ATSDR -EVALUATING DOSE MEASUREMENTS OF GAMMA RADIATION

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ATSDR HEALTH CONSULTATION
EVALUATING DOSE MEASUREMENTS OF GAMMA RADIATION
FOR RESIDENTS NEAR THE STAUFFER CHEMICAL COMPANY SUPERFUND SITE
AND VICINITY PROPERTIES
TARPON SPRINGS AND HOLIDAY, FLORIDA
CERCLIS # FLD010596013
JANUARY 16, 2002

Energy Section

Federal Facilities Assessment Branch

Division of Health Assessment and Consultation

Agency for Toxic Substances and Disease Registry

TABLE OF CONTENTS

Summary

Background and Statement of Issues

Table 1. Doses for People Living Near Stauffer

Table 2. Doses for People Not Living Near Stauffer

Conclusions

Recommendation

References

Summary

From 1947 to 1981, the Stauffer Chemical Company in Tarpon Springs, Florida, made elemental phosphorus from phosphate ore. While the plant was in operation, phosphorus slag was transported off the site and used as aggregate in road bedding, road and driveway paving, and in concrete structures. Residents in the area are concerned about possible adverse health effects resulting from exposure to gamma radiation from phosphorus slag that was used in nearby roads, buildings, and homes. Gamma radiation, or gamma rays, consists of bundles of electromagnetic energy and is the same type of radiation as medical x-rays.

In 1999, at their request, residents of the community surrounding the former Stauffer chemical plant were given thermoluminescent dosimeters (TLDs) by the Pinellas County Health Department to monitor their individual gamma radiation dose measurements for a 30-day period. As a follow-up to the previous public health assessment addendum for the site issued in June 1999 and to a draft public health response plan for the site released in June 2001, the Agency for Toxic Substances and Disease Registry (ATSDR) reviewed the individual dose measurements recorded by the Pinellas County Health Department for the residents of this Tarpon Springs, Florida, community.

Background, or naturally occurring radiation, varies by location in the United States and is measured in one-thousandth of rem, or millirem (mrem). Background gamma radiation dose rates for the United States average anywhere from 44 to 133 mrem per year. The average dose to the residents monitored in Pinellas and Pasco counties was 92 mrem per year, although it was not possible to quantify the contribution from slag. Those monitored residents in homes near the Stauffer site had an average annual dose of 91 mrem, which was not statistically different from the average dose of 95 mrem per year to those monitored residents living farther from the site.

These measurements show that the combined gamma radiation doses from homes and pavement with phosphorus slag are not elevated and do not pose a health threat.

Background and Statement of Issues

As a follow-up action to the previous public health assessment addendum for the Stauffer Chemical Company site and Vicinity Properties in Tarpon Springs and Holiday, Florida, which was issued in June 1999, and to a draft public health response plan for the site released in 2001, the Agency for Toxic Substances and Disease Registry (ATSDR) evaluated the gamma radiation doses measured by the Pinellas County Health Department for residents near the site who had requested this assessment. The Pinellas County Health Department, responding to public demand, provided thermoluminescent dosimeters (TLDs) to persons who wanted their radiation dose measured and who lived near the former Stauffer chemical plant in Tarpon Springs, Florida. TLDs are made of crystalline material (solid state) that emits light in proportion to the ionizing radiation absorbed, when the device is heated.

Dose measurements performed at the residents' request were purely voluntary. TLDs were distributed to residents of the communities surrounding the former plant, regardless of whether they had phosphorus slag on their property. These residents were asked to wear the TLDs all day for a 30-day period, but not during medical procedures (e.g., x-rays), and measurements were extrapolated, or projected, to yearly doses. The measurements were taken during the last few months of 1999. The Pinellas County Health Department assumed that participants were exposed to slag, based on the distance of their homes from the former Stauffer site. Those participants living closer to the site were assumed to be more exposed to radiation from the slag. Table 1 displays the doses for persons living near the Stauffer Superfund site and who were assumed to have slag in their homes. Table 2 shows the doses for persons who did not live near the site and who were assumed to not have slag in their homes⁽¹⁾. Use of phosphorus slag is widespread in this part of Florida, and most people are, to some degree, exposed to gamma radiation from the slag.

Table 1. Doses for People Living Near Stauffer

Subject #	City	Gamma Dose (mrem/yr)
2	Tarpon Springs	78
4	Tarpon Springs	84
5	Holiday	88
6	Tarpon Springs	86
7	Tarpon Springs	90
8	Holiday	100
10	Holiday	62
12	Tarpon Springs	88
13	Tarpon Springs	122
14	Tarpon Springs	89
15	Tarpon Springs	76
16	Holiday	94
17	Holiday	101
18	Holiday	83
19	Holiday	88
20	Holiday	94
22	Holiday	102
23	Holiday	91
24	Holiday	84
25	Holiday	90
28	Tarpon Springs	116
29	Holiday	86
30	New Port Ritchie	91
34	Holiday	85
36	Holiday	79
39	Holiday	85
41	Tarpon Springs	79
42	Tarpon Springs	90
43	Holiday	103
45	Holiday	72
46	Holiday	85
47	Holiday	73
48	Holiday	94
49	Tarpon Springs	166
51	Holiday	70
52	Tarpon Springs	83
54	Tarpon Springs	95
56	Holiday	116
57	Tarpon Springs	73
59	Palm Harbor	91

Table 2. Doses for People Not Living Near Stauffer

Subject #	City	Gamma Dose (mrem/yr)
1	Palm Harbor	82
3	New Port Ritchie	95
9	Palm Harbor	113
11	New Port Ritchie	110
21	Palm Harbor	88
26	Palm Harbor	97
27	New Port Ritchie	90
31	Holiday	112
32	New Port Ritchie	82
33	Palm Harbor	100
35	Holiday	80
37	Clearwater	95
44	Palm Harbor	79
53	Shady Hills	83
58	Palm Harbor	120
60	New Port Ritchie	95

The average dose for those living in homes assumed to contain slag was 91 mrem per year and 95 mrem per year for those living in homes assumed not to contain slag. A simple two-sample t-test and Welch modified two-sample t-test both showed no statistically significant difference in means at the 95% confidence level. The 95% confidence intervals were nearly identical, being 56 - 125 mrem/year for residents near the Stauffer site and 69 - 121 mrem/year for residents farther from the site. Graphs of the dosimetry data are presented in Figures 1 and 2, with Figure 1 depicting data for those in homes near the Stauffer site and Figure 2 showing data for those not near the site.

The average dose rate to all participants was 92 mrem per year. All but one of the doses measured were within the range of normal background doses for the contiguous United States. Average background doses from terrestrial and cosmic gamma radiation for cities in the United States range from 44 to 133 mrem per year⁽²⁾.

The average dose to those residents assumed to have no slag in their homes was 4.5 mrem higher than the dose to those with slag in their homes. There was no statistical difference in average doses. Moreover, these measured doses are consistent with published values for background doses from external ionizing radiation in this area⁽³⁾.

In Figure 1, the block at 166 mrem is based on a single individual dose for subject #49 and is outside the normal range of background doses. According to Chauvenet's criterion⁽⁴⁾, this measurement is clearly an outlier and is more than four standard deviations above the mean.

Conclusions

1. The combined gamma radiation doses from homes and pavement with phosphorus slag measured for residents near the former Stauffer chemical plant are consistent with background and do not pose a health threat to the community. Because assumptions were made about which homes contained slag and which homes did not contain slag, the contribution to annual radiation doses from phosphorus slag at this location cannot be quantified. The average dose to monitored residents in homes assumed to contain slag (91 mrem) was statistically similar to the average dose to those evaluated in homes assumed not to contain slag (95 mrem).

2. The individual that received 166 mrem dose is outside the normal range of background. According to Chauvenet's Criterion, this measurement is clearly an outlier and is more than 4 standard deviations above the mean, although not of sufficient magnitude to warrant concern from a health standpoint.

Recommendation

Pinellas County or the State of Florida should re-measure the dose and perform a radiation survey at the location where the 166 mrem level was observed.
If the initial measurement is validated, explore what, if any, ALARA measures might be appropriate.

Prepared by:

Michael D. Brooks, CHP
Health Physicist

Peer Reviewed by:

Clinton Cox, PhD, CIH
Ronald L. Kathren, PhD, CHP
James E. Watson, PhD

References

1. Pinellas-Pasco Regional Radiation Study, Pinellas County Health Department. Prepared by D. Michael Flanery, Feb. 4, 2000.

2. Eisenbud M, Gesell T. Environmental radioactivity from natural, industrial, and military sources. 4th ed. San Diego (CA): Academic Press; 1997. p. 183.

3. Exposure of population in the United States and Canada from natural background radiation. Bethesda (MD): National Council on Radiation Protection and Measurements; 1987. NCRP Report No. 94.

4. Young, H. D. Statistical Treatment of Experimental Data; McGraw-Hill: New York,1962.

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This page last updated on January 23, 2002

Contact Name: Joanne D. Cox/ JDCox@cdc.gov