Assessment of Zn, Cu, Pb and Ni Contamination in Wetland Soils and Plants in the Lake Victoria Basin
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Int. J. Environ. Sci. Tech., 5 (1), 65-74, Winter 2008 ISSN: 1735-1472 G. Nabulo, et al. © IRSEN, CEERS, IAU Assessment of Zn, Cu, Pb and Ni contamination in wetland soils and plants in the Lake Victoria basin 1*G. Nabulo, 2H. Oryem Origa, 3G. W. Nasinyama, 4D. Cole 1The University of Nottingham, Plant Science Division, Sutton Bonington Campus, Loughborough, Leicestershire, LE12 5RD, United Kingdom 2Makerere University, Department of Botany, P.O. Box 7062, Kampala, Uganda 3Makerere University Graduate School, P.O. Box 7062, Kampala, Uganda 4Department of Public Health Sciences, Health Sciences Building, 155 College Street, Toronto, Ontario M5T 3M7 Received 14 September 2007; revised 8 October 2007; accepted 15 November 2007 ABSTRACT: The impact of waste disposal on trace metal contamination was investigated in eleven wetlands in the Lake Victoria Basin. Samples of soil, water and plants were analysed for total Zn, Cu, Pb and Ni concentrations using flame atomic absorption spectrophotometry. The trace metal concentrations in soil were the highest in Katanga wetland with the highest mean concentrations of 387.5±86.5 mg/kg Zn, 171.5±36.2 mg/kg Pb, 51.20±6.69 mg/kg Cu and 21.33±2.23 mg/kg Ni compared to the lowest levels observed at Butabika (30.7±3.2 mg/kg Zn, 15.3±1.7 mg/kg Pb, 12.77±1.35 mg/kg Cu and 6.97±1.49 mg/kg Ni). Katanga receives waste from multiple industrial sources including a major referral city hospital while Butabika is a former solid waste dumpsite. Wetland soil near a copper smelter had a Cu concentration of 5936.3±56.2 mg/kg. Trace metal concentrations in industrial effluents were above international limits for irrigation water with the highest concentrations of 357,000 µg/L Cu and 1480 µg/L Zn at a Cu smelter and 5600 µg/L Pb at a battery assembling facility compared to the lowest of 50 µg/L Cu and 50 µg/L Zn in water discharged from Wakaliga dumpsite. Uptake of trace metals from soil differed from plant to plant and site to site. Higher levels of trace metals accumulated in the root rather than in the rhizome and the least amount was in the leaf. The study identifies industry as a potential source of trace metal contamination of water and the environment pent-up need for policy intervention in industrial waste management . Key words: Environment, industry, public health, risk assessment, trace metals, waste management INTRODUCTION Lake Victoria is a multi functional resource shared degradation of the wetlands and the quality of Lake between Uganda, Kenya and Tanzania. The lake is Victoria through uncontrolled human activity, waste currently undergoing severe degradation resulting dumping from industry and settlements in and around from waste disposal in the surrounding wetlands in the wetlands. It is estimated that a half of the world’s the region. Wetlands are a potential source of population now lives in towns or cities and many are livelihood for the surrounding communities in the lake already facing severe problems of food and nutrition region providing a wealth of ecological, social and insecurity and over 54% of the African population will economic functions (Mafabi, et al., 1998; Namakambo, be living in urban areas by the year 2025 (UNCHS, 2000 and Swallow, et al., 2001) to the countries in the 1998). In Kampala city, due to rapid urbanization and region. Industries impacting on the wetlands of the growing urban unemployment, people are utilising Lake Victoria basin are concentrated in Kampala and hazardous places unsuitable for development to grow Jinja (Muwanga and Barifaijo, 2006). Kampala is one of crops. Such places include road verges, banks of the developing cities of the world undergoing rapid drainage channels, wetlands and contaminated sites urbanization. This has resulted into densely populated such as scrap yards and dumpsites for solid and liquid settlements in the lake region. High population increase wastes. The poorest groups involved in urban and rapid industrialisation have contributed to the agriculture are most likely to utilise high-risk sites *Corresponding Author Email: [email protected] whose toxic history is unknown (Maxwell, 1994; Sawio, Tel.:+44 115 951 6377; Fax: +44 115 951 6334 1998). Hardoy and Satterwaite, (1997) observed a direct G. Nabulo, et al. correlation between the level of poverty and the degree the Lake Victoria region is therefore of urgent need to of vulnerability to health hazards. Wetlands around control and monitor environmental degradation and the city are subject to waste disposal from industry, functioning of the dying Lake. This study seeks to municipality, mining and domestic sources. This poses assess the impact of industry on trace metal a health risk on urban communities growing and contamination of the Lake Victoria basin. consuming food crops and vegetables grown in the wetlands. The hazards of wastewater and solid waste MATERIALS AND METHODS use in urban and peri-urban agriculture (UPA) have The study was carried out in wetlands around the been categorized into three groups: biological agents, Kampala city and Jinja districts; these are the most chemical and physical hazards (Cole, et al., 2003). industrialized areas in the Lake Victoria region in Biological agents include bacteria, helianthus, viruses, Uganda. The Kampala city is situated between 32ºE protozoa and micro-fauna. While physical hazards and 33º E and between 0ºN and 1ºN (Atlas of Uganda, include sharp objects, psychosocial discrimination, 1967). Kampala, as a city district, is divided into five insecurity and land tenure. Chemical contamination is administrative divisions of Nakawa, Makindye, Rubaga, a potential risk associated with waste reuse, notably in Kawempe and Central covering approx. 189 km2 of land municipal solid waste and wastewater, especially if it is (Fig. 1). The district has a resident population of of industrial origin. Chemical hazards include chemical 1,208,544 persons with a population density of 7378 agents such as heavy metals, nutrients such as persons per km2. (UBOS, 2003). The study sites nitrogenous compounds, phosphorus compounds, included Banda, Kinawataka, Busega, Namuwongo, minerals, insecticides, pesticides, fertilizers, fungicides, Munyonyo, Bukasa, Murchison Bay, Butabika, herbicides and organic hazards. The contamination of Katanga, Kyebando, the industrial area in Bugolobi, soils by chemicals, the potential uptake by crops, and Wakaliga and Bwaise. These sites were selected the possible chronic and long-term toxic effects in considering that they are subject to either industrial humans are discussed by Chang, et al., (1995) and Birley waste discharge, municipal, sewage, toxic waste and Lock, (1999). Plant uptake of heavy metals depends disposal and wastewater irrigation activities taking significantly on the metal as well as soil conditions, place. Soil and water samples were collected from each such as acidity and organic matter content. Similar metal one of the six plots measuring 25 m2 randomly selected, amounts in different soils can be harmful in one and using a 5 m x 5 m quadrant. The plots were located 20 m harmless in another. Metals in municipal waste come apart along a line transect cut across the wetland. Soil from a variety of sources. Batteries, consumer samples were collected from a depth of 20 cm at various electronics, ceramics, electric light bulbs, house dust locations in each quadrant to form a composite sample and paint chips, used motor oils, plastics and some using a soil auger. The soils were placed in polythene inks and glass can all introduce metal contaminants bags, stored in cooled boxes and transported to the into the solid waste stream. Several studies have research laboratory in the Department of Botany at indicated that crops grown on heavy metal Makerere University. Water samples were taken from contaminated soils have higher concentrations of the same locations as soil. Six replicate water samples heavy metals than those grown on uncontaminated were collected in sample bottles from pits dug along soil (Dowdy and Larson, 1975; Nabulo, 2006). with soil auger 30 cm deep from each of the six Wastewater containing industrial effluents poses an quadrants. The samples were transported to the additional problem of chemical pollutants such as research laboratory and filtered through a 0.2 µm filter. heavy metals (Cornish, et al., 1999). Vegetables take The water samples were acidified to a pH<2 using up heavy metals from absorbing them by contaminated concentrated HNO3. Effluents from various industries soils as well as deposits on parts of the vegetables were also sampled at the point source before their exposed to air in polluted environment. It is observed discharge into the wetlands. Plants of different species that the priority public health risks associated with growing at each quadrant were all collected from wastewater use in low income developing countries various locations within each quadrant. Where several are infections with soil transmitted Helminths such as plants of the same species existed in one quadrant, hookworm and roundworm (Shuval, et al., 1986). The three plants were randomly selected and combined to study of trace metal contamination in wetlands around form a composite sample for each plot. The plant 66 Int. J. Environ. Sci.G. Tech.,Nabulo, 5 (1), et al.65-74, Winter 2008 450000 460000 Komamboga Mpererwe Kawempe Kawe mpe 4 0 0 0 0 40000 Kyebando Bukoto Katanga Banda Central Kampala Kmawataka Rubaga Butabka Busega Bukasa Namuwong Makindye Murchis on bay 3 0 Najjanankumbi 0 0 Lake victoria 0 30000 0 1 Wetland sites Munyonyo River Road Railway Administrative boundary Division boundary Kampala District boundary Land cover/use types Built-up area Wetland Open water 450000 460000 Fig. 1: Distribution of wetlands and selected solid waste dumping sites in Kampala city samples were packed in polythene bags and transported determine the total nitrogen by converting organic and in cool boxes to the research laboratory.