Atomic Elements, Human, Non-Essential or Toxic Elements

Cadmium (Cd)

23
May

Cadmium (Cd) is a naturally occurring chemical element known for its toxicity rather than any nutritional or health benefits. Unlike essential minerals like zinc or calcium, cadmium has no beneficial role in the human body and poses significant health risks even at low levels of exposure. This article provides a clear, engaging, and scientifically accurate overview of cadmium, empowering you to understand its properties, risks, and practical steps to minimize exposure for better health.

What Is Cadmium?

Basic Chemical and Physical Properties

  • Atomic Number: 48
  • Symbol: Cd
  • Appearance: Cadmium is a soft, silvery-white metal with a slight bluish tinge and a shiny luster.
  • Classification: A heavy metal in the periodic table, often found in ores alongside zinc, such as sphalerite.
  • Properties: Cadmium is malleable, ductile, and corrosion-resistant, making it valuable in industrial applications like batteries, pigments, and coatings. However, its toxicity makes it a significant public health concern.

Cadmium has no confirmed physiological function in humans, but its presence in the environment requires careful management.

Where Is Cadmium Found?

Natural Occurrence and Common Sources

  • Environmental Presence: Cadmium occurs naturally in the Earth’s crust, primarily in zinc ores, and is released through volcanic activity, weathering, and human activities like mining and smelting.
  • Exposure Routes:
    • Dietary Sources:
      • Crops grown in cadmium-contaminated soil, such as rice, leafy greens (e.g., spinach, lettuce), and root vegetables (e.g., potatoes, carrots).
      • Shellfish and organ meats (e.g., liver, kidney) from animals exposed to cadmium.
      • Contaminated water from industrial runoff or leaching from pipes.
    • Environmental Sources:
      • Soil and dust near industrial sites, mines, or smelters.
      • Air pollution from coal burning, waste incineration, or cigarette smoke (tobacco plants readily absorb cadmium).
      • Phosphate fertilizers, which may contain trace cadmium, contaminating agricultural soils.
    • Other Sources:
      • Occupational exposure in industries like battery manufacturing, metal plating, or pigment production.
      • Consumer products like cheap jewelry, ceramics, or plastics with cadmium-based pigments.
      • Nickel-cadmium (NiCd) batteries, though their use is declining due to environmental concerns.

Most dietary cadmium comes from plant-based foods and shellfish, with exposure varying by region and soil conditions.

Cadmium in the Human Body

Biological Importance and Functions

  • No Beneficial Role: Cadmium has no known biological function in humans and is classified as a toxic heavy metal.
  • Metabolism: Cadmium is absorbed primarily through ingestion or inhalation, with about 5–10% of ingested cadmium absorbed in the gut. It binds to proteins like metallothionein in the liver and accumulates in kidneys, with a half-life of 10–30 years in the body.
  • Accumulation: Cadmium primarily accumulates in the kidneys and liver, but also in bones and other tissues, leading to long-term health risks.

How It Affects the Body

  • Cadmium disrupts cellular processes by interfering with enzyme functions and causing oxidative stress (cellular damage from free radicals).
  • It mimics zinc and calcium, displacing these essential minerals and impairing their roles in the body.

Health Impacts of Cadmium Exposure

Health Risks and Toxicity

Cadmium is a potent toxin and a known human carcinogen, as classified by the International Agency for Research on Cancer (IARC). Health effects depend on exposure level and duration:

  • Cancer:
    • Chronic exposure is linked to lung, prostate, and kidney cancers, particularly from inhalation (e.g., occupational or smoking-related exposure).
  • Kidney Damage:
    • Cadmium is a leading cause of kidney dysfunction, damaging renal tubules and leading to proteinuria (excess protein in urine) or renal failure.
  • Bone Health:
    • Long-term exposure can weaken bones, causing osteomalacia or osteoporosis, as seen in “Itai-Itai” disease in Japan, linked to cadmium poisoning from contaminated rice.
  • Cardiovascular Effects:
    • Cadmium increases the risk of hypertension and heart disease.
  • Respiratory Effects:
    • Inhalation (e.g., from cigarette smoke or industrial dust) can cause lung damage or chronic obstructive pulmonary disease.
  • Reproductive and Developmental Toxicity:
    • Cadmium may reduce fertility and cause developmental issues in fetuses.

Symptoms of Acute Exposure

  • High-level exposure (e.g., industrial accidents or ingestion of contaminated food) may cause:
    • Nausea, vomiting, and abdominal pain.
    • Respiratory distress or chest pain (from inhalation).
    • Dizziness, headache, or fever.

Symptoms of Chronic Exposure

  • Low-level, long-term exposure may result in:
    • Kidney dysfunction (e.g., frequent urination, protein in urine).
    • Bone pain or fractures.
    • Fatigue, anemia, or weight loss.

Cadmium in Supplements or Nutrition

Not Used in Supplements

  • Cadmium is not an ingredient in dietary supplements or fortified foods due to its toxicity.
  • Trace contamination may occur in supplements derived from plants or marine sources grown in cadmium-rich soils or waters. Choose supplements from reputable brands that test for heavy metals.

Recommended Intake and Exposure Limits

No Recommended Intake

  • Cadmium is not a nutrient, so there’s no dietary requirement.
  • Health organizations set tolerable exposure limits:
    • The World Health Organization (WHO) sets a Provisional Tolerable Monthly Intake (PTMI) of 25 micrograms per kilogram body weight (e.g., ~1.75 mg/month for a 70 kg adult, or ~60 μg/day).
    • The U.S. Environmental Protection Agency (EPA) sets a reference dose of 0.5 μg/kg/day for dietary exposure (e.g., 35 μg/day for a 70 kg adult).
    • The WHO and CDC state no safe level of cadmium exposure exists, as even low levels can accumulate and cause harm over time.

Typical Exposure

  • Dietary intake typically ranges from 10–50 μg/day, with higher levels in regions with contaminated soils or heavy rice consumption.
  • Smokers face higher exposure due to cadmium in tobacco (1–2 μg per cigarette).

Minimizing Exposure

  • Dietary Choices:
    • Diversify diet to reduce reliance on rice or leafy greens from cadmium-contaminated areas.
    • Wash produce thoroughly to remove contaminated soil.
    • Limit consumption of shellfish or organ meats, which may concentrate cadmium.
  • Home Safety:
    • Test well water for cadmium in areas near industrial or mining sites.
    • Avoid using ceramics or plastics with cadmium-based pigments for food storage.
  • Lifestyle:
    • Quit smoking or avoid secondhand smoke, as tobacco is a major cadmium source.
    • Wash hands and surfaces to reduce dust exposure in contaminated areas.
  • Supplements:
    • Choose brands with third-party testing for heavy metal content to avoid contamination.

Safety Considerations and Toxicity Risks

Safety Profile

  • Cadmium is highly toxic, with children, pregnant women, and individuals with kidney disease or poor nutrition being most vulnerable.
  • Populations at higher risk include:
    • Residents in areas with cadmium-rich soils or industrial pollution.
    • Smokers or those exposed to secondhand smoke.
    • Workers in industries like battery production, metal plating, or mining.

Toxicity Thresholds

  • Chronic Low-Level Exposure: Harmful effects, including kidney damage and cancer risk, occur at dietary intakes as low as 30–50 μg/day over years.
  • Acute Poisoning: Rare but possible at high doses (e.g., ingesting contaminated food or inhaling fumes), causing severe gastrointestinal or respiratory symptoms.

Interactions

  • Cadmium competes with essential nutrients:
    • Zinc: Adequate zinc intake may reduce cadmium absorption, as they compete for binding sites.
    • Iron: Iron deficiency increases cadmium uptake, particularly in children and pregnant women.
    • Calcium: Sufficient calcium may mitigate cadmium’s effects on bones.
  • A nutrient-rich diet with adequate zinc, iron, and calcium can help protect against cadmium toxicity.

Fun Fact

Did you know cadmium was once used to create vibrant yellow and red pigments in artists’ paints? Iconic painters like Monet used cadmium-based colors for their vivid hues, but these paints are now restricted due to toxicity concerns, replaced by safer alternatives.

Empowering Your Health Choices

Cadmium is a toxic heavy metal with no place in human nutrition, and minimizing exposure is critical for long-term health. By choosing clean water, diversifying your diet, avoiding tobacco, selecting high-quality supplements, and testing your environment for cadmium, you can protect yourself and your family from its harmful effects. If you suspect cadmium exposure, consult a healthcare provider for testing and guidance. Stay informed and proactive to keep your health first!