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News article29 March 2023Directorate-General for Environment

Biobased biodegradable polymers may amplify absorption of mercury from the marine environment

Issue 598: Biobased polymers, designed to be used instead of fossil-based plastics, are growing in use worldwide.

Biobased biodegradable polymers may amplify absorption of mercury from the marine environment
Photo by Meaw_stocker, Shutterstock

As plastic littering in the environment is of great concern, the effects of littered biobased biodegradable plastics in aquatic habitats may be amplified by their capacity to interact with mercury (Hg). This study sought to understand better how ultraviolet (UV) ageing affects biobased polymers in water, and whether the amount of mercury that can attach to these polymers increases as a result.

Mercury is a neurotoxic metal, which persists in the marine environment. Levels of mercury have tripled compared to 150 years ago, with the rise likely resulting from human-related activities, such as artisanal small-scale gold mining and burning fossil fuels. Mercury has a high affinity (i.e., the strength by which two or more molecules interact or bind) to biological materials such as banana peel or rice husk (or bioremediators). As biobased polymers have similar chemical structures to bioremediators, there is a further concern about unintended leakage when they enter highly contaminated aquatic ecosystems.

At present, both biobased polymers, derived from biomass, and those derived from fossil fuels may be biodegradable depending on their specific composition. However, as laid out in the recently adopted Communication on Biobased, biodegradable and compostable plastics COM(2022)682, “for that [a full biodegradation of plastic] to happen, in addition to the characteristics of the plastic material, suitable conditions in the receiving environment and sufficient time are necessary. This is why plastic biodegradation must be considered not only in terms of the properties of the material, but above all in terms of a ‘system-property’ where material-related and environment-related factors are equally important”. When a biobased plastic polymer breaks down, it forms micro- and nano-biobased plastic particles, similar to fossil-based micro- and nanoplastics. It may be that the ability of micro- and nano-biobased plastics to retain micropollutants on the surface increases with smaller size – as it does with fossil-based plastic particles.

This study is the first to investigate whether UV-aged biobased and biodegradable polymers undergo structural changes, that increase their ability to attach mercury at high concentrations in aquatic environments. Understanding how biobased biodegradable plastic degrades, and any potential it has to attach mercury, is important for understanding potential bioaccumulation of mercury in the food chain. This could happen when biobased plastic is dropped as litter in the environment and the micro and nano-biobased plastic particles that have absorbed mercury in highly polluted water are ingested by animals, thus allowing them to enter the food chain.

Safe biodegradation of biobased, biodegradable and compostable plastics, is a priority for the European Commission which recently adopted a policy framework on biobased, compostable and biodegradable plastics – stipulating additives used to manufacture biodegradable or compostable plastics should biodegrade safely. The researchers exposed squares of polyethylene and a commercially available biobased polymer composed of a blend of starch and polyester to UV light and water, which is biodegradable, using accelerated-weathering test equipment. They used two types of UV radiation on two different batches of samples – one mimicking the sunlight at noon, the other a UVB lamp replicating the later stages of breakdown. They obtained chemical profiles of the biobased polymers and polyethylene specimens using light spectroscopy equipment. 

The researchers tested two concentrations of mercury in saltwater – one being the maximum concentration of mercury allowed in waste-water discharges in Portugal (50 microgrammes (μg L-1)), and the other being a lower one (5 μg L-1).The researchers submerged samples of aged biobased plastic and polyethylene samples in the mercury solutions and took aliquots (exact portions of a sample taken for chemical analysis) of the solutions over the course of 48 hours – noting the amount of mercury removed from the liquid.

The researchers noticed a greater change in the biobased polymer’s microstructure, physicochemical, and mechanical properties after UV weathering than in the polyethylene sample. The UV-aged biobased biodegradable polymer removed far more mercury from the synthetic seawater with a high concentration of mercury (50 μg L-1 ) – 82% – than the original biobased plastic sample (26%), unlike the polyethylene, where no great difference was noted. The polyethylene in 50 μg L-1 mercurysaltwater solution only removed 14% of the mercury.

These results highlight that UV-aged biobased plastic can swiftly bind and concentrate mercury ions found in a highly polluted marine environment. This could cause degraded biobased biodegradable polymers to act as a carrier material for mercury into marine organisms when it is ingested. This could lead to bioaccumulation of mercury in their bodies.

This study offers new insight into potential environmental risks associated with the breakdown of some types of biobased biodegradable polymers in the marine environment. It suggests directions for research to design biobased biodegradable plastics that do not concentrate mercury.


Pinto, J., Dias, M., Amaral, J., Ivanov, M., Paixão, J.A., Coimbra, M.A., Ferreira, P., Pereira, E. and Gonçalves, I., (2022) Influence of UV degradation of bioplastics on the amplification of mercury bioavailability in aquatic environments. Marine Pollution Bulletin, 180: 113806. Available from:

To cite this article/service: 

Science for Environment Policy”: European Commission DG Environment News Alert Service, edited by the Science Communication Unit, The University of the West of England, Bristol. 

Notes on content: 

The contents and views included in Science for Environment Policy are based on independent, peer reviewed research and do not necessarily reflect the position of the European Commission. Please note that this article is a summary of only one study. Other studies may come to other conclusions.


Publication date
29 March 2023
Directorate-General for Environment

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