In this post, Jennifer Freeman, a professor of toxicology in the College of Health and Human Sciences and a member of the Purdue Institute for a Sustainable Future, discusses her recently published research “Adverse developmental impacts in progeny of zebrafish exposed to the agricultural herbicide atrazine during embryogenesis,” which appears in Environment International, with the support of the National Institutes of Health, National Institute of Environmental Health Sciences, and the National Center for Advancing Translational Sciences.
What did you want to know?
Atrazine is an herbicide routinely used in corn fields in the Midwestern US and other areas around the world. We know that wherever atrazine is applied on crop fields there is an increased risk for this herbicide to contaminate drinking water supplies. Given unknowns surrounding potential for adverse health impacts of exposure and likelihood of exposure through drinking water sources the European Union banned atrazine. The US EPA regulates atrazine in drinking water at a concentration of 3 parts per billion (ppb) and recognizes that atrazine can change hormonal signaling known as endocrine disruption in the brain that can impact multiple biological systems including developmental processes. Currently the US EPA concludes that the regulatory level in drinking water is sufficient to not present harm, but this finding is controversial and every few years research data is reviewed to address questions related to atrazine and safe levels of exposure. In this study we used a well-recognized animal model for biomedical research, the zebrafish, to determine if developmental parameters would be altered in offspring of atrazine exposed fish. The parental fish were only exposed to atrazine during their early development (embryogenesis). They were raised in normal conditions with no additional chemical exposure except the developmental atrazine exposure and bred to produce offspring. The offspring were not directly exposed to the herbicide.
What did you achieve?
Our exposure concentrations encompassed those around the current US EPA regulatory levels in drinking water including 0.3, 3, and 30 ppb plus a control condition with no atrazine treatment. First, we completed a proteomics assessment, where we identified how the parental atrazine exposure altered protein expression of their larval offspring. We found protein changes were associated with neurological development and disease and organ and organismal morphology, development, and injury. Specifically, we identified changes in proteins associated with the skeletal and muscular systems. Based on these results, we measured various morphological and growth-related parameters. We found head length and ratio of head length to total length was increased indicating a larger head size in offspring of atrazine exposed parents. In addition, we observed changes related to delays in bone and skeletal formation in the head and face. We coupled these findings to behavioral assays where larvae from atrazine exposed parents were hyperactive and had a decreased response to an acoustic startle. The weakened response to the acoustic startle was aligned to a specific change in saccular otoliths, which are structures important in hearing.
What is the impact of this research?
There are current questions regarding potential adverse developmental impacts associated with atrazine exposure. We took that question one step further by addressing alterations in offspring that were not directly exposed to atrazine but instead had parents that were exposed only during their early developmental phase. Development of cranioskeletal structures and the acoustic startle behavior response is similar in vertebrates allowing for comparison of our findings in the zebrafish to questions on the potential impacts in humans with atrazine exposure. The disruptions we observed in these developmental structures and behavior are similar to what has been observed in other organisms including chicks, frogs, and rodents. This is important as usually the more species showing a similar outcome builds confidence that a similar effect may also occur in humans. Overall, the current study agrees with past studies in humans, rodents, and other organisms that developmental atrazine exposures at or around the current regulatory concentration in US drinking water of 3 ppb and well below that of the World Health Organization at 100 ppb is sufficient to alter growth parameters and behavior, warranting continued assessment to better understand the health risks of these observations. It should also be noted that the regulatory levels are monitored for those with homes on public drinking water supplies but does not account for households attaining their drinking water from a private well and are at risk of contamination if homes are in areas where atrazine is applied on agricultural fields.