Pesticide use, while it's been tied to a decline in honeybee populations and other pollinators, now may also threaten global freshwater biodiversity, according to new research.

Specifically, it's insecticides, a type of pesticide that is used to specifically target and kill insects, that are the problem. Despite the fact that insecticide use is regulated, and cannot surpass legally-accepted regulatory threshold levels (RTLs), it appears that they are still causing problems for various ecosystems and aquatic wildlife.

Researchers at the Institute for Environmental Science of the University of Koblenz-Landau evaluated for the first time comprehensive global insecticide contamination data for agricultural surface waters. They found that in water-phase samples, with hints of insecticide concentration, more than 40 percent exceeded respective RTLs. What's more, in sediment samples, more than 80 percent of the insecticide concentrations exceeded RTLs.

"Potential reasons for these findings are failures of current risk assessment procedures or farmers' non-adherence to pesticide application prescriptions," Ralf Schulz, one of the researchers, said in a statement.

The findings suggest that the current regulatory risk assessment schemes and pesticide authorization procedures fail to protect the aquatic environment, and need to be changed. The researchers recommend improving basic global conventional agricultural systems and adopting approaches from organic farming as possible ways to both provide enough food for a growing human population, and protect global ecosystems from agricultural insecticides.

The environmental risk assessment for pesticides, which is mandatory and conducted by regulatory agencies prior to their authorization, is generally seen as an elaborate process. Not only are RTLs established for each insecticide - a threshold beyond which the ecological effects are considered unacceptable - but also farmers themselves must adhere to specific application guidelines.

For example, they cannot spray within 20 meters (66 feet) of a surface water body in order to ensure that the RTL is not exceeded in the field. (Scroll to read on...)

Normally, these rules should safeguard aquatic and terrestrial ecosystems, as well as human health, which may be negatively impacted by the use of insecticides. However, the results published in the journal Proceedings of the National Academy of Sciences suggest otherwise.

During the study, researchers looked at 28 insecticide compounds, the majority of which are currently allowed in the United States or European Union (EU). In total, they found 11,300 insecticide concentrations in more than 2,500 surface water sites located in 73 countries. And out of all the concentrations detected, more than 52 percent exceeded the RTL, in parts up to a factor of 10,000 and beyond.

And this is just in areas where insecticide levels exceed the RTL. Insecticide concentrations that equal the RTL, and are typically considered acceptable, already led to a 30 percent reduction of freshwater biodiversity.

What's more, the global situation may actually be even worse than this study indicates. Researchers only obtained data from about 10 percent of global agricultural surface waters. This means that they don't know what insecticide contamination of surface waters is like in large parts of the world - especially concerning Russia or large parts of South America.

In addition, insecticide concentrations in surface waters are very hard to detect as they occur even in highly contaminated surface waters very briefly - only during a few days per year. However, due to the high toxicity of insecticides for aquatic organisms, these short-term spurts lead to substantial and long-lasting adverse effects on aquatic communities.

And newer, increasingly used insecticides, such as pyrethroids, exceeded the RTLs by 66 percent - that's way more compared to older ones.

Even in the United States, where insecticide use is supposedly well regulated, insecticides are threatening global freshwater biodiversity. And while it has been suggested that some biodiversity loss can be reversed, nonetheless, scientists fear for the world's freshwater ecosystems.

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