Micro- and Nanoplastic Exposure Effects in Microalgae: A Meta-Analysis of Standard Growth Inhibition Tests

Abstract

Background: Ecological impacts of micro-and nanoplastics particles (MNP) are among the most discussed environmental concerns. In algae, MNP are commonly hypothesized to reduce growth, which is a standard ecotoxicological endpoint. However, the reported test outcomes vary, with both growth inhibition and stimulation being observed. Due to this conflict of information, a data synthesis for MNP potential to cause growth inhibition in toxicity testing is needed. Methods: We performed a meta-analysis study to assess the effect of MNP exposure on algal growth. Twenty studies published between 2010 and 2020 and representing 16 algal species and five polymer materials administered as particles in size range 0.04-3,000 µm were included in this meta-analysis. A random-effect model was used to estimate the effect size in three datasets: (1) Low concentration range (<100 mg/L), (2) High concentration range (≥100 mg/L), and (3) Full range model (0.004-1,100 mg/L), which encompassed all studies using the combination of experimental settings (test species, MNP concentration, polymer material, and particle size) yielding the highest effect size within a study. Reichelt and Gorokhova Nano/Microplastic Effects on Algal Growth particulates in the test system, and, hence, does not allow to attribute observed effects to the test polymers.

Algal Growth at Environmentally Relevant Concentrations of Suspended Solids: Implications for Microplastic Hazard Assessment

“…Current test methods in ecotoxicology are intended for soluble (at least partially) chemicals, whereas testing particle suspensions, such as microplastic, requires different approaches (Paul-Pont et al, 2018;Gerdes et al, 2019). Moreover, plastics are diverse: they represent different polymers and materials that include a broad array of chemical additives and come in many sizes, colors, and shapes (Rochman et al, 2019), which complicates comparisons between the effect studies (Reichelt and Gorokhova, 2020). It is also essential to keep in mind that plastic is only a kind of persistent solid waste pollution, and common approaches for the risk assessment are needed (Coe et al, 2019).…”

“…Despite environmental health concerns, only a few studies have shown consistent adverse effects of microplastics (Foley et al, 2018;Reichelt and Gorokhova, 2020), usually observed at very high microplastic concentrations. As a rule, these concentrations exceed levels that are recognized as environmentally relevant (Lenz et al, 2016;Phuong et al, 2016).…”

“…For such studies, a valid critique is a high probability that these effects are not necessarily specific to the microplastic but arise from the exposure to any suspended solids that have no nutrition value for animals and-in the case of photosynthetic microorganisms-a capacity to cause shading effects and sorb nutrients and microelements, thus decreasing their availability for the test algae (Ogonowski et al, 2018b). Hence, the existing protocols for hazard assessment do not explicitly address the effects of microplastic but those of particulate matter (PM) that change light and nutrient availability for the test organisms, such as algae and periphyton, during the exposure, with possible downstream effects on nutrient acquisition pathways, photosynthesis efficiency, and, ultimately, growth (Reichelt and Gorokhova, 2020).…”

“…However, the reported effects are not consistent across the studies, and no-effect reports are also published (Prata et al, 2019). As shown in the recent meta-analysis of the growth inhibition effects in algae exposed to nano-and microplastic, the lack of proper controls and methodological variability between the studies make it difficult to understand the driving forces, such as particle size, concentration, polymer type, behind the observed effects (Reichelt and Gorokhova, 2020). What is also essential is that similar effects on the same endpoints can be induced by natural suspended solids, such as clay and sand (Bilotta and Brazier, 2008;Chapman et al, 2017).…”

“…Considering the abundance of various non-plastic particulates in the pelagia, the occurrence of non-aggregated sphaerical particles in the water column is highly unlikely. Moreover, given that microbeads are a minor contributor to microplastic contamination globally, it is questionable whether the broad use of uniform spherical MP in experiments, including algal growth inhibition tests (Reichelt and Gorokhova, 2020), is justifiable from ecological and ecotoxicological viewpoints. Hence, using aged polymer fragments to mimic the environmentally realistic exposure scenario has been advocated (Ogonowski et al, 2018b).…”