Abrasion of tire wear is one of the largest sources of microplastics to the environment. Although most tire particles settle into soils, studies on their ecotoxicological impacts on the terrestrial environment are scarce. Here, the effects of tire particles (<180 μm) on three ecologically relevant soil invertebrate species, the enchytraeid worm Enchytraeus crypticus, the springtail Folsomia candida and the woodlouse Porcellio scaber, were studied. These species were exposed to tire particles spiked in soil or in food at concentrations of 0.02%, 0.06%, 0.17%, 0.5% and 1.5% (w/w). Tire particles contained a variety of potentially harmful substances. Zinc (21 900 mg kg^-1) was the dominant trace element, whilst the highest concentrations of the measured organic compounds were detected for benzothiazole (89.2 mg kg^-1), pyrene (4.85 mg kg^-1), chlorpyrifos (0.351 mg kg^-1), HCB (0.134 mg kg^-1), methoxychlor (0.116 mg kg^-1) and BDE 28 (0.100 mg kg^-1). At the highest test concentration in soil (1.5%), the tire particles decreased F. candida reproduction by 38% and survival by 24%, and acetylcholinesterase (AChE) activity of P. scaber by 65%, whilst the slight decrease in the reproduction of E. crypticus was not dose-dependent. In food, the highest test concentration of tire particles reduced F. candida survival by 38%. These results suggest that micro-sized tire particles can affect soil invertebrates at concentrations found at roadsides, whilst short-term impacts at concentrations found further from the roadsides are unlikely.

Various plastic materials are used in contact with agricultural soil, like mulching films, crop covers, weed controlling fabrics and nets. Polyethylene (PE) mulches have already been recognized as a significant source of plastic in soil and they have been shown to contain additives like phthalates, known as endocrine disruptors. However, other agricultural plastics are less studied, and little is known on the substances potentially released from them endangering biodiversity and the human health. This research aims to assess whether different agricultural plastics release additives into soil and to compare the release among various materials. We collected soil samples from 38 agricultural fields where conventional mulching films (PE), weed controlling fabrics (PP), biodegradable mulches based on polybutylene adipate terephthalate (PBAT), frost covers (PP), and oxo-degradable films (at least OXO-PE) were used. We analyzed the soils for phthalates and acetyl tributyl citrate (ATBC), used as plastic additives, and for polycyclic aromatic hydrocarbons (PAH) and dodecane that have high affinity for plastics. In comparison to the control soils, dibutylphthalate (DBP) and ATBC concentrations were significantly higher in soils mulched with PE and, partly, with biodegradable films. DBP concentration found in soil samples ranged between below the limit of quantification at a control site (1.5 μg kg^-1) to 135 μg kg^-1 at a site mulched with OXO-PE. The highest ATBC concentration, 22±6 μg kg^-1, was registered in a site mulched with PE, showing a statistically significant difference not only in comparison to the controls but also when compared to sites mulched with OXO-PE (p=0.029) and PBAT (p<0.009). On the contrary, the use of agricultural plastics did not influence the concentration of PAHs and dodecane. Our results indicate that agricultural plastics are a source of some organic chemicals to agricultural soils, including phthalates that are known for posing threat to soil ecosystem and human health.

The increasing use of agricultural plastics (APs) and resulting accumulation of microplastics (MPs) in soils potentially affects soil organisms. This study assessed the effects of polypropylene MPs derived from commonly used black ribbon and white fleece mulching fabrics on four soil invertebrates. Animals were exposed to MP concentrations of 0.005 % - 5 % in Lufa 2.2 soil to assess effects on survival, reproduction (Enchytraeus crypticus, Folsomia candida) and behavior (Eisenia andrei, Porcellio scaber). Both MP types dose-relatedly decreased soil bulk density, and increased soil water holding capacity at high concentrations. The MPs from white fleece mulching fabric also increased soil pH at all concentrations tested. Reproduction was affected more by MPs from black ribbon fabric than from white fleece mulching fabric, significantly affecting enchytraeids at 1 % and 5 %, and at 5 %, respectively, and springtails only at 5 % for the black ribbon fabric MPs. Earthworms avoided soil at 5 % of the first or 0.5 % and 5 % of the second MP type. Isopods seemed attracted, but also showed different walking behavior at 5 % of black ribbon fabric MPs. MPs derived from commonly used APs were shown to affect soil properties at low concentrations and the reproduction and behavior of soil invertebrates.

The increasing use of plastics in agriculture, e.g., mulching films, may lead to an accumulation of microplastics (MPs) in soil. This study assessed the effects of a 1:1 mixture of MPs produced from two commonly applied types of mulching film, conventional low-density polyethylene (LDPE) based and biodegradable starch polybutylene adipate terephthalate (PBAT-BD) blend-based plastics, under realistic conditions in terrestrial mesocosms. To assess the potential role of earthworms on the effects of microplastics, the study included treatments with and without earthworms. After 12 weeks of exposure, effects were determined on different endpoints: soil pH, soil compaction, carbon and nitrogen mineralization, and plant growth and biochemistry. MPs increased soil compaction, especially in the absence of earthworms, suggesting that earthworm activity can mitigate their physical impact on soil structure. MPs stimulated soil respiration at high concentrations, while simultaneously reducing nitrogen mineralization. This suggests these MPs acted both as a stimulant and a stressor for soil microbial communities. Although plant growth and chlorophyll content were unaffected by MP exposure, significant biochemical responses in lettuce, such as oxidative stress and activation of defence mechanisms, indicate that MPs can impact plant health at the molecular level, even in the absence of visible symptoms. Nitrogen mineralization was significantly increased in the mesocosms with earthworms, probably due to bioturbation and consequent increased aeration of the soil. However, the presence of earthworms did not have significant effects on other microbial and plant-related endpoints, suggesting that the earthworms affected the toxicity of the MPs only to a limited extent.

Agricultural soils receive a wide range of organic and inorganic contaminants through long-term fertilization, yet field-based evidence linking complex contaminant mixtures to biological exposure of soil organisms under realistic agricultural conditions remains limited. Here, soils and endogeic earthworms (Aporrectodea cf. caliginosa) were sampled from two adjacent agricultural fields in Finland after more than two decades of contrasting fertilization with sewage sludge-based products and broiler litter. A broad suite of organic contaminants together with multiple metals was analyzed in both matrices, and bioaccumulation factors were used to assess soil-biota transfer. Distinct fertilization-specific contaminant profiles were observed in soils, with higher concentrations of several organic contaminants under sewage sludge fertilization. In earthworms, per- and polyfluoroalkyl substances (PFAS) dominated contaminant profiles and showed pronounced bioaccumulation, particularly for long-chain PFAS including perfluorooctane sulfonate (PFOS). Other contaminants showed variable, compound-specific transfer, and biological exposure was not consistently reflected by bulk soil concentrations. These results provide field-based evidence of distinct soil contaminant profiles under contrasting long-term fertilization histories, but biological exposure cannot be reliably inferred from bulk soil concentrations alone. Instead, contaminant transfer to soil organisms was more consistent with bioavailability-related and substance-specific properties reported in previous studies, highlighting the importance of integrating biota-based measurements into assessments of agricultural soil contamination.

Soils are considered to be a major sink for microplastics (MPs) in the environment, with the application of agricultural mulch films being one of the most important pathways to enter soil. Once in the soil, plastic particles are exposed to various environmental factors leading to MP ageing, characterised by morphological and structural changes. Soil aggregates can play a crucial role for these degradation processes, potentially preserving MP within them.Therefore, the aim of this study was to investigate the degradation differences between MPs originating from mulching films inside and outside of soil aggregates over a two-year exposure period in European agricultural topsoils.To do so, we analysed samples from field plot trials in Finland, Spain and Germany where MPs (< 1 mm) derived from recycled low-density polyethylene and starch - polybutylene adipate terephthalate films were incorporated into topsoil (0-10 cm) at a concentration of 0.05%. Barley was grown there in two consecutive years and soil samples were taken immediately after harvest.Free MP and MP embedded in soil aggregates were separated using a combination of plastic extraction and aggregate separation techniques, ensuring that these methods did not alter the surface or structure of the MPs. The degradation state was assessed using a correlative multimodal approach, including scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX), nano-computed tomography (nano-CT) and Fourier transform infrared spectroscopy (FTIR).Exposure to soil resulted in significant ageing effects of MPs, such as surface cracking, increased oxygen content and the formation of new functional group, a higher proportion of pores, and the attachment of microorganisms. Notably, the ageing effects were more pronounced for MPs outside the aggregates compared to those embedded in the aggregates. In addition, differences were observed that were influenced by the specific conditions in each country. The results of this study reflect the complexity of environmental ageing, which depends on the soil conditions in each country. In conclusion, aggregates protect MPs from degradation, favouring plastic accumulation in the soil.