There is nothing definitive, but in 2006 people thought there might be: http://ieeexplore.ieee.org/document/1673553/?reload=true&tp=&arnumber=1673553&url=http:

There is nothing definitive, but in 2006 people thought there might be: http://ieeexplore.ieee.org/document/1673553/?reload=true&tp=&arnumber=1673553&url=http:%2F%2Fieeexplore.ieee.org%2Fxpls%2Fabs_all.jsp%3Farnumber%3D1673553 http://ieeexplore.ieee.org/document/1673553/?reload=true&tp=... I haven't heard of any conclusive evidence that it doesn't harm either (and how could there be one, since they haven't been used for that long), but why take the risk in the first place