The discovery suggests that the animals can trap plastic pollution from seawater within their porous skeletons, potentially turning them into natural records of microplastic contamination.

Before becoming a household object used for washing, a sea sponge is an animal anchored to the seabed. Unable to move to cleaner waters, it constantly pumps seawater through a network of pores and canals to feed. Along with nutrients, it takes in particles suspended in the water, making the sponge a potential record of the environment around it.

An international team of physicists, chemists and biotechnologists, including scientists from Adam Mickiewicz University in Poznań and Poznań University of Technology, examined the skeletons of two commercially harvested species: Spongia tubilifera from the Caribbean and Hippospongia communis from the Mediterranean.

Their structural framework is made of spongin, a durable protein arranged in a three-dimensional network of fibres. Within this structure, the researchers found fibres, particles and film fragments made of various plastics. Their findings were published in the scientific journal Environmental Chemistry and Ecotoxicology.

The researchers used several spectroscopic methods to analyse the suspicious particles and distinguish natural materials from synthetic ones. They identified polyethylene, polypropylene, polyamide, PET, polystyrene, polyurethane and acrylic.

Polypropylene was the most frequently detected. The lightweight and durable plastic is widely used in products including packaging, food containers, bottle caps, non-woven fabrics, ropes and fishing nets.

The plastic was not simply sitting on the surface of the sponges. Particles were embedded within their porous skeletons, while in some places natural spongin fibres had wrapped around synthetic fibres.

The finding raises questions about how long the plastic remains trapped and what happens to the particles when the sponge decomposes.

The researchers suggest that this ability could also make sponge skeletons useful as natural indicators of microplastic pollution. Unlike a single water sample, which provides a snapshot of conditions at one moment, a sponge filters seawater continuously over a much longer period.

The study does not show that every natural sponge contains microplastics or that using sponges poses a risk to human health. The researchers did not investigate whether particles are released during washing, their effects on the skin or the health effects on the animals themselves.

The study also examined only two species from two specific regions, meaning the findings cannot be used to compare or rank the cleanliness of different seas. (PAP)

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