PUBLIC HEALTH ASSESSMENT
USA DEFENSE DEPOT MEMPHIS
MEMPHIS, SHELBY COUNTY, TENNESSEE
Available environmental data for the site are evaluated in this section of the PHA. Emphasis will be on what the results mean as far as the potential for exposure of area residents to site contaminants.
Environmental Data Evaluated
There are 4 major sources of environmental data on DDMT (3,8-10). The first was a 1990 remedial investigation done under the Installation Restoration Program (IRP) of the Department of Defense (3). Based on historical data, the investigation focused on possible sources of contamination. Samples of ground water were obtained from 9 monitoring wells on Dunn Field, 3 wells just west of Dunn Field, and 15 wells located on the DDMT Main Facility. Surface soil samples were taken from 45 locations on the Main Facility and 5 on Dunn Field. Samples of subsurface soil were taken at 3-4 different depths at 4 locations on the Main Facility and 4 on Dunn Field. Samples were taken of surface water from ditches draining the site at 13 locations on the Main Facility and 3 on Dunn Field. Sediment samples were taken at five locations on the DDMT Main Facility. No sampling of sediment was done on Dunn Field. About 130 chemicals were tested for in soil, groundwater, surface water, and sediment including volatile organic compounds (VOCs), semi-volatile organic compounds, pesticides and PCBs, and metals.
In 1995 - 1998, samples were taken from about 450 locations on the Main Facility, 12 Dunn Field locations (sediment only), and 22 locations in the area around DDMT during 4 related sampling programs (Screening Sites, Remedial Investigation, Base Realignment and Closure [BRAC], and DDMT area) (8-10,57).3 The media tested were surface and subsurface soil, surface water, and sediment. About 200 parameters were analyzed in the Screening Sites program, 60 in the Remedial Investigation program, 120 in the BRAC program, and 170 in the background sampling. The specific parameters tested in these four sampling efforts are listed in Appendix A starting on page 57.
Results of these 4 sampling programs were provided as electronic files to ATSDR by the U.S. Army Corps of Engineers' contractor, CH2MHILL, in September 1998 and March 1999. The Corps of Engineers is the agency that conducts environmental sampling at federal facilities like DDMT. Data on the geographic locations where samples were taken were included in the information that ATSDR received.
How Data Were Evaluated
The process by which ATSDR evaluates the possible health impact of contaminants is summarized here and described in more detail in Appendix B starting on page 62. ATSDR uses comparison values to determine which chemicals to examine more closely (Appendix C). Comparison values are health-based thresholds below which no known or anticipated adverse human health effects occur. Exceeding a comparison value does not mean that health effects will occur, just that more evaluation is needed.
Further evaluation focuses on identifying which chemicals and exposure situations could be a health hazard. The first step is the calculation of child and adult exposure doses, as described in Appendix D. These are then compared to an appropriate health guideline for a chemical. The results of these calculations are presented in Tables D1 and D2 starting on page 67. Any exposure situation, in which the exposure dose is lower than a health guideline, is eliminated from further evaluation.
The next step is the revision of the exposure dose to better match probable rather than worst-case exposure scenarios. Lastly, these revised exposure doses are compared to known toxicologic values for the chemical of concern. This is mainly the no observed and lowest observed adverse health effects levels (NOAEL & LOAEL) identified in ATSDR Toxicological Profiles. If the chemical of concern is a carcinogen, the cancer risk is recalculated using the revised exposure dose. These comparisons are the basis for stating whether the exposure is a health hazard.
The sampling of Dunn Field was adequate for sediment and ground water but not for surface soil or water. No contaminants were found in this sampling that represented a health hazard either because concentrations were too low or because opportunity was not sufficient for exposure to result in health effects.
Results of Environmental Sampling
Only limited sampling of surface soil has been done at Dunn Field (3). A more detailed evaluation has been done of groundwater contamination including the geology of the Dunn Field area. The locations on Dunn Field where hazardous and other materials were probably buried has been determined and are displayed on Figure 3 (5).
ATSDR's review of the data for Dunn Field indicates that 45 of the approximately 170 chemicals tested for in surface soil were actually detected at least one sampling location. As displayed in Table 1, 9 chemicals had at least one concentration above its comparison value (CV).
In sediment, 81 chemicals were detected among the 12 locations sampled on or near Dunn Field in 1995 (57). Among the chemicals detected were arsenic, dieldrin, lead, and several members of the dioxin and polycyclic aromatic hydrocarbon (PAH) groups. As displayed on Table E1 on page 70, only six of the 81 had at least one concentration above a comparison value. These six were beryllium, benzo(a)anthracene, benzo(b)fluoranthene, benzo(a)pyrene, dibenz(a,h)anthracene, and indeno(1,2,3-c,d)pyrene.
As indicated in Table E2 on page 70, none of the levels of the 11 substances detected from three Dunn Field surface water sampling locations exceeded a comparison value. The chemicals detected were acetone, barium, benzoic acid, bis(2-ethylhexyl)phthalate, cadmium, copper, dieldrin, lead, methylene chloride, n-nitrosodiphenylamine, and zinc. No further evaluation will be done because the maximum concentrations in surface water were two to more than 1,000,000 times lower than the appropriate comparison value.
Adequacy of Environmental Sampling
The soil and surface water sampling of Dunn Field is not adequate for public health purposes because it focused on suspected contamination source areas and only a few locations were tested (3). A definitive answer will be possible once results of the comprehensive sampling of Dunn Field in late 1998 and early 1999, are released in early 2000. The 1995 sampling of sediment on and near Dunn Field does appear to be adequate because several samples were taken in each of the drainages from Dunn Field (57).
Possible Health Consequences of Chemicals found on Dunn Field
When a sample concentration exceeded a CV, the maximum level of that chemical was used to calculate an exposure dose, which is then compared to an appropriate health guideline. The results of these evaluations are summarized here and described in more detail in Appendix F on page 75.
|Contaminant||Range in Soil in mg/kg1||Samples > DL2||Samples > CV3||CV in mg/kg||CV Source4|
|Arsenic||ND - 35||4/5||4/45||0.5/206||CREG7/EMEG8|
|Benzo(a)pyrene||ND - 68||3/5||3||0.1||CREG7|
|Dieldrin||ND - 0.5||3/5||3/0||0.04/3||CREG7/EMEG8|
|Benzo(a)anthracene||ND - 81||3/5||1||0.9||EPA SSL9|
|Benzo(b)fluoranthene||ND - 68||3/5||1||0.9||EPA SSL9|
|Indeno(1,2,3-c,d)pyrene||ND - 44||2/5||1||0.9||EPA SSL9|
|Alpha-chlordane||ND - 1.5||1/5||1/05||0.5/36||CREG7/RMEG10|
|Benzo(k)fluoranthene||ND - 28||1/5||1||9||EPA SSL9|
|Dibenz(a,h)anthracene||ND - 26||1/5||1||0.09||EPA SSL9|
|* The source of these data is the 1990 remedial
1 - mg/kg = milligrams of chemical per kilogram of soil. mg/kg = parts per million (ppm)
2 - DL = detection limit
3 - CV = comparison value
4 -These comparison values are described in Appendix B starting on page 62.
5 - The first number is the samples above the CREG and the second the samples above the EMEG or RMEG.
6 -The first number is the CREG and the second is the EMEG or RMEG.
7 - CREG = cancer risk evaluation guide
8 - EMEG = environmental media evaluation guide
9 - SSL = soil screening level
10 - RMEG = remedial media evaluation guide
Only adult exposure doses were calculated because access of small children to Dunn Field contaminants appears very unlikely because Dunn Field is and, reportedly, has always been fenced.4 As indicated above, the conclusions are applicable only to the locations sampled and not to all of Dunn Field because of inadequate sample numbers and extent of sampling.
As indicated on Table D1 (page 67), health effects due to exposure to arsenic, alpha-chlordane, dieldrin are not likely to occur because the concentrations are too low even when it is assumed that workers were exposed 5 days a week for 30 years. This assumption is unlikely to be true for Dunn Field because no one regularly worked on Dunn Field.5
Six of the substances found in Dunn Field soil above comparison values are members of the chemical group, polycyclic aromatic hydrocarbons [PAHs] (58). The additional cancer risk for each of the 6 PAHs is moderate for someone who was exposed 5 days a week for 30 years. The cumulative risk for exposure to all 6 PAHs is elevated. However, although cancer risk is elevated, the actual chance of anyone being harmed is very low or non-existent. Regular long-term exposure of any individual is unlikely because no one went on-site on a regular basis. Go to page 76 for a more detailed discussion.
As discussed in more detail on page 76, health effects due to the contaminants in Dunn Field sediment are very unlikely, even with daily exposure. Daily exposure to contaminated sediment appears unlikely. As indicated on Table E2, the average levels of beryllium and PAHs at all 12 locations are similar to the means identified in the background sampling of the DDMT area. In addition, the PAH concentrations are within the levels of 0.2 - 61 ppm typically found in urban soil (58).
Very extensive sampling has been done of the soil, sediment, and surface water from the DDMT Main Facility. About 100 different chemicals were found among these three media. However, only polycyclic aromatic hydrocarbons (PAHs) in soil were found at concentrations that might have been harmful if an individual contacted the contaminated soil daily. These potentially harmful exposures could have occurred at only a few locations on the Main Facility.
Results of Environmental Sampling
Thirty-one of the 114 chemicals identified in surface soil had at least one concentration above a comparison value (CV) as displayed in Table E3 on page 71. The 10 contaminants with the most concentrations above a CV are on Table 2 on page 19. Further evaluation will focus on those 10 chemicals. The locations where the contaminant levels for arsenic, benzo(a)pyrene, dieldrin, and lead exceeded their CVs are displayed on Figures G1 - G4 beginning on page 82.
- Sediment Sampling
Fifteen of the 95 chemicals identified in sediment had at least one concentration above a CV as displayed in Table E4 on page 72. Further evaluation will focus on those 15 chemicals. The locations where the contaminant levels for arsenic and benzo(a)pyrene exceeded their CV are displayed on Figures G5 and G6 beginning on page 86.
Surface Water Sampling
Two of the 40 chemicals identified in surface water had at least one concentration above a CV as displayed in Table E5 on page 72. Further evaluation will be of these 2 chemicals. The locations where the contaminant levels for arsenic and dieldrin exceeded their CV are displayed on Figures G7 and G8 beginning on page 88.
Possible Health Consequences of Chemicals found on DDMT Main Facility
When a sample concentration exceeded a CV, the maximum level of that chemical was used to calculate an exposure dose, which was then compared to an appropriate health guideline. Results of these evaluations are summarized here and described in more detail in Appendix F starting on page 77.
Of the 10 chemicals present on Table 2, it is unlikely that health effects could occur from exposure to 8 of them. These were arsenic, benzo(a)anthracene, benzo(b)fluoranthene, beryllium, dieldrin, DDT, indeno(1,2,3-c,d)pyrene, and lead. For these 8 chemicals, contaminant concentrations were too low to result in health effects given the amount of exposure that could have occurred or is occurring. There is a chemical-by-chemical evaluation of the possibility of health consequences from exposure to these 8 chemicals beginning on page 77.
Table 2 - Top Soil Contaminants*
|Contaminant||Range in Soil in mg/kg1||Mean2 in mg/kg1||Samples > DL3||Samples > CV4||CV in mg/kg1||CV Source5|
|Arsenic||ND - 101||14.3||352/361||351/706||0.5/207||CREG8/EMEG9|
|Benzo(a)pyrene||ND - 450||5.5||164/349||121||0.1||CREG8|
|Dieldrin||ND - 10||0.4||180/324||125/96||0.04/37||CREG8/EMEG9|
|Benzo(b)fluoranthene||ND - 540||5.7||174/359||59||0.9||EPA SSL10|
|Lead||ND - 17,500||300.6||371/372||42||400||EPA SSL10|
|Benzo(a)anthracene||ND - 970||7.1||167/352||59||0.9||EPA SSL10|
|Indeno(1,2,3-c,d)pyrene||ND - 310||5||132/302||48||0.9||EPA SSL10|
|Beryllium||ND - 2||0.4||162/319||142/06||0.2/3007||CREG8/RMEG11|
|Dibenz(a,h)anthracene||ND - 160||0.7||21/334||15||0.09||EPA SSL10|
|DDT||ND - 59||0.6||205/334||15/16||2/307||CREG8/RMEG11|
1 - mg/kg = milligrams of chemical per kilogram of soil.
mg/kg = parts per million (ppm)
The 2 chemicals in soil at the Main Facility for which health effects might occur are benzo(a)pyrene and dibenz(a,h)anthracene. The health effect possible is an increased risk of cancer. Individuals who may have this risk are workers who had daily exposure to soil from around the south side of Building 249, between Buildings 689 and 690, or around the west side of Building 629. Risk of cancer does not appear to be elevated for the rest of the DDMT Main Facility because concentrations of these 2 chemicals and other members of the polycyclic aromatic hydrocarbons (PAHs) are considerably lower. Most PAH levels found at the Main Facility sampling locations are within the PAH levels (0.2 - 61 ppm) typically found in urban soil (58). More detailed discussions on begin on page 78.
Chemicals in sediment with concentrations above a CV (Table E4), do not represent public health hazards. The 15 chemicals above their CVs are arsenic, antimony, benzo(a)anthracene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(a)pyrene, beryllium, cadmium, chromium, dibenz(a,h)anthracene, DDT, gamma-chlordane, iron, lead, and total polynuclear aromatic hydrocarbons (PAHs). Regular exposure to sediment from any of the sampling locations with concentrations above a CV does not appear to be plausible for anyone. This is because no facility operations appear to have been conducted at these locations so worker contact would have been minimal (47). More information on the possibility of health consequences from exposure to chemicals in on-site sediment is on page 79.
Chemicals in surface water with concentrations above CVs (Table E5), do not present public health hazards. Arsenic and dieldrin were the chemicals above CVs. The maximum levels of arsenic and dieldrin are well below the noncarcinogenic health effects comparison values. The additional lifetime cancer risk from exposure to them is not significant (2 in 1,000,000 to 4 in 100,000). This conclusion is based on the great difference between the average lifetime risk of cancer in the United States of 3 cancers per 10 individuals, and the 2 in 1,000,000 to 4 in 100,000 additional risk for exposure to these contaminants.
With the possible exception of the Rozelle neighborhood west of Dunn Field, contaminants from DDMT do not currently represent public health hazards (i.e., either exposure is nonexistent or not enough to cause harm) and have not since at least 1989. This conclusion is based on an evaluation of the possible ways that residents in the area around DDMT might be exposed to site contaminants, and a review of available contaminant data. Included in these data are the results of sampling of surface soil, sediment, and surface water from locations around DDMT. Exposure pathways analyses indicate that limited exposure to site contaminants may have occurred through the water-borne transport to two areas other than the Rozelle neighborhood. These areas are 1) south of the southeast corner of the main facility, and 2) the yards on either side of Tarrent Branch which flows from the west edge of the main facility. The number of individuals in the residential areas around DDMT that could have been exposed is between 500 and 3,000.
Determining whether site-related health effects could have occurred from exposures since the opening of DDMT in 1942 until 1989 is not possible.
The basis for these two conclusions will be described in the following paragraphs.
Analysis of Environmental Exposure Pathways
Surface water and sediment, and ground water are the principal ways DDMT contaminants can move, are moving, or have moved off the site. Short-term exposure to airborne contaminants from DDMT has occurred. Long-term air exposures may have occurred but appear to have been limited to the area near the southwest corner of the main facility. Food chain and soil do not appear to be viable pathways for long-term exposure.
For surface water and sediment, current human contact with contaminants in water from DDMT is almost entirely restricted to 3 surface water drainages. An estimated 500 - 3,000 persons could potentially have regular contact with water in these drainages. This contact would be limited to chemicals in surface water or sediment, or soil contaminated by surface water. Contact with contaminants that become airborne from the surface water probably does not occur because the contaminant levels are too low for this to happen.
The contaminant levels in those drainages since at least 1989 were not and are not a public health hazard to individuals living around DDMT. Sampling data are insufficient before 1989 to estimate what the contaminant levels in those drainages might have been.
For ground water, movement of site contaminants off-site is primarily restricted to the northwest corner of Dunn Field. No one drinks this contaminated groundwater.
Surface Water and Sediment
Movement of surface water and sediment off DDMT is focused at specific locations around the Main Facility and Dunn Field as seen on Figure 5 (page 24) and discussed in Appendix H (page 90) (3). Contact would have been to contaminants in surface water or sediment, or soil contaminated by site surface water, but would not have included chemicals that become airborne after leaving the site in water. Contaminant concentrations are too low to move into the air (59-61).
Where Exposure to DDMT Contaminants in Surface Water could be occurring
Current and past exposure to site contaminants carried off DDMT in water and sediment might occur and may have occurred in the following areas.
(1) In or near the un- and concrete-lined ditches that pass through or by the Rozelle neighborhood just west of Dunn Field. This exposure is ongoing and could have occurred in the past. Little or no opportunity for exposure exists once the water has passed through the Rozelle neighborhood because the ditches join, then this ditch flows into a pipe at the Illinois Central Railroad tracks (Figure 5). In the Rozelle neighborhood, exposure to site contaminants would be daily for individuals contacting soil contaminated by surface water or sediment from Dunn Field. The areas where soil contamination appears possible are yards at the southern end of Rozelle Street, and to either side of the shallow ditch that runs through the middle of the neighborhood.
However, although daily contact with site surface water or sediments may occur, health effects from that contact are unlikely. The concentrations of chemicals in sediment and surface water on Dunn Field and in sediment from the ditches in the Rozelle neighborhood are too low. As indicated in Table E2 on page 70, 11 chemicals were detected in surface water from Dunn Field; levels for all 11 were below the health-based comparison values.
Six chemicals were identified in sediment samples from Dunn Field and the Rozelle neighborhood (Table E1, page 70). As discussed on pages 14 - 17, they do not present health risks. In addition, sediment levels from western Dunn Field and the Rozelle neighborhood are similar to the levels for 22 samples taken off-site in the DDMT area.
Although contaminants currently moving off the western side of Dunn Field in surface water or sediment do not represent public health hazards, additional soil sampling is needed in the Rozelle neighborhood to determine whether a public health hazard exists. Soil, now present in the Rozelle area, may have been contaminated in the past through the overflowing of ditches in this neighborhood. No sampling has been done of the soil around these ditches.
(2) In or near Tarrent Branch. As indicated on Figure 5, Tarrent Branch drains the western third of the DDMT Main Facility, which is the area where most of the hazardous materials storage took place (3,5,7). This intermittent stream runs through the neighborhood west of DDMT and eventually flows into Nonconnah Creek. Tarrent Branch was a natural stream but is now a concrete-lined and fenced ditch. Therefore, exposure is currently unlikely because regularly contacting water and sediment from this ditch would be difficult.
Regular exposure to the water and sediment could have occurred before the ditch (Tarrent Branch) was fenced. A long-time resident indicates that she and others used to play in Tarrent Branch as children.6
Even if contact with surface water and sediment from DDMT were ongoing, it would not result in health effects. As indicated on pages 17 - 20, the contaminants identified in sediment and surface water identified on the Main Facility do not represent health risks. This includes the sampling points on the western edge of DDMT.
Determining whether exposure to site contaminants in this drainage before 1989 may have been enough to result in health effects is not possible. Before 1989, insufficient environmental data exist to estimate contaminant levels.
(3) In or near the 4 ditches that flow south from the southeast corner of the DDMT Main Facility (Figure 5). These 4 ditches drain the southeast corner of the Main Facility where a golf course, clubhouse, swimming pool, Lake Danielson, a pond, and the base housing units are located (3,5,7). These ditches join south of the DDMT boundary and then flow into Nonconnah Creek. At least some portions of these ditches are shallow and unlined which means that more opportunity exists for contamination of the soil around the ditch with site contaminants. Thus, exposure to site contaminants could occur to individuals who had daily or nearly daily contact with sediment or surface water from the ditches or the soil immediately around the ditches. These exposures could occur now and in the past. One of the 4 ditches passes along Mueller Street between Ball and Ketchum Roads. ATSDR staff recently observed children playing in this ditch (48).
Health effects due to regular current contact with surface water and sediment from these 4 ditches in the southeast corner of DDMT are unlikely. As described on pages 17 - 20, the contaminant levels in sediment and surface water identified on the Main Facility, including sampling points on the southern side of DDMT, do not represent a health risk.
Determining whether sufficient exposure to site contaminants in this drainage occurred before 1989 to result in health effects is not possible. The rationale for this is the same as described above for the Tarrent Branch drainage.
Figure 5. Open Drainage from Memphis Defense Depot
Where Exposure to DDMT Contaminants in Surface Water is not occurring
Regular exposure to site contaminants carried off DDMT in water and sediment does not occur in the following areas. As will be described, exposure to site contaminants may have occurred in some of these drainages in the past. (For additional explanation of the rationale for these conclusions see Appendix H on page 90.)
(1) The area north of the DDMT Main Facility and east of Dunn Field. This area is bordered by Hayes Road on the west, Airways Boulevard on the east, Person Avenue on the north, and Dunn Road on the south. Water from the site flows through an industrial park in pipes or lined ditches. It does not flow through any of the residential portion of this area (47). Thus, individuals in this area would not have opportunity to contact surface water and sediment from DDMT either currently or in the past.
(2) The area east of the DDMT Main Facility. This area is bordered by Airways Boulevard on the west, the Burlington and Northern Railroad tracks on the east and north, and Nonconnah Creek on the south. The only flow of surface water from DDMT through this area occurs presently in Memphis storm sewer pipes. The opportunity for exposure does not currently exist and likely has not existed since at least 1953 (47,62). This conclusion is based on a 1953 Drainage Plan for DDMT that identified the storm sewer drainage points as existing then (62).
(3) Most of the area on the south side of the main facility. This area is bordered by Orchard Street on the east, Ball Street on the north, Perry Street on the West, and Nonconnah Creek on the south. The drainage at the southeast corner of the main facility is not included in this area. The opportunity for contact with site surface water is currently non-existent because no open drainage ditches exist (3). In the past, 2 discharge points existed midway between the east and west ends of the main facility (3,5). Ditches from these 2 points joined shortly after crossing Ball Road, and this single ditch then flowed south into Nonconnah Creek.
(4) The area west of the DDMT Main Facility with the exception of homes near Tarrent Branch. This is the area bordered by Perry Road on the east, Elvis Presley Boulevard on the west, Dunn Road on the north, and Ball Road and Mallory Avenue on the south. The only current opportunity for contact with site surface water is restricted to the area around Tarrent Branch (47). In the past, a second open ditch existed west of DDMT and between Dunn Road and Tarrent Branch as shown on maps of the DDMT area from 1982, 1960, and 1953 (7,62,63). The maps we examined did not identify the course of this ditch.
(5) The area northwest of the main facility and Dunn Field. The Illinois Central Railroad tracks on the east, Person Avenue on the north, and Elvis Presley Boulevard on the west are the borders of this area. This includes the area around and south of Hamilton High. Water from DDMT is only found in Cane Creek (47). The opportunity for contact with water in Cane Creek is limited because the creek is concrete-lined and fenced from the Ragan Street Bridge to the Elvis Presley Boulevard Bridge.
As indicated in Appendix H, sources for water from DDMT in Cane Creek upstream of Hamilton High are the northeast corner of the DDMT Main Facility and a small portion of Dunn Field. The contribution of water from DDMT to the overall flow of Cane Creek appears to be small. This would further dilute the already low levels of contaminants coming from DDMT.
However, the opportunity for exposure probably was greater in the past because water from the Dunn Field area used to flow through the area between the western side of Dunn Field and Hamilton High School in an open ditch rather than in the pipe in which it currently flows.7
Estimate of Number of Persons in Surface Water Exposure Pathways
ATSDR estimates that about 500 - 3,000 persons could have had regular contact with surface water from DDMT. This represents about 2 -10 % of the 30,720 persons living within a mile of DDMT. This estimate was made by determining the number of people living within 100 feet and within 500 feet of the five drainage areas identified on Figure 5. One hundred feet from a ditch is a conservative estimate of the extent of contamination that might occur during flooding. Five hundred feet from a ditch is an estimate of the maximum distance that a small child might reasonably be able to travel to have regular contact with contaminated sediment, surface water, or soil.8
Contaminants from DDMT have moved off site in ground water at the northeast corner of Dunn Field and a small area just south of the DDMT Main Facility (3,47). About 8-10 contaminants were found in offsite groundwater above an EPA maximum contaminant level (MCL) or risk-based concentration (RBC) in sampling conducted in October of 1998 (47). About half (all volatile organic compounds [VOCs]) these chemicals were clearly site-related. The rest were considered to be background or natural levels.
Available data indicate that contaminants from DDMT have not moved into the Allen Well Field which lies west of Dunn Field (3,47). This well field is one of several used to supply drinking water to Memphis area residents. Concern exists that site contaminants may eventually pollute this well field, so a system of wells was recently installed at the edge of Dunn Field to stop or reduce flow of groundwater contaminants off Dunn Field.
Exposure to site contaminants in drinking water does not appear to have been possible. This is because the likely sources of contaminants in groundwater were not buried in Dunn Field until 1955 (47). All residences around the site were connected to the Memphis public water supply by 1953 (6).
Short-term exposure to airborne contaminants from DDMT probably has occurred at least once (64). In 1988, the cover of a hazardous materials storage building called a Span Dome collapsed during a severe thunderstorm (64). This collapse resulted in release to the air of 327 - 2,000 gallons of the 250,000 gallons of the hazardous materials stored in this building (64,65).9 The chemicals stored were acetone, isopropyl alcohol, methyl ethyl ketone, methyl isobutyl ketone, toluene, and xylene, which are all commonly-used solvents (66).
The Memphis Fire Department's (MFD) report indicates that, during the first hours of this incident, the leaking materials were detected at high levels at the northern perimeter of the DDMT Main Facility (64). This location is about 1,300 feet north of the collapsed Span Dome (67). The Span Dome is located near the western boundary of the main facility and north of the corner of Perry and Elliston Roads. Thus, some exposure could have occurred in the area west and northwest of the Span Dome. A more detailed description of this incident starts on page 39.
Long-term residents have indicated that several other air releases from DDMT have occurred (40,43). DDMT operated for 55 years and stored large amounts of hazardous substances, so some likelihood exists that accidental releases could have taken place (7). However, ATSDR did not identify other reports of confirmed air releases from DDMT.
Although short-term exposures to airborne DDMT chemicals may have occurred occasionally, there is little in the data available that indicates to ATSDR that long-term exposure to site contaminants of all or most residents around DDMT occurred via the air (3,5,7). Only one operation, spray painting of vehicles and equipment, appears to have existed on DDMT that could have resulted in regular release of contaminants to the air. As indicated on Figure 2, three or four paint spray booths existed at various times on the main facility. The stacks from these booths appear to have been relatively short which would result in contaminants being carried only short distances.
This is confirmed by soil sampling data for the areas around the booths. The soil near these paint booths does have elevated levels of lead, PAHs, and other chemicals. However, levels of these chemicals are not elevated in samples taken at the DDMT perimeter. This indicates that very little of the chemicals, emitted from the paint booths, actually moved off-site.
Exposure to site contaminants through food is unlikely. The known contaminant concentrations in surface water appear to be too low to result in significant contamination of crops, fish, or wild or domestic animals from the DDMT area.
Very little or no opportunity was available for DDMT area residents to catch and eat fish within a mile of the site. Ditches draining DDMT are often dry and thus could not sustain a fish population. The nearest off-site body of water with a viable fish population is Nonconnah Creek, which eventually receives all the water draining from DDMT. This creek has been posted as a no fish consumption area since 1982, primarily because of chlordane contamination from a nearby pesticide production facility and chlordane's use around homes (68).
Individuals catching and eating fish from the bodies of water on DDMT, Lake Danielson and the golf course pond, may have had some exposure to chlordane, DDT, and PCBs because these chemicals have been found in fish, sediment, and water from this lake and pond (3,6,8-10). Former workers indicated to John Crellin that people did catch fish from the lake and pond.
No systematic evaluation has been done of surface soil from any specific off-site area. Indirect evidence suggests that any contamination of soil off-site with DDMT materials would be limited. Off-site soil could have been contaminated through the overflow of ditches that drain DDMT and the deposition of chemicals carried in this surface water and sediment. However, as discussed earlier, only a limited number of places exists where this could occur. ATSDR is recommending that at least some of these areas be sampled.
Soil could also have been contaminated by the deposition of airborne materials from the site. As discussed earlier, only the paint spray booths could have been such a source, and soil sampling data do not indicate that a significant amount of the materials moved off site.
Evaluation of Sampling Data from the Area around DDMT
Low concentrations of chemicals are in soil, sediment, and surface water from the area around DDMT. Available data indicate that DDMT is not a major source for these chemicals.
Surface soil, surface water, and sediment samples from the area around DDMT were analyzed for about 170 parameters.10 Soil samples were taken from 11 locations just off DDMT and 11 locations away from DDMT including four schools (Alcy, Charjean, and Dunn Elementary Schools; and Airways Middle School), Alcy West Park, and Pine Hills Golf Course. Surface water and sediment were sampled at 22 locations including Nonconnah and Cane Creeks; and lakes in Medal of Honor and Audubon Parks, and Botanical and Chickasaw Gardens.
The best indication that no widespread contamination of the area occurred around DDMT by chemicals from the site can be found in Table 3. In this table, the average concentrations of the most common contaminants found in DDMT soil are compared with averages for the same chemicals from soil sampling locations around DDMT. With the exception of arsenic and iron, on-site levels are considerably higher than those off-site. In addition, little difference was found in concentration between the soil samples taken at the perimeter of DDMT and those taken further away (Table 4).
Most surface water and sediment sampling locations from the area around DDMT receive little or no water from DDMT. Thus, chemicals found in this sampling program come from sources other than DDMT. Recent sampling indicates that polluted surface water is found throughout Memphis (69).
Tables E6 and E7 on page 73 identify the 13 chemicals found in sediment and one in surface water with at least one concentration above a comparison value. Although comparison values were exceeded, further analysis identified no significant health risk. Even daily exposure to the highest concentrations represents insignificant cancer risk (maximum risk of 1 in 100,000).
Table 3 - Comparison of BRAC1/RI2, SS3, and DDMT Area Soil Means*
|DDMT Area Mean
|* Non-detected chemicals were accounted for
by calculating the mean using ½ of the detection limit as the value for
the non-detected chemical.
** mg/kg = milligrams of chemical per kilogram of soil
1 - BRAC = base realignment and closure
2 - RI = remedial investigation
3 - SS = screening sites
Table 4 - Comparison of Perimeter And Off Site Soil Means*
|Contaminant||Perimeter Mean in Mg/kg**||Off Site Mean in Mg/kg**|
|* Non-detected chemicals were accounted for
by calculating the mean using ½ of the detection limit as the value for
the non-detected chemical.
**mg/kg = milligrams of chemical per kilogram of soil
Evaluation of Health Outcome Data
The Superfund law requires that health outcome (i.e., mortality and morbidity) data (HOD) be considered in a public health assessment (70). This consideration is done using specific guidance in ATSDR's Public Health Assessment Guidance Manual and a 1996 revision to that guidance (71,72). The main requirements for evaluating HOD are presence of a completed human exposure pathway, great enough contaminant levels to result in measurable health effects, sufficient persons in the completed pathway for health effects to be measured, and a health outcome database in which disease rates for population of concern can be identified (72).
This site does not meet the requirements for including an evaluation of HOD in this public health assessment. Although completed human exposure pathways exist at this site, neither the contaminant levels nor the exposed population are great enough to permit meaningful measurements of possible site-related health effects as identified in existing HOD.
However, although using HOD to identify health effects possibly related to DDMT is not possible, evaluating HOD to determine whether the community's assertions of excess disease can be confirmed is good public health practice. Two preliminary evaluations of cancer mortality have already been done by the Tennessee Department of Health (TDH) and ATSDR to evaluate these assertions (73,74).
In the most recent report, TDH and ATSDR investigated the age- and race-adjusted cancer rates within 1-1½ miles of DDMT for 1990 - 1996 by evaluating 23 types of cancer for men and women.(74). Overall, the cancer rates for the area around DDMT were near or below the rates expected from Shelby County and the State of Tennessee.
Although this investigation did not identify overall excesses of cancer, the rates for other diseases or health conditions might be excessive. ATSDR is recommending that these other diseases be investigated, if possible (74).
The following issues were identified in conversations with DDMT area residents and in ATSDR's review of the data for the site.
- Were people exposed to ANY depot chemicals and radiation (40)? -- please give a
direct answer, not an indirect one as in 1995 public health assessment.
Response: The answer is yes for depot chemicals based on the discussion in the previous section. Some residents may have had infrequent, short-term exposure to depot chemicals in air due to accidental releases, or in surface water or sediment due to accidental leaks or spills or intentional discharges. However, daily or nearly daily long-term exposure of area residents to depot chemicals is not very likely. If it did occur, it could have taken place in 3 surface water drainages and to an estimated 500 - 3,000 people. In the past, two additional surface water drainages appear to have existed.
The answer is no for radiation. No DDMT area resident was likely to have been exposed to site-related radiation (radioactive materials) because only small amounts were stored on-site. This storage appears to have been properly done so very little chance of releases to the environment existed.11
- Depot had uncontrolled access until the 1960s or 70s and children played on-site (40).
Response: The DDMT Main Facility and Dunn Field have been fenced and guarded since the facility opened in 1942 according to DDMT staff and the literature available to ATSDR.12
- Residents around DDMT were exposed to contaminants through surface water flowing
off-site in 21 open drainage ditches (40). Exposure was not only to contaminants in
surface water, but also to site contaminants in the air and in the food chain (e.g., fish,
rabbits, plants) (43).
Response: Transportation of contaminants off-site could have occurred whenever sufficient rain created water flow in the ditches draining the site. Exposure to site contaminants could have been through ingestion or having skin contact with surface water, or soil or sediments contaminated by chemicals in the surface water. These ditches could have been polluted by leaks, spills, or intentional discharges of DDMT chemicals.
ATSDR confirmed that 14 points do or did exist where water discharges from DDMT into open ditches (Figure 5). Eleven of these currently exist and 3 existed in the past. One of these 3 ditches was located between Tarrent Branch and Dunn Road on the westside of the main facility and the other 2 on the southside of the main facility about midway between the east and west ends.
ATSDR identified seven other points where water is and was discharged off site through storm sewers. These discharges into storm sewers appear to have been occurring since 1953 (62). Before 1953, we were unable to determine whether water flowed off-site at these 7 locations in storm sewers or in open ditches. Therefore, there may have been 21 open drainage ditches coming off DDMT before 1953.
As indicated earlier (page 20), about 500 - 3,000 residents may be at risk of exposure to small amounts of site contaminants transported off-site in surface water. The chance of exposure appears to have been the greatest in the Rozelle neighborhood just west of Dunn Field. The current chance of exposure in that neighborhood could be more accurately evaluated by determining levels of site contaminants in residential soil. ATSDR is planning to conduct sampling to do this.
However, any exposure to site contaminants through air or food is and was very unlikely. The known contaminant concentrations in surface water appear to be too low to result in releases of site contaminants to the air. Levels also appear to be too low to result in substantial contamination of crops grown in the area, or in fish, or wild or domestic animals.
Exposure of individuals off-site through ingestion of contaminated fish does not appear to be possible because the ditches draining the site are often dry. Thus these ditches would not sustain a fish population. A viable fish population exists in Nonconnah Creek, which eventually receives all the water draining from DDMT. This creek has been posted as a no fish consumption area since 1982 largely because of chlordane from a nearby pesticide production facility and its use around homes (68).
- Individuals living in the Bunker Hill area and students at Hamilton High School were
exposed to contaminants through surface water run-off in drainage ditches (40).
Response: As described starting on page 25, residents of the Bunker Hill area or students at Hamilton High School are very unlikely to currently be exposed to site contaminants transported off-site by surface water. Water from the western side of Dunn Field does go through the residential areas between Dunn Field and Hamilton High, but, except for the Rozelle area, currently does so entirely in pipes.
Currently, direct contact with water-borne site contaminants is very unlikely in the area around Hamilton High. Cane Creek, which runs under Hamilton High, has been fenced and concrete-lined between the Ragan Street and Elvis Presley Boulevard bridges since the early 1970s. In addition, the concentration of site contaminants in the water going under Hamilton High would be much lower than levels at the site boundaries because DDMT contributes only a small portion of the water that flows under the school. See section (5) on page 25 and Appendix H on page 90 for more details.
However, direct contact with contaminants could have occurred before Cane Creek was fenced and lined in the 1970s, and when water from Dunn Field flowed through the Bunker Hill area in an open ditch.
Indirect contact of Hamilton High students and staff with DDMT contaminants moving from water in Cane Creek into the air appears extremely unlikely. The known surface water concentrations at the DDMT boundary are too low to result in release of contaminants to the air (59-61).
- One resident was concerned about possible health effects from playing in the drainage
ditches in the Rozelle area in 1945 (44). This same individual indicated that he and his
family drank water from a private well at that time. His father's fruit trees either didn't
grow or didn't produce fruit. Another individual asserted that children played in
drainage ditches, immediately off-site, and found many items including gas mask
canisters (40). When this occurred was not indicated.
Response: Very little information exists about the operation of the Depot for 1942 - 1945 so we are unable to provide a specific response to these concerns (5).
- Exposure took place to liquid toxic substances from the Depot that drained near Perry
Avenue (40). Drainage of these toxic substances occurred on a regular basis because
DDMT workers disposed of toxic substances down the facility drains as instructed by
Response: Contaminants from DDMT could have gotten into on-site drains and ditches from intentional disposal, leaks or accidental spills. However, this apparently did not result in substantial exposure off-site, at least in the recent past. This conclusion is based on the fact that known contaminant levels in surface water and sediment from DDMT are low. These contaminant levels are described starting on page 20.
The disposal of toxic substances down facility drains could not have led to contamination of the drainage ditches and surrounding areas on- and off-site if most, if not all, of this disposal was in the drains inside DDMT buildings. This is because drains inside DDMT buildings were and are connected to the sanitary sewer system (3,7). Thus, no opportunity would exist for off-site exposure because the sanitary sewer system is entirely closed with no open drainage.
- Outbreaks of rashes occurred because of contact with soil in the Freemont and Cascade
Response: Although people may have experienced these rashes, DDMT contaminants are not likely to have been the cause. ATSDR did not identify a mechanism by which DDMT contaminants could have been transported to the surface soil in the Freemont/Cascade area. A ditch from DDMT exists to the east of Freemont (Figure 5). However, materials from this ditch are unlikely to have contaminated Freemont area surface soil because the ditch appears to be at an elevation lower than Freemont.14 See page 25 and Appendix H (page 90) for more discussion of drainage in this area.
- Did exposure to site contaminants in drinking water occur from private wells used
before 1950 (40)?
Response: Exposure to site contaminants in drinking water from private wells before 1950 does not appear possible. This is because the likely sources of contaminants in groundwater were not buried in Dunn Field until 1955 (6,47). All residences around the site were connected to the Memphis public water supply by 1953.
- Have contaminants from the Depot affected the aquifer near site (43)?
Response: Contaminants buried on Dunn Field have polluted the Fluvial (shallow) aquifer under and to the west of the northern tip of Dunn Field. Contamination also occurred to a small portion of the shallow aquifer under the main facility (3). Three aquifers are under DDMT: the Fluvial, Memphis Sand, and Fort Pillow Sand with the Fluvial the shallowest and Fort Pillow the deepest. Contaminants from Dunn Field or the main facility have not moved down to the Memphis Sand Aquifer. This aquifer provides 95% of the drinking water in Memphis. However, a clear potential exists for the contaminants to move down to the Memphis Sand some time in the future.
- Fumes released from the Depot in the evenings and nights of 1968 caused people to
have reoccurring skin rashes and burning eyes, and caused animals to die (40).
Response: We were unable to identify any information about this issue.
- People were exposed in the evenings of 1978 to air releases from Dunn Field near the
corner of Person and Hayes (40). These releases had a foul odor, and those who
inhaled it experienced nausea and sleepless nights.
Response: We are unable to provide a definitive answer to this concern. ATSDR did not identify any information about air releases from DDMT in 1978. This location is the northeast corner of Dunn Field. Available data do indicate that this area of Dunn Field appears to have been used as a burial area for impregnite in the 1940s (47). This substance was used to make clothes and shoes resistant to chemical agents. This material is unlikely to have produced the reported air releases in 1978 because it is solid. ATSDR did not find any other indication in the documents reviewed that other materials were buried in this area.
- Persons across the street from the mounds on Dunn Field were exposed to dust blowing
off them (40).
Response: Exposure to dust from these mounds probably has not resulted in any health effects. The mounds are national stockpiles of bauxite and fluorspar. These substances are not very toxic (i.e., it takes a lot to cause harm). These mounds were covered most of the time thus eliminating or greatly reducing the amount of dust blowing into the neighborhood east of the mounds (Figure 3). The combination of low toxicity and infrequent exposure makes health effects improbable.
- The mustard bomb casings are in publicly assessable areas near Dunn and Perry Roads (40).
Response: As displayed on Figure 3, the information available to ATSDR indicates that the mustard bomb casings were buried on Dunn Field (3,5). Public access is unlikely because Dunn Field reportedly has always been fenced.
- Depot-related exposures caused various illnesses such as cancer, breast cancer,
prostate cancer, strokes, heart attacks, hypertension, thyroid diseases, miscarriages,
birth defects, liver disease, numbness (hands, feet, or face), ear-nose-throat problems
(40,43).15 This was asserted to have been confirmed in state reports (43).
Response: ATSDR found 3 reports that focus on or mention disease or death in the DDMT area (73-75). None of them identify any diseases that are attributed to exposure to DDMT contaminants.
Reviews of cancer data have taken place, one by the Tennessee Department of Health (TDH), and the other by TDH and ATSDR (73,74). In the most recent report, TDH and ATSDR investigated the age- and race-adjusted cancer incidence rates within 1-1½ miles of DDMT for 1990 - 1996 (74). Twenty-three types of cancer were evaluated for men and women. Overall, the cancer rates for the area around DDMT were near or below the rates expected from Shelby County and Tennessee. The only cancer with an elevated rate was Endometrial (corpus uteri) cancer in women. Six cancers had rates lower than expected - esophageal and lung cancer in men; and lung, breast, pancreatic, and bladder cancer in women. As described starting on page 20, off site exposures were probably too infrequent and at concentrations too low to cause any health effects from long-term exposures. The one cancer that was elevated, Endometrial, is not known to be caused by any of chemicals found on DDMT (76).
The third report was a 1998 article in the Memphis Commercial Appeal in which the Memphis-Shelby County Health Department (MSCHD) reported the number of deaths in Shelby County for 1993 - 1997 (75). The deaths were broken down by census tracts. The census tracts with the highest numbers of deaths were in the South Memphis area including a tract close to DDMT. This higher number of deaths was attributed to there being proportionally greater number of elderly people in these census tracts compared with the other census tracts. As described in the Demographics section on page 10, a larger portion of the population within a mile of DDMT is 65 or older compared to the rest of Shelby County. This report had no information on the causes of death.
- Toxicity data for a chemical come from studies of Caucasian males and the results
might not apply to African-American communities (40).
Response: The toxicity data used in this public health assessment come from animal studies and epidemiologic investigations of actual human exposures. They did not come from studies of Caucasian males. The toxicity data used in this document are applicable for African-Americans and all other racial groups.
ATSDR prefers to use data from investigations of human exposures to a chemical. However, most of the data used come from studies of laboratory mice and rats, or other animals such as dogs and monkeys because valid human data are lacking for many chemicals (71).
In this document, human toxicity data were used for arsenic, cadmium, and lead (77-79). For arsenic, the main study used to identify toxicity was of non-Caucasians (residents of Tawain) who had drunk arsenic-contaminated water for years (77). For cadmium, the main study is of Japanese (78). For lead, toxicity data come mostly from studies of children exposed to lead in urban areas (79). The children evaluated included African-Americans, Caucasians, and other racial or ethnic groups.
- In 1970s or 1980s, people wearing protective clothing and masks tested the west side of
Depot, removed contaminated soil, and replaced it with new soil and gravel (40).
Response: This was probably the removal of the pentachlorophenol (PCP) dipping vat and contaminated soil in 1985 (80). The location of this vat is identified on Figure 2. The vat was used regularly to treat wood with the preservative PCP from about 1952 to 1971 and infrequently after that until it was removed in 1985. The emptying and repacking of PCP in the vat would require workers to wear protective clothing and masks.
- German prisoners of war, who were housed in a camp on the southwest portion of the
main facility, may have contaminated the environment during World War II (40).
Response: ATSDR was unable to identify any information on this issue. However, even if these prisoners of war contaminated the environment, the environmental data reviewed in this document indicate that the current amount of contamination on-site is relatively low.
- The Depot is similar to Love Canal where chemicals were buried in a dump, and health effects appeared 27 years later (40).
Response: At Love Canal, many homes were built on top of areas where hazardous waste was dumped (81). At DDMT, all available data indicate that homes were not built on top of hazardous waste disposal sites.
- Fallen and damaged trees were observed on Dunn Field in 1997 (40). Were any tests
performed to determine why this occurred, and if they were, what were the results?
Response: The two arborists (tree doctors) who evaluated the dead or damaged trees for DDMT, indicated that this problem was due to natural causes such as wind damage and the trees reaching the end of their lifespan (82).
- In March 1998, two residents found two dead birds just off-site of the west boundary of
Dunn Field.16 They were concerned that the birds' deaths were due to site contaminants
possibly released from nearby location on Dunn Field. A few days before, small vials
had been uncovered at that location during the installation of a utility line.
Response: Using descriptions of what happened, it appears unlikely that these birds died because of this incident. The materials uncovered in this incident were metal canisters with small glass vials packed in them (28,83,84).17 The burial site for these vials was not identified in the records of materials disposal at Dunn Field. However, the crew doing the remedial work was checking for buried materials before they disturbed the soil and had indications that something was there. What they found were metals canisters with small glass vials inside. These canisters were similar to those in which 35mm film is packaged. Some of the vials contained small amounts of liquid. The materials uncovered at this location (whole and damaged canisters and glass vials, and the soil around them) were certified as non-toxic by the Tennessee Department of Environmental Conservation (TDEC). These materials were disposed of at a Shelby County landfill.
- A resident wondered whether students at Dunn School had been medically evaluated
after the chemical warfare building blew up in 1988.2 Another resident asked why
Norris Elementary School wasn't closed during this incident, if Dunn School, which is
about the same distance from DDMT, was closed.18
Response: Dunn Elementary School was closed during a hazardous materials incident in 1988, but no medical evaluations of the students from this school were performed (64). This incident had nothing to do with chemical warfare materials because the large scale storage of them ended in 1947 and all were gone by 1961 (5).
In the January 19 - 21, 1988, hazardous material incident, the cover of a hazardous materials storage building called a Span Dome, as identified on Figure 2, collapsed during a severe thunderstorm (64). This building was located about 1,400 feet south of the corner of Perry and Dunn Avenues and about 500 feet from Perry Avenue (67). The collapse resulted in the release to the environment of about 327 - 2,000 gallons of the 250,000 gallons of the hazardous materials stored in this building and an identical building right beside it (64). The chemicals stored were acetone, isopropyl alcohol, methyl ethyl ketone, methyl isobutyl ketone, toluene, and xylene. All these are commonly-used solvents (66).
The Memphis Fire Department's (MFD) report indicates that, during the first hours of this incident, "The odors of the products and gas trac readings of flammability were very high at the north perimeter of the Depot (Dunn Street), indicating much leakage. These readings and odors were surprising at this distance considering the first four to five hours of the incident occurred while heavy thunderstorms were crossing the Memphis area" (64). [Note: As indicated on Figure 2, Dunn Avenue is about 1,300 feet north of the building (67).] MFD took measures to prevent or greatly reduce air releases. However, short-term exposures to these hazardous materials could have occurred before these measures were taken.
On January 20, Dunn School was closed as a precautionary measure while the collapsed structure was being cleared away and the spilled chemicals cleaned up (64). A shut-in was also evacuated from his or her house on the 20th.
As indicated on Figure 1, Norris Elementary School is near the southwest corner of DDMT and Dunn School is near the northwest corner. Both are about the same distance from the Span Dome. Decisions to close or evacuate schools or residential areas during hazardous materials incidents are largely based on wind direction. It appears that MFD assumed that the wind was blowing to the north (i.e., towards Dunn School) on the day the structure was cleared away. Thus, they closed Dunn School but left Norris School open.
- Could the cleanup of the dieldrin-contaminated soil near the base housing units on the
Airways Boulevard side of DDMT have polluted the soil in the apartment complex just
across the fence from where the cleanup was done?
Response: This cleanup probably did not result in contamination of apartment complex soil with dieldrin. DDMT staff indicated in presentations to the DDMT Restoration Advisory Board (RAB) that the cleanup was done using procedures that would prevent this from happening (85,86). This included monitoring the air during the removal in which dieldrin was not detected. In addition, dieldrin levels in soil represented a risk for cancer if someone was exposed to them for a long time, but not a risk for other health effects.
ATSDR is recommending that soil from this complex be sampled because it is not known whether past use of dieldrin and other chemicals in the base housing area could have led to contamination of the soil across the DDMT boundary fence.
- Could the combined effect of the mixture of chemicals found at DDMT have caused
cancer or other health effects, even though the concentration of each chemical may not
be harmful by itself?19 20
Response: The answer to this question is no, based on the information available to ATSDR on the health effects of mixtures and the actual concentrations of chemicals found on DDMT. ATSDR has sponsored research for many years on the mixtures issue because of its importance in evaluating the possible health impact of a site and because it is often a community concern. A common finding of the ATSDR-sponsored and other investigations of this issue is that adverse effects are unlikely when the chemicals in a mixture are present at concentrations well below the toxicologic thresholds21 for that chemical (87-90). ATSDR identified the toxicologic thresholds for the site contaminants and found that the maximum contaminant levels result in doses many times (100s to 1,000s) lower than the thresholds. This suggests that exposures to combinations of DDMT contaminants are unlikely to result in adverse effects.
Further analysis of exposure to a mixture of DDMT contaminants was done by identifying the possible interactions among the chemicals contributing most of the potential risk. For soil and sediment, 4 metals (lead, iron, chromium, and arsenic) contribute more than 95% of the total noncarcinogenic hazard. The chemical interactions that would increase risk appear to be counterbalanced by those that reduce risk. For example, cadmium may enhance the noncarcinogenic toxicity of arsenic but chromium reduces it (77,78,91).
- Do any data exist that indicate that DDMT workers were exposed to site contaminants
at concentrations great enough to cause health effects?22
Response: Concentrations of benzo(a)pyrene, dibenz(a,h)anthracene, or all polycyclic aromatic hydrocarbons (PAHs) together may have been great enough in the soil around several locations at DDMT to result in an increased cancer risk for individuals who daily contacted and ingested that contaminated soil (3,8-10). For this to happen, an individual would have to have worked in the soil rather than just walk over it. A more detailed discussion of those possible exposures is on page 78.
Besides these possible exposures in areas around specific buildings, former workers reportedly could have been exposed to toxic substances because of work practices inside the DDMT buildings that resulted in contact with chemicals (51). Evaluation of these situations is not within the scope and purpose of a public health assessment.
- Residents know of locations where materials from DDMT were dumped or buried off-site. In at least one instance, this may have led to the sinking of a portion of a
residential yard (38).
Response: Anyone knowing of locations where DDMT materials were dumped or buried off-site should report this to Mr. Jordan English (901-368-7953) at the Memphis Office of the Tennessee Department of Environmental Conservation, or Mr. Turpin Ballard (404-562-8553) at EPA/Atlanta. These agencies have the responsibility to investigate reports of buried hazardous materials.