Objectives

The goal of ARTF was to generate a database of generic agricultural reentry transfer coefficients (TCs) applicable to all crop/activity scenarios. ARTF was made possible by a growing recognition that TCs can be generically applied to any pesticide product, regardless of the test substance used to generate the TC. This approach is based on the principle that, for a given crop and task, the magnitude of the TC depends on the degree of contact between the worker and the crop foliage, and not on the chemical nature of the compound. However, the amount of residue that is available on leaf surfaces at a particular time after treatment (i.e., dislodgeable foliar reside or DFR) is product specific. The crop- and activity-specific transfer coefficient is used along with product-specific DFR data to conduct the risk assessments that establish appropriate REIs for each product.

The ARTF members addressed these data requirements in two parts:

1. Collectively, ARTF members used dermal and inhalation exposure data that were purchased or generated by ARTF to build a generic TC database.
2. Product-specific DFR data are being generated by each member company for their particular products. This is done by collecting leaf samples from a variety of treated crops, washing them, and measuring the residue found in the wash solution to estimate residue occurring on the leaf surfaces.

In an exposure assessment, the concentration of residue on leaf surfaces, as estimated by DFR measurements, is multiplied by a generic TC from ARTF exposure studies to yield the amount of residue that would be expected to rub off onto farm workers performing a specific task in a specific crop. With a complete set of DFR data, this can be done at any time following application with the following equation:

Exposure = DFR x TC
[mg/hour = mg/cm² x cm²/hour]

ARTF generated generic transfer coefficients through the following steps:

1. Conducting a survey of North American growers
2. Developing a reentry TC database model
3. Purchasing existing exposure studies
4. Identifying potential surrogate test compounds
5. Preparing for ARTF exposure studies
6. Conducting ARTF exposure studies