While pesticides applied to seeds and crops are intended to protect them from hungry animals, pesky insects or even microbial infections, they also affect other vital organisms, including bees and earthworms.
A study published in Letters on Environmental Science and Technology from ACS shows that worms are affected by relatively small amounts of chemicals that can leach from pesticide-treated seeds. Exposure to nonlethal amounts of these insecticides and fungicides resulted in modest weight gain and damage to the worms’ mitochondrial DNA (mtDNA).
Pesticide treatment can be introduced at different stages of a plant’s life, be it covering seeds before sowing or spraying already grown plants. Different chemicals are often applied simultaneously to maximize their effectiveness.
Neonicotinoids, also called neonics, are a common class of insecticides used today in the United States and other countries, although many of them are banned in the European Union. Recent research has shown that pesticides used on seeds and crops remain in groundwater and soil where worms can encounter them.
One way to monitor the health of affected worms is through weight changes and mtDNA damage. Unlike the DNA contained in the cell nucleus, mtDNA is not as good at repairing itself and therefore may help indicate less obvious “off” effects of a particular environmental toxin. Chensheng (Alex) Lu and his colleagues wanted to use this approach to investigate how realistic amounts and combinations of neonics and the fungicide difenoconazole (DIF) affect earthworms.
Laboratory experiments to evaluate pesticides used on seeds
In laboratory experiments, the team exposed a group of young earthworms (Eisenia fetida) to pesticides individually and combinations of neonics and DIF, at concentrations that mimic the residues pesticides leave on seeds
After 30 days, the worms were weighed and their mtDNA was examined for damage. While all worms survived, earthworms in soil treated with a single pesticide gained 30 to 80% less weight during this period than a control group living in untreated soil.
Additionally, worms simultaneously exposed to one of the four neonicotinoids tested and DIF gained significantly less weight than those exposed to just one compound. Pesticide exposure also led to a significant increase in mtDNA damage. Because mitochondria generate most of the energy in cells, damage to their DNA could disrupt cellular functions and other metabolic processes.
The researchers say these results provide a link between neonics and fungicide mixtures likely present in the environment and earthworm health, which may indicate unexpected risks of using pesticides on seeds.
The authors thank the National Natural Science Foundation of China for funding.
The abstract of the article is available here: http://pubs.acs.org/doi/abs/10.1021/acs.estlett.3c00914
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