The 1,329 samples used in the analysis were split nearly evenly between systems that add fluoride (49%) and those that do not (51%) (Table 1). Post-treatment samples taken from fluoridated systems had a mean fluoride concentration of 0.53 mg/L (SD 0.13 mg/L) compared to 0.12 mg/L (SD 0.21 mg/L) in non-fluoridated systems. Arsenic concentrations in the water entering the drinking water treatment system (raw) did not differ significantly by fluoridation status. Arsenic concentrations did decrease after treatment for both fluoridated and non-fluoridated systems; however, the amount of decrease was less in fluoridated systems (0.17 μg/L, SD 0.30 μg/L) than in non-fluoridated systems (0.22 μg/L, SD 0.32 μg/L). With respect to treatment, 83% of fluoridated systems used coagulation, whereas only 67% of non-fluoridated systems used coagulation and 3% of fluoridated systems used ultrafiltration while 10% of non-fluoridated systems used ultrafiltration. Seven percent of fluoridated systems had ground water as a source in comparison to 28% of non-fluoridated systems.
Descriptive statistics of study variables by fluoridation status. n = 1,329
| Variable . | Number (percentage) or mean (standard deviation) . | ||
|---|---|---|---|
| Overall . | Fluoridated . | Non-fluoridated . | |
| Total sample | 1,329 (100%) | 653 (49%) | 676 (51%) |
| Mean raw arsenic (μg/L) | 0.67 (0.37) | 0.69 (0.39) | 0.66 (0.35) |
| Mean treated arsenic ** (μg/L) | 0.48 (0.31) | 0.51 (0.33) | 0.44 (0.28) |
| Mean treated-raw arsenic* (μg/L) | −0.20 (0.31) | −0.17 (0.30) | −0.22 (0.32) |
| Mean raw fluoride** (mg/L) | 0.11 (0.19)a | 0.07 (0.06)b | 0.14 (0.25)c |
| Mean treated fluoride** (mg/L) | 0.32 (0.27)a | 0.53 (0.13)b | 0.12 (0.21)c |
| Coagulation** | |||
| Yes | 994 (75%) | 543 (83%) | 451 (67%) |
| No | 335 (25%) | 110 (17%) | 225 (33%) |
| Ultrafiltration** | |||
| Yes | 86 (6%) | 19 (3%) | 67 (10%) |
| No | 1,243 (94%) | 634 (97%) | 609 (90%) |
| Microfiltration | |||
| Yes | 80 (6%) | 35 (5%) | 45 (7%) |
| No | 1,249 (94%) | 618 (95%) | 631 (93%) |
| Source water** | |||
| Ground | 236 (18%) | 47 (7%) | 189 (28%) |
| Surface | 1,093 (82%) | 606 (93%) | 487 (72%) |
| Variable . | Number (percentage) or mean (standard deviation) . | ||
|---|---|---|---|
| Overall . | Fluoridated . | Non-fluoridated . | |
| Total sample | 1,329 (100%) | 653 (49%) | 676 (51%) |
| Mean raw arsenic (μg/L) | 0.67 (0.37) | 0.69 (0.39) | 0.66 (0.35) |
| Mean treated arsenic ** (μg/L) | 0.48 (0.31) | 0.51 (0.33) | 0.44 (0.28) |
| Mean treated-raw arsenic* (μg/L) | −0.20 (0.31) | −0.17 (0.30) | −0.22 (0.32) |
| Mean raw fluoride** (mg/L) | 0.11 (0.19)a | 0.07 (0.06)b | 0.14 (0.25)c |
| Mean treated fluoride** (mg/L) | 0.32 (0.27)a | 0.53 (0.13)b | 0.12 (0.21)c |
| Coagulation** | |||
| Yes | 994 (75%) | 543 (83%) | 451 (67%) |
| No | 335 (25%) | 110 (17%) | 225 (33%) |
| Ultrafiltration** | |||
| Yes | 86 (6%) | 19 (3%) | 67 (10%) |
| No | 1,243 (94%) | 634 (97%) | 609 (90%) |
| Microfiltration | |||
| Yes | 80 (6%) | 35 (5%) | 45 (7%) |
| No | 1,249 (94%) | 618 (95%) | 631 (93%) |
| Source water** | |||
| Ground | 236 (18%) | 47 (7%) | 189 (28%) |
| Surface | 1,093 (82%) | 606 (93%) | 487 (72%) |
*P < 0.0.
**P < 0.001 significantly different in fluoridated and non-fluoridated systems based on t-test or chi-square.
aMissing 139 samples.
bMissing 72 samples.
cMissing 67 samples.