Don't be tempted to touch anything on a roadside, or even near a road, there are a number of really serious (and painful) conditions you could end up with. In addition, a number of these poisons are acclumative, i.e. they lie in fatty tissues and you do not really notice the effects until the toxicity reaches a certain level in the body. In some other cases, there is no cure and/or any damage done is irreversible. Just in case you were wondering:
Roadside foods can contain:
Lead:
This is absorbed through soft fruit skins: interferes with the normal formation of red blood cells by inhibiting important enzymes, damages red blood cell membranes and interferes with cell metabolism. :- anaemia, brain damage, cancer, the effects of lead is now thought to increase with age.
Benzene: is a hyro-carbon that is absorbed through leaves and bark: has a suppressive effect on bone marrow and impairs the development of red blood cells. Exposure to the chemical may result in cytopenia (total bone marrow loss).
Polycyclic hydrocarbons from partially unburnt fuel (there are many of them) are absorbed by different parts of the plants and are also thought to be carcinogenic.
Finally, it has only recently been shown that very small particles can have a really huge impact on materials they interact with, as an example, gold is a stable element and will not react with many other chemicals, when made as small particles however, it reacts with everything! It can be therefore devastating if it gets into the body.
The point here is that injestion is the easiest way to get these particles into the body, they can then be absorbed quickly and easily through the gut, however, there is very little research or information on this at present.
The European Commission is worried about the possible effects of these and other pollutants, i.e. from diesel exhausts, which produce a carbon-nanoparticles, that it has started projects to examine the effects of these materials on human health (e.g.
http://www.impart-nanotox.org/, and
http://www.cpa.ed.ac.uk/news/research/31/4.html).
There are also traces of other heavy metals in car exhausts, and from the materials used to build the road in the first place, for an interesting article on the effects on the human body have a look here:
http://chge.med.harvard.edu/education/course/toxic/heavy/documents/mccally.pdf
Hope that helps
Greg