Variation of pesticide concentration in sheep dips operated according to traditional and revised methods.
OBJECTIVE
To quantify stripping in traditional dipping operations and to revise dipping methods, based on prediction of stripping so that a more stable concentration of pesticide in the dipwash is achieved.


METHODS
Plunge and shower dips were operated sequentially according to traditional and revised dipping instructions. Dips were operated by continuous and intermittent replenishment. Samples of mixed dipwash were collected periodically and assayed for pesticide (diazinon) concentration.


RESULTS
Diagrammatic representations of pesticide concentration versus number of sheep dipped indicated traditional dipping leads to wide variations in the concentration of pesticide in dipwash during dipping. Intermittent replenishment led to a 'saw-tooth' pattern in the pesticide concentration. Traditional continuous replenishment (using the starting concentration of pesticide) indicated both the rate and extent of stripping was higher in shower dipping. If sufficient sheep were dipped, equilibrium was reached between the rate of pesticide replenishment and removal. An alternative method of dip operation by continuous replenishment, using a low starting concentration of pesticide and a replenishment concentration high enough to offset the pesticide loss through stripping resulted in a more stable concentration of pesticide in the dip.


CONCLUSIONS
Revision of dipping instructions can lead to exposure of sheep to stable concentrations of stripping pesticide during dipping.
Sherwood
N
N
TLC Research, New South Wales.
Watts
T
T
Allan
C
C
Chandler
D
D
D000287:Administration, Topical; D000818:Animals; D001494:Baths / Q000662:veterinary; D003976:Diazinon / Q000008:administration & dosage / Q000737:chemistry*; D007306:Insecticides / Q000008:administration & dosage / Q000737:chemistry*; D008924:Mite Infestations / Q000517:prevention & control / Q000662:veterinary*; D012756:Sheep; D012757:Sheep Diseases / Q000517:prevention & control*
D007306:Insecticides; D003976:Diazinon