Environmental health: solar disinfection: practice question

A PSM question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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PSM · Environmental health: solar disinfection

Sample item

Solar disinfection (SODIS) of drinking water at household level involves:

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

B. Filling clear plastic bottles and exposing them to sunlight for about 6 hours

In SODIS, transparent PET bottles filled with clear water are placed in direct sunlight for at least 6 hours, and UV-A radiation and heat inactivate pathogens. Turbid water should be pre-filtered.

Option by option

  • A. Adding bleaching powder before exposure to sun

    Adding bleach is a different disinfection method.

  • B. Filling clear plastic bottles and exposing them to sunlight for about 6 hours (correct)

    Correct. Clear bottles in sunlight for about 6 hours.

  • C. Storing water in an opaque container in the shade

    Opaque containers in shade block the UV needed.

  • D. Boiling water in sunlight for 10 minutes

    Boiling is a separate method.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this PSM question

What is the answer to this PSM question?

The best answer is B, Filling clear plastic bottles and exposing them to sunlight for about 6 hours. In SODIS, transparent PET bottles filled with clear water are placed in direct sunlight for at least 6 hours, and UV-A radiation and heat inactivate pathogens.

Why is "Adding bleaching powder before exposure to sun" not the answer?

Adding bleach is a different disinfection method.

Why is "Storing water in an opaque container in the shade" not the answer?

Opaque containers in shade block the UV needed.

Why is "Boiling water in sunlight for 10 minutes" not the answer?

Boiling is a separate method.

What concept does this question test?

It tests Environmental health: solar disinfection in PSM. Turbid water should be pre-filtered.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Environmental health: solar disinfection?

Practise biostatistics with small calculations until sensitivity, predictive values and risk measures are automatic. Then use the flashcards and the other PSM questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.