• Clive Roper

A NAM for Respiratory Toxicology; EPA Risk Assessment

I was very fortunate to be involved in a new approach methodology (NAM) for respiratory toxicology with Syngenta and the US EPA. Last week, the EPA issued their draft risk assessment for chlorothalonil utilising the NAM: This formal risk assessment utilised the 3D human derived upper airway model, MucilAir™ (, computational fluid dynamic (CFD), particle size distribution (PSD) and human operator exposure measurements to calculate point of departure (POD) which were used to determine human equivalent concentrations (HEC) and human equivalent doses (HED) for different operator exposure scenarios.

What did this actually entail?

The first experiment (Vinall, 2017;, resulted in the EPA evaluating the NAM with an independent Scientific Advisory Panel (SAP) meeting in December 2018 ( I was invited to attend to support in the defense of this NAM. The SAP produced a formal report ( with recommendations for further development of the NAM.

After considerable discussion and planning further work was performed using MucilAir was performed (Paulo, 2020; The same process was performed to calculate PODs. Data was submitted to the EPA and they calculated HECs and HEDs and generated the risk assessment (

What did we achieve from this work?

  • We replaced a 90-day repeat dose toxicity test with MucilAir, CFD, PSD and OPEX measurements.

  • We gained an acceptable risk assessment.

  • We demonstrated that bringing all stakeholders together, we can create new ways to perform toxicology.

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