Perchlorate Contamination in the Citizens Utilities'
Suburban and Security Park Water Service Areas
RANCHO CORDOVA, SACRAMENTO COUNTY, CALIFORNIA
In late January and early February 1997, Aerojet, as a part of their ongoing monitoring of certain off-site public drinking water wells, detected perchlorate in five off-site public drinking water wells west of Aerojet (none of these wells are Citizens Utility wells)(11). To analyze these water samples, Aerojet used a refined or improved analytical method such that instead of a reporting level of 400 ppb, they were able to obtain a detection limit of 35 ppb. The five drinking water wells showed detectable levels of perchlorate ranging from 92 to 280 ppb with a detection limit of 35 ppb. Subsequent re-testing of the wells showed comparable levels. These detectable levels of perchlorate exceeded the concentration (4 to 18 ppb) suggested by the USEPA provisional reference dose (1 to 5E-4 mg/kg/day) based on a 70 kg individual consuming 2 liters of water a day (12).
In March 1997, the Sacramento District field staff of the CDHS Division of Drinking Water (DDW) sampled 41 public water supply wells in the area of the known perchlorate contaminated wells, including 14 Suburban system wells and the two Beta wells in the Security Park area (13). The well samples were processed by the CDHS's Radiation and Sanitation Laboratory with a detection limit of 4 ppb (Table 1). Perchlorate was detected but not quantifiable (<4 ppb) in one Suburban well (Citizens Utility well #32, the Malaga well). All other wells had no detectable levels (<4 ppb) of perchlorate in March 1997. Citizens Utilities has taken the Malaga well with detectable level of perchlorate off-line and it will only be used if needed for fire protection.
The DDW field staff have continued to monitor for perchlorate contamination in drinking water sources. In April, DDW staff sampled 22 wells, including the off-line Suburban well #29 and the Security Park well #2 (13). In May, DDW staff sampled 43 locations, including 15 Suburban system wells and the Security Park well #2. In June, DDW staff sampled 47 locations, including 14 Suburban wells and the Security Park well #2 (13). In July, DDW staff analyzed water from 40 locations, including 12 wells in the Suburban System and 2 wells in the Security Park System (14). In July, perchlorate was detected but not quantifiable in another Suburban System well (Citizens Utility well #27, the Rockingham well). In August, DDW staff analyzed water from 42 locations, including 15 wells in the Suburban System and the Security Park System well #2 (15). Perchlorate has not been detected in any well except wells #27 and #32, both of which have levels less than 4 ppb.
The Citizens Utility staff have shared information about perchlorate contamination with their customers in the Suburban District and they report receiving only a few calls regarding this issue.
When the DDW sampling results became available, Citizens Utilities had their consultants prepare a notice notifying Suburban and Rosemont customers that 14 wells had no detectable levels and one well had a trace amount of perchlorate (see Attachment A). In this notice, Citizens Utilities notified their customers that they had taken the well with detectable level of perchlorate off line. Citizens Utilities, based on their customer demographics, translated the notice into five languages besides English (Vietnamese, Hmong, Cambodian, Russian, and Spanish). Citizens Utilities listed a phone number in the brochure that could be called if more information was needed. CDHS cooperative agreement staff prepared a fact sheet focusing on health issues related to perchlorate and made this available to water purveyors (16). Apparently, Citizens Utilities was making this fact sheet available to those people who called the information line and wanted information about perchlorate toxicity.
The sampling of Citizens Utility's Suburban and Security Park Systems wells has shown no quantifiable levels of perchlorate. However, exposure to certain Suburban System customers did occur as a result of the water that came through the intertie with the Mather Main Base water system. This exposure to the perchlorate contaminated water occurred at two discrete times (July to November 1995 and May to October 1996) in the past when water from Mather Air Force Base (now called Mather Field) was delivered through this intertie to the Suburban System customers (9, 10). No such exposure is currently occurring or has occurred since November 1996, the last time the intertie was open.
The Suburban System wells provide water to 10,192 connections, approximately 33,600 customers, mostly residents (7). The number of people potentially exposed to the larger amounts of perchlorate is likely much smaller because the intertie, when it was being used, only provided a fraction of the drinking water to the system. The commercial and residential users closest to the intertie connection are likely the highest exposed.
For a target population to be exposed to environmental contamination, there must be a mechanism by which that contamination comes into direct contact with the target population (17). An exposure pathway is the description of this mechanism. A completed exposure pathway consists of five parts: a source of contamination, an environmental medium and transport mechanism, a point of exposure, a route of exposure, and a receptor population. For a population to be exposed to an environmental contamination, a completed exposure pathway (all five elements) must be present. If any one of these is missing, then there is no exposure, though the presence of contamination may still be significant and require remediation. This is especially true if there is a possibility of an in complete exposure pathway becoming complete in the future.
In the next few paragraphs, CDHS will describe how we evaluated the completed exposure pathway related to the perchlorate contamination from the Main Base intertie for three receptor populations: adult resident, worker, and frequent adult customer/visitor (Table 2).
CDHS considers that no current exposure pathway exists with the Citizens Utility Water System because there is no quantifiable levels of perchlorate being delivered to the user. CDHS estimates there to be a potential future exposure pathway from perchlorate-contaminated water, since the perchlorate groundwater plume is moving toward the Citizens Utility Suburban System wells. Even if this exposure does reach these wells, Citizens Utility Company has already demonstrated a desire to prevent such exposure. For instance, they have taken well #32, the Malaga well off-line, as a result of perchlorate being detected but not quantifiable (<4 ppb) in that well. Thus, it seems very unlikely a future exposure pathway exists for Suburban System users.
For the Security Park System, no past or current exposure pathway exists. Future exposure seems unlikely based on the movement of the perchlorate-contaminated groundwater (Figure 1). However, there is no redundancy in the system. Thus, if the only well that serves the Security System does become contaminated, a potential for exposure may exist.
When evaluating the potential health impact from exposure to contaminated potable water, CDHS considered all routes of exposure to perchlorate in the water. The most important route of exposure is through ingestion of the water. We did not evaluate exposure from eating homegrown fruits and vegetables that were irrigated with perchlorate-contaminated water, because we were not aware of bioconcentration parameters related to perchlorate (there are investigations into this issue, see Public Health Recommendations and Actions Section). We did not evaluate inhalation exposure to perchlorate in the potable water because perchlorate is not volatile (does not become a gas).
For certain chemicals, skin contact with contaminated water can be an important route of exposure. Generally speaking, skin absorption of a chemical is based on how much that chemical likes to be in fat-like surroundings. Inorganic ions like perchlorate do not like being in fat-like surroundings and thus their uptake by the skin, a fat-like environment, are typically less than 10% and frequently less than 1%. Since the permeability characteristic for perchlorate is not known, we used the permeability characteristic of another anion, chloride (1 x 10-10 cm/sec) to evaluate skin exposure to perchlorate (18). We found that skin contact would result in an exposure dose estimate that is less than 0.0005% of the dose estimate that would be received by ingesting the water. Therefore, CDHS focused on ingestion in calculating dose estimates.
The amount of Suburban System perchlorate-contaminated water that is ingested will be determined for each exposure pathway; however, when the route of exposure is ingestion, it will be assumed that there is 100% absorption of perchlorate into the body from the gut from the amount water that is ingested.
This health consultation focuses on perchlorate exposure and thus the toxicological evaluation will focus on perchlorate. CDHS acknowledges that there low levels (below the drinking water standard) nitrates and nitrite, naturally-occurring and agriculturally-related, in the well water; however, the affect of nitrates/nitrites in combination with perchlorate will not be evaluated due to lack of toxicological information that would allow such an evaluation.
Most of the information about the toxicity of perchlorate comes from studies of potassium perchlorate as a treatment for hyperthyroidism, resulting from Graves' Disease. Perchlorate inhibits the secretion of thyroid hormones (and can thus relieve the symptoms of Graves' Disease) by competitively inhibiting the accumulation of iodide in the thyroid (19). Discontinued administration of the ammonium perchlorate to Graves' Disease patients does result in a return to their hyperthyroid condition (20). People who have been treated with perchlorate have reported gastrointestinal irritation, skin rash, and hematological effects including agranulocytosis, aplastic anemia, and lymphadenopathy (19). The severe hematological effects seem to be more likely to occur when large doses of more than 1,000 mg/day (approximately 14 mg/kg/day for a 154 pound man) are used (21).
Potassium perchlorate was extensively used for treatment of Graves' Disease patients in the late 1950s and 1960s. After the reports of the severe hematological effects, potassium perchlorate was not used for many years (22). In the early 1980s, physicians in Europe began using it again for the treatment of Graves Disease, and reporting no serious side effects occurring as long as the dose was kept below 1,000 mg/day (approximately 14mg/kg/day for a 154 pound man)(21). In addition, potassium perchlorate has also been found helpful in treating thyrotoxicosis resulting as a side effect from other drug therapies (23-27).
There are only a few studies of the short-term exposure in persons without Graves Disease (28). The animal studies that have been conducted have also involved short-term exposures and the doses were too high to see a level where there was no effect on the thyroid. Both human and animal studies have primarily examined the effects of perchlorate on the thyroid, interference with the production of thyroid hormones resulting in a below normal level of thyroid hormone in circulation (hypothyroidism). The effect of perchlorate on systems other than the thyroid needs to be explored, especially, effects on the blood system (described above) and developmental effects (described below).
Children are not little adults, their bodies are not fully developed, and may not respond to a perchlorate in the same manner as an adult. For instance, thyroid hormone is critical to normal brain and physical development, and the critical period for this dependency on thyroid hormone begins in the uterus and extends up until three years of age. After the age of 3, thyroid hormone continues to play a primary role in physical development until puberty. Thus, a low level or absence of thyroid hormone in utero or in childhood may lead to irreversible mental retardation and retarded physical growth.
Perchlorate can cross the placenta and thus could affect the developing fetus, though these effects have not been studied in humans. It is known, however, that drugs currently being used to treat Graves' Disease such as propylthiouracil do cross the placenta and can produce neonatal hypothyroidism (29, 30) and fetal in utero goiter (enlargement of the thyroid)(31-33). In fact, because the developing fetus's thyroid is immature, propylthiouracil is a more potent suppressor of thyroid function in the fetus than in the mother (34).
In a study of the effects of potassium perchlorate (740mg/kg/day for the mother) fed to pregnant guinea pigs during pregnancy, a 15-fold enlargement of thyroid of the newborns was noted, even though no increase in size of the mother's thyroids occurred (35). Thyroid hormone levels of the newborn guinea pig were not measured in this study. Another animal study in which the mother was given fairly high levels of perchlorate, also resulted in increased thyroid weight in the offspring and the mother (36). At this time, it is unclear whether lower doses of perchlorate would affect the thyroid of the developing fetus and young child and thus affect thyroid function at a time when normal thyroid hormone production is important to brain development.
There are animal studies underway which are exploring the toxicity of perchlorate, including effects on the immune system and developmental effects (see the Recommendations section at the end of the text for more information).
In 1992 and 1995, USEPA staff reviewed the perchlorate toxicology studies and derived a provisional reference dose (RfD)(12, 28). An RfD is a dose to which a person could be exposed over long-term period without having any appreciable risk of a noncancer health effect. The USEPA applied an uncertainty factor of 300 or 1000 to the No Observable Adverse Effect Level of 0.14 mg/kg/day (NOAEL)(28, 37) to derive an RfD of 1 to 5 x 10-4 mg/kg/day (12). (If one assumes that a person drinks 2 liters/day of water and weighs 70 kilograms, the reference dose range corresponds to an acceptable range of perchlorate in drinking water of 4 to 18 ppb).
The uncertainty factor of 300 or 1000 is derived from multiplying the following (12):
|*||An uncertainty factor of 10 to account for extrapolation from the acute exposure in the NOAEL study to chronic exposure of an RfD;
|*||An uncertainty factor for database deficiencies (3 or 10) to account for data limitations including limited data on subchronic and chronic exposure to low doses of perchlorate, limited data on other organ system effects, limited data on the effects on the hematopoietic system, and a lack of reproductive and multigenerational data;
|*||An uncertainty factor of 10 to protect sensitive subpopulations which would include groups such as hypothyroid patients and individuals with low iodine diets or with genetically impaired iodine accumulation.|
The only information about the possible carcinogenicity of perchlorate has to do with cancers of the follicular thyroid cells (12). Interference with the normal thyroid-pituitary feedback mechanism, such as that caused by perchlorate, can theoretically lead to thyroid follicular cell neoplasia. Several animal studies found that thyroid tumors were induced in both rats and mice by long-term administration of high doses of perchlorate. However, humans are not supposed to be as sensitive as the rat to thyroid cancer (38, 39). Since perchlorate's possible carcinogenic effects on the thyroid are based on the same mechanism (interfering with the thyroid-pituitary homeostasis) that determines its noncarcinogenic effects, it may be appropriate to consider the RfD as a dose which does not pose a significant risk of thyroid cancer (28).
It is even harder to determine whether or not perchlorate exposure can cause any other type of cancer. If a link is discovered, it will probably be based on perchlorate acting not as a mutagen (causing genetic changes) but rather as a growth promoter, an effect associated with a threshold. In other words, below a certain threshold, perchlorate would not have cancer-causing effects. More toxicological information is needed to ascertain whether perchlorate can cause cancer and if it can, at what dose this effect may start occurring.
Using USEPA's provisional reference dose (0.0001 to 0.0005 mg/kg/day) based on perchlorate's effect on the thyroid, CDHS evaluated the noncancer (thyroid) health impact of the completed exposure pathway from exposure to perchlorate-contaminated water through the intertie with the Mather Main Base System for several months in 1995 (35 weeks) and 1996 (22 weeks). We evaluated this completed exposure pathway for three different receptor populations: adult resident, worker and frequent adult customer/visitor (Table 2).
Though it is possible to estimate a dose for a child living near the Mather Main Base intertie, CDHS did not calculate this dose because we are not confident about how to interpret the dose estimate. To compare the estimate of a child's dose with toxicological information based on adult exposure ignores the fact that a child is not a small adult, especially when it comes to the importance of the thyroid in normal brain and physical development (see above). Thus, until there is more information about perchlorate's effect on children, CDHS is not able to evaluate past exposures to a young child living near the Mather intertie.
The water from the intertie came from the Mather Main Base Area. It is hard to estimate what concentration of perchlorate was delivered to the user from the Mather Main Base Water System in 1995 and 1996, because perchlorate was not analyzed in the water during those times using an analytical method that had a sensitive enough endpoint. It may be possible to recreate past exposures through a time intensive analysis of the historical documentation of the Main Base well logs and other water system documentation. However, for this health consultation, we will instead evaluate three well contribution scenarios: Main Base well #1 was delivering 100% of the water, Main Base well #2 was delivering 100% of the water, and all wells were equally contributing to the water being delivered to the user (so the concentration of perchlorate being delivered to the user in the third scenario is the average of the four well levels). By evaluating these three scenarios, we will be considering the worst case scenario, when well #2 was the lead well; the second worst situation, when well #1 was the lead well; and a rough approximation of the automated, rotational use of the wells with the storage tank being the place where the blending of the water occurs.
CDHS will use the concentrations of perchlorate measured in the Mather Main Base Water System wells when DDW sampled in March 1997 (Well #1= 67 ppb, Well #2=120 ppb, and the average of all four wells= 51 ppb). Thus we will be evaluating past exposure based on recent perchlorate concentrations. Perchlorate levels in Mather wells and in other water purveyor wells (see other health consultations) have fluctuated a bit over the past several months of reliable perchlorate analysis, but on the whole seem to be relatively constant. This would mean that the dose estimates that we calculate may reflect exposures that have occurred in the near past, 1995 and 1996.
Adult residential exposure in the Suburban System: CDHS estimated the exposure for a adult resident who lives 24 hours per day, seven days a week, for 35 weeks in 1995 and 22 weeks in 1996 in a house located near the Suburban System intertie with the Mather Main Base Water System (Table 3 is a list of the exposure parameters used in the toxicological evaluation). CDHS estimated the dose if the adult resident was exposed to water as described in the three water contribution scenarios described above.
The estimated dose for a adult resident living in a house located near the Suburban System intertie with the Mather Main Base Water System for each of the three well contribution scenarios (0.0019, 0.0034, and 0.0015 mg/kg/day, respectively) exceeds the provisional reference dose range (0.0001 to 0.0005 mg/kg/day) which means that noncancer (thyroid depression) health effects may have occurred when adult residents of the Suburban Water System received water from the Mather through the intertie. However, because there is a very large uncertainty factor associated with the provisional reference dose and the estimated dose does not approach the NOAEL (0.14 mg/kg/day), it is unlikely that adult residential exposure to the Mather Main Base water through the intertie with the Suburban System caused any noncancer health effects.
Worker exposure in the Suburban System: CDHS estimated the exposure for a worker who worked eight hours a day, five days a week, for 35 weeks in 1995 and 21 weeks in 1996 at a business that is located near the Suburban System intertie with the Mather Main Base Water System (Table 3 is a list of the exposure parameters used in the toxicological evaluation). CDHS estimated the dose if the worker was exposed to water as described in the three water contribution scenarios described above.
The estimated dose for a worker at a business located near the Suburban System intertie with the Mather Main Base Water System for the second scenario, when Mather Main Base well #2 was the lead well (0.0008 mg/kg/day) exceeds the provisional reference dose range (0.0001 to 0.0005 mg/kg/day) which means that noncancer (thyroid depression) health effects may have occurred when the worker drank water delivered from Mather and well #2 was the lead well. However, because there is a very large uncertainty factor associated with the provisional reference dose and the estimated dose does not approach the NOAEL (0.14 mg/kg/day), it is unlikely that worker exposure to the Mather Main Base water through the intertie with the Suburban System caused any noncancer health effects.
The estimated dose for worker exposure to water from the Main Base water system through the intertie in each of the first and third well contribution scenarios (0.0004 and 0.0003 mg/kg/day, respectively) does not exceed the provisional reference dose range (0.0001 to 0.0005 mg/kg/day). This means that noncancer (thyroid depression) health effects would not have occurred to the frequent adult customer/visitor drinking or washing with water from the Main Base water system through the intertie when well #1 was the lead well or when their was a rotation of four wells serving the water.
Frequent adult customer or visitor exposure at a Suburban business: CDHS estimated the exposure for a adult visitor or adult customer who went once a day, five days a week, for 50 weeks of the year to a business located near the Suburban System intertie with the Mather Main Base Water System (Table 3 is a list of the exposure parameters used in the toxicological evaluation). CDHS will assume that the adult customer/visitor drank one cup of water (0.24 liters) per trip to the business. CDHS estimated the dose if the frequent adult customer/visitor was exposed to water as described in the three water contribution scenarios described above.
The estimated dose for a frequent adult customer/visitor exposure to water from the Main Base water system through the intertie in each of the three well contribution scenarios (0.00016, 0.00028, and 0.00012 mg/kg/day, respectively) does not exceed the provisional reference dose range (0.0001 to 0.0005 mg/kg/day). This means that noncancer (thyroid depression) health effects would not have occurred to the frequent adult customer/visitor drinking or washing with water from the Main Base water system through the intertie.