Toxicity of Heavy Metals and Treatments

Heavy Metal Toxicity

• Heavy metal poisoning inhibits enzymes containing SH groups.
• Stomach tube washing is a treatment for most heavy metals except barium chloride and antimony trichloride.

Arsenic Toxicity

• Absorption occurs in the descending colon, excretion through the gastrointestinal tract.
• Arsenic is used in weed killers and wood preservatives.
• Arsenic storage occurs in bone and keratinized tissues.
• Arsenic can be detected even in decomposed remains.
• Arsenic elimination from the body takes 2 weeks after treatment, 6 weeks after stopping arsenic-based drug administration.
• Acute arsenic toxicity leads to rice-watery diarrhea and bloody dysentery.
• Antidotes for arsenic poisoning include freshly prepared ferric hydroxide solution and British Anti-Lewisite (BAL).

Mercury Toxicity

• Mercury is re-excreted through the cecum.
• Mercury permanently inhibits selenoenzymes like thioredoxin reductase.
• Symptoms of mercury poisoning include aphthous patches on the mouth's mucous membrane.
• Antidotes for mercury poisoning include BAL (British Anti-Lewisite) and albumin. Leishica solution (500 ml skimmed milk, 50 g glucose, 20 g sodium bicarbonate, 3 egg whites, and barley water) is another treatment.

Antimony Toxicity

• Antimony poisoning can cause loss of smell and aphthous patches in the mouth's mucous membrane.

Lead Toxicity

• Lead is not easily excreted in urine.
• Chronic lead poisoning is called plumbism.
• Lead inhibits enzymes 8-ALAD and ferrochelatase, crucial for haem production.
• Lead poisoning symptoms include microcytic hypochromic anemia, erythrocytic basophilic stippling, and acid-fast inclusion bodies in the renal cortex.
• Lead poisoning treatment uses CaNa2EDTA and D-penicillamine.

Cadmium Toxicity

• Cadmium interferes with zinc-related metabolic processes.
• Chronic cadmium exposure causes Itai-Itai disease (osteomalacia and osteoporosis).

Fluorine Toxicity

• Fluorine binds to enzymes like aconitase and AChE.
• Fluorine poisoning causes hyperesthesia and tooth mottling.
• Chronic exposure causes osteomalacia and osteoporosis.
• Aluminium sulphate can precipitate leftover fluorine in the stomach.
• Fluoride detection is not possible in decomposed remains.

Selenium Toxicity

• Selenium poisoning in fish causes various symptoms like nephrocalcinosis, ascites, localized eye haemorrhage, cataracts, exophthalmia, lordosis, and kyphosis.
• Tributyltin (TBT) can cause localised eye and base haemorrhage as well as cataracts in fish.
• Copper poisoning causes kyphosis in fish.
• Zinc poisoning causes a fuzzy appearance in fish gills.

Reproductive Toxicity (Female)

• Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) stimulate estrogen production in ovarian follicles.
• Early pregnancy stages involve pre-implantation and organogenesis.
• The fetal period begins with organ formation and extends to birth.
• Exposure to toxins during pregnancy can lead to growth retardation and neonatal jaundice in offspring.
• Exposure to toxins in females before puberty can cause irreversible infertility.

Reproductive Toxicity (Male)

• Sertoli cells in the testes provide support to spermatogenic cells, forming a blood-testis barrier to help with sperm maturation.
• Leydig cells produce testosterone.
• Spermatogenic cells develop into sperm cells.
• Spermatogenesis (sperm development) takes 50-54 days in rats.
• Immature spermatozoa are released from Sertoli cells into the seminiferous tubules.

Genotoxicity

• Genotoxicity is a substance's ability to damage DNA.
• Types of mutations include reverse phenotype, transition, transversion, missense, and frameshift.
• Monosomy involves a missing chromosome; trisomy involves an extra chromosome.
• Examples are Turner syndrome (47, X), Down syndrome (trisomy 21), Klinefelter syndrome (47, XXY), and other sex chromosome trisomies (47, XXX).
• Oncogenes are mutated proto-oncogenes causing uncontrolled cell growth.
• Tumor suppressor genes prevent uncontrolled cell growth, mutations increase cancer risk.
• Substances like aflatoxins, cosmetics, bromouracil, and mitomycin can generate reactive radicals that react with DNA forming adducts.

Neurotoxicity

• Neurotoxicity damages the nervous system.
• Oligodendrocytes and Schwann cells myelinate nerve fibers.
• Astrocytes and endothelial cells form the blood-brain barrier.
• Lipophilic toxins easily cross the blood-brain barrier.
• Anterograde transport moves substances from the cell body to nerve terminals.
• Retrograde transport moves substances in the opposite direction.
• Substances like nitrogen trichloride, aluminium, organophosphates (causing neuropathy) and toxins affecting the synthesis of glutathione can cause neurotoxicity via dying-back processes and glial scar formation.

Insecticides

• Type I pyrethroids inhibit Ca2+/Mg2+ ATPase.
• Secondary messengers relay signals in cells.
• Some neurotoxins interfere with secondary messenger systems and ion channels.
• Anticholinesterase insecticides (organophosphates and carbamates) inhibit acetylcholinesterase (AChE), critical for nerve signal transmission.
• Organophosphates bind to AChE, resulting in irreversible inhibition.
• Atropine blocks muscarinic receptors, while oximes (pralidoxime, obidoxime) reactivate AChE.
• Organochlorine insecticides, like DDT, are non-biodegradable.

Rodenticides

• Zinc phosphide is a black, rotten fish-smelling rodenticide.
• Sodium fluoroacetate and fluoroacetamide block the citric acid cycle by inhibiting aconitase.
• ANTU reacts with sulfhydryl (SH) groups in the body.

Mycotoxins

• Mycotoxins are toxins produced by fungi, characterized by low lipid/water solubility and large molecular weights.
• Fusarium mycotoxins include aflatoxins (e.g., aflatoxin B1).
• Aflatoxins (e.g., aflatoxin B1) are metabolized to reactive epoxides that bind to DNA, leading to liver damage.

Permissible Levels

• Permissible levels for aflatoxin B1 are 20 ppb in food for humans and animals.

Other Toxic Substances

• Carbon Monoxide (CO) binds to hemoglobin, inhibiting oxygen transport.
• Other toxins include ochratoxin, citrinin, nitrous oxide, and chlorine and bromine compounds.

Poisonous Plants

• Various plants and their parts (seeds, fruit, etc.) are toxic, containing proteins like ricin, atropine, solanine, and alkaloids like narcotine, morphine, and narceine.

Toxicodynamics

• Toxicodynamics is the effect of toxins on the body, including enzyme inhibition (e.g., AChE) and receptor binding (mimicking or blocking endogenous substances).
• Toxin damage to cell membranes leading to cell death is another mechanism.
• Other routes of absorption and excretion include sweat, tears, breast milk, and exhalation.

This quiz explores the toxic effects of heavy metals such as arsenic and mercury, including their absorption, excretion, and treatment options. Learn about the symptoms of poisoning and the specific antidotes for chemical toxicity. Gain a better understanding of heavy metal toxicity to enhance your knowledge in toxicology.