The nor-halimane diterpenoid tessmannic acid and its methyl, 2-methylisopropyl and 1-methylbutyl esters, the unusual isocoumarins 8-hydroxy-6-methoxy-3-pentylisocoumarin and 7-chloro-8-hydroxy-6-methoxy-3-pentylisocoumarin, and 5-pentyl-3-methoxy-N-butylaniline were isolated from the stem and root bark extracts of Tessmannia densiflora Harms (Caesalpiniaceae) that showed mosquito larvicidal activity. The structures were determined on interpretation of spectroscopic data. Tessmannic acid and its methyl ester exhibited antibacterial and antifungal activity. The compounds also caused high larvae and adult Anopheles gambiae mosquitoe mortality effects, and stronger mosquito repellency than that shown by the standard repellent DEET, hence indicating Tessmannia species to be potential sources of bioactive natural products.

This work presents the concentrations of five pesticide residues, lindane, chlorpyrifos, endosulfan, p, p'-DDE and p, p'-DDD in soil samples collected from tomato fields in Ngarenanyuki, Tanzania. Endosulfan sulphate was detected in 100 % of the sample analysed with mean concentration of 0.2407 mg/kg dw. Chlorpyrifos was detected in 87 % of the samples with mean concentration of 0.1253 mg/kg dw. p, p'-DDE and p, p'-DDD were detected in 46 and 40 % of the samples analysed with mean concentrations of 0.1482 and 0.154 mg/kg dw, respectively. Lindane was the least detected pesticide. It was detected in 5 (33 %) of soil samples analysed with mean concentration of 0.2126 mg/kg dw. Low concentrations detected indicate the past usage of the pesticides. @ JASEM

Pesticide residues lindane, chlorpyrifos and endosulfan sulphate were detected in water from the spring source, within field and return channel of vegetable farms in Ngarenanyuki, Tanzania. Extraction of the pesticide residues were conducted by liquid-liquid extraction (LLE) method. The detection and concentrations of pesticide residues were determined by gas chromatography equipped with electron capture detector (GC-ECD). The percentage detections in return channel and within field were observed to be 67 and 33 respectively whereas no pesticides were detected in the spring source. The average concentrations for lindane, chlorpyrifos and endosulfan sulphate within field and return channel were 3.0, 0.27 and 3.35, and 2.8, 0.06 and 3.13 mg/L, respectively. Absence of residues detection in spring source indicates that the source of pesticides in water from the field and return channel were the applications of pesticides in vegetable farms. This work, thus, seeks to provide information on levels of pesticide residues in water that will assist in a scientific assessment of the impact of pesticides application on public health and ecosystem in Tanzania.

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