Microplastics Effects on Reproduction and Body Length of the Soil-Dwelling Nematode Caenorhabditis elegans

Sven Marhan,Ellen Kandeler,Uwe Schnepf,Holger Pagel,Franz Brümmer,Liliane Ruess,Ralph Menzel,Lion Schöpfer

doi:10.3389/fenvs.2020.00041

Abstract

Microplastics (MP) are pervasive in the environment. There is ample evidence of negative MP effects on biota in aquatic ecosystems, though little is known about MP effects in terrestrial ecosystems. Given numerous entry routes into soils, soil organisms are likely to be exposed to MP. We compared potential toxicological effects of MP from (i) low-density polyethylene (LDPE) (mean diameter ± standard deviation: 57 ± 40 µm) or (ii) a blend of biodegradable polymers polylactide (PLA) and poly(butylene adipate-co-terephthalate) (PBAT) (40 ± 31 µm) on the reproduction and body length of the soil-dwelling bacterivorous nematode Caenorhabditis elegans. Feed suspensions without (control) or with MP (treatments) at concentrations of 1, 10, and 100 mg MP L -1 were prepared and nematodes were exposed to those suspensions on NGM agar plates until completion of their reproductive phase (~ 6 days). Using Nile red-stained PLA/PBAT MP particles and fluorescence microscopy, we demonstrated the ingestion of MP by C. elegans into pharynges and intestines. Under MP exposure, nematodes had fewer offspring (up to 22.9%) compared to nematodes in the control group. This decline was independent on the plastic type. We detected a tendency towards greater decreases in offspring at higher concentrations. Despite hints of negative effects on nematode body length under MP exposure, we could not derive a consistent pattern. We conclude that in MP-contaminated soils, the reproduction of nematodes, central actors in the soil food web, can be affected, with potentially negative implications for key soil functions, e.g., the regulation of soil biogeochemical cycles.

Highlights

Microplastics (MP) have only recently been recognized as an environmental threat to terrestrial ecosystems
We evaluated the biological endpoints of reproduction and body length in the model organism C. elegans in response to MP exposure at different concentrations
Two types of plastics were used in the experiment: (1) lowdensity polyethylene (LDPE) in the form of granules (Lupolen 2420 H, LyondellBasell Industries N.V., Rotterdam, Netherlands) and (2) a blend consisting of the polymers polylactide (PLA, IngeoTM Biopolymer 7001D, NatureWorks LLC, Minnetonka, MN, United States) and poly(butylene adipate-co-terephthalate) (PBAT, Ecoflex F Blend C1200, BASF SE, Ludwigshafen, Germany) with a mixing ratio of 80/20% w/w compounded at the “Institut für Kunststofftechnik” (University of Stuttgart, Stuttgart, Germany)

Summary

Introduction

Microplastics (MP) have only recently been recognized as an environmental threat to terrestrial ecosystems. Reliable data on the prevalence of MP in soils is scarce (Watteau et al, 2018), soils are presumably large sinks for MP and MP may harm soil organisms (Bläsing and Amelung, 2018; Hurley and Nizzetto, 2018) It has been shown for aquatic organisms such as mussels, langoustines, copepods, short crabs, and lugworms that the ingestion of MP can lead to negative effects on growth, reproduction and survival (Galloway et al, 2017; Foley et al, 2018; Franzellitti et al, 2019). Studies on earthworms under MP exposure indicated that some biological functions could be inhibited (Huerta Lwanga et al, 2016; Cao et al, 2017). Evidence on the accumulation of MP from soil to earthworms to chicken feces (Huerta Lwanga et al, 2017b) indicates that MP may enter terrestrial food webs through trophic transfers

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