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Dye concentrations are expressed in ppb. Although the dye concentration in water samples expressed in ppb is an accurate quantitative measurement of the amount of dye in the
stream at the time the sample was collected, the same is not true for the eluted charcoal samples. It is only semi-quantitative compared with the actual quantity of dye in the water passing over the receptor. The quantity of dye absorbed by the
charcoal is a function of the dye concentration in the water and the quantity, velocity, temperature and duration of exposure. Turbidity and the quantity and species of molecules competing with the dye for the charcoal acceptor sites can reduce the
quantity of dye absorbed onto the charcoal. Also, the quantity of dye eluted from the charcoal is dependent on the amount of charcoal and eluent used, the type of eluent, whether the charcoal is wet or dry before elution, and the length of time the
charcoal is eluted before being analyzed. The laboratory procedures can be standardized but the exposure variabilities while the receptor is in the stream cannot be. Although, dye concentrations for eluted samples are measured and recorded in ppb,
these values will virtually always be much higher than the dye concentrations ever reached in the stream. Also, because of the several water exposure variables, the concentration of dye absorbed by the charcoal does not even accurately represent the
quantity of dye that flowed in the stream past the dye receptor. Analysis of two dye receptors placed in the same general area of the same stream for the same time period will often result in differences when expressed in ppb. Therefore, the following
abbreviations are used to express the interpretation of the dye concentration in more general terms rather than ppb:
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