I believe you are right Richard and that the fertilizer is where a lot a the mercury comes from in the sulphurous veg, so even organic ain't so good if it was fertilized with chicken droppings, being that a lot a chickens are fed from fish products and the hg is in a more concentrated form in the poop. I only use high quality horse ordure but I don't rightly know how much better that is, just feel kinda better about it lookin at what all horses eat.I make sometimes a fertilizer/ soil treatment from steeped comfrey and maybe nettles...
I'm thinkin biodynamically produced food is better than organic ,but then in America y'all can buy organic food thats been genetically modified for cryin out loud!