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Plastic pollution caused by conventional plastics has promoted the development and application of biodegradable plastics. However, biodegradable plastics do not degrade readily in water, instead, they can generate countless micro- and nanoplastics. Compared to microplastics, nanoplastics are more likely to cause negative impacts to the aquatic environment due to their smaller size. The impacts of biodegradable nanoplastics highly depend on their aggregation behavior and colloidal stability, which still remain unknown. Here, we studied the aggregation kinetics of polybutylene adipate co-terephthalate (PBAT) nanoplastics in both NaCl and CaCl2 solutions before and after artificial weathering. We further studied the effect of proteins on aggregation kinetics with both negatively charged bovine serum albumin (BSA) and positively charged lysozyme (LSZ). We found that divalent cations (Ca2+) destabilized PBAT nanoplastics more aggressively than monovalent cations (Na+); weathering stabilized PBAT nanoplastics profoundly, with no aggregation observed in NaCl nor in CaCl2; both BSA and LSZ promoted the aggregation of pristine PBAT nanoplastics, with LSZ showing more pronounced effect. These results suggest that biodegradable nanoplastics, especially weathered biodegradable nanoplastics, are highly stable in the aquatic environment.

Agricultural soils have been recognized as a major reservoir of microplastics, and concerns have arisen about the impacts of microplastics on soil properties and functioning. Here, we investigated the effects of microplastics on hydraulic properties of soils and determine the underlining mechanisms contributing to the effects. We measured the responses of a silt loam soil, a typical agricultural soil, to the incorporation of pristine as well as UV-weathered polypropylene granules and polyester fibers, two common types and shapes of microplastics, in terms of bulk density, saturated hydraulic conductivity, field capacity, permanent wilting point, water holding capacity, wet aggregate size distribution, and contact angle. We mixed polypropylene granules and polyester fibers into soil at different volume-based concentrations to elucidate the effect of microplastic shape. We also studied how weathering (UV and soil burial exposure) will affect the impact of microplastics on soil hydraulic properties. Due to the generally hydrophobic nature of plastic particles, the soil was found to lose some of its water holding capacity when contaminated with plastics. Fibrous microplastics rearrange soil structure and thus trigger more pronounced responses of soil hydraulic properties than granular microplastics. The results of this study provide fundamental knowledge about how microplastics interact with soil matrices and affect soil hydraulic properties, and advance current understanding about the impacts of microplastics on soil health.

Plastics pollution of terrestrial environments is a global problem, and plastics have been observed even in remote areas. However, how much plastic is present in terrestrial ecosystems is not well known. Here, we present a theoretical framework for representative sampling of randomly distributed plastic particles in soils or sediments. Based on geostatistical analysis, we determined optimal sampling strategies to quantify micro- and nanoplastics in soils or sediments. We used numerical simulations to test the sampling of randomly distributed plastic particles, and determined the sampling support (number of cores or sampling area) needed to obtain plastic concentrations within a specific error. Plastic pollution in the field was numerically simulated by placing plastic particles randomly in two dimensional space. We then took soil samples with differently sized cores, and determined plastic concentration as a function of number of cores taken. We will show how many cores are needed to determine the plastic concentrations within a given error.

Phytophthora cactorum, is an economically important plant pathogen causing sever damage on a wide range of crops, fruits, and ornamental plants. P. cactorum's infective potential and its spatial dissemination relies on rapid and copious production of asexual zoospores. However, little is known about P. cactorum zoospore transport behavior in porous media, impeding the development of effective technology in controlling infection and disease spreading. In this study, we investigated the transport and retention of P. cactorum zoospores in sand columns at three levels of water saturation (100%, 65%, 48%). Both motile and encysted zoospores were studied as well as carboxylate-modified polystyrene microspheres with the same size as the zoospores (10 um). We hypothesized that (1) motile zoospores are more readily transported than polystyrene microspheres under the same conditions, implying the minor role of size (straining) and the critical role of zoospore motility in controlling zoospore transport; (2) the higher mobility of motile zoospores compared to that of encysted zoospores is caused by the lack of sticky chemicals and the existence of flagella on the surface of motile zoospores; and (3) transport of motile and encysted zoospores, as well as of polystyrene microspheres is enhanced as column saturation increases.