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Residents from Tarpon Springs, and Holiday, Florida expressed concern about adverse health effects resulting from exposure to radium and heavy metals leaching from phosphate slag that was used in nearby roads and buildings. Besides radium, other contaminants of concern to residents were arsenic, beryllium, uranium, radon, and ionizing radiation.



A. Contamination

The ATSDR reviewed the report of the radiological survey that EPA Region IV conducted during the week of August 23, 1998 (2). The gamma radiation surveys were taken at four residences near the Stauffer Chemical Superfund site in Tarpon Springs, Florida. Slag and soil samples were taken at 10 residences and chemically analyzed (3) to determine if there was a toxicological risk to the public and also to compare the contaminants in the off site slag to those at the Stauffer site. Slag appeared to be in a sintered form (i.e., a glass like material), consistent with an arc furnace extraction process. Samples were analyzed for aluminum, antimony, arsenic, asbestos, barium, beryllium, cadmium, chromium, cobalt, copper, iron, manganese, mercury, nickel, radium, selenium, silver, thallium, vanadium, fluoride, and zinc.

ATSDR staff also reviewed relevant tests conducted by EPA representatives (2,3) and health-related reports issued by the Florida Department of Health (FDOH). The FDOH, through a cooperative agreement with the ATSDR, has issued a public health assessment for the Stauffer site (4) and a health consultation for the Gulfside Elementary School in Holiday, Florida (5).

Appendix A contains the radiological survey and sampling data from the site visit (Stauffer Chemical Vicinity Properties) during the week of August 23, 1998.

Static gamma radiation surveys were taken in four residences using a pressurized ion chamber (PIC). This instrument is calibrated in microrad per hour (µrad/hr) and was provided and operated by the EPA's National Air, Radiation and Environmental Laboratory (NAREL) . Comparison surveys were taken at the same locations with a Bicron Micro Rem meter, S/N B792W, calibration date of August 4, 1998. Measurements were taken at both waist level (normal standard for exposure surveys) and ground level for comparison purposes.

The hurricane proof construction style of residence #1 (see Table 1) is different from that of any other home encountered. The floors and some walls on both levels are poured concrete that use phosphate slag as aggregate. This resulted in the basement floors having more than twice the gamma dose rate of the upstairs living space.

B. Quality Assurance and Quality Control

In preparing this public health assessment (PHA), the ATSDR relied on the information provided in the referenced documents. The agency assumed that adequate quality assurance and quality control measures were followed with regard to chain-of-authority, laboratory procedures, and data reporting. The validity of the analyses and the conclusions drawn in this document was determined by the availability and reliability of the referenced information.



As of June, 1998, there was a completed exposure pathway from ionizing radiation from elevated background, but not at levels expected to cause adverse health effects. EPA samples of selected residences found that driveways, yard fill, home foundations, and other concrete structures contained phosphate slag with measurable concentrations of the natural radium isotope Ra-226 (3). Phosphate slag is a naturally-occurring radioactive material, not a man-made radioactive material or a licensed radioactive material.

Radiation dose measurements in several homes were elevated compared to background measurements, but not sufficient to represent a health hazard. The normal background for the Tarpon Springs area was about 60 millirem per year (mrem/yr), excluding the contribution from radon. If the dose from radon for this part of Florida is included, the annual background dose is about 160 mrem/yr. Florida has a low background dose compared to Denver, Colorado, which is about 300 millirem (including the contribution to total dose from radon). The International Council on Radiation Protection (ICRP) (6) and the National Council on Radiation Protection and Measurements (NCRP) (8) both consider phosphate slag in building materials to be part of background.

The NCRP, in its report number 116, on page 50, gives the average dose from background radiation (excluding contribution from radon) to be 100 millirem per year and recommends that doses from background should be remediated if they exceed 500 millirem per year (8). To put this in perspective, the ICRP recommends that radiation doses to the public not exceed 500 millirem in any 5 year period and should be less than 100 millirem per year over a lifetime, excluding doses from background (i.e., natural sources like phosphate slag), diagnostic (e.g., x-rays) and other medical exposures(6). The lowest observed adverse effect level (LOAEL) from ionizing radiation is from 10,000 to 50,000 millirem in one exposure and is seen as a slight decrease in blood cell count (7).

Radon samples in homes were all below EPA's action level of 4 pCi/L. There was no radon gas coming from slag containing radium. The lack of radon would be expected from the glass-like character of the slag. Although phosphate slag contains heavy metals, leach testing of the samples taken by EPA, did not find measurable heavy metals. The glass-like property of the slag would also explain why heavy metals were not detected in leachate.

We made theoretical radiation dose calculations for the four properties in which gamma measurements were taken. We assumed a more conservative (high) occupancy factor of 18 hours per day in residence #1 and one hour on a slag aggregate driveway for 350 days per year, because of the young child present. For the other residences sampled, we assumed an occupancy factor of 17 hours in parts of the residence containing slag aggregate for 350 days per year. The calculated doses from building materials ranged from a high of 210 millirem per year (mrem/yr) at residence #1 (see Table 1 in Appendix A) to a low of 41 mrem/yr at residence #3 (see Table 3 in Appendix A). No infants or elderly individuals, who might be expected to be home more than 18 hours per day, lived in the homes with the greatest amounts of slag aggregate. Using a conservative exposure model for a maximally exposed child in the most affected home, the expected annual dose was well below the NCRP's remediation recommendation of 500 mrem/yr (8).



All the radium levels sampled at off site residences and the associated gamma radiation were elevated above the local average for background radiation. The National Council on Radiation Protection and Measurements (NCRP), in its report number 116 on page 50, states that some building materials can contain naturally occurring radioactive materials and should only be remediated if annual doses exceed 500 millirem per year (8). The lowest observed adverse effect level (LOAEL) from ionizing radiation is from 10,000 to 50,000 millirem in a short period of time (i.e., less than a week) and is seen as a slight decrease in blood cell count (7). (Note: A millirem is equivalent to a millirad for gamma radiation.)

Of the four homes sampled in the Tarpon Springs area, only one exceeded 100 millirem per year, from structural building materials. Residence #1 had elevated radiation levels, especially in the basement. Using a conservative scenario, the annual dose to a young child living in a basement bedroom could receive about 210 mrem/yr additional background dose, which is well below the NCRP's 500 mrem/yr guideline (8).

The ICRP and NCRP recommendations are very conservative and are a factor of 100 below the LOAEL for acute exposure to ionizing radiation. Even though the total dose including radon would be 310 mrem/yr, this is still roughly the national average background dose in the United States of 300 mrem/yr (9). No adverse health effects would be expected from residing in the most affected home.

Phosphate slag at sampled vicinity properties does not appear to contain sufficient heavy metals to represent a public health hazard, based on current medical, epidemiological and toxicological information. For non-radioactive chemicals and metals, the ATSDR uses comparison values (contaminant concentrations in specific media and for specific exposure routes believed to be without risk of adverse health effects) to select contaminants for further evaluation. The ATSDR and other agencies have developed the values to provide guidelines for estimating media contaminant concentrations that are not likely to cause adverse health effects, given a standard daily ingestion rate and standard body weight. Table 5 lists environmental media exposure guidelines (EMEGs) and reference media exposure guidelines (RMEGs).

Many of these values have been derived from animal studies. Health effects are related not only to the exposure dose, but to the route of entry into the body and the amount of chemical absorbed by the body. Several comparison values might be available for a specific contaminant. To protect the most sensitive segment of the population, the ATSDR generally selects the comparison value that uses the most conservative exposure assumptions.

Natural Background Radiation

Natural radiation and naturally occurring radioactive materials in the environment provide the major source of radiation exposure to the public. For this reason, natural background radiation is often used as a comparison for man-made sources of ionizing radiation. Background radiation comes from cosmic sources, naturally occurring radioactive materials including radon, and global fallout as it exists in the environment from testing of nuclear explosive devices. Although numerous epidemiological studies have attempted to relate the health effects to exposures from elevated natural radiation, none has provided definitive results (10).

The average annual effective dose in the United States population from natural background radiation circa 1980 - 82 was 300 millirem per year (mrem/yr). Radon and its decay products account for roughly 200 mrem/yr. Cosmic radiation contributes 26 mrem/yr at sea-level and greater than 50 mrem/yr in Denver. Terrestrial gamma radiation from the earth and building material contributes an average of 28 mrem/yr, but in certain areas with uranium or phosphate ore bodies and coastal areas with deposits of monazite sands, the contribution can be as high as 2000 mrem/yr. The contribution from internal radioactive materials, such as potassium-40 and polonium-210, is about 39 mrem/yr (9).

Special Considerations of Women and Children

Radiation doses are calculated at ½ meter (20 inches) from the floor to better estimate the dose to children. Although there is elevated background radiation from radium-containing slag and aggregate, the dose to children is approximately the national average background dose of 300 mrem per year and is not expected to result in any adverse health effects. Phosphate slag at sampled vicinity properties does not appear to contain sufficient heavy metals to represent a health hazard to women or children, based on current medical, epidemiological and toxicological information

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