HEALTH CONSULTATION
LOCUST GROVE MERCURY RESPONSE SITE
LOCUST GROVE, HENRY COUNTY, GEORGIA
The Georgia Division of Public Health (GDPH) received a request from the U.S. Environmental Protection Agency (EPA) for assistance in investigating and evaluating the public health implications of a mercury theft and release incident, which took place in Locust Grove, Henry County, Georgia on March 29, 2003 [1]. Because mercury was precariously handled (resulting in a residential release), GDPH determined that a health consultation assessing the potential for adverse health effects associated with metallic mercury exposure was warranted. This health consultation evaluates potential pathways of exposure to metallic mercury based on a review of incident documentation and sampling data provided by the U.S. Environmental Protection Agency (EPA).
The mercury spill site is located in the Indian Creek Mobile Home Community, Locust Grove, Henry County, Georgia. Specifically, the spill site is within the interior of a doublewide trailer home located on Mohican Maze (hereafter called Mohican Maze). The home sits on a small residential lot in the Indian Creek Mobile Home Community. The community has no commercial or industrial activities onsite. Indian Creek Mobile Home Community has a clubhouse, swimming pool, recreation area, and contains more than 50 homes. The population within 1 mile of the site is estimated to be 300-400 persons and is primarily residential in a rural setting. No effort was made to identify vulnerable animal populations, habitats, or other natural resources since the release was limited to the interior of the house [2].
On April 1, 2003, the EPA Region IV On-Scene Coordinator and EPA contractors responded to a metallic mercury spill at a residential property in the Indian Creek Mobile Home Community, approximately 35 miles south of Atlanta, Georgia. The mercury spill was a result of an incident that happened the evening of March 29, 2003, while the Mohican Maze homeowner was receiving treatment for an unrelated illness at a local hospital. Several teenage friends accompanied the Mohican Maze homeowner to the hospital, during which, two teenagers entered a locked emergency room and dismantled two sphygmomanometers (blood pressure gauges) to obtain mercury to play with [1]. Each sphygmomanometer contains approximately 84 grams of metallic mercury (1). If this amount of mercury were spherical, its size would be roughly equivalent to a large marble. The mercury was taken to Mohican Maze and played with by approximately five individuals in the living room and the kitchen table of the home. These individuals threw globules at each other and reportedly attempted to "melt" the mercury by placing it on a spoon and heating it with a lighter [3]. Because of their actions, mercury fell onto the carpeting. One of the EPA contractor's reported that the homeowner stated that one of the teenagers ate a small amount of mercury because he wanted to convince his friends that the substance was not harmful [4]. As people walked on the mercury, it contaminated their shoes, and was carried throughout the home. Some of the mercury was reportedly dumped in the trash outside the home and in the kitchen sink (the homeowner has a septic system). A 3-month old child of the homeowner was living in the home during this episode. Family members attempted to clean up the mercury but were unable to collect all of it.
Metallic mercury has a melting point of -38ºF (-38.9ºC). Metallic mercury begins to vaporize once the melting point is exceeded. When uncontained, metallic mercury can easily evaporate into the atmosphere-the higher the temperature the greater the mercury vapor concentration. The vaporization rate increases rapidly at temperature above 80ºF. It is important to note that the day and night temperatures were very cool over the March 29 through April 1, 2003 period, hence the home was being heated and the windows were most likely closed allowing little, if any, ventilation of vaporized mercury to the outdoors [3].
Concerned about the potential effects of mercury, the mother of the Mohican Maze homeowner (who also lives in the home) contacted the EPA Regional Response Center and the National Response Center. On April 1, 2003, EPA dispatched an On-Scene Coordinator (OSC) and EPA's Superfund Technical Assistance and Response Team (START) contractor to assess the release. EPA's OSC and START contractor performed initial air sampling. Mercury release was confirmed by a Lumex mercury vapor analyzer (Lumex). Air contamination throughout the home was above action levels although metallic mercury was only observed in the carpeting of the dining room area. Mercury vapor readings in the residence were in the range of 27,630 to 36,250 nanograms per cubic meter (ng/m3), with a mean concentration of 34,478 ng/m3. A nanogram is one billionth of a gram. Outdoor background levels of mercury were approximately 26 ng/m3. The survey inside the home was conducted from the breathing zone (2) in each room, from the flooring in each room, and from the source area (kitchen table) [2]. The EPA Region IV action level (3) for cleanup of mercury vapor is 300 ng/m3. The occupants were relocated until remedial actions were completed.
On April 2, 2003, EPA contractors removed all furnishings, clothing, appliances, and carpeting found to be contaminated from the home, along with porous materials that mercury vapor may have penetrated. All surfaces in the home were then washed with HgX® Mercury Decontamination Powder (HgX®) solution to stabilize any remaining mercury contamination. The home was then heated overnight using the furnace system and then ventilated the following morning (April 3, 2003). This process of removing items from the home, decontaminating remaining surfaces, heating, and venting the home was repeated five times through April 8, 2003, when the target action level of approximately 300 ng/m3 was confirmed using the Lumex air monitor [2]. The items removed from the home were heated and vented in a similar fashion to treatment of the home. The procedure involved placing the items in plastic bags outside for the sun to heat up, and periodically purging the airspace in the bag to release the volatized mercury. After the items were heated and purged three times, measurements were made inside each bag using the Lumex. Items that sustained reading at or below 10,000 ng/m3 were eventually returned to the home. Items that sustained readings above 10,000 ng/m3 were packaged for proper disposal [2]. Photographs 1 and 2 illustrate some of the remediation activities which took place at Mohican Maze.
Photograph 1: EPA contactor removing mercury-contaminated carpeting from the
Mohican Maze for off-site disposal.
Photograph 2: Mercury contaminated household items undergoing remediation and/or
disposal preparation at the Mohican Maze residence.
EPA's contractor also monitored the vehicle and home of a friend who had accompanied the homeowner to the hospital on March 29, 2003. Mercury vapor concentration in the vehicle was monitored by the Lumex and showed mercury concentrations ranging from 900 to 12,500 ng/m3, with spike readings as high as 34,600 ng/m3. This vehicle was allegedly used during the trip to the emergency room, and was used to bring the metallic mercury to Mohican Maze. The interior of the car was cleaned using a Miele vacuum, sprayed with HgX® solution, and heated and vented before being returned to the owner [2].
GDPH identified the names and home addresses of individuals who may have come in contact with the metallic mercury at Mohican Maze and transferred that contamination to other locations. During the remediation activities at Mohican Maze, EPA's contractor surveyed four additional homes (2, 3, 4, and 5) located in the area. All the homes revealed the presence of mercury brought in by shoes and clothing worn by individuals who had played with mercury at Mohican Maze, but only one home on Sioux Street contained mercury contamination high enough to warrant remediation. The Sioux Street home, located a few blocks from Mohican Maze, contained mercury vapor at concentrations ranging from approximately 2,400 to 28,000 ng/m3. The highest readings came from one of the bedrooms of the mobile home. This bedroom belongs to a friend of the Mohican Maze homeowner who was with the Mohican Maze homeowner the day of the incident. Ambient outdoor background concentrations of mercury were approximately 36 ng/m3. On April 5, 2003, the residents at the Sioux Street home were relocated to a nearby hotel. The same remediation process used at Mohican Maze was used on the Sioux Street home [4].
The EPA contractor implemented a confirmation sampling and analytical program after the remediation effort was completed at each of the two homes. The program was designed to determine if the remediation activities were successful in reducing mercury levels to acceptable recommended levels for residences. After the initial treatment, confirmation sampling at Mohican Maze and on Sioux Street was performed on April 8, 2003. At Mohican Maze, air sampling results confirmed that treatment was successful in reducing mercury concentrations to near the recommended atmospheric exposure limits for mercury in residential establishments. The mean level of metallic mercury was 422 ng/m3 [5]. Air sampling analytical results indicated that the home on Sioux Street required retreatment. Following retreatment, a second round of confirmation samples were collected on April 11, 2003. Analytical results confirmed the second treatment was successful in reducing mercury concentrations below the recommended atmospheric exposure limits for mercury in residences. The mean level of metallic mercury was 244ng/m3 [5]. The mercury vapor levels in these homes will decrease over time through normal ventilation.
Three other residences (homes 2, 3 and 4) were also monitored shortly after the emergency response action at Mohican Maze. These residences were monitored because of the potential for mercury contamination brought into these homes on the shoes and clothing of the individuals who had played with metallic mercury at Mohican Maze. The mean household mercury vapor concentrations measured at homes 2, 3 and 4 were: 1491 ng/m3, 989 ng/m3, and 859 ng/m3, respectively. EPA determined that these levels did not represent a public health threat, and subsequently, did not perform any remedial actions. The mercury vapor levels in these homes will decrease over time through normal ventilation.
For each environmental medium (e.g., air, soil, groundwater), GDPH examines the types and concentrations of regulated contaminants. In preparing this document, GDPH used the Agency for Toxic Substances and Disease Registry (ATSDR) comparison values, and other agencies' reference values to screen metallic mercury contaminant levels--that may warrant further evaluation. Comparison values are concentrations of chemicals that can reasonably (and conservatively) be regarded as harmless, assuming default conditions of exposure. The comparison values generally include ample safety factors to ensure protection of sensitive populations. Because comparison values do not represent thresholds of toxicity, exposure to contaminant concentrations above comparison values will not necessarily lead to adverse health effects. Comparison values used in this document are discussed in Appendix B. GDPH then considers how people may come into contact with the contaminants. Because the level of exposure depends on the route and frequency of exposure and the concentration of the contaminants, this exposure information is essential to determine if a public health hazard exists.
GDPH identifies pathways of human exposure by identifying environmental and human components that might lead to contact with chemicals of concern. A pathways analysis considers five principle elements: a source of contamination, transport through an environmental medium, a point of exposure, a route of human exposure, and a receptor population. Completed exposure pathways are those of which all five elements are evident, and indicate that exposure to a contaminant has occurred in the past, is currently occurring, or will continue in the future. GDPH regards people who come in contact with contamination as exposed. For example, people who reside in an area with contaminants in air, or who drink water known to be contaminated, or who work or play in contaminated soil are considered to be exposed to contamination. Potential exposure pathways are those for which exposure seems possible, but one or more of the elements is not clearly defined. Potential pathways indicate that exposure to a contaminant could have occurred in the past, could be occurring now, or could occur in the future. However, key information regarding a potential pathway may not be available. It should be noted that the identification of an exposure pathway does not imply that health effects will occur. Exposures may, or may not be not be substantive. Thus, even if exposure has occurred, human health effects may not necessarily result [6].
The individuals who played with metallic mercury at Mohican Maze handled it precariously. This led to subsequent exposure to metallic mercury and mercury vapor. At a minimum, the individuals who played with the mercury at Mohican Maze, and the two other residents living in the mobile home inhaled mercury vapors. Some of the individuals also handled the metallic mercury and were likely exposed to dermal (skin) absorption as well. Allegedly, one individual ingested a small amount of mercury. No urine or blood samples were obtained on the exposed individuals after the incident occurred; therefore, actual body burden levels were not determined. Because of the physical and chemical properties of metallic mercury and the known toxicity characteristics associated with exposure to metallic mercury, the inhalation of mercury vapor raises the most concern. For more detailed information on the mechanistic effects of mercury exposure, please refer to Appendix D.
Different forms of mercury have different effects on the nervous system, because they do not all move through the body in the same way. When metallic mercury vapors are inhaled, they readily enter the blood stream and are carried throughout the body, as well as crossing the placental and blood-brain barrier [7]. The biological half-life of mercury in the human brain is reported to be 21 days [8].
The kidneys are also sensitive to the effects of mercury because mercury accumulates in the kidneys and causes higher exposures to these tissues, thus more damage. All forms of mercury can cause kidney damage if large enough amounts enter the body. If the damage to kidneys is not too great, the kidneys are likely to recover once the body clears itself of the contaminant [7]. The biological half-life of mercury in the kidney is reported to be 64 days [8].
The residents of Mohican Maze were exposed to indoor air contaminated with mercury vapor for approximately 3 days before being relocated during the remediation of their home. The residents at the Sioux Street home were exposed for approximately 7 days before being relocated during the remediation of their home. The residents of both locations, as well as friends who had visited Mohican Maze on March 29, 2003, were acutely exposed to mercury vapors greater than the action level. Acute exposure is defined as short-term exposure. Completed exposure pathways are represented in Table 1.
Table 1. Completed Exposure Pathways
| Pathway | Exposure Pathway Elements | Time | ||||
| Source | Medium | Point of Exposure | Route of Exposure | Exposed Population | ||
| Indoor Air | Metallic Mercury from Hospital Blood Pressure Gauges | Air | Respiration, Dermal Contact, Intentional Ingestion |
Inhalation Ingestion |
Homeowner and family; friends, and their home occupants
who came into contact with mercury. (@8) 1 who ingested purposely |
Past |
To assess exposure, GDPH calculates site-specific exposure doses and compares them with safe doses (also referred to as health guidelines), which indicate levels below which health effects are unlikely to occur from exposure. The health guidelines are health-protective values that have incorporated various safety factors to account for human susceptibility and the use of animal data to evaluate human exposure. In the event that the calculated, site-specific exposure dose from a chemical is greater than the established health guideline, it is then compared to the exposure doses from individual studies documented in the scientific literature that have reported health effects. In the event that a health guideline does not exist for a chemical of concern, or that a health guideline does not exist for site-specific exposure durations, GDPH uses health-based references derived from other agencies. Such health-based references can include EPA inhalation reference concentrations (RfCs) [9]; and other references as necessary, such as the California acute reference exposure limit (REL) [10]. The derivations of the health-based reference values used for this health consultation are further explained in Appendix C.
Because mercury vapor concentration was first measured 3 days after the incident at Mohican Maze, GDPH is unable to determine what the mercury vapor concentrations over the first 3 days may have been. Likewise, because the mercury vapor concentration was first measured 7 days after the individual who lives on Sioux Street had most likely contaminated his home, GDPH is unable to determine what the mercury vapor concentrations over the first 7 days may have been. The mercury vapor concentrations were most likely higher before these homes were monitored for mercury vapor. Exposure doses were calculated on the average (mean) mercury vapor concentration measured in the respective households before residents were relocated during the remediation of their homes. Although it is unlikely that the residents occupied these homes 24 hours per day, the exposure dose calculation was based on this premise.
Table 2 illustrates the mean exposure levels, comparison values, and estimated exposure doses for the 3-day period of exposure at Mohican Maze.
TABLE 2. Comparison of Mercury Vapor Monitoring Results at Mohican Maze to Applicable Comparison Values for Inhalation.
| Contaminant | Mean Monitoring Level Before Cleanup (ng/m3) |
Air Comparison Value* | Estimated Dose (mg/kg/day) and MRL* |
|
| Concentration (ng/m3) |
Reference | |||
| Metallic Mercury Vapor | 34,478 | 200.0 300.0 1,800 |
EMEGchronic EPA RfC1 California REL2 |
Child: 0.003 Adult: 0.005 MRL=0.00023 |
ng/m3: nanograms per cubic meter
mg/kg/day: milligrams per kilogram of body weight per day
MRL: inhalation Minimal Risk Level.
1 US EPA reference concentration
2 Acute reference exposure levels developed by the California OEHHA
(May 2000)
3 MRL based on chronic oral exposure. MRL is equal to the chronic
EMEG
Source: ATSDR, air comparison values (Fall 2003)
An evaluation of the Mohican Maze Lumex monitoring results indicate that the estimated dose via inhalation of metallic mercury is 0.005 milligrams per kilogram per day (mg/kg/day) for adults and 0.003 mg/kg/day for the infant. ATSDR has published health guidelines for only chronic (>365 days) mercury vapor exposure doses; however, this value is included for comparative purposes. The calculated adult exposure dose exceeds the chronic MRL by 23 times, while the calculated infant exposure dose exceeds the chronic MRL by 15 times. The mercury vapor concentration exceeded the California acute REL for mercury vapor by approximately 19 times. Calculating the daily intake of metallic mercury, assuming the individuals were at home 24 hours/day, the adults present at Mohican Maze inhaled approximately 0.76 mg/day (760,000 ng/day). The infant present in the home inhaled approximately 0.08 mg/day (80,000 ng/day). The estimated maximum adult mercury vapor inhalation at this residence could be as high as 2.28 mg (2,280,000 ng), and the estimated maximum child mercury vapor inhalation at this residence could be as high as 0.24 mg (240,000 ng), based on 3 days of constant exposure.
For the residents occupying the Sioux Street home, two comparisons were made, one for the mean household level, and one for the bedroom that contained a higher concentration of mercury vapor. Tables 3 and 4 illustrate these comparisons.
TABLE 3. Comparison of Mercury Vapor Monitoring Results at the Sioux Street Home to Applicable Comparison Values for Inhalation.
| Contaminant | Whole House Mean Monitoring Level Before
Cleanup (ng/m3) |
Air Comparison Value* | Estimated Dose (mg/kg/day) and MRL* |
|
| Concentration (ng/m3) |
Reference | |||
| Metallic Mercury Vapor | 10,351 | 200.0 300.0 1,800 |
EMEGchronic EPA RfC1 California REL2 |
Adult: 0.003 |
TABLE 4. Comparison of Mercury Vapor Monitoring Results
at the Sioux Street residence to Applicable Comparison Values for Inhalation.
| Contaminant | Bedroom Mean Monitoring Level Before Cleanup (ng/m3) |
Air Comparison Value* | Estimated Dose (mg/kg/day) and MRL* |
|
| Concentration (ng/m3) |
Reference | |||
| Metallic Mercury Vapor | 22,667 | 200.0 300.0 1,800 |
EMEGchronic EPA RfC1 California REL2 |
Adult: 0.003 |
ng/m3: nanograms per cubic meter
mg/kg/day: milligrams per kilogram of body weight per day
MRL: Minimal Risk Level.
1 US EPA reference concentration
2 Acute reference exposure levels developed by the California OEHHA
(May 2000)
3 MRL based on chronic oral exposure. MRL is equal to the chronic
EMEG
* Source: ATSDR, Air comparison values (Fall 2003)
The whole house calculated exposure dose for individuals occupying the home was calculated on the unlikely assumption that these individuals occupied the home 24 hour/day for 7 days before being temporarily relocated. An evaluation of the home from Lumex monitoring results indicate that the calculated dose via inhalation of metallic mercury is 0.003 mg/kg/day. The estimated exposure dose received from the bedroom exhibiting a higher concentration of mercury vapor was based on the assumption that the individual occupying this bedroom occupied it 12 hours/day. Hence, the estimated exposure doses for each of these scenarios are approximately the same. In both cases, the exposure dose estimate exceeded the chronic MRL by 15 times. The California REL for acute mercury exposure was exceeded by approximately 6 times. Calculating the daily intake of metallic mercury, assuming the individuals were at home 24 hours/day, the individuals occupying the Sioux Street home inhaled approximately 0.23 mg/day (230,000 ng/day). The estimated maximum mercury vapor inhalation at this residence could be as high as 1.61 mg (1,610,000 ng), assuming the individuals occupied this home over 7 consecutive days.
For the 3 other residences (homes 2, 3 and 4) that were also monitored shortly after the emergency response action at Mohican Maze, if an estimated exposure dose was calculated and compared to ATSDR's chronic MRL, the estimated exposure dose would be approximately 2 to 2.5 times lower than the chronic MRL for the residents occupying these homes, assuming an exposure duration of 7 days. The mercury vapor levels in these homes will decrease over time through normal ventilation.
Inhalation
Acute mercury vapor exposure levels exceeded the California Acute REL 19-fold for the residents at Mohican Maze, and 6-fold for the residents on Sioux Street. These levels, however, are approximately 52 and 174 times lower, respectively, than levels at which developmental disturbances were seen in the offspring of pregnant rats. Pregnant rats that were exposed by inhalation to 1.8 mg/m3 (1,800,000 ng/m3) of metallic mercury for 1 hour or 3 hours/day during gestation (days 11 through 14 plus days 17 through 20) bore pups that displayed significant dose-dependent deficits in behavioral measurement 3-7 months after birth compared to unexposed controls [11]. Behaviors measured included spontaneous motor activity, performance of a spatial learning task, and habituation to the automated test chamber. The pups also showed dose-dependent, increased mercury levels in their brains, livers, and kidneys 2-3 days after birth [10]. The metallic mercury vapor levels at which these disturbances were observed were used by the California Office of Environmental Health Hazard Assessment (OEHHA) in the determination of the California Acute REL [10].
Because blood and urine mercury levels were not obtained from any of the potentially exposed population during and after the initial emergency response, actual metallic mercury absorption levels are unknown. Since the biological half-life of mercury retention in the brain is approximately 21 days, and approximately 64 days for the kidney, most of the retained mercury in the exposed population has most likely been eliminated.
There is no evidence from epidemiological studies that indicates inhalation of metallic mercury produces cancer in humans [12].
Ingesting small amounts of metallic mercury such as contained in a standard thermometer (about 1 gram) does not produce symptoms of intoxication [7]. Reports of ingestion of substantial amounts of metallic mercury indicate that absorption is negligible. Two case histories were identified on acute effects of relatively large ingestions of metallic mercury. One case history described an ingestion of 15 milliliters (204 grams) of metallic mercury by a 17 year-old male storekeeper who swallowed mercury from the pendulum of a clock (apparently out of curiosity rather than a suicide attempt). On hospital emission, and 24 hours later, he was symptom free, and the physical examination was normal. The patient had no gastrointestinal symptoms, and was treated with laxatives and mild bed rest. The results of serial daily urine mercury levels were normal (all less than 50 micrograms). A radiological investigation illustrated a characteristic pattern of finely divided globules of mercury in the gastrointestinal tract [7]. Most of the mercury was excreted in the feces. The other case history was not specifically relevant to ingestion exposure because the individual had been chronically exposed to mercury vapor throughout his adolescent and adult life.
It is not likely that the person who allegedly swallowed metallic mercury suffered adverse health effects associated with the ingestion. Following ingestion of metallic mercury, elimination would have occurred through urine, feces, and expired air.
Dermal Absorption (Skin Contact)
Dermal (skin) absorption of mercury vapor is a very minor hazard compared to inhalation. Hursh et. al. (1989) measured dermal absorption of radiolabelled metallic mercury vapor in five human volunteers, using arm skin as representing whole body skin. About half of the mercury taken up was shed by desquamation (scaling off) of epidermal (skin) cells during the following several weeks. The remainder was slowly and diffusely released into general circulation in contrast to the rapid release from the lungs. When absorption for the total skin area (as represented by the forearm skin) was compared with the inhalation route for the same ambient concentration, the dermal route absorbed was estimated at 2.6% of the amount absorbed by the lung [13]. No information on the dermal absorption of liquid metallic mercury was found. Unless the skin surface was damaged, the likelihood of dermal absorption would not be expected to be high [7]. Therefore, exposure to mercury by dermal absorption is likely to be negligible for the individuals who came into direct skin contact with the mercury at Mohican Maze.
CHILDRENS HEALTH CONSIDERATIONS
ATSDR and GDPH recognize that the unique vulnerabilities of infants and children demand special emphasis in communities faced with contamination of their water, soil, air, or food. Children are more likely to be exposed because they play outdoors and they often bring food into contaminated areas. Children are more likely to come into contact with dust, soil, and heavy vapors close to the ground. Also, children receive higher doses of chemical exposure due to lower body weights. The developing body systems of children can sustain permanent damage if toxic exposure occurs during critical growth stages.
For similar exposure routes and forms of mercury, the harmful effects seen in children are similar to the effects seen in adults [7]. Kidney damage is very common after exposure to toxic levels of inorganic mercury (oxidized divalent inorganic cation of metallic mercury) [7]. Although the 3-month-old infant was exposed to metallic mercury vapor 19 times higher the California Acute REL, these levels are nonetheless approximately 52 times lower than exposure levels whereby developmental and neurological damage was sustained to pups of pregnant rats and are not expected to produce adverse health effects [10].
Based on the data evaluated, GDPH developed the following conclusions and assigned a public health hazard category to the site. A description of public health categories is provided in Appendix A.
No further public health action measures are planned.
PREPARERS AND REVIEWERS OF REPORT
Author
Franklin Sanchez, REHS
Program Consultant
Chemical Hazards Program
Georgia Division of Public Health
Reviewers
Jane Perry, MPH
Director
Chemical Hazards Program
Georgia Division of Public Health
Robert Rosen
On Scene Coordinator
US Environmental Protection Agency
CDR William T. Going III, MPH
ATSDR Technical Project Officer
Robert E. Safay, MS
ATSDR Regional Representative
(8/21/03).The Georgia Department of Human Resources prepared this Rummel Fibre Company, Rome, Floyd County, Georgia health consultation under a cooperative agreement with the Agency for Toxic Substances and Disease Registry (ATSDR). It is in accordance with approved methodology and procedures existing at the time the health consultation was begun.
William T. Going III
Technical Project Officer, SSAB, DHAC
The Division of Health Assessment and Consultation, ATSDR, has reviewed this public health consultation and concurs with the findings.
Roberta Erlwein
Lead,
Cooperative Agreement Team, SSAB, DHAC, ATSDR
APPENDIX A: ATSDR PUBLIC HEALTH HAZARD CONCLUSION CATEGORIES
No Public Health Hazard
A category used in ATSDR's public health assessment documents for sites where people have never and will never come into contact with harmful amounts of site-related substances
No Apparent Public Health Hazard
A category used in ATSDR's public health assessments for sites where human exposure to contaminated media might be occurring, might have occurred in the past, or might occur in the future, but where the exposure is not expected to cause any harmful health effects
Indeterminate Public Health Hazard
The category used in ATSDR's public health assessment documents when a professional judgment about the level of health hazard cannot be made because information critical to such a decision is lacking.
Public Health Hazard
A category used in ATSDR's public health assessments for sites that pose a public health hazard because of long-term exposures (greater than 1 year) to sufficiently high levels of hazardous substances or radionuclides that could result in harmful health effects
Urgent Public Health Hazard
A category used in ATSDR's public health assessments for sites where short-term exposures (less than 1 year) to hazardous substances or conditions could result in harmful health effects that require rapid intervention.
Comparison values are contaminant concentrations that are found in specific environmental media (air, soil, and drinking water) and are used to select these contaminants for further evaluation if people are exposed to the contamination. The comparison value used in this document is defined in the following below.
Environmental Media Evaluation Guides (EMEGs) are specific comparison values developed by ATSDR for use in selecting environmental contaminants for non-cancer health concerns. EMEG's are derived from Minimal Risk Levels (see below). Exposure to a level of contaminant below this level should not result in any noncancer, adverse health effects.
Minimal Risk Levels (MRLs) are estimates of daily humans exposure to a chemical that is likely to be without an appreciable risk of harmful effects (noncarcinogenic) over a specified duration of exposure. MRL's are based on human and animal studies and are reported for Acute (14 days or less), intermediate (15-354 days), and chronic (365 days or more).
Reference Concentrations (RfCs) EPA inhalation Reference Concentration (RfC) for mercury vapor is based on the assumption that thresholds exist for certain toxic effects such as cellular necrosis. The inhalation RfC considers toxic effects for both the respiratory system (portal-of-entry) and for effects peripheral to the respiratory system (extrarespiratory effects). It is expressed in units of mg/m3 (milligrams/cubic meter). In general, the RfC is an estimate (with uncertainty spanning perhaps an order of magnitude-10x) of chronic daily inhalation exposure of the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime.
California acute REL is an acute reference exposure level (REL) for mercury vapor based on developmental effects in the offspring of exposed rats. Exposure to a level of contaminant below this level should not result in any adverse developmental effects in exposed offspring.
APPENDIX C: DERIVATION OF RFC AND CALIFORNIA ACUTE REL FOR METALLIC MERCURY
The EPA inhalation Reference Concentration (RfC) for mercury vapor is based on the assumption that thresholds exist for certain toxic effects such as cellular necrosis. The inhalation RfC considers toxic effects for both the respiratory system (portal-of-entry) and for effects peripheral to the respiratory system (extrarespiratory effects). It is expressed in units of mg/m3 (milligrams/cubic meter). In general, the RfC is an estimate (with uncertainty spanning perhaps an order of magnitude) of chronic daily inhalation exposure of the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. The RfC for chronic exposure to mercury is 300 ng/m3 [9]. The mercury RfC is based on multiple studies of occupational workers. Most studies were conducted by studying employees of chlor-alkali plants who were exposed to mercury vapor. The critical effects seen were: hand tremors, increases in memory disturbances, and slight objective and subjective evidence of autonomic nervous system dysfunction. The lowest observable adverse effects level (LOAEL) in the occupational studies was at 25 micrograms/m3 (ug/m3). Adjusted to a 24 hour, 7 day per week exposure, the LOAELadj = 9.0 ug/m3 (9,000 ng/m3). An uncertainty factor of 30 was applied to the LOAELadj to reduce the RfC to a level that is assumed to be associated with no adverse health effects, thus resulting in 300 ng/m3. This uncertainty factor includes a factor of 10 for human variation in sensitivity, and a factor of 3 for lack of studies on the reproductive and developmental effects of metallic mercury. Therefore, it is presumed that exposure below the RfC will incur no adverse health effect [14].
Minimal Risk Levels (MRLs) are estimates of daily human exposure to a chemical that is likely to be without an appreciable risk of (noncarcinogenic) harmful effects over a specified duration of exposure. MRLs are based on human and animal studies and are reported for acute (14 days or less), intermediate (15-354 days), and chronic (365 days or more) exposures. However, ATSDR has only developed a chronic exposure MRL for metallic mercury. ATSDR has a health-based chronic MRL level for mercury of 200 ng/m3. This MRL is calculated on the same data that was used to calculate the RfC. However, the MRL calculations assumes that in an occupational exposure, 1/3 of daily inhaled air each working day is contaminated, whereas the RfC assumes that ½ of the working daily inhalation is contaminated [14].
However, the individuals exposed to metallic mercury were not exposed chronically, but for just a few days. Neither ATSDR nor EPA has developed acute exposure screening values for mercury vapor inhalation that are likely to be without an appreciable risk of harmful effects. The California Office of Environmental Health Hazard Assessment (California OEHHA) has developed an acute reference exposure level (REL) for mercury vapor based on developmental effects in the offspring of exposed rats [10]. Pregnant rats that were exposed by inhalation to 1.8 mg/m3 of metallic mercury for 1 hour or 3 hours/day during gestation (days 11 through 14 plus days 17 through 20) bore pups that displayed significant dose-dependent deficits in behavioral measurement 3-7 months after birth compared to unexposed controls [11]. Behaviors measured included spontaneous motor activity, performance of a spatial learning task, and habituation to the automated test chamber. The pups also showed dose-dependent, increased mercury levels in their brains, livers, and kidneys 2-3 days after birth [10].
The acute REL for mercury vapor inhalation is based on the LOAEL of 1.8 mg/m3 where central nervous system disturbances occur in offspring. A cumulative uncertainty factor of 1000 is applied to derive an acute REL of 0.0018 mg/m3 (1.8 ug/m3, 1,800 ng/m3). The cumulative uncertainty factor is based on an LOAEL uncertainty of 10; an interspecies (rat-human) uncertainty factor of 10; and an intraspecies (different types of rodents) uncertainty factor of 10 [10].
APPENDIX D: GENERAL EFFECTS OF MERCURY EXPOSURE
Limited quantitative data on the absorption of metallic mercury vapor after inhalation exposure exists. Metallic mercury is highly lipophilic (having affinity for fats or lipids, such as cell membranes), and absorption of the inhaled vapor, followed by rapid diffusion across the alveolar membranes of the lungs into the blood, has been reported to be substantial. Exposure to 0.1-0.2 mg/m3 (100,000-200,000 ng/m3) of metallic mercury vapor resulted in approximately 74-80% of inhaled mercury vapor being retained in human tissues [8]. Because of its high lipophilicity, metallic mercury can also be readily transferred across the placenta and blood-brain barrier. The oxidation of metallic mercury to inorganic divalent cation in the brain can result in retention in the brain [7].
The kidney is the major organ of mercury deposition after inhalation exposure to metallic mercury vapor. Mercury concentrations in the kidneys are orders of magnitude higher than in other tissues [15]. Monkeys exposed to metallic mercury vapor from amalgam in dental fillings accumulated mercury in the spinal ganglia, anterior pituitary, adrenal, medulla, liver, kidneys lungs, and intestinal lymph glands [16]. The largest deposits of mercury were found in the kidneys, specifically in the proximal tubule cells.
The kidney contains metallothionein, a metal-binding protein that is also found in fetal and maternal livers and other organs. In the kidneys, the production of metallothionein is stimulated by exposure to mercury. The increased levels of metallothionein increase the amount of mercuric ion binding in the kidneys [17]. Low molecular weight complexes of mercury have been identified in the urine, suggesting that they may exist in the kidneys and contribute to the accumulation of mercury [18].
The mechanism of mercury toxicity is not fully known. High affinity binding of the divalent mercuric ion to thiol (-SH) or sulfhydryl groups of proteins is believed to be a major mechanism for the biological activity of mercury. Because proteins containing sulfhydryl groups occur in both extracellular and intracellular membranes and organelles (specialized structures within cells), and because most sulfhydryl groups play an integral part in the structure and function of most proteins, the precise target(s) for mercury is not easily determined, if indeed there is a specific target [7]. Possibilities of action include the inactivation of various enzymes, structural proteins, or transport processes; or alteration of cell membrane permeability by the formation of thiolates - derivatives of thiol in which a metal, such as mercury replaces the hydrogen attached to the sulfur atom [19].
APPENDIX E: EXPOSURE DOSE CALCULATIONS
Exposure Doses are derived by calculating the amount of contaminant that is taken into the body of and exposed person over a period of time. The following equation is used to estimate the exposure doses resulting from inhalation of known metallic mercury vapor concentrations:
where;
ID = inhalation exposure dose (mg/kg/day)
C = mean contaminant concentration (mg/m3)
IR = inhalation rate (m3/day). The average daily inhalation for an adult male is 23m3, and for an adult women, 21m3. For the purposes of these calculations, 22m3 is used because both men and women were exposed. A one-year-old child has an average daily inhalation of 3.8m3, while a newborn has an average daily inhalation of 0.8m3. An estimation of the daily inhalation of a 3-month-old child must be made. For the purposes if this calculation, the daily inhalation of the 3-month-old child used is 2.3m3. This estimation is based on the average of the daily inhalation between a one year old and an infant child.
EF = exposure factor (based on frequency of exposure, exposure duration, and time of exposure). The exposure factor used for the residents residing at Mohican Maze is 0.43, based on 3 days of exposure, before being moved to a motel. The exposure factor used for the residents located at 341 Sioux Street is 1.0, based on seven days of exposure being moved to a motel.
BW = body weight (based on average rates for adults: 70 kg; child: 10 kg)
