Marine debris, especially plastic debris, is widely recognized as a global environmental problem. There has been substantial research on the impacts of plastic marine debris, such as entanglement and ingestion. These impacts are largely due to the physical presence of plastic debris. In recent years there has been an increasing focus on the impacts of toxic chemicals as they relate to plastic debris. Some plastic debris acts as a source of toxic chemicals: substances that were added to the plastic during manufacturing leach from plastic debris. Plastic debris also acts as a sink for toxic chemicals. Plastic sorbs persistent, bioaccumulative, and toxic substances (PBTs), such as polychlorinated biphenyls (PCBs) and dioxins, from the water or sediment. These PBTs may desorb when the plastic is ingested by any of a variety of marine species. This broad look at the current research suggests that while there is significant uncertainty and complexity in the kinetics and thermodynamics of the interaction, plastic debris appears to act as a vector transferring PBTs from the water to the food web, increasing risk throughout the marine food web, including humans. Because of the extremely long lifetime of plastic and PBTs in the ocean, prevention strategies are vital to minimizing these risks.

Rates of acid-catalyzed methoxy exchange between methanol and the three diastereomers of 2-methoxy-4,6-dimethyl-1,3-dioxane (6) were measured in benzene, and the rates for the two cis diastereomers were measured in methanol/chloroform. Rate constants were evaluated using a 1D-EXSY NMR pulse sequence and a weighted linear least squares analysis. Rates of methanol attack on the cationic intermediate (8) show 24-fold axial selectivity in benzene and 9-fold selectivity in methanol/chloroform. A ring-opening mechanism for equatorial exchange can be rejected, since rate constants k ea and k ae for direct axial/equatorial epimerization are zero. These results demonstrate that antiperiplanar lone pairs are more effective in this system than syn, although the effect is worth no more than 2 kcal/mol.

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