Plastic debris as a vector in transporting toxic additive chemicals in the marine environment: hexabromocyclododecanes in expanded polystyrene fragments

Abstract

Expanded polystyrene (EPS) is commonly known as Styrofoam. There has been enormous growth in EPS market in the last decades by virtue of many useful properties such as insulation, lightweight, durability and low cost. Annual production of EPS in Korea is 200,000 tons, among witch 1.25% are used for aquaculture buoy. In South Korea, oyster farms employ the suspended culture technique, in which longlines supported by numerous floating EPS buoys are used. And the buoys are also widely used along the southern coast by fishermen as markers, floats, fishing fly holders and underwater net-trap lifters. As a result, EPS buoy and its fragments become the most dominant macro (>2.5cm) and micro (1mm<size<5mm) debris on the beaches of South Korea, accounting for 12% and 99% to total number of debris, respectively.At our previous study, we found the enrichment of hexabromocyclododecane (HBCD), a brominated flame retardants, in sediment near oyster farms where are not located near known sources of HBCD, such as industrial factories and sewage treatment plants. We suspected that the EPS buoys used for oyster farm could contain HBCD. HBCD is most commonly used in polystyrene foams. Since HBCDs are additive type of flame retardants and are not covalently bonded to the material, they easily leach from the product during its use or disposal and are released into the environment. On 10 May 2013, HBCD put its name to a list of 22 other substances targeted for global elimination under the Stockholm Convention. In order to answer our qestion, we purchased new EPS buoys in market and collected stranded EPS buoys along the coasts, and conducted chemical analysis. HBCD concentration showed wide variation among buoys produced by the same manufacturer and even in one buoy. The overall concentration of HBCDs deteced in EPS buoys were in the range of 0.02-422 &#61549 g/g with a median concentration of 40 &#61549 g/g. The inner fresh layer of stranded EPS buoy showed relatively higher level of HBCDs than the outside weathered layer, which confirms the leaching of HBCDs from the buoys surface throughout their lifetime. The stranded EPS spherules on beaches also showed a similar level of HBCDs (range: 34-53 ug/g, median value: 41 ug/g). Because of their exposure to salt and hard-fouling organisms and their high water content, EPS buoys that are not disposed of appropriately can end up in the marine environment as a debris. EPS buoy can gradually fragment into millions of spherules with a diameter 1-5 mm that float on the water’s surface or become stranded on the shoreline. The fragmentation of EPS buoys increases the surface-to-volume ratio and thus enhances the leaching rate of HBCDs into the surrounding environment. In a lab experiment, 15-20% of HBCDs were rapidely leached out from EPS fragments within 96h and 80% of HBCDs were remined inside the fragments for a long time. This result implies that EPS debris can be a moving source of transporting HBCDs to the marine environment.