Cellulose microbeads were produced from solutions ofmicrocrystalline cellulose (MC) dissolved in an organicelectrolyte solution (OES) dispersed as droplets via acontinuous cross-flow membrane emulsification processfollowed by phase inversion in ethanol (Figure 2)

Many plastic types are considered to be bio-inert [6] and thus not biodegradable [13]

Combining the two microplastic size classes, they account for 92.4% of the global particle count, and when compared to each other, the smallest microplastic category (0.33–1.00 mm) had roughly 40% fewer particles than larger microplastics (1.01–4.75 mm) (Table 1). Most small microplastics were fragments resulting from the breakdown of larger plastic items; therefore we expected the smallest microplastics to be more abundant than larger microplastics.

If we assume 99% of microbeads are captured during sedimentation, the remaining 800 trillion microbeads settle into the sludge. Sludge is often spread over areas of land and thus runoff from precipitation and irrigation may enable these particles to enter aquatic habitats (Figure 1).

Estos micropl ́asticos frecuentemente no sonremovidos en las PTAR debido a su peque ̃no tama ̃noy flotabilidad

Micropl ́asticos primarios: Son pl ́asticos manufactu-rados con un tama ̃no menor de 5 mm [9]. Estos incluyenpellets industriales como tambi ́en fragmentos pl ́asticosincluidos en productos de cuidado personal tales comocrema de dientes, geles de ba ̃no y productos para el cui-dado de la piel (Figura 2).Micropl ́asticos secundarios: Estos se forman por ladegradaci ́on qu ́ımica (oxidaci ́on), f ́ısica (calor, luz UV,acci ́on mec ́anica) y/o degradaci ́on microbial de los pro-ductos pl ́asticos (Figura 2 [9, 10]).

En-tre los principales residuos pl ́asticos encontrados en lascostas est ́an las botellas de bebidas, las tapas de bote-llas, pitillos, bolsas pl ́asticas, bolsas de mercado, platosy vasos pl ́asticos, colillas de cigarrillo y envolturas dealimentos.

Degradation initiated by solar UV radiation is a very efficient mechanism in plastics exposed in air or lying on a beach surface. But when the same plastic material is exposed to sunlight at the same location but while floating in seawater, degradation is severely retarded.

With common polymers such as LDPE, HDPE, PP and nylons exposed to the marine environment it is primarily the UV-B radiation in sunlight that initiates photo-oxidative degradation. Once initiated, the degradation can also proceed thermooxidatively for some time without the need for further exposure to UV radiation. The autocatalytic degradation reaction sequence can progress as long as oxygen is available to the system.

Persistent organic pollutants (POPs) that occur universally in sea water at very low concentrations are picked up by meso-/microplastics via partitioning. It is the hydrophobicity of POPs that facilitate their concentration in the meso-/microplastic litter at a level that is several orders of magnitude higher than that in sea water. These contaminated plastics when ingested by marine species presents a credible route by which the POPs can enter the marine food web.

The term ‘microplastcs’ and ‘microlitter’ has been defined differently by various researchers. Gregory and Andrady (2003) defined microlitter as the barely visible particles that pass through a 500 μm sieve but retained by a 67 μm sieve (∼0.06–0.5 mm in diameter) while particles larger than this were called mesolitter.

Table 1. Classes of plastics that are commonly encountered in the marine environment.Plastic ClassSpecific GravityPercentage production#Products and typical originLow-density polyethyleneLDPE LLDPE0.91–0.9321%Plastic bags, six-pack rings, bottles, netting, drinking strawsHigh-density polyethyleneHDPE0.9417%Milk and juice jugsPolypropylenePP0.85–0.8324%Rope, bottle caps, nettingPolystyrenePS1.056%Plastic utensils, food containersFoamed PolystyreneFloats, bait boxes, foam cupsNylonPA<3%Netting and trapsThermoplastic PolyesterPET1.377%Plastic beverage bottlesPoly(vinyl chloride)PVC1.3819%Plastic film, bottles, cupsCellulose AcetateCACigarette filters

Several broad classes of plastics are used in packaging: Polyethyelene (PE), Polypropylene (PP), Polystyrene (PS), Poly(ethylene terephthalate) (PET); and Poly(vinyl chloride) (PVC).