Zn seems to be the major metal of concern.

http://www.ncbi.nlm.nih.gov/pubmed/9085433

http://water.usgs.gov/nrp/proj.bib/Publications/councell.duckenfield.landa.callender.pdf

Not sure about effects of sunlight, but toxicants leach out in fresh water from the tire surface. Zinc is added to tires in the manufacturing process, but there are a host of organic compounds that leach out as well, only some of which have been identified.

Hartwell, S.I., D.M. Jordahl and C.O. Dawson. 2000. The Effect of Salinity on Tire Leachate Toxicity. Water, Air and Soil Pollution. 121:119-131.

http://download.springer.com/static/pdf/320/art%253A10.1023%252FA%253A1005282201554.pdf?auth66=1397152655_6966e72df5cf8dbb19cb7d5c5995e15c&ext=.pdf

Hartwell, S.I., D.M. Jordahl, C.O. Dawson and A.S. Ives. 1998. Toxicity of Scrap Tire Artificial Reef Leachates in Estuarine Salinities: Are Tires Acceptable for Artificial Reefs? Trans. Am. Fish. Soc. 127:796-806.

http://dx.doi.org/10.1577/1548-8659(1998)1272.0.CO;2

Anthony, D.H.J., A. Latawiec, S. I. Hartwell and D. M. Jordahl. 1996. A Spectrometric and Chromatographic Chemical Comparison of Solvent Extracts of Whole Tire Leachate and of Shredded Tire Leachates Obtained at Varying Salinity. Environ. Canada, National Water Research Inst., Burlington, Ont., Canada, 95-112. 41pp.

There are four groups of chemicals released: 15 metals , 20 volatile

organic compounds (VOCs), 14 semi-volatile organic compounds , and particulates

Look further:

http://www.calrecycle.ca.gov/publications/Documents/Tires%5C62206013.pdf

Thank you for your responses, especially regarding the level of metals (and particularly zinc) released by tires! The information on products made from recycled tires could also be informative, especially regarding metal release, but I'm unsure how similar the recycled tire products are (in terms of VOCs and other organics) compared to tires that been simply discarded. Specifically, I'm wondering if levels of VOCs, rubber-treatment compounds applied to the tires (and lost during the recycling process) or applied to finish/stabilize the recycled product may differ. However, the cancer risk estimated from hand-mouth contact in playground-age children suggests that the potential for hazard remains, which is interesting (albeit disturbing).

For a review on aromatic amines (actually undergoing peer review) I have included a result from a German report for the Umweltbundesamt (equivalent to EPA): "Tire wear particles could be a significant source of the human carcinogen ortho-toluidine since extracts from shredded used tires contained on average 58.2 mg/kg (range 0.07-130) of ortho-toluidine." The full text of the report (in German!) can be downloaded: http://kinderumweltgesundheit.de/index2/pdf/dokumente/50076_1.pdf

Ortho-toluidine is blamed for increased bladder cancer incidence in a rubber manufacturing plant in New York State: for review see Carréon, T, Hein, MJ, Hanley, KW, Viet, SM, Ruder, AM: Bladder cancer incidence among workers exposed to o-toluidine, aniline and nitrobenzene at a rubber chemical manufacturing plant. Occup Environ Med 71, 175-182 (2014)

Thank you Elmar! Fortunately my wife is fluent in German, so I might be able to convince her to read me portions of that report- otherwise I would be at a loss.