I'd say your lasagna beds are less of a risk than the neighbors growing a veggie patch dependent on chemical fertilizer and pesticides and having the big tanker truck come spray their lawn 3 times a year.

One raised bed with nothing more than organic matter in it may not contribute any more pollution than a 10 acre field with 5 percent organic matter because it is the total volume of OM in the total soil volume (what is under your raised bed) that is the determanent. In answer to the question, "Can you have too much organic matter in your soil?", the answer is, "Yes, you can." but very few of us can get that much to add to the total soil volume in our yards. If you start to get too much moisture retention and your garden beds start to smell swampy you could be contributing to the pollution.

if these beds count as potential polluters and if so, what is the difference between these high OM beds and a slow compost pile

Excellent question!!

IF one bought into the claim/theory that excess organic matter in the soil causes water and air pollution, in addition to your question about compost piles there is also all the forests and pastures and fallow fields full of years of natural decomposed organic matter, all the lasagna beds, all the square foot gardening beds, and even all the containers filled with soil-less mixes contributing to world wide air and water pollution.

The soil food web would be labeled the ultimate source of world pollution and composting, square foot gardening and building lasagna beds would be criminal offenses.

Sorry, I just can't buy into the claim that "if you add too much organic matter, you are causing pollution to ground water and the air". No pun intended, but the claim just doesn't hold water or even air for me.

JMO

Dave