Microplastics - Back to Reality: Impact of Pristine and Aged Microplastics in Soil on Earthworm Eisenia fetida under Environmentally Relevant Conditions.

Recently, studies have highlighted the potential danger for soil organisms posed by film-derived microplastics (MPs). However, the majority of those does not accurately reflect the field conditions and the degree of MP contamination that can be found in actual settings. To fill the gap between laboratory and field scenarios, the polyethylene (PE) plastic film was made into PE-MPs and aged. Toxicity and molecular mechanisms of pristine PE-MPs (PMPs) and aged PE-MPs (AMPs) with the concentration at 500 mg/kg of dry weight were determined after 14 days of exposure by measuring the oxidative stress, osmoregulation pressure, gut microbiota, and metabolic responses in earthworms under environmentally relevant conditions. Our research showed that, when compared to PMPs (13.13 ± 1.99 items/g), AMPs accumulated more (16.19 ± 8.47 items/g), caused more severe tissue lesions, and caused a higher increase of cell membrane osmotic pressure in earthworms' intestines. Furthermore, the proportion of probiotic bacteria Lactobacillus johnsonii in the gut bacterial communities was 24.26%, 23.26%, and 12.96%, while the proportion of pathogenic bacteria of the phylum Verrucomicrobia was 2.28%, 4.79%, and 10.39% in the control and PMP- and AMP-exposed earthworms, indicating that the decrease in number of probiotic bacteria and the increase in number of pathogenic bacteria were more pronounced in the gut of AMP- rather than PMP-exposed earthworms. Metabolomic analysis showed that AMP exposure reduced earthworm energy metabolites. Consequently, the constant need for energy may result in protein catabolism, which raises levels of some amino acids, disturbs normal cell homeostasis, causes changes of cell membrane osmolarity, and destroys the cell structure. Our studies showed that aged MPs, with the same characteristics as those found in the environment, have greater toxicity than pristine MPs. The results of this study broaden our understanding of the toxicological effects of MPs on soil organisms under environmentally relevant conditions.

Predictive Capability of QSAR Models Based on the CompTox Zebrafish Embryo Assays: An Imbalanced Classification Problem.

The CompTox Chemistry Dashboard (ToxCast) contains one of the largest public databases on Zebrafish (Danio rerio) developmental toxicity. The data consists of 19 toxicological endpoints on unique 1018 compounds measured in relatively low concentration ranges. The endpoints are related to developmental effects occurring in dechorionated zebrafish embryos for 120 hours post fertilization and monitored via gross malformations and mortality. We report the predictive capability of 209 quantitative structure-activity relationship (QSAR) models developed by machine learning methods using penalization techniques and diverse model quality metrics to cope with the imbalanced endpoints. All these QSAR models were generated to test how the imbalanced classification (toxic or non-toxic) endpoints could be predicted regardless which of three algorithms is used: logistic regression, multi-layer perceptron, or random forests. Additionally, QSAR toxicity models are developed starting from sets of classical molecular descriptors, structural fingerprints and their combinations. Only 8 out of 209 models passed the 0.20 Matthew's correlation coefficient value defined a priori as a threshold for acceptable model quality on the test sets. The best models were obtained for endpoints mortality (MORT), ActivityScore and JAW (deformation). The low predictability of the QSAR model developed from the zebrafish embryotoxicity data in the database is mainly due to a higher sensitivity of 19 measurements of endpoints carried out on dechorionated embryos at low concentrations.

Toxicological effects of polystyrene microplastics on earthworm (Eisenia fetida).

Microplastics are plastic fragments of particle sizes less than 5 mm, which are widely distributed in marine and terrestrial environments. In this study, earthworms Eisenia fetida were exposed to 100 and 1000 µg of 100 nm and 1300 nm fluorescent polystyrene microplastics (PS-MPs) per kg of artificial soil for 14 days. Uptake or accumulation of PS-MPs in earthworm intestines, histopathological changes, oxidative stress, and DNA damage were assessed to determine the toxicological effects of PS-MPs on E. fetida. The results showed that the average accumulated concentrations in the earthworm intestines were higher for 1300 nm PS-MPs (0.084 ± 0.005 and 0.094 ± 0.003 µg/mg for 100 and 1000 µg/kg, respectively) than for 100 nm PS-MPs (0.015 ± 0.001 and 0.033 ± 0.002 µg/mg for 100 and 1000 µg/kg, respectively). In addition, histopathological analysis indicated that the intestinal cells were damaged after exposure to PS-MPs. Furthermore, PS-MPs significantly changed glutathione (GSH) level and superoxide dismutase (SOD) activity. The GSH levels were 86.991 ± 7.723, 165.436 ± 4.256-167.767 ± 18.642, and 93.590 ± 4.279-173.980 ± 15.523 µmol/L in the control, 100 nm, and 1300 nm PS-MPs treatment groups. In addition, the SOD activities were 10.566 ± 0.621, 9.039 ± 0.787-9.408 ± 0.493, and 7.959 ± 0.422-9.195 ± 0.327 U/mg protein for the control, 100 nm, and 1300 nm PS-MPs treatment groups, respectively, indicating that oxidative stress was induced after PS-MPs exposure. Furthermore, the comet assay suggested that exposure to PS-MPs induced DNA damage in earthworms. Overall, 1300 nm PS-MPs showed more toxic effect than 100 nm PS-MPs on earthworms. These findings provide new insights regarding the toxicological effects of low concentrations of microplastics on earthworms, and on the ecological risks of microplastics to soil animals.

Ecotoxicity and genotoxicity of polystyrene microplastics on higher plant Vicia faba.

Nano- and microplastics have been widely spread in environmental matrices, especially in marine and terrestrial systems. In this study, higher plant Vicia faba root tips were exposed to 5 µm and 100 nm with 10, 50 and 100 mg/L polystyrene fluorescent microplastics (PS-MPs) for 48 h. Root length, weight, oxidative stress and genotoxicity of V. faba were assessed to investigate toxic effects of PS-MPs. The results showed that the biomass and catalase (CAT) enzymes activity of V. faba roots decreased under 5 µm PS-MPs whereas superoxide dismutase (SOD) and peroxidase (POD) enzymes activity significantly increased. Under the 100 nm PS-MPs exposure a significant decrease of growth was observed only at the highest concentration (100 mg/L). However, micronucleus (MN) test and antioxidative enzymes activities showed that 100 nm PS-MPs induce higher genotoxic and oxidative damage to V. faba than 5 µm PS-MPs. Furthermore, the laser confocal scanning microscopy (LCSM) demonstrated that 100 nm PS-MPs can accumulate in V. faba root and most probably block cell connections or cell wall pores for transport of nutrients. These findings provide a new insight into the toxic effects of microplastics on V. faba, and further apply to the ecological risk assessment of microplastics on higher plants.