No increase in marine microplastic concentration over the last three decades – A case study from the Baltic Sea

Abstract

Microplastic is considered a potential threat to marine life as it is ingested by a wide variety of species. Most studies on microplastic ingestion are short-term investigations and little is currently known about how this potential threat has developed over the last decades where global plastic production has increased exponentially. Here we present the first long-term study on microplastic in the marine environment, covering three decades from 1987 to 2015, based on a unique sample set originally collected and conserved for food web studies. We investigated the microplastic concentration in plankton samples and in digestive tracts of two economically and ecologically important planktivorous forage fish species, Atlantic herring (Clupea harengus) and European sprat (Sprattus sprattus), in the Baltic Sea, an ecosystem which is under high anthropogenic pressure and has undergone considerable changes over the past decades. Surprisingly, neither the concentration of microplastic in the plankton samples nor in the digestive tracts changed significantly over the investigated time period. Average microplastic concentration in the plankton samples was 0.21±0.15particlesm. Of 814 fish examined, 20% contained plastic particles, of which 95% were characterized as microplastic (<5mm) and of these 93% were fibres. There were no significant differences in the plastic content between species, locations, or time of day the fish were caught. However, fish size and microplastic in the digestive tracts were positively correlated, and the fish contained more plastic during summer than during spring, which may be explained by increased food uptake with size and seasonal differences in feeding activity. This study highlights that even though microplastic has been present in the Baltic environment and the digestive tracts of fishes for decades, the levels have not changed in this period. This underscores the need for greater understanding of how plastic is cycled through marine ecosystems. The stability of plastic concentration and contamination over time observed here indicates that the type and level of microplastic pollution may be more closely correlated to specific human activities in a region than to global plastic production and utilization as such.

Consistent microplastic ingestion by deep-sea invertebrates over the last four decades (1976–2015), a study from the North East Atlantic

“…Similar to the results presented here, Beer et al, (2017) found no trends in the abundance of microplastics ingested by pelagic fish from the Baltic sea over a 28 year dataset (1987 -2015), however the authors did not characterise polymer types preventing comparison with our findings. In fact, the current study appears to be the first long-term (decadal/multi-decadal) investigation to characterise microplastic polymers.…”

“…With the continued and increasing input of plastic to the oceans (Geyer et al, 2017) it might be expected that surface concentrations would also increase over time, however data reveal inconsistencies. The North Pacific Subtropical Gyre has been documented to be accumulating plastics (Goldstein et al, 2012;Lebreton et al, 2018) while no such trends have been observed in other surface waters (Beer et al, 2017;Law et al, 2014Law et al, , 2010ter Halle et al, 2016). Global ocean budgeting identifies large discrepancies between expected and observed surface quantities (Cozar et al, 2014;Eriksen et al, 2014).…”

Toward an Improved Understanding of the Ingestion and Trophic Transfer of Microplastic Particles: Critical Review and Implications for Future Research

“…Under OSPAR an example of a threshold value for assessing Good Environmental Status would be based on monitoring the quantity and incidence of litter ingested by Fulmarus glacialis , North Sea northern fulmars, where a quantitative level target of <10% of North Sea fulmars should have no more than 0.1 g of plastic in their stomach over a continuous period of at least 5 yr in all North Sea regions (OSPAR Commission 2008; European Commission 2013). Generally, the stomach contents of northern fulmars have proved to be a cost‐effective biomonitor and can provide timely information related to the effectiveness of mitigation efforts at reducing plastic pollution by assessing both increasing and decreasing trends (van Franeker et al 2011; Avery‐Gomm et al 2012; Trevail et al 2015; Beer et al 2018).…”

Assessment of Marine Litter in the Barents Sea, a Part of the Joint Norwegian–Russian Ecosystem Survey

“…For example, an increase in litter densities at sea floor has been reported from the Arctic deep-sea observatory HAUSGARTEN between 2002 and 2011 (Bergmann and Klages, 2012). On the other hand, studies of microplastics in the surface and the water column in the Baltic Sea (Beer et al, 2017) and at the surface in the North Atlantic subtropical gyre (Law et al, 2010) and East FIGURE 8 | (A) Sailing routes for fisheries (green lines), (B) sailing routes for other than fisheries: oil tankers (brown), chemicals/product tankers (red), bulk ship (orange), general cargo ship (blue), cooling/freezing (magenta), passenger (yellow), other activities (peach). Taken from the website havbase.no, period: August 2016.…”