Scientists used a fish called the inland silverside (Menidia beryllina) to show that even small amounts of man-made chemicals that are commonly found in waterways affect the genetics of the animals. The study, reported in Frontiers in Marine Science used pervasive synthetic chemicals that are known to mimic hormones (endocrine disruptors), and have been previously shown to alter sex ratios, affect the immune system, and cause abnormalities in fish reproduction. The new study showed that even low levels of endocrine disruptors can cause genetic changes that could be passed down to future generations that are never exposed to the chemicals.
"What that gets at is something your grandparents may have come into contact with in their environment can still be affecting the overall structure of your DNA in your life today," said the lead author of the report Kaley Major, a postdoctoral scholar at Oregon State University (OSU).
Researchers have known that chemical exposure can change the genome in ways that can be passed down. This research, which looked at how low levels of chemicals affected silversides, can help us learn more about how man-made chemicals in the environment are affecting animals and people.
"It's really important to understand how animals can deal with stress in the environment, particularly when we are introducing new stressors on a daily basis," said Susanne Brander, an assistant professor and aquatic toxicologist in OSU's Department of Fisheries and Wildlife. "Our research helps show what animals do to respond to these changes and how quickly they can respond to them. That's going to help us understand our impact on the environment in the long run."
In this work, the fish were exposed to an endocrine disruptor at levels that are equivalent to a few drops in an Olympic-size swimming pool. The researchers observed the fish for 21 months to examine the impacts of the chemical.
The genomic changes that it caused involve epigenetics, chemical tags that are added to the genome and can affect gene expression. One well-known epigenetic tag is methylation; a methyl group is added to the DNA molecule. Endocrine disrupters (one of the most well-known is bisphenol A or BPA, which can be found in many plastics) have been shown to alter methylation in previous work.
When they looked at the impact of low levels of these chemicals in this new report, the scientists found that methylation patterns were altered after exposure, for three generations of fish, even when the first generation was the only one exposed to endocrine disrupters, and only for a few weeks in early life.
The scientists suggested that these changes in methylation may be responsible for skewing sex ratios and causing developmental defects. More work will be needed to show exactly how that happens.