Weight of Evidence for the Microplastic Vector Effect in the Context of Chemical Risk Assessment

Abstract

The concern that in nature, ingestion of microplastic (MP) increases exposure of organisms to plastic-associated chemicals (the ‘MP vector effect’) plays an important role in the current picture of the risks of microplastic for the environment and human health. An increasing number of studies on this topic have been conducted using a wide variety of approaches and techniques. At present, the MP vector effect is usually framed as ‘complex’, ‘under debate’ or ‘controversial’. Studies that critically discuss the approaches and techniques used to study the MP vector effect, and that provide suggestions for the harmonization needed to advance this debate, are scarce. Furthermore, only a few studies have strived at interpreting study outcomes in the light of environmentally relevant conditions. This constitutes a major research gap, because these are the conditions that are most relevant when informing risk assessment and management decisions. Based on a review of 61 publications, we propose evaluation criteria and guidance for MP vector studies and discuss current study designs using these criteria. The criteria are designed such that studies, which fulfil them, will be relevant to inform risk assessment. By critically reviewing the existing literature in the light of these criteria, a weight of evidence assessment is provided. We demonstrate that several studies did not meet the standards for their conclusions on the MP vector effect to stand, whereas others provided overwhelming evidence that the vector effect is unlikely to affect chemical risks under present natural conditions.

Micro(nano)plastics Prevalence, Food Web Interactions, and Toxicity Assessment in Aquatic Organisms: A Review

“…It is well known that organisms in freshwater ecosystems are constituents of complex trophic food chain, feeding on a plethora of different types of food items, using a variety of distinct feeding methods including filter, fluid, suspension, sediment, and suction feeding. Filter and suspension feeders including planktonic crustaceans (e.g., Daphnids), mussels, protozoans, and rotifers are particularly susceptible to microplastics intake due to their frequent ingestion of living (bioseston e.g., nekton and plankton) and non-living (tripton e.g., plant debris) particulate matter suspended in freshwater bodies (Thouvenot et al, 1999;Browne et al, 2008;Scherer et al, 2018;Koelmans et al, 2022). These interactions and trophic processes are poorly understood and further complicate our understanding of their MPs impacts and toxicosis to freshwater biota (Castro-Castellon et al, 2021;Ma and You, 2021;Ain Bhutto and You, 2022).…”

Development and Application of Nanoparticle-Nanopolymer Composite Spheres for the Study of Environmental Processes

“…tissue). It should be noted, as these studies continue to be refined, evidence increasingly suggests that MP vector transport might not be a significant contributor to their risk ( Koelmans et al, 2016 ; Koelmans et al, 2021 ).…”

Microplastics’ journey into the gut : human exposure to microplastics and associated chemicals

“…17 On the other hand, the chemical toxicity of microplastics (also commonly referred to as the chemical vector effect) has been highly debated in the scientific community. 18 Few studies have interpreted their outcomes on the chemical vector effect in light of environmentally relevant conditions. Additionally, the extent of the chemical vector effect is especially unknown for humans.…”

“…60 When ingested, microplastics have the potential to act as vectors and transfer chemicals to organisms under certain conditions. 18 These plastic particles contain a mixture of chemicals, which may either be intentionally or unintentionally added. During the manufacturing process, monomers, plasticizers, and additives are usually added to plastics to achieve the appropriate structure for the designated application.…”

“…121 As a carrier for a mixture of chemicals, these plastic particles may release chemicals in the organisms' digestive tracts when ingested, potentially increasing exposure and risks. 18,43 An established approach to investigate the chemical vector effect of microplastics when ingested is by performing in vitro gut fluid experiments. This type of experiment has been widely used to investigate chemical bioavailability from indigestible particles such as sediment, asphalt and soot in human and animal digestive tracts.…”