I heard that some types of fish oil are esterified and can dissolve plastic foam (polystyrene or Styrofoam). Is this right and, if so, should I be concerned?
It is true that the ethyl ester form of fish oil will dissolve Styrofoam (polystyrene) -- going through the bottom of a cup, for example, in just a few minutes, while the re-esterified triglyceride form will not. This effect (due to differences in the polarities of the forms) is not a health concern, but there are slight differences between the forms in terms of how they are absorbed (up to a 76% difference), which you can learn about in the "Forms of Fish Oil" section of the Fish Oil Supplements Review. You can also find out which form of fish oil is claimed to be in each product by looking at the second column of the test results table of the Review.