Heavy Metals. General concepts (EHL0036)

Transcription

1 Heavy Metals General concepts (EHL0036)

2 Introduction Metals of concern; include Aluminium, antimony, arsenic, bismuth, cadmium, cerium, chromium, cobalt, copper, gallium, gold, iron, lead, manganese, mercury, nickel, platinum, silver, tellurium, thallium, tin, uranium, vanadium, and zinc

3 Heavy metal toxicity Damaged or reduced mental and central nervous function, Lower energy levels, and Damage to blood composition, lungs, kidneys, liver, and other vital organs. Long-term exposure may result in slowly progressing physical, muscular, and neurological degenerative processes that mimic Alzheimer's disease, Parkinson's disease, muscular dystrophy, and multiple sclerosis. Allergies are not uncommon and repeated long-term contact with some metals or their compounds may even cause cancer

4 Toxic levels For some just above the background concentrations naturally found in nature Heavy metal toxicity is an uncommon medical condition Where it occurs it is a clinically significant condition. If unrecognized or inappropriately treated, toxicity can result in significant illness and reduced quality of life

5 The association of symptoms indicative of acute toxicity the symptoms are usually severe, rapid in onset, and associated with a known exposure or ingestion cramping, nausea, and vomiting; pain; sweating; headaches; difficulty breathing; impaired cognitive, motor, and language skills; mania; and convulsions

6 The association of symptoms indicative of chronic toxicity Symptoms: impaired cognitive, motor, and language skills; learning difficulties; nervousness and emotional instability; insomnia, nausea, lethargy, and feeling ill Sometimes the symptoms of chronic exposure actually abate from time to time

7 Definition of a Heavy Metal "Heavy metals" are chemical elements with a specific gravity that is at least 5 times the specific gravity of water. The specific gravity of water is 1 at 4 C Simply stated, specific gravity is a measure of density of a given amount of a solid substance when it is compared to an equal amount of water. Some well-known toxic metallic elements with a specific gravity that is 5 or more times that of water are arsenic, 5.7; cadmium, 8.65; iron, 7.9; lead, 11.34; and mercury,

8 Beneficial Heavy Metals In small quantities, certain heavy metals are nutritionally essential for a healthy life. Some of these are referred to as the trace elements (e.g., iron, copper, manganese, and zinc). Commonly found naturally in foodstuffs, in fruits and vegetables, and in commercially available multivitamin products Diagnostic medical applications Heavy metals are also common in industrial applications Many of these products are in our homes

9 Toxic Heavy Metals Heavy metals become toxic when they are not metabolized by the body and accumulate in the soft tissues. Heavy metals may enter the human body through food, water, air, or absorption through the skin ( agriculture and in manufacturing, pharmaceutical, industrial, or residential settings. Industrial exposure common route for adults. Ingestion common route in children

10 Symptoms of Exposure and Toxicity Exposure to toxic heavy metals is generally classified as acute, 14 days or less; intermediate, days; and chronic, more than 365 days Acute toxicity udden or unexpected exposure to a high level of the heavy metal an accidental spill or release of toxic material Chronic toxicity repeated or continuous exposure, leading to an accumulation of the toxic

11 Arsenic Highlights Exposure to higher than average levels of arsenic occur mostly in the workplace, near hazardous waste sites, or in areas with high natural levels. At high levels, inorganic arsenic can cause death. Exposure to lower levels for a long time can cause a discoloration of the skin and the appearance of small corns or warts.

12 Arsenic Exposure workplace, near hazardous waste sites, or in areas with high natural levels

13 Acute Arsenic poisoning Sore throat Reddened skin at contact point, or severe abdominal pain, vomiting, and diarrhoea, anorexia, fever, mucosal irritation, Cardiovascular changes are often subtle in the early stages but can progress to cardiovascular collapse.

14 Chronic or lower levels of poisonng progressive peripheral and central nervous changes, sensory changes, numbness and tingling, and muscle tenderness. burning sensation in hands and feet. Neuropathy Hyperpigmentation Hyperkeratosis White bands of arsenic deposits across the bed of the fingernails (usually 4-6 weeks after exposure). Birth defects, liver injury, and malignancy are possible Arsenic has also been used in homicides and suicides.

15 Arsenic (EFSA summary) Arsenic is a naturally occurring element, Regions with high geological occurrence of inorganic arsenic In Europe, environmental arsenic levels are rather low, with the exception of distinct geological or industrial areas. Arsenic is a metalloid, displaying different valences (-3, 0, +3, +5) Inorganic and organic forms of arsenic also differ significantly in their toxicity, The organic arsenic compounds exhibiting a very low toxic potential. Potential adverse effects of arsenic to animal (and human) health are determined by the inorganic fraction. Drinking water many contain significant amounts of inorganic arsenic and upper limits have been set in most countries. major source of arsenic in the human diet Seafood and fish have been identified as, Animal feed materials that contain products derived from fish or other marine organisms.

16 Human dietary exposure in most countries the major source of arsenic in the human diet is seafood marine waters >> brackish waters, >> freshwater lakes and rivers => 100:10:1 An intake estimation remains complicated and uncertain

17 Legitimate use of Arsenic It is present in flue dust from the roasting of ores copper smelting In the 1960s, use for As 2 O 3 in the USA pesticides(77%) glass(18%), industrial chemicals(4%) and medicine(1%) late 1980s/90s Timber treatment Herbicides Agricultural chemicals glass Others (semiconductors)

18 Lead Mined in Turkey about 6500 BC Lead toxicity was first recognized as early as 2000 BC Gout in ancient Rome, is thought to be the result of lead, or leaded eating and drinking vessels. Lead sugar (lead acetate) sweeten wine, gout that resulted from this was known as saturnine gout. Lead was used in makeup.

19 Lead Today, most exposure in developed countries occupational hazards, leaded paint, and leaded gasoline (which continues to be phased out in most countries). Acute exposure likely to occur in the workplace, particularly in manufacturing processes that include the use of lead e.g., where batteries are manufactured or lead is recycled). Even printing ink, gasoline, and fertilizer contain lead. Symptoms include abdominal pain, convulsions, hypertension, renal dysfunction, loss of appetite, fatigue, and sleeplessness. Other symptoms are hallucinations, headache, numbness, arthritis, and vertigo.

20 Acute exposure to Lead abdominal pain, convulsions, hypertension, renal dysfunction, loss of appetite, fatigue, and sleeplessness. Other symptoms are hallucinations, headache, numbness, arthritis, and vertigo.

21 Chronic exposure to Lead birth defects, mental retardation, autism, psychosis, allergies, dyslexia, hyperactivity, weight loss, shaky hands, muscular weakness, and paralysis (beginning in the forearms). Children are particularly sensitive to lead are prone to ingesting lead because they chew on painted surfaces and eat products not intended for human consumption (e.g., hobby paints, cosmetics, hair colorings with lead-based pigments, and even playground dirt). In addition to the symptoms found in acute lead exposure, symptoms of chronic lead exposure could be allergies, arthritis, autism, colic, hyperactivity, mood swings, nausea, numbness, lack of concentration, seizures, and weight loss.

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24 Lead Health Effects Interferes with normal cell function and various physiological process: peripheral and central nervous systems, blood cell production, metabolism of vitamin D and calcium, kidneys, reproductive system Probable human carcinogen (classified B2 by USEPA)

25 Lead Health Effects (cont.) Children and pregnant women at highest risk Children higher exposures and postnatal susceptibility For every 10 ug/dl increase in concentration there is a one to three-point drop in IQ Pregnant women lead crosses the placenta and damages nervous system Lead in the foetus tends to equilibrate with maternal lead

26 Lead Health Effects (cont d) Symptoms of lead poisoning Early symptoms are vague and nonspecific Pallor, vomiting, abdominal pain, constipation, stupor, loss of appetite, irritability, and loss of muscular coordination Classic signs include lead colic, lead lines on the gums and wrist drop

27 Lead Biological Fate Inorganic lead not metabolized directly absorbed, distributed and excreted Inhaled lead completely absorbed; typically 10-15% of ingested lead absorbed from the GI tract Lead half lives in adults Blood 25 days Soft tissue 40 days Bone 25+ years Lead poisoning does not require major acute exposure - body accumulates over lifetime and releases slowly Under stress, body may metabolize lead stores, thus increasing blood lead levels

28 Health Effects at Various Blood Lead Levels Health Effect (ug/dl) Blood Lead Level of concern for fetal effects <10 Blood enzyme changes IQ deficiencies in children <25 Clinical anemia, children 40 Clinical anemia, adults 50 Reproductive effects in adults 50 Mental losses (writing/speech problems, retardation) Irreversible brain damage 100

29 Mercury Exposure Mining and industry (manufacturing of fungicides, thermometers, and thermostats) Spills are difficult to control

30 Symptoms of Exposure to Mercury Acute cough, sore throat, and shortness of breath; metallic taste in the mouth, abdominal pain, nausea, vomiting and diarrhoea; headaches, weakness, visual disturbances, tachycardia, and hypertension

31 Symptoms of Exposure to Mercury Chronic permanent damage to the central nervous system and kidneys. can also cross the placenta from the mother's body to the foetus and accumulate, resulting in mental retardation, brain damage, cerebral palsy, blindness, seizures, and inability to speak. Dental amalgam is also suspected as being a possible source of mercury toxicity from chronic exposure No scientific evidence to corroborate this!!

32 Sources of Mercury Exposure Highest exposures have been from industrial or pesticide poisonings (Minamata, Japan Chlor-alkali; Iraq Wheat fungicide) General population mostly exposed by eating contaminated fish (methylmercury) Fish bioaccumulate methyl mercury with 99% of mercury in fish in the the methylated form Older and larger carnivorous fish have the highest levels (swordfish, tuna, shark, king mackerel) Can of tuna contains 0.20 ppm

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34 Sources of Mercury Exposure (cont.) Occupational (primarily elemental mercury vapour) chlor-alkali plants, laboratory personnel, miners and processors of cinnabar, gold, silver, copper, and zinc, metallurgists, electroplaters, explosive manufacturers Hobbies fishing Environmental atmospheric deposition from coalfired power plants, incineration of municipal and solid waste, latex paints, fish consumptions Substance use folk medicines, cosmetic; dental amalgams have not been proven to cause adverse effects.

35 Mercury Health Effects Effects depend on duration, intensity, and route of exposure, and chemical form Central nervous system and kidneys are key targets Elemental mercury: nervous system Mercury salts: respiratory or GI (acute exposure); kidneys (chronic exposure) Organic mercury: nervous system; developmental effects Elemental mercury not classified with respect to carcinogenicity (USEPA Class D)

36 Observed Effects of Methylmercury Toxicity Iraq and Minamata (Japan) Effects in utero quite different from childhood or adult exposures Foetus is the most sensitive Methylmercury exposed women have delivered infants with severe behavioral and sensory deficits, including deafness and blindness without maternal toxicity Prenatal exposure results in a widespread pattern of adverse effects on brain development and organization Alters the normal migration of neurons to cerebellar and cerebral cortices during brain development Reduced brain size

37 Mercury Controversy Two recent studies of predominately fish eating populations: Faroese Islands Dose dependent relationship seen (delayed language, reduced memory and attention spans) Seychelles Islands No health effects observed Many experts strongly advise pregnant women and women of child bearing age to limit exposure However, fish is a significant source of protein throughout the world, some argue that the benefits outweigh the potential risk from low-level exposure

38 Mercury Biological Fate Chemical and physical form of mercury determine absorption, metabolism, distribution, and excretion pathways Elemental mercury: nearly completely absorbed when inhaled; poorly absorbed when ingested or via dermal contact; readily crosses blood-brain barrier Mercury salts: Mercuric Hg 2+ ) salts are generally more soluble, and therefore more toxic than mercurous (Hg 1 +) salts; on average, less than 10% of ingested salts absorbed in GI tract; do not cross blood-brain barrier as readily Organic mercury: readily absorbed by inhalation, dermal, contact, and ingestion; distributed uniformly to all tissues, although concentrated mostly in blood and brain.