Toxicokinetics of Imidacloprid-Coated Wheat Seeds in Japanese Quail (Coturnix japonica) and an Evaluation of Hazard

Abstract

Birds are potentially exposed to neonicotinoid insecticides by ingestion of coated seeds during crop planting. Adult male Japanese quail were orally dosed with wheat seeds coated with an imidacloprid (IMI) formulation at either 0.9 or 2.7 mg/kg body weight (BW) (∼3 and 9% of IMI LD50 for Japanese quail, respectively) for 1 or 10 days. Quail were euthanized between 1 and 24 h postexposure to assess toxicokinetics. Analysis revealed rapid absorption (1 h) into blood and distribution to the brain, muscle, kidney, and liver. Clearance to below detection limits occurred at both dose levels and exposure durations in all tissues within 24 h. Metabolism was extensive, with 5-OH-IMI and IMI-olefin detected at greater concentrations than IMI in tissues and fecal samples. There was no lethality or overt signs of toxicity at either dose level. Furthermore, no evidence of enhanced expression of mRNA genes associated with hepatic xenobiotic metabolism, oxidative DNA damage, or alterations in concentrations of corticosterone and thyroid hormones was observed. Application of the toxicokinetic data was used to predict IMI residue levels in the liver with reasonable results for some field exposure and avian mortality events. It would appear that some affected species of birds are either consuming larger quantities of seeds or exhibit differences in ADME or sensitivity than predicted by read-across from these data.

Hummingbirds and bumble bees exposed to neonicotinoid and organophosphate insecticides in the Fraser Valley, British Columbia, Canada

“…If pesticides are metabolized similarly, detections in cloacal fluid may represent exposure in the previous several hours or less if the exposure route is primarily through nectar consumption. In quail ( Coturnix japonica), clearance of imidacloprid from plasma is rapid (with a single dose, elimination half‐lives were estimated to be 1–7 h [low dose] and 1–5 h [high dose]; Bean et al ). Imidacloprid in plasma was only detectable in 2 of 16 quail 24 h post exposure.…”

“…Concentrations per gram of feces were 1 to 2 orders of magnitude greater than concentrations per gram of tissue. Thus, it appears that imidacloprid is rapidly cleared from quail as polar metabolites (Bean et al ). This is similar to results for neonicotinoids fed to rats in which the administered doses of methylene‐ 14 C imidacloprid and imadizolidine 4,5‐ 14 C imidacloprid were rapidly absorbed (peak plasma concentrations at 1–2.5 h and 1–4 h post dosing, respectively), and 90% was eliminated within 24 h following oral exposure.…”

Sublethal and Lethal Methods to Detect Recent Imidacloprid Exposure in Birds with Application to Field Studies

“…We used similar doses to other avian studies (Lopez-Antia et al 2013;Bean et al 2019) and bracketed environmentally realistic exposure concentrations (Mineau and Palmer 2013). Our study design involved daily exposures for 7 d to mimic the availability of neonicotinoid-treated seeds to wild granivorous birds for 1 wk after planting in an agriculturally dominated landscape, followed by use of nontreated seeds for 2 wk.…”

“…Currently, specific biomarkers are not available to indirectly indicate exposure. Furthermore, neonicotinoids are rapidly excreted from the body (Bednarska et al 2013;Bean et al 2019), which may make detection of recent exposures more difficult.…”

“…For these reasons, toxicokinetics of neonicotinoids in birds has received recent attention. Japanese quail (Coturnix japonica) dosed with 3 and 9% of a median lethal dose (LD50) had rapid absorption (<1 h) of imidacloprid parent compound into blood; rapid elimination from kidney, liver, brain, and muscle within 24 h; and extensive metabolism to 5-OHimidacloprid and imidacloprid-olefin in tissues and feces (Bean et al 2019). In that study, the instrument limits of detection (LODs) for the parent compound were 0.3 ng/mL in plasma and 0.3 to 0.5 ng/g in tissues and feces, and method LODs (the quantification/reporting limit) were 1.0 ng/mL in plasma and 1.7 to 8.3 ng/g in tissue and feces.…”