Performance evaluations of laboratories testing for asbestos in drinking water according to USEPA Test Method 100.1 or 100.2 are complicated by the difficulty of providing stable sample dispersions of asbestos in water. Reference samples of a graduated series of chrysotile asbestos concentrations dispersed in glass-distilled water were prepared in December of 1989 to address this concern.

Sealed glass ampuls, containing the reference dispersions, were sent to volunteer asbestos testing laboratories. The number of participating labs varied from 33 to 50. The data reported here was compiled from the four most recent test rounds performed.

Statistical analysis of data from the volunteer laboratories indicate that further work is needed to develop asbestos reference samples that produce data with less variability.

Details of the preparation of the samples, laboratory analytical procedures and statistical analysis of the results are presented, along with a discussion of issues suggested by the data.