These values imply that plastic meso- and microparticles in the ocean will at equilibrium yield a highly concentrated source of POPs. A recent study by Rios and Moore (2007) on plastic mesooparticles on four Hawaiian, one Mexican and five California beaches showed very significant levels of pollutants in the particles. The ranges of values reported were: ∑ PAH = 39–1200 ng/g: ∑ PCB = 27–980 ng/g: ∑ DDT = 22–7100 ng/g. These are cumulative values for 13 PCB congeners and 15 PAHs.The cumulative levels found in plastic pellets collected from locations near industrial sites were understandably much higher. Highest values reported were ∑ PAH = 12,000 ng/g and DDT = 7100 ng/g. A 2009 study reported

Mitomycin C mw data for 8 US beaches (of which 6 were in CA) as follows (Ogata et al., 2009): ∑ PCB = 32–605 ng/g; ∑ DDT = 2–106 ng/g; and ∑ HCH(4 isomers) = 0–0.94 ng/g. The levels of pollutants in plastic pellets floating in surface layers are comparable to the range observed for sediment concentration

of the same compounds. Recent work has suggested that micro- and mesoplastic debris may also concentrate metals (Ashton et al., 2010) in addition to the POPs. This is an unexpected finding as the plastics are hydrophobic but the oxidised surface could carry functionalities that can bind metals. The situation is reversed in the case of residual monomer and additives compounded into plastics as well as partially degraded plastics carrying degradation products. These plastics

debris will slowly leach out a small fraction of DNA Damage inhibitor the POPs (additives, monomer or products) into the sea water until the appropriate KP/W [L/kg] value is reached. The equilibrium is a dynamic one and the POPs are never irreversibly bound to the polymer but diffuse in an out of the plastic fragment depending Interleukin-3 receptor on changes in the concentration of the POP in sea water. In contrast to ‘cleaning’ of sea water by virgin plastics these tend to leach a small amount of the POPs into seawater However, while no good estimates or models are available for the process, the total plastics debris-mediated pollutant load introduced into seawater is likely to be at least several orders of magnitude smaller than that introduced from air and waste water influx into oceans. The critical ecological risk is not due to low-levels of POPs in water but from the bioavailability of highly concentrated pools of POPs in microplastics that can potentially enter the food web via ingestion by marine biota. Microparticles and nanoparticles fall well within the size range of the staple phytoplankton diet of zooplanktons such as the Pacific Krill. There is little doubt that these can be ingested. Plastic microbeads have been commonly used in zooplankton feeding research. There are numerous references in the literature (Berk et al.