Endotoxin measurement: aerosol sampling and application of a new Limulus method.

A new Limulus test was designed specifically for measuring endotoxin in environmental aerosols. The new Limulus method has a detection limit for airborne endotoxin of 2.2 pg (NP-1 activity)/m3 and can precisely quantitate aerosols containing 14 or more pg/m3 from samples representing 6.5 m3 of air. Aerosols in the range 100 to 500 pg/m3 were measured with 95% confidence of +/- 32% and an aerosol of 10 pg/m3 with 95% confidence of +/- 50%. Qualitative information about airborne endotoxin was also obtained from the assay. A wide variety of filter media were found to inactivate lipopolysaccharide in solution. This implies that airborne endotoxin can be measured only relative to the conditions of a particular study and that comparison of endotoxin aerosol measurements made under different circumstances are invalid. The research and policy implications of this observation are discussed. The need for improved collection and extraction methods notwithstanding, it was proposed that a buffered, parallel-line Limulus assay method be adopted as the standard method for measuring environmental endotoxin. The kinetic-turbidimetric Limulus assay with resistant-parallel-line estimates (KLARE), rate response method, should be considered a prime candidate for the standard method because of its precision, sensitivity, resistance to interference by pH, internal validation of estimates, and ability to provide qualitative as well as quantitative information about airborne endotoxin.