The condition for methemoglobinemia by drinking water is
(a) 50 ppm nitrate
(b) 50 ppm chloride

Q: What exactly is methemoglobinemia?

It is a blood disorder in which an abnormal amount of methemoglobin is produced. Hemoglobin is the protein in red blood cells that carries and distributes oxygen to the body. Methemoglobin cannot carry oxygen effectively, leading to a bluish tint to the skin, hence the name 'Blue baby syndrome'.

Q: Why does nitrate cause this?

When ingested, nitrate is converted to nitrite in the digestive system. Nitrite then reacts with hemoglobin to form methemoglobin, which cannot carry oxygen.

Q: What is ppm?

ppm stands for parts per million. It is a unit of concentration that expresses the mass of solute per one million parts of total mass. For dilute aqueous solutions, $1 \text{ ppm} = 1 \text{ mg/L}$.

Q: Are there other harmful ions in drinking water?

Yes, excess of fluoride, sulfate, lead, and other heavy metals can also cause severe health issues. For example, excess fluoride causes mottling of teeth, and excess lead damages the kidneys.

Q: How can we remove excess nitrate from drinking water?

Nitrate can be removed by processes like reverse osmosis, ion exchange, or distillation. Note that simply boiling water does NOT remove nitrate; in fact, it can concentrate it by evaporating the water.

Question

The condition for methemoglobinemia by drinking water is

Options:

(A) $> 50 	ext{ ppm}$ nitrate

(B) $> 50 	ext{ ppm}$ chloride

(C) $> 50 	ext{ ppm}$ lead

(D) $> 100 	ext{ ppm}$ sulphate

Sigma Percentile · Accepted Answer

### Understanding Methemoglobinemia

Have you ever heard of 'Blue baby syndrome'? It is a rather alarming condition, scientifically known as methemoglobinemia. This is a disease caused by an excess of certain specific ions in our drinking water.

When we drink water, we assume it is pure and life-giving. However, groundwater can often be contaminated with agricultural runoff, which brings us to the main culprit behind this condition.

### The Culprit: Nitrate Ions

According to the European Environment Commission (EEC), if the concentration of nitrate ions, $	ext{NO}_3^-$, in drinking water exceeds a certain limit, it can lead to this disease.

Imagine this: if the water we drink has excess nitrate, it enters our digestive system where it is converted into nitrite. This nitrite then reacts with the hemoglobin in our blood to form methemoglobin. Unlike normal hemoglobin, methemoglobin cannot carry oxygen effectively. This lack of oxygen gives the skin a bluish tint, which is why it is commonly called 'Blue baby syndrome' when it affects infants.

### The Threshold Limit

So, what is the safe limit? The threshold limit set by environmental agencies is $50 	ext{ ppm}$ (parts per million).

If the concentration of nitrate exceeds $50 	ext{ ppm}$, it becomes highly toxic. Not only does it cause blue baby syndrome, but prolonged exposure to such high levels of nitrate can also lead to severe complications like stomach cancer. This is a favorite factual concept for JEE, so it is crucial to commit this value to memory.

### Final Calculation

Looking at our options, the condition for methemoglobinemia is clearly an excess of nitrate. Therefore, the correct answer is **$> 50 	ext{ ppm}$ nitrate**.

### Beyond Nitrate: Other Pollutants

While nitrate is the focus of this question, it is equally important to remember the limits for other common water pollutants. For instance, excess fluoride ($> 10 	ext{ ppm}$) is harmful to bones and teeth, excess sulphate ($> 500 	ext{ ppm}$) can have a laxative effect, and excess lead ($> 50 	ext{ ppb}$) can damage the kidneys and liver. Make sure to revise these limits from your NCERT textbook!

Animated Solution for Chemistry - Environmental Chemistry: The condition for methemoglobinemia by drinking water is

Select Answer:

Visualized Solution

$Methemoglobinemia$

$Cause of the Disease$

$Threshold Limit$

$Conclusion$

$Other Pollutants$

The Sigma Insight: Water and Soil Pollution

Understanding Methemoglobinemia

The Culprit

The Threshold Limit

Final Calculation

Beyond Nitrate

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