Annex IV
REVIEW OF HEAVY METALS IN THE AFRICAN AQUATIC ENVIRONMENT (continued)

7. LEVELS OF HEAVY METALS IN DIFFERENT ENVIRONMENTAL COMPARTMENTS (continued)

7.3 Concentration of metals in aquatic fauna

Heavy metal concentrations in freshwater fish muscle are presented in Table VI. Some differences between water bodies were observed with respect to the levels of certain elements in finfish. For example, zinc showed relatively higher values in samples from Lake Nakuru, Kenya, followed in decreasing order by those from Zimbabwe and South Africa, Egypt, Nigeria and Ghana. Likewise, copper concentrations were higher in samples from Egypt and lakes Nakuru and Mcllwaine. Although data for iron were scare, the concentration of this element also seemed higher in samples from Egypt.

However, on the whole, the levels of metals in inland water fish muscle were below WHO limits, except for lead in Macrobrachium sp. from the Niger Delta, Nigeria and lower Volta River, Ghana.

Data on heavy metal concentrations in marine finfish and shellfish are summarized in Table VII. As for inland waters, the levels in marine organisms were generally below WHO limits except for some hot-spots. Cadmium and mercury for example showed the same low trends in both fin- and shellfish. In contrast, marine organisms from Nigeria had lead levels which exceeded the WHO limit. This may be attributed to a higher state of contamination from the use of leaded gasoline.

In support of what has been reported in several studies (Hellawell, 1986; Kakulu and Osibanjo, 1986; Kakulu et al., 1987a; Institute of Aquatic Biology, 1990), shellfish had higher concentrations of most metals. The highest concentrations of cadmium, copper and zinc occurred in Crassostrea sp. which has a great capacity to accumulate contaminants and is a biological indicator of pollution.

7.4 Concentration of Metals in Aquatic Flora

Aquatic plants have been shown to accumulate heavy metals in their tissues and therefore have been used as biological indicators for metal pollution monitoring in the aquatic ecosystem. Table VIII shows the distribution of heavy metals in aquatic plants. Generally, the levels in aquatic plants from inland waters were higher than in those from coastal waters. The variability in the levels of heavy metals in different regions could be ascribed to biological variation between the species rather than environmental factors. Nonetheless, higher concentrations of cadmium were found in Ceratophyllum from industrial areas in Egypt compared to relatively unpolluted areas (Fayed and Abd El-Shafy, 1985). Furthermore, it is significant that an excessively high value of lead (78.0 μg g^-1) was found in blue-green algae from Lake Mcllwaine, Zimbabwe (Greichus et al., 1978) compared to the rest of the region.

Table V
Mean metal concentrations in marine sediments (μg g^-1 dry weight)

Location		Hg	Cd	Pb	Cu	Zn	As	Fe(x10³)	Reference
MEDITERRANEAN
	Abu-Kir Bay, Egypt		2.02		12	102		4.5	Saad et al., 1981b
	Port Said, Egypt		3.2		14	50		2.5	Saad et al., 1981b
	Eastern Harbour, Alexandria, Egypt		2.89		14	51		1.1	Saad et al., 1981b
	El Mex, Egypt		2.18		24.1	35.4		1.47	Saad et al., 1981
	South-western Mediterranean	0.12							Bernhard, 1988

GULF OF GUINEA
	Ebrié Lagoon, Côte d'Ivoire	0.35		57.6	37.0	187		52.40	Kouadio and Trefry, 1987
	Lagos Lagoon, Nigeria		4.10	178.9	15.0	147		36.38	Okoye et al., 1991
	Atlantic coast, Nigeria*	0.10	2.30	67.5		72.5	6.2		Ndiokwere, 1984

INDIAN OCEAN
	Knysna Lagoon, South Africa	0.019	0.23	48.4	6.7	40.6			Watling and Watling, 1982a
UNPOLLUTED SEDIMENTS		0.01–0.08	0.2–5.0	8–60			14		GESAMP, 1985, 1988

* Median values

Table VI
Mean metal concentrations in inland water fish (μg g^-1 fresh weight)

Location		Hg	Cd	Pb	As	Cu	Zn	Mn	Fe	References
FINFISH
	Lake Mariut, Egypt		0.15			3.7	7.6	0.9	11.2	Saad et al., 1981a
	Lakes ldku,Mariut, Egypt	0.01	0.004	0.67	0.031	1.77	7.4			El Nabawi et al., 1987
	Nozha Hydrodome, Egypt		0.05			3.14	8.0		12.6	Saad, 1987
	Kpong Headpond, Ghana	0.053	<0.10	0.43		0.36	5.6	0.63	3.8	Biney, 1991
	River Wiwi, Ghana	0.37	0.19	0.47		0.18	3.0			Biney and Beeko, 1991
	Niger Delta, Nigeria	0.034	0.03	0.48		0.70	4.8	1.1	5.4	Kakulu et al., 1987a
	Lake Nakuru, Kenya	0.044	0.05	0.17	0.36	2.0	22	1.8		Greichus et al., 1978a
	Lake Victoria, Kenya*		0.04–0.12	0.4–1.1		0.15–0.53	2.21–7.02	0.22–0.74	0.53–4.65	Wandiga and Onyari, 1787
	Lake Mcllwaine, Zimb.		0.02	0.17	0.28	1.08	9.6	5.4		Greichus et al., 1978
	Hartbeesport Dam, S.A.		0.02	0.05	0.26	0.66	11.8	1.6		Greichus et al., 1977
	Voelvlei Dam, S. Africa		0.01	<0.02	0.40	0.30	6.6	0.24		Greichus et al., 1977

SHELLFISH
Macrobrachium sp.
	Lower Volta R., Ghana	0.04	<0.10	4.36		11.0	16.1			Biney, 1991
	Niger Delta, Nigeria	0.02	0.04	2.47		8.5	14.1			Kakulu et al., 1987a
Egeria radiata
	Lower Volta R., Ghana	0.05	<0.10	1.37		4.5	20.2			Biney, 1991
WHO Limits		0.05**	2.0	2.0		30	1000			Kakulu et al., 1987a

* Range values
** Action level adopted in many countries

Table VII
Mean metal concentrations in marine fish (μg g^-1 fresh weight)

Location		Hg	Cd	Pb	Cu	Zn	Reference
FINFISH
	Egypt	0.077	0.004	0.07	1.65	4.23	El Nabawi et al., 1987
	Senegal	0.17	<0.10	0.50	0.73	4.55	Ba, 1988
	Côte d'Ivoire	0.11	<0.25		<0.80	4.86	Metongo, 1988
	Ghana	0.064	<0.10	0.36	0.46	4.63	Institute of Aquatic Biology, 1990
	Ghana	0.24					Ntow and Khwaja, 1989
	Nigeria		<0.10	2.28	11.3	27.5	Okoye, 1991
	Cameroon	0.09	0.26				Mbome et al., 1985
	Cameroon	0.06	<0.10	1.83	0.75	5.55	Mbome, 1988
	Kenya*		0.04–0.38	1.22–6.48	0.36–2.04	4.67–40.8	Wandiga and Onyari, 1987

SHELLFISH
Penaeus sp.
	Senegal	0.17	<0.10	<0.50	4.68	13.9	Ba, 1988
	Cote d'Ivoire	0.042	<0.25		6.02	17.9	Metongo, 1988
	Ghana	0.033	<0.10	0.82	6.16	14.9	Institute of Aquatic Biology, 1990
	Nigeria		0.18	5.10	23.6	240	Okoye, 1991
	Cameroon	0.057	<0.10				Mbome et al., 1985
	Cameroon	0.070	0.21		9.5	40.4	Mbome, 1988
Crassostrea sp.
	Cote d'Ivoire	0.125	0.65		24.5	1205	Metongo, 1991
	Nigeria		0.17	2.09	5.80	628	Okoye, 1991
	Cameroon	0.072	0.56				Mbome et al., 1985
	Cameroon	0.083	0.25		8.45	407	Mbome, 1988
	South Africa		1.62	0.08	2.35	213	Watling and Watling, 1982a
	WHO Limits	0.5**	2.0	2.0	30.0	1000	Kakulu et al., 1987a

* Range values
** Action level adopted in many countries

Table VIII
Mean metal concentrations in aquatic plants (μg g^-1 dry weight)

Location		Hg	Cd	Pb	As	Cu	Zn	Mn	Fe	References
INLAND WATERS

River Nile, Egypt
	Ceratophyllum (clean site)		<0.05	2.7		2.7	13.8			Fayed and Abd El-Shafy, 1985
	Ceratophyllum (industrial site)		0.30	22.2		36.4	117.0			Fayed and Abd El-Shafy, 1985

Lower Volta River, Ghana
	Ceratophyllum	0.37	0.99	17.4		12.2	45.4	3332	2579	Biney, 1991
	Pistia stratiotes	0.31	0.93	22.6		12.6	39.8	2259	3852	Biney, 1991
	Potamogeton octandrus	0.25	<0.20	9.4		5.3	12.5	2370	1113	Biney, 1991
	Vallisneria aethiopica	0.13	1.33	23.2		12.6	42.9	1809	3560	Biney, 1991

Lake Mcllwaine, Zimbabwe
	Blue-green algae	0.26	1.5	78	2.9		190	220		Greichus et al., 1978

Harbeespoort Dam, S. Africa
	Algae	1.6	0.06	<0.10	1.5	2.7	39.0	96		Greichus et al., 1977
	Eichhornia	0.71	0.23	2.6	4.1	12.0	42.0	840		Greichus et al., 1977

COASTAL WATERS

Accra, Ghana
	Ulva fasciatus (Green algae)	<0.10	<0.2	8.3		6.9	24.8		163	Environ. Management Associates, 1989
	Sargassum vulgare (Brown algae)	<0.10	<0.2	8.5		7.2	37.8		342	Environ. Management Associates, 1989
	Polycavernosa dentata (Red Algae)	<0.10	1.4	8.6		4.5	33.0		452	Environ. Management Associates, 1989

7.5 Comparison between metal contents in sediments and biota

Comparisons between heavy metal concentrations in sediments and biota of selected African waters are shown in Table IX. In Egypt all metals except cadmium showed higher values in the sediments than in fish (Saad, 1985a, 1987). In Ghana only iron and lead followed this pattern, whereas the other metals gave higher values in certain flora and fauna (Biney, 1991a). In Kenya the metals accumulated in higher concentrations in sediments than in fish (Wandiga and Onyari, 1987). In Southern Africa the same pattern occurred with few exception (Greichus et al., 1977). The levels of accumulation of metals in the different flora and fauna did not follow the same pattern.

7.6 Comparison between different sub-regions in Africa

In Tables X and XI are presented the trace metal concentrations in sediments and in fish muscle and shellfish from the major African sub-regions, Northern, Western, Eastern and Southern Africa. The data presented are ranges of means based on Tables IV and V for sediments and Tables VI and VII for fin- and shellfish. Hot-spots, i.e., abnormally high concentrations were excluded form the calculations since the objective is to compare actual background levels from the different sub-regions in Africa.

An inspection of Tables X and XI shows inadequacy of data especially for the coastal and marine areas. In spite of this, the four regions exhibit comparable concentrations of trace metals in both inland and coastal fish and sediment. Mercury for example, occurred in finfish within the narrow ranges of 0.01 to 0.053μg g^-1 fresh weight for inland fishes and 0.06 to 0.17 for marine fishes. Corresponding values for cadmium were 0.004 to 0.19 and 0.004 to 0.36 μg g^-1 fresh weight.

Where comparable data were available, coastal fishes showed slightly higher maximum values of trace metals than inland fishes. This was also true for sediments and may be due to the data originating mainly from coastal lagoons which are normally heavily influenced by anthropogenic activities.

7.7 Comparison of African data with some other areas of the world

The levels of heavy metals in sediments and finfish from African inland and coastal waters are presented alongside data from some other areas of the world in Tables XII and XIII. The means and ranges for African waters were calculated from Tables IV and V for sediments and Tables VII and VIII for fish, excluding the hot spots.

Comparison of such data may be difficult since data calculated for the whole African region are being judged in relation to selected individual areas and sites of the world which may not be representative for their regions. Moreover, different species of fish and fractions of sediments were analyzed. Also, information on sex and weight is often lacking, and comparison is further complicated by the differences in data presentation. For example, analytical results may be presented as means or ranges on a dry or wet weight basis.

Table IX
Comparison of trace metal concentrations in sediments, fauna and flora (μg g^-1 dry weight)

Matrix		Hg	Cd	Pb	Cu	Zn	Mn	Fe	As	References
INLAND WATERS

Lake Mariut, Egypt
	Sediment		0.07		91	162		4747		Saad, 1985a
	Finfish		0.25		23	59		257		Saad, 1985a

Nozha Hydrodome, Egypt
	Sediment		0.16		133	156		8628		Saad, 1987
	Finfish		0.47		34	41		109		Saad, 1987

Lower Volta River, Ghana
	Sediment		<0.2	21.7	29.5	39.1	318	56821		Biney, 1991
	Macrophytes	0.29	0.89	18.8	11.2	37.6	2560	2922		Biney, 1991
	Shellfish	0.19	<0.2	6.0	38.2	69.1	33.2	80.1		Biney, 1991
	Finfish	0.29	<0.2	2.3	2.0	30.7	3.4	19.0		Biney, 1991

Hartbeesport Dam, S.Afr.
	Sediment	0.60	0.87	63	41	260	680		75	Greichus et al., 1977
	Algae	1.60	0.06	<0.1	2.7	39	96		1.5	Greichus et al., 1977
	Macrophytes	0.71	0.23	2.6	12	42	840		4.1	Greichus et al., 1977
	Finfish	0.52	0.05	1.0	2.9	120	12		2.3	Greichus et al., 1977

Lake Victoria, Kenya*
	Sediment		0.55–1.02	6.02–69.4	0.19–78.6	2.54–265.2	53.7–616	1180–52880		Wandiga and Onyari,87
	Finfish		0.04–0.12	0.39–1.08	0.15–0.53	2.2–7.02	0.12–0.74	0.53–4.65		Wandiga and Onyari,87

COASTAL WATERS

Mediterranean, Egypt										Saad et al., 1981
	Sediment		2.18		24.1	35.4	151	1470		El Nabawi et al., 1987
	Finfish		0.02		8.25	21.2

* Range values

Table X
Metal concentrations in sediment from the major African sub-regions (μg g^-1 dry weight)

Sub-region		Hg	Cd	Pb	Cu	Zn	Mn	Fe(× 10³)
INLAND WATERS

	Northern Africa		0.15–0.20	7.3–10.6	38.0–85.6	94–139	387–958	0.46–58
	Western and Central Africa	0.21–0.33	0.16–0.20	13.4–16.7	24.7–30.3	16–62	295–352	55–60
	Eastern Africa	<0.05	0.27–1.02	6.02–18.1	0.96–6.2	2.54–140	53–550	1.18–69
	Southern Africa	0.02–0.28	0.19–1.0	9.0–17.8	10.5–41.0	36–289	150–350	12–16

COASTAL WATERS

	Northern Africa	0.12	2.02–3.20		12–14	35–51		1.1–4.5
	Western and Central Africa	0.10–0.35	2.30–4.10	57.6–67.5	13–37	73–187		36–52
	Southern Africa	0.019	0.23	48.4	6.7	41

Annex IV REVIEW OF HEAVY METALS IN THE AFRICAN AQUATIC ENVIRONMENT (continued)

7. LEVELS OF HEAVY METALS IN DIFFERENT ENVIRONMENTAL COMPARTMENTS (continued)

Annex IV
REVIEW OF HEAVY METALS IN THE AFRICAN AQUATIC ENVIRONMENT (continued)