Difficulties with ATP Measurements in Inshore Waters

When inshore waters are filtered for microbial biomass determinations, the amount of ATP recovered in the extracts is directly proportional to the volume filtered up to about 0.5 liter. With sample volumes of 1-3 liters, there is an apparent loss of ATP which can amount to 10-50% of that originally present. This loss is not due to cell lysis during filtration, but rather seems related to adsorption phenomena associated with the load of detrital or sedimentary material in suspension. When working in inshore waters it is therefore advisable to determine if such an inflection point occurs for ATP loss and to use smaller sample volumes if necessary to ensure against any loss of ATP. There is no such loss of ATP from open ocean samples.