Insecticides Cause Slow Starvation In Aquatic Organisms, Discovery Shows Limits Of Conventional Toxicity Tests

A very commonly used insecticide, imidacloprid (a neonicotinoid), has now been found by new research to be extremely toxic to aquatic organisms, often leading to their death. It’s very important to note that the “slow starvation” caused by the insecticide is undetectable by conventional toxicity tests, which are done on a much shorter time frame than the new research was. Which means that many chemicals which are now considered to be “non-toxic”, in various regards, may have effects completely undetected by the most-commonly used toxicity tests.

Image Credit: EAWAG, Swiss Federal Institute of Aquatic Science and Technology
Image Credit: EAWAG, Swiss Federal Institute of Aquatic Science and Technology

The new research looked specifically at the effects of imidacloprid on native freshwater shrimps (gammarids). The shrimps “were exposed to pulsed high and to constant low concentrations of imidacloprid. Peak concentrations typically occur when rain falls on farmland during or shortly after the application of insecticides; these soluble but persistent substances can then enter surface waters via runoff. Interestingly, pulses lasting no more than a day proved less harmful to the organisms than concentrations that were much lower but persisted for several days or weeks. While organisms transferred to clean water after pulsed exposure recovered relatively rapidly, constant exposure led to starvation after 2 to 3 weeks. This was because the organisms’ mobility and feeding behavior was impaired by the neurotoxin.”

“The slow starvation effect observed under constant exposure to low levels of neonicotinoids is not detected by conventional toxicity tests, as they are not carried out over a period of several weeks. In addition, the study indicated that seasonal and environmental factors can be crucial: the results of the experiments are significantly affected by organisms’ initial fitness and lipid reserves. To eliminate these effects and to identify processes other than starvation that influence survival rates in aquatic organisms, the research team has also developed a mathematical model which makes it possible to predict harmful concentrations and exposure times.”

Neonicotinoids are a group of widely-used insecticides that have been previously linked, by a growing body of research, to honeybee decline and colony collapse disorder.

As the press release from Eawag notes: “At the end of April, the EU imposed a 2-year ban on the use of neurotoxic agents belonging to the neonicotinoid group. In Switzerland, the Federal Office for Agriculture (FOAG) has followed suit, suspending the authorizations of three insecticides used on oilseed rape and maize fields. These measures have been taken in response to evidence that neonicotinoids are toxic to honeybees and are contributing to the decline of bee colonies.”

The new research was just published in the journal PLOS ONE.

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