Knowledge and data – microplastics pitches

July 6th, 2023

Risk characterisation of microplastics in recycled organic wastes – getting the right count [pdf] – Sijing Li (CSIRO)

Although the majority of microplastics released into the environment are discharged into terrestrial ecosystems, significantly less attention has been focussed on the characterisation of risk in these systems. Risk characterisation requires accurate and reliable quantitative measurement of microplastics in complex environmental samples. Understanding risks in terrestrial systems is particularly urgent as Circular Economy principles are increasingly embraced and unintentional leakage of microplastics into the environment will occur to a greater extent. Based on our previous work in quantifying microplastics in wastewater and associated sludges, we are working to establish microplastic loads in three organic wastes commonly used for soil amendment; wastewater sludge, composts and organics from construction waste. This project involves collaboration with other laboratories using spectroscopic and mass spectrometry techniques to (1) verify baseline quantities of microplastics; (2) establish the most effective methodology for large scale monitoring programs; and (3) contribute to microplastic risk characterisation in land-applied organic wastes.

Role of water shear force for microplsatics fragmentation into nanoplastics in the wastewater treatment plants [pdf not available for download] Biplob Pramanik (RMIT University)

Wastewater treatment plants (WWTPs) contribute to secondary microplastics (MPs) and nanoplastics (NPs) production due to mechanical stress from the mixing process. We investigated the fragmentation of pristine and weathered polystyrene (PS) particles (250 and 106 μm) using a four-blade mechanical impeller. Results revealed that pristine PS particles broke down into mean sizes of 120.6 and 95.6 nm, respectively, at 100 KJ/L energy density. The fragmented PS particles exhibited cracks, pores, damages, and rough structures, confirming the impact of mechanical stress. Crack propagation on particle surfaces, caused by water shear force, was identified as the primary MP fragmentation mechanism into NP. NP levels increased significantly after 40 minutes of mixing, with a 28-fold increase at 32 KJ/L energy density. These findings indicate that MP breakdown into NP is a continuous process during wastewater treatment, presenting a considerable risk to water environments due to NP release by WWTP effluents.

Detecting microplastics in organic-rich materials and their potential risks to earthworms in agroecosystems [pdf not available for download] – Chengrong Chen (Griffith University)

We determined microplastics’ concentration, size-distribution, and chemical composition in 3 biosolids and 6 biosolid-amended soils. We also assessed short-term risks of MPs to earthworms’ (Amynthas Gracilis and Eisenia Fetida) survival rate and fitness (28 days exposure study). Biosolid-amended soils showed ≈30 times lower MPs content than biosolids, with microplastic fragment to fibre ratios between 0.2 – 0.6 and 0.3 – 0.4 in soils and biosolids, respectively. 77% and 80% of plastic fragments had diameter lower than 500 µm, while 50% and 67% of plastic fibres had length of less than 1000 µm in soil and biosolid samples, respectively. Polyethylene was major source of microplastic contamination in biosolid-amended soils, while polyethylene terephthalate showed highest concentration in biosolid samples. Spiked polyethylene MPs did not show any significant effect on earthworms’ survival rate. However, biosolid application significantly decreased survival rate of E. Fetida (81%) but showed no significant effect in A. Gracilis (93%).

Bringing the Micro Into View Through a Microlitter Reduction Framework [pdf] – Juniper Riordan (Australian Microplastic Assessment Project – AUSMAP)

A lack of a strategy to reduce microlitter (1-5mm) has contributed to ill-informed management of a growing pollution problem. In response, AUSMAP has created a Microlitter Reduction Framework based on hotspot identification, source tracking and stakeholder action. The framework was piloted in Dee Why Lagoon, NSW, which had been shown to be a microplastic hotspot. AUSMAP traced microlitter up-catchment from the lagoon through end-of-pipe sampling and demonstrated that microlitter varied in volume and type between land use types. Further, pit traps were installed across these areas with results showing that they prevented 450 kg of debris from entering the Lagoon over an 8 month period. Extrapolation of this data across the Dee Why catchment indicated that over a 12 month period, 3.1 million microplastics would enter the Lagoon. An education campaign with key stakeholders and controls on targeted sources followed. The process behind a successful MRF will be discussed.