Publications

Improper pesticide application has resulted in high toxicity levels causing environmental risk. The objective of the study was to determine pesticide preferences and pattern of use in farms along the shore of Lake Naivasha. Interviewer administered questionnaires and researcher observation were used to collect data on pesticides being used and pattern of use in 20 major horticultural farms around Lake Naivasha. Secondary data from journals, standards and materials safety data sheets from manufacturers were also used to determine pesticide properties such as toxicity. The results showed there were 4.3% (6) WHO class I and 14.3% (20) class II pesticides of the 141 pesticides used along the shore of Lake Naivasha. The pattern of pesticide use in the area was moderate to high and all the farms were also using Integrated Pest Management (IPM) to control pests. It was concluded that some pesticides in WHO class I that were being used along the shore of Lake Naivasha (e.g. oxamyl, methomyl and fenamiphos) are very toxic to human beings and aquatic organisms since they cause cholinesterase inhibition poisoning by inactivating the enzyme acetylcholinesterase.

Keywords: Pesticides, Environmental pollution, integrated pest management, Lake Naivasha.

Nanowires made of materials with non-centrosymmetric crystal structures are expected to be ideal building blocks for self-powered nanodevices due to their piezoelectric properties, yet a controversial explanation of the effective operational mechanisms and size effects still delays their real exploitation. To solve this controversy, we propose a methodology based on DFT calculations of the response of nanostructures to external deformations that allows us to distinguish between the different (bulk and surface) contributions: we apply this scheme to evaluate the piezoelectric properties of ZnO [0001] nanowires, with a diameter up to 2.3 nm. Our results reveal that, while surface and confinement effects are negligible, effective strain energies, and thus the nanowire mechanical response, are dependent on size. Our unified approach allows for a proper definition of piezoelectric coefficients for nanostructures, and explains in a rigorous way the reason why nanowires are found to be more sensitive to mechanical deformation than the corresponding bulk material.