DPA (or diphenylamine) is a type of antioxidant that is added to plastics like polyethylene (the plastic sandwich bags are made of) as a stabilizer. Stabilizers in plastics help to prevent degradation of the plastic caused by free radicals that are generated from exposure to heat and ultraviolet light, much like antioxidants in foods like berries help protect the cells in your body against free radicals. This helps the plastic to last longer and be resistant to weathering effects.

It is very important which additives like stabilizers and plasticizers are used in plastics because over time these chemicals can leach out of the plastic and into the contents of the container. In the case of plastic containers used to store food and beverages this can be quite a problem if the additives are dangerous to human health. An example of this concern is the controversy over the Food and Drug Administration (FDA)-approved plasticizer BPA (bisphenol A), which in some studies has been shown to be cause health problems. However the FDA and regulatory agencies in other countries maintain that BPA is safe at the levels of exposure caused by food packaging.

I was unable to confirm whether DPA is used in sandwich bags and could not find any announcements of its removal from them. Ziploc and Glad make no mention of removing DPA from sandwich bags on the FAQ sections of their websites, although they do both confirm that their bags are BPA-free. If you could let us know where you saw the announcement, I would be happy to research the topic further.

While DPA can be dangerous to human health in large doses, it is actually considered fairly safe in small doses. DPA is approved for use by the Environmental Protection Agency (EPA) in agriculture, where it is used as a coating on apples to protect the apple skin from oxidation during storage. I was unable to find FDA regulations about DPA.

References:
http://en.wikipedia.org/wiki/Polyethylene
http://en.wikipedia.org/wiki/Diphenylamine
http://en.wikipedia.org /wiki/Stabilizer_for_polymers
Patent: Polyethylene stabilized with diphenylamine. US 2543329 A.
http://www.fda.gov/Food/IngredientsPackagingLabeling/FoodAdditivesIngredients/ucm355155.htm
http://www.epa.gov/oppsrrd1/REDs/factsheets/2210fact.pdf
http://www.ziploc.com/pages/TopFAQs.aspx
http://www.glad.com/faq/
http://www.epa.gov/hpv/pubs/summaries/subdipha/c13378.pdf

I think you might mean BPA, which stands for Bisphenol A, a chemical used in the production of certain plastic materials. BPA has been used very ubiquitously in commercial products since the 1960s.

Various studies have shown that it is an important pollutant in the environment, affecting phenomena such as nitrogen fixation in certain plants, and the reproduction and development of aquatic organisms like fish, crustaceans, and amphibians. BPA has such a significant impact on the environment because it is used in many products, and when those products get thrown away, BPA can seep into the soil or water where the trash is discarded. Because there are so many of these products being dumped into the environment, it can have a large role as a pollutant and affect many organisms.

It has been seen that low levels of BPA can leach into food. However, agencies such as the World Health Organization and the Food and Drug Administration have stated that the low levels of BPA that occur in some foods is still safe. It's important to recognize the difference between the amount of BPA an individual person might be exposed to, vs. how much BPA is being discarded to contribute to pollution.

Nevertheless, there are on-going studies to see how BPA affects people, and there are more and more products on the market that are BPA-free.