Sources, characterisation and exposure risk of airborne microplastic emissions from municipal solid waste dumping site in Nigeria

Abstract

Walton, Christopher - Associate SupervisorAirborne microplastics (AMPs) represent an emerging environmental and public health challenge, with their sources, transport mechanisms, and impacts still poorly understood, particularly in developing regions with inadequate waste management systems. This research addresses three key gaps: the need for cost-effective and efficient AMP sampling tools, the AMP flux estimations under different environmental conditions, and the modelling of AMP dispersion to understand their transport and potential exposure risks downwind. This research tackles these challenges by developing a low-cost sampler for AMP collection. The low-cost sampler was validated against the commercial sampler (SKC Deployable Sampler equipped with a Total Suspended Particulate (TSP) head), with a focus on fibres, fragments, and films across diverse environmental conditions. The emission of AMPs was quantified using a modified Fick’s law, which incorporates sitespecific parameters such as wind speed, temperature, and particle properties. Seasonal variation in AMP emissions was analysed by collecting and processing 226 environmental samples (42 soil and 184 air) from the municipal solid waste disposal site and its environment during dry and wet seasons. Dispersion modelling was conducted using SCREEN3 to simulate the downwind transport of AMPs. A low-cost sampler (LCS) was developed and evaluated against a commercial sampler, demonstrating a strong correlation (ρ = 0.976) and high accuracy (94.12%) compared to a reference sampler. The LCS effectively captured seasonal variations in AMP abundance. Polymer analysis identified five predominant polymers, with nylon (fibres), PVC (fragments), and PE (films) accounting for the majority of microplastics. The cost analysis revealed that the LCS offers 61% savings over second-hand and 98% over new commercial samplers, making it a reliable and affordable tool for AMP research in resource-limited settings. The airborne microplastics measured on-site reveal seasonal variations in concentrations. Notably, the dry season reveals higher concentrations (mean: 14.37 ± 3.87 MP/m³) comparable to the wet season (mean: 11.31 ± 3.00 MP/m³). Upwind concentrations were considerably lower, averaging 4.25 ± 1.17 MP/m³ during the dry season and 2.75 ± 1.43 MP/m³ during the wet season, reflecting contributions from distant fibre-rich sources, likely indoor emissions. On-site, films exhibited the lowest emissions but retained moderate mobility during the wet season. Fibres showed the highest diffusion coefficients, indicating potential for long-range transport. Fragments were the most abundant microplastic type (55% dry, 53% wet), with high emission factors (188 µg/day dry, 170 µg/day wet). Rising velocities were higher during the dry season due to favourable wind conditions, with values of 0.1056 m/s for nylon fibres, 0.0835 m/s for PVC fragments, and 0.0742 m/s for PE films. The rising velocities and flux measurements highlighted the influence of soil porosity and wind speed on resuspension and transport of microplastics. The SCREEN3 dispersion model reveals distinct seasonal variations in the transport of AMP from MSW sites. Peak AMP concentrations occurred at 100–107 m downwind, with wet season levels (fibres: 2.28 × 10⁻² μg/m³, fragments: 6.81 × 10⁻² μg/m³, films: 2.41 × 10⁻³ μg/m³) exceeding dry season concentrations by 2.1–2.2 times. Fragments posed the highest health risks (Level III), particularly during short-term exposures, while fibres and films showed lower risks. SCREEN3 agreed well with ground measurements (R2 = 0.98 to 0.96) and identified key drivers such as stability classes and precipitation, affirming its utility for AMP transport modelling and risk assessment. This study highlights the significant environmental and health implications of airborne microplastic (AMP) emissions from municipal solid waste (MSW) sites. Fragments pose the greatest risks, particularly during the wet season. The development of a lowcost sampler and advanced dispersion modelling provides essential tools for AMP monitoring. To mitigate AMP impacts, improved waste management practices, such as minimising open burning, are necessary. Integrating AMP data into air quality monitoring frameworks and prioritising seasonal mitigation measures are also recommended. Future studies should investigate long-range transport mechanisms, refine emission factor models, and chronic exposure risks to develop comprehensive strategies for mitigating AMP impacts globally.PhD in Energy and Powe