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Photo: Allan Lasser/Massive

Fish can change their DNA in response to contamination, but it's still unclear how our bodies cope with the issue.

Bad news: Unless you live in a bubble, you are full of contaminants. Somewhat more reassuring news: every other living creature on Earth seems to share this condition with you.

Both terrifying and unifying, widespread contamination in humans and wildlife arises due to the slow and constant accumulation of chemicals in living creatures from their surrounding environment and diet, in a pathway known as bioaccumulation. Virtually everything you or any other living creature do contributes to this build-up: consumer products, food, textiles, building materials, household dust, drinking water, surface water, deep water, soil, and even air have all been found to contain multitudes of human-created chemicals. A recent study has even found microplastic fibers in municipal drinking water supplies across the country and globe.

Despite our chemical-laden lifestyles, we have almost no comprehensive idea how the accumulation of these compounds impacts living creatures, particularly wildlife, beyond acute effects. Yes, some chemicals have been shown to cause cancer or seriously mess up hormone production in humans or wildlife. But most chemicals in the environment primarily act by changing or weakening organisms' overall health in ways that don't outright kill them.

This poor understanding stems from the fact that it is difficult to pin down definitive or causal relationships between pollution and its consequences when so many other factors could be at play in complex living systems. When a human gets cancer or a bird is having trouble laying eggs, it is nearly impossible to parse out how contaminants contributed in conjunction with variables like age, genetic inclination, nutritional state, and other environmental stressors.

Yet the challenging nature of the problem hasn't dissuaded researchers from broaching it, and we are slowly starting to better understand how contaminants impact living beings. One recent study in particular helps highlight just how far we've come in understanding the sub-lethal metabolic effects contaminants have on wildlife.


The international team, led by Nishad Jayasundara of the University of Maine–Orono, focused on the mummichog, a common and well-studied fish that primarily lives in estuaries, marshes, and coastal environments. Mummichogs have long demonstrated a unique ability to adapt to polluted environments, with various lab and field research documenting genetic and physical adaptions to a variety of contaminants like heavy metals, pesticides, and other organic chemicals.

The team built upon this prior research by taking advantage of a natural experiment ongoing in the Elizabeth River along the coast of Virginia. Mummichog populations in the Elizabeth inhabit differently contaminated sub-environments within the larger river system. The team collected live fish from sites known to contain high, medium, and low levels of polyaromatic hydrocarbons (PAHs), a toxic and carcinogenic pollutant. The fish were then allowed to acclimate to environmental conditions in captivity before undergoing comprehensive evaluation.

After the acclimation period, the researchers first focused on genetics, and used previously existing work to identify genes that are different in contaminated and uncontaminated fish. They specifically looked at genes related to metabolism. From there, it was time for fish "Olympics." The researchers made the fish swim until tired while measuring their oxygen consumption, metabolic rate, swimming ability, and tolerance to increased temperatures. The results of these measurements were fed into a statistical model to extrapolate how differential fish physical fitness impacts how the fish moves and responds within its environment.

Using this multi-tiered strategy, the researchers described how pollution had cumulative effects at the levels of DNA, animal, and ecosystem. They found something surprising. Mummichogs deal with PAH exposure by changing their gene make-up.

Let that sink in a minute: Fish DNA actually changes to cope with polluted environments. This alters metabolism and energy allocation, thereby compromising the fish's ability to deal with other stressors in their environment. In this study, fish from polluted environments were less able to cope with increased temperatures; this has huge implications in a warming world where climate change is at work to increase water temperatures around the globe.

This is also troubling because mummichogs are considered extremely habitat-flexible, dealing with wide ranges in temperature and salinity. If any creature should be able to cope with thermal stress, it's these guys. Additionally, the modeling work suggested the compounded effects of altered genes, metabolism, and coping ability translates to fish being less capable of finding and traveling to an optimal environment, meaning contaminant exposure has the potential to alter the very way fish interact with the surrounding environment.


But what about all the wildlife that's bigger than the size of a finger? How do contaminants sub-lethally impact cats, pigs, sharks, weasels, deer, or seabirds? Unfortunately, when larger creatures are factored into the conversation, we are reminded that we understand close to zilch when it comes to sub-lethal impacts of contaminants in wildlife.

A recent study focusing on Arctic seabirds embodies such existing gaps and highlights how tough it is to figure out how contaminants are undermining wildlife processes and function. Few studies have tackled contaminant impacts on metabolism in birds, thanks to how hard it is to compare features of very different species, as well as the fact that studying live creatures in the wild is much harder than analyzing samples. Those that have forged ahead looking at bird hormone production and metabolism have seen conflicting results.

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