Chemical Testing

• Chemical testing typically measures the total concentration of a pollutant in an environmental sample. Chemical testing is relatively cheap, quick, easy and repeatable, but it can provide a false impression of the amount of pollutant that is actually available to living organisms.
  
  

Bioavailability

• The amount of a pollutant that is available to living organisms -- i.e., that which can be taken up by them either by ingestion or osmosis -- is referred to as the bioavailability. The fraction of a pollutant concentration that is not bioavailable may, for example, be bound up quite tightly to soil or clay particles, and so will not affect any living organisms.
  
  

Biological Testing

• Biological testing seeks to measure the amount of bioavailable pollutant by exposing organisms, such as bacteria, to the environmental sample and measuring how their growth is affected or how much of the pollutant they take up. This can give a better indication of the bioavailability of a pollutant, but it is slower and less reliably repeatable than chemical testing. Also, bioavailability can also be species specific, so results may not always be relevant.