This is a response from soil scientist, Garn Wallace, who specializes in metals in soils. Daniel E. Bowman, Richard Y. Evans and Linda L. Dodge (HortScience, 1994, volume 29, pages 774 - 776) found that automotive tire crumb rubber was toxic to Chrysanthemum and demonstrated that the toxicity was due to the accumulation of zinc. Subsequently, Edward Bush, Kris Leader and Allen Owings found that automobile tire crumbs were toxic to river birch, lacebark elm and pecan. (Journal of Plant Nutrition, volume 24, 2001, pages 503- 510 and Journal of Plant Nutrition, volume 26, 2003, pages 1413-1425) have confirmed the toxicity of zinc in crumb rubber. The toxicity of zinc in crumb rubber has been conveyed to growers, Media Notes for North Carolina Growers, April 1997. Zinc is essential both for plant and animals. Zinc functions at the active sites of some enzymes. However excessive levels of zinc are toxic as are all nutrients. Zinc is used as a biocide in skin creams and in some paint formulations. The chemistry of zinc contains a full shell of electrons called the "D" shell. Two other elements with similar chemistry as zinc which are in the some grouping since all of the them have a full "D" shell of electrons are cadmium and mercury. Modest levels of zinc are essential nevertheless high levels of zinc inhibit growth. Some species are more tolerant than others. Grasses are the most tolerant. The symptoms that I have noted in tomatoes included early senescence before the fruit ripens and discoloration of the older leaves with yellow/orange and scorching of the leaf margins. The addition of zinc containing materials is desirable for media and soil low in zinc. Zinc is not generally low in urban soils since zinc is a commonly present. It is in tire dust, galvanized steel including chain link fencing, rain gutters, downspouts, plumbing, etc., exterior paints, some fertilizers and some organic amendments.