zero or the LOQ to nondetectable residues had little effect on the overall outcome of the committee's calculations for benomyl. A principal reason for this finding is that a relatively high number of benomyl samples contained detectable residues. Certain impacts on exposure estimates would be seen for pesticides where a relatively low number of samples contained detectable residues.
The evaluation of short-term peak exposures is illustrated using data on aldicarb residues in potatoes and bananas. Aldicarb is an acutely toxic pesticide whose use on potatoes and bananas was voluntarily suspended by the manufacturer in 1990 and 1992, respectively. It is an N-methyl carbamate that exerts its toxic effects by inhibiting the enzyme cholinesterase in the central and peripheral nervous system and at the neuromuscular junctions. Single oral doses of 25 µg/kg bw in humans produces approximately 50% inhibition of blood cholinesterase (NRC, 1986). Inhibition above 30% is usually of concern in humans.
Aldicarb is a systemic toxicant that is used primarily as an insecticide and nematocide. It is absorbed by the roots, stems, leaves, and fruits of plants. Aldicarb sulfoxide is a toxic metabolite that is distributed throughout the plant and degrades relatively slowly. Aldicarb-treated crops commonly eaten by children include potatoes, bananas, and citrus fruits. As demonstrated in Chapter 5, infants and children consume proportionately more of these foods than do adults with the exception that infants do not eat potatoes.
In 1970 Union Carbide gave three groups of four healthy male adult volunteers doses of aldicarb at concentrations of 25, 50, or 100 µg/kg bw. Subjects given the highest dose became acutely ill; one of those who received the lowest dose developed severe mood symptoms (i.e., anxiety reaction). Whole blood cholinesterase depression was observed in all the subjects. After reviewing the results of this study, the Safe Drinking Water Committee of the National Research Council estimated a no-observed-adverse-effect level (NOAEL) of 10 µg/kg bw/day (NRC, 1986). Applying a 10-fold uncertainty factor, the EPA established an RfD, formerly an acceptable daily intake (ADI), for aldicarb at 1.0 µg/kg bw/day.
Studies in the dog demonstrate depression of plasma cholinesterase at doses as low as 1 ppm (20 µg/kg bw/day). At doses of 50 µg/kg bw/day,