Environmental Engineering Reference
In-Depth Information
Common types of plastics found as ocean debris are listed along with their
sink and invariably end up in the marine sediment. The long-term fate of
even the floating plastics, however, will be the same. A surface biofilm of
bacteria and diatoms develops on the samples almost immediately once in
water (LobelleandCunliffe, 2011). Thisbiofilm issooncolonized byamix of
hydroids, ectocarpales, bryozoans, and barnacles (Andrady and Song, 1991).
How rich the foulant layer will grow to be and the course of succession of
speciestherein,varieswiththelocationofexposure.Undertheweightofthe
fouling organisms, especially the encrusting epibionts, floating plastics will
eventually sink in seawater (Andrady and Song, 1991; Costerton and Cheng,
1987; Railkin, 2003). However, once submerged, the rich surface growth on
these is foraged by fish (or the algae dies off due to lack of light) and the
plastic now rendered less dense reemerge may to the surface. A slow cyclic
“bobbing” motion of floating plastic debris attributed to this cyclic change
in density on submersion below a certain depth of water, first proposed by
Andrady and Song (1991), was later confirmed by others (Stevens, 1992;
Stevens and Gregory, 1996). Invariably, these plastics also end up in the
mid-watercolumnorthesediment.Theoceansedimentalreadyshowssigns
of significant plastic pollution (Backhurst and Cole, 2000; Katsanevakis
et al., 2007; Stefatos and Charalampakis, 1999). For instance in the NE
Mediterranean, 135 bottom trawls samples yielded on the average 0.72 kg
of debris per hour of trawling and 73% of it was plastic (Eryaşar et al.,
2014). Packaging material was the most abundant (53%) while fishing gear
amounted to only 7%.
