April 15 (UPI) -- For the first time, scientists have a conducted a Gulf-wide survey of oil pollution among fish populations.
The massive study -- comprising samples from 2,500 fish representing 91 species spread across 359 locations in the Gulf of Mexico -- suggests contamination from oil pollution remains widespread roughly 10 years after the Deepwater Horizon spill.
Researchers published the results of the record survey on Wednesday in the journal Scientific Reports.
"This is the largest comprehensive fish survey ever conducted in a large marine ecosystem and provides the first spatial and temporal baselines for polycyclic aromatic hydrocarbon in fishes in the Gulf of Mexico," study author Erin L. Pulster, marine scientist and postdoctoral researcher at the University of South Florida, told UPI in an email.
Polycyclic aromatic hydrocarbons, or PAHs, are one of the most toxic chemical components found in crude oil. The toxins, which have been linked to heart disease and cancers in humans, get trapped in the bile of fish.
"This study demonstrates the chronic and widespread oil pollution in this ecosystem," Pulster said. "Given the extensive oil and gas extraction activities in the Gulf of Mexico for the last eight decades, it is unclear why this has not been conducted prior to the Deepwater Horizon oil spill."
The new survey revealed elevated levels of PAH in every surveyed fish species living in the Gulf, but the highest levels were found in yellowfin tuna, golden tilefish and red drum.
Elevated levels were expected in tilefish, which spend most of their lives stirring up seafloor sediment, where oil pollution settles. But researchers were surprised to find such elevated PAH levels in tuna, which live their lives in the water column, where oil pollution tends to persist for only short amounts of time.
As part their research, scientists also mined data from previous PAH exposure surveys. The research team found evidence of elevated PAH levels in the tissue and bile of 10 popular grouper species.
"The elevated and increasing PAH levels in fish is the result of a combination of sources which include both anthropogenic and natural sources," Pulster said. "Anthropogenic sources include the Deepwater Horizon oil spill, leaking infrastructure, riverine discharge, marine vessel traffic and the resuspension of contaminated sediments. Natural sources are mainly natural oil seeps and submarine groundwater discharge located throughout the Gulf of Mexico."
Not all fish populations show the same levels of contamination. Scientists measure higher concentrations of the toxins near places with greater oil and gas activity. Researchers also found PAH hotspots among fish populations near coastal cities like Tampa Bay, which suggests urban runoff can exacerbate oil pollution problems.
"The continued degradation of the Gulf of Mexico ecosystem is demonstrated by the chronic, widespread oil pollution," Pulster said.
Despite the alarming results, scientists suggest the evidence of PAH contamination is more concerning for the health of Gulf ecosystems and fish populations than the health and safety of consumers of Gulf seafood. Toxin levels in the flesh of commercial fish species are closely monitored and PAH levels in fish flesh remain below public health advisory levels.
However, prolonged exposure to elevated PAH and other oil-related toxins can cause the liver to shutdown, threatening the health of fish in the Gulf. Previous studies have revealed 50 to 80 percent population declines in deep water, or mesopelagic, fish populations near the Deepwater Horizon blowout site.
Researchers hope their baseline study of PAH contamination among Gulf fish is only the beginning of a more robust monitoring effort.
"Providing funding is available, our research efforts will continue to monitor and evaluate PAH levels in fish and the subsequent sub lethal effects," Pulster said. "Additionally, a major research focus will be geared toward identifying the sources of PAHs in surface waters that are impacting pelagic [openwater] species."