Re-entry exposure

One of the first items of importance when attempting to select an agricultural site at which to perform a worker exposure/re-entry study is to review the label on the product. Such a review will reveal the areas where the product is to be used and the conditions under which the product is to be applied. One should look for whether a product is to be applied by ground or air and if there are any restrictions as to the locations where the product is to be used. One must also pay attention to label directions concerning types of soil where the product is to be used since this could affect rates of use. 

When planning a worker exposure/re-entry study, the number of sites selected should reflect the use pattern of the product. Usually three different sites, each in a different geographical location, are recommended to ensure good representation of the areas when the product has wide use. The different geographical locations offer the researcher diversity in equipment used to treat the crops as well as diversity in the work habits of the individuals in the study. 

The field laboratory set up by the field research group is a key element to completing successful worker exposure/re-entry research. The field laboratory may be set up in close proximity to the treated field, but should be located at a reasonable distance from the treated area to avoid cross-contamination of field samples and field controls. 

Portable weather stations are useful to have available at the field laboratory for acquiring weather data during the course of the worker exposure/re-entry study. There are a variety of portable weather stations available from a variety of suppliers. Weather data to be collected are rainfall, wind direction, wind speed, air temperature, and relative humidity. These electronic weather stations will record the necessary weather parameters on a routine basis. The data are stored and can be transferred to a laptop computer or disk as desired by the Field Scientist. Such portable electronic weather stations are useful during the course of the dislodgeable residue portion of a worker re-entry study when dislodgeable residue samples are taken from remote test sites over the course of a 30-day period. 

All equipment to be used at the field site should be calibrated at or near the field laboratory or field site prior to the application of the test substance (pesticide product). Most weather equipment will have been calibrated at the manufacturer and can be checked for functionality prior to the worker exposure/re-entry test by comparing weather readings from the nearest airport or National Oceanic and Atmospheric Administration (NOAA) weather reporting station with the weather readings compiled by the portable weather station. Hand-held weather instmments could also be checked with current weather reading from local airports or NOAA facilities. 

Meeting and selecting the volunteers for a worker exposure/re-entry... 

Volunteers for a worker exposure or re-entry study should be selected with care and with confidentiality. The volunteer s privacy and also respect for the volunteer should be kept in mind during the field phase of the study. With all worker exposure/re-entry studies, the worker volunteer is the key to a successful study. 

Execution of the field portion of the worker exposure/re-entry study... 

Field techniques for performing worker exposure/re-entry research direct measurement of exposure... 

In addition, the use of field fortification samples measures the carefulness factor of the Field Scientist during the field research and allows a Study Director/Manager or distant observer to obtain a quality control estimate on the field portion of the study. For this reason, the field fortification samples are usually meant to be different from laboratory procedural fortifications and are meant to be prepared under field conditions, which are considerably more rigorous than are controlled laboratory conditions. For example, environmental factors such as heat, humidity, wind, human stress, and other human factors such as fatigue to the Field Scientist are an integral part of any field worker exposure/re-entry study. Field fortifications made to matrices under these conditions will test and readily demonstrate the ability of the Field Scientist to perform such a difficult study under trying circumstances. 

The preparation, maintenance, and integrity of field fortification solutions during a worker exposure/re-entry field study are of the utmost importance in maintaining the integrity of such a study. 

USEPA, Adams, J.D. (1984). Pesticide Assessment Guidelines, Subdivision K, Exposure Re-entry Protection, Report No. 540/9-84-001, Washington, DC, USA. 

Dislodgeable soil residue (DSR) studies are used to determine exposure of re-entry workers to soil surface residues. Soil surface residues are defined as test substance residue levels in <150-q.m soil particles (i.e. soil dust which can stick to a worker s skin, or can be inhaled). 

To calculate the safe re-entry interval (REI), the margin of exposure (MOE) must be considered. Worker risk is measured as a margin of exposure and is related to how closely the occupational exposure comes to the no observed adverse effect level (NOAEL, for oxamyl 50 mg kg day ). MOE is defined as... 

Using the nonlinear model substituting 0.915 p.gcm (the DFR value from the model 1 day after application) into Equation (6) yields a dose of 1.05 mgkg day" and an MOL from Equation (5) of 47, below the required value of 100 for margin of exposure. Performing the same calculation on the day 2 data gives a dose of 0.344 mg kg day and an MOE of 145, which is above the level of 100 required to establish a safe re-entry level. Therefore, a 2-day period is adequate to ensure worker safety. The observed values of 0.936 and 0.234 qg cm for days 1 and 2 match closely the values predicted by the model. 

Field methods for performing farm worker exposure and re-entry studies... 

Among the first dermal dosimeters used in exposure research were 4 x 4-in cellulose or gauze patches which were pinned to the outer and inner surfaces of clothing or vests which farm workers would wear during the application or re-entry phase of the smdy. These patches were easy to manufacture and when pinned to the shirt or pants of the worker made for an easily used dosimeter pad. The major advantage to the use of the patch to estimate worker exposure was this method s ability to differentiate the relative contributions of pesticide residues to different parts of the worker s body. This sampling technique in turn could lead to recommendations (i.e., the use of... 

Based on the patch method to assess worker or re-entry exposure, researchers have developed a database, which may be used to estimate exposure. Each patch from an individual in a study can be entered into the database separately, the residue data from patches from various body areas can be summed to yield a whole-body exposure number, and the data may be sorted as to worker tasks, equipment used, protective clothing worn, formulation types and other parameters. This is the basis for the currently used Pesticide Handlers Data Base (PHED), which was developed through a joint effort in the 1980s of CropLife America [formerly known as American Crop Protection Association (ACPA) and National Agricultural Chemicals Association (NACA)], the Environmental Protection Agency (ERA) and Health Canada. " The PHED is discussed in detail in another article in this book. 

The purpose of this article is to present a detailed description of the current field methods for collection of samples while measuring exposure of pesticides to farm workers. These current field methods encompass detailed descriptions of the methods for measuring respiratory and also dermal exposure for workers who handle the pesticide products directly (mixer-loaders and applicators) and for re-entry workers who are exposed to pesticide dislodgeable residues when re-entering treated crops. 

Current field methods for measuring mixer-loader and re-entry worker exposure to pesticide residues... 

Preparing a detailed protocol according to GLP standards may be useful for researchers planning a worker exposure or re-entry study, even though the study may never be submitted to the EPA to support the registration of a pesticide product. Having a detailed protocol helps to solidify one s plans for the study, and assists in the documentation phase of the study. This documentation phase will be addressed in some detail later. 

One of the most important aspects of designing a successful worker exposure or re-entry study is the selection of the agricultural site at which to perform the study. One must first define the growing region in which the pesticide is to be used to the widest extent possible. This is important since this region would have the most farms, farmers, commercial applicators, or re-entry workers which would have work habits, equipment, and land, which would best represent the use of the product. 

The other type of site, which is less commonly used for worker exposure and/or re-entry studies, may be found on a research farm. These research farm facilities may... 

In addition, there are hand-held psychrometers for measuring air temperature and relative humidity available, and also hand-held wind meters, which measure wind speed. When using such hand-held equipment, readings should be taken each hour during the course of the day when worker exposure volunteers or re-entry worker volunteers are performing the test. 

The test substance may be acquired in a number of ways. One common method is to purchase the product from a chemical dealer. This method of acquiring the test substance for a worker exposure or re-entry study allows one to proceed rapidly with the execution of the field portion of the study without the serious delays encountered while waiting for a test substance to be manufactured, assayed, and shipped to the site. Although having a test substance formulation which has been assayed under GLP standards and for which a certificate of analysis has been shipped to the test site is desirable, there are several instances when this is not practical. For example, one may encounter a worker exposure study where the pesticide to be evaluated is sold only in mini-bulk or even large bulk quantities holding as much as 2000 gal. In this case, duplicate 5-10-g or 5-10-mL retainer samples should be taken from the bulk or mini-bulk tanks for assay after the worker exposure study is in progress. 

In many instances under GLP, the test substance may be manufactured and assayed for the specific purpose of use in a worker exposure or re-entry study. This is normally done when the amounts of the product to be used are relatively small, and the product is not sold in bulk. In this case, a certificate of analysis should be obtained prior to the initiation of the field portion of the smdy. In this case, the manufacturer should retain some of the material for periodic reassay to meet GLP requirements. 

The test substance should be stored in a locked facility at or near the test site. Most pesticide products are manufactured to withstand extreme temperatures, therefore most test substances used for re-entry and worker exposure studies may be stored under ambient conditions. One should read the label of the product carefully to discern if there are any extraordinary storage conditions required for the pesticide product. Temperatures at the test substance storage location should be monitored daily using a max/min thermometer or similar device that can record daily fluctuations of temperatures. 

The consent form is a document to be used to acquire the consent of worker volunteers to become a part of a worker exposure study or re-entry exposure study and is an integral part of ensuring the ethical integrity of the research project. This form is normally in English but should be translated into Spanish or any other language... 

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