Pesticide guideline in drinking water The threshold limit value (TLV) / guideline value for aldrin in a public water supply is approximately how many micrograms per litre (μg/L)?

Introduction / Context:
Aldrin is an organochlorine pesticide with high persistence and toxicity. For public health, guideline values for drinking water are set at extremely low concentrations. Engineers and operators must be familiar with the order of magnitude of these limits to select appropriate monitoring and treatment approaches (e.g., granular activated carbon, advanced oxidation, or source protection).

Given Data / Assumptions:

• We are considering a typical exam-style threshold for public supply water.
• Units are in micrograms per litre (μg/L), equivalent to parts per billion (ppb) in water.
• Aldrin is grouped with dieldrin in many guidelines at very low allowable levels.

Concept / Approach:
Because aldrin is bioaccumulative and toxic, guideline values are set in the sub-ppb to low-ppb range. Among the options presented, 0.5 μg/L matches the expected magnitude for a stringent potable water limit, whereas higher values (tens to thousands of μg/L) would not be protective. This selection reflects conservative health-based standards commonly cited in regulatory and design references for organochlorines.

Step-by-Step Solution:

Verification / Alternative check:
Public health documents and historical standards list aldrin/dieldrin limits in the sub-microgram per litre range; treatment plants often target nondetect levels to ensure safety.

Why Other Options Are Wrong:

• 17, 357, 1097 μg/L: Orders of magnitude too high for a toxic, persistent pesticide in potable water.
• 50 μg/L: Still far above conservative health-based guidelines.

Common Pitfalls:
Mixing up micrograms per litre with milligrams per litre; 0.5 mg/L equals 500 μg/L and would be dangerously high.

Final Answer:
0.5