The earth's minerals are commonly absorbed and incorporated into the fruits and vegetables we eat--in fact, that's one of the reasons they're recommended--so you can get your zinc and selenium and copper, for example. But some toxic metals are also absorbed.
Arsenic is one of those. We don't need or use it in our bodies, but it can accumulate and eventually contribute to tumor/cancer formation if it's in significant quantities. Of course, we don't know how much is too much--so that is being studied. We do know, however, that arsenic is particularly well taken up by rice, more so than by other foods. And if it's in rice, it's going to be in products made from it, like rice cereal and rice syrup. This then poses a specific problem for infants who are introduced to rice and often consume it daily as a source of protein and minerals, or to thicken their formula to lessen reflux.
So the FDA is obtaining over 1300 samples from the 30 food categories--and they will be announcing their findings. So stay tuned and if you're interested, link to their webpages describing their efforts and answering a variety of questions.
In the mean time, it might be best to limit your intake of rice and vary the cereals you feed your baby, since oat, wheat, barley and mixed grains are of equal nutritional value--though only oat should be used initially for infants where a sibling or parent has celiac disease--at least in the beginning. For more on this topic, see What to Feed Your Baby.