LAUSR

O the first step in identifying the ecotoxicological risk and producing regulatory guidance for new chemical substances is the performance of standardized toxicity tests. Protocols described within the test guidelines of the Organisation for Economic Cooperation and Development’s “Effects on Biotic Systems” outline methodologies to determine toxicities, defined by specific end points and model organisms within the aquatic environment. These procedures are equipped for the assessement of chemical solutes, but critical deficiencies in standardized test guidelines are increasingly apparent in the determination of toxicities resulting from the dispersion of particulates in water. Our aim is to highlight these shortcomings and promote discussion of how testing methods could be adapted to an increasingly common form of contaminant. In the past decade two of the most prominent research areas in ecotoxicology have been engineered nanomaterials (ENMs, one dimension <100 nm in size (see Virtual Issue on Environmental Nanotoxicology (http://pubs.acs.org/page/vi/ enviro_nanotoxicology.html)) and microplastics (MPs; synthetic organic polymers produced (primary MPs) or degraded (secondary MPs) to <5 mm in size). The emerging issue of nanoplastics (i.e., plastics in the nanosize range) continues this focus on particulates. The inadequacies of standardized testing have been previously highlighted with regard to specific particulates (ENMs). Although some of these considerations could be generalized to many anthropogenic waterborne particulates, a reassessment of standardized approaches and their application to particulates is now timely. We describe five specific limitations of standardized test methods that, while designed for chemical solutes, fail to capture the intricies of particulate exposures: