A natural or man-made chemical present in the environment does not always lead to human or animal exposure. Exposure requires contact by touching, breathing, ingesting or injecting substances which contain the chemical. Exposure itself is not necessarily harmful; several other factors determine whether contact leads to harmful effects and the type and severity of these effects (Anon. 1990). These factors include the dose (how much), the duration (how long), the timing (when in the life cycle), the route of exposure (injection, inhalation, ingestion, contact) and individual characteristics and lifestyles (sex, age, health, habits, fitness, genetic predisposition).
Populations that are unusually susceptible to toxic effects from silver are those with dietary deficiencies of vitamin E or selenium, or those with genetically-based deficiencies in the metabolism of these essential nutrients. Those populations with damaged livers and those exposed to very high selenium levels in their diet are also at higher risk. Some people may exhibit an allergic response to silver (Anon. 1991).