Question

What is the concentration above which sulphate causes laxative effect?
A) $500\text{ ppm}$
B) $500\text{ ppb}$
C) $100\text{ ppm}$
D) $100\text{ ppb}$

Answer 1

The concentration of any cation or anion in water has a fixed value as set out by the Bureau of Indian Standards or BIS, beyond which if the cation or anion is present in drinking water then it is considered to be unfit for drinking.

Complete step by step solution:
Sulphates may have laxative effects causing dehydration and diarrhoea, mainly in infants, at concentration above $\text{250 ppb}$ and as a safety measure, water with sulphate concentration above $\text{400 ppb}$ are considered to be unfit for making baby food. But with time people get acclimatized to the sulphur and hence the symptoms disappear.

So, the correct answer is option B, i.e. $500\text{ ppb}$.

Note:
There are three treatment methods by which sulphate can be removed from drinking water: reverse osmosis, distillation, and ion exchange. Reverse Osmosis is a treatment method in which most of the dissolved elements and chemicals are removed from water by pushing the water through a plastic surface known as the semi-permeable membrane. It can eliminate upto 99% sulphate from water.
Distillation is the method of boiling water and then the steam is cooled and condensed in a separate container. The dissolved substances remain in the pot where the water was boiled and hence pure water is obtained.
Lastly, the ion-exchange method is the most known method of eliminating huge quantities of sulphate from water for public, livestock requirements and commercial supplies. In this process there are resins fitted in the columns that attach the sulphate ions releasing any other similar sized non-toxic ions in return.