Why is phase contrast microscopy (PCM) not advised for analyzing asbestos in air?

Phase contrast microscopy (PCM) is not recommended for analyzing asbestos in air primarily because it measures all fibers indiscriminately, without differentiating between asbestos fibers and non-asbestos fibers. PCM, while useful for counting fibers, does not provide sufficient specificity to identify asbestos, leading to potential misinterpretation of the results.

Identifying and quantifying asbestos fibers accurately is crucial for ensuring public health and safety, especially in environments where asbestos exposure is a concern. The indiscriminate nature of PCM means that it may count non-asbestos fibers as part of its total fiber count, which can skew data and result in misleading assessments of air quality. Alternative methods, such as transmission electron microscopy (TEM), are much more precise in this regard, as they can accurately identify and differentiate asbestos fibers from other types of fibers present in the air.