Frontiers Microplastic effects on soil nitrogen storage, nitrogen emissions, and ammonia volatilization in relation to soil health and crop productivity: mechanism and future consideration Incorporation of polylactic acid microplastics into the carbon cycle as a carbon source to remodel the endogenous metabolism of the gut PNAS Microplastics contamination in food products: Occurrence, analytical techniques and potential impacts on human health ScienceDirect Microplastic sources, formation, toxicity and remediation: a review Environmental Chemistry Letters Springer Nature Link