Mottled Teeth in Nagaur: Ranking Three Sources and Checking a 50:50 Blend
A primary health centre in Nagaur district reports that 27 of 180 schoolchildren have mottled brown enamel on their permanent teeth, and four adults complain of spinal stiffness and joint pain. Three drinking-water sources are tested. Source A, a 90 m tube well: fluoride 3.2 mg/L, TDS 2,400 mg/L, nitrate 62 mg/L, hardness 780 mg/L. Source B, a 30 m hand pump: fluoride 1.1 mg/L, TDS 1,900 mg/L, nitrate 148 mg/L, hardness 640 mg/L. Source C, a seasonal tank fed by a canal: fluoride 0.4 mg/L, TDS 520 mg/L, nitrate 8 mg/L, hardness 260 mg/L, turbidity 12 NTU in the monsoon. The village has no RO plant. The sarpanch wants Source A sealed immediately. The junior engineer proposes blending A with C, 50:50, and calls that 'fully solved'.
1. Interpret the clinical picture and rank the three sources for potable use, naming the specific limit each one breaches.
Read the worked answer
Clinical reading. Symmetrical brown mottling of permanent enamel in children plus spinal stiffness and joint pain in adults is the classic dental fluorosis plus skeletal fluorosis presentation. It is chronic, cumulative and irreversible; sealing a source today does not treat the adults already affected.
Standards (BIS 10500:2012)
- Fluoride: 1.0 mg/L desirable, 1.5 mg/L permissible where no alternative exists.
- Nitrate: 45 mg/L.
- TDS: 500 desirable, 2,000 permissible. Hardness: 300 desirable, 600 permissible.
Ranking
- Source C - usable, with treatment. Fluoride 0.4, nitrate 8, TDS 520, hardness 260: all within limits. The only defect is monsoon turbidity (12 NTU) - a disinfection and filtration problem, not a chemical one. Boil-water advice must be paired with the caution that boiling concentrates fluoride and nitrate.
- Source B - unfit as it stands. Fluoride 1.1 is acceptable, but nitrate 148 mg/L is over three times the limit, indicating sewage or fertiliser ingress into a shallow 30 m aquifer. Exclude until the source is protected and re-tested; nitrate causes methaemoglobinaemia in infants.
- Source A - unfit. Fluoride 3.2 is more than double the permissible limit; TDS 2,400 and hardness 780 also exceed permissible limits, and nitrate 62 exceeds 45.
So the sarpanch is right about A's chemistry but wrong to think sealing it is free - it is the highest-yield source.
2. Evaluate the engineer's 50:50 blend of A and C. Compute the maximum safe proportion of A, propose a workable blend, and say what must be planned for the dry season.
Read the worked answer
The 50:50 blend fails. Fluoride = (0.5 × 3.2) + (0.5 × 0.4) = 1.6 + 0.2 = 1.8 mg/L, above the 1.5 permissible limit - and directly against a population already showing skeletal fluorosis, the target should be the 1.0 mg/L desirable level, not the maximum.
Maximum safe fraction of A (let x be the fraction of A) 3.2x + 0.4(1 − x) ≤ 1.5 → 2.8x ≤ 1.1 → x ≤ 0.393.
A practical 35:65 blend
- Fluoride = 0.35 × 3.2 + 0.65 × 0.4 = 1.12 + 0.26 = 1.38 mg/L (acceptable; still not ideal).
- TDS = 840 + 338 = 1,178 mg/L - within permissible.
- Nitrate = 21.7 + 5.2 = 26.9 mg/L - within 45.
- Hardness = 273 + 169 = 442 mg/L - within 600.
So blending works, but only at a ratio the engineer did not propose, and only with continuous fluoride testing at the delivery point, because the blend ratio drifts with tank level.
Dry-season plan. Source C is canal-fed and seasonal; in May–June the village reverts entirely to A and the exposure returns. Plan now: rainwater storage sized to the dry months, a community defluoridation unit (activated alumina or Nalgonda alum-lime, which also reduces hardness), and an alternative source investigation. Do not simply seal A - that removes water the village cannot replace.
3. Design the surveillance and communication response for the next twelve months, and state what must NOT be told to the community.
Read the worked answer
Surveillance
- Screen all children under 12 in the village, not only the 180 at the school; record Dean's fluorosis index scores so that a baseline exists.
- Test urine fluoride in a sample of children and adults; a spot value adds biological confirmation that water data alone cannot give.
- Refer the four adults with spinal stiffness for radiological assessment; skeletal fluorosis needs a clinical, not a water-testing, diagnosis.
- Retest all three sources quarterly, including bacteriological testing of B, and add turbidity and free residual chlorine checks on C after treatment.
- Check dietary calcium and iron status, since poor nutrition worsens fluorosis severity at the same intake.
Communication
- Tell the community which source to drink from and which to avoid, in Hindi and local idiom, with the numbers behind the decision.
- Tell them blending is supervised at the tank, not something each household can improvise - household mixing is uncontrolled and unsafe.
Must NOT be said
- That mottled teeth will 'clear' - dental fluorosis is permanent.
- That boiling makes the water safe - it concentrates both fluoride and nitrate.
- That sealing Source A has solved the problem - the seasonal dependence on A and the nitrate problem in B remain.