Toxicity and The Risks of Environmental Lead Exposure
Lead is a naturally occurring element and does not break down. This means that lead will change chemically over time which influences its exposure but it will still be recognizable as lead. Lead used hundreds of years ago is still potentially available as a toxic chemical. Current regulations published by the USEPA are not eliminating all of the potential exposures to lead. Lead waste piles from mines and smelters dating back to the late 1800’s have been found to still present a lead exposure hazard. Lead-containing water service lines can be found in large older cities and water passing through the lines can present hazards to residents. Lead is still present in air from open combustion. Lead-based paint although now eliminated from use still has presents problems, especially for young children. Renovation work for remediation of lead-based paint must be done using the regulatory requirements of the EPA otherwise residential exposure to lead dust can result. Lead can be present in foods. All of these sources contribute to the total body burden.
According to ATSDR Toxicological Profile for Lead, this profile outlines where the lead was taken into the body will migrate. The most common measurement of body lead is blood lead. Lead inside the body is dynamic, and, if the person (child or adult) has been exposed to lead from any source, it will be present in the blood of that person. However, blood is not the principal storage medium for the lead. It is just the carrier between storage and removal. In round numbers for adults, about 90% of the lead absorbed is stored in bones and teeth. For children, about 74% is retained, primarily in the bones.
The retention time of lead within the person varies by age. The overarching concern is the time and concentrations of lead found in each compartment. For example, lead can replace calcium in developing bones. Extended exposures can lead to medical issues related to bone density, but not only in children. Adults, primarily female, can develop osteoporosis later in life as a result of elevated body lead coupled with aging.
The USEPA in June 2013 published the Integrated Science Assessment (ISA) of Lead. This document outlined the chemical, physical and toxicological characteristics of lead. Significantly, the authors examined the extent of the data and applied it to toxic effects associated with lead exposure and ranked the likelihood of exposure to the effect. Presented below are some of the reported critical findings of health effects either caused or likely caused by lead exposure to children and adults.
Children – Causal: Nervous System Effects including Cognitive Function Decrements and Externalizing Behaviors (attention decrements, impulsivity, and hyperactivity). Likely Causal: Externalizing Behaviors: Conduct Disorders in Children and Young Adults, Internalizing Behaviors (depression and anxiety), Auditory Function Decrements, and Motor Function Decrements.
Adults – Causal: Hypertension, Coronary Heart Disease, Decreased Red Blood Cell (RBC) Survival and Function, Development (delayed pubertal onset for girls and boys), and Male Reproductive Function. Likely Causal Nervous System Effects: Cognitive Function Decrements (executive function, visuospatial skills, learning and memory in adults >50 years), Psychopathological Effects (depression and anxiety), and Cancer (strong evidence for long-term exposure and high concentrations of Pb inducing tumor development).
Assessing the risks from the exposure is different in children than in adults. Much of the literature recognizes the sensitivity of children to lead exposure is greater than in adults. However, while children are more sensitive to lower levels of exposure than adults, as noted in the list above, can have serious health effects from continuing exposure to lead.
For children, the most significant exposures generally come from residences contaminated with lead-based paint. While lead-based paint has been eliminated from the lines of commerce since the early 1980’s, lead can still be found in residences built before the ban on the sale of lead paint for house paint. Both EPA and HUD have published estimates of the percentage of structures contaminated with lead-based paint. Generally speaking, residential structures in older cities have the higher percentages, but any house built before the ban and phase out can have lead-based paint and this paint will degrade to release small particles of lead into the interior of the structure.
In adults, most exposure will come from occupational or hobby-based exposure. While OSHA has promulgated safety rules for hazardous metal exposures in industrial settings, it is not a fool-proof system of control. If an adult has clinical signs of metals toxicity, a series of blood tests can provide information identifying the type of metal responsible for the symptoms