Measuring toluene diisocyanate concentrations in accordance with the ACGIH® inhalable fraction and vapor (IFV) notation

Abstract

Toluene diisocyanate (TDI) is an irritant (skin, eye and respiratory) and a sensitizer. This compound is used to manufacture polyurethane materials such as flexible foams. The use of isocyanates may lead to exposure by inhalation and/or skin contact and isocyanates are recognized as a cause of occupational asthma. The American Conference of Governmental Industrial Hygienists (ACGIH®) recommends a threshold limit value (TLV) for TDI of 1 part per billion (ppb) (7 μg m⁻³) with the inhalable fraction and vapor (IFV) notation. This notation means that the inhalable fraction of particles and the vapor phase of TDI may contribute to the exposure, and therefore the evaluation methods must comply with the IFV notation. This study aimed at developing and validating a TDI measurement method, compliant with the ACGIH IFV notation, using an IOM sampler with an impregnated filter. The new sampling method (IOM-IFV) used an IOM sampler (stainless steel cassette) with a glass fiber filter coated with 1,2-(methoxyphenyl)piperazine (MP) and diethyl phthalate. The sample was extracted using acetonitrile and analyzed by UPLC-MS. This application of the IOM sampler for such a reactive chemical was characterized and tested in the laboratory to ensure efficient TDI recovery from both spiked samples and air samples. Based on a sampling time of 2 hours, the method has a measuring range of 0.3 to 15 μg m⁻³. At its reporting limit, the method is capable of measuring 8% of the 15 min short-term TLV (36 μg m⁻³). Method comparisons using a laboratory generation system showed that, under the conditions tested, the OSHA 5002 method was in agreement with the new IOM-IFV method. The ISO 17334-1 method showed a significant negative bias of −40% compared to the IOM-IFV method. The new IOM-IFV method demonstrated its suitability for measuring exposure to TDI for comparison with the ACGIH® TLVs, i.e. the STEL (15 min) and the TWA (8 h). A comparative study should be carried out in occupational settings to confirm the conclusions obtained in the laboratory.