PUBLIC HEALTH ASSESSMENT
MOUNTAIN PINE PRESSURE TREATING
PLAINVIEW, YELL COUNTY, ARKANSAS
The Agency for Toxic Substances and Disease Registry (ATSDR) was established under the mandate of the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) of 1980. This act, also known as the "Superfund" law, authorized the U.S. Environmental Protection Agency (EPA) to conduct clean-up activities at hazardous waste sites. EPA was directed to compile a list of sites considered hazardous to public health. This list is termed the National Priorities List (NPL). The 1986 Superfund Amendments and Reauthorization Act (SARA) directed ATSDR to prepare a Public Health Assessment (PHA) for each NPL site. Note: Appendix D provides a glossary of terms used in this report.
In conducting the PHA, three types of information are used: environmental data, community health concerns, and health outcome data. The environmental data are reviewed to determine whether people in the community might be exposed to hazardous materials from the NPL facility. If people are being exposed to hazardous substances, ATSDR will determine whether the exposure is at levels which might cause harm. Community health concerns are collected to determine whether health concerns expressed by community members could be related to exposure to substances released from the NPL facility. If the community raises concerns about specific diseases in the community, health outcome data (information from state and local databases or health care providers) can be used to address the community concerns. Also, if ATSDR finds that harmful exposures have occurred, health outcome data can be used to determine if illnesses are occurring which could be associated with the hazardous substances released from the NPL facility.
In accordance with the Interagency Cooperative Agreement between ATSDR and the Arkansas Department of Health (ADH), ATSDR and ADH have prepared this PHA for the Mountain Pine Pressure Treating, Inc. NPL site. This PHA presents conclusions about whether exposures are occurring, and whether a health threat is present. In some cases, it is possible to determine whether exposures occurred in the past; however, lack of appropriate historical data often makes it difficult to quantify past exposures. If it is found that a threat to public health exists, recommendations are made to stop or reduce the threat to public health.
The Arkansas Department of Health (ADH) under a cooperative agreement with the Agency for Toxic Substances and Disease Registry (ATSDR) prepared this Public Health Assessment (PHA) to evaluate the soil, sediment, water, and fish data provided by the Arkansas Department of Environmental Quality (ADEQ) and the United States Environmental Protection Agency (EPA) to determine if a public health hazard exists at the site and, if so, recommend appropriate public health actions to minimize known exposures. ADH reviewed available data and exposure information and determined that this site poses a public health hazard.
The Mountain Pine Pressure Treating, Inc. site is a former wood treating facility located on the western border of Plainview, Yell County, Arkansas. The site consists of three facilities situated on 95 acres. The facilities treated lumber with solutions of pentachlorophenol and chromated copper arsenate from 1965 to 1986 and briefly in the summer of 1989.
In preparing this PHA, ADH reviewed available data from EPA, ADEQ, and the city of Plainview. ADH also spoke with community members about their health concerns. From these actions, ADH identified several exposure situations for evaluation. These exposure situations include possible contact with site contaminants in the soil, sediment, groundwater, surface water and fish. ADH considered off-site soil as the primary pathway of concern because it is a known completed exposure pathway. Because insufficient off-site data was available, the off-site soil pathway is categorized as an indeterminate public health hazard. Also, due to limited fish sampling, the fish ingestion pathway is categorized as an indeterminate public health hazard. In the future, additional off-site data could change the overall conclusion category for the site. Based on potential exposure to on-site soils, we have concluded that Mountain Pine Pressure Treating Inc. poses a public health hazard.
The Mountain Pine Pressure Treating, Inc. (MPPT) site is a former wood treating facility consisting of three related contiguous facilities situated on 95 acres located on the western border of Plainview, Yell County, Arkansas (Figure 1). The three facilities are MPPT, Plainview Lumber, and the Chromated Copper Arsenate (CCA) Treatment Plant. MPPT, a subsidiary of Plainview Lumber Company, treated lumber with solutions of pentachlorophenol (PCP) and CCA from 1965 to 1981. The CCA Treatment Plant used a closed loop system to treat lumber with CCA solutions. It operated from 1980 to 1986 and reopened briefly in the summer of 1989. Contaminants of concern include PCP, arsenic, copper, lead, chromium, and dioxin (2,3,7,8- TCDD). The site was finalized to the EPA's National Priorities List in 1999.
The site is bordered on the north by State Highway 28. The west side of the property is bounded by Sunlight Bay Road, which also serves as part of the east boundary of the Nimrod Wildlife and Conservation area. Porter Creek, which runs through the Nimrod Wildlife and Conservation area, is a major tributary of Nimrod Lake and contains a designated wetland. Nimrod Lake contains an intake that supplies drinking water for the City of Plainview, and is used for flood control, fishing, hunting, boating, and camping. The property to the south of the site is grass and woodlands. The east boundary of the site is Tippy Lane in the city of Plainview, which had a population of 685 residents in 1990 and is presently estimated to have a population of 718 residents.
Two distinct treatment processes --the PCP process and the CCA process--occurred during site operations. The Mountain Pine Pressure Treating waste management system consisted of separate PCP and CCA drip tracks, a recovery holding pond, separate PCP and CCA treatment cylinders, a spray evaporation pond, and an oil separator. During both operations, the treated lumber was placed on the drip tracks and the excess solution was allowed to drain onto the tracks. At the CCA process site, the CCA drip tracks were sloped toward a sump under the treatment cylinder. From this sump, the waste CCA solution was pumped to a second sump inside the containment wall of the CCA plant. From there, the CCA waste solution was pumped through a series of pipes to a mix tank situated behind the building. Rainwater was collected and pumped into the mix tank for reuse in the process. The oil separator, located between the drip tracks and the holding pond separated PCP oil from the excess solution. The liquid remaining after PCP oil was removed was discharged into the holding pond. When the holding pond was full, the excess water was pumped to the evaporation pond via an above ground pipeline. In 1987, the dike surrounding the holding pond was breached allowing wastewater and sludge containing PCP and CCA to enter the adjacent drainage ditch, Porter Creek, and wetlands along the creek. EPA conducted a removal action in 1988 to alleviate releases from the recovery holding pond. Excess wastewater from the holding pond was transferred to the spray evaporation pond to relieve the leaking dike. In 1988, the remaining sludge in the holding pond was mixed and solidified. The solidified sludge had high concentrations of chlorinated dibenzo-p-dioxins (CDD) and chlorinated dibenzofurans (CDF). The holding pond was backfilled with site soils and a 2-foot cap was placed over the holding pond.
In 1988, a site inspection involving on- and off-site sampling revealed widespread contamination attributable to CCA and PCP treatment operations at the site. There was off-site migration of contaminants along the surface water migration pathway and there was extensive contamination along the soil exposure pathway. In 1991, removal actions disposed of wastewater in the concrete containment systems around the CCA cylinder and storage tanks. The wastewater contained arsenic, chromium, and copper. An expanded site inspection in 1993 detected wood treatment preservatives and traces of CDD and CDF in the on- and off-site soil and sediment samples. A release to the wetland contiguous with Porter Creek was documented during the site inspection (1). In 1994, dioxin containing waste sealed in an on-site treatment cylinder was collected and shipped to a disposal facility. At some time before 1996, the holding pond was backfilled, capped, and vegetated, but there are no records to indicate who was responsible for this action. An evaporation pond and much of the spray evaporation apparatus remain on the site.
The Preliminary Assessment was completed in October of 1987, and the Site Investigation was completed in May of 1988. The MPPT site was proposed to the National Priorities List on April 23, 1999, and was finalized to the list July 22, 1999.
Representatives of the Arkansas Department of Health conducted an initial site visit on July 20, 1999. Three hours were spent examining the site and its vicinity. All buildings were in disrepair. The drip tracks, warehouses, and other structures on the site were examined.
The MPPT site was accessible. It was not completely enclosed by fencing. The fence that was in place had several breaks providing trespassers easy access to the property.
Residences are located directly north and east of the site boundary. There are no residences south and west of the site. The nearest residences on the north and east sides of the site are approximately 75 meters (80 yards) from the site. There is a school (grades K through 12) located 500 meters (550 yards) from the northeast edge of the site. A day care center and the city park are less than 1- mile from the site. The land west of the property is a wildlife management wetlands with no residents. The property south of the site boundary is owned by the U.S. Army Corps of Engineers and is covered with native grasses and herbaceous plants.
Fescue and other indigenous grasses covered most of the site between the structures. There was no evidence that younger children frequent the site; however there was graffiti on walls in several of the structures. Several empty beer and beverage cans were found in one structure indicating that trespassers were using the structure for transient activities.
Additional site visits were conducted in October 1999, March and September 2000, May 2001, and March 2002. There have been no significant changes in the site since the initial site visit.
There are approximately 200 people living within ½-mile of the site. According to the 1990 U.S. Census bureau, the population of Plainview is 685 people. It is estimated to have increased in population by 4.8 percent since 1990 (2). The entire city of Plainview is within a 1-mile radius of the MPPT site. The total population within a 1-mile radius of the site is estimated to be 755 people.
It is not known how many people worked at MPPT in the past.
The area around the site is a combination of residential, agricultural, wetlands preserve, and game management areas. Surface water drainage is to the western and eastern edges of the site toward Porter Creek and Prairie Creek, respectively. Both Porter and Prairie Creeks flow into the Nimrod Lake. There is an intake at Nimrod Lake that supplies drinking water for the city of Plainview. There are no known private drinking water source wells located within 1-mile of the facility. There are no public water supply wells within 1-mile of the site. Downstream from the site, surface water is used for recreational fishing, boating and swimming.
The topography around MPPT is very hilly. The general stratigraphic dip in the surface topography is primarily to the southwest. Drainage from the site is toward Porter and Prairie Creeks. All surface water in the vicinity of the site drains south towards the Fourche LaFave River and Nimrod Lake (3).
The site is located in Yell County in the Arkansas Valley of the Ouachita Mountains. The geology of the area is dominated by outcrops of the lower and middle Atoka Formation which consists primarily of shale, sandstone, and siltstone. Groundwater occurs in an unconfined water table aquifer and at depth in the Atoka Formation. The groundwater flow beneath the site is consistently south by southwest. The first aquifer beneath the site occurs about 10-feet beneath the surface in dark grey shale with minor sandstone layers. This aquifer is most likely to intercept and transmit any hazardous substances from the site.
Groundwater in the Atoka Formation occurs in consolidated deposits. Locally, the Atoka Formation yields small quantities of water from joints, fractures and faults, generally within 150- feet of the surface (4).
Exposure to, or contact with, hazardous contaminants drive the ATSDR public health assessment process. The release or disposal of chemical contaminants into the environment does not always result in exposure or contact; and, chemicals only have the potential to cause adverse health effects if people actually come into contact with them. People may be exposed to chemicals by breathing, eating, or drinking a substance containing the contaminant or by skin (dermal) contact with a substance containing the contaminant.
When people are exposed to contaminants, the exposure does not always result in adverse health effects. The type and severity of health effects that may occur in an individual from contact with contaminants depend on the toxicologic properties of the contaminants; how much of the contaminant to which the individual is exposed; how often and/or how long the exposure is allowed to occur; the manner in which the contaminant enters or contacts the body (breathing, eating, drinking, or skin/eye contact); and the number of contaminants to which an individual is exposed (combinations of contaminants). Once exposure occurs, characteristics such as age, sex, nutritional status, genetics, life style, and health status of the exposed individual influence how the individual absorbs, distributes, metabolizes, and excretes the contaminant. These factors and characteristics influence whether exposure to a contaminant could or would result in adverse health effects.
To assess the potential health risks associated with contaminants at this site, we compared contaminant concentrations to health assessment comparison values. Health assessment comparison values are media specific contaminant concentrations that are used to screen contaminants for further evaluation. Non-cancer health assessment comparison values are called environmental media evaluation guides (EMEGs) or reference dose media evaluation guides (RMEGs) and are respectively based on ATSDR's minimal risk levels (MRLs) or EPA's reference doses (RfDs). MRLs and RfDs are estimates of a daily human exposure to a contaminant that is unlikely to cause adverse non-cancer health effects. Cancer risk evaluation guides (CREGs) are based on EPA's chemical specific cancer slope factors and an estimated excess lifetime cancer risk of one-in-one-million persons exposed for a lifetime. We used standard assumptions to calculate appropriate health assessment comparison values (5).
In some instances, we compare contaminant concentrations in water to EPA's maximum contaminant levels (MCLs). MCLs are chemical specific maximum concentrations allowed in water delivered to the users of a public water system; they are considered protective of public health over a lifetime (70 years) of exposure at an ingestion rate of 2- liters per day. MCLs may be based on available technology and economic feasibility. Although MCLs only apply to public water supply systems, we often use them to help assess the public health implications of contaminants found in water from other sources.
While exceeding a health assessment comparison value does not necessarily mean that a contaminant represents a public health threat, it does suggest that the contaminant warrants further consideration. The public health significance of contaminants that exceed comparison values may be assessed by reviewing and integrating relevant toxicological information with plausible exposure scenarios. Estimated exposures may be compared to reported "No Observable" and "Lowest Observable" Adverse Effects Levels (NOAELs and LOAELs) and to known effect levels in humans, when available.
Soil, sediment, surface water, groundwater, and fish data included in our evaluation of the MPPT site were collected during the ADEQ's September 16 and 17, 1997, and May 14, 1998, screening site investigations and EPA's expanded site inspection done in 1993. Thirteen soil samples, eight sediment samples, and three groundwater samples were collected from the site on September 16 and 17, 1997. Groundwater samples were only taken from two on-site monitoring wells. Five residential wells had been tested in 1988 and no site related contaminants were detected. The wells were not used, at the time of the sampling, as drinking water sources, and no information was available on the past use of the wells. Sediment (two samples collected) and fish (one each of small mouth buffalo, channel catfish, and large mouth bass mouth from Porter Creek; and one each small mouth buffalo and large mouth bass from intake valve of Nimrod Lake) tissue samples were collected at the mouth of Porter Creek and near the intake valve in Nimrod Lake on May 14, 1998.
No off-site soil or sediment samples were collected for the ADEQ's site investigations in 1997 and 1998, so off-site soil sediment samples from the Expanded Site Inspection in 1993 were evaluated. Reported concentrations and concentration ranges for each of the contaminants detected are presented in Appendix B; Tables 1 through 6. ATSDR comparison values for each of the contaminants also are listed in the tables. In preparing this PHA, ADH staff members relied on the information provided in the referenced documents and assumed that adequate Quality Assurance/Quality Control measures were followed with regard to chain-of-custody, laboratory procedures, and data reporting to ensure that field work and laboratory analysis met established standards. The data packages were reviewed and validated by EPA Region 6, according to the EPA Contract Laboratory Protocol Statement of Work. ADEQ reviewed the inorganic and organic analyses to ensure accuracy, precision, representativeness, comparability, field custody and completeness. The analyses and conclusions in this PHA are valid only if the referenced information is valid and complete.
In this section we evaluated the possible pathways for exposure to contamination at MPPT. We examined possible exposure pathways to determine if people near the site can be exposed to (or come into contact with) contaminants from the site. Exposure pathways consist of five elements: 1) a source of contamination, 2) transport through an environmental medium, 3) a point of exposure, 4) a plausible manner (route) for the contaminant to get into the body, and 5) a receptor population. Exposure pathways fall into one of three categories:
- Completed Exposure Pathway: ATSDR calls a pathway "complete" if it is certain that people are exposed to contaminated media. Completed pathways require that the five elements exist and indicate that exposure to the contaminant has occurred, is occurring, or will occur.
- Potential Exposure Pathway: Potential pathways are those in which at least one of the five elements is missing but could exist. Potential pathways indicate that exposure to a contaminant could have occurred, could be occurring, or could occur in the future. Potential exposure pathways refer to those pathways where (1) exposure is documented, but there is not enough information available to determine whether the environmental medium is contaminated, or (2) an environmental medium has been documented as contaminated, but it is unknown whether people have been, or may be, exposed to the medium.
- Eliminated Exposure Pathway: In an eliminated exposure pathway, at least one of the five elements is missing and will never be present. From a human health perspective, pathways can be eliminated from further consideration if ATSDR is able to show that (1) an environmental medium is not contaminated, or (2) no one is exposed to contaminated media.
ATSDR and ADH have identified a completed exposure pathway to off-site soil through exposures to soil at the school and the residences located nearest the site. ATSDR and ADH have determined the exposures to on-site soil, on and off-site sediment, groundwater and contaminants in the food chain constitute potential exposure pathways. The specific elements associated with each identified pathway are summarized in Table 7. The following text also describes both the completed and potential exposure pathways identified for this site. Contaminants whose concentrations did not exceed ATSDR comparison values were excluded from the pathways analysis.
Completed Exposure Pathways
Off-site soil samples taken in 1991 had concentrations of arsenic, chromium, and copper exceeding the background concentrations for the area. Because chromated copper arsenate was used on the site as a wood treatment chemical, the presence of contaminants in all three of the soil samples that were taken at off-site locations indicates that soil migration from the site is the probable source of the contamination. On-site soil samples taken during the same sampling event that were in the vicinity of the off-site samples had concentrations of arsenic and chromium that well exceeded the ATSDR comparison values. Soil may have blown to off-site locations, or may have been carried to off-site locations during flood events. Routes of potential exposure include dermal contact and incidental ingestion of off-site surface soil. Arsenic was present in the off-site samples in concentrations slightly below the non cancer comparison values, but exceeding the cancer risk evaluation guide. Chromium samples were reported as total chromium. One of the off-site samples exceeded the EPA risk based concentration screening level, and the other two were slightly below the screening level. The ATDSR comparison values for chromium were not exceeded in any of the three samples. Because the percentage of hexavalent chromium was not reported, the conservative approach of comparing total chromium concentrations to hexavalent chromium toxicities for screening was used in the toxicology discussion that follows. No samples have been collected from off-site locations since 1991, and the levels detected in the three 1991 samples may not be indicative of the present levels of contaminants in soil throughout the surrounding residential area.
Potential Exposure Pathways
Residential homes, a school, and a home that is used for after school care are close to the site. Trespassers on the MPPT site come into contact with on-site surface soil. Nine out of the thirteen soil samples had concentrations of arsenic that exceeded the ATSDR comparison value. Five of the samples had concentrations of chromium that exceeded the comparison value. Three of the thirteen samples had concentrations of pentachlorophenol that exceeded the ATSDR comparison value. On-site residents and trespassers may have been, and may continue to be, exposed to on-site surface soil.
In 1997, the ADEQ collected sediment samples from the drainage ditches bordering the site, as well as from the Porter Creek. Arsenic and chromium were detected above ATSDR comparison values in the on-site drainage ditches. Benzo(a)pyrene was detected in the sediment at the mouth of Porter Creek, but was not detected in any of the on-site samples. Children can play in the drainage ditches bordering the site and in Porter Creek. Exposures to contaminants in sediment could occur during these activities, and both direct skin contact and incidental ingestion could be routes of exposure.
The food chain exposure pathway is considered a potential exposure pathway because there is an opportunity for fish and game animals to contact site contaminants moving off of the site in surface water and sediment. Porter Creek sediment samples indicate that arsenic and chromium from the MPPT site are continuing to move off site. Between the 1991 and 1997 sampling events, concentrations of arsenic and chromium increased at down gradient sampling points in Porter Creek and in a drainage ditch that feeds into Porter Creek. Porter Creek empties into the Fourche LaFave River and Nimrod Lake, which are popular recreational fishing areas.
Exposure to groundwater pathway is considered very unlikely under present site conditions and community water usage. Every household and the school in Plainview are connected to the public water supply which is not contaminated. The public water system for Plainview treats water drawn from an intake in Nimrod Lake. ADEQ reported locating a groundwater well in the vicinity of the site that was in disrepair and did not appear to be in use, but that had not been properly abandoned in accordance with ADH guidelines. Although abandoned wells in the area are potential exposure points, their reutilization as potable water sources is unlikely. The analysis of samples taken from residential wells by the Field Investigation Team during the 1988 sampling event indicated that no site related contaminants were present in the well water (6).
Past exposures to ground water used for drinking, bathing, and irrigating have not been documented, but the presence of residential wells in the area would indicate that exposures have occurred in the past. There was insufficient data concerning groundwater exposure in the past to analyze this pathway.
There is a potential for future groundwater exposure to occur since uncapped wells are still present in the area. There is also a potential for future groundwater exposure to occur if water usage in the community or neighboring rural areas changes and new wells are dug.
Although in the past, on-site workers and trespassers could have come into contact with contaminants in the soil, sediment, and groundwater, we were not able to evaluate the public health significance of these potential exposures from an analysis of available information.
In this section, ATSDR addresses the likelihood that exposure to contaminants at the maximum concentrations detected would result in adverse health effects. While the relative toxicity of a chemical is important, the response of the human body to a chemical exposure is determined by several additional factors, including the concentration (how much); the duration of exposure (how long); and the route of exposure (breathing, eating, drinking, or skin contact). Lifestyle factors (i.e., occupation and personal habits) have a major impact on the likelihood, magnitude, and duration of exposure. Individual characteristics such as age, sex, nutritional status, overall health, and genetic constitution affect how a human body absorbs, distributes, metabolizes, and eliminates a contaminant. A unique combination of all these factors will determine the individual's physiologic response to a chemical contaminant and any adverse health effects the individual may suffer as a result of the chemical exposure.
ATSDR has determined levels of chemicals that can reasonably (and conservatively) be regarded as harmless, based on the scientific data the agency has collected in its toxicological profiles. The resulting comparison values and health guidelines are used to screen contaminant concentrations at a site and to select substances that warrant closer scrutiny by agency health assessors and toxicologists. It is of key importance that ATSDR's (and EPA's) comparison values and health guidelines represent conservative levels of safety and not thresholds of toxicity. Thus, although concentrations at or below a comparison value may reasonably be considered safe, it does not automatically follow that any concentration above a comparison value will necessarily produce toxic effects. To the contrary, ATSDR's (and EPA's) comparison values are intentionally designed to be much lower than the corresponding no-effect levels (or lowest-effect levels) determined in laboratory studies. ATSDR uses comparison values (regardless of source) solely for the purpose of screening individual contaminants. ATSDR considers that a compound warrants further evaluation if the highest single recorded concentration of that contaminant in the medium in question exceeds that compound's lowest available comparison value (e.g., cancer risk evaluation guides or other chronic exposure values) for the most sensitive, potentially exposed individuals (e.g., children or pica children). This process results in the selection of many contaminants as "chemicals of concern" that will not, upon closer scrutiny, be judged to pose any hazard to human health. Even those contaminants of concern that are ultimately labeled in the toxicologic evaluation as potential public health hazards are so identified solely on the basis of the maximum concentration detected. The reader should keep in mind the protectiveness of this approach when considering the potential health implications of ATSDR's toxicologic evaluations.
Because a contaminant must first enter the body before it can produce an effect, adverse or otherwise, on the body, the toxicologic evaluation in public health assessments focuses primarily on completed pathways of exposure and potential pathways where there is a high probability that exposures have occurred or will occur.
A completed exposure pathway to off-site soil was identified at two residences and the Plainview-Rover school. ATSDR and ADH evaluated whether exposures to this soil would pose a public health hazard. While this toxicologic evaluation section focuses primarily on soil contaminants, the contaminants in sediment and possible exposure through the food chain are also briefly discussed.
Off-site Soil and Sediments
Summary: Exposure to contaminants in off-site soils is considered to be an indeterminate public health hazard due to insufficient characterization of the soils. Although concentrations of arsenic and chromium were not detected at levels that would result in exposure doses that could result in adverse health effects, the analysis of three samples is insufficient to conclude that the pathway is not a public health hazard. The wide range of concentrations detected in the on-site soils indicates that more extensive off-site sampling is warranted. No off-site soil samples were collected during the 1997 sampling event which limited the evaluation to samples from 1991.
Exposure to off-site soil represents the only completed pathway identified at this site where exposure to contaminants is known, or may reasonably expected to be occurring. Limited data (three samples) was available from off-site sampling of soils. The maximum detected concentration of arsenic was 14 parts per million (ppm) which does not exceed EPA's non cancer risk based concentration nor ATSDR's chronic child environmental media evaluation guide (EMEG) of 20 ppm. The concentration does exceed the cancer risk evaluation guide of 0.5 ppm and the EMEG of 0.6 ppm for children displaying pica behavior (ingestion of soil at a greater volume than occurs with incidental contact). The soil samples were taken from two residences and a schoolyard. Children have daily presence on the sites from which the soil samples were taken. Because the data that was used for this evaluation was derived from samples taken in 1991, an assumption was made for soil ingestion dose estimations that the concentrations remained the same over a nine year period.
Soil ingestion doses were estimated for adults, 10 kilogram (kg) and 16 kg children, and pica children assuming an exposure to the soil five days a week for nine years. The estimated doses for 10 kg children and children displaying pica behavior exceeded ATSDR's minimum risk level for non cancer effects. The estimated doses did not exceed EPA's oral slope factor which estimates an increased risk of cancer due to contaminant exposure. Using default assumptions of exposure rate (i.e., daily ingestion of 200 milligrams [mg] soil), this maximum detected concentration would correspond to less than 7 micrograms arsenic/day (µg/day). This is lower than typical dietary exposures and is comparable to average arsenic exposures from US drinking water. Assuming a child body weight of 10 kg, this level of exposure would be less than the estimated human no observed adverse effect level (NOAEL) of 0.8 micrograms per kg per day (µg/kg/day) on which ATSDR's chronic minimal risk level (MRL) is based (7). (The chronic oral MRL of 0.3 µg/kg/day, which is based on exposure to arsenic in drinking water, rather than soil, contains a safety factor of 3.)
Historical evidence suggests that the carcinogenic effects of arsenic may exhibit a threshold at 200 to 400 µg/day, and virtually all known cases of arsenical skin cancer have been associated with occupational exposures (8). Because all 200 mg of the soil that a child might ingest every day will not come exclusively from any single point, actual exposures to arsenic in soil may be substantially less (or substantially higher) than the maximally contaminated soil sample would imply. However, the off-site soils have not been adequately characterized to estimate exposure doses based on a range of concentrations.
Off-site sediment samples were collected at five down gradient sites during the 1991 sampling event. The maximum concentration of arsenic detected in the sediments was 53.3 ppm with a mean concentration of 32.1 ppm. Two up-gradient sediment samples had a mean concentration of 8.8 ppm arsenic. This indicates that the source for the elevated arsenic is the MPPT site. During the 1997 sampling event, three soil samples were taken inside the fence line, but within 100 meters of the nearest residence. Arsenic was detected in concentrations of 36.5 ppm, 751 ppm, and 2,182 ppm, indicating that there is a wide range of arsenic soil concentrations on the site. Off-site sediment samples and on-site soil samples in close proximity to the off-site soil sample locations indicate that the three off-site soil samples contained concentrations considerably lower than concentrations in neighboring and adjacent areas. This is an indicator that the off-site soils have not been adequately characterized. If the soil samples are not indicative of mean concentrations of arsenic in the soil, then the calculated doses would be an underestimation of the potential exposure dose. Therefore, ATSDR and ADH conclude that the off-site soil around the site is an indeterminate public health hazard, because insufficient data are available for the off-site soils. In this situation, more information is required to adequately define the potential health hazard.
One of the off-site soil samples and six sediment samples exceeded the EPA risk based concentration for hexavalent chromium, but did not exceed the risk based concentration for total chromium. Because the percentage of hexavalent chromium cannot be determined, and due to the limited number of samples, chromium was not toxicologically evaluated for off-site soils and sediment.
On-site Soil and Sediments
Summary: Potential exposure to contaminated soils located on the MPPT site are considered a public health hazard. Elevated arsenic concentrations are not restricted to a few isolated "hot spots," but are found throughout the site. The accessibility of the site creates an exposure scenario that could result in incidental ingestion of soils that could result in adverse health effects. The proximity of the site to residential homes and a school creates a risk for contamination of off-site soils and sediments due to migration from the site.
Areas with contaminated soil on the site and areas with contaminated sediments both on and off-site continue to be accessible; however, on-site exposures due to trespassing or incidental contact with sediments are likely to be short-term and infrequent. Exposure frequency of trespassers is difficult to determine, but infrequent exposure to arsenic and chromium in the soil and sediment at the site could still result in a dose with a potential for adverse health effects. Residential areas are located adjacent to the east and southeast site boundaries. A school and day care center are located less than one mile from the northeast corner of the site. Children can easily enter the site through openings in the fence.
Trespassers with infrequent exposure to soils could potentially ingest amounts of arsenic that exceed the ATSDR minimal risk level. Arsenic concentrations in on-site soils range from 6.6 ppm to 2,182 ppm with a mean concentration of 430.5 ppm. A 16 kg (35 pound) child who visited the site for greater than eight hours per week and ingested 100 mg of soil a day for one year could be exposed to arsenic levels that exceed the ATSDR MRL of 0.0003 mg/kg/day. In an exposure scenario where a child (10 kg ingesting 200 mg/day) or an adult (70 kg ingesting 100 mg/day) spent one day a week for one year on the site at exposure points containing the highest arsenic concentrations, the calculated doses for either individual would exceed the ATSDR MRL for arsenic. Doses were calculated for 10 kg and 16 kg children and adults with an exposure scenario of one day a week for one year for 21 soil and sediment sample concentrations. Nineteen of the calculated doses for 10 kg children exceeded the ATSDR MRL for arsenic. Ten of the calculated doses for a 16 kg child exceeded the MRL. Five of the calculated doses for an adult exceeded the MRL. Doses were also calculated using the mean soil concentration. The estimated dose for an 10 and 16 kg children exposed to soil containing the mean concentration exceeded the MRL. Thirteen of the 10 kg child doses, eight 16 kg child doses, five adult doses, all the pica behavior doses, as well as the mean doses for all groups except adults, exceeded the NOAEL of 0.8 micrograms per kilogram per day (µg/kg/day). Five of the 10 kg child doses and eleven pica doses, as well as the pica mean dose exceeded the threshold effects levels of 200 micrograms per day (µg/day). Health effects that can result from ingesting doses in the calculated range include serious effects including cardiac arrhythmia, anemia, gastrointestinal bleeding, and cirrhosis of the liver to less serious effects including vomiting, diarrhea, hyperkeratosis, and lethargy (7).
Dermal absorption was considered as a potential route of exposure, but dermal absorption of inorganic arsenic in humans is highly inefficient. Studies indicate that less than 5% of applied doses of arsenic are absorbed through the skin and that the majority of arsenic that is absorbed is promptly excreted in the urine (7). Dermal contact with arsenic contaminated soils at MPPT should not result in any adverse health effects.
Chromium concentrations on the site ranged from 29.2 ppm to 2,984 ppm with a mean concentration of 594 ppm. The same assumptions that were used for arsenic were used to calculate doses for chromium. Chromium was reported as total chromium, so the percentage of hexavalent chromium could not be determined. ATSDR's MRL for chromium is based on the inhalation route, so the lowest observed adverse effect level (LOAEL) for ingestion of 0.036 mg/kg/day was used as the health effect risk comparison value instead of the MRL. This health effect value is based on a study applying a dose of hexavalent chromium as potassium dichromate to chromium sensitive individuals which resulted in worsened dermatitis (9). This is a very conservative delimiter. Four of the 10 kg child estimated doses and twelve of the pica behavior doses exceeded the LOAEL. The highest estimated dose for a child with pica behavior ingesting soil with the greatest concentration of chromium was 2.1 mg/kg/day. The only adverse human heath effects reported at doses of 2.1 mg/kg/day or below resulted from chronic exposure to drinking water contaminated with hexavalent chromium. The health effects associated with doses of 2.1 mg/kg/day or below were less serious effects including abdominal pain, diarrhea, and minor hematological effects (10). Because health effect doses would only result from ingestion of soil from "hot spots" and the potential receptor population are occasional trespassers, actual exposures to chromium in soil are likely to be substantially less than the isolated, highly contaminated soil samples would imply. Therefore, ATSDR and ADH consider that, under site specific conditions of exposure, the average doses of chromium from the on-site soil and both on and off-site sediments that might result from incidental or intentional soil ingestion are not likely to pose any hazard to public health.
Chromium can penetrate human skin to some extent, especially if the skin is damaged. Systemic toxicity has been observed in humans following dermal exposure to chromium compounds indicating significant cutaneous absorption. It is very difficult to estimate the potential for dermal absorption because the potential is dependent on the amount of soil that adheres to the skin. For children ages one through11, a conservative default value of 5,250 mg of adhered soil was used to evaluate the potential for an exposure based health effect. Five times weekly exposure to soil with the highest concentration of chromium (2,984 ppm or .02984 mg/mg of soil) for a year would result in an estimated dose of 0.15 mg/kg/day available to a 30 kg (66 pounds) child. This estimation does not take into account the pharmacokinetics of absorbed chromium and assumes that all absorbed chromium is available. Serious adverse health effects associated with dermal exposure to chromium are not observed below 1 mg/kg. Exposure to the highest concentration soils could result in less serious effects such as erythema (reddening of the skin) or skin ulcers (10). The risk of this type of exposure is low and therefore ADH does not consider the dermal pathway a health hazard.
Pentachlorophenol concentrations on the site ranged from 10.65 ppm to 202 ppm with a mean concentration of 107 ppm. Estimated doses for three of the four sample concentrations for a 10 kg child who ingests 200 mg of soil exceed ATSDR's intermediate oral MRL of 0.001 mg/kg/day for pentachlorophenol. The highest estimated dose (a pica child trespassing on the site five times a week for a year) was 0.14 mg/kg/day. The MRL was derived from an animal study where a LOAEL of increases in the serum enzyme alanine aminotransferase (ALT) was observed in male rats that were fed diets containing 1.4 mg/kg/day of technical grade pentachlorophenol for six weeks. The NOAEL for oral exposure to pentachlorophenol is 1 mg/kg/day (11). Because the highest estimated dose is below the NOAEL and the actual LOAEL reference dose, ADH and ATSDR do not consider pentachlorophenol under the site specific conditions to be a health hazard.
Although pentachlorophenol is well absorbed following percutaneous application in soil, there are insufficient studies describing significant levels of dermal exposure to pentachlorophenol to adequately evaluate the dermal pathway (11).
Dioxin and dioxin-like compounds are structurally related groups of chemicals from the family of halogenated aromatic hydrocarbons. Depending on the number of chlorine-substituted positions, there are several congeners in each group. A congener is a chemical compound that is closely related to another in composition that exhibits similar or antagonistic effects. The most studied of these congeners is TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin).
Toxicity equivalency factors (TEFs) were developed to compare the relative toxicity of individual dioxin-like compounds to that of TCDD. This comparison is based on the assumption that dioxin and dioxin-like compounds act through the same mechanism of action. The TEF for TCDD is defined as one, whereas TEF values for all other dioxin-like compounds are less than or equal to one. Toxicity equivalents (TEQ) are used to assess the risk of exposure to a mixture of dioxin-like compounds. A TEQ is defined as the product of the concentration of an individual "dioxin-like compound" in a complex environmental mixture and the corresponding TCDD toxicity equivalency factor for that compound. The total TEQ is the sum of the TEQs for each of the congeners in a given mixture. Although trespassers could contact soil containing dioxin like congeners at levels above their carcinogenic risk screening value, using a conservative exposure scenario, we estimate that chronic exposure to this soil would result in no apparent increased lifetime risk for the development of cancer (12). If future land use patterns change to those approximating a residential setting, the public health significance of the dioxin contaminated soil should be re-evaluated.
Summary: Potential exposure to contaminants through the food chain is considered to be an indeterminate public health hazard. Although available data do not indicate that people are being or have been exposed to levels of contamination that would be expected to cause adverse health effects, data are not available for all environmental media to which people may be exposed. Benzo(a)pyrene, octochlorodibenzo-p-dioxin (OCDD), and hexachlorodibenzofuran (HCDF) were detected at low concentrations in the sediment samples from Nimrod Lake. Phenol, phenanthrene, naphthalene, and 4-chloro-3-methyl phenol (p-cresol) were detected in low concentrations in the bottom feeding fish (small mouth buffalo and/or channel catfish), but not in the principal game fish (large mouth bass) from Nimrod Lake. Arsenic and chromium were not detected in the fish samples and were detected in very low concentrations in the sediment samples from Nimrod Lake and the mouth of Porter Creek.
Fish and sediment samples were collected at two Lake Nimrod locations. The first location was near the mouth of Porter Creek where a sediment sample, one small mouth buffalo, one channel catfish, and one large mouth bass were collected and analyzed. Sediment, one small mouth buffalo, and one large mouth bass were collected from a sample location near the surface water intake of Lake Nimrod and analyzed. The contaminants that were detected in the Nimrod Lake sediment and fish samples were contaminants that are commonly detected in the surface waters in Arkansas. Mercury was the only contaminant that was detected in all three species of fish and the only contaminant detected in the bass that were analyzed. Mercury was detected at levels exceeding health based guidelines, but it is highly unlikely that the mercury originated at the MPPT site, because mercury was not detected at elevated levels in the on-site soil or sediment samples. Nimrod Lake and the Fourche LaFave River are under a fish consumption advisory notice because of elevated mercury levels (13). The elevated mercury has been attributed to multiple sources. The phenol, phenanthrene, naphthalene, and p-cresol concentrations in the buffalo and catfish were detected below health based comparison values.
The benzo(a)pyrene, OCDD, and HCDF detected in the sediment samples are all classified as possible human carcinogens. Detecting levels of a possible carcinogen in sediment samples does not necessarily result in uptake and accumulation of the detected contaminant by aquatic species, but creates the potential for a completed food chain exposure pathway. The analysis of the fish samples indicates that the levels of chromium and arsenic in sediments from Porter Creek and Nimrod Lake are not significantly accumulating in elements of the aquatic food chain that are consumed by humans. Because the data for the food chain pathway are limited to one 1998 Lake Nimrod sampling event, ADH and ATSDR assessed this pathway as an indeterminate public health hazard.
As part of the public health assessment process, ADH and ATSDR try to learn what concerns people in the area may have about the impact of the site on their health. Consequently, attempts are made to actively gather information and comments from people who live or work near the site. To obtain community health concerns related to the MPPT site, we contacted different agencies and individuals by telephone or personal visit. The local health unit in Yell County and the Arkansas Department of Environmental Quality were contacted in 1999 and questioned regarding community health concerns. In addition to state agencies we contacted community, elected and private sector leaders who work and live in the vicinity of the Mountain Pine Pressure Treatment site. A public meeting was held on April 18, 2000, to give citizens an opportunity to record any personal or public health concerns on a survey form. The only concerns that were reported at the meeting were for the potential of groundwater contamination and contamination of Nimrod Lake (the city's drinking water source.) No community member reported any health problems that they thought could be attributed to exposure of site contaminants, but there were multiple inquiries concerning the potential for exposure related health problems.
No additional health concerns or public comments were reported to ADH during the public comment period for the Public Health Assessment from March 15, 2001 to April 30, 2001.
Health Outcome Data Evaluation
Certain health conditions that occur in populations are recorded in health outcome databases. These data can provide information on the general health of communities living near a hazardous waste site. They also can provide information on patterns of specified health conditions. Some examples of health outcome databases are tumor registries, birth defects registries, and vital statistics. Information from local hospitals and other health care providers also may be used to investigate patterns of disease in a specific population. ADH and ATSDR look at appropriate and available health outcome data when there is a completed exposure pathway or community concern. Because no specific community health concerns nor known exposed populations were identified, we did not review health outcome data.
ATSDR's Child Health Initiative recognizes that the unique vulnerabilities of infants and children demand special emphasis in communities faced with contamination of their water, soil, air, or food. Children are at greater risk than adults from certain kinds of exposures to hazardous substances emitted from waste sites and emergency events. They are more likely to be exposed because they play outdoors and they often bring food into contaminated areas. They are shorter than adults, which means they breathe dust, soil, and heavy vapors close to the ground. Children are also smaller, resulting in higher doses of chemical exposure per body weight. The developing body systems of children can sustain permanent damage if toxic exposures occur during critical growth stages. Most importantly, children depend completely on adults for risk identification and management decisions, housing decisions, and access to medical care.
ATSDR and ADH evaluated the likelihood for children living in the vicinity of the MTTP site for exposure to site contaminants at levels of health concern. The off-site soils have not been sufficiently characterized to determine if exposures to site specific contaminants are likely to result in any adverse impact on children's health. We did identify situations at the school and at residences near the site in which children were likely to have been exposed to site contaminants. But due to lack of ample off-site samples, we were unable to estimate exposure doses. The proximity of the school and the day care center to the MTTP site create a potential for children to access areas within the boundaries of the site. There are no documented accounts of children trespassing on the site, although graffiti located in the abandoned buildings indicates that access is not sufficiently restricted to preclude trespassing. If children were to frequently trespass on this site they would be at risk from chemical contaminants and from physical hazards on the site. In the toxicological evaluation section, potential health effects associated with doses calculated for children weighing 10 kilograms (22 pounds) and 16 kilograms (35 pounds) were discussed. One time incidental ingestion of soils by children from the arsenic "hot spots" on the site could result in doses that exceed the acute exposure LOAEL for humans of 0.02 mg/kg/day (7). Symptoms associated with short term exposures to the potential doses delivered during a trespassing exposure scenario generally decline within a short time after exposure ceases; however, there is a great risk that children who wander onto the site or deliberately trespass onto the site could be exposed to levels of arsenic that would result in adverse health effects.
On the basis of available environmental and toxicologic information, ADH and ATSDR conclude that the Mountain Pine Pressure Treating site in Plainview, Arkansas, poses a public health hazard. This determination is based on the following site specific conditions:
- Exposure to arsenic in the soil and sediment on the site can result in exposure doses that exceed ATSDR's health guidelines. There is sufficient site evidence to conclude that trespassers are frequenting the site and are coming into contact with contaminants in amounts sufficient to pose a public health hazard. If the site is used for residential purposes in the future, there is a potential for a significant public health impact.
- There is a potential for the surface water in Porter and Prairie Creeks to be impacted by runoff from the site that could adversely impact Nimrod Lake which is a public water system source.
- Concentrations of arsenic, chromium, and pentachlorophenol on the site pose an unacceptable risk for potential contamination of off-site soils.
- Because of the limited number of fish sampled, there is insufficient data to assess the public health implications of exposure to site contaminants through the food chain (fish). Exposure to contaminants through the food chain is an indeterminate public health hazard.
- Conduct additional soil sampling in residential yards north and east of the MPPT site and on the Plainview Rover School grounds to more accurately characterize off-site contaminant concentrations.
- Conduct additional sediment sampling in the drainage ditches south of the site to determine if contaminants are migrating to Porter Creek from the south side of the site.
- Enhance the physical barriers around the site to mitigate or eliminate trespassing.
- Conduct a well survey to identify all (old) residential wells in the area. The wells should be located, plugged, and capped to eliminate the potential for groundwater exposure points.
- Conduct additional game fish sampling at the mouth of Porter Creek and near the vicinity of the water intake in Lake Nimrod to ensure that none of the game fish are adversely effected by site-related contaminants.
- EPA conducted a Remedial Investigation/Feasibility Study (RI/FS) and initiated a response action contract with a private contractor.
- ADH conducted a public meeting to gather community health concerns and distributed fact sheets.
Ongoing and Planned Actions
- Supplemental field sampling activities are being conducted by the response action contractor.
- Soils that contain elevated concentrations of metals will be treated according to the findings of the RI/FS.
- If data gathered during the ongoing investigations and sampling indicate that additional contamination is present at MPPT and exposures are occurring, ADH and ATSDR will review these data to determine if potential public health hazards exist and issue a health consult or addendum to this PHA.
- ICF Technology Inc. Expanded Site Inspection Report. Mountain Pine Pressure Treating, Yell County, Arkansas. ARD049658628. Prepared in Cooperation with the U.S. Environmental Protection Agency. 1993 Feb.
- Bureau of the Census. 1990 Census of Population and Housing: Summary Tape File 1A, machine readable data files. Washington: US Department of Commerce, 1991.
- Arkansas Department of Environmental Quality. Hazard Ranking System Documentation Record. Volume 1 for Mountain Pine Pressure Treating, Plainview, Yell County, Arkansas. EPA ID No. ARD049658628. 1999 Apr.
- Arkansas Department of Environmental Quality. Comprehensive Site Assessment and Facility Investigation Scope of Work. Plainview Lumber Company. Prepared in Cooperation with the US Environmental Protection Agency. 1997 Mar.
- Agency for Toxic Substances and Disease Registry. Public health assessment guidance manual. Atlanta: U S Department of Health and Human Services: 1992.
- ICF Technology Inc. FIT Sampling Inspection Report. Mountain Pine Pressure Treating, Yell County, Arkansas. ARD049658628. Prepared in Cooperation with the U S Environmental Protection Agency. 1988 Nov.
- Agency for Toxic Substances and Disease Registry. Toxicological Profile for Arsenic. Atlanta: U S Department of Health and Human Services. 1998 Aug.
- Marcus and Rispin. Threshold carcinogenicity using arsenic as an example. In: Cothren CR, Mehlman MA, Marcus WL, editors. Risk Assessment and Risk Management of Industrial and Environmental Chemicals. Vol. XV. Princeton, NJ: Princeton Scientific Publishing Co. p 133-158. 1988.
- Kaaber K, Veien NK. The significance of chromate ingestion in patients allergic to chromate. Acta Derm Venereol 57 321-3. 1977.
- Agency for Toxic Substances and Disease Registry. Toxicological Profile for Chromium. Atlanta: U S Department of Health and Human Services. 1998 Aug.
- ATSDR, 1999. Agency for Toxic Substances and Disease Registry. Toxicological Profile for Pentachlorophenol. Atlanta: U S Department of Health and Human Services. 1999 Aug.
- ATSDR, 1998. Agency for Toxic Substances and Disease Registry. Toxicological Profile for Chlorinated Dibenzo-p-Dioxins. Atlanta: U S Department of Health and Human Services. 1998 Dec.
- Arkansas Department of Health, Arkansas Game and Fish Commission, and Arkansas Department of Environmental Quality. Fish Consumption Notice. 1999 Mar.
Arkansas Department of Health:
ATSDR Regional Representative:
Senior Regional Representative
ATSDR - Region 6
ATSDR Technical Project Officer:
Technical Project Officer
Division of Health Assessment and Consultation
This Public Health Assessment for the Mountain Pine Pressure Treating Inc., site in Plainview, Arkansas, was prepared by the Arkansas Department of Health under a cooperative agreement with the Agency for Toxic Substances and Disease Registry (ATSDR). It is in accordance with approved methodology and procedures existing at the time the public health assessment was begun.
Tammie McRae, MS
Technical Project Officer
Superfund Site Assessment Branch (SSAB)
Division of Health Assessment and Consultation (DHAC)
The Division of Health Assessment and Consultation, ATSDR has reviewed this public health assessment, and concurs with its findings.
Section Chief, SSAB, DHAC, ATSDR