Field fortification procedures

Field fortification (commonly referred to as field spiking) is the procedure used to prepare study sample matrices to which have been added a known amount of the active ingredient of the test product. The purpose for having field fortification samples available in a worker exposure study is to provide some idea of what happens to the test chemical under the exact environmental field conditions which the worker experiences and to determine the field storage stability of the test substance on or in the field matrix materials. Field fortifications do not serve the purpose of making precise decisions about the chemical, which can better be tested in a controlled laboratory environment. The researcher should not assume that a field fortification sample by its nature provides 100% recovery of the active ingredient at all times. For example, a field fortification sample by its very nature may be prone to cross-contamination of the sample from environmental contaminants expected or not expected to be present at the field site. 

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. 

When fortifying air tubes or air filters, the use of the formulated active ingredient in water is not recommended since the material on the air tube or filter must dry before air is drawn over the matrix. If the field fortification is nol dry on tiie sorbenf or air filter, breakthrough of the fortification solution may occur through the air filter or air tube into the back portion of the air tube and invalidate the procedure. 

One alternative method for preparing field fortifications solutions/suspensions is to prepare each fortification sample of each matrix in a separate mini-vial in the analytical laboratory and ship the vials to the field for use. This procedure precludes the use of pipets in the field and may be useful when Field Scientists not experienced in the use of pipets are involved in the field fortification process. One disadvantage of this procedure is that the mini-vials, if not designed correctly, will be hard to handle in the field, and surface tension of the suspension or fortification solution will tend to leave unacceptable amounts of the solution/suspension in the vial or at the lip of the vial and not on the matrix in question. This procedure may lead to cross-contamination of samples as the field fortification liquid is forced from the top... 

Travel fortification samples are a type of field fortification that is usually prepared in the fleld to allow the investigator to determine the stability of the active ingredient on matrices without weathering. Such matrices are fortified and placed immediately in frozen storage. Usually, one set of travel fortification samples for each matrix is prepared for each five sets of weathered fleld fortification samples. The samples are then stored and shipped using the same procedures as all other samples prepared in the fleld. 

Fortifying laboratory water samples approaches actually recovering field samples if a pesticide is completely dissolved and not associated with suspended matter and the other water quality characteristics are similar to natural water (pH, T, ionic strength). In another approach natural water characteristics are altered to laboratory fortification specification to obtain maximum efficiency and to be able to standardize extraction procedures. DiflEerent standardization procedures are needed for samples from diflEerent water environments—e.g., a river water with high turbidity, a clear stream, sea water, or organically polluted lake water. Many different water quality parameters (Table II) and solvents (Table I) are possible to standardize and quantitate LLE. The best choice should be defined for each water type. 

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