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February 10, 1998

Mobile Bay Makes the List

Major Waterways and Sampling Stations of Mobile Bay Estuary System. T1 = Tier 1 (adverse effects are probable); T2 = Tier 2 (adverse effects are possible but expected infrequently); T3 = Tier 3 (no indication of adverse effects) Source: The Incidence and Severity of Sediment Contamination in Surface Waters of the United States, EPA, January, 1998.
by Edmund Tsang

In a January, 1998 press release on the Environmental Protection Agency (EPA) web site, the federal agency places Mobile Bay on a list of 96 watersheds whose "sediment may be contaminated at levels that may adversely affect aquatic life and human health." The press release further states that most of the 96 watersheds of "probable concern" are "already well-known to state and local government agencies and the general public." The press release announced the results of a study as part of EPA's response to the Waster Resources Development Act of 1992, which is based on data taken from 1980 to 1993 from sampling stations across the continental U.S. to characterize the toxic contaminants found in sediments. The study classifies a watershed as an area of "probable concern" if it either contains 10 or more Tier 1 sampling stations or if 75 percent or more of all the sampling stations in that watershed were classified as either Tier 1 or Tier 2. A Tier 1 sampling station is one where 'adverse effects are probable" while a Tier 2 sample station is one where "adverse effects are possible but expected infrequently"; a sample station is classified as Tier 3 if there is "no indication of adverse effects."

Using this classification, EPA identifies 96 watersheds, or 7 percent of 1,363 watersheds surveyed, as "sufficiently contaminated to pose potential risk to people to eat fish from them and to fish and wildlife. More than two-thirds of these watersheds already have active fish consumption advisories in place." The report states that the risks posed by these contaminated watersheds "pertain to subsistence fishers and others who fish those contaminated waters for food and do not apply to people who eat fish that are commercially available from grocery stores and restaurants."

Mobile Bay

The data used by EPA to evaluate Mobile Bay came from eight monitoring programs performed by federal agencies, including National Oceanic and Atmospheric Administration (NOAA), the U.S. Army Corp. of Engineers, U.S. Fish and Wildlife Services (USFWS), and state agencies such as the Alabama Department of Environmental Management (ADEM) from 1981 to 1991. Chemicals responsible for Mobile Bay's place on the "probable areas of concern" range from heavy metals such as chromium, lead, arsenic and mercury, to pesticides such as the banned DDT, and to industrial chemicals such as polychlorinated biphenyls (PCBs). The table below lists the chemicals found in sampling stations that EPA classifies as either Tier 1 or Tier 1 and Tier 2. According to the EPA report, 15 sampling stations in the Mobile Bay estuarine system are classified as Tier 1, three are classified as Tier 1 and Tier 2, seven are classified as Tier 2, and one is classified as Tier 3 (no indication of associated adverse effects).

In addition to Mobile Bay, Perdido Bay in southern Alabama, Guntersville Lake and Middle Tennessee Chickamauga (joining Alabama to Georgia and Tennessee), and Pickwick Lake (linking Alabama, Mississippi and Tennessee) are the Alabama watersheds that EPA classifies as "areas of probable concern."


A list of the contaminated waterways can be found on the EPA's web page at http://www.epa.gov/OST/Events/sedlist.html


Sediment Chemicals Responsible for Sampling Station Classification
as Tier 1 or Tier 2

ChemicalMean (ppb)Median (ppb)Max. (ppb)Min. (ppb)
Acenaphthylene0.970.0026.291.11
Anthracene31.520.001,2003.46
Arsenic11,772.644,900.00106,000700
Benzo(a)anthracene41.350.001,600.007.70
Benzo(a)pyrene23.680.00640.009.72
Benzo(a)fluoranthene25.490.00430.0010.90
BHC0.020.000.500.02
Cadmium596.41300.006,000.0030.00
Chlordane0.870.0030.00.10
Chromium54,15258,500120,5001,900
Chrysene65.990.002,5008.55
Copper13,91814,11666,000500
Dibenzo(a,b)anthracene6.790.0070.003.30
Dieldrn0.040.000.750.04
DDT1.030.0030.000.01
Fluoranthene62.470.002,20010.95
Fluorene27.940.001,2002.26
HMW_PAHs175.7876.25909.090.92
Lead16,24016,397100,000650
LMW_PAHs158.3529.361,008.562.30
Mercury280.8954.702,550.0010.00
Naphthalene111.580.001,960.03.99
Nickel11,599.986,625.0040,400625
Phenanthrene90.170.004,200.006.39
Polychlorinated biphenyls0.230.008.570.89
Pyrene63.750.002,200.0010.00
Silver2,615.2396.0033,000.0040.00
SEM_est1.912.623.010.07
Zinc86,88279,500847,5003,000

Tissue Residue Data

ChemicalMean (ppb)Median (ppb)Max. (ppb)Min. (ppb)
Arsenic7,833.576,050.0016,000.003,500.00
Benzo(a)anthracene59.6355.9098.1025.60
Benzo(a)pyrene23.5023.5023.5023.50
BHC1.321.313.390.41
Cadmium2,596.482,490.004,570.000.70
Chlordane7.887.3719.763.53
Chromium655.75390.001,760.000.50
Chrysene94.8165.40216.7023.00
Copper93,857.4997,500.00187,0004.80
Dibenzo(a,b)anthracene21.8021.8021.8021.80
Dieldrn6.784.7516.762.71
DDT45.4723.68247.140.52
Fluoranthene156.6277.40502.9021.00
Fluorene27.940.001,2002.26
Lead349.21356.50680200
Manganese13,491.6711,150.0026,000.007,700.00
Mercury63.5068.00160.000.03
Nickel1,230.061,085.002,400.000.90
Polychlorinated biphenyls109.92102.20229.402.20
Pyrene133.2448.90418.2021.70
Selenium1,738.571,840.002,780.001,390.00
Silver1,707.221,995.002,300.001.01
Zinc1,379,4291,001,5004,430,00012.50

Tier 1: Adverse effects are probable
Tier 2: Adverse effects are possible, but expected infrequently

* ppb = parts per billion

Source: Mobile Bay data from The Incidence and Severity of Sediment Contamination in Surface Waters of the United States, EPA, January, 1998.


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