Microplastics in the Tuscany Sea
R.T. Baino, M. Ria, F. Lavista, R. Biancalana, G. Marino, A. Voliani, C. Mancusi, D. Verniani, E. Cecchi, F. Fani, G. Benedettini ARPAT, Agenzia Regionale per la Protezione Ambientale della Toscana
Introduction
The problem of plastic wastes at sea and in the oceans is a mainstream issue. Since most of the objects tend to shatter, monitoring of the microplastics fragments along the coasts has been activated on a European basis. Here we analyse the data set that arise from a 4 years sampling (2015-2018) supporting of the Marine Strategy Framework Directive.
Experimental
In each season (spring and autumn) 4 transects were performed along the Tuscany coast (Foce Fiume Morto, Donoratico, Follonica, Foce Fiume Ombrone), each of which consists of 3 stations at 0.5, 1.5 and 6 nautical miles up the coast. At each station the manta net, with a mouth of 50 * 30 cm were towed for 20 minutes in order to collect all plastic fragments over 5 mm. All sampled objects are then analysed by number, shape and colour. The sampled surface were calculated through GPS coordinates, the filtered volume with the use of a flow-meter. So far 84 samples have been performed in the Tuscany waters that have been processed by ARPAT laboratories. The statistical distribution of the data (4 orders of magnitude) is of the Poisson (or lognormal) type with a 93% correlation between the observed values and the expected values. Therefore the arithmetic means are not a valid estimates, but the log-transformed data and therefore the geometric means must be used.
This feature is also known in large ocean litter deposits and is due to oceanographic features such as to coastal and non-coastal currents, to upwelling or to surface vortices (litter gyre).
Risultati
The geometric mean abundance in number is 0.1 (range 0.01- 11.84) objects per cubic meter and 0.02 (range 0.002-2.455) objects per square meter. Considering the confidence limits, these numeric estimates of microplastic objects have an accuracy of about 15%. The arithmetic mean is 0,38 (±1,38) objects per cubic meter0,09 (± 0,30) objects per square meter.
On the time axis in the 4 years of sampling there is no significant trend , similarly to the observations in the other regions in the Mediterranean. The abundance values of microplastics, related to the distance from the coast, show a slight increase in values while moving offshore (although this increase is neither generalized, nor statistically significant) which would confirm the hypothesis that microplastics tend to concentrate in gyre far away from the coast. The highest values observed in 6 samplings of the April 2016 campaign are due to the presence of a nucleus of concentration of microplastics at that time (6 and 7 April) in the area south of Elba (Follonica and Foce Ombrone); concentration that is absent both in the northern area and in the other years samplings. The colour pattern of plastic fragments appears to be common to all areas:
the transparent and the white are the dominant colours (45%
and 25% respectively), but it is not clear at the moment whether this is due to staining phenomena or is the native colour of the plastic. Among the coloured fragments, blue is the most common (8%) and red is the least common (1%).
Among the 4 predefined typologies, the fragments are dominant (90%) perhaps also as a consequence of the more general definition, with respect to geometrically more defined terms such as sphere, sheet or filament, which are in fact the forms that are more scarce everywhere.
Conclusions
From the samples taken in the last 4 years, in the Tuscany Sea there are a total of 0.1 microplastic objects per cubic meter, that is 0.02 objects per square meter, equivalent to 163 objects on a football field. The arithmetic mean were slightly smaller compared to mean value from Western Mediterranean Sea even tough sampling variability should be considered in the data comparison.
In the sea of southern Tuscany there is an increase in microplastics moving away from the coast, but this is not observed in northern Tuscany. Generally there are greater concentrations in spring.
Transparent and white are the dominant colours (70%), but among the really coloured fragments, blue is the most common and red is the least common.
The shape of the most common objects is that of the fragments (90%) perhaps also consequently to the more general definition, with respect to terms such as sheet, filament or sphere.
While these result, generally reflect the Mediterranean situation, more data collection, especially offshore, is needed to identify the global pattern of plastic micro-litter and the possible presence of gyres.
Dati da Programma di monitoraggio ARPA-Microrifiuti MSFD 2015-2017 (Report Ispra 2018)
