Temperature Dependence of Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) Biodegradation in Agricultural Soils

TL;DR

This study examines how temperature affects the breakdown of a biodegradable polyester in agricultural soils.

Contribution

The work establishes a temperature-dependent biodegradation model for PHBHHx in soils using kinetic analysis.

Findings

Higher temperatures increased biodegradation rates of PHBHHx in agricultural soils.

Arrhenius analysis showed soil-specific activation energies affecting biodegradation rates.

Fungal and bacterial colonization increased with rising temperature on PHBHHx films.

Abstract

Biodegradable polyesters
are increasingly used in agricultural
applications with soil biodegradation as the targeted postapplication
end-of-life. Soil biodegradability is typically established in laboratory
soil incubations at constant temperatures exceeding those in many
field soils, highlighting the need for robust temperature-biodegradability
relationships to transfer laboratory-determined biodegradation rates
to field conditions. This work systematically assesses the temperature
dependence of the biodegradation of three poly­(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) variants, containing differing
molar amounts of 3-hydroxyhexanoate (where x = 5, 9, and 12%) in three
agricultural soils. Scanning electron microscopy images of PHBHH9
films incubated for 18 days showed increasing film surface colonization
by fungi and/or filamentous bacteria from 5 to 15, 25, and 35 °C,
with dense hyphal networks and film disintegration at the higher tested
temperatures. Soil biodegradation of PHBHHx powders over the same
temperature range was followed by extracting and quantifying residual
PHBHHx mass over time by proton nuclear magnetic resonance spectroscopy.
Fitting of these residual masses with a shoulder-log linear kinetic
model yielded PHBHHx-variant-independent initial lag phases and biodegradation
rate constants. Increasing the temperature shortened the initial lag
phase and increased the subsequent rate of PHBHHx biodegradation.
Arrhenius rate law analysis revealed soil-specific activation energies
that correspond to approximately 2- to 5-fold changes in biodegradation
rates per 10 °C. This work establishes temperature as a key abiotic
factor controlling polyester biodegradation rates in soils and guides
more accurate extrapolation of laboratory-determined biodegradation
rates at elevated temperatures to field conditions.

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