Entry Routes
Exposure to lead and lead chemicals can occur through ingestion, inhalation, dermal absorption, and trans-placental (endogenous) routes.
The two primary entry routes into the body for lead are ingestion (eating) and inhalation (breathing). Lead (except for certain organic lead compounds not covered by the standard, such as tetraethyl lead) is not absorbed through your skin. When lead is scattered in the air as a dust, fume or mist it can be inhaled and absorbed through your lungs and upper respiratory tract. Inhalation of airborne lead is generally the most important source of occupational lead absorption. You can also absorb lead through your digestive system if you handle contaminated items or handle them with hands contaminated with lead.
Exposure routes:
Lead exposure in the general population (including children) occurs primarily through ingestion, making it the route that most commonly leads to elevated BLLs. This includes swallowing a foreign body containing lead (i.e., jewelry, etc.).
From 20% to 70% of ingested lead is absorbed into the body, (with children generally absorbing a higher percentage than adults).
- Lead paint is the major source of higher lead level exposures in children in the United States. As higher lead content paint:
- Deteriorates,
- Peels,
- Chips,
- Is removed (e.g., during renovation),
- Or crumbles due to friction (e.g., in windowsills, steps, and doors), house dust and surrounding soil may become contaminated. Lead then enters the body through normal hand-to-mouth activity.
- Ingestion of contaminated
- Food,
- Water, or
- Alcohol may be significant for some populations. In addition, ingesting certain traditional, folk or home remedy medicines may expose people to lead or lead compounds.
- When fine particulate lead is inhaled, it can be absorbed directly through the lungs or could also be carried by the mucociliary tree to the throat where it can be swallowed and absorbed via the GI system.
Inhalation is the second major pathway of exposure for the general population in the United States. The amount absorbed from the respiratory system depends on particle size, respiratory volume, amount of deposition, and the mucociliary clearance of the inhaled lead.
- Almost all inhaled lead is absorbed into the body (with children generally absorbing a higher percentage than adults, as they have a higher respiratory frequency).
- Since leaded gasoline additives were phased out beginning in the 1970s and control measures were implemented in industries to reduce air emissions, inhalation from these sources is no longer the major exposure pathway to lead for the general population in the United States.
- Leaded gasoline is still used in only a handful of countries, but the resulting emissions pose a major public health threat.
- Inhalation may be the primary route of exposure for some workers in industries that involve lead.
- Inhalation may be the primary route of exposure for adults involved in home renovation activities, and hobbies like lead glass making, stained glass making/soldering.
- Lead is a component of tobacco and tobacco smoke, and smokers have higher blood lead levels (BLLs) than do nonsmokers.
- Second hand smoke may contribute to increased BLLs in U.S. children. Lead dust concentrations, usually ingested during hand to mouth activity, do not appear to mediate this association, suggesting inhalation of second hand smoke is a major pathway of exposure.
- Eliminating second hand smoke exposure may reduce lead exposure in children.
Dermal exposure plays a role for exposure to organic lead among workers, but is not considered a significant pathway for the general population.
- Organic lead may be absorbed directly through the skin.
- Organic lead (tetraethyl lead) is more likely to be absorbed through the skin than inorganic lead.
- Dermal exposure is most likely among people who work with lead or materials that contain lead.
Endogenous exposure to lead may contribute significantly to an individual's current BLL. Numerous reports document lead poisoning resulting from retained bullet or shrapnel fragments; thus, a history of military or other penetrating trauma may be important. If in a pregnant woman, this poses a particular risk to the developing fetus. Trans-placental exposure to the unborn child can happen if the mother is exposed to lead.
- Once absorbed into the body, lead may be stored for long periods in mineralizing tissue (e.g., teeth and bones).
- The stored lead may be released again into the bloodstream, especially in times of calcium stress (e.g., pregnancy, lactation, osteoporosis) or calcium deficiency.
Acute and Chronic Exposure
There is no sharp dividing line between rapidly developing acute effects of lead, and chronic effects which take longer to acquire. Lead adversely affects numerous body systems, and causes forms of health impairment and disease which arise after periods of exposure as short as a few days or as long as several years.
Acute, short-term overexposure: Lead is a potent, systemic poison that serves no known useful function once absorbed by your body. Taken in unusually large doses, lead can kill you in a matter of days.
Chronic, long-term overexposure: Prolonged exposure can result in significant harm to your blood-forming, nervous, urinary, and reproductive systems.
Knowledge Check Choose the best answer for the question.
1-6. Lead can cause health impairment and disease after periods of exposure as short as a few _____.
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