Shem O. Wandiga

Termites: A Potentially Large Source of Atmospheric Methane, Carbon Dioxide, and Molecular Hydrogen

Termites may emit large quantities of methane, carbon dioxide, and molecular hydrogen into the atmosphere. Global annual emissions calculated from laboratory measurements could reach 1.5 x 1014 grams of methane and 5 x 1016 grams of carbon dioxide. As much as 2 x 1014 grams of molecular hydrogen may also be produced. Field measurements of methane emissions from two termite nests in Guatemala corroborated the laboratory results. The largest emissions should occur in tropical areas disturbed by human activities.

Mitigation of environmental problems in Lake Victoria, East Africa: causal chain and policy options analyses

Abstract Lake Victoria is an international waterbody that offers the riparian communities a large number of extremely important environmental services. Over the past three decades or so, the lake has come under increasing and considerable pressure from a variety of interlinked human activities such as overfishing, species introductions, industrial pollution, eutrophication, and sedimentation. In this paper we examine the root causes for overfishing and pollution in Lake Victoria and give possible policy options that can help remediate or mitigate the environmental degradation.

Use and distribution of organochlorine pesticides. The future in Africa

Pesticides have been used in the continent for about eight decades. Major use has been in agriculture, livestock development, and disease vectors control. Recent international conventions have been made with little scientific data and information on the tropical situation. Rapid development of resistance to pesticides demands better scientific understanding of pest management. Tropical research data on organochlorine pesticides show rapid degradation pattern, low residue levels, and widespread distribution. Given the above, there is a need to factor into consideration tropical climatological calamities in any future pesticide policy. Continued use of pesticides is anticipated in the tropics.

Biofuel availability and domestic use patterns in Kenya.

Abstract The annual domestic consumption levels and patterns of various common biofuels in Kenya were surveyed. The main fuelwood sources were farmland trees, indigenous forests, woodlands and timber off-cuts from plantations. In 1997, about 15.4 million tonnes of firewood (air-dried) were consumed and an equivalent of 17.1 million tonnes round wood wet weight (w/w) was converted to charcoal. In the same year, 1.4 million tonnes of a variety of crop residues were also consumed as domestic fuel. Biofuel availability was the major factor influencing the reported annual spatial species use and consumption patterns. Competing demand for the commonly-used tree species (mainly eucalyptus trees) for commercial and other purposes accounts, to a large extent, for the reported dwindling amounts. Communities in various regions have responded by gradually shifting to other available types including those in gazetted forests. Such a response strategy has implications on the long-term spatial and temporal biofuel use patterns.

Distribution of Cr, Pb, Cd, Zn, Fe and Mn in Lake Victoria sediments, east Africa.

The presence of many metals at trace or ultra-trace levels in the human environment has received increased global attention. Sediments as a sink for pollutants are widely recognized pollution sources and diagenesis and biochemical transformations within the sediment may mobilize pollutants posing a threat to a wider biological community. The natural (background) concentrations of heavy metals in lake sediments can be estimated either by analysis of surface sediments in non-polluted regions or by analysis of core samples antedating modern pollution. The distribution pattern of heavy metals in tropical freshwater systems has been little studied. The authors found increased concentrations of lead and other trace metals in Lake Victoria. Thus this study was initiated in order to further investigate the distribution patterns of lead and other metals in Lake Victoria.

Environmental assessment of the East African Rift Valley lakes

An assessment of the East African Rift Valley lakes was initiated by the United Nations Environment Programme (UNEP) with funding from Global Environment Facility as part of the Global International Waters Assessment (GIWA). The purpose of GIWA was to produce globally comparable assessments and examine stresses on international waters: marine, coastal and fresh; surface and groundwaters. The assessment of the East African Rift Valley lakes was undertaken from the perspective of water quality and quantity, associated biodiversity and habitats, their use by society and societal causes of the regionally identified issues and problems. Assuming intrinsic values of aquatic ecosystems, the assessment of social perspective focused on human use of water and considered the incremental costs of measures to encourage sustainable development. The assessment identified the major concerns facing the East African Rift Valley lakes.By and large, pollution and unsustainable exploitation of fisheries and other living resources emerged as critical concerns attributable to human activities. East Africa has a very high concentration of humans and economic activities. Pollution is from uncontrolled discharge of wastes directly into the lakes. Unsustainable exploitation of fisheries and other living resources is caused by over-fishing, destructive fishing practices, and introduction of non-native species that affect the composition of the native communities, resulting sometimes in the collapse of certain species and dominance by resilient ones. Loss of biodiversity also was identified as a major concern; and the issues of excessive by-catch and discards are also relevant. Trawling using undersized mesh-nets for target species and indiscriminate fishing gear or poison is serious, in most cases resulting in indiscriminate catches, including juvenile fish. Given the transboundary nature of the issues identified in this assessment, appropriate multilateral policy and institutional arrangements need to be established in East Africa to address the main concerns of these large lakes. Riparian countries must pay attention to the regional management of these transboundary water bodies, and appropriate planning of human population sizes and their settlement, land-use and waste disposal to control pollution. Although East African lakes contribute relatively little emission of greenhouse gases, there is a need to reduce the rate of deforestation and even restore cleared areas since forests serve as sinks of greenhouse gases towards mitigating adverse climatic changes.

The major environmental factors that influence rapid disappearance of pesticides from tropical soils in Kenya

Results of field and laboratory studies on adsorption/desorption, leaching, dissipation, bound residue formation and metabolism of DDT, DDE, lindane, parathion, malathion, dimethoate and carbofuran in tropical soils in various regions in Kenya are summarized in this paper. Based on reported half‐lives of dissipation in temperate soils, DDT, DDE and lindane were found to dissipate much more rapidly in tropical soil conditions with half‐lives of dissipation of 64.5–245.6, 145 and 5–8 days, respectively. Carbofuran (t 1/2 = 66–115.5 days), malathion (t 1/2 = 36.7–770 days), parathion (t 1/2 = 48days) and dimethoate (t 1/2 = 72 days) were also less persistent. The major environmental factors, wind, rainfall, solar radiation intensity and soil moisture content that contributed to this rapid disappearance are presented, explaining also the influence of important soil characteristics such as pH, % organic carbon, texture and microbial activity on pesticide distribution and degradation in soil.

Lead contamination in street soils of Nairobi City and Mombasa Island, Kenya.

The advent of modern industrialization and, in particular, the motor vehicle has witnessed dramatic increases in lead usage both as a component of lead-acid storage battery and from 1923 as organic lead alkyl anti-knock additive in petroleum. Several workers have established a correlation between increasing lead concentration in roadside soils and vehicular traffic density. Although researchers studied the heavy metal content in Lake Victoria sediments, no urban roadside soils were investigated. Since lead is used as a petrol additive in Kenya, it is necessary to document the extent and magnitude of lead contamination of roadside soils in inland and coastal urban environments and evaluate its environmental implications.

The effect of boiling on the removal of persistent malathion residues from stored grains

Abstract This study aimed at finding the fate of malathion in maize grains and beans stored in a tropical laboratory for 12 months at temperatures of 20–24°C, relative humidity of 42–80% and grain moisture contents of 11.7–12.5% in maize grains and 14.1–15.3% in beans. Malathion and its degradation products malaoxon, malathion α-monocarboxylic acid and β-monocarboxylic acid were found in stored maize grains and beans treated with a mixture of pure radiolabelled malathion and 2% malathion dust after 12 months of storage. A significant percentage of these residues were removed from the grains by cooking in boiling water. Though malathion and its polar metabolites, malathion α- and malathion β-monocarboxylic acids were completely eliminated by boiling, malaoxon was still detected in quite high quantities in the solvent extracts of cooked beans and maize. Addition of NaCl to the grains increased the rate of removal of the residues from both maize grains and beans by boiling water. The data obtained clearly showed a distinction in persistence, distribution and metabolism of malathion between the two types of crop, indicating also that more adverse windy, humid and hot tropical conditions contributed to higher rates of metabolism and loss of the pesticide from the grains. The accuracy and ease of using radiolabelled malathion in investigating its fate and behaviour in the two matrices is shown in this study.

The distribution of organochlorine pesticides in marine samples along the Indian Ocean coast of Kenya.

The concentrations of organochlorine residues of lindane, aldrin, ∝- endosulfan, dieldrin, endrin, p,p′-DDE, p,p′-DDD and p,p′-DDT in samples of seawater, sediment, fish and seaweed from different locations along the coast of Kenya are discussed in relation to the geographical location of the sampling sites and potential sources of residue over a period of two years. All sediment samples were found to contain very low levels of organic carbon except those sampled from Sabaki River that had high (4.7%) organic carbon due to greater primary activity. Most of the pesticides residues (112 samples analysed in 1997 and 258 analysed in 1998/99) were detected in fish, water, sediments and seaweed. The concentration of some residues was higher during the wet season than the dry season in 1997, but no marked seasonal variation was observed in 1998/99. Lindane, aldrin, p,p′-DDT and p,p′-DDE were the most frequently observed residues in all samples while ∝-endosulfan, dieldrin, p,p′-DDD and endrin were either present in low concentrations or absent in most samples. Water samples had the lowest concentrations of residues (range 0.503 - 9.025 ng g−1). Sediments had the second highest levels of pesticides residues with a range of 0.584 - 59.00 ng g−1 while fish lipid content had the highest levels of residues in 1989/99 with p,p′-DDT concentration of 1011 ng g−1 and 418 ng g−1 p,p′-DDD in Siganus rivulatus.