| Summary: | Until the early 1970's, organochlorine (OC) insecticides were used primarily to control a wide range of pests in North America. Following several restrictions on the usage, OCs were replaced with more acutely toxic, but less persistent insecticides, primarily organophosphates and carbamates. However, many OCs, particularly DDT-related compounds, persist at high concentrations in areas of past intensive usage, such as fruit orchards. Organophosphates, such as azinphos-methyl, and fungicides, such as mancozeb, are commonly used insecticides in fruit orchards, applied alone or as tank mixtures. There are no data available on the toxicity of this common mixture or whether these currently used pesticides can have synergistic effects with DDE (a persistent metabolite of DDT). This study examined effects of DDE alone and in combination with current-use pesticides, using the Zebra finch (Taeniopygia guttata) as a laboratory model. The objectives were to determine 1) the dose-response relationship of azinphos-methyl on brain and plasma cholinesterase (ChE) activity in Zebra finches, 2) the effects of DDE, mancozeb and azinphos-methyl exposure on egg production and yolk precursor levels, and 3) the effects of DDE, mancozeb and azinphos-methyl exposure on passerine reproduction on the post-hatch period. In the first study, although, Zebra finches experienced ChE inhibition following exposure to azinphos-methyl, they appeared to be less sensitive compared to other songbird species. In addition, p,p'-DDE did not appear to affect the degree of ChE inhibition following subsequent azinphos-methyl exposure, however, it did appear to result in stimulation of the immune system. In the second study we found little evidence that dosing of breeding females with current-use pesticides, including azinphos-methyl and mancozeb, either alone or in combination with p,p'- DDE, had significant negative effects on reproductive traits (timing of laying, egg size and number, yolk precursor levels) or immune statues (percent hematocrit and leucocrit and H/L ratio) in female Zebra finches. However, birds with previous exposure to p,p'-DDE (one year prior to the start of the experiment) may be negatively impacted in terms of yolk precursor levels and immune response. In the final study, we found no evidence that dosing of adult Zebra finches with current-use pesticides, including azinphos-methyl and mancozeb, either alone or in combination with p,p'-DDE, had significant negative effects on reproductive traits or immune status in female Zebra finches. Future studies to determine potential effects of in ovo exposure to pesticides on reproduction post-fledging as well as later reproductive success would be beneficial in explaining effects of pesticides on songbirds species. In addition, the possibility of long-term exposure of p,p'-DDE on immune function should be further studied. These data are essential for developing strategies to sustain healthy songbird populations in orchards and will allow for excellent comparative data for a complimentary field study being conducted in Ontario, Canada. === Land and Food Systems, Faculty of === Graduate
|
|---|
