Metals in Settled Dust Sampling Instructions

Metals contamination may be found in dust from a variety of sources. The metals may be present due to a poorly performed remediation, from decaying building materials, from catastrophic events or even routine activities. Regardless of the source metals in dust may be toxic and a source for concern. Metals found in dust are generally in trace quantities which can be released into the air when the dust is disturbed. The most common means for collection of settled dust is a dust wipe.

There are four (4) methods most commonly utilized for the analysis of dust wipes for trace metals: EPA SW846 Method 7000B (lead, FLAA), EPA SW-846 Method 6010D/NIOSH 9102 (most trace metals, ICP-OES), OSHA ID-145 (particulate mercury, CVAA) and OSHA ID-215 (hexavalent chromium).

Notes:

• SW-846 Method 6020B (ICP-MS) is often mentioned as an analytical option but is not recommended due to the significantly higher cost for lower reporting limits that are usually unnecessary.
• The reporting limits (RLs) for metals such as lead are typically 5-20X lower by ICP-OES than FLAA.
• Sampling media is crucial for proper analysis; interferences will occur if using improper media. Use of baby wipes, paper towels or tape is not acceptable for validated analytical results.
• While these analytical methods have been used for metals analysis for many years the only current regulatory limit for metals in settled dust is the dust lead action level (DLAL) set by EPA. There may be other generally accepted levels for concern in federal, state or local guidance documents.
• Results are typically reported in units of mass/area (e.g., µg/ft.2 , µg/100 cm2 etc.) based upon a known wipe area provided by the sample collector.
• These methods are designed for dust; dust is different from debris. If you believe that your sampling area consists of debris, please contact the lab for alternative analysis options.

The summaries of all analytical methods are relatively similar. The dust wipe is digested/extracted with mineral acids(s) and/or other reagents, then diluted to a known volume with water. The aqueous solution is filtered and aspirated/injected whereby the instrument absorbance/emission intensity or peak area is used to determine solution concentration. From this value the total analyte (metal) mass is calculated an correlated with the wipe area for result in units of mass/area.

The appropriate wipe area is determined by several factors:
1) the analytical sensitivity of each metal for each instrumental method
2) regulatory requirements and
3) the extent of probable sample loading (e.g., risk assessment vs. clearance monitoring). The most common wipe areas are 1.0 ft.2 or 100 cm2 ; however, a smaller area should be considered for a location with heavy dust accumulation while for a location with extremely light dust a larger area can be sampled (e.g., 288 in.2 is necessary for lead analysis on floors by FLAA). It is important to always provide the sampling area sizes on the chain of custody as they are used in calculations.