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A 1993 examination of fish and blue crabs collected from Clear Creek revealed the presence of several chemicals. Taken from a creek section immediately downstream of the Brio Refinery National Priorities Superfund site, the samples contained volatile organic compounds (VOCs), chlordane, other chlorinated pesticides, and low levels of mercury and zinc. As expected, contaminant levels declined as the distance from the Superfund site increased. On November 18, 1993, based on data from this examination, the Texas Department of Health (TDH) issued Advisory 7 (ADV-7). The advisory, which remains in effect today, recommends no one consume fish or crabs taken from Clear Creek upstream and west of Texas Highway 3 [1]. A December 1993 follow-up sampling of Clear Creek fish and crabs revealed trace levels of VOCs, various chlorinated pesticides, mercury, and zinc as far downstream as Interstate 45. Cumulative cancer risk from carcinogenic contaminants in these samples exceeded health department guidelines then in effect for protection of human health. Accordingly, the Texas Natural Resource Conservation Commission (TNRCC) added Clear Creek to its 303(d) list. Consequent to this action, the TNRCC requested, in 2000, that TDH reevaluate Clear Creek seafood for adverse health effects that could result from consumption of contaminated fish or blue crabs. TDH undertook that study, which the TNRCC funded through a grant to the Seafood Safety Division (SSD).

On September 19 and 20, 2000, the SSD collected, from four sites along Clear Creek, 16 finfish samples: two blue catfish, two channel catfish, five smallmouth buffalo, three common carp, one southern flounder, and three white crappie. TDH also collected four blue crab composite samples (5 crabs/sample) from Clear Creek. The TDH laboratory analyzed all samples for seven common metals: arsenic, cadmium, copper, lead, mercury, selenium, and zinc. The laboratory also analyzed for volatile organic compounds (VOCs), semivolatile organic compounds (SVOCs), pesticides, and polychlorinated biphenyls (PCBs).

Table 1 is a summary of the analytical results from these samples. Very low levels of cadmium, copper, lead, mercury, selenium, and zinc were detected in one or more samples. Very low concentrations of several pesticides were also identified in several samples. These consisted of chlordane, DDE, diazinon, dieldrin, hexachlorobenzene, beta hexachlorocyclohexane (beta benzene hexachloride), lindane, heptachlor epoxide, and Malathion. Extremely low levels of several VOCs–benzene, chloroform, ethylbenzene, toluene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, and ortho-, para-, and meta-xylene–were also observed in some finfish. These contaminants were found primarily in smallmouth buffalo–again, at extremely low levels. One fish, a white crappie, contained a very low concentration of di-2(ethylhexyl) phthalate (DEHP), a plasticizer that is no longer manufactured or used in the U.S., but that can remain in the environment for many years after use ends. Blue crabs contained only low levels of chlordane. No PCBs or other semivolatile organic compounds were observed in fish or blue crab composites from Clear Creek. Acetone, a common field or laboratory volatile organic contaminant, was present in a few samples.


Sample Collection and Data Analysis

To evaluate potential health risks to recreational and subsistence fishers who consume environmentally contaminated seafood, the Texas Department of Health (TDH) collects and analyzes samples from the state's public waters. These samples are representative of available species, trophic levels, lipid content, and legal sizes. When it is appropriate and practical, TDH collects samples from several locations within a water body to characterize the distribution of contaminants in seafood from that water body. It is important to note that people eating contaminated seafood are most likely exposed over the long term through consumption of one or more species contaminated with low concentrations of environmental pollutants. Consequently, people exposed to environmental contaminants through consumption of seafood are unlikely to display acute or overt toxicity. Instead, subtle, delayed, or chronic adverse health effects may be more commonly expected. Thus, the main purpose of TDH contaminant studies is to examine human exposure to species commonly consumed over time. TDH may use average concentrations of chemical contaminants across species and/or sites to assess the probability of adverse health outcomes from low-level, long-term exposure. Despite the possibility that using average concentrations to estimate risk may lead to over- or underestimates of actual exposures or risks, use of averages is a reasonable approach to predicting long-term exposure to low levels of contaminants. Although TDH routinely uses average concentrations for determining external exposure doses, the agency has used and continues to use other statistical procedures to assess the likelihood of adverse health effects from consumption of contaminated seafood when these procedures are appropriate.

Deriving Health-based Assessment Comparison Values (HACs)

TDH evaluated chemical contaminants in fish and crabs from Clear Creek by comparing average concentrations of chemical contaminants in the samples with health-based assessment comparison (HAC) values for non-cancer and cancer endpoints. TDH used the U.S. Environmental Protection Agency's (USEPA) reference doses (RfDs) or the Agency for Toxic Substances and Disease Registry's (ATSDR) minimal risk levels (MRLs) to derive the noncancer HAC values. RfDs and MRLs are estimates of daily exposures to contaminants that are unlikely to cause adverse noncancer health effects, even if exposure occurs over a lifetime. The cancer risk comparison values in this health consultation are based on the USEPA's chemical-specific cancer slope factors (SF), an estimated lifetime risk of 1 excess cancer in 10,000 (1 x 10-4) people exposed, and an exposure period of 30 years. TDH used standard assumptions for body weight (70 kilograms, adult; 35 kilograms, child) and fish consumption (30 grams per day, adult; 15 grams per day, child) to calculate the HAC values [2]. Many of the constants used to calculate HAC values have margins of safety built into them. Thus, adverse health effects will not necessarily occur simply because concentrations of toxicants in seafood exceed HAC values. Moreover, health-based assessment comparison values do not represent a sharp dividing line between safe and unsafe exposures. In fact, TDH views it as unacceptable when consumption of less than one meal per week would result in an exposure exceeding a HAC value or a cumulative risk factor. Thus in the final analysis, the strict demarcation between acceptable and unacceptable levels of exposure or risk is primarily a tool used by risk managers to ensure protection of public health.

Addressing the Potential for Cumulative Effects

When multiple chemicals affect the same target organ, or when several chemicals present in seafood could be carcinogens, TDH assumes that adverse health effects are cumulative (i.e., additive). To evaluate the potential public health impact of additive noncancerous health effects, TDH calculates a hazard index (HI), which is the sum of the ratios of the estimated exposure doses for each contaminant divided by its respective RfD or MRL. A HI of less than 1 suggests that exposure to combined contaminants at specified exposure levels is unlikely to cause adverse noncancerous health effects, even if that exposure continues for many years. On the other hand, while a HI greater than 1 does not necessarily mean exposure to the contaminants will result in adverse health effects, it does suggest that the agency might consider some public health intervention. To estimate the potential excess lifetime cancer risk from simultaneous exposure to multiple carcinogens, TDH calculates the cumulative risk by summing the estimated risk for each contaminant. TDH recommends limiting consumption of seafood contaminated with multiple carcinogenic chemicals to amounts resulting in an estimated theoretical excess lifetime cancer risk of not more than 1 excess cancer in 10,000 persons exposed through seafood.

Addressing the Unique Vulnerabilities of Children

TDH recognizes that fetuses, infants, and children may be uniquely vulnerable to the effects of toxic chemicals and that any such vulnerabilities demand special attention. Windows of vulnerability, i.e., critical periods, exist during development. These critical periods are particularly evident during early gestation, but also appear throughout pregnancy, infancy, childhood, and adolescence–indeed, at any time when toxicants can permanently impair or alter structure or function [4]. Unique childhood vulnerabilities result, at least in part, from the fact that at birth, many organs and body systems, including the lungs, immune, endocrine, reproductive, and nervous systems, have not achieved structural or functional maturity; these organ systems continue to develop throughout childhood and adolescence. Children can also differ from adults in absorption, metabolism, storage, and excretion of toxicants, any of which differences could result in higher biologically effective doses to target organs. Children's exposure to toxicants may be more extensive than that of adults because children consume more food and liquids in proportion to their body weight than do adults [4]. Children can also ingest toxicants through breast milk–often unrecognized as an exposure pathway. Thus, children can experience toxic effects at a lower exposure dose than would affect adults. Stated differently, children could react more severely than would adults to an equivalent exposure dose [4]. Children are also more prone than are adults to developing certain cancers from chemical exposures (e.g., specific types of leukemia). Therefore, in accordance with ATSDR's Child Health Initiative [5] and USEPA's National Agenda to Protect Children's Health from Environmental Threats [4], TDH evaluated the potential public health hazards to children who eat fish or crabs from Clear Creek. Based on this health consultation, TDH concludes that children who consume fish or blue crabs from Clear Creek have no greater risk of adverse health effects than would children who do not consume fish or crabs from this stream and that such consumption poses no apparent public health hazard for children.

Characterizing the Risk

Assessing Individual and Cumulative Noncancer Health Effects

Contaminant levels in fish and crabs taken from the survey area were below their respective noncancer HAC values (Table 1). Thus, consumption of fish or blue crabs from Clear Creek containing any single contaminant is unlikely to result in adverse, noncancerous health effects. Nevertheless, several chlorinated pesticides, including chlordane, DDD, DDE, DDT, dieldrin, heptachlor epoxide, and hexachlorobenzene–as well as all VOCs identified at low levels in finfish from Clear Creek–are known to produce adverse noncancerous effects on the livers of experimental animals [3]. Assuming these effects to be additive, TDH calculated a hazard index for consumption of seafood from Clear Creek. The HI was less than 1 for average concentrations of all contaminants of concern across all species and collection sites (Table 2). The HI for smallmouth buffalo, the most heavily contaminated species, was approximately 1. Thus, consumption of fish and crabs from Clear Creek is unlikely to result in cumulative adverse noncancerous health effects.

Assessing Individual and Cumulative Risk of Cancer Health Effects

Average concentrations of all contaminants of concern in fish and crabs from Clear Creek were below their respective cancer HAC values (Table 1). This suggests that an increase in the risk of cancer from exposure to individual contaminants is unlikely. USEPA, however, classifies many contaminants found in the Clear Creek samples as possible or probable human carcinogens (Groups C, B2) [3]. Those who eat fish or crabs from Clear Creek could be simultaneously exposed to several of these chemicals. As a result, carcinogenic effects could be cumulative. TDH estimated cumulative cancer risk for persons exposed to environmental contaminants in seafood taken from Clear Creek by adding the individual risk for each carcinogenic contaminant (Table 2). Based on this calculation, the cumulative risk of excess cancers resulting from exposure to contaminants in fish and blue crabs from Clear Creek did not exceed TDH guidelines (Table 2) for increased risk of cancer. Qualitatively, TDH interprets the cumulative risk as posing no apparent increase in the risk of cancer.


The Texas Department of Health concludes that regular consumption of fish or crabs taken from Clear Creek would not result in exposure doses exceeding TDH risk management guidelines. Thus, consumption of fish or blue crabs from Clear Creek poses no apparent public health hazard to those who consume these species.


The Texas Department of Health has established criteria for issuing fish consumption advisories based in part on USEPA guidelines [2]. When the data indicate that eating less than one meal per week (8 ounces, adult; 4 ounces, child) results in exposures exceeding a health-based guideline, risk managers at TDH generally recommend that the Texas Commissioner of Health issue a consumption advisory. Based on the findings of this health consultation, the Seafood Safety Division and the Environmental Epidemiology and Toxicology Division recommend the following for Clear Creek:

  1. That TDH reevaluates its existing consumption advisory recommending that people not consume fish or blue crabs from Clear Creek upstream of, and west of, Texas Highway 3 because concentrations of contaminants in samples from the present survey area do not exceed health-based assessment comparison values.

  2. That TDH continues to monitor fish and blue crabs taken from Clear Creek as contaminant data become available.


Information about fish consumption advisories and bans issued by the Texas Department of Health is available to the public through the Seafood Safety Division (512-719-0215) or on the World Wide Web at URL . Health consultations dealing with contaminants in seafood from Texas waters may also be available to the public from the Agency for Toxic Substances and Disease Registry ( The Texas Department of Health provides this information to the U.S. Environmental Protection Agency ( ), the Texas Natural Resource Conservation Commission (TNRCC; ) and to the Texas Parks and Wildlife Department (TPWD; ). Each year, the TWPD informs the fishing and hunting public of closure areas in an official hunting and fishing regulations booklet [9] that is available at some state parks and at establishments that sell fishing licenses.

Should readers have questions or concerns about the scientific information presented in this health consultation, they may telephone the Seafood Safety Division (512-719-0215) or the Environmental Epidemiology and Toxicology Division (512- 458-7269) at the Texas Department of Health. Toxicological information is also available from the Agency for Toxic Substances and Disease Registry (ATSDR), Division of Toxicology, in Atlanta, Georgia. The toll-free number for obtaining such information is (800-447-1544).


Table 1.

Contaminants (mg/kg) in fish and crabs from Clear Creek from Year 2000 (20 samples: 16 finfish, 4 blue crabs)
Chemical Number Affected/ Sampled Average Concentration
(Min-Max) *
Health-based Assessment Comparison Value Basis for Comparison Value
Chlordane 15/20 0.124 (nd-0.72) 1.2 USEPA chronic oral RfD: 0.0005 mg/kg/day
1.6 USEPA slope factor: 0.35 per (mg/kg)/day
p,p'-DDE 8/20 0.011 (nd-0.048) 1.6 USEPA slope factor: 0.34 per (mg/kg)/day
b- hexachlorocyclohexane 3/20 0.0019 (nd-0.016) 0.30 USEPA slope factor: 1.8 per ( mg/kg)/ day
Diazinon 8/20 0.0265 (nd-0.160) 0.467 ATSDR chronic oral MRL: 0.0002 mg/kg/day
Lindane 2/20 0.0007 (nd-0.007) 0.7 USEPA chronic oral RfD: 0.0003 mg/kg/day
Hexachlorobenzene 3/20 0.001 (nd-0.010) 1.867 USEPA chronic oral RfD: 0.0008 mg/kg/day
0.34 USEPA slope factor: 16 per (mg/kg)/day
Dieldrin 2/20 0.0009 (nd-0.010) 0.034 USEPA chronic oral RfD: 0.00005 mg/kg day
0.117 USEPA slope factor: 16 per (mg/kg)/day
Heptachlor epoxide 4/20 0.003 (nd-0.024) 0.03 USEPA chronic oral RfD: 0.000013 mg/kg/day
0.06 USEPA slope factor 9.1 per (mg/kg)/day
Malathion 4/20 0.005 (nd- 0.028) 46.7 USEPA chronic oral RfD: 0.02 mg/kg/day
Volatile Organic Compounds (VOCs)
Benzene 1/20 0.0007 (0.014) 9.9 USEPA slope factor: 0.055 per (mg/kg)/day
Chloroform 2/20 0.002 (nd-0.026) 30 USEPA chronic oral RfD: 0.01 mg/kg/day
89 USEPA slope factor: 0.0061 per (mg/kg)/day
Ethylbenzene 2/20 0.0015 (nd-0.017) 233 USEPA chronic oral RfD: 0.1 mg/kg/day
Toluene 3/20 0.003 (nd-0.021) 467 USEPA slope factor: 0.2 per (mg/kg)/day
1,2,4-trimethylbenzene 3/20 0.007 (nd-0.074) --------- Not Available
1,3,5-trimethylbenzene 3/20 0.004 (nd-0.041) --------- Not Available
Xylene, total 3/20 0.006 (nd-0.063) 4667 USEPA chronic oral RfD: 2.0 mg/kg/day
Cadmium 3/20 0.004 (nd-0.033) 0.47 ATSDR chronic oral MRL: 0.0002 mg/kg/day
Copper 10/20 2.25 (nd-14.6) -------- Not Available
Lead 6/20 0.008 (nd-0.045) -------- Not Available
Mercury 9/20 0.094 (nd-0.419) 0.7 ATSDR chronic oral MRL: 0.0003 mg/kg/day
Selenium 20/20 0.30 (0.15-0.49) 2 TDH Guidelines
Zinc 20/20 11.0 (2.3-41.0) 700 ATSDR chronic oral MRL/USEPA chronic oral RfD: 0.3 mg/kg/day

* Minimum concentration to Maximum concentration (to calculate the range, subtract the minimum concentration from the maximum concentration).
Derived from the MRL or RfD for noncarcinogens or the USEPA slope factor for carcinogens; assumes a body weight of 70 kg, and a consumption rate of 30 grams per day, and assumes a 30-year exposure period for carcinogens and an excess lifetime cancer risk of 1x10-4 .
nd-not detected at concentrations above the laboratory reporting limit.

Table 2.

Theoretical Risk of Noncancerous or Cancer Adverse Health Effects from Consuming Fish and Crabs from Clear Creek
Contaminant Hazard Ratio Cancer Risk
Chlordane 0.106 8.0 X 10-6
p,p'-DDE 0.009 6.6 X 10-7
b- Hexachlorocyclohexane (b-BHC) ---------- 6.3 X 10-7
Ethylbenzene 0.000006 -----------
Lindane 0.0009 -----------
Hexachlorobenzene 0.0006 3.1 X 10-7
Dieldrin 0.008 2.6 X 10-6
Heptachlor epoxide 0.100 5.1 X 10-6
Benzene ---------- 7.1 X 10-9
Chloroform 0.00006 2.1 X 10-9
Xylene, ortho-, para-, & meta- 0.000001 2.3 X 10-6
Toluene 0.000005 9.2 X 10-8
CUMULATIVE RISK 0.225 2.0 X 10-5


  1. [TDH] Texas Department of Health. Fish advisories and bans. Seafood Safety Division. Austin, Texas: 2001.

  2. [USEPA] US Environmental Protection Agency. Guidance for assessing chemical contaminant data for use in fish advisories. Volume 2, risk assessment and fish consumption limits, 3rd ed. Washington, D.C.: 2000.

  3. [IRIS] Integrated risk information system. US Environmental Protection Agency. Office of Research and Development, National Center for Environmental Assessment. Available from URL:

  4. [USEPA] US Environmental Protection Agency. Office of Research and Development. Strategy for research on environmental risks to children, section 1.2. USEPA/600/R-00/068. Washington D.C.: 2000.

  5. [ATSDR] Agency for Toxic Substances and Disease Registry. Office of Children's Health. Child health initiative. Atlanta, Ga. US Department of Health and Human Services: 1995.


Jerry Ann Ward, Ph.D.
Seafood Safety Division
Bureau of Food and Drug Safety

Eric Fonken, D.V.M., M.P.Aff.
Assistant Director
Seafood Safety Division
Bureau of Food and Drug Safety

Susan Bush, B.S.
Survey Branch Chief
Seafood Safety Division
Bureau of Food and Drug Safety

G. Kirk Wiles, R.S.
Seafood Safety Division
Bureau of Food and Drug Safety

Lisa Williams, M.S.
Environmental Epidemiology and Toxicology Division
Bureau of Epidemiology

John F. Villanacci, Ph.D.
Environmental Epidemiology and Toxicology Division
Bureau of Epidemiology


George Pettigrew, P.E.
Senior Regional Representative
ATSDR - Region 6


Alan W. Yarbrough
Environmental Health Scientist
Division of Health Assessment and Consultation
Superfund Site Assessment Branch
State Programs Section


This Clear Creek Health Consultation was prepared by the Texas 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 health consultation was initiated.

Alan W. Yarbrough
Technical Project Officer, SPS, SSAB, DHAC, ATSDR

The Division of Health Assessment and Consultation, ATSDR, has reviewed this health consultation and concurs with its findings.

Richard Gillig
Chief, Superfund Site Assessment Branch, DHAC, ATSDR

Table of Contents The U.S. Government's Official Web PortalDepartment of Health and Human Services
Agency for Toxic Substances and Disease Registry, 4770 Buford Hwy NE, Atlanta, GA 30341
Contact CDC: 800-232-4636 / TTY: 888-232-6348

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