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The State of the Bay Galveston Bay Area Project

Metals in Galveston Bay Sediments


Under normal conditions, the concentrations of mercury, lead, cadmium, and arsenic in the water is low and often cannot be detected by standard instrumental methods. Thus, metals dissolved in water are not monitored frequently. The most frequently used sampling protocol for metals involves their detection in sediments. Metals may also be found in fish tissue; the results of those monitoring efforts are discussed in Chapter 9.

In the 1970s and 1980s, the majority of metals in sediment samples were collected from the tributaries to Galveston Bay, especially the Houston Ship Channel and Clear Creek. That changed in the 1990s as stations in the subbays of Galveston Bay were increasingly monitored. The number of monitoring samples for selected metals (arsenic, cadmium, chromium, copper, lead, mercury, nickel, silver, and zinc) in sediment is now greater in subbays (1,655 samples since 2000) than in the tributaries (1,523 samples since 2000). The increase in subbay sampling reduces the uncertainty associated with drawing conclusions about metal pollution in the bay. We can now state with more certainty that metal pollution is of decreasing concern in Galveston Bay.

Analyses by the Galveston Bay Status and Trends Project during 2009–10 compared concentrations of metals in sediment to screening levels established by the TCEQ Ecological Assessment Program (TCEQ 2008). The TCEQ screening levels replace NOAA probable effect levels (PELs) used in prior Status and Trends assessments. Major subbays and tributaries of the bay were rated based on the percentage of samples exceeding TCEQ screening levels for marine waters in a given subbay or tributary in a given decade. The methodology was initially developed by the Galveston Bay Indicators Project (Lester and Gonzalez 2005).

As seen in the figure below, the 5 subbays of Galveston Bay generally rate good or very good in terms of sediment concentrations of metals in the 1970s and very good in the decade since 2000.  Warnken et al. (2009) reported that less than 20 percent of the pollutant trace metal load in waters of the Trinity River enters Galveston Bay. The remainder is lost to the sediments of 23 artificial lakes along the river’s course. The most problematic area in terms of the greatest number of metals exceedences in the Lower Galveston Bay watershed has historically been the Houston Ship Channel and even that area has shown improvement. Samples were collected from 1973-2009.

metals indicator chart

Since 1973, 141 metals exceedences (85 percent of all metals exceedences reported in the subbays and tributaries of Galveston Bay) have been documented in the Houston Ship Channel. In the 1970s the Houston Ship Channel rated moderate with high silver and zinc concentrations. There were also some issues of contamination of sediments by lead and mercury. In the years since 2000, the picture has improved, with the number of cadmium, lead, silver, and zinc exceedences decreasing. Concentrations of mercury remain high in the upper Houston Ship Channel, particularly at locations such as Patrick Bayou in Deer Park, which has been listed on the National Priority List as a Superfund site since 2002. This is illustrative of the effect pollution hot spots can have on the assessment of conditions in the bay.


Literature Cited:

Lester, L. J., and L. A. Gonzalez. 2005. Galveston Bay Indicators Project Final Report. Webster, Texas: Texas Commission on Environmental Quality (TCEQ), Galveston Bay Estuary Program (GBEP).

TCEQ. 2008a. Guidance for assessing and reporting surface water quality in Texas. Austin, Texas: Texas Commission on Environmental Quality.

Warnken, K. W., and P. H. Santschi. 2009. "Delivery of Trace Metals (Al, Fe, Mn, V, Co, Ni, Cu, Cd, Ag, Pb) from the Trinity River Watershed Towards the Ocean." Estuaries and Coasts no. 32 (1):158-172.


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