The ecotoxicology of rodenticide use on farms
thesisposted on 15.12.2014, 10:33 by Helen J. MacVicker
The major findings of the study were as follows:;1. Rats ate significantly more coumatetralyl than brodifacoum, and rats in an area of physiological resistance (central southern England) ate greater quantities of rodenticide than rats in the east midlands. Coumatetralyl failed to achieve rat control on farms in central southern England.;2. Physiological resistance was suspected on two farms in the east midlands (near Lincoln) where rats ate excessive quantities of coumatetralyl and the control programme was unexpectedly extended.;3. GCMS analyses performed on extracts of 169 whole rodents revealed that some rats had eaten levels of coumatetralyl that far exceeded a lethal dose for susceptible animals. Excessive bait consumption occurred mostly in the area of physiological resistance, but also on the two sites in the east midlands where resistance was suspected. Brodifacoum consumption by some rats was also high, but complete control was usually achieved with brodifacoum and there was no evidence of any resistance to brodifacoum.;4. HPLC analyses carried out on 10 rats from coumatetralyl sites (five from each region), revealed that trapped, physiologically-resistant animals are capable of carrying 50 times the LD50 of coumatetralyl without any obvious ill effect. Rats from the east midlands carried a significantly lower load of coumatetralyl.;5. Video observations gave no evidence to support a bait point monopoly theory. Interactions at feeding sites were common.;6. This study has revealed that the potential exposure of non-target predators and scavengers to rodenticides is considerably higher in areas where rats show physiological resistance. This fact is discussed with reference to the regulation and monitoring of pesticides in the UK.