Investigations into the environmental fate and effects of microplastics have been gaining momentum. Small, insoluble polymeric particles are implicated by scientists in a wide variety of studies that are used to suggest a potential for widespread impacts in freshwater and marine pelagic and sediment environments. An exponential growth in scientific publications and an increase in regulatory attention have occurred. However, despite these efforts, the environmental hazard of these particles is still unknown. To evaluate the hazard of microplastics within a risk assessment context, we need a way to evaluate the quality of experimental studies. We performed a thorough review of the quality and focus of environmental microplastic research, to understand the methodologies employed and how this may assist or distract from the ability of environmental risk assessors to evaluate microplastics. We provide guidance to improve the reliability and relevance of ecotoxicological studies for regulatory and broader environmental assessments. Nine areas of needed improvement are identified and discussed. Important data gaps and experimental limitations are highlighted. Environ Toxicol Chem 2017;36:1697-1703. © 2017 SETAC.

Selective serotonin reuptake inhibitors (SSRIs) represent a class of pharmaceuticals previously reported in aquatic ecosystems. SSRIs are designed to treat depression and other disorders in humans, but are recognized to elicit a variety of effects on aquatic organisms, ranging from neuroendocrine disruption to behavioral perturbations. However, an understanding of the relationships among mechanistic responses associated with SSRI targets and ecologically important behavioral responses of fish remains elusive. Herein, linking Adverse Outcomes Pathways (AOP) models with internal dosimetry represent potential approaches for developing an understanding of pharmaceutical risks to aquatic life. We selected sertraline as a model SSRI for a 28-d study with adult male fathead minnows. Binding activity of the serotonin reuptake transporter (SERT), previously demonstrated in mammals and fish models to respond to sertraline exposure, was selected as an endpoint associated with therapeutic activity. Shelter-seeking behavior was monitored using digital tracking software to diagnose behavioral abnormalities. Fish plasma levels of sertraline exceeding human therapeutic doses were accurately modeled from external exposure concentrations when pH influences on ionization and log D were considered. We observed statistically significant decreases in binding at the therapeutic target (SERT) and shelter-seeking behavior when fish plasma levels exceeded human therapeutic thresholds. Such observations highlights the strengths of coupling physiologically based pharmacokinetic modeling and AOP approaches and suggest that internal dosimetry should be monitored to advance an understanding of the ecological consequences of SSRI exposure to aquatic vertebrates.

Though pharmaceuticals are increasingly observed in a variety of organisms from coastal and inland aquatic systems, trophic transfer of pharmaceuticals in aquatic food webs have not been reported. In this study, bioaccumulation of select pharmaceuticals was investigated in a lower order effluent-dependent stream in central Texas, USA, using isotope dilution liquid chromatography–tandem mass spectrometry (MS). A fish plasma model, initially developed from laboratory studies, was tested to examine observed versus predicted internal dose of select pharmaceuticals. Pharmaceuticals accumulated to higher concentrations in invertebrates relative to fish; elevated concentrations of the antidepressant sertraline and its primary metabolite desmethylsertraline were observed in the Asian clam, Corbicula fluminea , and two unionid mussel species. Trophic positions were determined from stable isotopes (δ 15 N and δ 13 C) collected by isotope ratio-MS; a Bayesian mixing model was then used to estimate diet contributions towards top fish predators. Because diphenhydramine and carbamazepine were the only target compounds detected in all species examined, trophic magnification factors (TMFs) were derived to evaluate potential trophic transfer of both compounds. TMFs for diphenhydramine (0.38) and carbamazepine (1.17) indicated neither compound experienced trophic magnification, which suggests that inhalational and not dietary exposure represented the primary route of uptake by fish in this effluent-dependent stream.