Effects of plastic-char on soil functions and crop productivity

Abstract

A significant quantity of plastic waste cannot be recycled. One way of processing this plastic is through pyrolysis, which produces feedstocks for polyolefin synthesis. This process produces a biochar like product called “plastic-char”. This study aimed to investigate the impact of plastic-char produced from mixed non-recyclable plastic waste on pore water elemental concentrations, plant growth and greenhouse gas (GHG) emissions using a series of pot experiments applied at 1 t ha^-1 and 10 t ha^-1 eq. Plastic-char was found to increase plant growth of Lolium perene by a cumulative total of approx. 60% over four harvests, with no significant impact on germination. Increases in pore water concentrations of approximately 200% were observed for Ca, K and Mg at 10 t ha^-1. Significant increases were observed in pore water concentrations for Sb (371%) Na (519%), and Ti (724%) at 10 t ha^-1, compared to the control, with no significant changes in Al, Cd, Co or Cr. The plastic-char significantly increased the production of CO₂ from the soil by approximately 330% over the 10 days compared to the control, when applied at 10 t ha^-1 eq. While we do not suggest that soil application of plastic-char from mixed plastic waste should be used as a means of waste disposal, evidence presented here suggests that there may be value in plastic-char in terms of plant nutrients from the ash fraction and potential GHG reduction from the carbon rich fraction if it can be shown to be sufficiently depleted in contaminants. As such, this represents a potential means of adding value to the mixed plastic waste management stream.