The ubiquity of microplastics (MPs), plastic particles less than 5 mm, in the environment is an issue that will remain long after the last piece of plastic is produced. MPs can be formed from the fragmentation of larger plastics in the environment or by the direct release of manufactured MPs. Despite their persistence in terrestrial environments, little is known about their effects. There are also currently no regulations on MP content in sludge for agricultural application. Herein, MPs were made by cutting sheets of high-density polyethylene with a blender and removing the fraction greater than ~1 mm using a metal strainer. Aluminum covered pots, each containing 4 strawberry plants, were used for an outdoor summer exposure for 98 days. Treatments included (i) 10 mg MP kg<sup>-1</sup> soil (ppm MP), (ii) 100 ppm MP, (iii) contaminants, (iv) contaminants + 100 ppm MP, and (v) control. Contaminants were selected based on their relevance in wastewater effluents and covered a wide range of partition coefficients, namely: caffeine, acetaminophen, sulfamethoxazole, diethyl phthalate, ibuprofen, and triclosan. The soil enzyme activity was measured for β-N-acetylhexosaminidase (ACE), xylan 1,4-β-xylosidase (XYL), β-glucosidase (GLU), arylsulfatase (SUL), and phosphatase (PHO) which are responsible for C, S, and P cycling. Enzyme activities were measured using a fluorescence assay with 4-methylumbelliferone linked substrates. Soils treated with 10 or 100 ppm MP showed either no change or had significantly higher ACE, XYL, GLU, and/or SUL activity at 6 d and 35 d after exposure when compared to the untreated control, while GLU activity at 98 d was significantly lower than the control. The existence of MPs in the presence of the contaminants significantly lowered ACE activity after 6 d, but otherwise did not affect enzyme activity. No significant differences were found in the dry biomass of plants as well as in the number of crowns, leaves, flower stalks, runners, or fruits produced per plant between the treatments and the control. Microbial community data will also be obtained. Taken together, the data from this study will give us insight on the potential impacts of MPs on soil health as measured by soil enzyme activity, plant growth, and microbial community composition.

Effect of polyethylene microplastics on strawberry plant growth, soil enzyme activity, and microbial community composition

2019 Fall National Meeting

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