Environmental Engineering Reference
In-Depth Information
Figure 10.3
SEM images of different surface textures on plastic beach
debris samples. (a) Flaking of surface, (b) vermiculite texture, (c)
microfracture of surface, (d) surface pitting, (e) signs of initial degradation,
(f) regions of preferential degradation, (g) horizontal notching from cracks,
(h) deep cracks and fractures.
Source: Reproduced with permission from Cooper and Corcoran (2010).
Extensive photothermal oxidation occurs at higher temperatures in plastics
on beaches or at the waterline. Plastics disposed directly into water,
however, are unlikely to be extensively degraded as discussed previously.
The identification of the beaches as the primary potential site for generation
of microplastics underlines the importance of beach cleanup efforts as a
mitigation strategy. Removing larger debris items from the beaches likely
reduces the chance of the debris generating microplastics via weathering
degradation.
10.3.2 Persistent Organic Pollutant in Microplastics
The most serious concern relating to micro- and mesoplastics is their
potential ingestion by marine organisms. Ingestion of plastic fragments can
sometimes cause distress to marine animals from physical obstruction of
their gut passage. Much more serious is the hazard posed by their potential
delivery of the toxic pollutant species concentrated from seawater to the
ingesting organism to the marine food web and perhaps even to human
consumers.
Numerous organic compounds from industrial activity and agricultural
runoff are present in seawater at very low concentrations. These have been
detected in all oceans as well as in bodies of fresh water. Most persistent
organic pollutants (POPs) of interest being hydrophobic and less denser
than seawater tend to concentrate in the surface layers of the ocean. The
common micro plastics (PE, PP, and EPS) debris also reside in the same
stratum of water because of their relatively density, allowing facile
partitioning of POPs into the hydrophobic plastics. At equilibrium,
concentration of POPs are several orders of magnitude higher in the plastic
particles compared to that in seawater (Endo et al., 2005; Koelmans et
al., 2013; Teuten et al., 2007). Therefore, meso- and microplastics are a
credible means of transport of POPs in the oceans (Zarfl and Matthies,
2010). The crucial question, however, is the bioavailability of the sorbed
