「生分解性」ティーバッグは環境中で容易に分解されず、ミミズに害を与える可能性があるとの研究結果(Study says ‘biodegradable’ teabags don’t readily degrade in the environment and can harm earthworms)

2024-05-31

2024-05-30 バース大学

新しい研究によると、プラスチック代替品で製造されたティーバッグの一部は土壌で分解せず、陸上生物に害を与える可能性があります。研究者たちは、ポリ乳酸（PLA）製ティーバッグの土壌中での分解状況を調査しました。PLAのみで作られたティーバッグは完全に残存し、セルロースとPLAの混合物から作られたものは60%から80%分解しました。さらに、PLAがミミズに与える影響も評価され、死亡率や繁殖に悪影響が確認されました。研究は、正確な廃棄情報の表示の重要性を強調しており、消費者の混乱を防ぐために明確なガイドラインの必要性を示しています。

＜関連情報＞

バイオベースのポリ乳酸プラスチック製ティーバッグの環境条件下での劣化と、それに伴うミミズへの影響 Deterioration of bio-based polylactic acid plastic teabags under environmental conditions and their associated effects on earthworms

W. Courtene-Jones, F. Burgevin, L. Munns, M.B.T. Shillam, F. De Falco, A. Buchard, R.D. Handy, R.C. Thompson, M.E. Hanley
Science of The Total Environment Available online: 20 May 2024
DOI:https://doi.org/10.1016/j.scitotenv.2024.172806

Highlights

Soil deterioration and ecotoxicity of cellulose:PLA teabags were studied.
The mass ratio of teabag cellulose:PLA decreased following 7-months field degradation.
Mass loss was attributed to degradation of cellulose (rather than PLA) fibres.
Treatment and dose-specific effects of teabags on E. fetida reproductive output
Bio-based ‘plastic substitutes’ require evaluation to avoid negative consequences.

Abstract

In response to the plastic waste crisis, teabag producers have substituted the petrochemical-plastic content of their products with bio-based, biodegradable polymers such as polylactic acid (PLA). Despite widespread use, the degradation rate of PLA/PLA-blended materials in natural soil and their effects on soil biota are poorly understood. This study examined the percentage mass deterioration of teabags with differing cellulose:PLA compositions following burial (−10 cm depth) in an arable field margin for 7-months, using a suite of analytical techniques, such as size exclusion chromatography, ¹H nuclear magnetic resonance, dynamic scanning calorimetry, and scanning electron microscopy. The effect of 28-d exposure to teabag discs at environmentally relevant concentrations (0.02 %, 0.04 % and 0.07 % w/w) on the survival, growth and reproduction (OECD TG 222 protocol) of the key soil detritivore Eisenia fetida was assessed in laboratory trials. After 7-month burial, Tbag-A (2.4:1 blend) and Tbag-B (3.5:1 cellulose:PLA blend) lost 66 ± 5 % and 78 ± 4 % of their total mass, primarily attributed to degradation of cellulose as identified by FTIR spectroscopy and a reduction in the cellulose:PLA mass ratio, while Tbag-C (PLA) remained unchanged. There were clear treatment and dose-specific effects on the growth and reproductive output of E. fetida. At 0.07 % w/w of Tbag-A adult mortality marginally increased (15 %) and both the quantity of egg cocoons and the average mass of juveniles also increased, while at concentrations ≥0.04 % w/w of Tbag-C, the quantity of cocoons was suppressed. Adverse effects are comparable to those reported for non-biodegradable petrochemical-based plastic, demonstrating that bio-based PLA does not offer a more ‘environmentally friendly’ alternative. Our study emphasises the necessity to better understand the environmental fate and ecotoxicity of PLA/PLA-blends to ensure interventions developed through the UN Plastic Pollution Treaty to use alternatives and substitutes to conventional plastics do not result in unintended negative consequences.