Exposure of Ground-Rig Applicators to the Herbicide Bromoxynil Applied as a 1:1 Mixture of Butyrate and Octanoate

Abstract

Bromoxynil is a herbicide used extensively on the Canadian prairies for weed control in cereal production. This is a report on exposure to and absorption of bromoxynil by farmers during handling, transferring, mixing, and then applying the herbicide to cereal crops using tractor-drawn ground-rigs. The 14 individual spray operations, in which farmers applied 9 kg of bromoxynil (phenol equivalent, p.e.) to 32 ha, lasted from 113 to 549 min and involved one to five tank fills. In five of the spray operations, the farmers wore neoprene gauntlet-style protective gloves. Tractors, equipped with cabs, were used in nine spray operations.

Air sampling, hand washes, and dermal patch dosimeters served as the basis to calculate the amount of bromoxynil (p.e.) available for inhalation, deposition on the hands, and deposition under a standardized set of protective clothing. Tractors, equipped with cabs, decreased inhalation exposure by a factor of ∼ 10. Use of gauntlet-style neoprene protective gloves decreased dermal exposure to the hands region of the body by 25 times, whereas two layers of laundered cotton provided a protective effect of > 15 in the chest region.

The median value for the amount of bromoxynil (p.e.) inhaled was 0.018 μg kg BW⁻¹ kg (p.e.)⁻¹ for the 14 spray operations. The hands region of the body was the area most exposed to bromoxynil (p.e.), the median value of dermal deposition to the hands being 808 μg (p.e.) compared to 1,600 μg (p.e.) for the whole body, when protective gloves were not worn. The urinary excretion pattern of bromoxynil (p.e.) did not demonstrate an obvious maximum followed by a continuous decline to background concentrations. Instead, the amounts excreted increased over the first few days after application and then tended to remain relatively constant during the remainder of the 10-day sampling period. The median value for urinary excretion was 2.22 ng g creat⁻¹ kg BW⁻¹ kg (p.e.)⁻¹.