Microplastics in the SML of estuarines

The pollution by industrial contaminants or plastic debris is an example of anthropogenic changes affecting marine ecosystems. Microplastics (MPs), defined as particles of plastic in the size range of 0.05 to 4.5 mm, are of major interest in present studies. Most recent findings suggest that MPs impact the marine environments in a great extend which is not fully understood. Therefore it is highly necessary to gain more data about the effect of plastic debris of all sizes. Usually MPs have a lower density than the surrounding seawater and depending on their composition and the state of biofouling they tend to float near or at the sea surface. Previous studies on coastal ecosystems or on the open ocean suggest a high presence of MPs in the sea surface microlayer (SML). The SML is characterized by a high microbial activity and the presence of marine microgels. It is already known that the accumulation of MPs in the SML can have an effect on the physical and chemical conditions altering the environment of inhabiting organisms.

This study (Anderson et al., 2018) focused on the accumulation of MPs in the SML of estuarine systems. Estuaries play a major component in the transfer of MPs originated of land-based sources to the open ocean. These highly productive ecosystems are being more and more urbanised and industrialised. A rapid increase of fishing and shipping industries has occurred since a few decades. As a result contamination by sewage, urban run-offs and MPs can be observed. Interestingly this study compared two differing estuarine systems, the Hamble estuary and the Beaulieu estuary. Both of a similar size are very close to each other and located in the southern part of the UK but vary in their stage of development. Hamble is a highly industrialised estuarine, the Beaulieu system is more pristine.

Samples where taken on two days using a multiplicity of methods allowing the extraction of sea surface water or sub surface water samples. The main aims were to evaluate the relatively novel dipped glass plate method for the characterization of the SML and to compare these to sub surface samples regarding the content in MPs. The glass-based method is very applicable for the characterization of the SML; this technique allows taking samples from a depth of 100 to 200 µm representing the SML precisely.

With the use of these methods MPs could be extracted from different water layers. Afterwards a characterization of the MPs took place regarding their colour, length and surface texture using a standard light microscope and a scanning electron microscope (SEM). Mainly fibres of MPs were identified during the two sampling days, as it is the most common type of microplastic in those estuaries. Reading the study I wondered for what reason the colour and size of the fibres were of importance if it doesn’t allow predicating the original source of contamination? In another study on microplastics researchers used Raman spectroscopy in order to determine the composition of plastic (Imhof et al., 2012), possibly leading to the source identification.

Using the dipped glass plate method the highest concentration of MPs was sampled at the Hamble site, which supports the hypothesis that in the SML MPs accumulate. But generally both sites had significant microplastic concentrations highlighting the ubiquitous existence of plastic particles in relatively pristine aquatic environments.

Generally the study provides a first insight in the accumulation of MPs in the SML in estuarine systems but an adequate comparison between estuaries and sampling days was not possible due to very small number of samples. Much more data would be needed to allow any comparisons or even any biological interpretations.

However this study approved the dipped glass method as a highly suitable SML sampling method.

Article Reviewed

Anderson, Z. T., Cundy, A. B., Croudace, I. W., Warwick, P. E., Celis-Hernandez, O., & Stead, J. L. (2018). A rapid method for assessing the accumulation of microplastics in the sea surface microlayer (SML) of estuarine systems. Scientific reports, 8(1), 9428.

References

Imhof, H. K., Schmid, J., Niessner, R., Ivleva, N. P., & Laforsch, C. (2012). A novel, highly efficient method for the separation and quantification of plastic particles in sediments of aquatic environments. Limnology and oceanography: methods, 10(7), 524-537.