N. O. Hashim

Estimation of annual effective dose due to radon and thoron concentrations in mud dwellings of Mrima Hill, Kenya

This study presents radon and thoron concentration measurements and the corresponding effective dose rates in mud dwellings located in the high background radiation area of Mrima Hill, Kenya. Discriminative technique was used for simultaneous measurement of radon and thoron. The effective dose was evaluated based on the concentration of the isotopes and the time spent indoors. Radon concentration ranged from 16 to 56 Bq m(-3) with an average of 35±14 Bq m(-3) and a corresponding annual effective dose of 0.67 mSv y(-1), while that of thoron ranged from 132 to 1295 Bq m(-3) with an average of 652±397 Bq m(-3) and an effective dose of 13.7 mSv y(-1).

Analysis of internal exposure associated with consumption of crops and groundwater from the high background radiation area of Mrima hill, Kenya

Specific concentrations of (226)Ra, (232)Th and (40)K were measured in cassava tubers, cassava leaves and groundwater obtained from the high background radiation area of Mrima hill and used in the evaluation of the ingested dose. Cassava tubers, cassava leaves and groundwater registered average (226)Ra concentrations of 60 ± 5, 141 ± 11 and 4.3 ± 0.3 Bq kg(-1), respectively. (232)Th was not detected in cassava leaves although it was present in cassava tubers as well as in groundwater in average concentrations of 35.3±61.5 and 2.0±0.1 Bq kg(-1), respectively. (40)K was present in all samples in average concentrations of 842±539 Bq kg(-1) in cassava tubers, 1708 ± 552 Bq kg(-1) in cassava leaves and 91.4 Bq kg(-1) in groundwater. The total annual effective dose due to ingestion was found to be 7.9 mSv y(-1) of which 2.4 mSv y(-1) was due to cassava tubers, 3.8 mSv y(-1) due to cassava leaves and 1.7 mSv y(-1) due to water.

Lead contamination of traditional hand-dug wells in parts of Kwale County, Kenya

Summary statistics of the samples analyzed. Parameter pH EC (µs/cm) Pb conc. (mg/L) Minimum value 5.8 85.3 BDL Maximum value 10.4 6060 1.395 Mean 9.18 930.35 0.33 WHO reference value - - 0.1 Samples exceeding WHO reference level 62.16% Table 3. Range mean and standard deviation values for Pb concentrations for each village. Village Range (mg/L) Mean Pb conc. (mg/l) STDEV (mg/L) Kanana-Shimoni BDL - 0.458 0.139 0.172 Munje BDL - 1.146 0.409 0.406 Ramisi BDL - 1.397 0.302 0.486 Shirazi 0.015 - 0.889 0.500 0.348 Table 4. Percentage of samples with Pb levels above WHO reference level. Village No. of samples Samples above WHO ref. level % above WHO ref. level Kanana-Shimoni 8 5 62.50 Munje 9 6 66.67 Ramisi 13 5 38.46 Shirazi 7 7 100.00 and 6060 µs/cm with a mean value of 930.35 µs/cm. The high conductivity could be due to sea water intrusion bearing in mind the region’s proximity to the Indian Ocean. Two of the wells with the highest conductivity (5770 and 6060 µs/cm) had extremely salty water and although the local residents did not use it for drinking, they used it for other domestic purposes like cleaning and cooking. Out of the 37 wells studied, 12 were covered while 25 were open. The mean Pb concentration in the closed wells was 0.229 mg/L with a standard deviation of 0.342 mg/L while that of closed wells was 0.378 mg/L with a standard deviation of 0.417 mg/L. A bigger proportion of contamination was observed in the open wells (68%) as compared to the closed wells (50%). The higher concentration of Pb in the open wells may be due to siltation. Table 3 shows the range, mean and standard deviation values of Pb in samples from each village while Table 4 looks at the number of wells sampled per village and the percentage of sampled wells with Pb levels above the WHO reference level. Samples from Kanana-Shimoni Village had the lowest mean value of Pb at 0.1 mg/L while those from Shirazi Village had the highest at 0.5 mg/L. Munje and Ramisi Villages had wells with mean Pb concentrations of 0.409 and 0.302 mg/L respectively. Despite registering the lowest mean Pb value, 62.5% of the sampled wells in Kanana-Shimoni Village were Pb contaminated which implies that lead bearing soils are more or less distributed throughout the village. 66.67% of the sampled wells in Munje Village and all the sampled wells in Shirazi Village had Pb levels above WHO action value. Ramisi Village had the least proportion of contaminated sampled wells at 38.46%. Ramisi Village is a settlement center of sorts unlike the other villages which are farmlands in which dwellings and consequently water wells are relatively far between. From information gathered from the villagers, underground streams are alleged to flow in Ramisi Village and this may explain the low percentage of wells that are Pb-contaminated. No prior study is carried out a site before a well is dug and consequently not all wells coincide with points of good water. Again, being a settlement center, the human population in Ramisi Village is high and therefore there exists a likelihood of well contamination resulting from improper disposal of human waste as well as from minor activities such as paint jobs and bicycle repair works. This may explain the high levels of Pb in some of the wells in the village.

EDXRF analysis of lead and other toxic trace elements in soil samples along two major highways of Kenya

Adjacent lands along most major highways of Kenya are left as open spaces, or used for small scale farming and grazing of cattle and livestock. Some grass and plants are expected to have high levels of lead and other toxic metals. So far, no study has been carried out to determine the concentrations of toxic metals in soil samples along Thika and Mombasa highways of Kenya. This work is important and essential to the study of the impact of pollution on health and the environment.