To obtain more nail masses, participants should be asked in advance not to trim their nails for a couple of weeks or longer. Nails are collected by clipping with a stainless steel clipper from the two great toes (or thumbs) and small toes (or other fingers). Instruction need to be given to the participants to obtain as much nail as possible and clippings should be from both feet and / or hands. The nail clippings from the great toes or thumbs and the rest of the toes or fingers are better to be stored separately since the time frame represented by the great toe or thumb is different from the rest of the toenails or fingers. These nail samples can be placed in a labeled envelope and stored at room temperature in the driest condition possible in a pre-designated area until the samples can be analyzed in the future. Participants can cut their nails at clinic or at home and then mail their sample in. No need to remove nail polish when collect nails samples.
Since trace elements levels in nails reflect both dietary and non-dietary exposure and the concentrations may be affected by a number of factors, it is useful to design a nail questionnaire to obtain relevant information on nail polish, medication on nails, and the frequency of using stainless steel cooking wares as well as wearing socks and shoes. Particularly, participants should be asked how often they have had polish on the nails. If the color of the polish is silver, gold, copper or bronze, the participant should record the polish whether or not she or he knows for certain that it contains a metal. As for using of medication on the nails, the use of foot powder, whether medicated or not, may not be recorded as it will not affect the nail samples. All this information collected may be useful for adjustment for potential confounders in the data analysis.