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PUBLIC HEALTH ASSESSMENT

THERMO CHEM INCORPORATED
MUSKEGON, MUSKEGON COUNTY, MICHIGAN

ENVIRONMENTAL CONTAMINANTS AND OTHER HAZARDS

Contaminants of concern at this site were selected from those chemicals for which the concentration in at least one environmental medium exceeded a health-based comparison value (Table 1). Lifetime exposure to a chemical in an environmental medium at concentrations at or below the corresponding comparison value is not expected to result in more than 1 case of cancer in 1 million people exposed or any increase in non-cancer health effects. Comparison values used in this assessment include:

    ATSDR Environmental Media Exposure Guides (EMEGs)

    ATSDR Cancer Risk Evaluation Guides (CREGs)

    ATSDR Reference Dose Media Exposure Guides (RMEGs), computed from the U.S. EPA Reference Dose (RfD) for chronic exposure of a child, assuming pica behavior for soil ingestion

    U.S. EPA Drinking Water Health Advisories (Lifetime)

    U.S. EPA Safe Drinking Water Act Maximum Contaminant Levels (MCLs).

If no comparison values for a chemical in a medium are available, or there is no CREG available for a carcinogen, the chemical is retained as a contaminant of concern. If members of the community have expressed specific concerns about exposure to a chemical, that chemical will be retained as a contaminant of concern.

To identify facilities which might contribute to the environmental contamination at the Thermo-Chem, Inc. site, the MDPH searched the Toxic Chemical Release Inventory (TRI) data base for 1987 through 1993. The U.S. EPA compiles the TRI from information provided by industries. The TRI contained no entries for the Thomas Solvent or Thermo-Chem, Inc. facilities on the site, either as a waste generator or as a receiver of waste from other facilities, because Thermo-Chem, Inc. closed in 1980 and the Thomas Solvent operation closed in 1986, before the TRI began collecting data in 1987. The TRI contained entries for 12 other facilities with the same postal zip code (49442) as the Thermo-Chem, Inc. site(3) and 7 in the zip code 49444, covering the neighboring territory to the south. According to their addresses, the facilities listed are all located 1.25 miles or more from the Thermo-Chem, Inc. site. Three facilities are east of the site, the rest are to the west. From the locations of these facilities, the releases from them are not likely to contribute to the environmental contamination at the Thermo-Chem, Inc. site.

All data in this section, unless cited otherwise, are from the RI report (2), the U.S. EPA TA investigation report (4), and Technical Memorandum No. 3 (8). For this Assessment, the site is defined as the Thermo-Chem, Inc. and Thomas Solvent Co. properties combined.

Compounds that did not meet the above criteria for contaminants of concern will not be specifically addressed in this Health Assessment.

A. On-Site Contamination

Soil Gas

The RI contractors collected soil gas samples on activated carbon tubes, and assessed ambient air in the field using an HNu photoionization detector. They collected samples on a 50-foot grid at a depth of 15 feet. In the process areas, they used a 25-foot grid interval and a 3-foot depth. They used seven compounds that had been found in significant concentrations during previous site investigations as indicator compounds: methylene chloride, dichloroethylene (DCE), trichloroethylene (TCE), tetrachloroethylene (PCE), trichloroethane (TCA), toluene, and xylene. The results of these analyses are summarized in Table 2.

Results of the field measurements at the 3-foot depth found several apparent source areas for VOCs in the soil gas: a groundwater contamination plume migrating from the Thomas Solvent site property; the concrete pads west of the process building near the solvent recovery stills; the northernmost (lined) seepage pit; and the reported disposal area in the southern portion of the cleared area of the site.

Field measurement data from the 15-foot depth complemented the results from the shallower measurements. Contamination detected in deeper samples in the northern portion of the site was greater than at the 3 foot zone.

The TA investigators collected two soil gas samples apiece from 83 locations; one from 3 feet below the ground surface and one from 14 feet below the surface. Samples were analyzed for the following volatile organic compounds: methylene chloride, DCE, TCA, TCE, PCE, toluene, ethylbenzene, benzene, and xylene. The results of these analyses are summarized in Table 2. Soil gas samples were also screened on a gas chromatograph equipped with a flame ionization detector (FID) and an electron capture detector (ECD).

The contractors used the results of these soil gas investigations to select soil sampling locations and monitoring well placement.

Surface (Shallow Subsurface) Soils

ATSDR criteria say that surface soil samples should be taken from the top 3 inches of soil to best represent that part of the soil most accessible to human exposure. The shallowest soil samples collected during the RI were composite samples that ranged from the surface to 2 feet deep, and the shallowest soil samples collected during the TA were composites of soil 2 to 4 feet deep. Results of the analysis of the shallow subsurface soil samples from the RI are summarized in Table 3.

Underground Storage Tanks

During the TA, the contractors attempted to collect samples of the contents of the 16 underground storage tanks located on the Thomas Solvent Co. property. Only seven of the 16 tanks contained enough liquid to easily sample. The analyses found VOCs, SVOCs, and hydrocarbons at concentrations as high as 453,000 ppm (see Table 4 for a summary). Polychlorinated biphenyls (PCBs) and pesticides were not detected above method detection limits. These wastes have since been removed from the site and disposed of in off-site facilities.

Subsurface Soils

During the RI, the contractors collected subsurface soil samples 45 soil borings and 8 test pit excavations on the site (Figure 2). Five of the borings were located along the east side of the Thermo-Chem, Inc. site on the narrow strip of Thomas Solvent property formerly used for drum storage. Soil samples were divided into three groups:

  1. Soil borings – soil samples from shallow soil borings to the water table (SB1 - SB13), soil samples from shallow monitor wells (MW1S - MW9S), and Round 2 soil samples that included new borings and repeat sampling of previous locations.
  2. Clay liner – samples from the clay liner of the northern seepage pit.

  3. Test Pits – a composite soil sample from the southern pit excavation designated TP1 as well as sludges collected from the northern test pit designated TP8.

Soil samples were analyzed for the Target Compound List (TCL) of volatile organic compounds (VOCs), semi-volatile organic compounds (SVOCs), PCBs, pesticides, and inorganic compounds. The maximum concentrations found during the RI are listed in Table 5.

The most frequently detected VOC in soil samples was PCE, in 22 soil samples plus the TP8 sludge sample. The maximum concentration of a single VOC was 4,400 parts per million (ppm) of 2-butanone in sludge collected from TP8. The maximum value for a single VOC compound from samples collected other than in TP8 or the north seepage pit was 13 ppm of acetone at MW7.

The most frequently detected SVOCs were phthalates, the maximum values (total) detected were 297 ppm from the seepage pit and 139 ppm from TP8. Excluding the northern seepage pit and TP8, the highest detected concentration was 28 ppm from the 6- to 8-foot depth sample at SB3, located northeast of TP8. The maximum concentration for a single phthalate compound was 140 ppm for bis(2-ethylhexyl)phthalate.

PCBs were detected in soil samples at two locations. Aroclor-1254 was detected at a concentration of 0.66 ppm in SB14, located just east of TP8, at a depth of 0 to 2 feet, and 0.46 ppm in a composite sample from SB3. Pesticides were detected in soils at three locations: SB9 (north seepage pit), SB10 (middle seepage pit), and SB13.

In general, the highest concentrations of inorganic analytes were found in samples from the clay liner and TP8. The arsenic, barium, cadmium, chromium, cobalt, copper, lead, mercury, nickel, silver, vanadium, and zinc concentrations exceeded either off-site background or western Michigan 99 percentile values (mean plus 3 standard deviations). There was no off-site local or regional data for antimony and beryllium. Cadmium, chromium, copper, lead, nickel, and zinc concentrations exceeded the range of concentrations found in the eastern U.S. There was no data available on silver concentrations in soil from the eastern U.S. (Reference 2, Table 4-10).

In samples other than in the clay liner or TP8, arsenic, barium, chromium, cobalt, lead, mercury, silver, vanadium, and zinc concentrations exceeded either off-site background or western Michigan 99 percentile values (mean plus 3 standard deviations). There was no off-site local or regional data for antimony and beryllium. Cadmium concentrations exceeded the range of concentrations found in the eastern U.S.

During the TA investigation in May and June 1990, five soil borings were drilled and sampled in the Thomas Solvent Co. property. The boring (SB-01 through SB-05) locations are shown in Figure 2. SB-01 through SB-04 were sampled every 2 feet to a depth of 16 feet; SB-05 was sampled every 5 feet to a depth of 25 feet. The concentrations of contaminants of concern found are summarized in Table 6.

Based on the data they collected, the TA investigators concluded that the underground storage tank farm and spillage from loading operations were the primary sources of contamination in the soil. The sample from 14-16 feet deep at SB-03 contained the highest total VOC concentration, 2,400 ppm. The highest concentrations of VOCs were found in the interval just above the water table (14-16 feet) in four of the five borings. The other boring, SB-02, had its highest VOC concentration at between 6-8 feet in depth. The organic contaminants with the highest concentrations were TCE, PCE, toluene, and ethyl benzene. The most commonly found VOC was toluene, in 12 of 15 samples, followed by PCE in 6 samples.

SVOCs were primarily found in the capillary zone (portion of soil water held by cohesion as a continuous film around the soil particles above the water table) from 14-16 feet with SB-03 being the most contaminated with total SVOC concentration of 3,800 ppm. SVOCs detected included bis-(2-ethylhexyl) phthalate, naphthalene, 2-methyl naphthalene, di-n-butylphthalate, and nitrobenzene. PCBs were detected at all depths in SB-03 with concentrations increasing with depth to the water table at 14-16 feet. Aroclor 1254 was present at a concentration of 1.3 ppm (14-16 feet) at SB-03.

Analysis for inorganic chemicals found that the highest concentration of the analytes occurred at or near the surface. The levels detected for all metals on the list of contaminants of concern were within western Michigan background levels.

Groundwater

During the RI, the contractors collected groundwater samples from on-site monitoring wells in two rounds, Round 1 in October and November 1989, and Round 2 sampling, in September 1990. Round 1 sampled monitoring wells MW1S,M through MW9S,M, and Round 2 added the newly installed MW4D (Figure 3). Monitoring wells designated with an "S" or "M" tap the upper aquifer; monitoring wells designated with a "D" tap the lower aquifer. The groundwater samples were analyzed for VOCs, SVOCs, and inorganic compounds. The results of groundwater sampling from on-site monitoring wells from the RI and the TA are summarized in Table 7. PCBs and pesticides were not detected in on-site groundwater samples in the study area.

The highest total concentration of VOCs was found in MW4M, located south of the three seepage pits, during Round 1. The concentrations decreased rapidly to the east, south, and west of MW4. Water from MW8, located upgradient of the former Thermo-Chem operations and immediately downgradient of the former Thomas Solvent operations, also contained elevated levels of VOCs. Round 2 analytical results show a similar horizontal and vertical extent of VOCs. In general, the VOCs concentrations in water from MW4 and MW8 were elevated in both rounds.

SVOC contamination appeared to follow the same pattern found during VOC analysis. The maximum concentration detected for a single SVOC was 4,500 ppb for bis(2-ethylhexyl)phthalate in water from MW8S. The SVOC concentrations found in water from MW4S were significantly lower than those in water from MW8S.

During the inorganic analysis, no consistent pattern was observed for Rounds 1 and 2. The maximum concentration detected was an estimated 3,720 ppb of zinc in water from MW1M, located in the southeastern portion of the site. In addition, lead was detected at a maximum concentration of 6.3 ppb in water from MW1M, chromium was found in 2 locations with 7.8 ppb detected in water from both MW1S (Round 1) and MW4S (Round 1). MW4S is located just south of the seepage pits. Cyanide was detected with a maximum concentration of 315 ppb in water from MW6S (Round 1), located just northwest of the seepage pits.

During the groundwater investigation that took place on the Thomas Solvent property during the TA, four existing 2-well clusters (installed by Keck in 1985), located on the Thomas Solvent Co. and adjacent Thermo-Chem, Inc. properties were sampled. Each of the four Keck clusters, MW-T1 through MW-T4(4), included one well screened at the water table interface ("S" for shallow) and the other below the clay ("M" for medium depth). The contractors for the TA installed 8 additional monitoring wells (two on-site, MW-T8D and a replacement well for MW-T3S in Figure 3, and the rest off-site). The concentrations of contaminants of concern from these samplings are included in the summary in Table 7.

The groundwater sampling and analysis found organic contamination primarily in the upper 10 feet of the saturated zone, particularly in wells on the Thomas Solvent Co. property. The medium depth wells MW-T1M through MW-T4M, located on the Thomas Solvent Co. property and northern portion of the Thermo-Chem property, showed no VOC contamination.

Water from the shallow upgradient on-site monitoring well, MW-T1S, contained no detectable VOCs. Water from the other three shallow on-site monitoring wells sampled in the TA did contain high concentrations of VOCs. MW-T2S, located just south of the tank farm, contained the highest total VOC concentration, 137,000 ppb. MW-T8D, screened at 50-55 feet in the absence of a confining layer, had a total VOC concentration of 1,200 ppb. 1,2-DCE, 1,1,1-TCA, TCE, PCE, toluene and ethylbenzene were present in water from MW-T2S, MW-T3S, and MW-T4S. Water from MW-T8D contained the latter 5 chemicals. The highest concentrations of the individual chemicals were found in MW-T2S. Values for each VOC contaminant significantly decreased from MW-T2S to MW-T3S to MW-T4S to MW-T8D, in all instances. A water sample from the original MW-T3S was orange-brown in color with a dense layer separating out in the sample jar. There is no report of chemical analysis of either phase of this sample (Reference 4, p. 20).

SVOC contamination was only found in the area around and south of the facility's buildings. The shallow monitor wells typically had higher total SVOC concentrations than the medium-depth wells. Concentrations decreased to the south and east from MW-T2S to MW-T3S to MW-T4S. Water from MW-T8D contained the highest SVOC concentrations of the medium-depth/deep wells on-site, 938 ppb total SVOCs.

Inorganic compounds analyzed for in all on-site wells were either at non-detectable levels or at very low concentrations. Lead was present in water from all on-site wells with a maximum concentration of 11.4 ppb in MW-T1M. Arsenic was detected in water from all but the medium-depth wells and MW-T1S with a maximum concentration of 9.6 ppb in MW-T2S.

B. Off-Site Contamination

Surface Soils

The RI contractors collected off-site soil samples, but the TA contractors did not. As mentioned in the On-Site Contamination section, samples taken from the 0 to 3 inch depth are considered surface soil samples by ATSDR. However, the soil samples taken closest to the surface during the investigations at the Thermo-Chem site were composite samples taken from the 0 to 2 foot depth. These are considered subsurface soil samples by MDPH and will be addressed accordingly.

Subsurface Soils

Soil samples taken off-site during the RI were background samples, collected at MW10S, located approximately 130 feet north of the site, and at three locations several hundred feet northwest of the Thermo-Chem, Inc. site (0-2 feet in depth). No organic contaminants were found in these samples and analysis for inorganic chemicals showed comparable levels for background levels in the area. There were no off-site soil samples taken during the TA.

Groundwater

The RI investigators drilled fourteen wells near the site, one 2-well cluster north (upgradient) of the site (MW10 in Figure 4) and four 3-well clusters south of the site (MW11 through MW14 in Figure 4). The TA investigators drilled 6 monitoring wells southwest of the Thomas Solvent Co. property (MW-T5D, -T6D, -T7S, -T7M, -T9S and -T9M in Figure 4). As with on-site sampling of groundwater in the RI, water collected from off-site monitoring wells was analyzed for VOCs, SVOCs, PCBs, pesticides, and inorganic compounds. The concentrations of contaminants of concern found in water samples from all these wells during both the RI and TA are summarized in Table 8.

Elevated levels of VOCs were detected in water from downgradient wells MW11, MW12 and MW14 (see Figure 4), located to the south of the site between Thermo-Chem, Inc. and Black Creek. Downgradient concentrations of VOCs were much higher than on-site concentrations. Water from MW11M contained the highest concentration of VOCs found in the study area (22,590 ppb total).

No significant levels of SVOCs were detected in water from any off-site monitoring wells. Endosulfan II, a pesticide, was reported at 0.13 ppb(5) in one sample from MW12M, and no other pesticide or PCB was detected.

Analysis of water from off-site monitoring wells for inorganic chemicals generally did not find any concentrations above background levels. However, water from MW12M contained an estimated 132 ppb of arsenic, and water from MW6D contained 2,050 ppb of manganese.

During the TA, 1,2-DCA was found at between 2,000 and 3,000 ppb in water from all off-site wells except MW-T9M. SVOCs were not found in water from off-site wells in the lower aquifer. Water from MW-T7M contained 15 ppb of bis(2-ethylhexyl) phthalate. Inorganic chemicals in water from off-site wells were either not detected or at very low levels.

To date, sampling of private wells near the site has not shown contamination. There are no residential wells immediately downgradient of the site. The closest residence to the site (old Musk house, now Ferguson house) is adjacent to the Thermo-Chem, Inc. site to the northwest. The well serving this residence was last sampled on April 14, 1992, and showed no chemical contamination.

Surface Water

As a part of the RI/FS (detailed in Technical Memorandum No. 3), the contractors collected surface water samples from seven locations along a portion of Black Creek to the south of the Thermo-Chem, Inc. site. Two of the sample locations (S7 and S6) were upstream of the site, the rest (S1 through S5) downstream. The samples were numbered from downstream to upstream, S1 was furthest downstream, S7 furthest upstream. Samples were collected near the midpoint of the stream at each sampling location. The samples were analyzed for VOCs, SVOCs, pesticides, PCBs, and metals and cyanides (Table 9).

No detectable VOCs were found in samples collected at locations S3 and S7. Samples collected at both S1 and S2 contained 1,2-DCE, 1,1-TCA, TCE, and toluene. The maximum VOC concentration detected was 12 ppb of 1,2-DCE in the sample from the furthest downstream location (S1). No SVOCs, pesticides, or PCBs were detected in any of the surface water samples.

Barium, chromium, and manganese were detected in one or more of the surface water samples at concentrations above the detection limits. Barium and manganese were found in all the surface water samples, while chromium was found only in the sample collected at location S7 (furthest upstream). The highest concentrations of other metals were detected in the samples collected from the furthest downstream location (S1). None of the surface water samples contained cyanide.

Sediments

The contractors collected sediment samples from Black Creek concurrently with the surface water samples described above and from approximately the same locations. Sediment samples were analyzed for the same analytes as the surface water samples. The maximum concentrations of contaminants of concern found are listed in Table 10.

VOCs were only detected in the sediment samples collected from three sample locations furthest downstream from the site (S1 through 13). The VOCs found included 1,2-DCE, 2-butanone, TCE, 4-methyl-2-pentanone, PCE, toluene, and ethylbenzene. The highest VOC concentrations detected were 21 ppb of PCE and 21 ppb of toluene. The total concentration of VOCs detected in the three samples ranged from 30 ppb to 66 ppb. No SVOCs were detected in any sediment samples.

All of the sediment samples contained detectable concentrations of metals. No distinct pattern (upstream vs. downstream) was observed in the concentrations of the metals in the sediment samples. Barium, chromium, copper, lead, manganese, vanadium, and zinc were found in all samples. Arsenic and nickel were detected in some, but not all, of the sediment samples. None of the samples contained detectable concentrations of antimony, beryllium, cadmium, cobalt, cyanide, or mercury.

Biota

In May 1987, the MDNR collected 3 brown trout (7-9 inches), 7 carp (20-25 inches), and 5 white suckers (15-18 inches) from Black Creek at the U.S. 31 bridge, approximately 4 miles downstream from the Thermo-Chem, Inc. site. The fish were filleted, the carp with the skin off, the others with the skin on. The fillets were then analyzed for mercury, PCBs, polybrominated biphenyls, DDT, chlordane, and other pesticides and pesticide residues. The results are summarized in Table 11 (15). The analysis found no contamination at or above the MDPH's levels of concern.(6) Later in 1987, the MDNR applied rotenone to Black Creek to kill the resident fish population, and later restocked the creek with game fish species. There is no record of later sampling of fish from the creek.

C. Quality Assurance and Quality Control

In preparing this Health Assessment, the MDPH relied on the information provided in the referenced documents and assumed that adequate quality assurance and quality control measures were followed with regard to chain-of-custody, laboratory procedures, and data reporting. The validity of the analysis and conclusions drawn for this Health Assessment is determined by the reliability of the referenced information.

In the RI, TA, and Technical Memorandum No. 3, many values are flagged with a "J" qualifier. This qualifier represents an estimated value for the concentration detected due to limitations identified in the Quality Assurance Review. The RI also presented values with a "T" qualifier, which indicates that the concentration detected was below the contracted detection limit, but above the instrument detection limit (248).

In the TA, values detected for lead and arsenic in groundwater samples had "B" qualifiers attached, because both lead and arsenic were detected in lab blanks and because the concentrations in the samples were not at least 5 times the levels found in the blanks (4).

D. Physical and Other Hazards

Rusty storage tanks, the old distillery, and other structures on the site could pose an hazard to children or other trespassers that come onto the site. Young trespassers might be tempted to climb and play on the equipment. However, part of the site has been fenced, which would deter trespass. At the time of an MDPH/ATSDR site visit in 1988, an old laboratory building on the Thermo-Chem, Inc. property was unlocked and easily accessible, even though it contained many chemicals in glass laboratory bottles. Although hazardous chemicals have since been removed from the old laboratory, remedial workers still use the building to house their equipment. The remedial workers keep the building locked when not in use (3).

PATHWAYS ANALYSES

To determine whether nearby residents are exposed to contaminants migrating from the site, ATSDR evaluates the environmental and human components of pathways that might lead to human exposure. An exposure pathway contains five major elements:

  1. A source of contamination (source of contaminant release into the environment or the environmental media responsible for causing contamination at a point of exposure if the original source of contamination is unknown).
  2. A transport process of contamination through an environmental medium which serves to move contaminants from the source to points where human exposure can occur.

  3. A point of exposure or point at which people contact a contaminated medium.

  4. A route of human exposure (means by which the contaminant actually enters or contacts the body).

  5. A receptor population (population that is exposed).

An exposure pathway is considered to be a completed pathway if there is evidence that all five of these elements are or have in the past been present. A pathway is considered to be a potential pathway if one or more of these elements is not known to be or have been present, but could be or have been. An exposure pathway can be eliminated from consideration if one of the elements is not present and could never be present. The following sections discuss the most important exposure pathways at this site.

A. Completed Exposure Pathways

Surface soil

Surface soil data (0 to 3 inches deep) for the site is lacking. Based on the history of past operations at the site and elevated contaminant levels found in subsurface soils, elevated concentrations of VOCs may be present in the surface soil on the site. Anyone coming onto the site could be exposed to contaminated surface soils via dermal contact or through incidental ingestion or inhalation of fugitive dust. Workers at Thermo-Chem, Inc. and the Thomas Solvent Co. were likely exposed to chemicals they handled or that were present in the surface soils of the site as result of accidental spills or leaks. In addition, there are reports and evidence that trespassers had been on the Thermo-Chem, Inc. property before the fence was installed. There is no evidence available of trespass on that part of the site since then. The Thomas Solvent Co. property remains unfenced except along the common property line with the Thermo-Chem, Inc. property.

B. Potential Exposure Pathways

Groundwater

Rainwater percolating through the contaminated areas on-site has leached contaminants into the groundwater beneath the site. Groundwater contamination has moved off-site in the direction of Black Creek, but there are no known private wells in the contaminated aquifer downgradient of the site. The investigations in the RI and TA have adequately defined the location of the contaminant plume and no known private wells are threatened by contaminants from this site.

There is no indication to date that any of the nearby private wells contain site-related contaminants. However, should a well be placed into the contaminated aquifer in the future, this pathway could become completed. Residents using water from contaminated wells could be exposed to contaminants in the water by ingestion, dermal exposure, or inhalation of volatile chemicals secondary to household use.

Surface Water and Sediments

Monitoring well sampling data has indicated that the contaminant plume is moving in a southerly direction toward Black Creek. Preliminary data gathered during the RI/FS (Technical Memorandum No. 3) has found some contamination of the surface water and sediments downstream from the site. Further investigation of the creek may be necessary to determine the amount of contamination entering the creek and the area of the creek affected by the contamination.

People who fish, swim, or play in Black Creek could be exposed to contaminants in the water, sediments, or fish of the creek via ingestion of biota and incidental ingestion of surface water or sediments. The ROD includes further sampling of Black Creek and its sediments as a part of Operable Unit. Residents of the site area probably use the creek for recreational activity but there is no evidence available that there is extensive recreational use. This route of potential exposure will be re-evaluated when data from the Operable Unit II investigation is available.

PUBLIC HEALTH IMPLICATIONS

A. Toxicological Evaluation

Exposure doses for the chemicals at this site are evaluated by comparison with health-related guidelines. The guidelines used for evaluation of non-cancer adverse health effects are the Minimal Risk Levels (MRLs) established by the ATSDR and Reference Doses (RfDs) and Reference Concentrations (RfCs) established by the U.S. EPA. If an exposure dose does not exceed the MRL, RfD, or RfC, it is generally accepted that there would be little risk of adverse non-cancer health effects occurring. These MRLs, RfDs, and RfCs may not be sufficiently protective for especially susceptible individuals, such as the very young, the elderly, those whose immune systems have been weakened by other causes (immunocompromised), or those with a heightened sensitivity to a specific chemical (hypersensitive).

The risk of contracting cancer after exposure to a carcinogen or potential carcinogen is computed from the extent of the exposure and a slope factor derived from experimental or epidemiologic studies. The risk determined is in terms of the number of additional cases of cancer, per person, that could develop in a large population that undergoes the exposure compared to an equal-size population that does not undergo the exposure. The slope factors are calculated as upper bounds, with appropriate safety factors, and the actual risk may in fact be zero. For this health assessment, a significant additional risk is taken to be one additional case of cancer in a population of 1 million people experiencing the exposure.

Exposure doses for this assessment are computed assuming the following standard individuals: an adult who weighs 70 kilograms (154 pounds) and incidentally ingests 100 milligrams of soil per day; a child who weighs 10 kilograms (22 pounds) and incidentally ingests 200 milligrams of soil per day, or, if subject to pica behavior, deliberately ingests 5 grams of soil per day. Pica is an abnormal urge to consume non-food substances, such as soil, that most commonly occurs between ages 2 and 5.

Most of the heavily contaminated media is limited to the Thermo-Chem, Inc. site area. The contamination that has been detected off-site is transported via groundwater to Black Creek (24). Surface water and sediment sampling of Black Creek in 1991 have found low levels of contamination. If people do swim, wade, or fish in Black Creek for limited periods during warm months (2 hours per day, 5 months per year), the amount of exposure would not be enough to create a health concern.

Documented completed exposure pathways at the site include past exposure of workers during operations at Thermo-Chem, Inc. and Thomas Solvent Co. Trespassers may also have been exposed to contaminated surface soils before the Thermo-Chem, Inc. portion of the site was fenced, however, the exposure levels and duration are unknown. Subsurface soil samples contain various contaminants of concern at levels of health concern. It is very likely that the concentrations of volatile organic chemicals in surface soil would be much lower than in the subsurface soil due to the volatile chemicals evaporating. Under current site conditions, it is unlikely that anyone except a remediation worker will visit the site regularly, or spend long periods in the contaminated zone. As an upper bound for an estimated exposure dose, this evaluation assumes an adult trespasser who spends 3 hours on the site once a week, and during this time incidentally ingests 25 milligrams of soil from the site.

VOC exposure levels would now probably be negligible from surface soil, because as they reach the surface, they will tend to volatilize into the air very rapidly. The structures and equipment left on the site pose physical hazards, but there are no records available that document any injuries to workers or trespassers on the site. The Thermo-Chem, Inc. property is currently fenced, though the Thomas Solvent Co. area is not.

The list of contaminants of concern includes 11 VOCs that the U.S. EPA has classified as a known human carcinogen, probable human carcinogen, or possible human carcinogen. Benzene has been classified as a known human carcinogen (U.S. EPA Class A). 1,2-DCA, carbon tetrachloride, and chloroform have been classified as probable human carcinogens (U.S. EPA Class B1 or B2). Styrene, TCE, and PCE are under consideration for probable (B2) or possible (U.S. EPA Class C) human carcinogens and 1,1-DCA, 1,1,2,2-tetrachloroethane, 1,1,2-TCA, and 1,1-DCE are classified as possible human carcinogens (C).

Exposure to VOCs in the surface soil, the only identified completed exposure pathway, would most likely be insignificant. Non-carcinogenic VOCs listed as contaminants of concern include acetone, 2-butanone (methyl ethyl ketone), 1,2-DCE, ethylbenzene, 4-methyl-2-pentanone, toluene, and 1,1,1-TCA. Other contaminants of concern that have been classified by the U.S. EPA as known, probable or possible human carcinogens include arsenic and chromium (VI) (Class A), cadmium, chrysene, bis(2-ethylhexyl)phthalate, pentachlorophenol, PCBs and beryllium (Class B1 or B2), and 2-methylphenol and 4-methylphenol (Class C). However, PCB is the only contaminant that exceeded its comparison value for surface soil and will be addressed below. For this toxicological evaluation, since true surface soil data is lacking, the results of soil sampling done from the 0 to 2 foot depth (Table 3) will be assumed to approximate surface soil concentrations.

The sampling data in Table 3 indicates that only 7 non-volatile contaminants exceeded their comparison value for that specific environmental medium. The seven identified contaminants included five (naphthalene, 2-methylnaphthalene, cobalt, copper, and lead) for which there are no comparison values available and PCB (Aroclor 1254), which exceeded the comparison value in two samples (maximum concentration, 1.3J ppm). The exposure dose of the chemicals present encountered by a trespasser would not likely exceed available MRLs or RfDs for non-cancer adverse health effects or result in a significant increased risk of contracting cancer based on available CREGs.

Naphthalene

The primary human health concerns associated with naphthalene relate to its hemolytic effects, particularly in individuals that are genetically sensitive as a result of an inherited deficit in red blood cell G6PD. Hemolysis has been reported in humans following exposure to naphthalene by inhalation, oral, and dermal routes. There is no data available indicating that either naphthalene or 2-methylnaphthalene is carcinogenic. No MRLs or RfDs have been derived for oral exposure to naphthalene. It is very unlikely that anyone would ingest enough naphthalene from the soil on the Thermo-Chem, Inc. site to exceed the doses at which adverse health effects have been observed in humans or laboratory animals. From the limited available data on health effects on dermal exposure to naphthalene, it is not likely that dermal contact with soil on the site will result in adverse health effects (17).

Polychlorinated Biphenyls (PCBs)

PCBs are a group of man-made chemicals that includes 209 individual compounds (congeners) with varying harmful health effects. In humans, PCB toxicity affects the skin and liver, and may also have developmental effects in the fetus and young children. Metabolic, reproductive, endocrine, and immunosuppressive effects have been documented in animals studied, but have not been adequately studied in humans. Although data from animal studies indicate that PCBs can cause cancer in animals, evidence of PCB as a human carcinogen is limited. The U.S. EPA has classified PCB as a probable human carcinogen (Class B2). Incidental ingestion of PCB-contaminated soils from the Thermo-Chem, Inc. site is not likely to result in an exposure dose in excess of the MRL, based on the data taken from the RI and TA investigation (18).

The PCB concentrations in fish collected from Black Creek in 1987 did not exceed the FDA Action Level or the MDPH Level of Concern. The MDPH has not issued any advisory covering fish from the creek.

Cobalt, Copper, and Lead

Cobalt, copper, and lead occur naturally in rocks, soil, surface water and groundwater. Cobalt and copper are essential elements in the diet at low levels but can be harmful at higher levels. Vitamin B12 contains cobalt. Cobalt has also been used as a treatment for anemia. Adverse health effects from exposure to cobalt or copper have been most commonly reported after inhalation exposure. There is not sufficient information available to determine whether cobalt and copper are carcinogenic in humans or animals (192021). ATSDR and the U.S. EPA have not developed MRLs, RfDs, and RfCs for cobalt or copper, however, estimated exposure doses at this site are substantially below the exposures at which adverse health effects have been seen.

Exposure to lead is particularly dangerous for unborn and young children. Young children tend to swallow more lead through normal mouthing activity, absorb more of the lead they swallow into their bodies, and are much more sensitive to its effects during development. In adults, high lead exposure may decrease reaction time and possibly affect memory. Lead may also cause weakness in fingers, wrists, or ankles and has been shown to cause increased blood pressure in middle-aged men. Health effects from exposures to low doses of lead are not certain, however, high levels of exposure to lead may cause abortion and damage the male reproductive system. The effects of lead are the same regardless of whether it enters the body through inhalation or ingestion (21).

The U.S. EPA has classified lead as a probable carcinogen. The ATSDR has not derived an MRL for lead in soils. Neither an RfC nor RfD exist for lead and its inorganic compounds because no thresholds have been identified for the most sensitive effects in humans (21). The lead concentration in the shallow subsurface soil samples does not exceed the health-based clean up level of 400 ppm for lead in soil developed by the MDNR/MDEQ under the provisions of the Michigan Environmental Response Act (Part 201 of Public Act 451, as amended). Under the exposure scenario described above for the Thermo-Chem, Inc. site and based on the available data, trespassers on the site are not likely to incur an increased risk of adverse health effects.

B. Health Outcome Data Evaluation

As mentioned above in the Health Outcome Data section, the preparers of this Health Assessment obtained cancer incidence data from the MDPH Office of the State Registrar and Center for Health Statistics for the area around the Thermo-Chem, Inc. Superfund site.

Cancer incidence data for 1985 through 1989 for the two zip code areas (49442, 49444) nearest the Thermo-Chem, Inc. site was compared to the number of cases expected based on age-specific annual rates from the National Cancer Institute Surveillance, Epidemiology, and End Results (SEER) program.(7) For both areas, the number of actual cases was lower than the expected number (Table 12) (23). The expected numbers may be unrealistically high if the populations are overestimated.

C. Community Health Concerns Evaluation

As mentioned in the Community Health Concerns section above, local state and environmental agencies have not received any community health concerns regarding the Thermo-Chem, Inc. site. If in the future, community health concerns are expressed, MDPH and ATSDR will address these concerns as they pertain to the site.

The Michigan Department of Public Health released a draft of this Public Health Assessment for public comment on January 31, 1996. The public comment period lasted until March 1, 1996. No comments were received in this period.


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