- When handling old books, neurotoxic agents such as mercury and lead are often present in the form of dust particles that accumulate over time.
- The most common route of exposure to these toxic substances is inhalation of dust particles.
- This occurs because dust containing lead or mercury can become airborne during handling, and once inhaled, these particles can enter the bloodstream through the lungs, leading to neurotoxic effects.

- While dermal absorption, ingestion from contaminated hands, and direct mucosal contact are possible routes of exposure, they are generally less significant in this context.
- The skin acts as a relatively effective barrier against many heavy metals, and ingestion typically requires hand-to-mouth contact after handling contaminated materials.

Therefore, to minimize risk, it is important to handle old books in a well-ventilated area and consider protective measures such as wearing masks or gloves.

Key points:
- Most common route: inhalation of dust particles
- Toxic substances present in dust on old books
- Skin absorption and ingestion are less common routes
- Preventive measures include good ventilation and protective equipment

Reference: Goldfrank's Toxicologic Emergencies, 11th Edition, Chapter 29 / Page 987