Trace element analysis of pollen, honey and bee tissue by energy dispersive X-ray fluorescence (EDXRF) and total reflection x-ray fluorescience (TXRF) techniques
Wamwangi, Muturi Daniel
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Energy dispersive x-ray fluorescence spectroscopy (EDXRF) is a proven technique for trace element analysis. The analytical technique is fast non-destructive and enables simultaneous determination of many elements with high sensitivity. In this work, EDXRF technique used utilised a radioisotope source109 C d (T 1/2 =453 days) for the sample excitation. The spectrometer as calibrated for quantitative analysis of environmental, biological and geological samples after optimization of the following: the pulse shaping time constant and the pole zero (P/Z) cancellation of the spectroscopy amplifier. Other parameters which were determined prior to calibration for quantiative analysis included the dead layer thickness of the Si(Li) detector. This was from measurements of spectral intensity ratios of the K lines for sulphur (S), potassium (K), Chlorine (CL) and chromium (Cr) of thick pellets of analar compounds KCI, K2 SO4 and K2 CrO4. The dead layer was determined to be 0.28μm. Pollen, honey and its products constitute environmental samples. They were collected from selected areas in Kenya-Kibwezi, Kitui, and Nyeri because they are major sources of honey production in the country. Samples of pollen and bee tissue were prepared in pellet form of about 0.05g/cm2, while honey samples were analyzed directly without any prior preparation. Honey samples from industialized countries-Australia and U.K were also analysed and the results compared to local samples. Spectral data analysis was done using the following software: QXAS and AXIL while Canberra S100 was used for data acquisition. Significant differences in the results of analysis of the pollen, bee tissue and honey is shown for samples from these areas. Results indicate that rubidium (Rb) and strontium (Sr) ratios vary from 2.69 to 4.39 for Nyeri and 0.36 to 0.99, for Kitui and Kibwezi areas respectively. In addition, the correlation matrices of the trace elements in these samples has been presented. Results of lead (Pb) levels are high in pollen; bee tissue and honey samples collected near major highways (37ug/g). The levels of iron (Fe), (8-15) μg/g, copper (Cu), (8-10) μg/g and zinc (Zn), (4-12) μg/g are in refined honey samples from Kenya, Australia and U.K and are essential to human health. Arsenic (As) levels in some samples from Nyeri are (2-9) μg/g and are possibly from fungicides, insecticides and pesticides used for agriculture purposes. Calcium (Ca), iron (Fe), copper (Cu), Zinc, Bromine (Br) and strontium (Sr) are identified as the main constituent elements in the raw honey samples from Nyeri, Kitui and Kibwezi. Iron (Fe), copper (Cu) and Zinc (Zn) levels are reportedly lower in refined honey samples by a factor of two than in the honey samples from the same region. In addition, high iron (Fe) values (20-30) μg/g and (2773-4090) μg/g are reported in all the bee tissue samples than in the pollen and honey samples from the corresponding are. Iron (Fe) values represent the highest concentration levels in pollen and bee tissue samples from all areas in the range (108-600μg/g) and (57-4090μg/g) respectively. Similar trends in the variations of strontium (Sr), bromine (Br), copper (Cu), rubidium (Rb) and manganese (Mn) are reported in all the bee tissue samples from Nyeri, Kibwezi and Kitui areas. High correlation (r=0.964) between pollen and honey samples are reported for the following elements; iron (Fe), copper (Cu), Zinc (Zn), bromine (Br), rubidium (Rb) and strontium (Sr) for samples from Nyeri. In addition, the colour of honey has been found to correlate with the levels of trace elements in some samples from Kibwezi. High levels of trace elements in all the samples from Nyeri than those from Kibwezi and Kitui could be due to the geology of Nyeri which is characterised by volcanic soils compared to that of Kibwezi and Kitui which are regions of metamorphic rocks. The accuracy of the analytic results has been verified by analysing some of these samples using TXRF for which concentration values are in close agreement for most with the exception of copper (Cu) and bromine (Br). High copper (Cu) values could be attributed to the contamination while low bromine (Br) values are obtained because it evaporates during samples digestion.