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.
Two complementary deoxyribonucleic acid (cDNA) clones encoding 2 different 70-kDa heat shock proteins (HSPs) were isolated from the prawn Macrobrachium rosenbergii.
Stress proteins (heat shock proteins, HSPs) have been proposed as general biomarkers for environmental monitoring. In the present study, we evaluated the environmental stress-burden on the aquatic midge Chironomus yoshimatsui using hsp70 expression. Larvae collected from streams receiving polluted runoff (field strain) were resistant to the organophosphorus insecticide, fenitrothion (F), and the synthetic pyrethroid, ethofenprox (E), whereas a strain originally collected from an unpolluted area (susceptible strain) showed low resistance to insecticide exposure. To examine the expression of an HSP70 gene in C. yoshimatsui, an hsp70 cDNA probe was prepared using RNA obtained from the field strain larvae and used for Northern blot analyses. The expression of this HSP70 gene in larvae collected from two field sites in May about 1 week after insecticide spraying in the fields was 2.3 (p = 0.018) to 3.3 fold higher than that in the susceptible strain and was also 4.6 and 1.4 (p = 0.033) fold higher than those collected in November 3 months after the cessation of insecticide spraying. In order to identify potential inducers of the HSP70 gene of the field strain, larvae of the susceptible strain were exposed to F or E for 24 h and hsp70 mRNA levels determined. Exposures to F at 0.4 microg/L and E at 1.1 microg/L increased hsp70 mRNA levels 2.7 (p = 0.049) and 4.4 (p = 0.043) fold over controls, respectively. These results suggest that larvae collected from polluted areas are burdened by environmental stressors and the tested insecticides are potential inducers of HSP70. The results also support the suggestion that HSP70 gene expression is a sensitive indicator of low level (nonlethal) exposures to certain insecticides.
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