RELATIONSHIP BETWEEN NITRATES, PHOSPHATES IN WATER, IODINE LEVELS IN TABLE SALT AND GOITER OCCURENCE: A CASE STUDY OF NANDI HILLS, KENYA

Abstract

Nitrates and phosphates are among the major inorganic pollutants in the environment, primarily contributed by nitrogenous and phosphate fertilizers, organic manures, human and animal wastes, and industrial effluents through biochemical activities of microorganisms. Beside other known detrimental effects, research findings suggest that increased nitrate and/or phosphate intake affects the functioning of the thyroid gland in humans. In Kenya, goiter remains endemic despite iodization of table salt in households. Notably, the area around Nandi hills in Nandi County has recorded high incidences of goiter in the recent past. This indicates that factors such as inorganic ion content of water (among others) may have etiological role in endemic goiter cases in the region. This study sought to determine the etiological factors leading to observed high prevalence of goiter. This was achieved through determination of concentration of nitrate ions and phosphate ions in drinking water and urine. Three samples were collected; urine, table salt and drinking water (stream and borehole). Urine samples were analyzed to determine the concentration of nitrate ions, phosphate ions, and Iodate ions using cadmium reduction method, UV-visible spectrophotometry and Salifert Iodine pro test kits respectively. Iodate ions in table salt were quantified using the same kits. From the results obtained in the study, stream water recorded nitrate and phosphate concentrations of 2.91±0.74 and 0.30±0.08 mg/l respectively. In addition, there was a significant difference (P<0.05) in both nitrate and phosphate levels among the three sampling points in the three streams. However, there was no significant difference (P>0.05) in both nitrate and phosphate concentrations among the three streams used in the study. In borehole water, nitrate and phosphate levels were 1.69±0.79 and 0.29±0.07mg/l respectively. Both nitrate and phosphate levels in stream and borehole water were found to be within the WHO acceptable limits. On the other hand, nitrate and phosphate levels in urine samples were 0.53±0.30 and 709.59±5.57mg/l respectively. Iodine concentration in salt used by respondents in the study area ranged between 43.78±9.47 and 69.21±5.08 when titration and saltPADs methods were used respectively. Pearson Correlation results reported an insignificant positive association (P>0.05 ; r>0)between nitrate, phosphate and iodine ions and occurrence of goiter in the study. The study therefore concluded that concentrations of nitrate and phosphate ions in drinking water and iodine ions in table salt are not the main cause of goiter in the study area. This calls for additional studies to be carried out on other possible causes of goiter in the study area.