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Saturday, September 18, 2021

Pesticide vs bacterioplankton: Who will win the battle?

The introduction of human-made chemicals in water bodies can have adverse effects not only on the bacterioplankton community but on water ecology as a whole.

Written by Ritvik Chaturvedi | Bengaluru |
Updated: August 27, 2021 6:53:47 pm
PlanktonThe major groups of planktons are phytoplankton, zooplankton, bacterioplankton, microplankton and virioplankton. (Wikimedia Commons)

Excessive pesticide use, which eventually finds its way into water bodies from agricultural run-off, can disrupt freshwater biodiversity. A recent study in Molecular Ecology examined the impact of a herbicide and an insecticide on bacterioplankton communities in freshwater. Plankton are tiny organisms found in water and as they can’t propel themselves are transported by the currents (planktos in Greek means drifter). The major groups of planktons are phytoplankton, zooplankton, bacterioplankton, microplankton and virioplankton.

The team studied the herbicide glyphosate and the insecticide called imidacloprid. The currently acceptable safety standards for both were established after experiments on multicellular organisms, but their impact on bacterial communities has been unclear.

Anthropogenic causes

The introduction of human-made chemicals in water bodies can have adverse effects not only on the bacterioplankton community but on water ecology as a whole. Many pesticides like DDT can accumulate in the fatty tissues in fish and magnify up the food chain. Other effects include the inhibition of the reproductive systems of fish and animals or DNA damage.

Another threat to freshwater ecology is eutrophication i.e. the excessive build-up of nutrients. Eutrophication triggers algal growth on the surface of the water body, which prevents penetration of sunlight. This inhibits photosynthetic activity in the water body and creates hypoxic (depleted in oxygen conditions) for the aquatic community.

Sensitive creatures

Bacterioplankton, in particular, due to their sensitivity to many environmental variables, can be particularly vulnerable to anthropogenic disturbances. Bacterial communities provide useful ecosystem services like the decomposition of organic matter and the cycling of nutrients. These services can be impaired if microbiomes are severely affected by excessive pesticide usage.

The study was conducted using controlled simulation of the natural environment that was exposed to either or both of the aforementioned pesticides in varying quantities. The simulated environment was an array of ponds at McGill University with no prior record of agricultural pollution.

The ponds were treated with different quantities of nitrogen and phosphorus – low levels of nutrients corresponding to oligotrophic conditions and high levels to eutrophic. Each of these nutrient treatments was further introduced to different levels of either glyphosate or imidacloprid or both in varying quantities.

It was observed that:

  • • bacterial cell density increased, albeit slightly, due to glyphosate
  • • carbon substrate utilisation witnessed negligible effect with the introduction of both glyphosate and imidacloprid
  • • Glyphosate together with imidacloprid, had a very minute effect on the bacterioplankton community. Moreover, bacterioplankton communities exhibited good recovery after the first and before the second strong glyphosate dose.

Selective survival

The team noticed that the glyphosate treatment favoured only certain species of bacterioplankton, specifically those that can break down glyphosate and use it as a source of phosphorus. Imidacloprid and its interactions with nutrients, on the other hand, had little effect on the bacterioplankton community structure.

The paper further states, in keeping with the above observations, that ‘bacterioplankton communities are resilient [to glyphosate application] at broad.’

– The author is a freelance science communicator. (mail[at]ritvikc[dot]com)

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