deduce that organic constituents originating from biological activity were the dominant source of F4 in the surface water.  However, the decrease in DO and the increase in salinity were the main environmental conditions affecting the increase in F4 in the bottom water of the WH.

 

Residual fraction (F5)

The residue remaining after the four preceding extractions consists essentially of detrital silicate minerals, resistant sulfides and a small quantity of refractory organic material.  Trace metals concentrations found in F5 were higher than those observed in any of the preceding extractions.  The annual value of F5 amounted to 68.19±  0.59 mg/g in the WH.

 

The highest regional average value of 92.10 ± 0.95 mg/g (Table 1) was found at station V, selected inside the Petroleum Basin of the harbour, where oil discharged from ships was distributed in this basin.

 

The monthly averages of F5 (Table 2) were highest in April (86.61±  14.95 mg/g) and June (76.17±  7.74 mg/g).  These coincided mainly with productivity abundance and consequently the high total particulate silicon during blooming seasons (spring and summer), as indicated by highest average chlorophyll-a levels those months.

 

The direct association between F5 and chlorophyll-a (r = 0.314, p < 0.030) in the surface water illustrate that a significant portion of F5 was of biogenic origin, i.e. associated with refractory organic materials rather than lithogenous alumino silicate materials.

 

Comparison between the annual mean values of particulate lead species in the present study with the similar means from other coastal marine areas in Egypt (Abdel-Moati,1990b) shows that the present F1 and F2 were comparable, whereas F3, F4 and F5 gave noticeable higher values.

 

References

Abdel-Moati A R (1981), M.Sc.Thesis, Fac.Sci.Alex.Univ.

Abdel-Moati A R (1990a), Est. Coast. Shelf Sci. 30: 153-165.

Abdel-Moati A R (1990b), In: Proc. 11th Int. Symp. Chemistry of  Mediterranean Primostern, Yugoslavia.

Abdel-Moati A R (1991), Water, Air and Soil Pollut. 59: 261-269.

Abdel-Moati A R,  El-Nady F S (1991), Thallassia Yugoslavia, 23: 11-25.

Abdel-Moneim M A, Khaled A M, Iskander M F (1994), In: Proc 4th  Conf. Environ. Protect. Must:155 - 174.

Aboul-Dahab O (1985), Ph. D. Thesis, Fac. Sci. Alex. Univ.

Badr N B (1993), M. Sc. Thesis, Fac. Sci. Alex. Univ.

Moore J W Ramamoorthy S (1984), Heavy metals in Natural Waters. Springer. Verlag. New York, Berlin, Heidelberg, Tokyo.

Rifaat A M (1982),  M.Sc. Thesis, Fac. Sci. Alex. Univ.

Sibley T H, Morgan J J (1975), In: Proc. Int. Conf. Heavy Metals. Environ., Toronto: 319-338.

Tessier A, Campbeil P G C, Bisson M (1979), Anal. Chem. 51 (7): 844-850.

 

                   Table 1 . Variations of the regional average values of TSM (mg/l), F1, F2, F3, F4 and F5 (mg/g)

                                   in the water column of the WH

 

 

Stations

Average

Depths (m)

 

TSM

 

F1

 

F2

 

F3

 

F4

 

F5
I

8.5

43.62

± 2.76

4.19+

 ±2.52

7.97+

 ±0.47

63.46+

 ±4.75

40.63

 ±2.04

70.39

 ±16.89

II

11.5

55.68

 ±16.19

1.80

 ±0.55

5.05

± 0.19

60.72

 ±1.30

35.33

± 0.78

62.65

 ±11.93

III

12.5

53.96

 ±2.58

1.81

 ±0.30

6.03

 ±2.83

56.03

 ±4.67

42.93

 ±13.67

54.04

± 8.98

IV

14.0

42.09-

 ±3.71

1.59

 ±0.05

4.70

 ±0.18

60.05

 ±6.78

37.65

 ±4.18

80.42

 ±12.66

V

14.5

54.11

 ±8.88

2.81

 ±0.47

4.45

 ±1.83

47.19

 ±7.63

28.99-

 ±14.59

92.10+

 ±0.95

VI

10.5

59.60+

 ±6.95

1.59

 ±0.93

3.93-

 ±1.77

38.27

 ±12.32

37.29

 ±11.95

49.84-

 ±2.08

VII

12.0

50.92

 ±9.13

3.81

 ±2.23

5.51

 ±2.86

32.90-

 ±15.12

31.90

 ±13.74

75.28

 ±24.94

VIII

11.0

51.94

 ±0.78

1.17-

 ±0.06

4.59

 ±0.09

51.53

 ±2.68

48.23+

 ±9.77

60.85

 ±9.27

Annual

Means

 

51.49

 ±0.30

2.35

 ±0.64

5.28

 ±0.79

51.27

 ±0.94

37.87

 ±1.66

68.19

 ±0.59

                                  N.B. The minimum values are designated by (-) and the maximum by (+).

 

 

                      Table 2. Variations of the seasonal average values of TSM (mg/l) F1, F2, F3, F4 and F5

                                   (mg/g) in the water column of WH

 

Parameters

Oct.

Dec.

Feb.

April

June

Aug.
TSM

38.40-

 ±7.30

65.49

± 3.04

69.38+

 ±23.63

44.10

± 11.74

45.53

± 9.72

46.01

 ±4.65

F1

1.42

 ±0.11

1.09-

 ±0.36

3.39

 ±1.12

4.41+

± 4.14

2.63

 ±0.35

1.15

 ±0.69

F2

1.87-

 ±0.40

2.29

 ±0.88

5.61

 ±2.10

4.31

 ±2.88

11.24+

 ±0.52

6.36

 ±3.98

F3

47.10

 ±0.91

34.66

 ±11.35

34.60-

 ±0.91

44.00

 ±10.79

75.65+

 ±7.94

71.59

 ±22.61

F4

16.17-

 ±3.44

21.65

 ±3.85

22.58

 ±4.78

37.44

 ±13.10

73.57+

 ±4.28

55.79

 ±5.51

F5

73.74

 ±3.04

62.93

 ±11.05

50.70-

 ±3.06

86.61+

 ±14.95

76.17

 ±7.74

59.01

 ±15.23

                                      N.B. The minimum values are designated by (-) and the maximum by (+).