Demography of the CKDu patients
Age of CKDu patients in Thunukkai Division ranged between 30 and 70 years old. Among the studied patients 24 were under 50-70 years, representing 63% of the total sample (table 1). CKDu was more prevalent among males as the M: F ratio was 4:1. Among them 90% were engaged in agriculture related occupation while the rest were laborers, drivers, or unemployed people.
According to the questionnaire data, alcohol consumption and smoking were identified as disease modifying habits where more than 20% engaged in either smoking or taking alcohol while another 20% involved in both.
Clinical characters among selected patients showed other noncommunicable diseases, such as hypertension (43% prevalence) and diabetes (17% prevalence) with 17% suffering from both the diseases. The disease history of the patients revealed that they were detected with hypertension and diabetics secondarily, only after they developed CKDu. Furthermore, a spotty pigmentation, which was similar to arsenic related keratosis was observed in the palms of three male patients of the study group.
Physicochemical characters of the drinking water
Dug wells and tube wells serve as the major source of drinking water in the study area. Thus, drinking water samples from 31 dug wells and 4 tube wells were collected and analysed for the physicochemical parameters. The results of the analyses were given in the table 2.0. Among the parameters, salinity, TDS and total hardness showed highest deviations with more than 50% of the samples exceeding the relevant values of the Sri Lankan standards, SLS 614:2013 for drinking water (Figure 2.0). Salinity ranged between 0.13-3.66 ppt with an average of 0.69 ppt (standard error of mean, SEM= 0.118), with 50% of the samples exceeding the standard value of 0.5 ppt (Figure 2a). Similarly, in 63% of the samples, TDS content exceeded the standard (400ppm) reporting an average value of 686.63 ppm (SEM= 115) and reaching a maximum of 3570ppm (Figure 2b). Total hardness of the samples ranged between 39.84 -683.26 ppm (SEM= 24.9) with 65% of the samples exceeding the standard (250ppm, Figure 2c).
Among other parameters, turbidity, fluoride, chloride, calcium and As contents showed higher deviations from the SLS 614:2013, with more than 20% samples exceeding the respective limits. Mean turbidity of the drinking water samples was 2.3 NTU (Nephelometric Turbidity Unit) (SEM= 0.745) reporting a range of 0.3-26.5 NTU, all exceeding the mean turbidity of control samples. 10 water samples (29%) exceeded the standard turbidity level (2NTU-SLS 614:2013).
Fluoride content averaged 1.73 ppm (0.1-22.3 ppm) (SEM= 0.693), with 39% samples exceeding the standard of 1ppm. Similarly, chloride content of 31% of the water samples exceeded the standard value of 250 ppm reporting an average of 367.27 ppm (6.95 -2066.53 ppm) (SEM=87.0). Calcium averaged 64.074 ppm (3.98- 193.22ppm) (SEM=7.3) with 21% of the samples reporting higher values than the standard value (100 mg/l) for calcium in drinking water. Even though, detected only in nine samples As content exceeded the standard value (0.01 mg/l) reaching as high as 0.03 ppm in some water samples.
Water quality parameters such as pH, electric conductivity, nitrate, phosphate and magnesium contents showed no substantial deviations, with only 10% of the samples exceeding the SLS 614:2013. pH was 8.18 on the average (SEM=0.07), ranging between 7.45 - 9.12. Only six samples reported more than 8.5 whereas no water sample reported pH below 6.5. The mean value of electrical conductivity was 1416.31μs/cm (SEM=216), with the values ranging from 330μs/cm - 6690μs/cm. 17% of the samples exceeded the standard (750μs/cm). Nitrate content of the samples averaged 28.13 mg/l, (SEM=9.01), with values ranging from 0-295 mg/l. Only 15% of the water samples contained higher nitrate levels than the standard value, 50 mg/l. The mean phosphate content was 0.84 ppm (0.06 -4.8 ppm) (SEM=0.109) with 10 % of the samples exceeding the desirable level. Magnesium content reported a mean value of 30.19ppm with 18% of samples reported beyond the standard value.
All the other physicochemical parameters including, Na, K, sulphate contents and alkalinity reported lower levels compared to their respective SL standards. Cadmium was not detected in any of the water samples collected from the sampling area.
According to the data gathered through the questionnaire, the serum creatinine levels of CKDu patients of Thunukkai ranged between 1.31-5.32 mg/dl, reporting an average of 1.906 ±0.845 (SEM= 0.143) mg/dl. Serum creatinine of the control samples reported an average, of 0.7 ±0.0557 mg/dl (SEM= 0.0321), as illustrated in figure 3, showing a significantly low value (t=8.24, p=0.0001).
Correlation between water quality parameters and CKDu patients
The effect of physicochemical characters of water on the occurrence of CKDu was evaluated by applying the linear regression model, where serum creatinine concentration was treated as the response variable while water quality parameters (nitrate, fluoride, phosphate, etc.) were treated as the explanatory variables. Results were given in the table 3.0 below.
R2 value of 0.5109 suggests, that six explanatory variables; fluoride, phosphate, TDS, total hardness and arsenic, together account for about 51.09% of variation in the serum creatine concentration of the CKDu patients. Among these physicochemical parameters, TDS and As showed significantly positive correlation (p<0.05) with the creatinine levels while phosphate showed significantly negative correlation (p<0.001, Figure 4). On the other hand, nitrates in the drinking water showed no influence on serum creatinine of the CKDu patients in Thunukkai.
Geophysical distribution of total hardness level, TDS, nitrate, fluoride, phosphate and arsenic in the drinking water of the study area are illustrated in figure 5 & 6. Analysis of the spatial distribution data of the patients indicated that seven sampling points recorded creatinine levels over 2mg/dl in the order of, A12> A9> A4>A1>A13>B13>A2. When these locations are overlapped on the geophysical maps distinct interrelations were identified in TDS, As and phosphate with the creatinine levels (Figure 5), showing the same trend observed in the regression analysis. Higher serum creatinine levels, over 2.5 mg/dl were appeared to be linked with higher total dissolved solids contents 650.9-1516 ppm (Figure 5a) and higher arsenic contents 0.0016-0.0297 ppm (Figure 5b) and low phosphate contents, 0.789-0.904 ppm (Figure 5c). Conversely, the spatial distribution of nitrate, fluoride and total hardness contents showed no direct influence on serum creatinine levels in the study samples (Figure 6 a, b & c).