Google led me to this: http://veggierevolution.blogspot.com/2010/10/experts-avoid-nonorganic-potatoes.html
That link she provides mentions how apples are very contaminated.
Sweet potatoes are supposedly mostly clean (one of the least contaminated types). Sweet potatoes have oxalates, however. (I limit oxalates a little.)
Contamination of conventional potatoes and apples
Blog entry posted by SickOfSickness, Feb 1, 2014.
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