Toxicity

Marked exposure to toxic trace elements may produce characteristic clinical sequelae. However, less severe exposure can produce non-specific effects which require biological monitoring for diagnosis. High exposure to lead, for example, produces renal tubular damage but lower exposure results in less obvious effects - fatigue, disturbed sleep, constipation, and effects on cognition and behaviour. Lead is the most carefully controlled trace element as a result of the Control of Lead at Work (CLAW) regulations which require that workers with potential exposure to lead are under medical surveillance including regular measurement of blood lead concentrations.

Significant exposure to other toxic trace elements may also warrant monitoring of workers, for example workers potentially exposed to arsenic compounds in glass making, electronics, and timber preservation.

Certain diets and some non-Western traditional medicines can also result in toxic trace element exposure. This is exemplified by two warnings by the Food Standards Agency: excessive consumption of predatory fish (shark, marlin, tuna, swordfish) because of possible mercury exposure; and potential lead exposure from Calabash chalk which is used to treat morning sickness particularly in African women.

Iatrogenic exposure to certain trace elements and vitamins is an uncommon but important cause of toxicity. The toxic effects of aluminium in haemodialysis patients are well known. Exposure to other toxic micronutrients (manganese, selenium, vitamin A and vitamin B6) may occur in patients on total parenteral nutrition or individuals who take regular mineral and vitamin supplements in high doses.