Looking at the korean regs, there appears to be a specified methodology as to how the migration tests are conducted, hence why they may have just indicated a final concentration rather than a surface area standard. My recommendation would be to get a hold of the test method they use and learn how it's conducted (which should include volume and surface area), and that will allow you to convert to the units you need.
Alternatively, it's possible that they only care about the final concentration of the migrant in the container under conditions of use, rather than the quality of the material itself, which would be a reasonable and more lenient risk management approach, in which case you would evaluate your products under the conditions of use with the values you have and see if it would be expected to cause a concentration increase in the final product.
QA Manager and food safety blogger in Oregon, USA.
Interested in more information on food safety and science? Check out Furfarmandfork.com for more insights!
Subscribe to have one post per week delivered straight to your inbox.