These particles’ minute size makes them exceptionally difficult to contain. Water from developed areas containing micropollutants undergoes treatment processes, but some particles are small enough to pass through filtration systems and runoff into bodies of water. Then, they are accidentally ingested by small marine organisms and are subject to bioaccumulation in larger ones. Thus, some micropollutants may end up being consumed by humans (Ohm, 2020). They are also very difficult to monitor. The smallest of these particles cannot be collected for research using filtration methods. Thus, scientists are unable to assess the extent of microparticulate pollution in marine ecosystems using this method (Girard et al., 2020).

However, marine sponges have recently been studied as a solution to this problem. Sponges are sessile, or immobile, organisms of the phylum porifera; they feed on dissolved organic carbon, prokaryotes, and phytoplankton by circulating water through their bodies (Girard et al., 2020). In doing this, they also ingest foreign material, such as sand. Sponges naturally retain some of these foreign particles up to 2mm in size to maintain their rigidity (Cerrano et al., 2007). These particles are often retained in the ectosome, a thin layer directly under the surface of the sponge (Cerrano et al., 2007). Along with naturally occurring foreign material, sponges will also ingest and retain micropollutants. Sponge samples can then be collected, and micropollutants can be isolated in the lab. This allows scientists to determine the type and concentration of micropollutants in different areas. The most abundant pollutant particles found in sponges sampled during a study in Indonesia, a region subject to severe water pollution, were cotton and polystyrene, better known as styrofoam (Girard et al., 2020).

Sponges’ ability to retain foreign material including microplastics is important because it allows scientists to collect pollutant particles which is not possible through mechanical filtration methods. Moving forward, scientists can better measure the recovery of reefs following legislation such as a microbead ban. This development may also be used to assess the effectiveness of treatment methods like biodegradation, the use of microorganisms to break down environmentally harmful substances.

Though sponges yield useful information by collecting micropollutant particles, they are not perfect indicators of pollutant concentrations. Sponges selectively retain the particles they filter in. Thus, they will eject many of the micropollutants they ingest (Cerrano et al., 2007). This means that scientists cannot determine the concentration of pollutant particles with great accuracy. Some micropollutants may even be harmful to sponges or carry bacteria which will disrupt normal filtration or retention of particles (Girard et al., 2020). Nevertheless, sponges are valuable for assessing the extent of micropollutants, and further research could potentially yield more accurate methods for determining concentrations.

References

Cerrano, C., Calcinal, B., Di Camillo, C. G., & Valisano, L. (2007, January). How and why do sponges incorporate foreign material? ResearchGate. Retrieved December 4, 2020, from https://www.researchgate.net/publication/313069876_How_and_why_do_sponges_incorporate_foreign_material_Strategies_in_Porifera

Girard, E. B., Fuchs, A., Kaliwoda, M., Lasut, M., Ploetz, E., Schmahl, W. W., & Worheide, G. (2020, May 26). Sponges as bioindicators for microparticulate pollutants. BioRxiv. Retrieved December 4, 2020, from https://www.biorxiv.org/content/10.1101/2020.05.26.116012v1.full

Ohm, C. (2020, August 6). The risks of microplastics to our health and marine ecosystems. Earth. Retrieved December 6, 2020, from https://earth.org/risks-of-microplastics-to-our-health-and-marine-ecosystems/