Researchers conducted laboratory experiments to assess the lethal and sublethal impacts of weathered and non-weathered crude oil exposure on red drum larvae. The scientists observed a 70% reduction in cardiac output in oil-exposed larvae, even at low oil concentrations. The reduction in cardiac output was proportional to the occurrence of pericardial edema, suggesting a relationship between the two variables. Oil exposure increased craniofacial deformities, spinal curvature, and pericardial edema (indicators of cardiotoxicity) in larvae. Weathering did not influence larvae’s sensitivity to oil, but the presence of micro-droplets, like those found in dispersed oil, reduced larval survival. The researchers published their findings in Science of the Total Environment: Cardiac function and survival are affected by crude oil in larval red drum, Sciaenops ocellatus.
The Deepwater Horizon oil spill occurred when many Gulf of Mexico fish species were spawning. This study provides the first definitive assessment of overall cardiac function in larval fish following oil exposure in a marine fish species native to the Gulf of Mexico. Specifically, this is the first study to measure cardiac function in a marine larval fish directly through cardiac output, which is a more complete and physiologically relevant measure of routine cardiac performance compared to indicators such as heart rate or rhythm.
The team used weathered oil collected from a Gulf of Mexico slick (June 2010) and non-weathered source oil from an approved surrogate source for Deepwater Horizon oil for high-energy water accommodated fractions (HEWAFs) exposure trials. The LC50 (concentration that kills half of the samples) and EC50 (induces a response halfway between the baseline and maximum) for all endpoints ranged from 2.2 to 21.3 ug/L. Total polycyclic aromatic hydrocarbon (PAH) concentrations observed in select coastal regions during the September 2010 spawning season ranged from 15 to 25 ng l− 1 (Allan et al., 2012). Other coastal areas maintained dissolved PAH44 concentrations of approximately 80 ng l− 1 a year after the spill (Hong et al., 2015), and concentrations in pelagic zones were as high as 85 ug/l (Bejarano et al, 2013; Diercks et al., 2010). The researchers also exposed larvae to weathered HEWAFs with micro-droplets (that contain oil components not completely dissolved) present and filtered out to assess how micro-droplets influence toxicity.
Using high-resolution imagery, researchers calculated cardiac output and documented changes in larval spinal curvature and the shape of head, jaw, and eyes. Craniofacial deformity, which may affect jaw function and feeding later in life, was as sensitive as pericardial edema to HEWAF exposure. Cardiotoxicity affected craniofacial deformities and pericardial edema more than spinal curvature. Impaired stroke volume was largely responsible for observed reductions in cardiac output.
Since the study found a relationship between cardiac output and pericardial edema (either may lead to reduced performance and mortality), the researchers recommend further research to determine if edema constrains stroke volume or if poor cardiac function triggers edema. Data from this study also have implications for land-based runoff and its effect on red drum larvae in coastal estuaries.
Data are publicly available through the Gulf of Mexico Research Initiative Information & Data Cooperative (GRIIDC) at doi:10.7266/N7H41PGC.
This research was made possible in part by a grant from the Gulf of Mexico Research Initiative (GoMRI) to the Relationship of Effects of Cardiac Outcomes in Fish for Validation of Ecological Risk (RECOVER) consortium.
The Gulf of Mexico Research Initiative (GoMRI) is a 10-year independent research program established to study the effect, and the potential associated impact, of hydrocarbon releases on the environment and public health, as well as to develop improved spill mitigation, oil detection, characterization and remediation technologies. An independent and academic 20-member Research Board makes the funding and research direction decisions to ensure the intellectual quality, effectiveness and academic independence of the GoMRI research. All research data, findings and publications will be made publicly available. The program was established through a $500 million financial commitment from BP. For more information, visit http://gulfresearchinitiative.org/.
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