**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** MICROPLASTICS CONTAINED IN WASTEWATER ARE REMOVED DURING WASTEWATER TREATMENT AND ACCUMULATE IN BIOSOLIDS. THE MAJORITY OF THESE BIOSOLIDS ARE LAND-APPLIED FOR AGRICULTURAL PURPOSES, WITH AN AVERAGE OF 60% USED THROUGHOUT THE U.S., AND 80% IN THE STATE OF WASHINGTON. LAND-APPLICATION OF BIOSOLIDS IS BENEFICIAL, AS THEY CONTAIN BOTH MACRO- AND MICRONUTRIENTS; HOWEVER, THE IMPACT OF PLASTICS IN BIOSOLIDS TO SOILS HAS NOT BEEN INVESTIGATED AND ITS LONG-TERM EFFECTS REMAIN UNKNOWN. WE HYPOTHESIZE THAT MICROPLASTICS ACCUMULATE IN AGRICULTURAL SOILS, AND THE GOAL OF THIS PROPOSAL IS TO EVALUATE THE RISK THAT THIS CONTAMINATION MAY POSE TO SOIL HEALTH. SPECIFIC OBJECTIVES ARE TO (1) QUANTIFY AND CHARACTERIZE MICROPLASTICS IN BIOSOLIDS OF A WASTEWATER TREATMENT PLANT; (2) DETERMINE WHETHER LONG-TERM APPLICATION OF BIOSOLIDS TO AGRICULTURAL SOILS HAS LED TO AN ACCUMULATION OF MICROPLASTICS OVER TIME; (3) EVALUATE THE INTERACTIONS OF MICRO- AND MACROPLASTICS WITH PLANT ROOTS, AND (4) DETERMINEWHETHER THERE IS ATMOSPHERIC INPUT OF MICROPLASTICS AT THE AGRICULTURAL FIELD SITE. OUR STUDY DESIGN INCLUDES A UNIQUE OPPORTUNITY TO INVESTIGATE SOILS FROM AN EXPERIMENTAL DRYLAND WHEAT CROPPING SYSTEM, WHERE BIOSOLIDS HAVE BEEN APPLIED FOR 20 YEARS. OUR PROJECT CONTRIBUTES TO THE PROGRAM AREA PRIORITY OF FOUNDATIONAL RESEARCH TO ADVANCE SCIENTIFIC UNDERSTANDING OF PROCESSES AND INTERACTIONS''.