Description of the problem
Vikuge State Farm is in Vikuge village, Soga ward in the Kibaha District of the lowland Coast Region, approximately 60 km northwest of Dar es Salaam, Tanzania. The area is surrounded by five neighbouring villages including Misufini and Zogowele in the west, Kongowe in the north, Viziwaziwa in the east and Soga in the south. The average distance from Vikuge to other villages is about 5 km. According to the 2002 census, the Soga ward that includes Vikuge village has a population of 6,704 persons6. The Vikuge area is characterised by savannah and deciduous forest woodland and there are only small altitude variations. Small temporary streams that empty to the north into the Ruvu River drain the area. There are several small villages and settlements in the area and small-scale agriculture where local farmers grow, among other crops, cereals and cassava. The villagers use pond water and water from shallow, dug wells for cooking, washing, recreation, and irrigation of subsistence agriculture. There is no large-scale agriculture in the close surroundings. Prior to the pesticide donation, Vikuge State Farm produced seeds, although at the time of the donation there was no activity on the farm. Today, the farm produces hay, most of which is sold as cattle feed in Dar es
Salaam.
The situation in Vikuge originated in 1986 when a private company in Greece, via the Greek government, donated partly expired pesticides to the government of Tanzania. The pesticides were placed in a shed at Vikuge State Farm. Most of the pesticides were delivered in small, household size packages with Greek labelling, impossible to read for those handling the material in Tanzania. Some packaging was already empty upon arrival. Observations at Vikuge in 1989 and 2001 showed that most of the donated pesticides were left unused in an open shed, which eventually collapsed. In 1995, a bush fire burned some of the pesticides, and in 1996 NEMC built a new better storage building with help from the Swedish International Development Cooperation Agency (SIDA). The remaining visible pesticides were collected, repacked, and placed in the new building. However, the soil around the old storage shed still lacks vegetation and there is a strong smell and scattered fragments of pesticide packaging and dead insects. Obviously, there is a risk of human exposure to the pesticides through drinking water from the wells close to the farm. Therefore, a cistern at the farm is filled three times a week with supposedly clean drinking water. However, the water is distributed to the village via a PVC pipe that runs in a shallow ditch that also drains the most severely contaminated part of the old storage area. Not much is known about the type and quantity of pesticides delivered to Vikuge, although DDT, telodrin, and organophosphorus pesticide containers were observed in 1989. Because of the collapse of the shed and the subsequent mixing, photodegradation, and burning of the pesticides, even less was known about which environmental pollutants were present in 2000 when we initiated our work. Assessing the
contamination
In 1998, a soil sample from the contaminated site was taken at 1 m depth and it contained over 100 mg/kg of p,p’-DDT4. To further map the contamination, the Pesticide Research group at the University of Dar es Salaam initiated a sampling campaign in 2000 together with the Swedish University of Agricultural Sciences. We took soil samples at three depths (0–5 cm, 20–25 cm and 50–55 cm) from the old storage site and its surroundings, and water samples from a pond (surface water) near the old storage site and from two dug groundwater wells. Well One is located near the storage site, and Well Two is close to a rice field somewhat further away. We also took soil samples (0–5 cm) along the shallow ditch draining the storage area in which the PVC pipe distributing drinking water from the cistern to the village runs and samples of the clean water from a tap in Vikuge village, that is after the water from the cistern had passed the contaminated area. We screened the samples for 89 pesticides including some metabolites. The methods for sampling and analysis are described in other studies7,8,9.
High levels of contaminants in soil and drinking water
We found high levels of DDT compounds (DDT, DDD, and DDE) and hexachlorocyclohexanes (HCHs; a compound class containing the insecticide lindane) in soil, well water, and surface water around the collapsed pesticide storage shed at Vikuge. In the soil we found residues of DDT and HCHs down to 50 cm depth. Surface soil samples contained up to 28% total DDT and 6% total HCH residues8, 9. At Vikuge, the worst contaminated area is about 30 x 30 m and most of the pesticides were within the top 20 cm soil layer, but reached a depth of at least 50 cm. Using these estimates to calculate the volume, about 180 m3 soil was contaminated with an average DDT concentration of 40 g/kg. We also found aldrin, azinphos-methyl, carbosulfan, gamma-chlordane, chlorprofam, heptachlor, hexazinone, metamitron, metazachlor, pendimethalin (up to 4%), and thiabendazole residues in the soil. The latter pesticides showed a patchy distribution at the old storage site and its
vicinities.
All water samples contained DDTs and HCHs. The highest concentrations were found in Well Two, which contained 30 µg/l of organochlorine pesticides in May 20018, 9. Notably, also the tap water supplied from the water cistern contained substantial levels of contaminants. The levels of the DDT compounds were higher than their solubility in water. These high concentrations must be due to high levels of contaminated colloids in the water. Therefore, filtering of the water may be a first step for cleaning the drinking water from contaminants bound to particles. Other pesticides found in some water samples were carbosulfan, chlorprofam, and
thiabendazole.
The World Health Organization (WHO) guideline for DDT residues in drinking water is 2 µg/l10 for protection of human health. This is calculated on the basis of a child (10 kg) drinking one litre per day, and DDT exposure through drinking water contributing only 1% of the total exposure. In Vikuge, the exposure through drinking water probably exceeds 1% of the total daily intake, especially if water is not filtered. The WHO guideline for HCHs in drinking water is also 2 µg/l10. The levels of both DDTs and HCHs in the sample from Well Two far exceed the guidelines. We also found fairly high levels of o,p’-DDT in some water samples. This DDT compound has known oestrogenic effects, causing developmental disorders and disturbances in reproductive functions11. An in-depth evaluation of the water contamination requires systematic sampling over at least a year, so that seasonal differences can be identified. The overall contamination of the drinking water resources may, therefore, be underestimated in this study, especially if there is substantial surface runoff during the biannual rainy
seasons.
We do not yet have sufficient data to make a full environmental impact assessment of the pesticide contamination at Vikuge such as leaching to the groundwater, surface runoff during heavy rains, volatilization to air, and wind drift of contaminated dust. According to the data at hand, the latter three processes seem to be the most important, at least for the DDTs and HCHs since the highest concentrations were found in the surface
soil.
The packaging material present at Vikuge in 1989 was from several compounds that were not detected in the analyses, most notably some organophosphorus insecticides and telodrin. The explanation may be a result of the patchy distribution of pesticides in the old storage area and that more water-soluble pesticides have infiltrated to groundwater or been washed away, but the high levels of DDT compounds and HCHs also are a major problem for the detection of other contaminants. The levels of DDTs and HCHs were so high that they probably masked the presence of other compounds in the analyses.
Donation of expired pesticides and pesticide waste
Much evidence at Vikuge indicates that the main intention with the donation was to solve domestic environmental problems in the donor country, Greece. As an example, packages of telodrin (isobenzan) were found at Vikuge in 1989. The production of telodrin stopped in 1965 due to its high persistence and toxicity to mammals12. Existing stocks were used throughout the world for some years after production had ceased, but the agricultural use was restricted. In this case telodrin was donated to Tanzania more than 20 years after production ended. Some of the residues at Vikuge clearly indicate that the donation also contained pesticide waste. Lindane should normally constitute 15-20% of the technical HCH product, but at Vikuge there is almost no lindane. Lindane is the only one of the HCH compounds that is insecticidal. In Europe and North America many countries banned the use of the technical HCH mixture around 1980. When pure lindane is produced a residue containing the other HCH compounds is left. The composition of HCH compounds at Vikuge indicates that the donation contained waste after lindane production and no lindane. If such waste is used organochlorine contaminants are spread in the environment without combating any insect
pest.
Among the DDT compounds there is a very high proportion of DDD at Vikuge, much higher than can be explained by conversion of DDT to DDD in the environment. Although DDD in itself had some use as insecticide during the 1960s, the insecticidal activity is weaker than DDT. If a hypothetical user in the 1980s did not know that it is DDD instead of DDT the dosage may have been too low to kill the insects. Instead it would add to the risk that resistance to DDT developed in the insects. These three examples indicate that a main reason for the donation in this case was to get rid of an old stock. Dealing with the problem becomes even more difficult when the documentation of what the shipment contained has been lost and many of the labels are in a language that few can read. A case like this stresses the responsibility of the authorities in both donor and recipient countries to make sure that donations are relevant and of good quality. Conclusion Although the visible remains of pesticides have been removed, the soil of the old storage site must be regarded as hazardous waste, and a complete degradation of the pesticides still present in the soil will take a long time if nothing is done to remediate the site. It is at present difficult to recommend any immediate action. Our knowledge of the extent of pollution is still incomplete and any measures taken might make the situation worse, for example by mobilizing bound pesticides and thereby spreading the local contamination even further. Actions to solve the acute problem of clean drinking water at Vikuge are needed. We also need to find the best possible solution to remediate the contaminated soil. To find the best possible remediation measure we need a more comprehensive study to allow for a full environmental impact assessment. The situation is probably similar at other sites with obsolete stocks of pesticides in developing countries.
References
1. FAO, Prevention and Disposal of Obsolete and Unwanted Pesticide Stocks in Africa and the Near East. Food and Agriculture Organization of the United Nations, FAO, Rome,
1995.
2. Kishimba, MA and Mihale, MJ Levels of Pesticide Residues and Metabolites in Soil at Vikuge Farm, Kibaha District, Tanzania – A Classic case of Soil Contamination by Obsolete pesticides. Tanzanian Journal of Science. 30 (2), 77-87,
2004.
3. FAO, FAO warns of pesticide waste time bomb in poor countries, FAO, Rome.2004.
4. NEMC, Chemical Waste Management in Tanzania. Report. National Environmental Management Council, Dar es Salaam, Tanzania,
1998.
5. Van Veen, F. and Breedveld, GD, Pesticide Wastes in Zanzibar Islands. Hague, The Netherlands TAUW Infra Consult b.v.,
1987.
6. The United Republic of Tanzania, 2002 Population and Housing Census. General Report. Central Census office, Dar es Salaam,
2003.
7. Ĺkerblom, M, Environmental Monitoring of Pesticide Residues. Guidelines for the SADC Region. SADC ELMS Monitoring Techniques Series Vol. 3, Maseru, Lesotho,
1995.
8. Mihale, MJ, Chemodynamics of Obsolete Pesticides at Vikuge Farm, Kibaha District, Tanzania. M.Sc. Thesis, University of Dar es Salaam, 2002.
9. Elfvendahl S., Mihale M., Kishimba MA and. Kylin H, Pesticide Pollution Remains Severe after Cleanup of a Stockpile of Obsolete Pesticides at Vikuge, Tanzania. Ambio 33:503-508,
2004.
10. WHO, Guidelines for Drinking Water Quality. Second edition, volume 1, World Health Organization, Geneva,
1993.
11. Colborn, T, Saal, FSV and Soto, AM, Developmental effects of endocrine-disrupting chemicals in wildlife and humans. Environmental Health Perspectives 101, 378-384, 1993.
12. WHO, Environmental Health Criteria, No 129: Isobenzan. World Health Organization, Geneva, 1992.
Michael A. Kishimba is Associate Professor of Chemistry, University of Dar es Salaam. kishimba@chem.udsm.ac.tz
Henrik Kylin is Full Professor of Environmental Chemistry, Swedish University of Agricultural Sciences, and Senior Scientist, Norwegian Institute for Air Research, Henrik.Kylin@ma.slu.se Henrik.Kylin@nilu.no
Matobola J. Mihale did this work as part of a master’s programme at the University of Dar es Salaam and is currently Research Analytical Chemist with the National Institute for Medical Research, Tanzania. matobola@yahoo.com
Sara Elfvendahl did this work as part of her master’s studies at the Swedish University of Agricultural Sciences and is currently Environmental Protection Officer with Norrbotten County. Sara.Elfvendahl@bd.lst.se
Acknowledgements: this work was supported by Sida/SAREC by scholarships and research funding to the University of Dar es Salaam and Swedish University of Agricultural Sciences. Management and personnel at NEMC and Börje Paulsson, Malin Ĺkerblom, Henk Bouwman, Sverker Molander, and Rosana Moraes are all acknowledged for the valuable co-operation and discussions.