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

Abstract

The global ubiquity and demonstrated toxicity of microplastics has led governments around the world to express the need for a risk assessment on microplastics. To conduct a risk assessment, scientists often draw upon frameworks from other contaminants, however we argue that microplastics are a unique pollutant and thus require a unique framework. Microplastics are a multidimensional contaminant, differing in size, shape, polymer type, and chemical cocktail. Each of these dimensions may influence the toxicity of the particle. Furthermore, microplastic pollution exists as a complex and dynamic mixture of particles, that varies over temporal and spatial scales. Thus, we propose a multidimensional risk framework for microplastics that incorporates, rather than simplifies, the multidimensionality of the contaminant as well as the contaminant mixture. With this framework, we can calculate a particle-specific hazard value that describes the potential for a single particle to cause harm based on its chemical and physical properties. The particle-specific hazard values can then be combined based on the number and type of particles in an environmental sample to inform the overall hazard value of the sample. The risk of the sample can then be calculated, which is dependent on the overall hazard value and the concentration of particles in the sample. Risk values among samples in the environment can be compared to illustrate differences among locations or seasons, or can be placed in a management framework with thresholds to guide regulatory decisions. To demonstrate the utility of our proposed framework, we perform a case study using data from San Francisco Bay. Our proposed framework is just that, and requires new research for application. To strengthen the ability of this framework to accurately predict risk, we propose a testing scheme that prioritizes strategic experimental designs that will increase our understanding of how each dimension of microplastics affect the toxicity (or hazard value) of a particle.

Chronic toxic effects of polystyrene microplastics on reproductive parameters of male rats

“…In examining the factors that contribute to microplastic-induced toxicity, Choi et al [47] reported that smaller microplastic size and long exposure time increased intracellular levels of reactive oxygen species. Smaller particles have been reported to induce more response due to large surface area that enhances their bioavailability [48][49][50]. These two factors; chronic exposure and the smaller components of the polystyrene microplastics may have contributed significantly to the adverse effects observed in this study.…”

Is There Evidence of Health Risks From Exposure to Micro- and Nanoplastics in Foods?

“…The second step includes the hazard characterization which is hampered by the fact that plastic particles can present three types of hazards, physical, chemical and biological, which makes the identification and characterization of hazards very extensive and complex (23)(24)(25)(26)(27)(28)(29)(30)(31)(32). Moreover, MP and NP are a multidimensional contaminant, differing in size, shape, polymer type, and additive cocktail, which could determine their toxicity (64,65). In addition, there is limited available data on toxicokinetics and only include absorption and distribution, whereas no information is available on metabolism, interaction with microbiota or excretion, key processes in toxicity assessment (18).…”

Risk characterization of microplastics in San Francisco Bay, California

“…Although this testing provides useful insights into potential effects and mechanisms of toxicity, testing at multiple relevant concentrations to establish a dose-response relationship is necessary to quantitatively characterize risk. Exacerbating this problem is that microplastics have a diversity of properties, such as size, shape, and polymer type, that can affect toxicity, and few studies have quantified the relative importance of these factors [8]. Most (72% out of 163) toxicity studies have been conducted using single-sized beads of a single polymer type [42] which is a poor representation of mixtures encountered in the ambient environment [54].…”