HEALTH CONSULTATION
Sediments in Stewarts Creek
CONROE CREOSOTING COMPANY
CONROE, MONTGOMERY COUNTY, TEXAS
SUMMARY AND STATEMENT OF ISSUES
The U.S. Environmental Protection Agency (EPA) Region 6 asked the Agency for Toxic Substances and Disease Registry (ATSDR) and the Texas Department of Health, Environmental Epidemiology and Toxicology Division (TDH), to evaluate the potential for contamination from the Conroe Creosoting Company (CCC) site to pose a public health hazard to people living downstream on Stewarts Creek.
The CCC site is east of the city limits of Conroe, Montgomery County, Texas (Figure 1). It sits on the north side of State Highway 105 at 1776 E. Davis. Stewarts Creek is to the west; an on-site lake and Little Caney Creek lie to the east.
From 1946 until 1997, workers at this facility treated lumber with chemicals--creosote, pentachlorophenol (PCP), or copper-chromated-arsenic (CCA)--to preserve the wood for use as fence posts, railroad ties, or utility poles. The Texas Natural Resource Conservation Commission (November 2001) and the EPA (January and November of 2002) documented contamination of site soil and sediment with these wood-treatment chemicals [1, 2, 3]. TDH staff noticed heavily stained soil areas and chemical odors, particularly around tanks and process areas, when they visited the site with EPA and ATSDR regional staff in May 2002.
The EPA began removing tanks, pipes, and other equipment from the site in the Fall 2002. A Resource Conservation and Recovery Act (RCRA) vault was built on the site to contain contaminated soil and sediment. Runoff from heavily contaminated areas was redirected and contained [3]. In the past, rain and runoff that contacted contaminated areas tended to flow into an on-site drainage ditch and then west into Stewarts Creek, which flows south past residential homes and yards that have flooded during heavy rainfall.
In November 2002, to better characterize off-site contaminant concentrations around the CCC site, a contractor for the EPA collected 111 sediment and five soil samples. These samples were analyzed for semi-volatile organic compounds (SVOCs) and metals [4]. In addition, 101 of the sediment samples and all five of the soil samples were analyzed for dioxins/furans. The sediment samples were collected along Stewarts Creek, along Little Caney Creek, at the on-site lake, and elsewhere on the CCC site. Soil samples also were collected from three residential yards and a schoolyard along Stewarts Creek.
Benzo(a)pyrene, an SVOC, exceeded its health-based screening value(1) in 44 of the sediment samples and in one of the soil samples.
Arsenic exceeded health-based screening values in 75 sediment samples and in all five of the soil samples (Table 1). However, the levels of arsenic in sediment from Stewarts Creek (not detected to 19 mg/kg) and Little Caney Creek (not detected to 4.1 mg/kg), as well as in soil from the residential yards (2.6-4.7 mg/kg) and the schoolyard (1.5-4.5 mg/kg), were comparable to background soil arsenic concentrations for uncontaminated soil [5]. Therefore, further consideration of arsenic in this health consultation was not warranted.
Dioxins, as 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin equivalents (TCDD), exceeded ATSDR's action level for soil of 0.001 milligrams TCDD per kilogram (mg/kg) [6] in one of the 101 sediment samples, but did not exceed this value in any of the five soil samples. The sediment sample with TCDD exceeding ATSDR's action level for soil was found where the on-site drainage ditch entered Stewarts Creek. This sediment has since been removed and transferred to the on-site RCRA vault. Since dioxins were below levels of concern in soil and sediment, it is unlikely that significant exposure opportunities existed. Therefore, further consideration of dioxins in this health consultation was not warranted.
In April 2003, more-focused sediment sampling was conducted by EPA along two sections of Stewarts Creek: 1) under and near the State Highway 105 bridge over the creek; and 2) near Avenue M. Forty-two (42) sediment samples from each location were analyzed for SVOCs.
For the State Highway 105 bridge location, 28 of the 42 samples exceeded the screening value for the SVOC benzo(a)pyrene. The maximum level of the benzo(a)pyrene measured at this location was 30 mg/kg. This sample was collected in a difficult-to-access area below the bridge. For the Avenue M area, 26 of the 42 samples had levels of benzo(a)pyrene exceeding screening values. The maximum level of benzo(a)pyrene measured in sediment from the Avenue M area was 1.4 mg/kg.
The environmental sampling data reviewed in this report includes data collected by EPA in 2002 and 2003. In preparing this report, TDH and ATSDR relied on those data and assumed adequate quality assurance/quality control (QA/QC) procedures were followed with regard to data collection, chain-of-custody, laboratory procedures, and data reporting.
Reviewers evaluated the results by comparing the contaminants to screening values and by selecting results that exceeded the screening level. Benzo(a)pyrene was selected for further consideration.
The most likely exposure route for benzo(a)pyrene in creek sediment or soil is through incidental ingestion of contaminated sediment or soil.(2) To assess the risk for those ingesting sediments, TDH used the following conservative exposure scenario: A worker ingesting 100 mg of sediment containing the highest level of benzo(a)pyrene measured in CCC area sediments (30 mg/kg) during his work week for 30 years might have a slightly elevated(1.34 X 10-4) risk of developing cancer over a lifetime of exposure. Because the area that had the highest level of benzo(a)pyrene under and near the State Highway 105 bridge is not readily accessible, the probability of exposure and subsequent potential for adverse health outcomes is low.
Similarly, a child or an adult regularly exposed to the maximum level of benzo(a)pyrene (1.4 mg/kg) measured along Stewarts Creek at Avenue M would have no apparent increased risk of developing cancer.
ATSDR's Child Health Initiative
We recognize that the unique vulnerabilities of children demand special attention. Windows of vulnerability (critical periods) exist during a child's development, particularly during early gestation but also throughout pregnancy, infancy, childhood, and adolescence--periods when toxicants may permanently impair or alter structure and function [7].
Unique childhood vulnerabilities may be present because at birth many organs and body systems (including the lungs and the immune, endocrine, reproductive, and nervous systems) have not achieved structural or functional maturity. These organ systems continue to develop throughout childhood and adolescence. Children may exhibit differences in absorption, metabolism, storage, and excretion of toxicants, possibly resulting in higher doses to target tissues. Depending on the media, exposure for children may be more than for adults because of behavior patterns specific to children, such as a tendency to ingest dirt. In an effort to account for children's unique vulnerabilities, and in accordance with ATSDR's Child Health Initiative [8] and EPA's National Agenda to Protect Children's Health from Environmental Threats [9], we used the potential exposure for children as a guide in assessing the potential public health implications of the contaminants.
Based on available information, we have concluded that current and future exposures to the sediment and soil in and along Stewarts Creek and Little Caney Creek, downstream from the Conroe Creosoting Company site, pose no apparent public health hazard to adults or children. This is either because contaminants are not present at levels expected to cause a health problem and/or because under current circumstances people are unlikely to come into contact with contaminated sediments often enough or for long enough duration to result in health problems. Therefore, TDH and ATSDR have classified this site as posing no apparent public health hazard.
This Health Consultation for the Conroe Creosoting-Stewards Creek Sediment was prepared by the Texas Department of Health (TDH) under a cooperative agreement with the federal Agency for Toxic Substances and Disease Registry (ATSDR). It is in accordance with approved methodology and procedures existing at the time the health consultation was initiated.
Robert Knowles
Technical Project Officer, SSAB, DHAC
The Division of Health Assessment and Consultation (DHAC), ATSDR, has reviewed this health consultation and concurs with its findings.
Roberta Erlwein
Section Chief, SPS, SSAB, DHAC, ATSDR
AUTHORS, TECHNICAL ADVISORS, AND ORGANIZATIONS
Preparers of the Report
Susan L. Prosperie, M.S., R.S.
Environmental Specialist
Environmental Epidemiology and Toxicology Division
Texas Department of Health
John F. Villanacci, Ph.D.
Director
Environmental Epidemiology and Toxicology Division
Texas Department of Health
ATSDR Regional Representative
Karl Markiewicz, Ph.D.
Regional Representative
ATSDR - Region 6
Jennifer Lyke
Regional representative
ATSDR, Region 6
ATSDR Technical Project Officer
Robert B. Knowles, M.S., R.E.H.S.
Environmental Health Scientist
Division of Health Assessment and Consultation
Superfund Site Assessment Branch
State Programs Section
APPENDIX A: ACRONYMS AND ABBREVIATIONS
| ATSDR | Agency for Toxic Substances and Disease Registry |
| CCA | Copper chromated arsenic |
| CCC | Conroe Creosoting Company |
| CERCLA | Comprehensive Environmental Response, Compensation and Liability Act of 1980 |
| CREG | Carcinogenic Risk Evaluation Guide |
| EMEG | Environmental Media Evaluation Guide |
| EPA | United States Environmental Protection Agency |
| HAC | Health Assessment Comparison Value |
| MRL | Minimal risk level |
| NPL | U.S. EPA National Priorities List |
| PAHs | Polycyclic aromatic hydrocarbons |
| PCBs | Polychlorinated biphenyls |
| PCP | Pentachlorophenol |
| RCRA | Resource Conservation and Recovery Act |
| RfD | Reference dose |
| RMEG | Reference Dose Media Evaluation Guide |
| SARA | Superfund Amendments and Reauthorization Act of 1986 |
| SVOCs | Semi-volatile organic compounds |
| TCDD | 2,3,7,8-tetrachlorodibenzo-p-dioxin |
| TDH | Texas Department of Health |
| TNRCC | Texas Natural Resource Conservation Commission |
| VOCs | Volatile organic compounds |
Figure 1. General Location and Demographic Information
Table 1. Constituents Exceeding Health-based Screening Values in Soil/Sediment Samples Collected November 13, 2003.
| Benzo(a)pyrene Range; #/#* | Arsenic Range; #/# | Dioxins† as TCDD equivalents #/# | |
| Sediment Samples (mg/kg) | |||
| Stewarts Creek | ND‡-3.0; 32/65 | 0.9U-19; 40/65 | 0/60 |
| Stewarts Creek upstream of CCC | ND-0.17§; 4/7 | 1.0-5.0; 3/7 | 0/6 |
| Onsite along Stewarts Creek | ND-2.1; 4/5 | 2.7-22; 4/5 | 0.001399; 1/4 |
| Little Caney Creek | ND-0.39J; 3/26 | 0.96U-4.1; 21/26 | 0/24 |
| Lake entry to Little Caney Creek | ND; 0/2 | 4.6-18; 2/2 | 0/2 |
| Lake | ND-1.3; 1/6 | 1.2-30; 6/6 | 0/5 |
| Soil Samples (mg/kg) | |||
| Residential | ND-0.18J; 1/3 | 2.6-4.7; 3/3 | 0/3 |
| School yard | ND; 0/2 | 1.5-4.5; 2/3 | 0/2 |
| Health-based screening values (mg/kg) | CREG¶ 0.1 | CREG 0.5 | <0.001 |
* #/# Number of samples exceeding health based screening value
per total number of samples collected
† ATSDR Action Level for TCDD equivalents in soil
‡ ND not detected
§ estimated value
¶ CREG Cancer Risk Evaluation Guide
Health assessment comparison (HAC) values are guidelines that specify levels of chemicals in specific environmental media (soil, air, and water) that are considered safe for human contact. Because many of the assumptions used to calculate HAC values are conservative with respect to protecting public health, exceeding a HAC value does not necessarily mean that adverse health effects will occur. However, exceeding a HAC value does suggest that potential site-specific exposure to the contaminant warrants further consideration.
2. Although dermal absorption via skin contact with contaminated soil/sediment may have been a concern during heavy rainfall and flooding of yards along the creek, the contaminants in the soil and sediment were more likely to remain joined on the soil/sediment particles than to cling to and absorb into the skin of people who may have come in contact with flood water.
