Clothianidin stunted onions and caused DNA damage in a toxicity study

Higher tested concentrations reduced onion growth and were linked to oxidative stress, genetic damage and changes in plant tissues.

Editorial illustration — not from the study.

A study of onion plants found that exposure to the insecticide clothianidin reduced germination, root growth and weight gain. The effects increased with the tested concentration, while cell division and photosynthetic pigments declined.

The exposed plants also showed more DNA and chromosome damage, signs of oxidative stress and changes to tissues including the epidermis, cortex and vascular tissue. The researchers say the results point to connected effects involving cell damage and oxidative stress.

Effects on onion plants

Clothianidin exposure produced dose-dependent effects in Allium cepa. Germination fell from 100% in the control group to 60%, root elongation declined from 9.66 to 2.45 centimeters, and weight gain dropped from 9.10 to 3.40 grams. The mitotic index, a measure of cells undergoing division, fell from 8.82% to 6.35% at the highest concentration.

Micronuclei and chromosome abnormalities became more frequent, including sticky and wandering chromosomes, chromosome fragments and uneven distribution of genetic material. Tail DNA, a measure used in the study to indicate DNA damage, increased from 3.30% in controls to 60.2% at the highest concentration.

The plants also showed biochemical signs of oxidative stress. Malondialdehyde increased from 2.13 to 10.6 micromoles per gram of fresh weight. Activity of the antioxidant enzymes superoxide dismutase and catalase also increased, from 53.1 to 125 units per milligram of fresh weight and from 0.47 to 1.17 optical-density units per minute per gram of fresh weight, respectively. Chlorophyll a fell by 60% and chlorophyll b by 68%. Tissue examinations found dose-dependent damage to epidermal and cortical cells, flattened nuclei and thickening of vascular tissue.

Why the findings matter

Clothianidin is widely used and can potentially affect plants that are not intended targets of an insecticide. In this study, the chemical affected onion growth alongside genetic material, antioxidant responses, photosynthetic pigments and tissue structure. Together, these results indicate that its effects on this plant involved more than reduced growth and support further investigation of possible risks to non-target plants.

Evidence and caveats

This was an experimental study in Allium cepa, commonly known as the onion, using clothianidin concentrations of 0.10, 0.67 and 20.0 micrograms per liter. Researchers assessed growth, cell division, chromosome changes, DNA damage, oxidative stress, photosynthetic pigments and tissue structure. The findings show effects under the tested conditions, but the abstract does not establish how these results translate to clothianidin exposure in field-grown plants or other species. It also identifies the need for further studies of the biological mechanisms involved.

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