Drinking-water toxic metals (India, BIS): What is the maximum desirable limit for mercury (Hg) in potable water supplied for human consumption, reported in mg/L?

Difficulty: Easy

Correct Answer: 0.001 mg/l

Explanation:


Introduction:
Mercury is a toxic heavy metal with severe neurological and developmental impacts, especially in methylmercury form. Strict limits in potable water reduce chronic exposure. Water standards specify low microgram-per-liter levels to protect public health and to guide treatment plant monitoring and corrective actions.


Given Data / Assumptions:

  • Concentration units: mg/L (milligrams per liter).
  • We seek the typical drinking-water limit used in Indian compliance contexts.
  • Values are selected to be protective across a broad population with consumption variability.


Concept / Approach:
The standard limit for mercury in drinking water is set at the microgram-per-liter scale. A widely recognized compliance value is 0.001 mg/L (which equals 1 μg/L). This threshold reflects achievable analytical detection, treatment capability, and health-based risk assessments.


Step-by-Step Solution:
Interpret units: 0.001 mg/L = 1 μg/L.Compare listed options to typical regulatory limits in potable water.Select 0.001 mg/L as the maximum allowable/desirable concentration.


Verification / Alternative check:
Public health guidance documents and water-quality manuals consistently specify mercury limits at or below 1 μg/L for treated drinking water, aligning with this numeric selection.


Why Other Options Are Wrong:

  • 0.05 or 0.1 mg/L: Orders of magnitude too high for drinking water.
  • 0.9 mg/L: Extremely high and unsafe.
  • 0.0001 mg/L: Stricter than the commonly enforced BIS limit; not the expected answer here.


Common Pitfalls:
Misreading mg/L versus μg/L; always convert correctly to interpret toxicity thresholds.


Final Answer:
0.001 mg/l

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