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The observed radiation background for similar residences was 6-7 microrad per hour (µrad/hr). Average dose rates in affected areas ranged from 15.4 to 39.1 µrad/hr. One thousand µrads are equivalent to one millirem for gamma radiation. The National Council on Radiation Protection and Measurements (NCRP) 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).

Table 1:

Table 1.

Stauffer Chemical Vicinity Properties - Residence 1
Location: Residence 1 µrad/hr (waist level) µrad/hr ground level Average
#1 basement 42 49 45
#2 basement 38 44 41
#3 basement 43 48 46
#4 basement 47 51 49
#5 basement 44 51 47
#6 basement 31 41 36
#7 basement 45 46 45
#8 basement 30 44 37
#9 basement 46 53 49
#10 basement 42 48 45
#11 bedroom 31 41 36
#12 bedroom 30 39 35
#13 1st floor 14 17 16
#14 1st floor 20 28 24
#15 1st floor 10 9 10
#16 1st floor 19 26 22
#17 1st floor 26 29 27
#18 1st floor 25 31 28
#19 1st floor 11 12 11
#20 1st floor 9 11 10
#21 driveway 29 38 34
#22 driveway 29 39 34
#23 driveway 60 73 67
Average living areas 16.7 (1st floor)
Annual Dose from Building Materials (mrem) 210

Note: One thousand microrad (µrad) are equivalent to one millirem (mrem) for gamma radiation.

To calculate an Annual Dose, because there were small children in the home, took an average of the one meter and ground level measurements, then for each area (e.g. bedroom, 1st floor) took an average of readings, then subtracted the local background of 6 µrad/hr and assumed 12 hours per day in the bedroom, 5 hours in the basement, one hour on the first floor and one hour on the driveway for 350 days per year.

Table 2.

Stauffer Chemical Vicinity Properties - Residence 2
Location: Residence 2 µrad/hr (waist level)
#1 bedroom 20
#2 bedroom 21
#3 bedroom 20
#4 bedroom 22
#5 bedroom 26
#6 bedroom 27
#7 bedroom 28
#8 bedroom 21
#9 bedroom 25
#10 bedroom 27
#11 bedroom 29
#12 bedroom 27
#13 bedroom 21
Annual Dose from building materials 76 (mrem)

Note: One thousand microrad (µrad) are equivalent to one millirem (mrem) for gamma radiation. To calculate an Annual Dose, averaged the readings, then subtracted local background of 6 µrad/hr and assumed 12 hours per day in the bedroom and 5 hours in other parts of the house for 350 days per year.

Table 3.

Stauffer Chemical Vicinity Properties - Residence 3
Location: Residence 3 µrad/hr (waist level)
#1 o/s slab 25
#2 o/s slab 25
#3 o/s slab 19
#4 o/s slab 19
#5 o/s slab 22
#6 o/s slab 29
#7 o/s slab 22
#8 o/s slab 23
#9 living room 22
#10 living room 19
#11 living room 19
#12 living room 20
#13 kitchen 20
#14 kitchen 19
#15 bathroom 15
#16 o/s bathroom 15
#17 side bedroom 8
#18 back left bedroom 7
#19 back right bedroom 15
#20 back right bed 7
Annual Dose from building materials 41 (mrem)

Note: One thousand microrad (µrad) are equivalent to one millirem (mrem) for gamma radiation. To calculate an Annual Dose subtracted local background of 6 µrad/hr, then for each area (e.g. bedroom) took an average of readings, and assumed 12 hours per day in the bedroom, 5 hours in other areas of the house and 1 hour on the outside slab for 350 days per year.

Table 4.

Stauffer Chemical Vicinity Properties - Residence 4
Location: Residence 4 µrad/hr (waist level)
#1 garage 21.5
#2 garage 25.7
#3 garage 21.7
#4 garage 21.5
#5 foyer 10.2
#6 foyer 9.4
#7 foyer (by door) 13.0
#8 adjacent bath 12.1
#9 adjacent bath 9.8
#10 back door 11.4
Annual Dose from building materials 50 (mrem)

Note: One thousand microrad (µrad) are equivalent to one millirem (mrem) for gamma radiation.. To calculate an Annual Dose, subtracted local background of 6 µrad/hr, then for each area (e.g. garage, foyer) took an average of readings, and assumed 12 hours per day in the house and 5 hours in the garage for 350 days per year.

Table 5.

Maximum Contaminant Concentrations in Parts per Million (ppm)
Contaminant Driveway Pavement Driveway Base Yard Soil Comparison Value
Antimony 0.0566 0.252 0.0469 20 (Chronic RMEGs Child)
Arsenic 4.85 3.84 0.829 20 (Chronic RMEGS Child)
Beryllium 1.24 1.92 0.749 100 (Chronic RMEGS Child)
Chromium 27.7 22.3 49.6 200 (Chronic RMEGS Child)
Lead 18.2 11.7 31.8 400 (EPA Screening Level)
Thallium 0.70 0.614 0.0658 5 (Chronic RMEGS Child)
Vanadium 33.9 26.3 17.2 200 (Intermediate EMEG Child)
Radium-226 70.2 (pCi/g) 6.21 (pCi/g) 25.1 (pCi/g) 5 pCi/g to 5 cm depth

15 pCi/g below 5 cm

(40 CFR 192 )

Key: Reference Media Exposure Guideline (RMEGS)
Environmental Media Exposure Guideline (EMEG)
EPA Standards for Uranium and Thorium Mill Tailings {40 CFR 192 (1983)}
Code of Federal Regulations (CFR)


The ATSDR responses to the following comments are in italics.

The ATSDR should be commended on this report since it conveys the radiological situation in Tarpon Springs to the public in a manner that is easy to understand. In addition, the radiation doses are put into proper perspective by comparison with the LOAEL and natural background. They should also be commended for their use of the word "guidelines" instead of "standards" when referencing the 100 mrem per year recommended dose limit. However, the report requires clarification on a number of issues.

The ATSDR should clarify that these guidelines do not apply to slag but are used to put the estimated doses into perspective. Phosphate slag is not a man-made radioactive material or a licensed radioactive material. It is a naturally-occurring radioactive material. It is appropriate to use these guidelines as a means of putting these estimated doses into perspective; however, the report fails to clarify this point.

Clarified throughout document that phosphate slag is a naturally occurring material.

As an example, the reports states that at one residence, the levels of ionizing radiation exceed both national and international guidelines for exposure by more than a factor of two. The report should indicate that these guidelines do not apply to phosphate slag, but only to licensed radioactive materials. The only guideline which could apply to phosphate slag is 500 mrem per year as recommended by the NCRP for continuous exposure to natural sources in remediation situations. In reference 6 (ICRP 60), the International Commission on Radiological Protection specifically states on page 44 that situations such that in Tarpon Springs are outside the scope of the dose limits for public exposure. Similarly, in reference 8 (NCRP 116), the National Council on Radiation Protection and Measurements states on page 45 that their recommended public dose limit of 100 mrem per year applies only to man-made sources of radioactivity. The radioactive material in phosphate slag is not man-made but naturally-occurring radioactivity. Yet, on page 7 of the ATSDR report, the reader is left with the impression that this guideline applies to exposures from phosphate slag. While the 100 mrem per year criterion is useful for comparison purposes, the public deserves to know that this criterion does not apply to radiation exposures from phosphate slag.

Corrected to make clear that the guideline for naturally occurring radioactive material in building materials comes from NCRP 116 and that this is not a man made radioactive material.

The report uses units of µrads, millirems, millrads, rems and rads. I would suggest that all the units be converted to millrems for clarity and ease of understanding. The reader is much more likely to understand a comparison between 300 mrem per year and 10,000 mrem than the comparison in Conclusion 3 between 300 mrem per year and 10 rem; and the comparison on page 7 between 100 millirem per year over a lifetime and 10 to 25 rem in one exposure. On page 7, for example, wording such as "The lowest observed adverse effect level from ionizing radiation is from 10,000 to 25,000 mrem in one exposure..." would be more understandable and provide a more useful perspective for the reader. The ATSDR should also be commended for the use of the LOAEL, since the public deserves to know that adverse health effects are not observed at dose levels such as those which are estimated in this report. The ATSDR should also list the occupational dose limit of 5,000 mrem per year as a level considered safe for occupational radiation workers.

Converted all units discussed to millirem.

The report indicates that the PIC is calibrated in µrad per hour. It is my understanding that a PIC is designed to measure gamma radiation in air, which is properly measured with the unit Roentgens per hour or micro-Roentgens per hour. The rad describes the absorption of energy in tissue, not air, although the conversion from Roentgens to rads is simple. I do not, however, recommend the use of this unit since all the units in the report should be converted, as accurately as possible, to millirem to avoid confusion. However, my understanding of the definition of the Roentgen indicates that the statement of calibration of the PIC may be incorrect.

The PIC is calibrated using a NIST traceable standard, so that readings can be converted to µrad per hour. The chamber is constructed from a tissue equivalent material, so that readings are tissue equivalent and energy independent.

On page 7, the report refers to "high" concentrations of radium-226 in phosphate slag. From a radiation protection standpoint, the concentrations of radium-226 found in phosphate slag cannot be considered high since concentrations of radium-226 can be found in the natural environment which exceed these levels. A more appropriate characterization would be "elevated" such as was appropriately used at the top of page 8 and in other parts of the report.

Changed to "elevated", as suggested.

This report goes to great lengths to educate the public as to the potential radiation doses which might be received by persons who may be exposed to phosphate slag in their homes and in the environment. The ATSDR's use of the LOAEL provides a comparison which is easy to understand if it is listed in the same units. However, the ATSDR should inform the reader as to the proper use of the radiation protection guidelines which are referenced in the report.

Attempted to clarify the proper use of ICRP and NCRP guidelines.

Radioactive materials off-site appear similar to radioactive materials on the SMC site. The slag, regardless of where it occurs, has a low-- but elevated-- level of radioactivity. Simply put, the degree of danger from any radioactivity is directly proportional to the amount of slag nearby.

Slag contains naturally occurring radioactive materials, which is considered part of background. Doses did not exceed any applicable guideline.

Prior to these studies, it was thought there might be "hot spots" from particularly radioactive batches of slag. This would be difficult to determine on-site due to the enormous amounts of slag. However, off-site it could manifest as unusually radioactive driveways or foundations. Fortunately, these studies show this is not the case.

No change necessary.

Since there is a proportional relationship between the amount of slag and radioactivity, the site itself represents the largest hazard to the community; however, some areas where large amounts of slag were incorporated into building foundations can represent a lesser threat. In particular, the residence constructed using "hurricane-proof" methods that incorporated slag into walls and sub-floors represents an obvious potential hazard to its occupants. There is too little data and far too much speculation on health effects in the PHA to support the conclusion that this residence is completely safe from slag radioactivity. Extrapolating from bomb data on the one hand, versus speculating on granite buildings on the other hand, is poor science.

A conservative dose estimate for a maximally exposed child residing in residence #1, was less than half the remediation guideline of the NCRP (8).

A study has been proposed for some time that would give residents radioactivity-sensitive film badges to accurately gauge individual exposure. This type of study affords another opportunity to view actual exposure, and such studies have been performed in other communities where there is a question of exposure. This data is needed before the full conclusions of the PHA can be accepted.

Film badges would not be sensitive enough and tend to fade. The ATSDR would recommend that any homeowner interested in measuring their individual dose obtain a Thermo-Luminescent Dosimeter (TLD) from a local accredited lab.

Conclusions in the PHA addendum regarding off-site arsenic cannot yet be accepted at face value. First, the report concludes arsenic is entirely trapped in vitreous "glass-like" material and therefore biologically unavailable. The studies authors seem to have jumped to this conclusion based on very little real data; to date the EPA has not provided compelling studies proving the "trapped arsenic" hypothesis. Secondly, the levels of arsenic considered toxic seem to be in debate. As far as can be determined, the ATSDR is deferring to the EPA, which is deferring to the State of Florida, which seems to be unable to offer any rationale for an arsenic threshold. Based on the discussions related so far it is doubtful if the state has a true policy regarding arsenic, and unlikely that any policy uses residential rather than commercial exposure level scenarios. Part of the picture is certainly political. According to a literature survey, arsenic has been a byproduct of numerous mining and manufacturing processes in Florida, as well as widely utilized in environmental control processes at golf courses and military institutions. Clearly, the State may not want to set a precedent for residential arsenic cleanup. Partly, the confusion over arsenic relates to its many different forms in the environment. As an element, arsenic will never be broken down, but arsenic can exist as soluble salts that are more toxic that the sintered form thought to occur in local Tarpon Springs residential areas.

EPA's samples of off-site slag were below health comparison values for arsenic.

There are soil extraction and toxicity tests that can answer some of the questions surrounding the safety of off-site materials. These studies could be designed to provide the toxicity answers thereby reducing community concerns. At the public meeting presenting the off-site findings, the EPA suggested that slag in the community be locally remediated as solid waste. This is also a logical opportunity to cancel the threat, or perceived threat, to local residents.

The ATSDR does not feel further sampling is warranted, based on current sample results.

The most obvious shortcoming, of this health assessment is that the findings on which it is based are incomplete and standards are either absent, presented without explanation (Table 5), ignored or dismissed.

There are not always good or consistent guidelines available to make public health evaluations. The ATSDR strives to make public health evaluations of completed or potential exposures. If there is no exposure possible, then there is no health risk.

Mathematical projections of radiation exposure have been made, which may or may not approximate the actual exposure of affected individuals. This would be acceptable if there were no alternative way to collect experiential data. This is not the case, however. A sampling of affected residents needs to be given radioactivity-sensitive film badges to wear (over a period of time to be determined by the scientific community) to more accurately measure individual exposures. The local citizens deserve to be advised on the basis of information about what exposure is actually happening, rather than OD projections that do not take into consideration the life style of the individuals involved. Since techniques do exist to monitor the actual accumulation of exposure to radioactivity, and since the costs associated with that technique are not outrageously high, it seems to us that prudence would dictate that any scientist - and we assume that these results are being analyzed by scientists, not actuaries or risk managers- would not only recommend but urge that this extra step be taken to measure the actual, not the projected, exposure of the affected citizens.

Film badges would not be sensitive enough and tend to fade. The ATSDR would recommend that any homeowner interested in measuring their individual dose obtain a Thermo-Luminescent Dosimeter (TLD) from a local accredited lab.

The solubility, and thus the toxicity levels, of arsenic in offsite materials have not been investigated. The theory that arsenic is trapped and chemically/biologically unavailable is unsubstantiated. There have been no specific studies indicating that this is the case in any or all contaminated areas being included in these generalized conclusions. Pursuant to this lack of convincing data of the solubility of arsenic and other chemical contaminants, the questions relating to potential groundwater contamination have gone unasked and unanswered. Wells located in any areas with significant slag need to be tested for the contaminants of concern. The question of contaminated groundwater below contaminated offsite areas has been ignored.

EPA samples were leach tested for heavy metals including arsenic and the lack of measurable quantities of arsenic and other heavy metals in leachate demonstrate that the material is insoluble and therefore not bioavailable.

There appears to be no agreement on what standards for arsenic are acceptable. While local citizens were once led to believe that 10 -6 risk levels for arsenic were to be applied as clean-up levels (.4 ppm or .8 ppm, depending on whether federal or state guidelines are referenced), this no longer seems to be the case. The PHA Draft itself makes no mention of the current disagreement over standards, and instead lists an RMEGS Comparison Value of 20, which has the affect of minimizing the high arsenic concentrations found, leading to the average reader's perception that the arsenic level is substantially below "standards." While the lack of clarity and the misleading nature of the information in Table 5 could be construed as an attempt to confuse local citizens concerning the degree of contamination found in the study, we must assume that there was no ill intent. We believe the problem is one of inattention to communication skills. Specifically, there is no definition and clarification of the actual meaning of the information in the "Comparison Value" column. The brief reference to this term on page 8 is not particularly enlightening or reassuring. In addition there is no information concerning the "commercial" and "residential" standards for the various heavy metal contaminants. We recognize that there is disagreement between the EPA and FDEP concerning certain standards and feel that this is of such importance that comment on the issue should have appeared in this report.

It is true to say that there is considerable disagreement on a standard for arsenic in various media. Because the ATSDR is not a regulatory body, we use media specific guidance from our staff of board certified toxicologists.

The Public Health Implications contain a number of confusing and inconsistent statements. While acknowledging that both the ICRP and the NCRP recommend limiting annual exposure to external radiation to 100 mrem/yr above background levels, and that the annual dose to a person living in Residence #1 could be over twice that limit, it goes on to predict that no adverse health effects would be expected from residing in that home. Within the space of the paragraphs, standards are described, a case in which the contamination considerably exceeds those standards is cited, and then the statement is made that no ill effects are anticipated. It is also stated on page 8 that contaminated slag does not appear to contain sufficient heavy metals to represent a public health hazard, ignoring the fact that levels of arsenic are well over the State of Florida's acceptable levels. Thus, there appears to be an arbitrary use of standards in this document. They are invoked when convenient. and at ether times ignored. The PHA lists standards for radiation and arsenic in some areas of the text, and then proceeds to ignore them in the Conclusion.

The 100 mrem/yr standard is mentioned only for comparison, as the source of radiation is from naturally occurring radioactive materials. Naturally occurring radioactive materials are considered part of background, and the 100 mrem/yr standard is to protect from man-made exposures. The NCRP (8) has recommended remediation only if the annual dose from naturally occurring radioactive material in building materials exceed 500 mrem/year.

How is the ATSDR able to legitimately state that no ill effects are expected when standards are violated? It appears that the ATSDR chooses which standards to ignore and then does not give any rationale for so doing. The words "arbitrary" and "capricious" are used in the legal and community to describe this lack of consistency in applying applicable rules and standards.

No health guidelines have been exceeded.

This report has done very little to allay the fears of concerned residents, or to convince them that they are being protected.

The ATSDR has taken the following steps to explain that there is no public health threat from the limited use of phosphate slag in buildings and roads:

A. Met with individual homeowners on numerous occasions,
B. Held public meetings and availability sessions,
C. Coordinated with the EPA and the State of Florida Department of Health,

D. Responded to numerous letters and phone calls from the press, the public and elected officials,
E. Preparing public health education in conjunction with the State of Florida Department of Health.

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