Adapting OECD Aquatic Toxicity Tests for Use with Manufactured Nanomaterials: Key Issues and Consensus Recommendations

Abstract

The unique or enhanced properties of manufactured nanomaterials (MNs) suggest that their use in nanoenabled products will continue to increase. This will result in increased potential for human and environmental exposure to MNs during manufacturing, use, and disposal of nanoenabled products. Scientifically based risk assessment for MNs necessitates the development of reproducible, standardized hazard testing methods such as those provided by the Organisation of Economic Cooperation and Development (OECD). Currently, there is no comprehensive guidance on how best to address testing issues specific to MN particulate, fibrous, or colloidal properties. This paper summarizes the findings from an expert workshop convened to develop a guidance document that addresses the difficulties encountered when testing MNs using OECD aquatic and sediment test guidelines. Critical components were identified by workshop participants that require specific guidance for MN testing: preparation of dispersions, dose metrics, the importance and challenges associated with maintaining and monitoring exposure levels, and the need for reliable methods to quantify MNs in complex media. To facilitate a scientific advance in the consistency of nanoecotoxicology test results, we identify and discuss critical considerations where expert consensus recommendations were and were not achieved and provide specific research recommendations to resolve issues for which consensus was not reached. This process will enable the development of prescriptive testing guidance for MNs. Critically, we highlight the need to quantify and properly interpret and express exposure during the bioassays used to determine hazard values.

Assessing nanomaterial exposures in aquatic ecotoxicological testing: Framework and case studies based on dispersion and dissolution

“…The 1 h settling time was based on elutriate preparation methods (USEPA/USACE, 1998). The ENMs were considered relatively stable in bioassay test media when mass concentration remained within ±20% of initial values for 24 h, as discussed in OECD ecotoxicity guidelines (Petersen et al, 2015).…”

“…We demonstrated hazard testing procedures with focus on critical issues for standardized ecotoxicity testing of ENMs discussed by others (Diamond et al, 2009;Handy et al, 2012;Holden et al, 2016;Hund-Rinke et al, 2015;Klaine et al, 2008;Petersen et al, 2015;Potthoff et al, 2015). Key testing issues derive from the particulate and fibrous nature of ENMs, and their tendency to agglomerate and settle out of suspension in bioassay media, resulting in significant exposure variation and thus complicated dosimetry.…”

“…Their properties, characteristics and behaviors present significant challenges at all levels of environmental health and safety, including regulation, risk management, exposure and hazard assessment; these challenges exist in part because current standards for dissolved chemicals are not directly applicable or prescribed for testing particles or colloids (Petersen et al, 2015). Formal, internationally recognized ENM-specific guidance has yet to be developed, resulting in inconsistent testing, interpretation and decisions regarding the material physical -chemical information to be provided in dossiers submitted to regulatory agencies (Collier et al, 2015;Hund-Rinke et al, 2016;Petersen et al, 2015;Potthoff et al, 2015).…”

“…The development of that strategy and the content of this paper was based on the literature describing the novel behaviors of ENMs (relative to soluble chemicals) and the difficulties in testing them (Petersen et al, 2015). The tiered strategy was inspired, in part, by testing approaches used in sediment dredging evaluations (USEPA/USACE, 1998), which also test complex homo-and heteroagglomerated particle and water mixtures that potentially contain chemical substances that can be released while settling in the water column (Kennedy et al, 2015a).…”

“…surface area, particle or agglomerate number) that may be used to quantify ENM exposure (Hull et al, 2012;Kennedy et al, 2015b). The absence of specific guidance for aquatic ecotoxicity testing of ENMs complicates risk management and assessment for ENM and greatly reduces the value of test results for predicting hazard and risk (Petersen et al, 2015). Recently, Potthoff et al (2015) described an approach to addressing testing issues using a conceptual, complex series of flow charts generally applicable to air, soil and water.…”