Aggressive Cancer in Sea Lions Linked to Ocean Pollution and Herpesvirus Precursor, Implications for Human Health
(Beyond Pesticides, February 11, 2021) California sea lions (Zalophus californianus)Â are experiencing high rates of urogenital carcinoma (UGC) cancer incidences from the combined effect of toxic âlegacyâ pesticides like DDT and the viral infection Otarine herpesvirus-1 (OtHV1), according to a new study published inÂ Frontiers in Marine Science.Â Previous research documents the role herpesvirus infection, genotype, and organochlorine pesticides play in sea lion cancer development. However, synergism (collaboration) between viral infection and toxic chemical exposure increases cancer development odds.
Pollution of the oceans with toxic chemicals lacks adequate regulation, is widespread and only getting worse. More than 80 percent of ocean pollution comes from land-based, anthropological activities. A recent study published inÂ Annals of Public HealthÂ finds toxic chemicals from pesticides, heavy metals, plastics, and other sources readily contaminate the ocean, especially near coastal regions where chemical inputs occur in higher concentrations.
Globally, pollution has major disease implications, causing the deaths of over nine million people annually. Therefore,Â it is essential to understand the co-effects of ocean pollution and diseases to protect human health. Authors of the study state, âThis study has implications for human health, as virally associated cancer occurs in humans, and likelihood of cancer development could similarly be increased by exposure to environmental contaminants. Efforts to prevent ecosystem contamination with persistent organic pollutants must be improved to protect both wildlife and human health.â
Scientists in this study assessed cancer incidences among 394 California sea lions for 20 years. Using a stepwise regression model, scientists find herpesvirus condition, exposure to contaminants, and blubber depth aid in UGC cancer development, but not the genotype. The risk of developing UGC is nearly 44 times higher in sea lions with herpesvirus infections. Furthermore, UGC risk increases 1.48-fold per every unit of contaminant concentration within blubber.
The oceans are essential to human health and well-being, feeding billions, supporting millions of jobs, and support medicinal materials. However, environmental contaminants like pesticides have on profound impact on the ecosystem. Pesticides expose terrestrial and marine organisms to toxic compounds known to have harmful biological consequences. AÂ 2014 studyÂ finds a 45 percent decline in invertebrate species and a steep decline in various marine bird species from water contamination. Additionally, coastal and offshore aquaculture (farming of aquatic organisms) presents a new, looming threat to marine health. Namely, the use of antibiotics andÂ pesticidesÂ on local marine ecosystems (i.e.,Â insecticides to control sea liceÂ in farmed salmon) results inÂ coastal habitat lossÂ andÂ genetic and health risksÂ to wild marine populations. Marine species biodiversity is already rapidly declining due to overfishing, global warming, pathogens, and pollution. This biodiversity loss may result in changes in marine and terrestrial ecosystem function and reduce ecosystem services.
Like marine invertebrates and birds, many marine mammals demonstrate signs of chemical poisonings, especially from persistent organic pollutants (POPs) like DDT and polychlorinated biphenyls (PCBs). Studies find dolphins can harbor high concentrations of organochlorine compounds in their brain tissue. However, POPs are not the only chemicals that contaminate marine mammal species. AÂ recent study findsÂ bottlenose dolphins and pygmy sperm whales along the eastern seaboard contain high levels of triclosan, BPA, and low levels of atrazine. All three chemicals display endocrine (hormonal) disrupting properties in a range of animals, including mammals, even atÂ infinitesimally low levels. AÂ 2018 studyÂ finds detectable levels of toxic industrial byproducts like âinertâ ingredients from pesticide products in bottlenose dolphins inhabiting the Gulf of Mexico. Furthermore, there is growing concern over organophosphorus compounds in flame retardants and pesticides. According to aÂ 2018 study, marine mammals may lack the functioning of a gene that helps terrestrial animals break down certain toxic chemicals. Therefore, manatees, dolphins, and other mammals may display heightened sensitivity to pesticides, particularly neurotoxic organophosphates.
This California-based study finds cancer incidents among sea lions are the highest of all mammals, including humans, with UGC emerging in 18 to 23 percent of California sea lions. Cancer is rare in wild animals. Therefore, it is essential to recognize the drivers of disease progression and fruition. California sea lions inhabit coastal areas prone to more frequent pollution inputs. The Los Angeles coast was a dumping ground for persistent chemicals like DDT, boasting an astoundingÂ half a millionÂ barrels of DDT waste on the ocean floor. Although officials designated coastalÂ Superfund sitesâa federally designated area of hazardous wasteâfor DDT dumping, some DDT waste disposers took shortcuts by unloading barrels near the coast or puncturing floating barrels. DDT is a stable chemical, taking generations to breakdown, and readily bioaccumulating in sediment and marine organism tissues. Many scientists blame the leaking of DDT into the surrounding waters on the increase in mysterious diseases among marine species. Since humans and sea lions live in similar habitats, using the same contaminated waters for swimming and acquiring food, the prevalence of cancer has implications for human health.
The impact of chemical contamination on sea lion health, notably in conjunction with disease susceptibility, highlights the need to identify ocean pollution sources to establish regulations that mitigate adverse effects. Although now-banned DDT is an ever-persistent ocean pollution issue, other forms of ocean pollution are not as stark as direct chemical contamination. In the report, “Human Health and Ocean Pollution,” scientists find indirect chemical contamination from microplastics and runoff, in addition to the synergy among climate effects and ocean pollution, all threaten marine species’ health and ecosystem function. Microplastics can leach toxic additives into the water and absorb other toxins within the water, poisoning organisms that encounter these substances via ingestion or dermal absorption. Many of these additives have endocrine-disrupting impacts, causing reproductive and neurological dysfunction spanning generations. Pesticide runoff from agriculture or manufacturing plantsâdue to rain or improper wastewater disposalâcan deplete global fish populations as chemicals bioaccumulate up the food chain. Furthermore, this nutrient-rich runoff can increase the frequency and severity of harmful algal blooms known to have neurotoxic effects on humans and animals. However, most concerning is the threat of antimicrobial resistance and bacterial pollution. Sea surface warming from global warming and pollution are beginning to trigger poleward migration of hazardous foodborne pathogens such asÂ Vibrio vulnificus,Â responsible for 95 percent of seafood-related deaths in the United States.
According to the ocean pollution report, global chemical manufacturing is on the rise, and researchers expect manufacturing to double by 2045. However, health and environmental protections from chemical pollution and waste disposal are often insufficient, particularly in low- and middle-income countries where over 60 percent of modern chemical production resides. Since all oceans connect, and oceanic biogeochemical cycling allows substances to transverse ocean basins, these toxic chemicals will eventually spread throughout the marine environment.
Overall, authors of California sea lion study conclude, âProtecting the planet is a global concern and our collective responsibility. World leaders who recognize the gravity of ocean pollution, acknowledge its growing dangers, engage civil society, and take bold, evidence-based action to stop pollution at source will be essential for preventing ocean pollution and safeguarding our own health.â
Chemical contamination is ubiquitous in terrestrial and marine environments. Therefore, mammals and other animals can act as sentinel species for chemical contamination, detecting risk to humans by exhibiting signs of environmental threat sooner than humans in the same environment. Unless more is done to address chemical pollution, humans will also continue to see similar declines in general health, fitness, and well-being. Furthermore, climate crisis implications likeÂ melting glaciersÂ present a new concern over the high levels of chemical concentrations in the oceans from DDT, its metabolites, and other persistent organic pollutants, including PCBs and PBDEs trapped in ice. ToÂ protect the nationâs and worldâs waterwaysÂ and reduce the number of pesticides that make their way into drinking water, toxic pesticide use must end. Replacing pesticides withÂ organic, non-toxic alternativesÂ is crucial for safeguarding public health, particularly communities vulnerable to pesticide toxicity. Learn more about the hazards pesticides pose to wildlife and what you can do throughÂ Beyond Pesticidesâ wildlife program page.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.