Understanding Radiation Exposure and the Health Risks in Japan

March 21, 2011
Reactor problems at Japan’s Fukushima Daiichi nuclear power plant could lead to exposure to large amounts of radioactivity, which can be lethal to humans and have long-term health consequences. An expert at Nova Southeastern University breaks down the types of radioactive materials, exposure and risks.

According to Robert C. Speth, Ph.D., professor of pharmaceutical sciences at Nova Southeastern University’s College of Pharmacy, radioactive substances are dangerous because they are unstable molecules that are continually exploding. When they explode, they emit ionizing radiation containing a high amount of energy. When particles emitted from an exploding molecule hit a cell in the body, considerable damage ensues. Ionizing radiation is like a fusillade of miniature bullets hitting the body or miniature bombs that explode within cells.

There are two types of radioactive exposure:

1) Acute exposure to ionizing radiation. Particles, or energy waves emanating from the radioactive source, can penetrate the body and damage vital cellular machinery. The greatest concern is when it damages DNA, preventing it from making new proteins to keep the cell alive. Worse yet, it may begin to copy itself abnormally, turning the cell into a cancer cell.

2) Chronic exposure arising from ingestion or inhalation of the radioactive material. Radioactive materials are released as gases or small particulates. The gases can be inhaled and absorbed into the body through the lungs. Particulates also are dispersed into the air and can be inhaled. The particulate ultimately will settle on the ground, contaminating everything it contacts. It’s incorporated into plants growing on the contaminated ground, entering the food chain. This results in long-term, sustained exposure to the radioactive molecules. Inside the body, the radioactive molecules continue to explode, damaging the cells in which they are located.

Four types of radioactive materials (radioiosotopes) generally are released during a nuclear meltdown:

Tritium (hydrogen-3) and nitrogen-16 are of moderate concern. The radioactive particles released from tritium travel less than a thousandth of an inch and have such low energy that they cannot penetrate skin. There is some danger from inhaled tritium because cells containing exploding tritium molecules can be damaged. Ingested tritium is eliminated from the body fairly rapidly.

Nitrogen-16 has a short half-life of 7 seconds. Within 1 minute of formation, less than 1 percent of it remains radioactive. However, it emits very high-energy gamma radiation waves. The concern for exposure to nitrogen-16 is primarily to individuals very close to the site at which the nitrogen-16 is formed.

The greatest danger comes from cesium-137 and iodine-131. These radioisotopes emit relatively large amounts of energy. Cesium-137 has a half-life of 30.1 years, so it takes 200 years to decrease to 1 percent of its radioactivity. When inhaled or ingested, it mimics potassium, accumulates in muscle and damages cells, especially their DNA. Damage to DNA is a leading cause of cancer.

Iodine-131 mimics non-radioactive iodine and accumulates in the thyroid gland. Iodine-131 has a half-life in the body of 7.6 days. The thyroid uses iodine to make thyroid hormone, which is critical for control of cellular metabolism. Iodine-131 accumulation in the thyroid gland can cause thyroid cancer. At excessive levels, it destroys the thyroid gland. Thyroid function is extremely important in infants because thyroid hormone is critical for brain development.

Japan continues working to stabilize several nuclear reactors damaged by the March 11 earthquake and tsunami. Workers attempting to cool fuel rods have been interrupted several times when they had to evacuate due to high radiation levels.

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