Isocyanic acid measurements in Swedish industries and environments

Isocyanic acid (ICA), the simplest monoisocyanate, is formed mainly as a by-product through thermal degradation of nitrogen-containing materials. Although ICA participates in protein carbamoylation, human health data remain limited. Existing studies have shown that certain industrial processes may generate substantial ICA emissions but other occupational settings have not been studied. Environmental concentrations are lower than industrial but have not been studied in Europe. This study aimed to survey ICA concentrations in a wide range of occupational and environmental settings in Sweden. In total, 173 air samples were collected in 16 environments. Both stationary and personal sampling were performed. Concentrations were compared to the only existing occupational exposure limit (OEL, 18 µg/m³ 8 h mean) to aid interpretation. High ICA concentrations were consistently observed in industries using urea-based binders at elevated temperatures, with maximum stationary levels exceeding 250 µg/m³. Newly installed mineral wool insulation during initial heating phases generated elevated emissions up to 64 µg/m³. Thermal processing of polyurethane produced lower but spatially widespread concentrations throughout large work areas. In contrast, ICA levels in newly investigated environments-including restaurants, food industries, linoleum welding, diathermy procedures, asphalt work and lawn mowing-were generally well below OEL or below detection limits. Outdoor air measurements in Gothenburg, Sweden, showed uniformly low concentrations (mean 0.12 µg/m³). Extremely high ICA levels were confirmed in direct cigarette smoke (4300 µg/m³), while side-stream exposure was considerably lower. Overall, the survey shows that higher ICA concentrations are mainly associated with industrial high-temperature handling of urea- or polyurethane-based materials, as well as cigarette smoke. Other investigated occupational settings showed low or negligible ICA levels under the conditions measured.