Occurrence of neonicotinoids in guttation liquid of maize – soil mobility and cross-contamination

ABSTRACT

Movement of clothianidin (CLO) and thiamethoxam (TMX) applied as maize seed dressing or pre-emergence spray application was determined in different soil types. Uptake of these neonicotinoids in plants emerging from coated or non-coated seeds was characterised via guttation liquid measurements. Applied in spray at a recommended dosage of 16.5 µmol/L, TMX and CLO occurred in the guttation liquid at peak concentrations of 1.82 and 1.63 mg/L, respectively, in plants in sandy soil and at 20–40% lower levels in plants in clay or loam soils. Peak emergence was substantially higher (above 100 mg/L) in the guttation liquid of plants emerging from neonicotinoid-coated seeds at dosages of 4.87 and 2.07 µmol per seed for CLO and TMX, respectively, strongly influenced by soil type. CLO and TMX levels in plants emerging from non-coated seeds in the proximity of neonicotinoid-coated seeds were demonstrated: cross-contamination may occur by uptake through soil from neighbouring plants. CLO appeared in the guttation liquid of plants emerging from non-coated seeds in proximity to coated ones at a peak concentration (approximately 53 mg/L) in 15 days corresponding to one-fifth of the levels in plants emerging from CLO-coated seeds; CLO concentrations gradually decreased to the same levels (6.6 ± 0.3 mg/L) after 24 days. A similar trend was observed for non-coated seeds near TMX-coated ones, with a gradual increase of TMX in 17–18 days, the levels in the guttation liquid of plants emerged from non-coated seeds (approximately 123 mg/L) corresponding to two-thirds of the levels in plants emerging from TMX-coated seeds. TMX concentrations dropped to the same levels in plants emerging from non-coated and coated seeds by day 20, and CLO occurred as a metabolite. To our knowledge, this is the first scientific record of neonicotinoid levels in guttation liquid of plants emerged from non-coated maize seeds.

KEYWORDS:

• Clothianidin
• thiamethoxam
• neonicotinoid
• guttation liquid
• cross-contamination
• soil
• spray application
• seed coating

Acknowledgement

The authors express their thanks to Zsanett Gál, Judit Juracsek, Orsolya Kereki, Csilla Magor and Klaudia Szternácsik for their technical assistance in the experiments.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Hungarian Scientific Research Fund [OTKA K109865], [OTKA K112978].