Which type of poison is characterized by the presence of "Mees lines" on nails?

Mees lines are transverse white lines that span the entire nail plate and are significant indicators of poisoning, particularly with arsenic. These lines occur as a result of systemic illness or toxic exposure, interrupting the normal growth of the nail matrix. The presence of Mees lines specifically highlights a history of arsenic exposure, as this toxin strongly affects keratin synthesis in the nail matrix, leading to the characteristic lines appearing several weeks after the exposure.

In contrast, the other substances listed do not typically produce Mees lines. Cyanide primarily causes cellular asphyxiation and does not have a recognizable effect on nail growth. Lead poisoning can lead to a range of symptoms, particularly affecting the nervous system and blood production, but Mees lines are not a notable consequence. Similarly, carbon monoxide affects oxygen transport in the blood, leading to symptoms like hypoxia, but it does not cause alterations in nail appearance like Mees lines do. Thus, arsenic is distinctly associated with this phenomenon.