Lead Flashcards
What are Heavy Metals
- Are naturally occurring elements found throughout the Earth’s crust
- Sometimes referred to as “trace elements”
- Have a high atomic weight
- Density is at least 5 times greater than water
- Some metals may also be essential nutrients
Explain Essential Heavy Metals
- Essential heavy metals required for biochemical and physiological functions in plants and animals
- Inadequate supply of these essential nutrients can result in a variety of diseases or syndromes
Ex: Zinc important in the development of the brain in children
Explain Non-Essential Metals
Non-essential heavy metals have no established biological functions
E.x., Lead, Mercury, Arsenic, Aluminum
Heavy Metals: Sources of Exposure (Anthropogenic)
- Contamination through activity
- Most exposure is due to anthropogenic activities
- Mining and smelting operations
- Industrial production and use
- Domestic and agricultural use of mental and metal-containing compounds
Heavy Metals: Sources of Exposure (Natural)
- Environment contamination can also occur through
- Metal corrosion
- Atmospheric deposition
- Soil erosion of metal ions and leaching of heavy metals
- Sediment resuspension
- Metal evaporation from water resources to soil & groundwater
- Natural phenomena (volcanic eruptions)
What are the three forms lead has been found in
- Metallic lead
- Inorganic lead and lead compounds (lead salt)
- Organic lead
What is Lead’s most common state
Lead most often occurs in its 2+ oxidation state (Pb2+) in various ores found near the surface of the Earth’s crust
Are the three lead ores
- “galena” (lead sulphide) (most important)
- “cerussite” (lead carbonate)
- “anglesite” (lead sulphate)
List the properties of lead that allow it to have many different applications
- high resistance to corrosion
- Softness
- low melting point
- high density
- relative low conductivity
Explain the distribution of lead through the environment
- Industrial and agricultural releases of lead to soil, water, air
- Lead is transferred continuously between air, water, and soil by natural processes
- Small amounts of lead reach the surface environment through natural weathering processes, volcanic emission, forest fires
What are the sources of Lead exposure
- food or beverages stores, cooked or served in lead-containing containers
- food grown in contaminated - soils
- cosmetics
- traditional remedies
- Smoking
- air pollution
- contaminated water
Has Lead exposure Increased or decreased over time
Exposure has decreased substantially over the past 10-30 years in countries where control measures are implemented
What is the most common source of lead exposure in children
Paint chips and leaded dust and soils released from ageing painted surfaces or during renovation
List the Four Biological Markers of Lead Exposure
- Bone
- Blood and Plasma
- Teeth
- Urine
Explain the Biological Bone Marker of Lead Exposure
- Exposure to lead over time results in the progressive accumulation in bone
- Greater than 95% of the total lead body burden
- A great indicator of lifetime exposure to lead
Explain the Biological Blood and Plasma Markers of Lead Exposure
- Reflect both recent and past exposures
- 90% or more of blood lead consists of mobilized bone-lead in exposed children
Explain the Biological Teeth Marker of Lead Exposure
- Suitable for children only (uses baby teeth)
- Estimated levels half of what is in the blood
- Not a good measure for adults
Explain the Biological Urine Marker of Lead Exposure
Urine has been used to monitor relative levels of exposure in workers with chronic occupational exposure
Why do we not look at Placenta as a measure of Lead Exposure
Not suitable for exposure monitoring because lead is not distributed uniformly throughout the tissue
What is the main target of Lead Toxicity
The CNS
What are the early symptoms of Lead Poisoning
- lethargy
- abdominal cramps
- irritability
- headache
- encephalopathy
- hallucinations
- memory loss
What are the later symptoms of Lead Poisoning
- vomiting
- clumsiness
- ataxia
- coma
- seizures
- death
Explain the toxic effect of Lead in terms of blood
Toxic effects also occur at very low blood lead levels
Explain the toxic effect of Lead in children based on blood
- Symptoms of severe lead poisoning in children are typically associated with a blood lead level of 70 μg/dL
- CDC blood lead level of 10 μg/dL should prompt public health actions
- Evidence that children’s physical and mental development can be affected at blood lead levels of < 10 μg/dL
Explain the effects of lifetime blood lead exposure in Children
Lifetime blood lead exposure < 5μg/dL may produce learning deficits greater than higher exposures
Where is the greatest environmental Lead intoxication threat ?
- Lead intoxication poses one of the greatest environmental threats to children in America
- 1 in 20 children has blood lead levels > 10 μg/dL (US)
- 38 million housing units in the US have lead-based paint
- 24 million have significant lead-based paint hazards
What are the developmental effects of Lead
- CNS effects are more prominent than peripheral effects in the developing nervous system (unlike adults)
- Developmental effects of lead occur during a critical time window (<7 years old)
List the 5 ways children are more vulnerable than adults to the effects of lead
- More likely to play in the dirt
- Most likely to put their hands and other objects into their mouths
- A greater proportion of ingested lead is absorbed from the GI tract
- More lead gains access to the brain
- Developing nervous system is far more vulnerable to the toxic effects of lead than the mature brain
Developmental Effects of Lead (Study by Bellinger et al., 1987)
Assessed the relationship between prenatal and postnatal exposure to low levels of lead and early cognitive development :
- Infants in the high in utero exposure group (> 10 μg/dL) scored lowered than infants in the medium and low groups
- Evidence of a direct link between low-level lead exposure during early development and deficits in intellectual impairment late in childhood
Developmental Effects of Lead (Study by Rosen et al., 1992)
Relationship between blood levels and intellectual function:
- Conclusion: Impact of increase in blood lead levels on intellectual functioning was greater for children with lower blood lead levels
Developmental Effects of Lead (Study by Needleman et al., 1998)
Exposure of lead and performance:
- Lower levels of lead exposure result in higher verbal IQ tests
- Overall, Inverse relationship between lead exposure and performance
Developmental Effects of lead (Study by Wright et al., 2008)
Association between prenatal and childhood blood lead levels and criminal arrests in early adulthood:
- For every 5 μg/dL increase in blood lead level at 6 years of age the risk of being arrested for violent crimes as a young adult increased by almost 50%
Explain the Impact of Socioeconomic Status and Lead (Brody et al., 1994)
Location of home and family income is associated with blood lead levels:
- Higher rates of blood lead levels in inner-city children compared to other children
- Medium rates from low-income families compared to others
- Low rates in children from middle to high-income families
- Could be related to an increased likelihood of living in older homes or homes that are not maintained well
- Could be related to poor nutrition
Socioeconomic impact on lead: poor nutrition
- Deficiencies in calcium, iron, and zinc are risk factors
- Calcium and iron deficiency increased retention of lead and severity of its toxic effects
- Zinc deficiency increases lead absorption which in turn increase zinc excretion (vicious cycle)
Lead and Environmental Enrichment (Learning)
- Environmental enrichment can reverse the learning deficits resulting from developmental lead exposure
- Approach effectively even after lead exposure had occurred
- Therefore, environmental enrichment may be a useful strategy for enhancing the learning capacity of children exposed to lead
Rat Acquisition Learning Task: Study of enrichment
- Rats: exposed to lead in utero and went through an enrichment period
- Acquisition learning task
- How long it takes them to find the platform
- The isolated lead animal doesn’t learn the task
- Enrichment animal learned quickly and low latency
Environmental enrichment can mediate the effects of lead on the developing rat brain
- Mediating cognitive effects
- High income > more resourced > less effects
Lead Exposure and ADHD
- An increased odds ratio of 2.52 of having ADHD with every log unit increase in blood lead levels
- Correlation between blood lead levels and parental/teacher ratings of ADHD
- Blood lead levels of < 10 μg/dL and even < 5 μg/dL have been linked to ADHD
Lead Exposure and Alzheimer’s Disease (based in rat research)
- Over-expression of amyloid precursor protein (APP) and aggregation of amyloid beta plaques in rats
- Increases amyloidogenesis, senile plaque deposition, and up regulates APP proteins in nonhuman primates
- Enhances expression of AD-associated protein tau, alters epigenetic markers of AD, and cognitive impairment in mice, but only when mice exposed as infants
Lead Exposure and Schizophrenia (mice research)
Chronic exposure of mDISC1 mice to Pb2+ (1500 ppb) produced phenotypes relevant to schizophrenia
- Hyperactivity
- Exaggerated responses to the NMDAR antagonist, MK-801
- Mildly impaired prepulse inhibition (PPI) of the acoustic startle
- Enlarged lateral ventricles
