1. In developing biomarkers, there are no “gold standards” against which a result or finding can be readily evaluated; in most cases, biomonitoring will afford the first opportunity for scientists to assess even qualitatively the extent to which humans are exposed to, absorb, and might be harmed by innumerable contaminants of the human-made and natural environment.

2. Measured concentrations of bio-markers are often extremely low (in the 1 part per billion range or below) and subject to highly uncertain causes of variation, such as individual genetic differences, age, diet, habits, weather conditions, time of day, recent activity, medication and illness, and other exposures.

3. Compared with measures of contaminants in air, water, or food, bio-monitoring results are intrinsically associated with a person and thereby have far greater potential to generate concern and action, for good or ill.

4. The social and political climate in which the new technology of bio-monitoring has emerged is itself volatile; contentious and potentially fractious policy debates and litigation surround the field and render it likely that studies will be conducted or interpreted to meet the agendas of specific parties unless great care is taken to establish uniformly agreed on scientific standards against which any study can be transparently judged.

I think it rather depends on where and why the monitoring program is being established. Is it on land or in water? Is it about monitoring species richness, species at risk, invasive alien species, or all of the above? There have been some successful advances in using crowd-sourcing for biomonitoring - just think oif all the birdwatchers out there. I have also heard of rpograms using school children to watch for rare species using their cell-phones to take pictures and GPS locations for expert reference.