Analyzing the influence of synthetic pollutants on fish populations has grown more and more relevant for researchers. Direct impacts of endocrine-disrupting chemicals like BPAs or hormones in birth control can lead to long-lasting side effects that extend far beyond the exposed generation. With intersex fish populations on the rise, birth defects and other long-term and multi-generational issues impacting generations of fish becoming more frequent, scientists at the U.S. Geological Survey were interested in seeing what synthetic chemicals precisely can have adverse effects on fish offspring up to three generations later.
“Our agency is focused on natural resource issues, including populations of fish, and as such we are concerned with fish exposure to these chemicals,” said Donald Tillitt, research toxicologist with the USGS. “There is so much we do not know, so studies like this one are intended to understand if adverse effects are even possible.”
The study’s results help illuminate the effects synthetic pollutants can have on fish populations. Synthetic pollutants like endocrine-disrupting chemicals bisphenol A (BPA) or 17a-ethinylestradiol (EE2) were examined specifically during the course of the study. Tillitt says that BPAs and EE2, the birth control hormone, were selected as target chemicals because they are easily modeled and can be measured in the environment.
The study exposed Japanese medaka fish to the chemicals during their developmental stages to make the discovery, using concentrations that are higher than those found in nature. In order to quantify the impacts observed, the researchers charted the effects on offspring, tracking things like gender reversals, fertilization rates and other reproductive abnormalities. The first week of observation was rather uneventful, but as the fish continued to be born, the researchers were able to observe the influence of the synthetic chemicals.
While the initial exposure to the chemicals did not appear to impact embryonic development, researchers did observe a significant decline in fertilization rates two generations later. The generation after that saw a drop in embryo survival rates.
“This is the first study to show transgenerational effects of these two important model EDCs (endocrine-disrupting chemicals),” said Tillitt. “These are only the initial steps in understanding if this is a real phenomenon in wild populations of fish, or other wildlife for that matter.” Tillitt continues, “Our next steps are to investigate lower concentrations to see if the same effects occur, and look into mixtures of EDCs.”
Since similar effects on offspring have been measured in mammals, the USGS researchers predicted that the same changes would be found in fish. Up next for the work is to look closer at interactions between endocrine disruptors in the natural world. The results of the USGS study reveal that adverse effects can be passed on through spawning—a phenomenon supported by a later study done at Oregon State University.
The Oregon State University study differed from the USGS study in that the team exposed the fish to extremely low levels of chemicals commonly found in waterways. The study focused on investigating the impacts of synthetic endocrine-disrupting chemicals, similar to the USGS study, which observed BPAs specifically. The chemicals the OSU study focused on can be found in a variety of products, ranging from food, toys, cosmetics, and pesticides.
Earth.com reports that the research team found that even with the lower levels of exposure, they still observed impacts of synthetic pollutants generations later. The fish were only exposed to the equivalent of a few drops of each endocrine disruptor in an Olympic-sized swimming pool, and tracked the results through DNA methylation.
The researchers found that despite never being exposed themselves, generations following the exposed group showed consistent patterns of methylation across all three generations of fish. It’s possible that these methylation patterns can influence gene expression and lead to altered sex ratios, reduced hatching, developmental defects, intersex fish and other mutations.
While both studies support that these synthetic pollutants are impacting fish populations in the long term, the gravity of these influences is still not entirely understood. As endocrine-disrupting chemicals continue to enter the waterway as waste, it will be an essential factor for conservation and restoration managers to consider in the near future.