A simple model approach for the desorption of DDT and related compounds from contaminated sediment to plastic polymers

Plastics including microplastic (MP) particles are widely distributed in the environment today. Microcontaminants - especially very persistent organic compounds and trace metals - are also detected to a large extent in the (aquatic) environment, which has led to a growing number of recent studies addressing interactions between organic contaminants and (micro)plastics in the environment. The background of these studies is the presumed function of plastic particles as vectors for biomagnification, leading to negative effects on the ecosystem. In the present work, interactions between two common plastic polymers, low-density polyethylene (LD-PE) and rigid polyvinyl chloride (H-PVC), and three organic persistent compounds, dichlorodiphenyltrichloroethane (DDT), methoxychlor (DMDT), and dicofol with different log K _ow -values, were investigated using a sorption assay and desorption experiments. A new and innovative experimental approach based on a static system resembling burial in deeper sediment layers was investigated. The experimental setup used additive-free plastic containers, resulting in an easy-to-use experiment instead of MP sorption. It is assumed that the basic mechanisms of interaction are evaluated and are material specific. The present sorption experiment demonstrated adsorption/incorporation of contaminants into the two polymers. Differences between the two polymers are addressed. In the sorption experiments, all target substances were detected in agreement with their hydrophobicity. In the desorption experiments, diffusion of contaminants from a contaminated sediment to the polymers was detected. As expected, sorption by PE was significantly higher. The differences between the two polymers are based on the different glass transition temperatures (Tg) and polymer structure. A comparison with published data from the Pellet Watch project shows a sorption capacity in the same concentration range. The simple approach is easy to use and illustrates the limited sorption capacity of the two polymers studied. It eliminates possible sorption effects on glass walls and simulates the ecosystem situation of a multiple aged contaminant mixture, which is usually not represented in laboratory experiments. The same approach is applicable to polystyrene, polypropylene and polyethylene terephthalate beside other polymer containers.