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Study: Mercury scattered in Duval river sediment, falling in some spots

September 24, 2021
Despite hotspots, river study says Duval 'does not exhibit unusual mercury contamination'
Mercury levels in the sediment of some Duval County riverbeds are apparently dropping over time, but the change isn’t happening everywhere, a new report for Jacksonville’s Environmental Protection Board has found.  The county “does not exhibit unusual mercury contamination in general,” said the study of the St. Johns River and its tributaries prepared by researchers at Jacksonville University.

But contamination issues are spotty, said Lucinda Sonnenberg, a JU chemistry professor, with some places around the Buckman Bridge, Julington Creek and the Ortega River having mercury concentrations in sediment up to four times higher than elsewhere.  “It’s very clearly related to organic matter content,” said Sonnenberg, a former EPB member who led the study. Organic matter includes plant debris that washes into waterways with the rain and settles on creek beds.

Mercury is a toxic metal that, in high enough levels, can cause neurological damage and pose risks for children's development.  People eating ordinary amounts of fish caught locally won’t take in enough mercury to raise any health concerns, the report said.  The rare people who eat local fish almost daily might have a chance of being affected, however, especially small women in their childbearing years and people who eat fish that preyed on other fish (spotted seatrout or white catfish, for example) and ingested the mercury their prey carried.

Even if they don’t affect people directly, mercury concentrations can affect wildlife living around hotspots, said the report, which the city commissioned in 2015 after a statewide report examined the maximum load of mercury waterways across Florida could handle.
Researchers surveyed mercury levels at 34 sites around the county for the new report. They then collected more information at six tributaries, including sites near the Northside Generating Station and the former St. Johns River Power Park (where coal-burning was blamed for mercury emissions into the air) and areas in the county’s southern half with past records of mercury contamination nearby. 

Researchers found the most contaminated sediments around Fishing Creek at Ortega Farms, and also found elevated mercury concentrations in the Ortega River near Naval Air Station Jacksonville, said the report.

Using results from testing between 2015 and 2017, the report said sediment patterns were different in the sandier riverbeds closer to the ocean in Jacksonville’s northern half and more lake-like areas farther south. Median mercury readings in the fresher southern areas were more than three times countywide levels, the report said.  Although the report questioned whether NAS Jacksonville might be tied somehow to the higher levels, it listed “no readily obvious potential sources of mercury in the area,” and said data about contaminants in the area “do not indicate the naval air station is currently a primary source of mercury to the surrounding environment.”

EPB members have suggested having Sonnenberg talk to the board this fall about the report’s findings.

Source:  Steve Patterson - Florida Times-Union