Effects of field exposure to diazinon on small mammals inhabiting a semienclosed prairie grassland ecosystem. I. Ecological and reproductive effects

Abstract

Abstract-The widespread use of cholinesterase-inhibiting pesticides in the environment presents increasing concerns about their effects on human, wildlife, and ecosystem health. As a group, these pesticides are generally highly toxic and have great potential for negatively affecting nontarget organisms. Small mammals have proven to be ideal biomonitors of environmental contaminants, and were used here to test for possible effects of a widely used cholinesterase-inhibiting insecticide, diazinon, in a natural field setting. Using 12 0.1-ha terrestrial mesocosms, we examined the effects of low-level diazinon exposure on the small mammal communities inhabiting semienclosed grassland ecosystems. Our primary objective was to test the hypothesis that diazinon, applied at two different recommended label application rates, would not cause any observable adverse ecological or reproductive effects on small mammal populations and communities. Experimental small mammal communities consisting of Sigmodon hispidus, Microtus ochrogaster, Reithrodontomys fulvescens, and Mus musculus were stocked at natural densities and sex ratios inside empty mesocosms. Diazinon 4E was applied at two different maximum recommended label application rates, 0.56 kg a.i./ha (1ϫ) and 4.5 kg a.i./ha (8ϫ), and controls remained unsprayed, with four enclosures (replicates) per treatment. Two 30-d trials were run during peak rodent breeding seasons and enclosures were sampled on days 2, 16, and 30 of each trial. Recovery of small mammals was not significantly different among treatments, although fewer animals were recovered from the diazinon-exposed enclosures in both trials. Analysis of trapping data suggested that the normally strong competitive relationship between Sigmodon and Microtus may be altered by the pesticide, favoring Microtus in the diazinon-exposed enclosures. Incidence of reproductive condition was found to be reduced 20 to 80% and 33 to 100% in diazinon-exposed males and females, respectively. Reproductive productivity, including percentage of pregnant females and of females giving birth, was significantly reduced in diazinon-exposed animals. Percentage of pregnant females ranged from 13.6 to 43.5% in diazinon-exposed animals compared to 40 to 80% for control animals, and percentage of females giving birth ranged from 0 to 17% in diazinon-exposed animals compared to 22 to 50% for control animals. Generally, the effects found in this study suggest that diazinon was relatively persistent in the sprayed enclosures and that oral routes of exposure (consumption of dead and dying arthropods, grooming) may have been important. Ecological relationships and reproduction in both herbivorous and omnivorous mammals were negatively impacted by diazinon exposure. Overall, ecological relationships in the enclosed prairie grassland ecosystem were disrupted by diazinon, probably through a combination of sublethal effects, particularly reproductive effects, impacting individuals and their populations. This suggests that negative impacts on populations and...

Outcomes of Schistosoma mansoni infection in outbred albino mice exposed to Larvin contaminant

“…Mice have proven to be ideal biomonitors of environmental contaminants (Sheffield and Lochmiller 2001) and were used here to test for possible effects of Larvin in an experimental setting. Findings of this study indicate that the development of adverse metabolic or histologic changes in the liver and spleen of healthy mice and in mice exposed to S. mansoni…”

A Review and Analysis of Study Endpoints Relevant to the Assessment of “Long Term” Pesticide Toxicity in Avian and Mammalian Wildlife

“…There was some appearance of reduced recruitment with some (but not all) of the higher treatment levels but no apparent decline in the proportion of females in reproductive conditionalthough the statistical power for that aspect of the work was low. Also, follow up studies in the same enclosures (but planted to denser vegetation) failed to show ay response at levels that had caused significant declines previously (reviewed in Sheffield and Lochmiller, 2001).…”

“…Another experiment with diazinon and four small mammal species (Sheffield and Lochmiller, 2001) demonstrated clearer reproductive effects although there was no evidence of adult mortality. Endpoints affected by treatment were field indices of reproductive competence (e.g.…”

“…capture of pregnant individuals, evidence of lactation, placental scars, etc. Several studies have attempted to link changes in small mammal age ratios with pesticide use but the results of many of these studies are often confounded by a failure to control for movements of adults and juveniles in and out of the treated area (see Sheffield and Lochmiller, 2001 for a review).…”

Ecological Impacts of Insecticides

“…For example, experimental prairie grasslands treated with diazinon reduced the reproductive capacity of the omnivorous cotton rat (Sigmodon hispidus) by 33-100% as it fed on contaminated arthropods, but did not affect herbivorous voles (Sheffield and Lochmiller 2001). Sublethal effects are normally detected after many years of observations that show declining trends in www.intechopen.com the population of some species.…”