New methods of mercury testing show safe levels of mercury in fish
Recent enhanced analysis of fish collected in the Ohio River indicates mercury levels in these fish are lower than previously estimated.
As a result of this more accurate data, the Kentucky Division of Water is proposing to remove from the list of impaired waters approximately 370 miles of the Ohio River from Louisville to the confluence with the Mississippi River. This stretch of the Ohio River has historically been listed as impaired because mercury levels in fish tissue previously exceeded the Kentucky water quality standard for fish tissue.
The 2012 Clean Water Act 303(d) list of Impaired Waters in Kentucky currently includes segments of the Ohio River from Louisville to the Mississippi River for failing to meet the water quality standard for mercury in fish tissue.
Recent data generated from testing of fish tissue by the Ohio River Sanitation Commission (ORSANCO) using improved analytical methods indicates that the Ohio River is meeting the water quality criteria for mercury in fish tissue.
The water quality standard for mercury in fish tissue is 0.3 mg/Kg of methyl-mercury. This standard is a fish-tissue based criterion intended to protect human health via the consumption of fish. Methyl-mercury is the bioavailable fraction of total mercury that represents the fraction of mercury that is of concern for fish consumption. When fish are consumed, methyl-mercury is the mercury that can be absorbed by the human body and at elevated concentrations can be harmful to humans. Excess mercury can result in impaired neurological development and other nervous system damage. Recent analysis of fish tissue using improved methods indicates that the fish in this section of the Ohio River are meeting the water quality standard for methyl-mercury. Previous analysis of fish tissue for mercury were based on the total amount of mercury present and did not identify the harmful form of methyl-mercury that the new testing capabilities are able to identify.
Re-analysis of fish tissue samples collected from 2009 to 2013 using these improved methods indicates that the Ohio River is meeting the water quality standard for mercury in fish tissue because levels of methyl-mercury in fish tissue are consistently below the 0.3 mg/Kg water quality standard. Consequently, the Division of Water has provided public notice that it intends to request of the U.S. Environmental Protection Agency that the Ohio River from Louisville to the Mississippi River be removed from the list of impaired waters with regards to mercury in fish tissue.
The division is receiving public comments on its proposed list of impaired waters. This request for removal from the 303(d) list will be sent to EPA for approval after the public notice comment period. This request for removal from the 303(d) list will be sent to EPA for approval after the public notice comment period.
The division’s draft 2014 303(d) list can be found at: http://water.ky.gov/Pages/PublicNotices.aspx. The document on this website includes the list of waters that the division is proposing to add to and remove from the list of impaired waters. Comments regarding this proposal can be provided to the Division of Water by emailing comments to Alicia.Jacobs@ky.gov. The public comment period will close on July 13, 2015.