Occurrence and distribution of microplastics in long-term biosolid-applied rehabilitation land: An overlooked pathway for microplastic entry into terrestrial ecosystems in Australia.

Wastewater treatment plants (WWTPs) efficiently eliminate over 98% of microplastics (MPs) from wastewater discharge, subsequently accumulating them in sludge. This sludge is frequently employed as fertilizer in agricultural practices or land rehabilitation. While there is significant research on biosolid application in agriculture, the discussion regarding its application in rehabilitating industrial zones and MPs contamination is limited. The current study investigates the abundance, distribution, and composition of MPs in rehabilitation land with long-term biosolid-application in Australia. Three minesite fields (designated 1-3), each with distinct biosolid application histories since 2011, 2012, and 2017, and a control field without any biosolid application history, were chosen for this study. The abundances of MPs in biosolid-applied fields 1-3 (6.04 ± 1.92 x 102 MP kg-1; 4.94 ± 0.73 x 102 MP kg-1; 2.48 ± 0.70 x 102 MP kg-1) were considerably higher compared to non-biosolid-applied field (0.70 ± 0.63 x 102 MP kg -1). This indicates that the application of biosolids significantly contributes to the presence of MPs in the soil. Moreover, the results suggest that with each successive application, the abundance of MPs increases. The abundance and size of MPs in both biosolid and non-biosolid soils decreased as the soil depth increased. Microbeads were dominant in soils where biosolids were applied (up to 61.9%), while fibres were dominant in non-biosolid soils (accounting for 85.7%). The distribution of plastic polymer types varied among fields and soil depths. Most MPs were microbeads of polyamide (PA), fragments of polyethylene (PE), foam of polystyrene (PS), and fibres of rayon. This research presents evidence that the extended utilization of biosolids results in elevated MP pollution in minesite rehabilitation land, highlighting a frequently overlooked origin of MP contamination in terrestrial settings. Additional evaluations needed to understand ecological risks of MPs in soil ecosystems affected by biosolid application.

Fate and transformation of microplastics due to electrocoagulation treatment: Impacts of polymer type and shape.

The prevalence and adverse impacts of microplastics requires the identification of science-based abatement measures. Electrocoagulation treatment is a cost-effective oxidation process that removes numerous pollutants, including to some extent, microplastics. The performance of a custom-built electrocoagulation reactor was determined by calculating the removal efficiency. The effects of the oxidation process on polymer types (polyamide (PA), polyethylene (PE), polyethylene terephthalate (PET) and polypropylene (PP)) and shapes (fibres and fragments) were investigated in synthetic wastewater and laundry wastewater. The calculated removal efficiency suggested that electrocoagulation treatment was an effective technology for microplastics abatement. More fibres tended to be removed than fragments, viz. 92% fibres removed versus 88% fragments. The findings also demonstrated that specific polymers were preferentially removed, viz. PET > LDPE > PP > PA. Further analysis indicated that the electrocoagulation treatment affected microplastic polymers physically, viz. flaking and changed surface conditions, as well as chemically, viz. changes in vibrational energies of C-O-C stretching bonds, C=O stretching bonds, C-H stretching bonds and formation of reactive oxygen species (ROS). Our findings indicate that whilst seemingly effective, electrocoagulation treatment induces changes to microplastic polymers that could beneficially lead to degradation, and/or further fragmentation or breakdown and thereby potentially generating more bioavailable toxic nanoplastic byproducts.