Organochlorine pesticide residues in the sediments of selected river bays in Lake Kariba, Zimbabwe

: Z "~. 7! the Science o f the Total Environment II ELSEVIER

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The Scienceof the Total Environment 142 (1994) 221-226

Organochlorine pesticide residues in the sediments of selected river bays in Lake Kariba, Zimbabwe M.F. Zaranyika,

E. M a m b o ,

J.M. Makhubalo

Chemistry Department, University of Zimbabwe, P.O. Box MP 167. Mount Pleasant, Harare, Zimbabwe

(Received 24 April 1992; accepted 3 September 1992)

Abstract

Sediment samples from seven of the major river bays on the Zimbabwe side of Lake Kariba were analysed for organochlorine pesticide residues by capillary gas chromatography and electron capture detection. The results obtained confirm contamination of most of the bays by DDT and its metabolites, endosulphan, aldrin, dieldrin, endrin and heptachlor. Key words: Organization pesticides; DDT; Pesticide residues; Sediment pollution; Environmental pollution

1. Introduction

Environmental pollution has become a global concern to which developing countries are slowly awakening. Of major concern in Zimbabwe is the impact of the increasing use of organochlorine pesticides to control agricultural pests, including tsetse fly (Glossina ssp.) and malaria vectors. Pesticide sprays for tsetse fly control in Zimbabwe began in the early 1960s. Pesticides which have been used include dieldrin (1962-1967) and DDT (1968 to the present) (Whitwell et al., 1974; Mpofu, 1987). Endosulphan and deltamethrin are also used, especially in aerial sprays (Chapman, 1976). In addition to its use in the control of tsetse fly and malaria vectors, DDT was used extensively in agriculture prior to 1983 when the use of DDT

in agriculture was banned. Dieldrin, endosulphan and deltamethrin are used extensively in agriculture. In addition several other organochlorine pesticides are in use. The combined area affected by tsetse fly and malaria carrying mosquitoes covers about twothirds of the country (Mpofu, 1987), hence huge quantities of DDT are sprayed each year. For instance 127 tonnes were used for tsetse control in the Binga, Gokwe and Hurungwe areas of the Zambezi operational front alone in 1983 (Department of Veterinary Services, Zimbabwe 1983) (see Fig. 1). Several surveys have been conducted to assess the impact of the use of these pesticides on the environment. Thus following the tsetse control spraying in 1962-1967 with dieldrin and in

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222

M.F Zaranyika et al./ScL Total Environ. 142 (1994) 221-226

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KE__ZY E~] 1984 ground and aerial spraying (DDT) limit. ~

Areas sprayed for L~etse control. Areas sprayed for malaria control.

lilT[1 Uninfested area. Fig. 1. Map of the Zambezi tsetse control operational front showing areas sprayed with DDT in 1984 for tsetse and malaria control. (The following Administration Districts fall within the Zambezi Operational Front: Hwange (H), Binga (B), Gokwe (G), Kariba (K), Hurungwe (U), Makonde (formerly Lomagundi) (M) and Guruve (formerly Sipolilo) (S).

1968-1971 with DDT, Phelps et al. carried out a nationwide survey to assess the impact of the spraying exercises on birds and other wildlife. The pesticides tested for included DDT, DDE, DDD, BHC, dieldrin, aldrin and endosulphan. The survey did not find evidence of a heavy build-up of pesticide residues in the terestial environment. It did, however, find evidence of pesticide build-up in lakes. The reason for this trend in the dispersal of the pesticides lies in the rainfall pattern as discussed below. Zimbabwe lies in the subtropical region of Southern Africa and the climate is such that rain falls only for 4-5 months of the year. A major factor in the dispersal dynamics of the pesticides is related to the fact that the rain falls in the form of short heavy storms which result in high erosive

run-off during the period that most pesticides are applied in agriculture. Since suspended particles are the major carriers of organic micro pollutants in the aquatic environment and relatively small amounts are transported in 'solution' (Japenga et al., 1987), much of the pesticides washed off the terrestial environment find their way directly into river and lake sediments. Indeed sediments have been used extensively to assess the pollution of water bodies (Meiggs, 1980). Direct analysis of lake sediments in Zimbabwe has been reported for Lake Chivero only (Greichus et al., 1978; Mhlanga and Madziwa, 1990). In this paper we report the analysis of sediments from seven of the major river bays on the Zimbabwe side of Lake Kariba, namely

M.F. Zaranyika et al./ Sci. Total Environ. 142 (1994) 221-226

223 ,Zambezi R. o

LAKE KARIBA

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/_. ZAMBIA

Sanyati R.

Ume R,

;N2 -Mwenda Sengwa R,

~uzirihuru R

ZIMBABWE

N vlasumo R,

Legend O ..... MLIBIZI

zbungwe R

i

Sampling stations International boundary J 50 Km

Fig. 2. Map of Lake Kariba showing the points from which sediment samples were collected (see also Table 1).

Charara, Nyaodza, Gachegache, Sanyati, Ume, Sengwa and Ruziruhuru (Fig. 2). The aim of the study was to assess the level of contamination of these bays by organochlorine pesticides since the area bordering the lake has received regular sprays for tsetse and malaria control. Figure 1 shows the areas sprayed for tsetse and malaria control in 1984 (Mpofu, 1987). High levels of DDT and its metabolites have been reported in fish, mussels, snails, prawns and birds from different localities and trophic levels of Kariba (Kubus and Berg, 1991). 2. Experimental

2.1. Sampling Figure 2 shows the points from which samples were collected. Sampling was done from a boat

using a sediment grabber (Hydrobios Sediment Grabber, Apparatebau, GmbH, Germany). The samples were placed in glass jars with plastic screw caps lined with aluminum foil. Once at the laboratory the samples were stored in a freezer.

2.2. Extraction and clean-up An aliquot corresponding to 1 g of the dry sediment was extracted with 200 ml of 1:2 benZene/hexane mixture in a soxhlet extractor and concentrated using a Kuderna-Danish concentrator according to the procedure described previously by Japenga et al. (1986, 1987). Humic substances and elemental sulphur were removed from the benzene/hexane extracts of chlorinated pesticides by passing the extracts through a chromatographic column containing basic alumina on which sodium sulphate and sodium

1

pesticides in sediments

.

--

4,4 TDE

/~-Endosulphan

--

1.67

--

--

DDT

Drins

Endosulphan

Heptachlor

C3

(SN) and Ruziruhuru

Total DDT,

74.8

.

and heptachlor

8.22

--

16.1

--

17.3

--

--

24.4

0.017

117.7

CI 12.3

S4

(Rz) River Bays in Lake

drins, endosulphan

--

Endrin

Table 2

16.7

.

Dieldrin

--

--

2,4 DDT

--

--

2,4 TDE

c~-Endosulphan

--

4,4 DDT

10.1

--

2,4 DDE

4,4 DDE

10.4

0.017

--

--

--

Cl

Heptachlor

C3

.

0.876

--

--

--

S6

Kariba

4.90

4.02

--

28.3

5.65

2.23

17.5

4.90

36.7

3.28

4.90

1.91

--

--

UM l

40.02

2.23

34.7

64.7

SN l

16.1

13.8

37.1

.

--

.

.

.

--

--

--

0.882

SN2

0.882

16.1

51.5

--

SN 2

.

.

.

--

--

2.27

4.30

.

3.69

.

.

.

5.65

--

0.019

RZl

.

0.019

--

2.27

9.34

Rz~

2.66

25.5

32.7

16.6

Rz 2

. .

2.66 --

4.10

.

6.42

5.12

15.4

5.62

--

--

--

--

G3

(UM),

(SN) and

1.73

16.5

41.0

22.8

2.80

9.06

--

3.93

3.59

N l

Sengwa

--

12.0

20.5

5.62

G3

20.4

G I

3.59

167.8

63.7

30.3

N l

(G), Sanyati (S), Ume (Um), Sengwa

8.88

10.8

17.8

16.6

.

.

(S), U m e

Rz2

-.

(G), Sanyati

(N), Gachegache

.

(N), Gachegache

(C), Nyaodza

0.822

1.52

0.702

from the Charara

--

--

1.91

--

--

--

--

--

(/zg/g)

in sediments

--

--

--

--

--

--

--

--

--

SNz

(C), Nyaodza

UM r

the Charara

0.876

S6

(/zg/g) f r o m

(Rz) river bays in Lake Kariba

Aldrin

Ruziruhuru

Organochlorine

Table

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225

M.F. Zaranyika et al. / Sci. Total Environ. 142 (1994) 221-226

hydroxide had been adsorbed and eluting with 25 ml of hexane (fraction I) and then with 25 ml of ether/pentane (1:9) (fraction II). These fractions were concentrated to a final volume of 1.0 ml using a Kuderna-Danish concentrator. All solvents used were of pesticide grade. 2.3. Gas chromatography

Organochlorine pesticides in the sample extracts were determined using a Varian Model 3300 Gas

chromatograph (Varian AB, Solna, Sweden) fitted with a microprocessor, a split/splitless capillary injector, a Varian Model 4400 integrator and a 63Ni electron capture detector (ECD). Separations were made using a DB-1701 30 m x 0.25-mm refined silica capillary column for pesticides and chlorinated aromatics (J and W Scientific, CA, USA) and ultrapure nitrogen carrier gas at 5 ml/min flow rate (make-up gas at 25 ml/min). Other gas chromatographic conditions used were as follows:

g O |

Fig. 3. A chromatogram of fraction 1 of the cleaned extract of one of the sediment samples (SEN 1).

226

100°C hold for 2 min Initial column temperature: 250°C hold for 23 min Final column temperature: 5°C/min Temperature programme rate: Injector temperature: 150°C Detector temperature: 300°C ECD attenuation: 8 on autozero ECD range: 10 Initial relays: -1 to 1 after 0.5 rain Table 1 shows the results obtained for the various samples analysed. The results of the two fractions from the clean-up step were combined to arrive at these figures. Fig. 3 shows a typical chromatogram obtained for one of the samples analysed. Quantitation was by the external standard method. 3. Results and discussion Table 2 shows the total DDT, total aldrins, dieldrin, endrin (drins), total endosulphans and heptachlor contamination levels for the grab samples from the different sampling points. The data for Ruziruhuru bay show that contamination levels are higher farther up the river mouth than in the bay itself. This finding is consistent with the fact that pesticide transport is closely associated with suspended particles. Table 2 further shows that DDT contamination is found in the Charara, Nyaodza, Gachegache and Sanyati areas at the lower end of the lake and in the Sengwa and Ruziruhuru areas further up the lake. The Ume area lying between these two areas appears to be relatively free of DDT, drins and endosulphans. At the lower end of the lake, heptachlor is only found in the Nyaodza bay, while farther up the lake it spreads from the Sanyati bay to the Ruziruhuru bay. Table 1 shows relatively high concentrations of metabolised DDT in the Charara, Sengwa and Ruziruhuru bays. Japenga et al. (1988) found relatively high concentrations of non-metabolised DDT in the sediments of the Rio de Janeiro coastal region in Brazil (compared to values obtained for European sea and river sediments) and suggested that this might be due to less effective biological degradation in the tropical environment.

M.F. Zaranyika et al./Sci. Total Environ. 142 (1994) 221-226

Our results above may suggest a relatively faster rate of degradation of DDT in the Lake Kariba environment compared to Rio de Janeiro coastal region in Brazil. 4. Acknowledgements This work was supported in part by a grant from the Research Board of the University of Zimbabwe and in part by a grant from the Swedish Agency for Research Cooperation with Developing countries (SAREC). We are grateful to Professor C. Magadza and his associates at the University of Zimbabwe Lake Kariba Research Station for the use of their facilities and to Dr. Leggett for assistance in the collection of the samples. 5. References Chapman, N.G., 1976. Aerial spraying of tsetse flies (Glossina ssp) in Rhodesia with ultra low volumes of endosulphan. Trans. Rhod. Sci. Assoc., 57 (2): 12-21. Department of Veterinary Services, Zimbabwe, Annual Report of the Branch of Tsetse and Trypanosomiasis Control for the year ended 30th September 1983, Ministry of Agriculture, Zimbabwe. Greichus, Y.A., A. Greichus, H.A. Draayer and B. Marshall, 1978. Insecticides, polychlorinated biphenyls and metals in African lake ecosystems: il Lake McLlwaine, Rhodesia. Bull. Environ. Contam Toxicol., 19 (4): 444-453. Japenga, J., R.C.C. Wagrnan, F. Freudenthal, G.A.L. de Karte, and G.S. Graenemeijen, 1986. A modified clean-up procedure for the determination of PCDDs in soil samples. Chemospbere, 15 (9-12): 1107-1112. Japenga, J., W.J. Wagenaar, F. Smedes and W. Salomons, 1987. A new, rapid clean-up procedure for the simultaneous determination of different groups of organic micropollutants in sediments: Application in two European estuarine sediment studies. Science Technol. Lett., 8 (1): 9-20. Japenga, J., W.J. Wagenaar and W. Salomons, 1988. Organic micropollutants in the Rio de Janeiro coastal region, Brazil. Sci. Total Environ., 75: 269. Kubus, M. and H. Berg, 1991. Pesticides in Lake Kariba, a report prepared for the Department of Systems Ecology, University of Stockholm 5-10691, Stockholm, Sweden. Meiggs, T.O., 1980. Contaminants and sediments. In: R.A. Baker (Ed.), Ann. Arbor. Sci. Publ. Mhlanga, A.T. and J.J. Madziva, 1990. Pesticide Residues in Lake McLIwaine. Ambio, 19: 368-372. Mpofu, S.M., 1987. DDT and its use in Zimbabwe. Zimbabwe Sci. News, 21: 31-36. Whitwell, A.C., R.J. Phelps and W.R. Thompson, 1974. Further records of chlorinated hydrocarbon pesticide residues in Rhodesia. Arnoldia (Rhodesia), 6 (37): I-7.