Criteria eligible for establishing reference concentrations of adverse chemicals under chronic inhalation exposure by extrapolation of the existing parameters

Some chemicals emitted into ambient air do not have eligible parameters for assessing associated non-carcinogenic health risks under chronic inhalation exposure. Therefore, it is relevant to extend the list of reference concentrations (RfC), among other things, to perform health risk assessment within implementation of the Clean Air Federal Project. The same reference concentrations and critical organs and systems can be fixed for different compounds of the same chemical in accordance with the Guide R 2.1.10.3968-23. This makes it possible to establish non-identified RfC values by extrapolating the existing parameters from a donor to an acceptor. The article suggests eligible criteria for establishing reference concentrations under chronic inhalation exposure by extrapolation of the existing parameters. They include identity of chemicals per selective toxicity towards target organs and / or systems upon chronic exposure, identical critical organs and systems, identical specific effects (sensitizing and mutagenic effects and reproductive toxicity) and similar physiochemical properties. Use of extrapolation criteria allowed suggesting RfC of cadmium oxide equal to 2•10-5 mg/m3; cadmium was employed as a donor for extrapolation. Verification results confirmed that the conventionally substantiated RfC value was consistent with the value obtained by extrapolation. At the same time, we found that it was unacceptable to establish RfC of cadmium sulfate by extrapolation from cadmium since the former chemical was more toxic in accordance with the suggested criteria as regards its mutagenic effects and reproductive toxicity. In addition, its physiochemical properties were different from those of cadmium.