5.1 A rapid and routine procedure for determining biomass of the living microorganisms in cultures, waters, wastewaters, and in plankton and periphyton samples taken from surface waters is frequently of vital importance. However, classical techniques such as direct microscope counts, turbidity, organic chemical analyses, cell tagging, and plate counts are expensive, time-consuming, or tend to underestimate total numbers. In addition, some of these methods do not distinguish between living and nonliving cells.
5.2 This test method measures the concentration of cellular-ATP present in the sample. ATP is a constituent of all living cells, including bacteria, algae, protozoa, and fungi. Consequently, the presence of cellular-ATP is an indicator of total metabolically active microbial contamination in water. ATP is not associated with matter of non-biological origin.
5.3 The ATP (luciferin-luciferase) method is a rapid, sensitive determination of viable microbial biomass. ATP is the primary energy donor for life processes, does not exist in association with nonliving detrital material, and the amount of ATP per unit of biomass (expressed in weight) is relatively constant. (ATP per cell varies with species and physiological state of the organism.)
5.4 This test method can be used to:
5.4.1 Estimate viable microbial biomass in cultures, waters, and wastewaters.
5.4.2 Estimate the amount of total viable biomass in plankton and periphyton samples.
5.4.3 Estimate the number of viable cells in a unispecies culture if the cATP content (or if the average amount of cATP) per cell is known.
5.4.4 Estimate and differentiate between zooplanktonic, phytoplanktonic, bacterial, and fungal cATP through size fractionation of water, and wastewater samples.
5.4.5 Measure the mortality rate of microorganisms in toxicity tests in entrainment studies, and in other situations where populations or assemblages of microorganisms are placed under stress.
5.5 This test method is similar to Test Methods D7687 and E2694 except for the volumes sampled, and omission of wash and drying steps used in Test Methods D7687 and E2694 to remove interferences (1.3).
5.6 Although ATP data generally covary with culture data in water samples, different factors affect cATP concentration than those that affect culturability.
5.6.1 Culturability is affected primarily by the ability of captured microbes to proliferate on the growth medium provided, under specific growth conditions. Consequently, a proportion of the active or inactive microbial population present in a sample......