"It is to FIPR's credit that this study is being conducted. I am not aware of any study that is so comprehensive in measuring all the parameters needed for a proper dose assessment. Through this study, we should be able to look at our dose estimates and be better able to report one of the most important factors influencing worker dose - the solubility of the inhaled materials in lung fluids. Presently, we are only able to provide guesses on particle solubility. This will be important to the total health physics community and will apply to the phosphate industry as well as other industries that deal with radiation and radioactivity."

Wesley E. Bolch, Ph.D., PE, CHP
Professor & Health Physics Program Director
Nuclear & Radiological Engineering/Biomedical Engineering
University of Florida
On: The FIPR-funded study to assess solubility of inhaled radioactive particles in the lung fluids

Radioactivity is a natural part of our environment. Over the millennia, radioactivity has accumulated deep underground where phosphate ore is found. The radioactivity is more concentrated near the ore deposits than in surface soil, but the concentration varies such that there is less in North Florida ore than Central Florida ore. There are many radioactive elements from uranium to lead, and there are many different forms (isotopes) of those elements. When the ore is handled during beneficiation, the process in which phosphate rock is separated from clay and sand, the radioactivity concentrations in the rock concentrate that goes on for further processing is very similar to the concentrations in the original ore that was mined. At the chemical processing plant that rock is reacted with acids and filtered. It is here, during the production of phosphoric acid and granulated fertilizers, that the different radioactive elements may be separated and concentrated, especially uranium and radium. Like many non-radioactive elements, radioactivity may become embedded in equipment or form scale precipitates on pipes or other objects. Radium-bearing scale, in particular, can build up to where radiation levels on site are of concern.

Since its inception, FIPR has studied the magnitude and consequences of radioactivity and radiation in the phosphate industry. There will always be new technologies and unforeseen situations that alter the accumulation, concentration and exposure to radioactive materials.

The science of radiation protection also grows and adapts as empirical data are obtained. The various scientific bodies mold the science into recommendations that are adopted in whole or in part by governing bodies that set regulatory limits. As the situations, recommendations and limits change, studies must be conducted to address them.

FIPR is currently conducting a study to evaluate the health risks to workers in the phosphate industry resulting from chronic inhalation of particulates containing radioactive material and/or potentially toxic chemicals. The study builds on two previous FIPR studies and is quantifying particle size, shape and chemical composition. It focuses on the solubility of inhaled radioactive particles in the lung fluids, which is a key factor in accurately assessing the internal dose to phosphate workers.

Radioactive particles embedded deep in the lungs are more likely to cause a health risk. Those particles can either stay there for a long time, emitting radiation into sensitive lung tissues, or dissolve to be distributed to other parts of the body. While in the lungs, particles are bathed in lung fluids. Some particles may dissolve slowly while others dissolve quickly depending upon things like particle shape and chemistry. Once dissolved, the body treats the liberated atoms and molecules from the particle like a resource it can either use or discard. For example, some dissolved portion may be filtered out of the blood stream as waste and eliminated from the body. Other parts are distributed throughout the body where they are needed. Radium looks similar to calcium to the body, so it may be used to build bone. Once radium is a part of bone, it emits radiation there instead of in the lungs. That is why it is important to know how much of the particle dissolves in lung fluid and how fast. That allows us to calculate doses to all parts of the body over time and sum them for a total dose.

Dose is important when trying to protect public health. To understand the concept of a radiation dose, imagine you are in a boxing ring. If 100 punches are thrown, you are exposed to your opponent's force 100 times. If 30 punches land on your jaw, you have received a dose of 30. For particles in the lung, consider alpha radiation as the punch. A dust particle deposited deep in the lung may have many radioactive atoms emitting alpha radiation. The lung is exposed to all that are emitted, but some are harmlessly stopped by fluids or non-sensitive tissues. However, some may impact sensitive dividing cells and cause damage. Those are landing the "punches" that give a radiation dose that also carries a risk of causing lung cancer.

In some areas of the phosphate granulated fertilizer facilities, there is some dust-bearing radioactivity suspended in the work environment air almost all the time. Our studies are designed to find out how much dust the workers breathe, what portion is the right size to stay in the lungs, how much of the dust dissolves in lung fluid and how fast, and the total radiation dose to the entire body during a worker's lifetime.

With the information this study may provide, the Radiological Health and Safety staffs of each phosphate company can develop informed policies with respect to respiratory protection in the workplace. Regulators in the State of Florida who are currently reviewing the need for respiratory protection programs in the phosphate industry can also use the information to provide realistic estimates of workers' doses.