An interesting article from the
Journal of Hazardous Materials, 2005 discusses the capacity of cilantro to bind inorganic and methyl mercury.
The implications are twofold;
1. Cilantro might possibly be good for treating mercury toxicity. More research needs to be done here, but it seems an interesting line of inquiry.
2. Depending on if it is grown near coal burning regions, cilantro could contain a higher level of mercury than other herbs.