title: Incorporation of microplastics from litter into burrows of Lumbricus terrestris.
abstract: Pollution caused by plastic debris is an urgent environmental problem. Here, we assessed the effects of microplastics in the soil surface litter on the formation and characterization of burrows built by the anecic earthworm Lumbricus terrestris in soil and quantified the amount of microplastics that was transported and deposited in L. terrestris burrows. Worms were exposed to soil surface litter treatments containing microplastics (Low Density Polyethylene) for 2 weeks at concentrations of 0%, 7%, 28%, 45% and 60%. The latter representing environmentally realistic concentrations found in hot spot soil locations. There were significantly more burrows found when soil was exposed to the surface treatment composed of 7% microplastics than in all other treatments. The highest amount of organic matter in the walls of the burrows was observed after using the treatments containing 28 and 45% microplastics. The highest microplastic bioturbation efficiency ratio (total microplastics (mg) in burrow walls/initial total surface litter microplastics (mg)) was found using the concentration of 7% microplastics, where L. terrestris introduced 73.5% of the surface microplastics into the burrow walls. The highest burrow wall microplastic content per unit weight of soil (11.8 ± 4.8 g kg-1) was found using a concentration of 60% microplastics. L. terrestris was responsible for size-selective downward transport when exposed to concentrations of 7, 28 and 45% microplastics in the surface litter, as the fraction ≤50 μm microplastics in burrow walls increased by 65% compared to this fraction in the original surface litter plastic. We conclude that the high biogenic incorporation rate of the small-fraction microplastics from surface litter into burrow walls causes a risk of leaching through preferential flow into groundwater bodies. Furthermore, this leaching may have implications for the subsequent availability of microplastics to terrestrial organisms or for the transport of plastic-associated organic contaminants in soil.
authors.affiliation: Agroecología, El Colegio de la Frontera Sur, Unidad Campeche, Av Polígono s/n, Cd. Industrial, Lerma, Campeche, Mexico; Soil Physics and Land Management Group, Wageningen University & Research, Droevendaalsesteeg 4, 6708PB Wageningen, The Netherlands. Electronic address: ehuerta@ecosur.mx.
authors.forename: Esperanza
authors.initials: E
authors.lastname: Huerta Lwanga
authors.affiliation: Soil Physics and Land Management Group, Wageningen University & Research, Droevendaalsesteeg 4, 6708PB Wageningen, The Netherlands.
authors.forename: Hennie
authors.initials: H
authors.lastname: Gertsen
authors.affiliation: Soil Physics and Land Management Group, Wageningen University & Research, Droevendaalsesteeg 4, 6708PB Wageningen, The Netherlands.
authors.forename: Harm
authors.initials: H
authors.lastname: Gooren
authors.affiliation: Soil Physics and Land Management Group, Wageningen University & Research, Droevendaalsesteeg 4, 6708PB Wageningen, The Netherlands.
authors.forename: Piet
authors.initials: P
authors.lastname: Peters
authors.affiliation: Soil Quality Department, Wageningen University & Research, Droevendaalsesteeg 4, 6708PB Wageningen, The Netherlands.
authors.forename: Tamás
authors.initials: T
authors.lastname: Salánki
authors.affiliation: Soil Physics and Land Management Group, Wageningen University & Research, Droevendaalsesteeg 4, 6708PB Wageningen, The Netherlands.
authors.forename: Martine
authors.initials: M
authors.lastname: van der Ploeg
authors.affiliation: Aquatic Ecology and Water Quality Management Group, Department of Environmental Sciences, Wageningen University & Research, P.O. Box 47, 6700 AA Wageningen, The Netherlands; Wageningen Marine Research, P.O. Box 68, 1970 AB IJmuiden, The Netherlands.
authors.forename: Ellen
authors.initials: E
authors.lastname: Besseling
authors.affiliation: Aquatic Ecology and Water Quality Management Group, Department of Environmental Sciences, Wageningen University & Research, P.O. Box 47, 6700 AA Wageningen, The Netherlands; Wageningen Marine Research, P.O. Box 68, 1970 AB IJmuiden, The Netherlands.
authors.forename: Albert A
authors.initials: AA
authors.lastname: Koelmans
authors.affiliation: Soil Physics and Land Management Group, Wageningen University & Research, Droevendaalsesteeg 4, 6708PB Wageningen, The Netherlands.
authors.forename: Violette
authors.initials: V
authors.lastname: Geissen
mesh_terms: D000818:Animals; D001522:Behavior, Animal; D004787:Environmental Pollution; D009835:Oligochaeta; D010316:Particle Size; D010969:Plastics / Q000032:analysis*; D012987:Soil / Q000737:chemistry*; D012989:Soil Pollutants / Q000032:analysis*
chemical_list: D010969:Plastics; D012987:Soil; D012989:Soil Pollutants
keywords: Lumbricus terrestris burrows; Microplastics; Risk assessment