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The United States Environmental Protection Agency (EPA) asked the Texas Department of Healthto evaluate potential human health risks associated with eating fish and crabs from Clear Lake orGalveston Bay near Clear Lake. Galveston Bay is the most economically and ecologically importantbay of the Texas coast. Home to a large fleet of commercial fishing, shrimp and oyster boats,Galveston Bay generates nearly a billion dollars per year in commercial and recreational seafoodharvests. Some 300,000 licensed recreational anglers annually spend two million hours sportfishing on Galveston Bay. The Houston Ship Channel and Upper Galveston Bay are presently undera consumption advisory due to the presence of dioxins in catfish and blue crabs.

Clear Lake, which empties into Galveston Bay, supports twenty-one marinas and has the largestnumber of recreational boats on the Texas coast. Recreational fishers use approximately sixthousand boat slips on the lake. Several major boat-refurbishment businesses are also on the shoresof Clear Lake. The EPA was especially interested in potential impacts to children's health and thepotential for toxicity from exposure to tri-n-butyltin (TBT). Intense recreational fishing in thepresence of boat-refurbishing activities on Clear Lake suggests that people eating fish and crabsfrom Clear Lake and nearby areas of Galveston Bay may be exposed to TBT in seafood. Tri-n-butyltin oxide (TBTO), a component of marine paints and varnishes that retards attachment ofinvertebrates to boats, is slowly released from these coatings into surrounding waters, from which itmay be absorbed by marine life. People who eat seafood from the study area may be exposed toTBTO through the seafood. Studies have shown that TBTO depresses immune function inexperimental animals and that juvenile animals may be more susceptible to those effects than areadult animals [1].

In the summer of 1999, the Seafood Safety Division (SSD) collected twelve composite blue crabsamples, one alligator gar, two black drum, one gafftop sailfish, two red drum, one sand seatrout, 15sheepshead, 11 southern flounder, and three spotted seatrout from Clear Lake and from GalvestonBay near Clear Lake. Samples were analyzed for mono-, di-, and tri-butyltin, arsenic, cadmium,copper, lead, mercury, selenium, zinc, polychlorinated biphenyls (PCBs), pesticides, volatile organiccompounds (VOCs), semivolatile organic compounds (SVOCs), and dioxins(1). This project wasfunded by a grant from the EPA.

Very low levels of mono-, di-, and tri-n-butyltin were observed in fish and crab samples from ClearLake and contiguous areas of Galveston Bay. As expected, TBT was higher in samples from ClearLake than in samples from Galveston Bay (t=2.719, df=16.27, p=.008)(2), as was total butyltinconcentration (Tables 1b, 2). Low levels of cadmium, copper, lead, mercury, selenium, and zincwere also observed in samples from both locations. Acetone, a laboratory contaminant, was presentin several samples. Very low concentrations of chlordane, DDE, Aroclor 1260, and dioxins werealso observed in fish or blue crabs from Clear Lake or Galveston Bay. Blue crabs from both sites contained low levels of pyridine.


Deriving Health-based Assessment Comparison Values (HACs)

TDH screened chemical contaminants in fish and crabs from Clear Lake and Galveston Bay forfurther consideration by comparing the average concentration of each contaminant to health-basedassessment comparison (HAC) values for non-cancer and cancer endpoints. We used the EPA'sreference 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 ofdaily exposures to contaminants that are unlikely to cause adverse noncancer health effects even ifexposure occurs for a lifetime. The cancer risk comparison values are based on EPA's chemical-specific cancer slope factors (SF), an estimated excess lifetime risk of one cancer in ten thousand (1X 10-4) persons exposed to the toxicant, and an exposure period of 30 years. We used standardassumptions for body weight (70 kilograms, adult; 35 kilograms, child) and fish consumption (30grams per day, adult; 15 grams per day, child) to calculate the HAC values [2].

Addressing the Potential for Cumulative Adverse Health Effects

When multiple chemicals affect the same target organ or when several chemicals present in seafoodtissues are carcinogens, we assume that the adverse effects are additive [3]. To evaluate thepotential public health impact of additive noncancerous health effects, we calculate the number ofmeals per week needed to exceed a hazard index (HI) of one (1.0). The HI is the sum of the ratios ofthe estimated exposure dose for each contaminant to its respective RfD or MRL. A hazard index ofless than 1.0 suggests that exposure to the combined contaminants, at the specified exposure levels,is unlikely to cause adverse noncancerous health effects, even if exposure occurs over many years. While an HI that is greater than 1.0 does not necessarily mean that exposure to the contaminantswill result in adverse health effects, it does suggest that some public health intervention should beconsidered. To estimate the potential excess lifetime cancer risk associated with multiplecarcinogens, we calculate a cumulative risk by adding the estimated risk associated with eachcontaminant. The Texas Department of Health recommends that people limit consumption ofseafood contaminated with carcinogenic chemicals to amounts that result in an estimated theoreticalexcess lifetime cancer risk of less than 1 in 10,000 persons exposed.

Addressing the Unique Vulnerabilities of Children

TDH, EPA, and ATSDR recognize that the unique vulnerabilities of infants and children demandspecial attention. For several reasons, children have a special susceptibility to some toxicsubstances. Children are smaller than adults, which results in higher doses of chemical exposure perunit of body weight. Their body systems are still developing, making them less able than adults tometabolize, detoxify or excrete some substances, and they may be more likely to absorb specifictoxicants. Children's developing body systems can sustain permanent damage if toxic exposuresoccur during critical growth stages. Children may be more prone than adults to developing certaincancers as a result of chemical exposures. Consequently, children who consume seafoodcontaminated with toxic chemicals may be at greater risk for toxic effects than adults. Therefore, inaccordance with ATSDR's Child Health Initiative [4] and EPA's National Agenda to ProtectChildren's Health from Environmental Threats [5], we evaluated potential public health hazards tochildren who eat fish and crabs from Clear Lake and Galveston Bay near Clear Lake.

Characterizing the Risk

Assessing Noncancer Health Effects

Individually, the contaminants in fish and crabs from Clear Lake or Galveston Bay near Clear Lakewere observed at average concentrations below their respective noncancer HAC values (Tables 1and 2)(3). The levels of tributyltin oxide (TBTO) and related compounds in these samples were morethan two hundred times lower than the HAC value for this contaminant (Table 2). The TexasDepartment of Health investigated the origin of pyridine in crab tissues. These studies concludedthat pyridine is a naturally-occurring component of crab tissue and is neither the result of, nor is it related to, environmental contamination [7].

Assessing Cancer Health Effects

Individual contaminants detected in fish and crabs from Clear Lake and Galveston Bay close toClear Lake were observed at concentrations below their respective cancer HAC values (Table 1). Several chemicals found in fish and crabs, however, are classified by the EPA as probable humancarcinogens (Group B2) based on an increase in the incidence of tumors in laboratory animalsexposed to those chemicals [1]. People who eat fish and crabs from Clear Lake or Galveston Bay inthe vicinity of Clear Lake may be exposed to several of the chemicals at the same time. Based onpreviously-stated assumptions, we calculated that the theoretical excess cancer risk for people eatingone meal per week of fish and crabs from these areas would be approximately 1 in 52,500 personsexposed to the combination of contaminants seen in the samples from Clear Lake and Galveston Bayin the near vicinity of Clear Lake. Qualitatively, this is interpreted as a low increased theoretical lifetime risk for development of cancer.


Consumption of fish and crabs from Clear Lake and Galveston Bay in the vicinity of Clear Lakeposes no apparent public health hazard because regular consumption of these species would be unlikely to have an adverse impact on human health.


The TDH Seafood Safety Division has established criteria for issuing fish consumption advisoriesbased on EPA guidelines [2]. If long-term consumption of one meal per week could have an adverseimpact on human health, the Seafood Safety Division recommends that the Commissioner of Healthissue a consumption advisory. Recommendations based on the findings of this health consultation are as follows:

  1. No consumption advisories are recommended at this time.

  2. TDH will continue to monitor seafood samples from this area as information becomesavailable.

Table 1a.

Organic Contaminants in Fish and Crabs from Clear Lake and Contiguous Portions of Galveston Bay
CONTAMINANT Number Affected/Sampled Average Concentration (Range) Comparison Value1 Basis for Comparison Value
Pesticides (mg/kg)
chlordane 36/48 0.053
1.17 EPA Chronic Oral RfD: 0.0005 mg/kg/day
1.6 EPA Slope Factor 0.35 (mg/kg/day)-1
DDD 7/48 0.0005 (nd-0.022) 2.3 EPA Slope Factor: 0.24 (mg/kg/day)-1
DDE 2/48 0.003 (nd-0.01) 1.6 EPA Slope Factor: 0.34 (mg/kg/day)-1
Polychlorinated Biphenyls (mg/kg)
Aroclor 1260 2/48 0.011
0.047 EPA chronic oral RfD for Aroclor 1260: 2 X 10-5 mg/kg/day
0.27 EPA slope factor: 2.0 (mg/kg/day) -1
Dioxins (ng/kg)
Toxicity-weighted Concentration3-crabs 6/12 0.547
2.33 ATSDR chronic oral MRL: 1.0 X 10-09 mg/kg/day
3.49 EPA slope factor: 1.56 X 10+05 (mg/kg/day)-1
Toxicity-weighted Concentration-finfish 20/36 0.346
2.33 ATSDR chronic oral MRL: 1.0 X 10-09 mg/kg/day
3.49 EPA slope factor: 1.56 X 10+05 (mg/kg/day)-1
Toxicity-weighted Concentration-all Samples 26/48 0.397
2.33 ATSDR chronic oral MRL: 1.0 X 10-09 mg/kg/day
3.49 EPA slope factor: 1.56 X 10+05 (mg/kg/day)-1
Volatile Organic Compounds (mg/kg)
Acetone 17/48 0.118
233 EPA chronic oral RfD: 0.1 mg/kg/day
Semivolatile Organic Compounds (mg/kg)
Pyridine-crabs 4 6/12 0.294
2.33 EPA chronic oral RfD: 0.001 mg/kg/day
1 Derived from the RfD or MRL for non-carcinogens, or from the EPA 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
2 Not detected at concentrations above laboratory reporting limits
3 Toxicity-weighted concentrations:
4 Pyridine was not detected in finfish from these sources

Table 1.

Metals and Organotin Contaminants (mg/kg) in Fish and Crabs from Clear Lake and Adjacent Areas of Galveston Bay
CONTAMINANT Number Affected/Sampled Average Concentration (Range) Comparison Value 1 Basis for Comparison Value
butyltin compounds2 20/23 0.0028
0.70 EPA chronic oral RfD 0.001 mg/kg/day
Clear Lake 13/15 0.00394
0.70 EPA chronic oral RfD 0.001 mg/kg/day
Galveston Bay 7/8 0.0008
0.70 EPA chronic oral RfD 0.001 mg/kg/day
cadmium 15/48 0.01
0.47 ATSDR chronic oral MRL 0.0002 mg/kg/day
copper 26/48 2.12
Not Applicable Not Available
lead 39/48 0.021
Not Applicable IEUBK 5
mercury 5/48 0.020
0.70 ATSDR chronic oral MRL 0.0003 mg/kg/day
selenium 48/48 0.538
12 ATSDR/EPA chronic oral MRL/RfD 0.005 mg/kg/day
zinc 48/48 11.8
700 ATSDR/EPA chronic oral MRL/RfD 0.3 mg/kg/day
1 Derived from the RfD or MRL for non-carcinogens, or from the EPA 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
2 Sum of tributyl-, dibutyl-, and monobutyltin
3 Not detected at concentrations above the reporting limit
4 Butyltin concentrations in samples from Clear Lake are significantly higher than those in Galveston Bay
5 Integrated Exposure Uptake Biokinetic Model, EPA

Table 2.

Average concentrations of butyltin compounds in Clear Lake and in areas of Galveston Bay near the outlet of Clear Lake
Tributyltin Dibutyltin Monobutyltin Total Organotin
Clear Lake 0.0025 0.0017 0.00048 0.00390
Galveston Bay 0.00071 0.0 0.00012 0.00081
All Sites 0.00171 0.00076 0.00036 0.00283


  1. IRIS. Integrated Risk Information System. September 2000. Environmental ProtectionAgency, Office of Research and Development, National Center for Environmental

  2. Environmental Protection Agency 1997. Guidance for assessing chemical contaminant data for use in fish advisories. Volume II, 2nd edition. Fish Sampling and Analysis. Office of Science and Technology, Office of Water, Washington, DC.

  3. Environmental Protection Agency 1986. Guidelines for the Health Risk Assessment ofChemical Mixtures. Office of Research and Development, Washington, DC.

  4. Agency for Toxic Substances and Disease Registry, Office of Children's Health. 1995. Child Health Initiative.

  5. Environmental Protection Agency (EPA), 1998. The Children's Environmental HealthYearbook.

  6. Van den Berg, et al., 1998. Toxic Equivalency Factories (TEFs) for PCBs, PCDDs, PCDFs for Humans and Wildlife. Environ. Health Perspect. 106(12):775-792.

  7. Fest G, Villanacci J, Ward J, Williams L et al., 2000. Assessment of the toxicological significance of pyridine in blue crabs from Texas water bodies, in preparation.


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

Susan Bush, B.S.
Natural Resource Specialist
Seafood Safety Division
Bureau of Food and Drug Safety

Eric Fonken, D.V.M.
Natural Resource Specialist
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 Lake Health Consultation was prepared by the Texas Department of Health under acooperative 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, State Programs Section, SSAB, DHAC, ATSDR

1. In this consultation, the term "dioxins" refers to combined polychlorinated di-benzo-p-dioxins and polychlorinated dibenzofurans.
2. One-tailed t because predicted that TBT concentrations within Clear Lake would be higher than those in the bay; df=degrees of freedom; df is not a whole number because assumption of unequal between-group variance was applied; p=significance level, alpha=.05.
3. 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) is considered the most toxic of the dioxin congeners. Therefore, other dioxins were converted to a concentration equivalent to that of 2,3,7,8-TCDD (toxicity-weighted concentration) using established toxic equivalent factors (TEFs) [6]. The calculated toxicity-weighted concentrations were then compared to HAC values for 2,3,7,8-TCDD.

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