Low paraquat inhalation exposure for applicators spraying properly with knapsacks

Abstract

Four field experiments of knapsack applications with paraquat mixtures, some with oxyfluorfen, in plantain (Musa acuminata x M. balbisiana AAB) were conducted to evaluate paraquat inhalation exposure from mist for applicators, and to reduce the amount of inhalation. The first and second experiments used four adjuvant variables and four nozzle variables, respectively, with products which claimed to reduce mist. In all the analyses of applicators' respirators, paraquat was below the limit of detection (less than 0.018 mg per respirator). As a check on this low level, two more experiments comparing two nozzles to spray paraquat, plus a standard adjuvant, were conducted under slightly different field conditions. Each applicator wore his respirator to spray three plots, instead of only one as before, to give a total exposure of 55.5 L per respirator. Analyses again showed paraquat below the detection limit of 0.025 ml of spray per respirator, thus indicating that less than 0.018 mg of paraquat ion reached the inhalation zone from nozzles held 1 m below. On the basis of less than 0.018 mg of paraquat per respirator detected in these last two experiments, the inhalation exposure was less than 0.020 mg/m3. This level of paraquat inhalation exposure per applicator is well below 0.10 mg/m³, the listed limit of the National Institute for Occupational Safety and Health (NIOSH). The standard analytical procedure for paraquat di-cation was used with a few modifications, the main one was to filter extracts from used respirators to remove microparliculates. Background absorbance before color reagent addition also had to be measured for subtracting from the absorbance with reagent, thus allowing detection down to 0.018 mg of the paraquat di-cation.