Biological monitoring of 2,4-dichlorophenoxyacetic acid-exposed workers in agriculture and forestry

This is a report on the application of a radioimmunossay (RIA) for the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) in biological monitoring of occupationally exposed sprayers. Urinalysis was conducted on two workers involved in spraying 2,4-D sodium salt solution with car mounted ground rigs in agriculture and on the pilot and the mixer-loader of a helicopter crew applying 2,4-D dimethylamine salt for brush control in forestry. All sprayers showed detectable quantitities of 2,4-D in morning urine samples voided over 4 or 6 days in the post-spraying period. The highest 2,4-D urinary concentrations of about 2.5 ppm could be measured in a car driver on the 3 day after exposure. The 2,4-D level in urine was much lower in forestry workers, with 0.365 ppm for the mixer-loader and 0.052 ppm for the pilot on the 1 day after spraying. Urinary 2,4-D concentrations in the agricultural study were adjusted for endogenous creatinine and, when normalized for body weight, resulted in a total 2,4-D uptake of about 5.7 or 84.9 μ/kg body wt. for a single spraying operation. Thus, the calculated absorbed dose was less than the NOAEL (no observed adverse effect level) of 10 mg/kg body weight per day by a large margin of safety. Further, the calculated amounts excreted seemed to be sufficiently reliable to be used for assessing the risk of human exposure to 2,4-D. However, more studies are desirable for confirmation of the association of urinary 2,4-D and creatinine excretion. Clearance occurs with a 12-h to 22-h half-life.