Bathtub Refinishing seals off lead
The most dangerous bathtubs would be porcelain bathtubs made before 1984. However, even bathtubs manufactured today will still contain lead. White bathtubs are not as bad as a colored bathtub. A good rule of thumb is if the bathtub still looks glossy then the glaze is safely sealing the lead away. To be absolutely sure you can purchase a lead test kit from your local home improvement store and test the bathtub surface.