On page iv of D70 and D200, or page xxii of D300 user manual, you will find the following:
Notice for customers in the State of California
WARNING: Handling the cord on this product may expose you to lead, a chemical known to the State of California to cause birth defects or other reproductive harm. Wash hands after handling.
Have you paid attention to this at all?
The existence of the label or warning on many products is the result of California “Proposition 65“, which basically requires all cords or cables that have surface contact layer with a lead content by weight of 0.03% (300 parts per million) or more come with a warning label, unless otherwise exempted. Usually, the lead is intentionally added to the plastic or rubber material used to cover the cord as a stabilizer and will have more than 300 ppm of lead by weight to be effective.
Similar warnings can also be found on the packaging of Nikon shutter release cable, TTL flash cord, etc. I am sure many similar products from other manufacturers have the same label. This is definitely not specific to Nikon products.
Although the warning is specifically addressed to customers in California, the potential danger exists on all product sold elsewhere. Better safe than sorry.