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.