Evaluating the fate of hexabromocyclododecanes in the coastal environment: Fugacity analysis using field data

Abundant use of plastic materials has increased the amount of microplastics (MPs) and related hazardous chemicals in the marine environment. Hexabromocyclododecanes (HBCDs), brominated flame retardants added to expanded polystyrene (EPS), have been detected in biotic and abiotic samples. In this study, the partition constants of HBCDs between plastics and seawater (K_Psw) were determined. Fugacities of HBCDs in EPS, seawater, sediment, and mussels were obtained to determine the directions of the diffusive flux. The fugacities in EPS (f_EPS) were greater than those in seawater (f_sw), sediment (f_sed), and mussels (f_swmussel-EPS and f_mussel-rock) by three orders of magnitude, indicating that EPS plastics are a significant source of HBCDs. The f_mussel-rock of α-HBCD in rock mussels was greater than f_sw by factors of 1.7, whereas the f_mussel-rock of γ-HBCD was smaller than f_sw by factors of 16, indicating the bioisomerization from γ-to α-HBCD. The relatively constant concentration ratio of β-HBCD to the total HBCDs indicated that β-HBCD is a sufficient tracer for determining the diffusive flux. The f_sed values of HBCDs were greater than f_sw by factors of 17-28, implying a probable advective vertical flow of HBCDs from the EPS plastics, which requires further investigation.