In a public water supply, what is the maximum permissible concentration (Threshold Limit Value, TLV) of DDT in drinking water, expressed in micrograms per litre (μg/L)?

Introduction / Context:
DDT is a persistent organochlorine pesticide with well-known environmental persistence and bioaccumulation. Drinking water standards assign very low allowable limits to protect human health. This question checks whether you recall the order of magnitude of the limit and can distinguish it from unrealistic high values.

Given Data / Assumptions:

• Parameter: DDT concentration in drinking water.
• Unit: micrograms per litre (μg/L).
• Context: public water supply compliance limit.

Concept / Approach:
Guideline and regulatory limits for persistent pesticides in drinking water are typically in the low microgram per litre range or lower. Values like tens, hundreds, or thousands of μg/L would be far above health-protective limits for DDT.

Step-by-Step Solution:

Verification / Alternative check:
Public-health guidance places DDT limits at very low levels to minimize chronic exposure risk, aligning with the lowest option provided in the set.

Why Other Options Are Wrong:
42 μg/L: Far too high for a persistent pesticide limit.
332 μg/L: Orders of magnitude higher than typical guidelines.
1050 μg/L: Not credible for potable water standards.

Common Pitfalls:
Misreading μg/L as mg/L; assuming legacy pesticides have lenient limits; forgetting that bioaccumulative chemicals are regulated stringently.

Final Answer:
2 μg/L