29
Aug
Ocean Mammals Genetically Vulnerable to Certain Pesticides
(Beyond Pesticides, August 29, 2018) As pesticides drain from agricultural fields, they can poison waterways and coastal areas and harm wildlife. Now, a study finds that a gene that helps terrestrial mammals break down certain toxic chemicals appears to be faulty in marine mammals — potentially leaving manatees, dolphins and other warm-blooded aquatic life more sensitive to toxic pesticides, especially organophosphates.
As marine mammals evolved to make water their primary habitat, they lost the ability to make a protein that has the effect of defending humans and other land-dwelling mammals from the neurotoxic effects of certain pesticides. The gene, PON1, carries instructions for making a protein that interacts with fatty acids ingested with food. But that protein has taken on another role in recent decades: breaking down toxic chemicals found in a popular class of pesticides – organophosphates. An inspection of the genetic instructions of 53 land mammal species in the study, “Ancient convergent losses of Paraoxonase 1 yield potential risks for modern marine mammals,” found the gene intact. But in six marine mammal species, Paraoxonase 1 (PON1) was riddled with mutations that made it useless. The gene became defunct about 64 million to 21 million years ago, possibly due to dietary or behavioral changes related to marine mammal ancestors’ move from land to sea, the researchers say. However, PON1 is the primary mammalian defense against organophosphorus toxicity. Marine mammals may be at a great disadvantage if run-off of these agricultural products into the marine environment continues.
Further, the researchers also gauged the rate at which two organophosphate chemicals — chlorpyrifos-oxon and diazoxon — broke down in blood samples from five land mammal species and six marine or semiaquatic mammal species. While blood from the terrestrial species, including sheep, goats, and ferrets show a decrease in toxic molecules over time, the marine species’ blood show almost no change. Mice genetically engineered to lack the gene could not break down the chemicals either.
“The big question is, why did they lose function at PON1 in the first place?” said lead author Wynn K. Meyer, Ph.D. “It’s hard to tell whether it was no longer necessary or whether it was preventing them from adapting to a marine environment. We know that ancient marine environments didn’t have organophosphate pesticides, so we think the loss might instead be related to PON1’s role in responding to the extreme oxidative stress generated by long periods of diving and rapid resurfacing. If we can figure out why these species don’t have functional PON1, we might learn more about the function of PON1 in human health, while also uncovering potential clues to help protect marine mammals most at risk.”
The implications of this discovery lead these researchers to call for monitoring our waterways to learn more about the impact of pesticides and agricultural run-off on marine mammals. Current real-world consequences of losing function at PON1, the researchers explain in their study, are, like in Florida, where “agricultural use of organophosphate pesticides is common and runoff can drain into manatee habitats. In Brevard County, where 70 percent of Atlantic Coast manatees are estimated to migrate or seasonally reside, agricultural lands frequently abut manatee protection zones and waterways.”
The researchers believe the next step is to launch a study that directly observes marine mammals during and shortly after periods of excess agricultural organophosphate run-off. Such a project would require increased monitoring of marine mammal habitats, as well as testing of tissues from deceased marine mammals for evidence of organophosphate exposure.
“Marine mammals, such as manatees or bottlenose dolphins, are sentinel species — the canary in the coal mine,” said senior author Nathan L. Clark, Ph.D., associate professor in Pitt’s Department of Computational and Systems Biology, and the Pittsburgh Center for Evolutionary Biology and Medicine. “If you follow their health, it will tell you a lot about potential environmental issues that could eventually affect humans.”
See Beyond Pesticides’ webpage Impact of Pesticides on Wildlife.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
For more information on the impacts of pesticides on marine and other wildlife, visit our Wildlife page
Source: ScienceNews
