More wildlife are experiencing strange reproductive abnormalities, but why? In a study released last year, the U.S. Geological Survey and U.S. Fish and Wildlife Service (USFW) tested male smallmouth and largemouth bass from 19 National Wildlife Refuges. The researchers found that 85% of the smallmouth bass “had signs of female reproductive parts.” Of the largemouth bass, 27% were intersex. What could be causing this?
Luke Iwanowicz, a USGS research biologist and lead author of the paper, says:
“It is not clear what the specific cause of intersex is in these fish. This study was designed to identify locations that may warrant further investigation. Chemical analyses of fish or water samples at collection sites were not conducted, so we cannot attribute the observation of intersex to specific, known estrogenic endocrine—disrupting chemicals.”
Referencing an older study also examining examining Intersex occurrence in freshwater fishes in the U.S. between 1995 and 2004, Fred Pinkney, a USFWS contaminants biologist and study coauthor, said:
“The results of this new study show the extent of endocrine disrupting chemicals on refuge lands using bass as an indicator for exposures that may affect fish and other aquatic species. To help address this issue, the U.S. Fish and Wildlife Service encourages management actions that reduce runoff into streams, ponds and lakes — both on and off of refuge lands.”
As Pinkney mentioned, chemical runoff could be a real issue here. There are a number of chemicals and contaminants that could be contributing to these reproductive problems, including:
- Organochlorine compounds such as chlordane and dieldrin
Glyphosate and atrazine are 2 agricultural chemicals made by Monsanto and Syngenta. These widely-used chemicals leak into U.S. lakes, rivers, streams, and reservoirs. Multiple studies also show that they are endocrine disruptors that may negatively affect reproductivity. 
According to a fact sheet on atrazine from Michigan State University:
“Atrazine is used on crops such as sugarcane, corn, pineapples, sorghum, and macadamia nuts, and on evergreen tree farms and for evergreen forest regrowth. It has also been used to keep weeds from growing on both highway and railroad rights-of-way. Atrazine can be sprayed on croplands before crops start growing and after they have emerged from the soil.”
The herbicide then seeps into lakes and waterways. Some of it moves from the surface into deeper soil layers, where it contaminates the groundwater.
“Only a few reports are available that examine the health effects of atrazine in humans. Some of these reports suggest that atrazine could affect pregnant women by causing their babies to grow more slowly than normal or by causing them to give birth early. However, the women in these studies were exposed to other chemicals in addition to atrazine, so it is not known how or if atrazine may have contributed to these effects.
Atrazine has been shown to cause changes in blood hormone levels in animals that affected ovulation and the ability to reproduce. These effects are not expected to occur in humans because of specific biological differences between humans and these types of animals. Atrazine also caused liver, kidney, and heart damage in animals; it is possible that atrazine could cause these effects in humans, though this has not been examined.”
Glyphosate – the other hormone disruptor –has been found in human urine, blood, and even breast milk, as corroborated by three different studies. Although biotechnology company Monsanto refutes the evidence of glyphosate’s possible negative impact on reproduction (based on non-human studies), other studies have shown that the chemical could hamper the reproductive systems of animals, including female Jundiá, zebrafish, and rats.   
Still, some research suggests that it may not be the worst culprit:
“The primary objective of our study was to measure the stress response in juenile largemouth bass, micropterus salmoides, that were exposed to the following aquatic herbicides: diquat, endothall, 2,4-D, fluridone, and glyphosate (Rodeo).
An analysis of glucose and osmolality levels showed that the intensity and the rate of occurrence of the stress response varied with each herbicide. These differences were also associated with the concentration of the herbicide and the length of exposure. Of the five herbicides tested, glyphosate elicited the lowest stress response in the bass. This response was not related to either dose or exposure period … 2,4-D elicited the most intense stress response in the bass … The magnitude of the stress response was greater for 2,4-D than for any other herbicide tested.
The results of this study suggest that of the aquatic herbicides tested, glyphosate and endothall may be the least stressful herbicide to juvenile largemouth bass.”
The quantity of glyphosate in the environment has been difficult to analyze due to its physicochemical properties, such as its relatively low molecular weight and low organic solvent solubility.
However, an innovative study used a magnetic particle immunoassay to test for the presence of glyphosate in roughly 140 samples of groundwater from Catalonia, Spain. The analysis, published in the journal Analytical and Bioanalytical Chemistry, found that glyphosate was present “above the limit of quantification” in 41% of the samples. This indicates that “despite manufacturer’s claims, it does not break down rapidly in the environment, and is accumulating there in concerning quantities.”
Needless to say, more research is needed.
The earlier referenced study examining Intersex occurrence in freshwater fishes in the U.S. between 1995 and 2004 mentions other chemicals, though doesn’t pinpoint them as the causes:
“Total mercury, trans-nonachlor, p,p′-DDE, p,p′-DDD, and total PCBs were the most commonly detected chemical contaminants at all sites, regardless of whether intersex was observed.”
What we can probably conclude is that the presence of these endocrine disruptors in our most protected waters – those of our National Wildlife Refuges – is likely threatening wildlife, and we should take further measures to protect the animals and environment as a whole.