The concentration of toxic compounds in Galveston Bay seafood has become a major issue for management of the bay in recent years. Contamination of bay waters by toxic compounds not only involves human derived synthetic compounds such as pesticides, polychlorinated biphenyls (PCBs) and dioxins, but also includes marine biotoxins produced by red tide organisms such as Karenia brevis. Data on concentrations of toxic chemicals in estuarine organisms are important indicators of ecosystem health and provide critical information on human health risks related to seafood consumption.
Human Health Effects from Toxics in Water and Sediment
Thousands of compounds, which could affect living organisms in an estuarine environment, occur in runoff and effluents. There are several categories of chemicals known to be associated with human health risks. The classes of chemicals which have been studied by the Texas Department of State Health Services (TDSHS) and others include: reactive hydrocarbons (phthalates), polynuclear aromatic hydrocarbons (PAHs), chlorinated pesticides (chlordane, DDE, DDD, etc.), polychlorinated biphenyls (PCBs), dioxins and furans, and trace metals.
Marine biotoxins can also also have adverse human health effects. Some species of phytoplankton produce toxins that accumulate in the tissues of shellfish and can, when ingested by humans, cause illness. Several of the most notorious phytoplankton-related pathologies include Amnesic Shellfish Poisoning (ASP), Paralytic Shellfish Poisoning (PSP), Ciguatera Fish Poisoning (CFP) and Neurotoxic Shellfish Poisoning (NSP). The toxins are heat stable and are not destroyed by cooking. Unfortunately, it is difficult to measure the true occurrence of these illnesses as they are frequently misdiagnosed or are not reported at all. The organism responsible for red tide algal blooms (Karenia brevis) produces a substance known as brevetoxin. When this toxin is ingested by humans, NSP can result. Symptoms may include dizziness and nausea and, although not life-threatening, can be debilitating.
There is no established program to regularly monitor the contamination of seafood in Galveston Bay. However, the TDSHS has performed episodic studies over the last 20 years that have documented the problem and TDSHS has reacted by issuing a number of health advisories.
Monitoring of toxics includes sampling for metals and a wide variety of synthetic organic compounds. It is difficult to detect most of these chemicals in the water, so most of the measurements that cause concern are obtained from samples of the sediment where the compounds are likely to accumulate or from seafood organisms in which some of the compounds bioaccummulate or biomagnify.
Water and sediment quality monitoring suggests that nearly all of Galveston Bay has levels of contamination by toxic metals and synthetic organics that are below levels of health concern. However, there are notable exceptions.
Sediment samples from the Houston Ship Channel sometimes show concentrations of PCB or dioxin that exceed the levels considered safe for human exposure. Sediment samples from the Houston Ship Channel contain high levels of such contamination, but there are no health based standards for sediment contamination (sediment contamination is assessed based on adverse ecological effects) and recreation is not allowed in the Houston Ship Channel due to acute risks presented by the shipping industry.
Table 1. Total Dioxin Concentrations Detected in Finfish by Several Studies of Galveston Bay as compared to TDSHS Health Assessment Comparison (HAC) values. Data source: (Rifai et al. 2005; TDSHS 2005a; TDSHS 2008b; TDSHS 2008a)
# Detects / # Samples
|Average PCDF/PCDD in Toxicity Equivalents (pg/g)*
|Houston Ship Channel1 (catfish only)
|Houston Ship Channel and Upper Galveston Bay2
|Trinity Bay and Upper Galveston Bay3
|Lower Galveston Bay4
|2008 TDSHS Health Assessment
Comparison (HAC) Values (pg/g)*
1 (Rifai et al. 2005); 2 (TDSHS 2005a); 3 (TDSHS 2008b); 4 (TDSHS 2008a) * picograms/gram
It is appropriate to develop plans that would improve management of bay waters to reduce contamination and return them to the quality related to their potential uses. In response to the contamination of seafood by Persistent Organic Pollutants (POPs), a TMDL has been conducted for Buffalo Bayou and the Houston Ship Channel. Intensive studies of dioxins and PCBs in water, sediment and biota have been performed (Correa et al. 2006; Howell et al. 2008). Sources of dioxin have been identified and planning is underway to reduce the loadings of dioxin into the Houston Ship Channel to a safe level.
Correa, O., L. Raun, H. Rifai, M. Suarez, T. Holsen and L. Koenig. 2006. "Depositional flux of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans in an urban setting." Chemosphere 64(9): 1550-1561.
Howell, N. L., M. P. Suarez, H. S. Rifai and L. Koenig. 2008. "Concentrations of polychlorinated biphenyls (PCBs) in water, sediment, and aquatic biota in the Houston Ship Channel, Texas." Chemosphere 70: 593-606
Lester, L. J. and L. A. Gonzalez, Eds. 2002. The state of the bay: a characterization of the Galveston Bay ecosystem, 2nd edition. Webster, Texas, Texas Commission on Environmental Quality, Galveston Bay Estuary Program. http://gbic.tamug.edu/SOBDoc/SOB2/sob2page.html.
Rifai, H., R. Palacheck and P. Jensen. 2005. Total Maximum Daily Loads for Dioxins in the Houston Ship Channel. Draft Final Report Contract No. 582-0-80121 for Texas Commission on Environmental Quality.: 555.
TDSHS. 1993. Health Commissioner advises "zero consumption" of fish from Clear Creek. Texas Department of Health Seafood Advisory News Release. Austin, Texas, Texas Department of Health.
TDSHS. 2008a. Characterization of Potential Adverse Health Effects Associated with Consuming Fish or Blue Crab from Lower Galveston Bay; Chambers, Galveston, and Harris Counties, Texas. D. f. R. S. Department of State Health Services, Policy, Standards, and Quality Assurance Unit, Seafood and Aquatic Life Group: 58 pp.
TDSHS. 2008b. Characterization of Potential Adverse Health Effects Associated with Consuming Fish or Blue Crab from Trinity Bay and Upper Galveston Bay: Chambers, Galveston, and Harris Counties, Texas, Department of State Health Services, Division for Regulatory Services, Policy, Standards, and Quality Assurance Unit, Seafood and Aquatic Life Group: 55 pp.