Contaminant Recognition and Sampling Strategy
Knowing what you are sampling for
Contaminants fall into broad families: biological (mold, bacteria, allergens), chemical (VOCs, formaldehyde, pesticides, combustion gases), particulate (PM, fibers), and radiological (radon). Each has appropriate sampling methods and interpretive frameworks.
Sampling strategy essentials
- Representativeness: sample locations, duration, and conditions must reflect the question being asked.
- Comparators: outdoor or unaffected-area samples help interpret indoor results; without them, a mold spore count is nearly meaningless.
- Air vs. surface vs. bulk sampling: air sampling captures inhalable exposure; surface sampling documents reservoirs; bulk sampling characterizes materials.
- Chain of custody: every sample labeled, sealed, and tracked from collection to laboratory.
- Quality assurance: blanks, duplicates, and calibration records support defensibility.
Traps
Common question traps include: treating a single air sample as diagnostic of a health condition; ignoring that spore counts vary seasonally and with activity; and forgetting that some methods (e.g., viable culture) capture only organisms that grow on the chosen media. Another trap is sampling after remediation began, destroying the baseline.
Rule of thumb
Sample to answer a specific question, with a comparator, using a method whose limits you can explain. If you cannot state what result would change your recommendation, do not collect the sample.
Worked example
A client wants "a mold test" in a bedroom. Correct approach: pair an indoor air sample with an outdoor comparator, document conditions, and interpret the indoor/outdoor ratio and species profile alongside the visual assessment - not as a stand-alone pass/fail.