Accumulation of HOCs via Precontaminated Microplastics by Earthworm Eisenia fetida in Soil

Abstract

Soil is a primary sink for plastics, but the influence of microplastics as carriers on terrestrial cycling of persistent contaminants is poorly understood as compared to aquatic systems. Studies to date have disregarded the potential fact that microplastics are generally contaminated before their entry into soil. In this study, earthworm Eisenia fetida was incubated for 28 d in a soil amended with five common types of microplastics precontaminated with polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) to elucidate contaminant transfer. Accumulation of HOCs in E. fetida varied greatly among different plastic types and HOCs. The freely dissolved concentration (C free ) of HOCs showed that desorption of HOCs from microplastics into soil was closely related to plastic types and HOC hydrophobicity and was much slower for polystyrene or polypropylene than polyethylene. Biodynamic model analysis suggested that ingestion of microplastics could act as a significant pathway for some microplastics, likely due to HOCs on the plastics being in an "over-equilibrium" state. This was in contrast with mixing clean microplastics into HOCcontaminated soil, where the microplastics decreased bioaccumulation. Therefore, whether microplastics serve as facilitators or inhibitors of HOC bioaccumulation depends on the fugacity gradient of HOCs between microplastics and soil, which highlights the importance of considering the sequence of contamination between the plastics and soil. These findings also question the validity of short-term experiments because of the generally very slow partition kinetics of HOCs on plastics.

Coronas of micro/nano plastics: a key determinant in their risk assessments

“…Persistent organic pollutants (POPs) are a class of organic compounds that are resistant to environmental degradation and have detrimental effects on the environment and human health [ 166 ]. Given that POPs and M/NPs are all from the wastes of engineered products, they may coincidentally exist in some specific areas, such as farmland, fishpond, and raw sewage [ 167 ]. M/NPs may stably adsorb hydrophobic POPs such as polycyclic aromatic hydrocarbons (PAHs) [ 168 ], polychlorinated biphenyls (PCBs) [ 169 ] and dichlorodiphenyltrichloroethane (DDT) [ 170 ] on their surfaces to form surface coronas.…”

Global Research Activities on Micro(nano)plastic Toxicity to Earthworms

“…In this context, some evidence has shown that micro(nano)plastics could increase the bioaccumulation of heavy metals Cu, Ni [ 52 ] and Cd [ 53 ], as well as HOCs dufulin [ 54 ], pyrene [ 55 ], PFOS and PFOA [ 56 ] in earthworms by enhancing their bioavailability. Conversely, other researchers suggested that microplastics, at amendment rates of ≥1% d.w., reduced the tissue concentrations of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyl (PCB) in earthworms [ 34 ], and this could potentially be related to the fugacity gradient of chemicals between microplastics and soils [ 57 ]. In general, combined exposure can induce greater oxidative damage to earthworms compared with exposure to micro(nano)plastics or other pollutants alone, and, thus, negative effects on growth, behavior and the immune system of earthworms can be heightened [ 20 , 53 , 54 ].…”

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

“…Experiment Koelmans et al (2016) modelled the experiment published by Rochman et al (2013) with aqueous concentration set to zero and ingestion rate and concentrations in food set at the values reported in the study. This model framework has been developed, applied and validated (Table 6.5) in a series of studies (Koelmans et al 2013a(Koelmans et al , b, 2014(Koelmans et al , 2016Koelmans 2015;Rochman et al 2017;Wang et al 2019Wang et al , 2020a. A similar model has been applied by Bakir et al (2016) to assess the relative contribution of chemical uptake pathways for marine worms, fish and seabirds.…”