Road salt can change sex ratios in frog populations

Common road salts used to melt ice on pavements have natural chemicals which were found to have affects sex ratio in nearby frog populations. This could lead to a reduction in the size of the population and its viability. A study done by researchers at Yale School of Forestry & Environmental Studies showed that in a tadpole population exposed to the road salt which contains sodium chloride, the proportion of females were reduced by 10 percent. The data lead the team to suggest that the salt has a "masculinizing" effect. More than 22 million metric tons of road salt is applied to roads in the United States each year.

"Many scientists have studied similar effects from exposure to pharmaceuticals and pesticides, but now we're seeing it from chemicals found in common road salt and leaf litter," said Max Lambert, a doctoral student at the university and lead author of the paper.

In the experiment, the team created water tanks containing various levels of salt and maple and oak leaves. The leaves were used to mimic a natural forest environment. The researchers took the data collected from different tanks and compared them. They found that in populations surrounded by leaves and no salt, there was a females-biased ratio of 63 percent. In the salt exposed population, the ratio was reduced by 10 percent. This discovery can cause concern for the frogs because the health and abundance of females are crucial to success. They also examined the tadpole sizes in various tanks. The results showed that the developing females were consistently larger than the males in the leaf litter environment; however, when exposed to salts, the females decreased in size. A smaller female may not be able to produce as much eggs as a normally larger female. The eggs produce might also be lower in quality.

So the researchers were seeing not only fewer females but less successfully reproductive ones too. They hypothesized that it is a phenomenon caused by a mechanism known as sex reversal during development. The salts used every winter do not stay on the roads. It turns into run-off which ends up in ponds and comes in contact with the frogs in the habitat. The sodium in the salts used bind to the receptors in the cells which mimics the action of testosterone.

This gives us glimpse of anthropogenic impacts on aquatic ecosystems occurring constantly. This article also touches upon ecology and environmental suitability which are both important to understand especially now, considering the current state of our planet.