Waddler - those numbers (in ug/L, of course) are great. We all have a certain load of heavy metals in our systems, Cr can be pretty high in background soil (at least in certain parts of Oregon). Not sure how that correlates to blood levels in folks living in those areas. You can expect that you'll incidentally ingest so much soil per day from dust, vege's, playing in the dirt,... I haven't seen much on Co, only that funny anectodal stuff about the Canadian beer drinkers and their head retention. Co is not generally very high in background soils, at least in my area. I'd like to find more historical tox info on Co. Hard to come by.
BTW - I was told by our public outreach person (formerly a journalist) that we (tech/geeks) should write to an 8th-grade level. Over the years I learned a lot from her about how to present info in a less technical way, but there is a slight problem whit it. It's very hard to make definitive black and white statements with varied data. The general public and media want the simple clear cut and sometimes more dramatic version. It's tough.