Discoloration and contaminant concentration in beached resin pellets.
We collected 55 pellets from a beach in Tokyo Bay and the pellets were characterized and analyzed individually (i.e., piece-by-piece). Based on the analytical results we discussed as follows:
"Fourteen of the 35 PE (40%) and 1 of the 20 PP (5%) pellets were discolored yellow or orange. Figure 7 shows the PCB concentrations in the resin pellets categorized in terms of discoloration and fouling. It suggests that the discolored (yellowing) PE pellets (fy and y) contained larger amounts of PCBs than their non-discolored counterparts, as most (12 out of 14) of the discolored PE samples had detectable amounts of PCBs, whereas half (10 out of 21) of the non-discolored PE pellets did not. In addition, both the highest and the second highest PCB concentrations were found in discolored pellets (2300 and 640 ng/g, which are 1 to 2 orders of magnitude greater than the others). The pellet with the highest PCB concentration was bright orange, and that with the second highest concentration was the most yellowed of the samples. These results suggest that factors causing discoloration may have positive effects on PCB sorption to resin pellets. " after Endo et al. (2005)
"Although discoloration of plastic polymers arises from many causes, additives, especially phenolic antioxidants, are the major reason for discoloration (Cooper, 1987; Bangee et al., 1995; Pospisil et al., 2002). Phenolic antioxidants quench free radicals generated by exposure to UV light, high-temperature polymerization, nitrogen oxides in the air, etc., preventing the polymer from oxidizing. The sacrificial reaction of phenolic antioxidants forms byproducts having quinonoidal structures that cause yellowing of the polymer (Cooper, 1987; Epacher et al., 1998; Pospisil et al., 2002). The extent of discoloration depends on various factors, including type and concentration of additives, ambient condition, and elapsed time after production of the polymer. The observation that discolored pellets had higher amounts of PCBs can be explained by the fact that more-discolored pellets have had longer residence time on the ocean and thus more time to oxidize and, as a result, have adsorbed more PCBs. That is, the degree of discoloring can be an index of residence time of the pellets in the seawater." after Endo et al. (2005)