Partitioning of selected hydrophobic organic chemicals between microplastics and seawater

Abstract

The occurrence of microplastics (MPs) in the ocean is an emerging world-wide concern. Although sorption of hydrophobic organic contaminants (HOCs) to microplastics may play an important role in the transport processes of HOCs, quantitative evaluation of sorption capacities of various plastic materials is scarce. Most of earlier studies focused on sorption of HOCs to passive sampling material such as low-density polyethylene. In this study, we measured partition coefficients between MPs and seawater (KMPsw) for 8 polycyclic aromatic hydrocarbons (PAHs), 4 hexachlorocyclohexanes (HCHs) and 2 chlorinated benzenes (CBs). Three different polymer materials (i.e., polyethylene, polypropylene, and polystyrene) were chosen because they are the major components of microplastic debris found in the ocean. A third-phase partitioning method was used for the reliable determination of KMPsw to avoid problems with the limited solubility of HOCs in seawater and long equilibration time. First, partition coefficients between polydimethylsiloxane (PDMS) and seawater (KPDMSsw) weremeasured. For the determination of KMPsw, the distribution of HOCs between PDMS or plastics and solvent mixture (methanol:water = 8:2 (v/v)) was determined after apparent equilibrium up to 12 weeks. Laboratory prepared plastic debris (320-440 ?m in thelongest dimension) was prepared by physical crushing. Partition coefficients between polyethylene and seawaterevaluation of sorption capacities of various plastic materials is scarce. Most of earlier studies focused on sorption of HOCs to passive sampling material such as low-density polyethylene. In this study, we measured partition coefficients between MPs and seawater (KMPsw) for 8 polycyclic aromatic hydrocarbons (PAHs), 4 hexachlorocyclohexanes (HCHs) and 2 chlorinated benzenes (CBs). Three different polymer materials (i.e., polyethylene, polypropylene, and polystyrene) were chosen because they are the major components of microplastic debris found in the ocean. A third-phase partitioning method was used for the reliable determination of KMPsw to avoid problems with the limited solubility of HOCs in seawater and long equilibration time. First, partition coefficients between polydimethylsiloxane (PDMS) and seawater (KPDMSsw) weremeasured. For the determination of KMPsw, the distribution of HOCs between PDMS or plastics and solvent mixture (methanol:water = 8:2 (v/v)) was determined after apparent equilibrium up to 12 weeks. Laboratory prepared plastic debris (320-440 ?m in thelongest dimension) was prepared by physical crushing. Partition coefficients between polyethylene and seawater