Microplastics

My first research interest was the economic valuation of microplastics. 

• We focused on microplastics it was a big deal in the public eye, they are often intentionally-added to consumer products, and most plastics degrade into microplastics anyway.

• My research demonstrates that respondents were willing to pay for measures to mitigate pollution. The WTP is relatively high, driven by precautionary attitudes, trust in experts, and perceptions of the harmfulness of microplastics.

• In my masters I had two projects; one a rudimentary contingent valuation survey, and another a cost-benefit analysis. The latter here has a bunch of citations mostly for the title I think. 

• In my PhD, the Environment Agency funded a stated preference survey (contingent valuation + choice experiment) to understand preferences for policies that would either reduce the uncertainty about microplastic pollution (through undertaking further research), or reduce the irreversibility (by mitigating pollution at the wastewater treatment plant level). Two chapters from the resulting thesis have since been published here and here. 

• I once presented at Society for Cost-Benefit Analysis the final chapter on cost-benefit analysis. The input data is imperfect, but one day I'd like to publish on using implicit+explicit distributional weights in evaluation. Let me know if you have a suitable context.

• We then won funding for a follow-up survey that recovered option prices for microplastic pollution control, echoing Trudy Cameron's 2005 paper here but adpated to the microplastic context. 

• I have supervised masters dissertations that follow-up that survey in different contexts. 

• If you would like to collaborate on surveys/valuation/microplastics I'd love to know!

Doctoral thesis:

• Estimation of the Value of Precautionary Restrictions on Microplastics.

• I was supported by a University Research Scholarship Award.

• Data collection supported by the Environment Agency.

• We found that:

  • Respondents may be willing to pay for measures to reduce microplastics in cosmetics.

  • I used hybrid choice models to show that precautionary attitudes influenced respondents preference for (a) reducing the irreversible release of microplastics over (b) reducing the uncertainty about microplastics effects. 

  • I calculated an indicative Cost-Benefit Analysis for these scenarios. 

    • Used implicit and explicit distributional weights.

• August 2021: I passed my viva with minor corrections thanks to examiners Dr Bruce Morley and Prof. Susana Mourato.

• Thesis: https://researchportal.bath.ac.uk/en/studentTheses/estimation-of-the-value-of-precautionary-restrictions-on-micropla

• Replication code and data: https://github.com/pmpk20/PhDPilotSurvey [I have written much much better code since!]

• Trivia: The Overleaf document compiled with ZERO LaTeX errors or warnings (underfull \hbox isn't real), and this was before AI.

Published:

• Willingness-to-pay for precautionary control of microplastics; a comparison of hybrid choice models (JEEP, 2022):

  • Open access: https://doi.org/10.1080/21606544.2022.2146757 

  • Old working paper version: 

Willingness-to-pay for precautionary control of microplastics; a comparison of hybrid choice models.

• • Replication code and data: 

https://github.com/pmpk20/PhDHybridChoiceModelPaper

• • Acknowledgements:

Dr Alistair Hunt and Dr Lucy O'Shea for all their supervision and guidance in the PhD, Dr Stavros Georgiou for funding acquisition and insightful comments, Richard Dean (Environment Agency), Caroline Rainsford (CTPA), and all the seminar audiences who offered comments.

• • We found that:

    • Precautionary attitudes can influence WTP for restrictions.

  • Why does it matter:

    • Stated preferences for policies on microplastic are probably exacerbated by public fears.

  • What changed in review: 

    • Removed section on estimating WTP with the hybrid choice model. 

    • Improved discussion.

• How confident are you in the ability of experts to provide reliable information? Evidence from a choice experiment on microplastics (EDE, 2025)

  • Open access: https://doi.org/10.1017/S1355770X25100077 

  • Replication code and data: 

https://github.com/pmpk20/PhD_CEPaper 

• • Acknowledgements [good]:

Dr Alistair Hunt, Dr Lucy O'Shea, Dr Stavros Georgiou, Richard Dean (Environment Agency), Caroline Rainsford (CTPA) for their insightful comments during the data collection. Thank you to the editors and two anonymous reviewers at EDE too for two rounds of insightful reviews.

• • Acknowledgements [bad]:

    • I will not be publishing at this journal again. I don't particularly mind that it took 6 months for the first review comments, but the communication on these, and other, delays was very poor. 

    • I completed the proofs, open-access request, and licensing on the 30th May 2025. The article then appeared online on the 20th August 2025. The reader is left to their own conclusions about whether this is a satisfactory timeline. 

  • We found that:

    • Lower pre-existing confidence in general experts' ability to provide reliable information makes a difference to (a) choosing the opt-out in a CE, (b) certainty of choices, and (c) maybe willingness-to-pay for attributes that are less familiar to respondents.

  • Why does it matter:

    • Falling public trust in experts in general can affect stated support for policies specifically.

  • What changed in review: 

    • Eagle-eyed reviewer found that I had accidentally defined an ASC on the wrong utility function in one model - now corrected with the effect of changing coefficient signs on the socioeconomic controls.

    • Reviewer 1 asked for more nuance (i.e., "pre-existing" and "general experts'") and to ensure that the introduction better situated this contribution in the literature. The manuscript is more precise thanks to their suggestions.

    • Reviewer 2 wanted further discussion on 'greenwashing' - not my area of expertise but I hope I signposted other studies on this for the interested reader.

• Individual Option Prices for Mitigating Microplastic Pollution (Under review)

  • First author with Christoph Rheinberger, Stavros Georgiou, Alistair Hunt. 

  • Data + code + survey: https://github.com/pmpk20/Microplastics