As many of you may already know, amphibians are generally regarded as interpretive bio-indicators due to their sensitivity to environmental degradation. When a local ecosystem is disrupted, amphibians are usually the first to sense the effects and will experience abnormalities such as genetic malformations, growth/developmental deformities and as this article highlights, reproductive/sexual trait alterations. “Feminization of male frogs in the wild” paints an alarming picture that highlights important concerns regarding the inadvertent damage we cause to the ecosystem while pursuing our never-ending quest to sustain the growing population. It specifically discusses the use of the herbicide atrazine and the detrimental effects it causes to local wildlife, specifically aquatic phase amphibians. The entirety of this research study is focused on specific frog species and what happens to them during morphological events when exposed to varying concentrations of atrazine. The results conclusively show that frogs are being negatively affected by our agricultural endeavors and that this environmental issue needs to be addressed sooner rather than later.
The paper summarizes data obtained from two different sources; laboratory experiments and field studies. For the lab research, larvae of the wild leopard frog (Rana pipiens) were subjected to differing levels (0, 0.1 or 25 parts-per-billion; ppb) of atrazine by immersing in a controlled, aquatic environment. Constant exposure to the herbicide was maintained from the point of hatching until just after tail reabsorption was complete. They reported that only exposed males underwent testicular oogenesis (hermaphroditism); 29% for 0.1 ppb exposure and 8% at 25 ppb levels. Retarded gonadal development (gonadal dysgenesis) was also seen in these groups; 36% at 0.1 ppb exposure and 12% for 25 ppb levels. For field study research, the group first determined which locations could potentially be contaminated with atrazine based off of local product sales. They considered heavy agricultural regions such as Nebraska, Nevada and Iowa to be likely sites of contamination and focused their efforts in these areas. Aiming to maintain experimental consistency, they again chose the wild leopard frog to observe and document any morphological changes. They found that every site with atrazine sales exceeding 0.4 kg/km² and with water-borne atrazine contamination above 0.2 ppb, contained male frogs with testicular oocytes.
One theory about the chemistry behind why sexual differentiation happens revolves around the fact that atrazine induces aromatase, an enzyme responsible for converting androgens into oestrogens. Based on this logic, scientists assume that increased levels of estrogen in male frogs are responsible for the observed sex changes to female. This reasoning relieves atrazine’s direct accountability from affecting sexual alterations yet confirms its responsibility for causing these changes indirectly.
Since the assigned paper proved to be a very brief summary of a legitimate environmental health concern, I sought out more information to further the discussion. This led me to a 2016 study published by the EPA (https://www.regulations.gov/document?D=EPA-HQ-OPP-2013-0266-0315 (Links to an external site.)Links to an external site.) that focused on in-depth research efforts to provide an assessment of ALL ecological risks from atrazine. Of relevance to the topic at hand are the following pages; 23 is a brief background on the usage of atrazine, 30 details health risks to aquatic phase amphibians following exposure, 34 is a US geographical map of atrazine distribution, 39 describes the timing of applications, 63 is a summary of physical and chemical properties, and lastly pages 174-178 provide an in-depth analysis of the toxicological effects that atrazine poses to amphibians. Since this is a discussion forum, I invite everyone to check out the mentioned pages if you need some topic starting points. In addition, I’ve posted a few of my own thoughts, listed below.
1) Any speculation as to why more sexual abnormalities seen at lower exposure levels?? One could assume the opposite to be true but based on the assigned paper’s results, this does not appear to be the case.
2) Acute versus chronic exposure; does continual atrazine exposure increase the likelihood of developing and adaptive resistance? And could that adaptation be passed on to offspring??
3) If most water sources (including rain) in the US contain more than the effective does of atrazine, then why aren’t ALL frogs female?? This data suggests that exposure levels are high over the entire country so why are sexual alterations limited to just agricultural areas?
Hayes, Tyrone, et al. “Herbicides: Feminization of Male Frogs in the Wild.” Nature, vol. 419, no. 6910, 2002, pp. 895–896., doi:10.1038/419895a.
Farruggia, Frank. “Refined Ecological Risk Assessment for Atrazine.” EPA.gov, 12 Apr. 2016, https://www.regulations.gov/document?D=EPA-HQ-OPP-2013-0266-0315 (Links to an external site.)Links to an external site..