Cadmium compounds

The most tragic demonstration of cadmium toxicity occurred in postwar Japan's Jinzu River valley, where rice paddies irrigated with water from a zinc mine upstream accumulated cadmium in grains eaten by local farmers [1]. The resulting disease — itai-itai ("ouch-ouch") disease — caused severe osteoporosis and kidney failure in hundreds of women, named for the cries of pain from fractured bones softened by cadmium-induced calcium loss. The first cases were diagnosed in the 1950s and the connection to cadmium was established in 1968 [2]. Cadmium is a byproduct of zinc smelting — it occurs naturally in zinc ores and is released wherever zinc is mined, refined, or used. Industrial sources include nickel-cadmium batteries (now largely replaced by lithium-ion), cadmium pigments in paints and plastics, metal plating, and phosphate fertilizers (which contain natural cadmium from the ore). Tobacco is the single largest source of cadmium for smokers — tobacco plants hyperaccumulate cadmium from soil [1]. Cadmium is essentially non-biodegradable: once in soil, it persists indefinitely [2].

The main exposure pathway for nonsmokers is food — especially rice, wheat, leafy vegetables, and shellfish grown in cadmium-contaminated soil or water [1]. A single pack-a-day smoker inhales approximately 1-3 µg of cadmium per day, doubling kidney cadmium compared to nonsmokers [2]. Occupational inhalation occurs in zinc/lead smelting, battery manufacturing, metal plating, and pigment production. Workers near historical cadmium-using facilities may encounter contaminated soil. People using phosphate fertilizers on gardens in high-cadmium soil areas can accumulate it in homegrown vegetables [1]. Kidney disease and bone loss from cadmium typically appear only after 20-30 years of cumulative exposure — meaning exposure decisions made now affect health decades later [2].

Cadmium is nearly entirely stored in the kidneys (cortex), with a biological half-life of 15-30 years — meaning it accumulates throughout life with little elimination [1]. It competes with zinc as a cofactor in numerous enzymes and disrupts metallothionein (the cell's zinc/copper buffer), leading to oxidative stress. The hallmark toxicity is proximal tubular nephropathy: cadmium damages the kidney tubules that reabsorb small proteins, calcium, phosphate, and glucose, causing low-molecular-weight proteinuria (beta-2-microglobulin spilling into urine) and eventually calcium wasting that leads to osteoporosis and fractures [2]. IARC classifies cadmium as a Group 1 carcinogen (lung cancer in occupationally exposed workers; prostate and kidney cancer associations in environmental exposures) [1].

Smokers absorb 2-4× more cadmium than nonsmokers over a lifetime [1]. Women are more susceptible to cadmium-induced bone effects because they have lower iron stores (iron deficiency increases cadmium absorption) and lose calcium from bones during menopause, accelerating cadmium-related osteoporosis [2]. Workers in nickel-cadmium battery production, cadmium pigment manufacturing, and zinc/lead smelting have the highest occupational exposures. People with dietary patterns high in rice and shellfish from contaminated growing regions (parts of Japan, China, South Asia) have elevated dietary intake [1]. Iron-deficient individuals absorb 3-5× more cadmium because cadmium uses the DMT-1 transporter that also absorbs dietary iron [2].

1. Quit smoking — tobacco is the largest modifiable source of cadmium for most people, and each cigarette deposits cadmium permanently in the kidney [1]. 2. Maintain adequate iron status — iron deficiency dramatically increases cadmium absorption from food; ask your doctor to check ferritin levels [2]. 3. Vary your diet across different grains and vegetables; avoid relying heavily on rice from regions with known cadmium soil contamination [1]. 4. Avoid NiCd batteries (choose NiMH or lithium-ion instead) and dispose of old batteries at certified recycling facilities — never incinerate [2]. 5. Occupational workers should use supplied-air respirators (not half-masks) during smelting and battery production, and participate in biological monitoring programs [1].