Levels of pesticide residues and metabolites in soil at Vikuge farm, Kibaha district, Tanzania – A classic case of soil contamination by obsolete pesticides

The paper reports on the state of soil contamination by obsolete pesticides at Vikuge State Farm, Coast Region, Tanzania, where, in 1986, a 170 m3 “donation” of partially expired pesticides were stored in an open shed that eventually collapsed. Analyses of soil samples collected in 2000 from the old storage site at the farm for 80 different pesticide residues and metabolites have revealed alarmingly high concentrations of pesticide residues to qualify Vikuge as one of the most contaminated sites in the world. Most of the residues found in the soil at high concentrations were organochlorines, their concentrations being up to 282,000 mg/kg dry weight for total DDT (28.2% by mass). Commercial formulations contain only between 5 and 10 % DDT. The concentrations of HCH were up to 63,360 mg/kg (6.4 % by dry mass). A herbicide, pendimethalin [N-(1-ethylpropyl)-2,6-dinitro-3,4-xylidine], was also found at concentrations up to 40,900 mg/kg dry weight (4% by mass). As expected, higher concentrations of the residues were found in the surface soil samples and the concentrations of the residues were decreased with increasing depth and distance from the point source. Immediate decontamination of this site is highly recommended. Tanzania Journal of Science Vol. 30 (2) 2004: pp. 77-8

Contamination of water and sediments by obsolete pesticides at Vikuge farm, Kibaha distric, Tanzania

Sediments and water from Vikuge State Farm, Coast Region, Tanzania, where, in 1986, a “donation” of 170 m3 of partially expired pesticides were stored in an open shed- which eventually collapsed, were analysed for 80 different pesticide residues and metabolites. DDT and HCH, two of the most persistent organochlorines pesticides, were the most dominant pesticides found in both matrices. In sediments the levels were up to 99,620 mg/kg dry weight of &#931DDT and up to 7,400 mg/kg dry weight of &#931HCH. The mean total HCH concentrations were 0.95 &#956g/l in tap water, 0.28 &#956g/l in surface water and 3.09 &#956g/l in ground water. Of the four common HCH isomers,&#945-HCH and &#946-HCH had the highest on average concentrations in the water. Mean total DDT concentrations were 1.76 &#956g/l in tap water, 0.18 &#956g/l in surface water and 9 &#956g/l in ground water. The only other pesticides detected were in sediments and water are azinphos-methyl, an organphosphorous insecticide and thiabendazol, a systemic fungicide, respectively. During the rainy season, the well-water, which is used for domestic purposes by the villagers, has levels of pesticides higher than those allowed by WHO for drinking water. It is thus recommended that immediate decontamination measures be undertaken. In the meantime, villagers should sediment the well-water and should not use not use it at all during the rainy seasons.. Tanzania Journal of Science Vol. 30 (2) 2004: pp. 21-3

Use of indigenous knowledge in the management of field and storage pests around Lake Victoria basin in Tanzania

Agriculture in Lake Victoria basin (LVB) in Tanzania is predominantly subsistence and is characterised by perennial food deficits, cyclic famines and poverty prompted largely by unreliable rainfall patterns, declining soil fertility and food grains pests and diseases. The pest problem is more pronounced as farmers are yet to fully integrate synthetic pesticides into their insect pest management systems due to subsistence nature of production and high poverty levels that make them rely on indigenous knowledge (IK) systems to meet their needs. The survey was conducted to document farmers’ IK on management of key field and storage insect pests in Magu and Misungwi districts in the LVB, Tanzania. Major crops grown were maize, rice, sorghum, finger millet, bean, groundnut, cowpea, green gram, brassicas, chicken pea, cassava, sweet potato, cotton and vegetables. Crops were mainly infested by Busseola fusca (Lepidoptera: Noctuidae), Spodoptera spp (Lepidoptera: Noctuidae), Agrotis spp (Lepidoptera: Noctuidae), Maruca vitrata (Lepidoptera: Crambidae), Rhopalosiphum maidis (Homoptera: Aphididae), Aphis fabae (Hemiptera: Aphididae), and grasshoppers in field and Stophilus spp (Coleoptera: Curculionidae), Prostephanus truncates (Coleoptera: Bostrichidae), Tribolium spp (Coleoptera: Tenebrionidae), Bruchus rufimanus (Coleoptera; Bruchidae), Rhyzopertha dominica (Coleoptera: Bostrichidae) and rodents on storage. IK based control methods used by farmers ranged from animal by-products (cow’s urine and dung), plant parts (Azadirachta indica (Meliaceae),Tephrosia vogelii (Fabaceae), Tamarindus indica (Fabaceae), Aloe spp (Asphodelaceae), red pepper, Capsicum spp (Solanaceae), Nicotiana tabasum (Solanaceae) to ash (general and specific) in the field. They also used neem, Chenopodium opulifolium (Chenopodiaceae), Ocimum suave (Labiatae), Senna siamea (Fabaceae or Caesalpinioideae), tobacco and Eucalyptus spp (Myrtaceae) and plant by-products (rice husks, ash from rice husks and red maize cobs and general ash) to control storage pests. Most of these products were used together with one or two others in different formulation mixtures. However, the formulations had variable amount taken during preparation, crop/ crop product treated, preparation times, modes and rates of application. Research is needed to unveil the amount for mixing, appropriate treatment, and application rate to ensure optimum concentration for specific pest. To ensure quality and safety, biosafety and quality studies are required for quality assessment of resulting product for human health. For understanding of active compounds in the formulations, chemical composition analysis of properly prepared solutions is required. Key words: Field and storage pests, indigenous knowledge, Tanzania, botanical formulation, Lake Victoria basin

Oral acute toxicity study of selected botanical pesticide plants used by subsistence farmers around the Lake Victoria Basin

A survey carried out around the Lake Victoria region showed evidence that people around this region use plant extracts, parts and powders to protect stored food commodities from insect pests. The widely used plants were identified and selected for biosafety assessments namely: Ocimum gratissimum, Tithonia diversifolia, Eucalyptus saligna, Eucalyptus globulus and Cupressus lusitanica. Wistar mice were acclimatized and divided into groups of six. Each mice group was administered with one extract at different concentrations. The extracts were administered orally and the animals were observed for 24 h. A control group was kept which received only the carrier substance orally. The LD50 values were determined by the use of the graphical method and regression analysis. Oral acute toxicity studies established the LD50 values for essential oils of O. gratissimum, E. saligna and C. lusitanica as 4.570, 2.290, and 3.311 mg/kg, respectively. For ethanol extracts, LD50 values were 12.882, 12.302, 14.996 and 11.481 mg/kg for O. gratissimum, E. globulus, C. lusitanica and T. diversifolia, respectively. For the aqueous extracts, the LD50 of T. diversifolia was found to be 12.302 mg/kg. For E. globulus and C. lusitanica, their aqueous LD50s were beyond 15.000 mg/kg. The oral acute toxicity tests showed weak toxicities for all the plant extracts investigated in the study. The low toxicity levels exhibited by these extracts may be the reason why these plant products have been used by local communities for long without adverse effects. Chronic studies should be carried out to assess whether these extracts have serious effects on experimental animals exposed to them at small doses for a long period of time.Key words: Oral acute toxicity, biopesticide, plant extracts, Lake Victoria Basin

Larvicidal, antimicrobial and brine shrimp activities of extracts from Cissampelos mucronata and Tephrosia villosa from coast region, Tanzania

<p>Abstract</p> <p>Background</p> <p>The leaves and roots of <it>Cissampelos mucronata </it>A. Rich (Menispermaceae) are widely used in the tropics and subtropics to manage various ailments such as gastro-intestinal complaints, menstrual problems, venereal diseases and malaria. In the Coast region, Tanzania, roots are used to treat wounds due to extraction of jigger. Leaves of <it>Tephrosia villosa </it>(L) Pers (Leguminosae) are reported to be used in the treatment of diabetes mellitus in India. In this study, extracts from the roots and aerial parts of <it>C. mucronata </it>and extracts from leaves, fruits, twigs and roots of <it>T. villosa </it>were evaluated for larvicidal activity, brine shrimps toxicity and antimicrobial activity.</p> <p>Methods</p> <p>Powdered materials from <it>C. mucronata </it>were extracted sequentially by dichloromethane followed by ethanol while materials from <it>T.villosa </it>were extracted by ethanol only. The extracts obtained were evaluated for larvicidal activity using <it>Culex quinquefasciatus </it>Say larvae, cytotoxicity using brine shrimp larvae and antimicrobial activity using bacteria and fungi.</p> <p>Results</p> <p>Extracts from aerial parts of <it>C. Mucronata </it>exhibited antibacterial activity against <it>Staphylococcus aureus</it>, <it>Escherichia coli</it>, <it>Pseudomonas aeruginosa</it>, <it>Salmonella typhi</it>, <it>Vibrio cholera</it>, <it>Bacillus anthracis</it>, <it>Streptococcus faecalis </it>and antifungal activity against <it>Candida albicans </it>and <it>Cryptococcus neoformans</it>. They exhibited very low toxicity to brine shrimps and had no larvicidal activity. The root extracts exhibited good larvicidal activity but weak antimicrobial activity. The root dichloromethane extracts from <it>C. mucronata </it>was found to be more toxic with an LC₅₀value of 59.608 μg/mL while ethanolic extracts from root were not toxic with LC₅₀>100 μg/mL). Ethanol extracts from fruits and roots of <it>T. villosa </it>were found to be very toxic with LC₅₀values of 9.690 μg/mL and 4.511 μg/mL, respectively, while, ethanol extracts from leaves and twigs of <it>T. villosa </it>were found to be non toxic (LC₅₀>100 μg/mL).</p> <p>Conclusion</p> <p>These results support the use of <it>C. mucronata </it>in traditional medicine for treatment of wounds. Extracts of <it>C. mucronata </it>have potential to yield active antimicrobial and larvicidal compounds. The high brine shrimp toxicity of <it>T. villosa </it>corroborates with literature reports that the plant is toxic to both livestock and fish. The results further suggest that <it>T. villosa </it>extracts have potential to yield larvicidal and possibly cytotoxic compounds. Further studies to investigate the bioactive compounds responsible for the observed biological effects are suggested.</p