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Each residence was evaluated for potential health risk to young children approximately 12-24 months of age (with some variation) using three screening methodologies. Results of each method were evaluated using available information concerning lead exposure and associated adverse health effects (CDC, 1997; ATSDR, 1999). These methods were utilized for the purpose of screening environmental concentrations at these residences and were not meant to predict actual blood lead levels or health effects in children living at these residences. Certain variables which impact exposure, such as activity patterns, climate and geography are not reflected in these methods. Because these residences were self-selected for sampling, they may not be representative of lead concentrations in the Basin. Details of each method are contained in Appendix B and results are in Appendix C.

  1. Method 1 quantifies risk through calculation of an estimated daily intake dose and comparison to an intake of concern for the population (IOC)* for lead developed by the Ontario Ministry of the Environment and Energy (MOEE, 1994; MOEE, 1996). The IOC of 1.85 µg Pb/kg/day is a daily intake which will result in greater than 95% of children exposed having blood lead levels less than 10 µg/dl (MOEE, 1994; MOEE, 1996). In this health consultation, these exposure dose estimates are compared to the toxicological literature to determine what health effects, if any, are possible.
  2. Method 2 utilizes the EPA's Integrated Exposure Uptake and Biokinetic Model (IEUBK) for predicting lead exposures in children (EPA, 1994) which provides estimates (geometric mean) of lead in blood. Surface soil and indoor dust samples were used as input values for the model in order to calculate expected children's blood lead levels. The default age range evaluated in the model is 0-84 months.
  3. Method 3 estimates blood lead levels using ATSDR's integrated exposure regression analysis model (Appendix D in ATSDR 1999). This approach utilizes slope values from selected studies which correlate environmental lead levels with blood lead levels, to integrate all exposures from various pathways, thus providing a cumulative exposure estimate expressed as total blood lead.

NOTE: The methods used in this health consultation are solely for the purpose of screening, and are not meant to predict actual conditions within the Basin. The intent of this screening is to identify those residences which should be considered further, particularly for blood lead screening and possible remedial activities.

Method 1 Summary Results:

External doses calculated from each route were summed to calculate total dose. This total estimated dose for each residence, in mg/kg/day, was then compared to the IOC by dividing the estimated dose by the IOC to determine how many times the estimated dose was greater than the IOC. The following were the results of this calculation:

Table 1.

Number of times the IOC was exceeded by estimated dose (dose/IOC).
Number of times dose exceeds IOC n Location ID
less than IOC 3 47, 72, 73
from = to IOC to less than (<)2 times the IOC 14 3, 4, 6, 8, 10, 17, 25,33, 35, 48, 49, 60, 75, 79
from 2 < 3 14 1, 20, 27, 29, 41, 42, 53, 54, 55, 56, 61, 63, 68, 71
3 < 4 13 2, 7, 9, 11, 18, 19, 24, 26, 31, 36, 37, 45, 80
4 < 5 9 14, 23, 38, 40, 52, 57, 66, 69, 78
5 < 6 7 5, 16, 28, 34, 59, 65, 70
6 < 7 4 21, 22, 30, 46
7 < 8 0  
8 < 9 1 77
9 < 10 2 58, 67
10 < 15 10 12, 15, 32, 43, 44, 51, 62, 64, 74, 76
15 < 20 0  
greater than 20 3 13, 39, 50
n = number of residences

Children living at these residences would have an estimated external dose an average of 5.8 times greater than the IOC, with a median value of 3.6, and a minimum and maximum of 0.3 and 60, respectively. Estimated doses range as high as 0.1114 mg/kg/day, with 21 dose estimates exceeding 0.01 mg/kg/day. Appendix D contains a table listing the studies in humans and animals which have shown effects at doses ranging from 0.01 mg/kg/day to 0.3 mg/kg/day.

Method 2 Summary Results:

Based upon inputs to the IEUBK model, residential locations had the following expected blood levels:

Table 2.

Average estimated blood lead levels for each residence
Average BPb level in µg/dl n Locations
Less than 10 48 1, 2, 3, 4, 6, 7, 8, 9, 10, 11, 14, 17, 18, 19, 20, 23, 24, 25, 26, 27, 29, 31, 33, 35, 36, 37, 41, 42, 45, 47, 48, 49, 53, 54, 55, 56, 57, 60, 61, 63, 68, 69, 71, 72, 73, 75, 79, 80
10-14 16 5, 16, 21, 22, 28, 30, 34, 38, 40, 46, 52, 59, 65, 66, 70, 78
15-19 8 12, 44, 51, 58, 62, 64, 67, 77
20-44 7 13, 15, 32, 43, 50, 74, 76
45-69 1 39
   n = number of residences

Estimated blood lead levels for these residences appear to be higher than the blood lead levels of children actually measured in the State of Idaho's Basin Exposure Assessment (see below; IDHW, 1999). One reason may be that the number of children tested in the Exposure Assessment was small (98) and thus may not be representative. Another reason may be due to high uncertainty regarding children's lead absorption and bioavailability in the IEUBK model (Mahaffey, 1998). This health consultation also made some assumptions about intake and bioavailability to determine which media may pose a risk for young children at these specific residences, and is not attempting to predict blood lead levels in these children nor for residents basin-wide. The State of Idaho is developing site specific bioavailability factors and intake rates for use in the IEUBK model as part of their Human Health Risk Assessment (HHRA) (Terragraphics, April 12, 2000).

The IEUBK model does not take into account activities such as education and other intervention activities which have been occurring in the Basin. If these activities are successful, observed blood lead levels should be less than levels which are predicted based upon environmental concentrations alone. All of the methods used in this health consultation are tools for predicting blood lead levels in Atypical children@ based upon hypothetical exposure scenarios, and would not be expected to predict current blood lead levels in individual children. Exposures and behaviors not accounted for in these methods may explain some of the differences between predicted and observed results.

Another reason for the apparent discrepancy between these modeled blood lead levels and what has been seen in the State of Idaho's Basin Exposure Assessment (IDHW, 1999) and in the annual blood lead screening in the Basin (Terragraphics, April 14, 2000), is the attempt in this health consultation to focus on one to two year old children. Young children of this age are likely to receive greater exposures in a residential setting because 1) they are more mobile than infants, 2) they have a greater likelihood of exhibiting hand to mouth behavior, and 3) they are likely to spend more time in the house and yard than older children (particularly 6 years and up). One and two year old children are also the most sensitive to the affects of lead exposure because of their developing nervous system. In the State of Idaho's Basin Exposure Assessment, as well as in the annual blood lead screening in the Basin, children from 9 months to 9 years of age were tested.

Nationwide, the CDC (1997) has found that one to two year old children are more likely to have elevated blood lead levels from exposure to lead based paint in the home than children of other ages. This may not be truly reflective of the Basin as contamination is primarily from sources other than lead paint, and older children are at risk from activities outside the house. However, it would be expected that the percentage of children with blood lead levels greater than 10 µg/dl in a sample of children from 9 months to 9 years old would be lower than the percentage in a sample of children age 1 to 2 years. Data from inside the ABox@ reflect the CDC finding, showing that the percentage of 1 to 2 year old children greater than or equal to 10 µg/dl (approximately 20% in 1998 and approximately 15% in 1999) has been at least twice as great as the percentage in children ages 3 to 9 (Terragraphics, April, 14,2000). The 1999 blood lead survey results for the Basin showed that 16% of children age 1 - 6 exceeded 10 µg/dl (Terragraphics, April 12, 2000). These results were not sorted by age, therefore, the percentage of 1-2 year old children exceeding 10 µg/dl could not be included in this discussion.

Method 3 Summary Results:

Based upon ATSDR's integrated exposure regression analysis model, residential locations had the following expected blood levels:

Table 3.

Estimated blood lead levels for each residence
Upper BPb level in µg/dl n Locations
Less than 10 62 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 14, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 33, 34, 35, 36, 37, 38, 41, 42, 45, 47, 48, 49, 52, 53, 54, 55, 56, 57, 59, 60, 61, 63, 65, 66, 68, 69, 70, 71, 72, 73, 75, 78, 79, 80
10-14 10 12, 40, 46, 51, 58, 62, 64, 67, 74, 77
15-19 3 15, 43, 76
20-44 3 13, 32, 50
45 & up 2 39, 44
n = number of residences

As noted in Appendix B, this method may be underestimating the number of residences at which blood leads in excess of 10 µg/dl may be seen and thus averages were not calculated. Where possible, actual blood lead levels should be determined. It should be noted that blood lead levels do not address historical exposures or the likelihood of future exposure. The utility of this method is to highlight those residences which are of particular concern and should first receive attention. The ATSDR integrated exposure regression analysis model estimates that 22.5% of 1 - 2 year old children in the Basin may have blood lead levels in excess of 10 µg/dl. This is a fairly reasonable estimate based upon results of blood lead screening in the ABox@ which show that blood lead levels in 1-2 year old children is at least twice that of 3-9 year old children (Terragraphics, April 14, 2000). Sixteen percent of 1-6 year old children exceeded 10 µg/dl in the 1999 blood lead screening in the Basin (Terragraphics, April 12, 2000).

It should be noted that while residences 18 and 37 did not show elevated blood lead levels, both of these residences had high concentrations of lead in drinking water samples and merit increased concern.

At the current time, we do not have information to determine how many young children living on these 80 properties actually participated in the basin blood lead screening. Matching of available residential sampling data with blood lead data of children who have had blood lead testing should be done to confirm the findings of this health consultation. Experience within the Bunker Hill ABox@ suggests that young children living on properties containing soil lead concentrations similar to those in the upper ranges of this data set (> 2,000 ppm), are at a high risk of having elevated blood leads. Blood lead levels in children living in the ABox@ have been declining as remediation of residential soil proceeds.

Comparisons between the three methods.

As can be seen by a comparison of Tables 1, 2, and 3, all methods were similar in ordering the residences relative to each other. In those residences where the IEUBK model predicted average blood leads to be greater than 10 µg/dl, the IOC was exceeded by 4 or more times. Since the IOC is roughly 2 the dose estimated to result in a blood lead level of 10 µg/dl, based upon this method, exposures at 63 of the 80 residences might be expected to exceed 10 µg/dl. Using the IEUBK model, only 32 residences have estimated average blood lead levels exceeding 10 µg/dl. The ATSDR integrated exposure regression analysis model as used was the least conservative, with only 18 residences having estimated blood lead ranges which exceeded 10 µg/dl. Combined results indicate the need to perform blood lead screening of children in these residences to determine the need for specific intervention and to evaluate the predictive ability of these methods.

Toxicological Implications

Blood lead levels and soil lead levels have been studied together in the Bunker Hill Superfund Site and the Coeur d'Alene River Basin previously. Soil lead was strongly correlated with, and was found to be a significant contributor to, children's blood lead levels in the Bunker Hill Superfund Site (PDHD, ET. AL., 1986). Contaminated house dust was also found to be a major contributor.

Low level exposure to lead primarily affects the central nervous system and blood; however, many parts of the body can be damaged by high exposures to lead (Figure 1). The most severe health effects of lead are not likely to be seen in exposed individuals in the Basin. At lower levels, lead produces subtle neurological effects that can usually only be seen in population based studies.* Effects on neurobehavioral function and reduced vitamin D metabolism have been seen at levels between 10 and 20 µg/dl (ATSDR, 1999). While less substantiated, there is evidence of health effects occurring at blood lead levels less than 10 µg/dl. Below 10 µg/dl, decreased IQ, hearing effects, and growth effects have been documented (ATSDR, 1999). A threshold below which lead does not affect IQ in children has not been identified (ATSDR, 1999). Lead has been shown to affect some parameters of heme synthesis at low blood lead levels with no apparent threshold. For more studies and their findings, see Table 2-1 in the Toxicological Profile for Lead (ATSDR, 1999).

At the exposure doses estimated and the blood lead levels modeled from soil and dust lead concentrations, children living within many of the residences sampled under FSPA06 may be at increased risk of subclinical neurobehavioral and developmental effects. Developmental, IQ, and hearing effects have been seen in populations at the doses estimated and blood lead levels modeled in this health consultation. The large number of estimated doses which exceed the IOC indicate a problem with the environmental levels of lead at many of the residences that are the focus of this health consultation. At the exposure doses calculated, effects including decreased motor activity, cardiovascular, hepatic, and reproductive effects have been seen in animal studies (Appendix D; ATSDR, 1999). While there are many difficulties with extrapolating data on animals to humans, these findings suggest additional reason for concern.

It is important to remember that this consult examines young children using typical ingestion rates. Consequently, children experiencing high level lead exposures through atypical activities or pica behaviors (ingesting large amounts of soil) may be at increased risk.

It must also be pointed out that while the dose estimates and modeled blood lead levels in this health consultation considered a number of pathways specific to residential living, there are other pathways within the basin which may add additional lead burdens to the children at these residences. These include exposure to lead based paint, the consumption of contaminated fish, game, or vegetation harvested from the basin, and recreational activities which may result in contact with highly contaminated sediments and soils along the Coeur d'Alene River and Lateral Lakes Chain. Children exposed to these additional sources would be at even greater risk of elevated blood leads.

FSPA 06 also examined the exterior paint of residences for the presence of lead based paint. As can be seen from Appendix A, elevated or even high levels of lead were seen. Lead based paint can be a significant source of exposure to children living in these residences. However, only lead based paint which is in deteriorating condition actually presents a hazard. Lead based paint which is peeling or flaking will result in small pieces which can be directly ingested, or become a component of both exterior surface soil and interior house dust. Lead based paint which is not deteriorating does not present a hazard. Care should be taken to properly maintain the paint in homes constructed prior to 1978, and regular physical examination of painted surfaces should be performed to identify early signs of deterioration.

ATSDR's Child Health Initiative recognizes that the unique vulnerabilities of infants and children demand special emphasis in communities faced with contamination of environmental media. As part of the ATSDR initiative, ATSDR health consultations must indicate whether any site-related exposures are of particular concern for children. At this site, sampling has identified contaminants and lead in the surface soil and indoor dust at residences where children are or will be present. Children are uniquely susceptible to the deleterious effects of lead because they absorb lead more easily than adults do and their body systems are still under development. One and two year old children are the most sensitive to the affects of lead exposure due to their developing nervous system. According to the CDC (1997), 1 to 2 year old children are also more likely to have elevated blood lead levels than children of other ages.

      * The Minister of Environment and Energy (MOEE) defines the IOC as the average daily intake from all media (food, drinking water, soil, air) which would present a low risk to children's health. MOEE's goal is to reduce children's blood lead levels below 10 µg/dl. 10 µg/dl is identified by MOEE as the Lowest Observed Adverse Effect Level (LOAEL) for lead in children. The IOC was developed by estimating what daily intake of lead would result in a blood lead of 10 µg/dl using a bioavailability factor of  0.21. This vlue of  3.7 µg Pb/kg/day was divided by an uncertainty factor of 2 (rational for this factor not provided) to obtain the IOC of 1.85 µg PB/kg/day. MOE believes this IOC will result in greater than 95% of children with blood lead levels lower than 10 µg/dl.

    * While these subtle effects may not be detected in an individual child, these effects have been seen in studies of larger populations. Based upon these population studies, the Centers for Disease Control and Prevention (CDC) has designated 10 µg/dl blood lead as a level of concern (CDC 1997), however effects would not be expected to show up in individuals until blood lead reaches higher levels.

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