My stainless steel kitchen sink arrived with the P65 warning for Nickel and Chromium. Will these chemicals leach into the water over time? Are they present on the surface? Can they be absorbed in my hands as I use the sink?
Simply wondering if there is a safer sink available without the P65 warning. Thanks!
Tongue in cheek: Your stainless steel sink is only dangerous if you live in California. Consider moving, and take the sink with you.
California passed proposition 65 which makes manufacturers liable for failure to include such notice, regardless of the level of low risk substances, so manufacturers put the notice on everything. As this NY Times article suggests, the notice has become a noisy alarm.
Chromium-free stainless steel is as common as unicorns producing rainbow ice-cream. Chromium, nickel and many other elements are common alloying elements to alter properties of the steel. They do "leave" the material, but under such conditions like welding, exposure to strong oxidizers, high-temperature exposures and such. Your sink is absolutely safe to be used as usual - you don't wash your plates in aqua regia (HCl+HNO3), do you?
Stainless steel contains chromium as a key element for its stainlessness. When the oxygen reacts on the surface it reacts with chromium first and form chromium oxide layer, which is chemically stable and dense enough to prevent further oxygen penetration into the steel.
Using chromated goods is similarly safe and the protection works a similar way with the difference that the chromium atoms do not need to diffuse to the surface.
The big difference here is the production. When alloying the steel with chromium the pure metal is added to the alloy prior to casting. The process is dangerous and the danger ends there. Chromating, on the other hand, is done usually by electrolysis of highly toxic chromium salts. If properly cleaned, the product is safe. The production line is not.
You can put P65 warning on almost anything, because there is 99% chance it contains carbon and nitrogen, and those elements form a cyanide group, which is substantial part of very strong poisons...
For stainless steel, as long as you are not conducting (pun) electrochemistry in your sink, the same applies: Given that your sensitivity is high enough, you will find these elements present in the water, but not in quantities that need concern.
Robert Johnson's answer correctly outlines that P65 has caused manufacturers to use the warning legally defensively when the science doesn't actually warrant it. Since none of the answers here explain the situation with chromium toxicity, I thought I'd supplement given how often one comes across chromium and stainless steel in construction. Every element has a different reactivity depending on its charge and participation in a broader molecular structure the later being measurable through bioavailability.
From the WP on chromium toxicity:
Chromium toxicity refers to any poisonous toxic effect in an organism or cell that results from exposure to specific forms of chromium—especially hexavalent chromium.1 Hexavalent chromium and its compounds are toxic when inhaled or ingested. Trivalent chromium is a trace mineral that is essential to human nutrition.
I would be more concerned about the water coming out of the tap than the P65 on the sink. Water deemed safe is often very borderline, or even toxic. My tap water not only tastes like a public swimming pool, but leaves black water marks, and was changing from blue tinted to yellowish last year... I don't know what's in it, but I filter it before use!