Estimate environmental exposure of source microplastics entering WWTPs, including:• Variable consumer use rate• Variability in wastewater sludge handling practices• Terrestrial transport using environmental factors• Hydrologic routing using well established datasets• Particle mass disposition within compartments• Spatially explicit: aggregation and examination• Scalable and extensible to other geographies

MODELLING EMISSIONS OF MICROPLASTICS IN EUROPE FROM WASTEWATER SOURCES, INCLUDING LAND APPLIED BIOSOLIDS

Christopher M. Holmes1, Joshua Amos1, Amy Ritter1, Marty Williams1 and Scott D. Dyer1,2,*1Waterborne Environmental, Virginia (USA) 2 LeTourneau University, Longview, TX (USA)

BACKGROUND AND OBJECTIVES

Science-based risk assessment must utilize both retrospective and prospective exposure information to effectively estimate potential risk to ecological receptors frommicroplastics in the environment. While monitoring data provide information at a few locations for several points in time, prospective models can estimate the potentialfor ecological exposures across many landscapes and over long periods of time. Wastewater treatment plants are often cited as a source of microplastics entering theenvironment. Microplastics are highly removed (generally >90%) via skimming of floating particles or sorption to solids and settling into sludge. Understanding theeventual fate of this sludge, and the potential for contained microplastics to re-enter surface water, is one step of many in determining the fate of microplastics in theaquatic environment.

We present a model which addresses both direct aquatic emissions into surface water via waste water effluent, as well as indirectly from land applied biosolids coupledwith spatially-defined surface runoff potential. Generalized runoff potential is estimated using defined scenarios and fate and transport models for plant protectionproducts. This spatially-explicit model is based on publicly available datasets, combined with a hydrologic framework containing geographically variable emissions linked toa river network simulating environmental transport via surface water.

CONCEPTUAL MODEL

The model was designed to be global in extent, but incorporate sufficient local processing to capture the geographic heterogeneity of usage, treatment and environmental factors. It captures household emissions to wastewater and accounts for handling of sludge containing microplastic particles

Credit: Larry Rosen

HydroSHEDS framework for characterization and routing

Mainstem river and lakes from HydroRIVERS and HydroLAKES

55 years of flow data from FLO1K, overlaid on river mainstem

Urban, ag and pasture landcover from JRC Corine Land Cover

Per capita water use from Eurostat and MS level sources

Municipal facilities from EEA WaterBase

Sewage sludge disposal from wastewater treatment - Eurostat

Microplastics captured in sludge and applied to agricultural land viabiosolids are modeled within PRZM using 15 scenarios covering weatherand soil characteristics. Scenarios were informed by a JRC dataset usingRUSLE2015 to estimate soil loss in Europe utilizing rainfall erosivity, soilerodibility, cover management, topography, and support practices(Panagos et al, 2015). Within each of the three defined EFSA zones, ageometric binning approach was used to identify 5 bins (0-50th, 51-75th,76th-87.5th, 87.6-93rd, 94th-100th) in order to ensure inclusion of higherosion areas.

A “baseline” PEC is calculated excluding episodic events such asagricultural runoff. This represents the steady-state condition fromcontinual WWTP effluent. Episodic events add additional mass for ashort “peak” duration.

Scenario:Per cap use: 1 mg/day(except Czech Republic and Slokavia) Total mass modelled 213 t/yrWWTP to effluent: 10%WWTP degradation: 0%WWTP to sludge: 90%Kd for soil modelling: 10000Soil aerobic half-life: 120 daysIn-river net-settling velocity: 1.0 m/d

Results from an example model run using inputs below can be summarized and visualized inseveral methods, from tabular output, spatial mapping, or aggregation to different spatiallevels or environmental compartments.

RESULTS AND VISUALIZATIONMOVEMENT FROM TERRESTRIAL ENVIRONMENT

IN-RIVER PARTICLE SETTLING

Particles settle in the river based on particle size, river depth, and timeof travel, using relationships from the NanoDUFLOW model (Besselinget al 2017). This incorporates processes such as homo-aggregation,hetero-aggregation with natural colloids, biofouling, settling andresuspension into a generalized net settling velocity.

The sub-basin is the unit of analysis forthe model. Each sub-basin (n=38,444 forEU-30) is attributed using a distinct inputdatabase. The spatial scale of theattribution can be refined over timewithout modifying the model code.

Erosion potential based on JRC soil loss data + PRZM pesticide model

SPATIAL UNITGLOBAL & REGIONAL ENVIRONMENTAL AND ANTHROPOGENIC DATA

Panagos et al., 2015. A new assessment of soil loss by water erosion in Europe. Env. Science & Policy 54 (2015) 438-447. http://dx.doi.org/10.1016/j.envsci.2015.08.012

Drift

Runoff / erosion

PRZM Water body

30-year annual average % of applied mass leaving the field

Besseling, E., Quik, J.T.K., Sun, M., and Koelmans, A.A., (2017). Fate of nano-and microplastic in freshwater systems: A modeling study. Environmental Pollution 220, 540–548.

Net settling velocities are configurable and canbe related to waterbody type, river velocity, orother local/regional characteristics as available.

Biosolid application occurred twice a year tomaize. One-half of the PRZM 30-year annualaverage % of applied mass leaving the fieldis conservatively assumed to occur twice ayear. These aspects are configurable.

Environmental Dispositionof Annual Emitted Mass:Marine 1.1%Freshwater 0.1%Sediment 8.7%Agricultural runoff 0.5%Agricultural Soil 34.5%Incinerated 25.9%Landfill 10.6%Compost 10.4%Other sludge 8.3%

Total Annual Modelled Mass Residing in the Environment Environmental Disposition of Total Annual Mass within each Country

Surface Water Predicted Environmental Concentrations (PECs) for Baseline Scenario

*More Information: dyers@waterborne-env.com

Baseline and Peak Surface Water PECs by Country