(CN) — New toxins and chemicals entering the market are bombarding the ocean and its inhabitants on a scale never seen. So researchers have turned to stranded dolphins and whales to determine the impact of plastics and other pollutants on marine life.
These animals function as a sort of coalmine canary, signaling the health of the larger ocean ecosystem. Researchers investigated stranded cetaceans off the southeastern coast of the United States to determine how they are being affected by new sources of pollution, analyzing blubber and liver samples to discover some of the highest levels of mercury and arsenic ever recorded in stranded marine mammals.
The researchers published their findings Tuesday in the journal Frontiers in Marine Science.
Plastics and their chemical components have long been considered harmful to marine life, adversely affecting the animals’ livers, kidneys, reproductive health and causing a range of other problems. Because whales and dolphins ingest a plethora of other creatures, they are among the first animals to be negatively impacted by the effects of pollution. And since humans eat many of these same animals, they can also provide a glimpse into the dangers awaiting us on the dinner table.
"Marine mammals are ecosystem sentinels that reflect anthropogenic threats through their health — which has implications for human health as well," said lead author Annie Page-Karjian of the Harbor Branch Oceanographic Institute at Florida Atlantic University in a statement accompanying the study.
"For example, many of the species in this study prey upon fishes that are also preferred species for human consumption — so monitoring concentrations of contaminants in these animals provides a relatively low-cost snapshot of the potential exposure risk in humans, as well as other marine animals."
Dr. Page-Karjian and her team studied 11 species that washed ashore in Florida and North Carolina, including two rarer species: white beaked dolphin and Gervais’ beaked whales. In all, they evaluated concentrations of toxicants found in the tissues and pathology data of 83 stranded odontocetes between 2012 and 2018. To ensure a thorough sampling the authors looked at a wide subset of each species, including both males and females, fetal, young and adult animals, and compared the differences between groups.
Using mass spectrometry, the authors analyzed blubber samples for toxicants, and liver samples for elements such as arsenic, lead and mercury. Along with the toxin bisphenol-A — commonly called BPA — these heavy metals stood out as particularly nefarious for their effect on the animals’ immune, nervous and reproductive systems, and because these agents bioaccumulate rapidly while being slow to biodegrade. They also compared essential elements found in healthy animals to look for obvious contrasts.
Compared to pygmy sperm whales, bottlenose dolphins displayed significantly higher concentrations of lead, manganese and mercury, and lower concentrations of arsenic, cadmium and cobalt. Adult bottlenose dolphins had higher levels of lead, mercury and selenium and lower levels of manganese compared with juveniles. Dolphins stranded in Florida displayed higher concentrations of lead, mercury and selenium and lower iron levels than those stranded in North Carolina. There was no obvious pattern to be found.
The vast majority of oceanic pollution begins on land. Septic tanks, vehicles, farms and ranches all use or produce pollutants that eventually make their way into the ocean thanks to runoff. Trash produced far inland eventually makes its way into the ocean via rivers and canals. Pollution pours in from every direction, much of it outside the jurisdiction of the U.S. Environmental Protection Agency. So-called microplastics have been especially pernicious in recent years, bypassing the filters of waste treatment plants and winding up in the bellies of marine animals.
The authors could not yet directly correlate the stranding of dolphins, whales and other cetaceans with the toxicants the animals have been exposed to. But they found the effects on the animals’ behavior suspicious, and say further research is needed to determine what, if any, connection exists.
"While exposure to contaminants and toxic elements may not lead directly to stranding, such exposure is thought to impact animal survival through indirect effects on behavior, reproduction, and immunity," Page-Karjian said. "This study highlights the importance of marine mammal stranding response efforts and exemplifies why it is necessary to conduct necropsies of these animals and collect and archive tissue samples for future research. In the face of ever-growing consumer chemical industries, toxicology should be consistently integrated into standardized health assessments of free-ranging wildlife."
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