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Lead Water? DIY
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DIY SALTING OUT water test (1g K2CrO4, 25g NaNO3 /30cm water sample at 25 C) for lead in water is
a chemical test which involves the precipitation of lead(II) chromate solid. This DIY method provides a
user-friendly alternative of ICP-MS to test for trace amount of lead in water. The amount of lead(II) ion
presence is determined by the measurement of absorbance of yellow chromate ion left in the water samples
using a spectrometer at 460nm available in a secondary school. In Hong Kong, some water samples
contained lead(II) ion more than the safety limit set by WHO (>10mg or 10ppb/L) Eg. drinking water from
元禧樓 contained 19ppb lead and running water from 清河邨 contained 10ppb lead.
ICP-MS is one scientific instrument to measure trace amount of lead(II) ion in water (Thibodeau, 2013). No
DIY (Do it yourself) method are available in HK to test the trace amount of lead(II) in water.
In this project , we suggest to do the following.
(a)
Investigating the precipitation of different metal chromate including lead(II) ion and tin(II) ion ; and the
salting out effect of lead(II) chromate solid using different soluble salts (DIY SALTING OUT water test for
lead)
(b)
Obtaining a calibration curve using standard lead(II) ion solutions by measurement of the absorbance of
yellow chromate ion left after precipitation of lead(II) chromate using the DIY SALTING OUT water test
for lead using a spectrometer at 460nm
(c)
Determination of the effect on the conc. of lead(II) ion in water by lead-containing solder using the DIY
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Lead Water? DIY
SALTING OUT method
(d)
Determination of the concentration of lead(II) ion in different water samples using the DIY SALTING
OUT water test for lead
(e)
Comparing the results of leaded water prepared using solder DIY as welding material at a temperature
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higher than 450 C and drinking water from 元禧樓 and 清河邨 using the DIY SALTING OUT water test
for lead, ICP-MS in the University of Science and Technology and the commercially available water test
for lead “Watersafe”
Results
1.
Lead(II) nitrate formed yellow precipitate of PbCrO4 with alkaline potassium chromate but not tin ion or
other metal ions commonly found in water sample. Besides, absorbance at 460nm of yellow chromate ion
decreased significantly with conc. of lead(II) ion in water samples.
2.
Stagnant water from pipes welded with solder DIY was found to leak lead(II) ion at a fast rate. Water was
safe (10
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0.83
ppb/L) in the first 3 days only.
Stagnant water from pipes welded with commercial solder did not contain lead(II) ions in the first 24 days.
7.4
Afterwards 10
ppb/L of lead(II) ion was found.
Lead Water? DIY
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3. The results of water from 元禧樓 and running water from 清河邨 using the DIY SALTING OUT water test,
the commercially available water test for lead “Watersafe” and ICP-MS in the University of Science and
Technology were consistent.
Lead content in drinking water from 元禧樓: DIY salting out method 22.9ppb (error 10.8ppg), ICP-MS in
UST 30ppb, HKSAR 19ppb, “WaterSafe” water test >15ppb
Lead content in running water from 清河邨: DIY salting out method 2.2ppb (error 0.39ppb), ICP-MS in
UST <2.5ppb, HKSAR 10ppb, “WaterSafe” water test <15ppb