Actually, all nutrients are toxic if too much is ingested; how much is too much depends on the nutrient. For essential minerals like copper, there is a definite gradation for health; if the intake is below the requirement, illness due to deficiency will develop; as the intake goes up, health will improve until a plateau is reached, where small increases in intake will not make any difference to health; above the top safe level (the end of the plateau), increases in intake will cause toxic illness. In extreme cases, both deficiency at one end and toxicity at the other end of the spectrum may get so severe as to cause death. This pattern is seen for all nutrients, including, for example, vitamins, macro-minerals, and protein.
Some will cause debilitating disease. A classic example is vanadium which can cause manic depression.
The third category of nonessential trace minerals is everything else: all the other minerals that are present in the body but are not essential in the diet and are not thought to have any function, and that do not cause any concern over toxicity or deficiency. In practice, virtually everything is essential.
Biting your nails becomes addictive because of the reward process. You're probably deficient in minerals.
(published with permission in writing from:http://www.mybodylanguage.co.uk)
