PUBLIC HEALTH ASSESSMENT
Plutonium 239 in Sewage Sludge
Used as a Soil or Soil Amendment in the Livermore Community
LAWRENCE LIVERMORE NATIONAL LABORATORY, MAIN SITE (U.S. DOE)
LIVERMORE, ALAMEDA COUNTY, CALIFORNIA
SECTION 4: PUBLIC HEALTH IMPLICATIONS
One hundred millirem per year (mrem/yr; above background) is the effective dose limit established for the general population by the International Commission on Radiological Protection (ICRP 1991; from ATSDR 1999) and used by ATSDR as the minimal risk level (MRL; ATSDR 1999b). An MRL is defined as "An estimate of daily human exposure to a dose of radiation or chemical that is likely to be without appreciable risk of adverse non-cancerous (8) effects over a specified period of time." The US EPA suggests that levels of 15 mrem/year or less (EDE) are protective of human health. The State of California uses an acceptable dose limit of 100 mrem/year for members of the public (Wong 2003).
Figure 5 shows the average Pu 239 soil concentrations that would be required to produce annual doses of 15, 25, and 100 mrem/year. The soil concentrations are derived from the RESRAD model output and also may be derived from linear extrapolation of the 0.31 mrem/year dose from a soil concentration of 2.5 pCi/g. In order to produce an annual dose of 15 mrem/year (considered to be health protective by the US EPA; EPA 1997), a residential yard would have to have an average Pu 239 concentration of more than 122 pCi/g. Similarly, to produce an annual dose of 25 mrem/year, a residential yard would have to have an average Pu 239 concentration of more than 204 pCi/g. A Pu 239 soil concentration of more than 816 pCi/g (average) would be required to produce an annual dose of 100 mrem/year (above background), which is considered health protective by the ATSDR and the ICRP (and is the dose limit used by the State of California).
These dose estimates and associated soil concentrations are derived using health protective assumptions for all exposure factors and durations. The estimated doses from these soil Pu 239 concentrations include ingestion of water and soil, inhalation of dust, ingestion of food grown in the soil, and direct external radiation. The intake rates and exposure durations for each of those routes of exposure are based on health-protective assumptions from the EPA exposure factor handbook or RESRAD default conditions as listed in the preceding section and Appendix 4.
Combining the above soil concentration-dose results with the LWRP gross alpha concentrations indicates that if the sludge was contaminated at a gross alpha concentration of 250 pCi/g, and that 108 truck loads of sludge were added to a 1/2 acre yard, the resulting dose would be less than the ATSDR MRL of 100 mrem/year. Although such an exposure scenario is possible, it is very unlikely. One or two truck loads of sludge at a concentration of 100 pCi/g, added to a yard would add a dose of 0.1 to 0.2 mrem/year to the natural background terrestrial dose of ~44 mrem/year (NCRP 1987). (9) Excess doses (above background) in the range of 0.1 to 0.2 mrem/year cannot be discriminated from natural background doses for the San Francisco area). The following sections will present a brief discussion of the toxicology of plutonium and the levels of radiation exposure that have been shown to produce cancer or other adverse health effects.
Plutonium is a silvery-white radioactive metal that is a solid under normal conditions. Produced in a nuclear reactor by the conversion of uranium, plutonium is found in the environment as the result of fallout from atmospheric nuclear testing. The most common forms of plutonium (isotopes) are plutonium 238 and plutonium 239, abbreviated Pu 238 and Pu 239. Because plutonium is a radioactive element, it constantly undergoes changes called "radioactive decays." In this decay process, energy is released and a new radioactive product is formed. Most plutonium is found in nature combined with other substances, for example, plutonium dioxide (plutonium with oxygen) or plutonium nitrate (plutonium with nitrogen and oxygen) (ATSDR, 1990). As the contaminant of concern for the sewage sludge release is Pu 239, the remainder of this section will only deal with Pu 239. Pu 239 is an alpha emitter and a gamma emitter. The energy released by the radioactive decays may cause damage to cells or the surrounding tissues. In order for damage to occur, the radiation must either be absorbed by the surrounding cells or some of the energy as the radiation passes through the cell must be transferred to the cell and the surrounding medium (Johns and Cunningham, 1983).
Plutonium enters the body mainly through two pathways, inhalation and ingestion. Studies have shown that plutonium is not absorbed through the skin; however, it can enter the body via cuts and wounds (ATSDR, 1990). For all pathways, the Pu leaves the body mostly by feces and urine. Any plutonium that is not eliminated is absorbed by the body where it deposits in the organs. The most common organs for deposition following ingestion include the bone surfaces (skeleton) and liver. The lung, however, is the most impacted organ following inhalation (ICRP, 1989). As a result of these intakes, the plutonium generally stays in the body for decades and continues to expose the surrounding tissues to radiation.
The intake of plutonium may eventually increase your chance of developing cancer, but it would be several years before such cancer effects became apparent, especially at extremely low exposures. The experimental evidence regarding cancer induction at low dose exposures is inconclusive, and studies of some human populations who have been exposed to low levels of plutonium have not definitely shown an increase in cancer. However, in laboratory animals, plutonium has been shown to cause both cancers and other damage, and might affect the ability to resist disease by reducing the immune response (ATSDR, 1990). The International Agency for Research on Cancer (IARC) states, "Dose-response relationships have been demonstrated for cancers of the lung, liver, and bone in both men and women exposed to a broad range of doses", and thus IARC has classified plutonium as carcinogenic to humans (Group 1).
Plutonium is not easily absorbed into the body. The International Commission on Radiation Protection (ICRP) has reviewed the literature and recommends that an absorption coefficient of 0.5% (infants) or 0.05% (adults) be used for ingestion. In the case of inhalation, the ICRP recommends an absorption coefficient of 0.1% (infants) and 0.01% (adults) for plutonium with very low solubility in the lung. The absorption coefficient is the fractional uptake of a radionuclide that would be absorbed into blood without radiological decay. The low values of these coefficients mean that 99.5% to 99.9% of the plutonium ingested or inhaled is not absorbed by the body. Of the amount transferred to the blood, less than 25% would be transferred to the skeleton and another 25% or less would be transferred to the liver (ICRP, 1989). In other words, if one were to ingest a picocurie of Pu 239, the amount that could be transferred to the skeleton or liver for possible deposition into the organs of interest is 0.00125 pCi for infants and 0.000125 pCi for adults. For an adult with a body weight of 70 kilograms (154 pounds), this is about 1.8 × 10-9 pCi/g body weight.
We do not know if plutonium deposited in the human body causes birth defects or affects the ability to have children. If plutonium can reach these sensitive target tissues, radioactivity from plutonium may produce these effects. A number of studies have documented levels of exposure that have caused no adverse health effects. Conversely, other studies have documented high levels of exposure that have caused adverse health effects. However, no information from peer-reviewed studies in humans or in animals has identified the specific level of exposure to plutonium in air, food, or water above which may result in harmful effects (ATSDR, 1990).
ATSDR also reported in its Toxicological Profile for Plutonium, a peer-reviewed analysis of the existing data, the following synopsis of the health effects of plutonium on humans (ATSDR 1990). Information on health effects in humans is very limited largely because exposed populations are small. Epidemiological studies of people who have been occupationally exposed by inhalation to plutonium have evaluated end points such as mortality, cancer, and systemic effects following chronic exposure. No information on health effects in humans after acute or intermediate exposure to plutonium was located. Nonetheless, the following observations were made in the toxicological profile:
Animal studies, however, have shown effects of plutonium exposure. For example, in dogs exposed to plutonium via inhalation, cancer and immunological effects were observed at a concentration of 1 pCi/g-animal weight (for an 8 kg dog, the dose would be 8,000 pCi). In mice, adverse health effects on the respiratory system were not observed following inhalation that resulted in a body burden of plutonium equivalent to 3 pCi/g-mouse weight. These exposures were over 2 weeks or less (ATSDR, 1990).
Rats given plutonium via ingestion over 2 weeks period had no adverse health effects with as much as 100 pCi/g body weight. The lowest observed effect level was approximately 300,000 pCi/g (ATSDR, 1990). These results indicate a significant difference in the dose effect from inhalation and ingestion. An inhaled dose is much more radiotoxic than an ingested dose. These factors are accounted for in the dose conversion factors and included in the RESRAD analysis (ANL, 2000).
Health effects associated with exposure to ionizing radiation
Exposure to radiation is expressed as two generic types, acute and chronic exposures. By definition, ATSDR considers acute exposures as exposures having a duration of less than 2 weeks; whereas, chronic exposures occur over a year or more (ATSDR, 1990, 1999).
The adverse health effects from acute exposures to radiation have been well defined as a result of the atomic bomb survivors, medical exposures and other medical accidents. The issues for this document are those health effects associated with chronic exposures to ionizing radiation. These health effects are more difficult to define, characterize, and discuss. ATSDR experience at sites contaminated with radioactive materials shows that chronic exposures are incremental in comparison to background. In the United States, background consists of naturally occurring radon (54%), terrestrial and cosmic radiation (8% each), and internal (11%). The remainder (19%) is associated with medical exposures and consumer products(ATSDR 1999). The typical average background radiation in the United States is 3.6 mSv (360 millirem) per year. Average external terrestrial (radionuclides in soil) background radiation exposures for the San Francisco area are about 44 mrem/year with a 95th percentile value of about 80 mrem/year (NCRP 1987).
There have never been any peer-reviewed studies to show that background levels of radiation are harmful. In fact, there are portions of the globe where the background is higher than the typical area in the United States. According to the United Nations, the background can vary from below 1 mSv (100 millirem) to above 6.4 mSv (640 millirem) per year or more. For example, for an area in China where elevated levels of natural background radiation are found, studies have shown a significant increase in chromosomal aberrations, but there have been no observed increases in adverse health effects (over the 20 or more years this area has been studied). Other areas in the world where there are high background radiation levels include India, Brazil, and Iran. The area in Iran, Ramsar, has verified doses as high as 130 mSv per year (13,000 millirem) (10).
Many studies have attempted to show a cause and effect from low-level chronic radiation exposure. In these studies, low dose has been defined as any dose less than 10 mSv (1,000 mrem). No studies exist for exposures or doses below this limit. For many of these low dose epidemiological studies, researchers used the standard mortality ratio (SMR) to estimate adverse health effects. The SMR is defined as the ratio of observed deaths in a population to the expected number of deaths as derived from rates in a standard population with adjustment of age and possibly other factors such as sex or race (Society for Risk Analysis). An SMR less than 1 indicates no causality or association.
An English study of over 95,000 radiation workers whose collective dose from external radiation is about 3200 man Sv (3200/95000 = 34 mSv or 3,400 mrem) only took into account external radiation exposure and dose. The results showed the standard mortality ratio for all cancers was less than 1 (Kendall et.al. 1992).
A later study by Cardis and coworkers included 95,000 nuclear industry workers in the United States, Canada, and the United Kingdom. The study participants were monitored for external radiation exposure (mostly gamma) and were employed for at least 6 months. In all, there were 15,825 deaths, of which 3976 were from cancer. The authors found no evidence of a dose response or mortality association from all causes or from all cancers. Of the cancer types, only leukemia (except for chronic lymphocytic and multiple myeloma) showed a significant association with cumulative external radiation dose (Cardis et.al. 1995). From the cardis paper - "The combined analysis of the data for the workers demonstrated a significant (P=0.046) association between mortality from leukemia excluding CCL and radiation dose in a population receiving protracted low-dose-rate exposures." They also state "The observed association between radiation dose and mortality from leukemia excluding CCL appeared to be restricted to myeloid leukemia, particularly CML ...."
In a cohort study to determine if children were at risk of developing leukemia or other cancers before 25 years of age, Roman and coworkers included 39,557 children of male nuclear industry workers and 8883 of female workers. The study suggested that the incidence of cancer and leukemia among children of nuclear industry employees is similar to that in the general population. The SMR for all cancers and leukemias for each sex of the worker was less than 1 (Roman et.al. 1999).
The effect of radiation on humans, in general, has been well studied. However, there are few studies, especially with plutonium exposure, that are specific for women or children. In estimating radiological doses, the ICRP calculates dose conversion factors based on 6 age groups: 0 to 12 months; 1 to 2 years; 2 to 7 years; 7 to 12 years; 12 to 17 years; and more than 17 years in the cases of adult exposures. In some cases, such as the factors for plutonium, the adult exposures are calculated for 25 years or more (up to 70 years for this assessment) using the age-specific dose conversion factors. Other exposure factors include exposure durations, body and organ weights time periods, body and organ weights, and intake rates that represent childhood exposures. Consequently, the dose assessment methodology, following the intake of radioactive materials by the general population, is representative of children and adults. Also an age-adjusted soil ingestion rate is used to account for childhood soil intake, which may be larger than adult intakes (EPA 1999). Food intake rates are based on the larger long-term adult rates which is health protective for children. Therefore, the ICRP methodology and the exposure factors used in this assessment are health protective for men, women, and children.
Plutonium Doses of Public Health Concern
In order to determine whether the potential exposures to Pu-contaminated sludge presents a public health hazard, ATSDR compared the estimated doses with benchmarks or screening doses that are derived from dose levels known to produce adverse health effects. For ionizing radiation, which includes plutonium and its decay products, ATSDR has developed minimal risk levels (MRLs) that cover brief exposures (acute, or less than 14 days) and longer term exposures (chronic, or more than a year).
An MRL is an estimate of the daily human exposure to a hazardous substance that is likely to be without appreciable risk of adverse non-cancer health effects over a specified duration of exposure. The MRL is derived from exposure levels observed to produce adverse effects, with uncertainties (or safety factors) incorporated into the value. Thus, MRLs are intended only to serve as a screening tool to help public health professionals decide which release situations require more extensive evaluation. While estimated exposure dose levels below an MRL are not likely to produce non-cancer adverse effects, exposure estimates above an MRL do not mean that adverse effects will occur. ATSDR then evaluates the potential for adverse health effects in an exposed community by comparing levels known to produce adverse effects to the estimated site-related doses. This margin of exposure (MOE) approach, along with an evaluation of available epidemiologic, toxicologic, and medical data, is used by health assessors as part of the public health determination to reach qualitative (rather than quantitative) decisions about hazards posed by site-specific conditions of exposure.
On the basis of an extensive review of the health studies and documented health effects from radiological exposures, ATSDR established an MRL of 400 mrem for acute duration (14 days or less) of external exposure (11) (ATSDR 1999) to ionizing radiation. The acute MRL is based on external dose levels that did not produce behavioral and/or neurological effects on the developing human embryo and fetus. Similarly, a chronic duration (a year or more) of external exposure MRL of 100 mrem/year (above background) has been established based on radiation doses that have not produced observable detrimental health effects in humans. Thus, the ATSDR acute and chronic MRLs for ionizing radiation (including tritium) are based on doses with No Observed Adverse Effect Levels (NOAELs). While ATSDR MRLs typically include only non-cancer health effects, all the studies on which the chronic MRL for ionizing radiation are based included cancer as the specific end-point. Consequently, the chronic MRL for ionizing radiation is considered protective for both cancer and non-cancer health effects.
Similarly, ATSDR also evaluates the potential for cancer risk by first comparing the estimated dose levels to a theoretical risk level, usually the dose level associated with a 10-6 risk (one in a million) as defined by other governmental agencies. ATSDR designates these screening levels as Cancer Risk Evaluation Guides (CREGs). As with the non-cancer approach, levels less than 10-6 require no further evaluation, while estimated dose levels that exceed the 10-6 value are evaluated further. The potential for observing adverse effects is made on the basis of dose evaluation (an MOE approach), rather than on the basis of theoretical risk calculations. (See below discussion on dose-based qualitative approaches for health assessment versus risk-based, quantiative approaches used by regulatory agencies).
In contrast to the dose-based health assessments conducted by ATSDR, the United
States Environmental Protection Agency (EPA) develops regulations based on risk
and policy decisions. To accommodate proper evaluation of the dose and risk
issues associated with radiation exposure, it is necessary to clearly define
the terms dose and risk. The International Society for Risk
Analysis (www.sra.org 
) defines risk
as "The potential for realization of unwanted, adverse consequences to human
life, health, property, or the environment; estimation of risk is usually based
on the expected value of the conditional probability of the event occurring
times the consequence of the event given that it has occurred." As defined,
risk is a statistical concept, and the threshold for acceptable risk, which
is not based on observable adverse health effects, is simply a policy statement.
Risk Assessments are useful in determining safe regulatory limits. The regulatory
limits have extra safety factors built into them and may in fact be orders of
magnitude below levels at which adverse effects have been documented to occur
in humans. Risk assessments are useful in providing comparative risk discussions
for purposes of prioritizing cleanup.
ATSDR defines dose as "The amount of a substance to which a person may be exposed, usually on a daily basis. Dose is often explained as "amount of substance(s) per body weight per day". Doses are the basis for determining levels of exposure that may cause adverse health effects and may be directly related to the assessment of public health. As noted, ATSDR uses risk assessment procedures as a screening tool in its evaluation, including MOE approaches along with the consideration of health effects data (epidemiologic, toxicologic, and medical) to reach conclusions about the potential for adverse effects being observed in the community.
More specifically, ATSDR uses radiation doses instead of risk in its public health documents for various reasons. Among these are the facts that dose coefficients are based on a more exact science; that is, the doses are based on physical constants and primary principles of physics such as energy absorption. Health effects resulting from radiation doses are based on a "weight-of-evidence" approach. ATSDR, in preparing its public health documents, also relies on site-specific parameters such as demographics, realistic land uses, and other pertinent data related to the site. Using dose coefficients and modifying the coefficients for chemical forms and particle sizes, which are not typically done for risk assessments, allows ATSDR to develop health-protective, albeit realistic, values for the dose assessments as they pertain to public health documents.
Similarly, radiation health studies use dose because there is a long history of research in which health outcomes were evaluated relative to the radiation dose and not on the numerical estimation of risk. ATSDR also recognizes there are uncertainties in these dose coefficients; however, those uncertainties are addressed by the use of health protective safety factors. Risk calculations include those uncertainties plus additional uncertainty associated with the risk estimation model. Consequently, the derivation of quantitative risk is much more uncertain that the underlying dose-based assessment.
The uncertainty in the dose effects lies within the middle ranges of exposure. Adverse health effects have been conclusively demonstrated for exposures greater than 10,000 mrem/year (ATSDR 1999). Numerous studies have also demonstrated that no adverse health effects have been documented for doses less than 360 mrem/year (ATSDR 1999). The ATSDR minimal risk level (MRL) for ionizing radiation is based on numerous evaluations of health effects from exposures to background and occupational levels of radiation. "The annual dose of 3.6 mSv per year (360 mrem/year) has not been associated with adverse health effects or increases in the incidence of cancers in humans or animals." (ATSDR 1999). Consequently, 360 mrem/year is defined as a "No Observed Adverse Effect Level" (NOAEL). The derived MRL, which is further reduced by a factor of 3 to account for human variability (and conservatively rounded down from 120 mrem/year to 100 mrem/year), is protective of human health.
The science associated with risk is based on a model that, at low doses typically associated with small multiples of background, cannot be proven. ATSDR also realizes that every action, radiation dose, or activity has an associated risk. However, because no adverse health effects have been observed at doses considerably higher than 100 mrem/year (above background), there is no public health basis for using highly uncertain, risk-based screening values. Acute exposures to plutonium via the inhalation, ingestion, and dermal pathways described in this health assessment that resulted in cumulative doses of less than 400 mrem or in chronic exposures less than 100 mrem/year (above background and averaged over 5 years) are unlikely to produce any adverse health effects and therefore are below levels of public health concern.
Adequacy of Available Data for Public Health Determination
The data underlying this public health assessment, as with all analytical data, have limitations involving sampling and measurement procedures. The most significant limitation is the lack of direct Pu 239 analyses of processed sludge following the 1964 and 1967 release events that may have been distributed to the Livermore community. (12) This limitation is resolved through the use of gross alpha data from both processed sludge and digester sludge. Available data indicate that gross alpha measurements will overestimate Pu 239 concentrations and that digester sludge concentrations will overestimate processed sludge concentrations. Consequently, use of digester sludge gross alpha concentrations is a health protective proxy for Pu 239 concentrations in processed sludge.
The use of the health protective gross alpha measurements presents another limitation. Because these values overestimate the processed sludge concentrations, they do not allow for direct evaluation of actual sludge concentrations. We only know that processed sludge Pu 239 concentrations are lower than the digester gross alpha values, we do not know how much lower. This limitation is not a problem as long as the Pu 239 doses calculated from the maximum, overestimated gross alpha concentrations are below levels of health concern. As the preceding sections indicate that the doses calculated from maximum gross alpha concentrations are below levels of health concern, this uncertainty in the available data does not present a significant problem in the use or evaluation of the available data.
Total reliance on the state-collected and analyzed digester gross alpha data set could also present several data limitations. There are several gaps in this data during the period 1960 to 1963, as well as after 1969 (Figure 3). However, during the period of those data gaps, sewer effluent and annual release data from LLNL are available. These data, which accurately track the CDHS digester gross alpha measurements during all other time periods, indicate that there were no significant Pu 239 (or gross alpha) releases during the time of the digester gross alpha data gaps.
Prior to May 1963, the state-collected digester gross alpha concentrations were reported as wet weight analyses (vs. dried weight analyses for all later time periods). (13) Although the difference in analytical methods may affect the absolute data values, the overall trends in the data indicate that the relative magnitudes are similar.
The 1964-65 time period includes the highest reported digester gross alpha concentration (297 pCi/g) as analyzed by CDPH. LLNL sewer effluent and annual release values during this same time period do indicate a release event(s), but not of the same magnitude as the May-June 1967 event. Processed sludge gross alpha concentrations for 1965 (~8-12 months following the digester gross alpha spike) reached 60 pCi/g (6 month average). These are the highest processed sludge gross alpha concentrations. The fact that digester sludge gross alpha concentrations for the 1964 and 1967 events were of similar magnitude (297 pCi/g vs. 258 pCi/g, respectively) suggests that processed sludge gross alpha concentrations following the 1967 release were also of a similar magnitude.
Community members have also expressed a concern that all of the data underlying this evaluation consist of gross alpha or Pu 239 concentrations averaged over different time periods. Digester concentrations are presented as monthly averages; processed sludge, LLNL sewer effluent, and annual release data are reported as 6 or 12 month average values (14). The basis of this concern seems to be that the 6 or 12 month average values may miss short term events or spikes in the Pu 239 concentrations. This apparent limitation is resolved by the mixing or averaging that occurs in the sewage treatment process.
Figure 6 shows the gross alpha concentrations from daily samples collected and analyzed by LLNL. These daily measurements have recently been recalculated from historic monitoring data records (McConachie 2003) and monthly averages of the daily values are included in Appendix 5. Maxima of the daily samples are about 4 times greater than the monthly composite samples analyzed by CDPH (Figure 3; Appendix 5). However, due to the mixing and dilution that occurs during the treatment process, the resulting processed sludge will not have similar short term Pu 239 concentration peaks.
Sewage treatment and sludge production is an averaging process. Material is added to and pumped from the digesters with an approximate processing duration of 1 month (see Appendix 2; also confirmed by J. Dupont, former LWRP plant manager, personal communication with M. Evans, ATSDR, 2002). Sludge from the digesters is added to the lagoons or drying beds over periods of 1 to 5 years. Processed, dried sludge is milled or ground before distribution resulting in further mixing. Thus, the production of sludge represents a mixing or averaging process over a period of at least one to several years. The use of 6 or 12 month average concentrations to represent this processed sludge will not result in the loss of useful information. Because of the mixing inherent in the sewage treatment system, short term releases to the sewer system will not occur as short term spikes in the Pu 239 concentration of processed sludge.
The validity of all of the historical data has also been questioned because current quality control and data management practices were not utilized for the collection and analysis of historical monitoring data. There have been many improvements in the analytical and data management procedures underlying environmental monitoring programs from those of the 1960s. The direction of these improvements is the reliable and accurate determination of very low contaminant concentrations. This public health evaluation of Pu 239 or gross alpha concentrations is based on determination of the maximum concentrations. These maximum concentrations are well within the basic limitations of the historic gas flow proportional counting technique used to measure gross alpha concentrations.
The overall utility of the historical data is indicated by the convergent and similar trends of the different data types. The similar patterns of digester sludge, LLNL sewer effluent, dried sludge, and annual release data over time (Figure 3) show similar peaks and declines, albeit with some time lags. The time lags are a necessary artifact of the treatment process and the duration of the time lags are appropriate to the sewage processing timeframe. In other words, digester gross alpha concentrations go up when effluent concentrations from LLNL indicate they should go up. Gross alpha concentrations in processed sludge go up 8 to 12 months after digester concentrations go up.
There is some inherent uncertainty in all monitoring or sampling data. This is because the measurement of the contaminant concentration in a very small "sample" is assumed to represent the contaminant concentration of the entire volume or mass of media of concern. Some community members have expressed a desire for additional soil sampling throughout the Livermore community to determine the Pu 239 concentrations in any areas where sludge from LWRP may have been distributed. Such sampling would be subject to the same types of uncertainty, with respect to sampling and analysis procedures, as past sampling. Further, the passage of more than 30 years following placement of any sludge from the 1967 release would make determination of appropriate locations to sample highly uncertain and increase the amount of dilution with non-contaminated soils.
Exposure and Health Evaluation
The purpose of this PHA is to evaluate the public health implications of the historical distribution of Pu-contaminated sludge to the Livermore community by answering three specific questions: 1) What concentrations of Pu 239 in sludge would produce doses of public health concern? 2) Were the concentrations of Pu 239 in the sludge distributed to the public by LWRP greater than the levels of potential health concern? 3) Do the available data provide an adequate basis for this exposure assessment and the resulting public health conclusions? The ATSDR MRL or 100 mrem/year is used as a basis for determining radiological doses of public health concern. No adverse health effects have ever been documented from radiological doses of 100 mrem/year or less (above background).
With regard to question 1, a soil (100 percent sludge cover) Pu 239 concentration of 816 pCi/g (averaged over entire area) is required to produce a dose of 100 mrem/year, as calculated using RESRAD. This calculation includes health-protective exposure factors and includes ingestion of soil and garden crops, inhalation of dust, and external exposure. This calculation also assumes that the contaminated area covers an area of ½ acre to a depth of 2 meters, ½ of the area is unvegetated (bare soil), and ½ of the resident's food is grown on the contaminated area. Considering that about 65% of the total dose comes from food crops grown in the residential yard and that ½ of all fruits, grains, and vegetables consumed are from the home garden, this is a very health protective assumption underlying the dose calculations. Further, because it would take 108 pick-up truck loads of sludge to cover a 1/2 acre lot (3 inch depth), such an exposure scenario, although possible, is very unlikely.
A nearly complete historical record of LWRP gross alpha concentrations for the period of 1960 through 1973 indicates that maximum digester sludge concentrations (as analyzed by CDPH) were less than 300 pCi/g. The digester sludge values show two distinct peaks corresponding with the 1964 and 1967 release episodes (297 pCi/g and 258 pCi/g, respectively). Gross alpha concentrations of LLNL effluent into the Livermore sewer system show the same peaks and provide supplementary data for those periods during which digester concentrations were not collected or analyzed. Collectively, the state analyzed digester sludge data and the LLNL analyzed effluent data indicate that the 1964 and 1967 release episodes represent the worst-case sludge concentrations.
As the concentrations of Pu 239 in processed sewage sludge following the 1964 episode of maximum digester sludge concentration were less than 816 pCi/g, it follows that the maximum Pu 239 concentrations in sludge were below levels of health concern. Although sludge concentrations following the 1967 event are not available, processed sludge gross alpha concentrations following the 297 pCi/g digester sludge values were approximately 60 pCi/g. This indicates that digester sludge gross alpha concentrations are considerably reduced during the treatment process. As processed sludge is further milled and mixed before disposal, it is expected that processed sludge concentrations would have been additionally reduced before distribution to the public.
Several areas where contaminated sludge was placed have been sampled for Pu 239 concentrations. These areas include Big Trees Park, residential yards of LLNL employees, and a test garden on the LLNL facility. Maximum Pu 239 concentrations of these locations were less than 2 pCi/g. Although the initial sludge concentration of most of these areas is unknown, sludge and soil sampling at the LLNL test garden indicated that sludge Pu 239 concentrations are reduced by a factor of more than 5 in the resulting soil. This indicates that tilling and mixing of applied sludge will additionally reduce residential soil Pu 239 concentrations.
Assuming that the available gross alpha concentrations in LWRP sludge and LLNL sewer effluent are a reasonable substitute for direct Pu 239 measurements, the available data clearly indicate that the Pu 239-contaminated sludge does not result in radiological doses of public health concern. Monthly nuclide specific and gross alpha monitoring data for 1973 indicate that gross alpha concentrations overestimate Pu 239 concentrations. Consequently, the use of gross alpha concentrations as a proxy for Pu 239 concentrations is a health protective assumption.
No single data set is adequate for making the above public health determinations. There is not a consistent time series of processed sludge Pu 239 or gross alpha concentrations. Similarly, there are gaps in the digester sludge measurements, and the LLNL effluent data do not provide specific levels of sludge contamination. However, collectively, the available data do provide an adequate basis for the public health assessment. The trends in the different data values support and reinforce the individual data sets. As the different data sets supplement each other, gaps in any one data source do not present a critical lack of information. Additionally, the health protective assumptions used in calculating doses provide additional certainty for the health conclusions. Consequently, the available data provide an adequate basis for public health assessment.
The data evaluated in this public health assessment clearly indicate that, although Pu 239-contaminated sludge was distributed to the Livermore community, the resulting radiological doses were below levels of public health concern. Some community members have doubts about the adequacy of the available data as a basis for the public health determination. They have recommended the collection of additional information on the historic distribution of contaminated sludge and soil sampling of areas determined to have received such sludge. As there is no public health basis for such sampling and the proposed sample results would be inconclusive, ATSDR is not currently recommending additional soil sampling.
SECTION 5. CONCLUSIONS, RECOMMENDATIONS, AND PUBLIC HEALTH ACTION PLAN
Pu 239 (including coincidentally measured Pu 240) was historically released from LLNL to the Livermore sewer system as both low level chronic releases and as higher concentration short-term episodes. Release episodes of particular concern occurred in 1964 and 1967. The sewage effluent from LLNL is both monitored and regulated and available data indicates that the historical releases, including the 1964 and 1967 episodes did not exceed permitted release concentrations.
Processed sludge from the LWRP was historically distributed to the Livermore community for use as a soil amendment or additive. There has been considerable community concern that exposure to the Pu 239-contaminated sewage sludge could result in radiological doses of health concern. These community health concerns have been exacerbated by the lack of direct measurements of Pu 239 concentrations in the processed sludge and some uncertainty about the specific distribution of sludge following the 1964 and 1967 releases. Historical monitoring involved measurement of gross alpha concentrations rather than nuclide-specific Pu 239 measurements.
The following conclusions are based on our current knowledge of radiation health effects and the data reviewed and evaluated in this health assessment:
Based on the above conclusions, the historic distribution of Pu-contaminated sewage sludge is determined to be no apparent public health hazard. This determination means that while exposure may have occurred, or may still be occurring, the resulting doses are unlikely to cause cancer, other illnesses, or death.
As the potential maximum radiological doses from exposures to Pu 239-contaminated sludge are below levels of health concern, ATSDR has no recommendations concerning additional soil sampling in areas of known or unknown sludge distribution. However, because the community may still have unresolved community concerns about this issue, ATSDR offers the following recommendations:
ANL 2001. RESRAD Version 6, Users Manual and Software, Argonne National Laboratory, ANL/EAD-04, Argonne IL.
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Mark W. Evans, Ph.D.
Environmental Geologist
Federal Facilities Assessment Branch
Division of Health Assessment and Consultation
Paul A. Charp, Ph.D.
Senior Health Physicist
Federal Facilities Assessment Branch
Division of Health Assessment and Consultation
Burt J. Cooper, M.S.
Supervisory Environmental Health Scientist
Energy Section Chief,
Federal Facilities Assessment Branch
Division of Health Assessment and Consultation
Sandra G. Isaacs
Chief,
Federal Facilities Assessment Branch
Division of Health Assessment and Consultation
William Nelson
Senior Regional Representative
Regional Services, Region IX
Office of Regional Operations
APPENDIX 1: GLOSSARY OF TECHNICAL TERMS
ATSDR defines an exposure pathway as having 5 parts:
1. Source of contamination,
2. Environmental Media and Transport Mechanism,
3. Point of Exposure,
4. Route of Exposure, and
5. Receptor Population.
When all 5 parts of an exposure pathway are present, it is called a Completed Exposure Pathway. Each of these 5 terms is defined in this Glossary.
APPENDIX 2: 1967 ASSESSMENT OF PU 239 RELEASE
Letter and Attachment concerning "Summary Hazards Analysis- PU-AM Release to Sanitary Sewer" from D.C. Sewell, Associate Director, LRL, to E.C. Shute, Manager, San Francisco Operations Office, U.S. Atomic Energy Commission, August 22, 1967.
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