Lecture 4 Heavy Metals & Lead PDF

ENVIRONMENTAL & INDUSTRIAL TOXINS PART II Dr. Abdullah Alnuqaydan Associate Professor & Consultant of Toxicology ami.alnuqaydan @ qu.edu.sa 2 . Industrial Toxins I. Heavy Metals Introduction • The term heavy metal refers to any metallic chemical element that has a relatively high density...

ENVIRONMENTAL & INDUSTRIAL TOXINS PART II Dr. Abdullah Alnuqaydan Associate Professor & Consultant of Toxicology ami.alnuqaydan @ qu.edu.sa 2 . Industrial Toxins I. Heavy Metals Introduction • The term heavy metal refers to any metallic chemical element that has a relatively high density and is toxic or poisonous at low concentrations. • Examples of heavy metals include: • Mercury (Hg). • Cadmium (Cd). • Arsenic (As). • Chromium (Cr). • Thallium (Tl). • Lead (Pb) (from the Latin plumbum) Introduction • Heavy metals are natural components of the Earth's crust. They cannot be degraded or destroyed. • To a small extent they enter our bodies via food, drinking water and air. • As trace elements, some heavy metals (e.g. copper, selenium, zinc) are essential to maintain the metabolism of the human body. However, at higher concentrations they can lead to poisoning. • Heavy metal poisoning could result, for instance, from drinking -water contamination (e.g. lead pipes), high ambient air concentrations near emission sources, or intake via the food chain. Mode of action • Heavy metals are dangerous because they tend to bioaccumulate. • Bioaccumulation means an increase in the concentration of a chemical in a biological organism over time, compared to the chemical's concentration in the environment. • Compounds accumulate in living things any time they are taken up and stored faster than they are broken down (metabolized) or excreted. • Heavy metals can enter a water supply by industrial and consumer waste, or even from acidic rain breaking down soils and releasing heavy metals into streams, lakes, rivers, and groundwater.  The most pollutants of heavy metals are: Lead, Arsenic, Cadmium, and Mercury. Arsenic Lead Mercury Lead Poisoning • Lead poisoning is one of the oldest occupational and environmental diseases in the world. • Environmental lead exposure, ubiquitous by virtue of the anthropogenic distribution of lead to air, water and food, has declined considerably due to diminished use of lead in gasoline and other applications. Sources of Exposure Sources of Exposure  Soil and dust  Paint chips  Contaminated water  Parents lead -related occupation  Folk remedies  Household plumbing. Health Effects • Lead serves no useful purpose in the human body. • Lead is slowly but consistently absorbed via the respiratory and gastrointestinal tracts. • Inorganic lead is poorly absorbed through the skin absorption via the GIT varies with the nature of the lead compound, but in general, adults absorb about 10% of the ingested amount while young children absorb closer to 50%. • The daily lead consumption is about 300μg. It is unsafe if consumed at a concentration greater than 0.5 mg/day for 3 months or more. • Once absorbed from the respiratory or GIT, lead is bound to erythrocytes and widely distributed initially to soft tissues, then to the subperiosteal surface of bone and bone matrix. Health Effects Health Effects • It has a half life of 2 -3 weeks in blood and 15 years in bone. • More than 90 % of the lead that is eliminated appears in the urine  Lead exerts multi systemic toxic effects through at least three mechanisms by; • Inhibiting enzyme activity. • Interfering with the action of essential cations, particularly calcium, iron, and zinc. • Altering the structure of cell membranes and receptors. • increased fragility and decreased survival time due to interference of sodium -potassium pump. Lead Paint  The use of lead in residential paint was banned in 1977  Lead -containing pigments still are used for outdoor paint products because of their bright colors and weather resistant properties  Tetraethyl and tetramethyl lead are still used as additives in gasoline in several countries Toxicokinetics and Toxicodynamics of lead toxicity  Absorption:  Lungs: depends on size particle  GI:  Adults: 20 -30%  Children: as much as 50% of dietary lead  Inadequate intake of iron, calcium, and total calories are associated with higher lead levels  Skin:  Inorganic lead is not absorbed  Organic lead is well absorbed  Lead is carried bound to the RBC Pharmacokinetics and Pharmacoynamics  Distributed extensively throughout tissues: bone, teeth, liver, lung, kidney, brain, and spleen Toxicokinetics and Toxicodynamics of lead toxicity  Body lead storage: bones - can constitute a source of remobilization and continued toxicity after the exposure has ceased  Lead crosses the blood brain barrier (BBB) and concentrates in the gray matter  Lead crosses the placenta  Excretion:  Kidneys. The excretion increases with increasing body stores ( 30  g -200  g/day)  Feces Clinical Manifestation  Acute toxicity  Acute encephalopathy, renal failure and severe GI symptoms Chronic and Long Term Toxicity - Pathophysiology  Lead has affinity for SH groups and is toxic to zinc -dependent enzyme systems  Heme synthesis: hemoglobin, cytochromes  Steroid metabolism and membrane integrity  Interference in vitamin D synthesis in renal tubular cells (conversion of 1 -hydroxyvitamin D to 1,25 -hydroxyvitamin D) General Signs and Symptoms of Lead Toxicity  Fatigue  Irritability  Lethargy  Paresthesis  Myalgias  Abdominal pain  Tremor  Headache  Vomiting  Weight loss  Constipation  Loss of libido  Motor neuropathy  Encephalopathy  Cerebral edema  Seizures  Coma  Severe abdominal cramping  Epiphyseal lead lines in children (growth arrest)  Renal failure General Signs and Symptoms of Lead Toxicity Lead poisoning symptoms in newborns Babies exposed to lead before birth might: •Be born prematurely •Have lower birth weight •Have slowed growth Blood lead levels Adults Children 10 g/dL Hypertension may occur •Crosses placenta •Impairment IQ, growth •Partial inhibition of heme synthesis 20 g/dL Inhibition of heme synthesis Increased erythrocyte protoporphyrin Beginning impairment of nerve conduction velocity 30 g/dL •Systolic hypertension •Impaired hearing( ) Impaired vitamin D metabolism 40 g/dL •Infertility in males •Renal effects •Neuropathy •Fatigue, headache, abd pain Hemoglobin synthesis inhibition 50 g/dL Anemia, GI sx, headache, tremor Colicky abd pain, neuropathy 100 g/dL Lethargy, seizures, encephalopathy Encephalopathy, anemia, nephropathy, seizures Range of Lead - induced Health Effects in Adults and Children Childhood Lead Poisoning  Childhood lead poisoning is now defined as a blood lead level of 10  g/dl  The average lead level of American children is 2  g/dl  8.9% of American children have lead poisoning  Lead intoxication is more prevalent in minority groups and among those living in the northeast Neurotoxicity of Lead in Childhood  Mental retardation in severe lead intoxication   5 points in IQ for every 10  g/dl  in blood lead level - population based studies  Other adverse developmental outcomes:  Aggression  Hyperactivity  Antisocial behaviors  Learning disability - impairment in memory, auditory processing, and visual -motor integration. The IQ is normal. These effects has been demonstrated with blood lead levels as low as 6  g/dl Diagnosis  Evaluation of clinical symptoms and signs  CBC  Serum iron levels, TIBC, ferritin  Abdominal radiographs (for recent ingestion of lead - containing material)  Whole blood lead level  X -ray fluorescence (XRF) - to asses body burden