Oct 11, 2011

Exposure measurement and assessment of nanoscale aerosols

(Nanowerk News) Various German leading institutions worked out a strategy paper ("Aerosols Released from Engineered Nanomaterials in Workplace Operations"; pdf) adressing the challenges of exposure measurement and assessment of nanoscale aerosols released from engineered nanomaterials in the workplace.

The working group aimed at a harmonized approach for exposure measurement and exposure assessment. The outcome is pragmatic and widely usable. This tiered approach can be widely used by small and medium sized enterprises as well as large chemical companies with global business operations.

The main findings of the working group can be summarized as follows:

Safe work places where ENMs are produced or pro cessed can be achieved, using existing technology, and which conforms with best industrial hygiene practices. Existing substance-specific, binding, health based OELs must be complied with and are not subject of or overridden by the current approach.

Exposure measurement of nanoscale aerosols released from ENMs in the work-place is possible and exposure assessment methodologies exist. However, methodologies are not yet standardized and more difficult to apply as in routine operations, e.g. gravimetric dust measurements according to DIN EN 481.

Equipment required for measurement of exposure to nanoscale aerosols released from ENMs is sophisticated and the results produced, e.g., total particle num ber concentration, have no direct correlation to the chemical identity. Calibration of equipment is still a challenge and validation using round robin testing, which is typically correlated with SMPS results, is difficult as no commonly accepted reference method is available.

At the moment, for a practitioner, a tiered approach to exposure assessment appears to be the most ap propriate strategy. This approach is split into 3 tiers. In the first step (Tier 1) information is gathered according to established industrial hygiene practices. In the next tier (Tier 2) a basic exposure assessment using a limi ted set of easy-to-use equipment is conducted, where as in the highest tier 6 (Tier 3) the latest state-of-theart measurement technology is employed to assess the potential for workplace exposure to nanoscale aerosols released from ENMs if required.

Existing legally binding OELs, e.g. synthetic amor phous silica [TRGS 900: EC No. 231-545-4], carbon black [ACGIH], etc., have to be complied with. Where no such substance-specific, binding, health-based OEL values for ENMs exist, the tiered approach is using 3 criteria for the assessment of the data: 1) Interference value exceeded for nanoscale aerosols released from ENMs. 2) Significant increase over aerosol background level in the workplace air. 3) Chemical identity of the nano-objects and their nanoscale aggregates and agglomerates detected in the aerosol.

The application of the decision logic leads in total to 7 different cases (Case A – G), which may guide the risk management decisions of the practitioner.

This step-by-step approach may need to be revisited as soon as new scientific findings are available (especially on binding, health-based occupational exposure limit values). The presented exposure assessment strategy of nanoscale aerosols released from ENMs in the workplace may serve as a starting point for further standardization.

Source: Verband der Chemischen Industrie