A living tool for the continued exploration of microplastic toxicity

Abstract

Throughout the past decade, many studies have reported adverse effects in biota following microplastic exposure. Yet, the field is still emerging as the current understanding of microplastic toxicity is limited. At the same time, recent legislative mandates have required environmental regulators to devise strategies to mitigate microplastic pollution and develop health-based thresholds for the protection of human and ecosystem health. The current publication rate also presents a unique challenge as scientists, environmental managers, and other communities may find it difficult to keep up with microplastic research as it rapidly evolves. At present, there is no tool that compiles and synthesizes the data from these studies to allow for visualization, interpretation, or analysis. Here, we present the Toxicity of Microplastics Explorer (ToMEx), an open access database and open source accompanying R Shiny web application that enables users to upload, search, visualize, and analyze microplastic toxicity data. Though ToMEx was originally created to facilitate the development of health-based thresholds to support California legislations, maintaining the database by the greater scientific community will be invaluable to furthering research and informing policies globally. The database and web applications may be accessed at https://microplastics.sccwrp.org/. Graphical Abstract

The emergence of microplastics: charting the path from research to regulations

“…32 The toxicity databases, tools to estimate particle characteristics, align toxicity studies, screen studies for quality criteria, and more were made freely available in an open-source and open-data repository utilizing an Rshiny web application called the Toxicity of Microplastics Explorer ("ToMEx") (https:// github.com/SCCWRP/aq_mp_tox_shiny). 31 Additionally, ToMEx allows users to upload additional published toxicity datatherefore enabling rapid and real-time meta-analyses and assessments of risk and reducing burdens of future assessments. 31 To inform California's management of MPs in aquatic ecosystems, the health effects workshop devised a framework that includes four risk-based threshold tiers each with increasing levels of critical actions recommended to be undertaken by the appropriate regulatory bodies, ranging from low concernprompting additional investigative monitoringto the highest level of concernpollution control measures.…”

“…31 Additionally, ToMEx allows users to upload additional published toxicity datatherefore enabling rapid and real-time meta-analyses and assessments of risk and reducing burdens of future assessments. 31 To inform California's management of MPs in aquatic ecosystems, the health effects workshop devised a framework that includes four risk-based threshold tiers each with increasing levels of critical actions recommended to be undertaken by the appropriate regulatory bodies, ranging from low concernprompting additional investigative monitoringto the highest level of concernpollution control measures. 10 Using the best available data, risk-based thresholds were derived using species sensitivity distributions 10a statistical approach which is commonly used by regulatory authorities in many jurisdictions globally to set limits in the environment.…”

“…10,30 Large, high-resolution environmental monitoring datasets across multiple locations were used to align data based on size, shape, and density distributions to enable broadly applicable compartment-specic thresholds, however site-specic monitoring data (if available) can be easily substituted to derive thresholds applicable to a given location using the ToMEx application. 10,31 The resulting thresholds derived by Mehinto et al (2022) range from ∼0.5 to 35 particles per L (1 to 5000 mm MPs) for food dilution, and 60 to 4100 particles per L (1 to 5000 mm MPs) for tissue translocation-mediated toxicities. Health effects workshop participants expressed high condence in both the management framework and the analytical process used to derive the thresholds but expressed medium condence in the resulting thresholds for food dilution and low condence for tissuetranslocation mediated effects due to the underlying studies not meeting all desired quality criteria (in particular, doseresponse effect concentrations such as EC50's).…”

“…Over 220 toxicity studies were mined for more than 70 unique variables relating to experimental design, test organisms, biological effects, and particle characteristics of MPs used. 31 Each study was then screened by two independent reviewers based on quality criteria developed by de Ruijter et al…”

Microplastics: a multidimensional contaminant requires a multidimensional framework for assessing risk

“…(see [8]). These thresholds could be guided by metaanalyses of the existing literature [22], or future toxicity tests designed to better answer these questions relevant to how the multidimensionality informs risk. An example of how this may look is in Fig.…”