Table 1.

Steps in environmental exposure assessment based on the methods applied as part of REACH, EUSES, and described in R.16 and the current challenge for nanomaterials

Steps in exposure assessment (based on R.16)	Method	Main challenge	Suggested solution
Release assessment a	(specific) Environmental release categories	Question if general approach valid, default values valid	Evaluation of default values by monitoring data can be based on MFA models (Wang and Nowack 2018), monitoring data (Gottschalk et al. 2013)
Sewage treatment plant	Fate in sewage treatment plant	Adaptation required	Use of existing SimpleTREAT (Struijs 2015), implementation based on experimental study review or monitoring data
Exposure estimation (including distribution and fate)	Models–Local	Adaptation required	Partially available based on experiences from: Praetorius et al. (2012); nanoDUFLOW (Quik et al. 2015); NanoFASE WSO (Lofts et al. 2019); LOTOS‐EUROS (Manders et al. 2019)
	Models–Regional	Adaptation required	SimpleBox4nano (Quik et al. 2019) Additional experiences from MendNano (Liu and Cohen 2014); NanoFATE (Garner et al. 2017)
	Measurements	Currently resource intensive and complex techniques	Development of standardized measurement protocols for environmental matrices

ERC = environmental release category; ESD = emission scenario documents; EUSES = European Union System for the Evaluation of Substances; MFA = material flow analysis; OECD = Organisation for Economic Co‐operation and Development; spERC = sector‐specific ERC.

^aFor the sake of completeness it should be mentioned that in addition to ERCs and spERCs according to R.16 (ECHA 2016a), further published information such as OECD ESDs or site‐specific information can be used for release estimation. As with the ERCs and spERCs, ESDs need to be examined for their applicability to nanomaterials.