I just wanted to let you know, as a (ex?) Natura Retailer, I have not received any contact to switch bags out for fresh.
This is not a post to stand by Natura.  I pulled their food off my shelf on 7/4, the day I saw the original post. 
I have received less contact than some here.  I would love to have positive feedback on these products.  They have been very popular.    Not anymore.

I also did the test where we soaked the kibble with contaminants.  I too ended up with murky water, nasty smell and grit in the bottom of the cup.
All this makes me just want to start my own petfood company.  At least that way I can control the quality. Oh well, i can't afford that.

We had those black and white chunks in our Karma (also a Natura product) and did our own very unscientific test on the Karma kibble.  We put about 6 oz bottled water in a clear drinking glass.  Put small amount of kibble in the water, which was room temp.  Left overnight.  Everything had dissolved.  No stirring.  The following morning (and this would be most likely some 9 hrs later) the water was just sort of cloudy and only very tiny specks of anything in it.  None of the chunks/particles or colored specks that might've been part of those particles.  This was in a way a relief, and it also would indicate to me that the white chunks were not bone (but not rice, either) but this glass of water/Karma had the foulest odor!  I had done a sniff test on the dry kibble when Jake refused to eat it, and I did not detect any odor from the kibble.  Jake the dog, otoh, must have, since he refused it w/out even one taste.  We tried mixing it in w/ his California Natural Herring and Sweet Potato (both dry kibble, nothing added) and he would take his paw, somewhat cat-like, and sweep the kibble onto the kitchen floor.  Then he would select only the Herring and Sweet Potato, leaving the Karma on the floor. 

As I said, the above is totally unscientific but did demonstrate in hindsight that chunks dissolved in plain water, leaving only tiny light brown speckles in cloudy water so we know those white/cream chunks were not bone.  Gave our microscope away decades ago.  Now regretting that!

A person in the pet food industry suggested that the most probable explanation for Jake's sudden refusal to eat Karma when new bag was opened was that this bag had mold on/in food.  Perhaps the same was true for the last bag of Karma biscuits that were not well received and hidden around the house.  All this is just speculation and has to do w/ Karma and nothing to do as far as explaining the Innova results from ExperTox.  Except for samples from our pet supply store, our Jake never had Innova...and those samples he did eat were almost a year ago.

I don't know if this is related to my cats eating Natura or not, but I thought I would share their latest test results.

During the recalls my 2 cats ate some of the tainted food.  Since then they have been on fluid therapy and 3 months ago when I last got bloodwork done the younger cat had kidney levels back to normal and my old, ancient cat still had levels that were slightly elevated.  Yesterday I got the results back for the most current round of bloodwork and my old kitty was about same, which is what I expected.  However, younger kitty's kidney levels were still fine, but the test showed elevated liver levels.  I understand if cats ingest some form of tylenol (don't feel like trying to spell the generic version) then the liver would be affected.  I can't say for sure that this is do to the food (they were eating mostly canned Innova, Cal Nat & a bit of Innova dry), especially since old, frail kitty didn't have any liver troubles and they pretty much eat the same thing.  Obviously this is very distressing to me as I thought my younger cat was kind of out of the woods.  I don't think I would feed my cats a Natura product again, but I really would like to know if this latest development is due to the food that I fed them.  Come on, Natura.  I need some answers here.
~kittylyda